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Amit Ramji – A4 – University of Hertfordshire
1
COURSEWORK ASSIGNMENT
Module Title: Mechanics and Properties of Materials Module Code: 6ACM0003
Assignment Title: Finite Element Analysis of a Wind
Tunnel Model
Individual
Tutor: Dr Y Xu/Dr A Chrysanthou Internal Moderator: Dr. Yong Chen
ASSIGNMENT SUBMISSION
Students, this section must be completed before your work is submitted.
Please print your forename and surname in capitals, provide your student registration number, your study year code
(e.g. ASE1, EE1), and your signature in the spaces provided below. For Group work, each team member must
complete this information. You may add or delete rows as required.
Copyright Statement
By completing the information below, I/we certify that this piece of assessment is my/our own work, that it is has not
been copied from elsewhere, and that any extracts from books, papers, or other sources have been properly
acknowledged as references or quotations.
Forename: Family Name: SRN: Year Code: Signature:
Amit Ramji 10241445 A4
Marks Awarded %: Marks Awarded after Lateness Penalty applied %:
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Amit Ramji – A4 – University of Hertfordshire
2
ASSIGNMENT BRIEF
Students, you should delete this section before submitting your work.
This Assignment assesses the following module Learning Outcomes:
4. Examine existing designs and actual components in engineering situations, using methods such as
finite element analysis, photoelasticity, non-destructive testing and fractography.
5. Limit the occurrence of failure in materials by appropriate modelling, design and materials selection.
6. Apply analytical methods to structural components subjected to complex stress/strain fields.
Assignment Brief:
In this assignment, you will create a finite element model of a wind tunnel model of a wing to be tested at
supersonic speeds in order to assess its structural integrity. You should carry out the modelling and write a
short report on your findings. Further details are provided on the attached sheets.
Submission Requirements:
Submission shall be through StudyNet
This assignment is worth 50 % of the overall in- course assessment for this module.
Marks Awarded for:
Validity of the FE results - 40%; Extent to which reporting requirements are met - 20%; concluding
remarks section – 20%; presentation of report - 20%.
A note to the Students:
1. For undergraduate modules, a score above 40% represent a pass performance at honours level.
2. For postgraduate modules, a score of 50% or above represents a pass mark.
3. Modules may have several components of assessment and may require a pass in all elements.
For further details, please consult the relevant Module Guide or ask the Module Leader.
Typical (hours) required by the student(s) to complete the assignment: 15 hours
Date Work handed out:
7
th
November 2013
Date Work to be handed in:
29
th
November 2013
Target Date for the return of
the marked assignment:
7
th
January 2014
Type of Feedback to be given for this assignment:
General feedback on StudyNet and individual feedback for each report.
Amit Ramji – A4 – University of Hertfordshire
3
Finite Element Analysis
ANSYS Report
Group E
Amit Ramji
10241445
University of Hertfordshire - Aerospace Engineering
Year 4 – Mechanics and Properties of Materials - 6ACM0003
26th
November 2013
Amit Ramji – A4 – University of Hertfordshire
4
Contents	
  
Introduction .......................................................................................................................................................................... 5	
  
Preliminary Analysis............................................................................................................................................................ 5	
  
Finite Element Analysis (FEA) Procedure........................................................................................................................... 5	
  
Analysis:............................................................................................................................................................................... 8	
  
Alternative methods of analysis ........................................................................................................................................... 9	
  
Conclusions:....................................................................................................................................................................... 10	
  
Discussion .......................................................................................................................................................................... 11	
  
References .......................................................................................................................................................................... 12	
  
Table	
  of	
  Figures	
  
Figure 1 – Cantilever Plate geometry....................................................................................................................................... 5	
  
Figure 2 – Material Properties Input ........................................................................................................................................ 6	
  
Figure 3 - Uniform stiffness properties.................................................................................................................................... 6	
  
Figure 4 - Uniform thickness properties .................................................................................................................................. 6	
  
Figure 5 - Selection of fine mesh ............................................................................................................................................. 6	
  
Figure 6 - Post meshing operation............................................................................................................................................ 6	
  
Figure 7 - Boundary conditions (Fix all DOF between Node ID’s E to F).............................................................................. 7	
  
Figure 8 - Applying Pressure Loading onto wind surface ....................................................................................................... 7	
  
Figure 9 – Nodal Displacements stating Max Deflection at Wing Tip (CD) is 1.596mm....................................................... 7	
  
Figure 10 - Stress Intensity Showing Highest Stress at Node F, lowest at Node A as expected. ............................................ 8	
  
Figure 11 - Von-Misses Stress peak at Node F as expected. ................................................................................................... 8	
  
Data	
  Tables	
  
Table 1 - Provided Parameters and calculated pressures ......................................................................................................... 5	
  
Table 2 - Cantilever Plate Coordinates .................................................................................................................................... 5	
  
Table 3 - Summary Material Properties ................................................................................................................................... 6	
  
Table 4 - Raw material properties from sample tests............................................................................................................... 6	
  
Table 5 - Post Processor Output Summary Table of results .................................................................................................... 8	
  
Table 6 - Roark's Stress and Strain simplification into Rectangular Plate............................................................................... 9	
  
Amit Ramji – A4 – University of Hertfordshire
5
Introduction	
  
This	
   study	
   considers	
   a	
   single	
   edge	
   cantilever	
   plate	
   bending	
   for	
   interpretation	
   and	
   simplification	
   of	
   a	
  
model	
   aircraft	
   wing	
   at	
   supersonic	
   speeds	
   for	
   wind	
   tunnel	
   testing.	
   The	
   objectives	
   are	
   to	
   evaluate	
   the	
  
pressure	
  loads	
  and	
  analyse	
  the	
  structural	
  integrity	
  of	
  the	
  wing	
  model	
  to	
  be	
  tested.	
  The	
  relation	
  to	
  a	
  real	
  
wing	
   allows	
   for	
   identification	
   of	
   stress	
   concentration	
   centre	
   and	
   maximum	
   stress	
   regions	
   which	
  
attention	
   can	
   be	
   paid	
   in	
   more	
   detail	
   by	
   further	
   analysis,	
   reinforcement	
   or	
   alternative	
   modelling	
  
techniques.	
   The	
   Finite	
   Element	
   methods	
   used	
   in	
   this	
   report	
   provide	
   a	
   basis	
   for	
   understanding	
   the	
  
properties	
  of	
  thin	
  plates	
  under	
  uniform	
  pressure	
  loads,	
  however	
  in	
  reality	
  the	
  loading	
  conditions	
  and	
  
boundary	
  conditions	
  are	
  very	
  complex.	
  Simple	
  analytical	
  methods	
  do	
  not	
  exist	
  for	
  complex	
  shapes	
  such	
  
as	
  a	
  wing	
  plan-­‐form,	
  hence	
  a	
  comparative	
  study	
  is	
  shown	
  using	
  rectangular	
  cantilever	
  plates	
  to	
  display	
  
that	
  the	
  theory	
  agrees	
  but	
  the	
  values	
  obtained	
  are	
  non	
  comparable.	
  Thus	
  providing	
  further	
  significance	
  
to	
  Finite	
  Element	
  Modelling	
  (FEM)	
  methods	
  in	
  order	
  to	
  analyse	
  the	
  part	
  geometry	
  chosen	
  for	
  design	
  in	
  
haste,	
  compared	
  to	
  non-­‐conservative	
  approximations	
  such	
  as	
  rectangular	
  plate	
  methods	
  described	
  later	
  
in	
  this	
  report.	
  
Table 1 - Provided Parameters and calculated pressures	
  
Preliminary	
  Analysis	
  
Sample	
  Calculation	
  of	
  Pressure	
  Loads	
  
∆𝑝 = 𝑞!
4
𝑀!
! − 1
𝛼
Calculation	
  of	
  Max	
  Pressure	
  Loading	
  from	
  Mach	
  No:	
  
𝑀!" = 1.5     ∴   𝑞!" = 260  𝑀𝑃𝑎     ∴    Δ𝑝!" = 𝑞!"
4
𝑀!"
!
− 1
8!
360
2𝜋
= 129.881  𝑀𝑃𝑎
𝑀!" = 2.5     ∴   𝑞!" = 275  𝑀𝑃𝑎   ∴    Δ𝑝!" = 𝑞!"
4
𝑀!"
!
− 1
8!
360
2𝜋
= 67.032  𝑀𝑃𝑎
∴    Δ𝑝!"# = 𝑆. 𝐹  ×  𝑀𝐴𝑋 Δ𝑝!" Δ𝑝!" = 𝟏𝟗𝟒. 𝟖𝟐𝟐  𝐌𝐏𝐚                              (𝑊ℎ𝑒𝑟𝑒  𝑆. 𝐹 = 1.5  𝑔𝑙𝑜𝑏𝑎𝑙)
Finite	
  Element	
  Analysis	
  (FEA)	
  Procedure	
  
Initially	
   set	
   up	
   the	
   geometry	
   of	
   a	
   flat	
   plate	
   with	
   the	
   dimensions	
   as	
   shown	
   in	
   Figure 1	
   and	
   tabulated	
  
coordinates	
  in	
  Table 2.	
  Later	
  set	
  up	
  the	
  plate	
  geometry	
  by	
  selecting	
  the	
  points	
  and	
  creating	
  the	
  lines	
  as	
  in	
  
Figure 1.	
  
Table 2 - Cantilever Plate Coordinates
Figure 1 – Cantilever Plate geometry
Given	
  Parameters	
  
	
  Angle	
  of	
  attack,  𝛼	
  (deg)	
   8.0	
   7.0	
   6.0	
   5.0	
   4.0	
   3.0	
   2.0	
   1.0	
  
Angle	
  of	
  attack,  𝛼	
  (rad)	
   0.13963	
   0.12217	
   0.10472	
   0.08727	
   0.06981	
   0.05236	
   0.03491	
   0.01745	
  
M01	
   1.5	
  
M02	
   2.5	
  
S.F	
  (Safety	
  Factor)	
   1.5	
  
Δ𝑝!"For	
  M01	
   129881.0	
   113645.9	
   97410.8	
   81175.6	
   64940.5	
   48705.4	
   32470.3	
   16235.1	
  
Δ𝑝!"	
  For	
  M02	
   67031.7	
   58652.8	
   50273.8	
   41894.8	
   33515.9	
   25136.9	
   16757.9	
   8379.0	
  
Node	
  ID	
   X	
  (m)	
   Y	
  (m)	
  
A	
   0	
   0.180	
  
B	
   0	
   0	
  
C	
   0.080	
   0.080	
  
D	
   0.030	
   0.080	
  
E	
   0	
   0.150	
  
F	
   0	
   0.025	
  
Amit Ramji – A4 – University of Hertfordshire
6
Secondly	
  set	
  up	
  the	
  linear	
  elastic	
  isotropic	
  material	
  properties	
  as	
  shown	
  below	
  in	
  Figure 2	
  and	
  Table 3,	
  
where	
  the	
  steel	
  plate	
  is	
  assumed	
  to	
  perfectly	
  manufactured	
  with	
  uniform	
  (isotropic)	
  properties	
  in	
  all	
  
directions,	
  perfectly	
  elastic,	
  and	
  without	
  consideration	
  of	
  thermal	
  expansion	
  as	
  the	
  plate	
  dimensions	
  are	
  
relatively	
  small.	
  
Table 3 - Summary Material Properties
Table 4 - Raw material properties from sample tests
Figure 2 – Material Properties Input
Next	
   set	
   up	
   the	
   thickness	
   properties	
   of	
   the	
   plate	
   to	
   account	
   for	
   the	
   stiffness	
   properties,	
   again	
   this	
  
assumes	
  the	
  material	
  stiffness	
  is	
  uniform	
  in	
  all	
  directions,	
  which	
  isn’t	
  the	
  case	
  for	
  all	
  material	
  scenarios.	
  
Figure 3 - Uniform stiffness properties
Figure 4 - Uniform thickness properties
Subsequently	
  set	
  up	
  a	
  Fine	
  4	
  Node	
  quadrilateral	
  mesh	
  using	
  the	
  surface	
  selection	
  tool.	
  This	
  type	
  of	
  mesh	
  
can	
   be	
   used	
   for	
   analysis	
   of	
   plane	
   stress	
   or	
   strain,	
   thin	
   plate	
   bending	
   and	
   for	
   shear	
   analysis	
   of	
   plates.	
  
Other	
  mesh	
  types	
  are	
  explained	
  in	
  Table	
  5.1	
  of	
  literature	
  [1],	
  also	
  in	
  [2]	
  and	
  new	
  approaches	
  found	
  in	
  [3-­‐
6].	
  Package	
  specific	
  FEA	
  guides	
  also	
  explain	
  the	
  use	
  and	
  types	
  of	
  mesh’s	
  and	
  their	
  applications	
  whereas	
  
tools	
  such	
  as	
  Abaqus,	
  Hypermesh	
  and	
  MSC	
  PATRAN	
  can	
  allow	
  specific	
  mesh	
  optimisation	
  in	
  key	
  areas,	
  
however	
  is	
  out	
  of	
  the	
  scope	
  in	
  this	
  application	
  of	
  simple	
  cantilever	
  plate	
  bending.	
  
	
   	
   	
  
Figure 5 - Selection of fine mesh
Figure 6 - Post meshing operation	
  
Steel	
  Plate	
  	
  
[Rolled:	
  tmin<3mm<tmax]	
   	
   Units	
  
Young’s	
  modulus,	
  E	
   200	
   Gpa	
  
Poisson’s	
  Ratio,	
  v	
   0.30	
   -­‐	
  
Tensile	
  strength	
  (Yield),	
   𝝈 𝑻𝒀𝑺	
   600	
   Mpa	
  
Tensile	
  strength	
  (Ultimate)	
   𝝈 𝑼𝑻𝑺	
   800	
   Mpa	
  
Amit Ramji – A4 – University of Hertfordshire
7
Following	
  meshing,	
  apply	
  boundary	
  conditions	
  and	
  load	
  cases	
  into	
  the	
  pre-­‐processor	
  menu,	
  where	
  the	
  
wing	
  root	
  is	
  treated	
  as	
  fixed	
  in	
  all	
  Degrees	
  of	
  Freedom	
  (DOF)	
  and	
  apply	
  the	
  uniform	
  maximum	
  pressure	
  
load	
  (Δp!"#)	
  as	
  calculated	
  in	
  the	
  Preliminary Analysis	
  section	
  of	
  this	
  report.	
  The	
  direction	
  of	
  the	
  pressure	
  
load	
  is	
  to	
  be	
  applied	
  normal	
  to	
  the	
  wing	
  surface,	
  however	
  as	
  the	
  analysis	
  is	
  linear,	
  geometry	
  above	
  and	
  
below	
  the	
  mid-­‐plane	
  is	
  symmetric,	
  weight	
  direction	
  is	
  not	
  considered,	
  therefore	
  the	
  loading	
  direction	
  
does	
  not	
  affect	
  the	
  results.	
  
Figure 7 - Boundary conditions (Fix all DOF between Node ID’s E to F)
Figure 8 - Applying Pressure Loading onto wind surface
Finally	
  proceed	
  with	
  simulation	
  of	
  the	
  load	
  case	
  and	
  view	
  the	
  solution	
  as	
  nodal	
  for	
  Displacements,	
  
Stress	
  intensity	
  and	
  Von-­‐Misses	
  stress.	
  
	
  
	
  
Figure 9 – Nodal Displacements stating Max Deflection at Wing Tip (CD) is 1.596mm	
  
Amit Ramji – A4 – University of Hertfordshire
8
Figure 10 - Stress Intensity Showing Highest Stress at Node F, lowest at Node A as expected.
Figure 11 - Von-Misses Stress peak at Node F as expected.
Post	
  Processor	
  Outputs	
   Output	
  (unit)	
   Output	
  (Required	
  unit)	
  
Displacement	
  (Normal	
  to	
  Wing	
  surface)	
   0.001596	
  (m)	
   1.596	
  (mm)	
  
Stress	
  Intensity	
  (Node	
  F)	
   729,000,000	
  (Pa)	
   729	
  (MPa)	
  
Von-­‐Misses	
  (Node	
  F)	
   694,000,000	
  (Pa)	
   694	
  (MPa)	
  
Table 5 - Post Processor Output Summary Table of results
Analysis:	
  	
  
From	
   the	
   Finite	
   Element	
   method	
   above,	
   the	
   results	
   state	
   that	
   the	
   maximum	
   stress	
   is	
   seen	
   at	
   Node	
   F,	
  
which	
   agrees	
   with	
   classical	
   static	
   mechanics.	
   Node	
   F	
   is	
   the	
   point	
   that	
   is	
   surrounded	
   by	
   most	
   of	
   the	
  
perpendicular	
  area	
  from	
  the	
  root	
  chord	
  therefore	
  will	
  have	
  the	
  highest	
  stress	
  concentration.	
  Additionally	
  
the	
  method	
  of	
  constraint	
  for	
  the	
  FE	
  modelling	
  means	
  that	
  this	
  area	
  is	
  showing	
  to	
  fail	
  and	
  go	
  beyond	
  the	
  
elastic	
  region	
  of	
  the	
  material,	
  however	
  the	
  truth	
  may	
  be	
  that	
  the	
  part	
  will	
  not	
  fail	
  in	
  this	
  region	
  and	
  is	
  a	
  
property	
  of	
  the	
  constraint	
  method	
  used	
  in	
  modelling.	
  
	
  
Furthermore	
  the	
  stress	
  distribution	
  will	
  become	
  smaller	
  as	
  the	
  leading	
  edge	
  (AC)	
  is	
  approached	
  until	
  the	
  
stress	
  is	
  the	
  same	
  as	
  the	
  wing	
  loading	
  pressure.	
  In	
  the	
  lateral	
  direction	
  moving	
  from	
  the	
  root	
  to	
  the	
  tip,	
  
the	
  stress	
  levels	
  will	
  decrease	
  as	
  the	
  constraint	
  is	
  moved	
  further	
  away	
  from	
  the	
  area	
  of	
  interest.	
  Thus	
  the	
  
stress	
  distribution	
  in	
  the	
  lateral	
  direction	
  will	
  decrease	
  to	
  the	
  pressure	
  loading	
  value	
  (wing	
  tip)	
  as	
  this	
  
case	
  is	
  considering	
  a	
  cantilever	
  solution.	
  The	
  maximum	
  deflection	
  nodes	
  are	
  also	
  as	
  expected	
  as	
  the	
  wing	
  
tip	
   is	
   furthest	
   from	
   the	
   support	
   of	
   the	
   root	
   structure,	
   hence	
   will	
   be	
   prone	
   to	
   relatively	
   high	
   levels	
   of	
  
deflections.	
  The	
  slope	
  of	
  deflection	
  at	
  the	
  root	
  will	
  be	
  greatest	
  as	
  once	
  again	
  the	
  constraint	
  is	
  present	
  in	
  
this	
  region	
  from	
  EF.	
  
	
  
Amit Ramji – A4 – University of Hertfordshire
9
Overall	
   the	
   FE	
   model	
   does	
   correctly	
   describes	
   what	
   is	
   true	
   regarding	
   cantilever	
   plate	
   bending	
   and	
  
justifies	
  a	
  reason	
  to	
  conduct	
  further	
  analysis	
  in	
  the	
  constraint	
  region	
  at	
  Node	
  F.	
  The	
  possibility	
  of	
  gradual	
  
increased	
  cross	
  section	
  can	
  be	
  justified	
  or	
  a	
  reinforcement	
  wing	
  spar	
  added.	
  However	
  for	
  this	
  analysis,	
  
the	
   Von	
   Misses	
   stress	
   is	
   shown	
   to	
   be	
   694	
   MPa	
   (Table 5),	
   the	
   material	
   Tensile	
   Yield	
   Strength	
  
(σ!"#)=600MPa	
  (Table 3),	
  therefore	
  suggests	
  this	
  cantilever	
  plate	
  has	
  exceeded	
  its	
  elastic	
  limits	
  and	
  could	
  
potentially	
  fail	
  rapidly	
  under	
  plastic	
  fast	
  fracture.	
  This	
  is	
  the	
  most	
  extreme	
  case,	
  judging	
  from	
  the	
  stress	
  
difference	
   between	
   beginning	
   of	
   plastic	
   region	
   and	
   maximum	
   Von-­‐Misses	
   stress,	
   the	
   difference	
   is	
   94	
  
MPa,	
  therefore	
  requires	
  further	
  investigation	
  if	
  reinforcement	
  is	
  not	
  to	
  be	
  carried	
  out.	
  
Alternative	
  methods	
  of	
  analysis	
  
	
  
There	
  can	
  be	
  many	
  methods,	
  which	
  attempt	
  to	
  calculate	
  the	
  stress	
  for	
  a	
  non-­‐rectangular	
  cantilever	
  plate	
  
to	
  calculate	
  the	
  stress	
  at	
  different	
  locations.	
  Using	
  integration	
  methods	
  to	
  work	
  out	
  the	
  areas	
  in	
  different	
  
locations	
  over	
  the	
  wing	
  and	
  discretizing	
  the	
  areas	
  into	
  dy	
  and	
  dx	
  of	
  which	
  the	
  product	
  is	
  a	
  small	
  element	
  
area.	
  The	
  slope	
  of	
  the	
  leading	
  edge	
  and	
  trailing	
  edge	
  will	
  lead	
  one	
  to	
  encounter	
  a	
  function	
  of	
  geometry	
  for	
  
the	
   integration	
   limits.	
   Later	
   the	
   pressure	
   loading	
   is	
   multiplied	
   to	
   acquire	
   a	
   loading	
   function	
   per	
   dydx	
  
area.	
   Subsequently	
   a	
   function	
   for	
   moment	
   arm	
   is	
   required	
   which	
   cantilever	
   beam	
   bending	
   theory	
  
provides	
  for	
  uniform	
  load	
  distribution.	
  However	
  this	
  is	
  the	
  exact	
  same	
  as	
  discretising	
  the	
  problem	
  into	
  4	
  
Node	
  Quad	
  Elements,	
  which	
  FEA	
  has	
  provided	
  a	
  solution	
  for	
  in	
  a	
  shorter	
  time.	
  
	
  
Other	
  methods	
  found	
  in	
  chapter	
  7	
  of	
  reference	
  [7]	
  by	
  Megson,	
  considers	
  a	
  pure	
  analytical	
  approach	
  is	
  
methods	
   using	
   Kirchhoff-­‐Love	
   plate	
   representation,	
   Navier	
   Solutions,	
   Mildlins	
   methods	
   for	
   thicker	
  
plates,	
  or	
  the	
  most	
  appropriate	
  for	
  the	
  current	
  case	
  would	
  be	
  to	
  utilise	
  Reissner-­‐Stein	
  Cantilever	
  plates.	
  
[1,	
  7-­‐13]	
  
Rectangular	
  plate	
  approximation	
  
An	
  attempt	
  to	
  show	
  the	
  trend	
  has	
  been	
  made	
  below	
  which	
  utilises	
  methods	
  based	
  on	
  stiffness	
  constants	
  
of	
  flat	
  plates	
  through	
  experimental	
  means	
  and	
  problem	
  simplification	
  into	
  a	
  rectangular	
  plate.	
  The	
  same	
  
solution	
  is	
  not	
  reached,	
  as	
  the	
  real	
  solution	
  would	
  require	
  an	
  iterative	
  and	
  element	
  wise	
  approach	
  as	
  FE	
  
provides	
   and	
   is	
   explained	
   above.	
   This	
   does	
   however	
   provide	
   a	
   justification	
   of	
   classic	
   mechanics	
   of	
  
perpendicular	
   moment	
   arms	
   being	
   kept	
   constant	
   and	
   the	
   wing	
   root	
   (parameter	
   “a”	
   below)	
   being	
  
increased.	
  
	
  
Table 6 - Roark's Stress and Strain simplification into Rectangular Plate.
From	
  the	
  above,	
  increasing	
  root	
  length	
  has	
  very	
  shallow	
  stress	
  climb	
  rate	
  compared	
  with	
  perpendicular	
  
distance	
  (Span)	
  increase,	
  thus	
  confirming	
  classic	
  beam	
  bending	
  theory.	
  
	
  
	
  
Roarks	
  [Table	
  11.4]	
  (Simplification	
  of	
  wing	
  into	
  Flat	
  Rectangular	
  Cantilever	
  Plate	
  to	
  observe	
  trend)	
  [1]	
  
t	
  (mm)	
   3	
  
a	
  (mm)	
   50	
   80	
   120	
   160	
   240	
  
b	
  (mm)	
   80	
  
a/b	
   0.625	
   1	
   1.5	
   2	
   3	
  
Δ𝑝!"#	
  (MPa)	
   -­‐0.194821529	
  
𝛽!	
   0.38	
   0.665	
   1.282	
   1.804	
   2.45	
  
𝛽!	
   0.386	
   0.565	
   0.73	
   0.688	
   0.434	
  
𝛾!	
   0.541	
   0.701	
   0.919	
   1.018	
   1.055	
  
𝛾!	
   0.526	
   0.832	
   1.491	
   1.979	
   2.401	
  
𝜎 =
−𝛽!Δ𝑝!"# 𝑏!
𝑡!
	
  
(at	
  centre	
  of	
  fixed	
  edge)	
  (MPa)	
   52.6451	
   92.1289	
   177.6080	
   249.9257	
   339.4224	
  
𝑅 =    𝛾!Δ𝑝!"# 𝑏	
  
(at	
  centre	
  of	
  fixed	
  edge)	
  (mm)	
   8.4319	
   10.9256	
   14.3233	
   15.8663	
   16.4429	
  
𝜎 =
−𝛽!Δ𝑝!"# 𝑏!
𝑡!
	
  
(at	
  centre	
  of	
  free	
  edge)	
  (MPa)	
   -­‐53.4763	
   -­‐78.2750	
   -­‐101.1340	
   -­‐95.3154	
   -­‐60.1263	
  
𝑅 =    𝛾!Δ𝑝!"# 𝑏	
  
(at	
  end	
  of	
  free	
  edge)	
  (mm)	
   8.1981	
   12.9673	
   23.2383	
   30.8441	
   37.4213	
  
Amit Ramji – A4 – University of Hertfordshire
10
Conclusions:	
  	
  
By	
  observing	
  the	
  Maximum	
  Von	
  Misses	
  stress	
  of	
  694	
  MPa	
  from	
  Table 5,	
  one	
  can	
  observe	
  that	
  some	
  areas	
  
have	
   indeed	
   surpassed	
   the	
   elastic	
   limit	
   of	
   steel	
   with	
   the	
   current	
   geometry	
   of	
   which	
   the	
   yield	
   limit	
   is	
  
shown	
  in	
  Table 3	
  of	
  600	
  MPa.	
  This	
  may	
  be	
  due	
  to	
  modelling	
  constraints	
  as	
  discusses	
  earlier,	
  where	
  the	
  
maximum	
  stressed	
  area	
  is	
  amplified	
  by	
  the	
  presence	
  of	
  constraint	
  features.	
  This	
  has	
  the	
  same	
  effect	
  as	
  
stress	
   concentration	
   factors	
   where	
   stresses	
   are	
   amplified	
   based	
   on	
   geometry,	
   further	
   reading	
   can	
   be	
  
found	
  in	
  Petersons	
  et	
  al	
  [14]	
  for	
  stress	
  concentrations	
  factors	
  (Kt)	
  based	
  on	
  geometry.	
  
	
  
The	
   structural	
   integrity	
   of	
   the	
   plate	
   wing	
   model	
   in	
   the	
   wind	
   tunnel	
   will	
   be	
   effected	
   as	
   the	
   stressed	
  
material	
  would	
  yield	
  in	
  some	
  places	
  as	
  indicated	
  by	
  FEA,	
  therefore	
  may	
  exhibit	
  fast	
  fracture.	
  To	
  reduce	
  
the	
  chances	
  of	
  failure	
  and	
  damage	
  to	
  the	
  wind	
  tunnel,	
  this	
  case	
  should	
  be	
  investigated	
  further	
  by;	
  Non-­‐
Linear	
  FEA,	
  a	
  better	
  representation	
  of	
  constraints,	
  possible	
  structural	
  improvements	
  such	
  as	
  a	
  thicker	
  
plate,	
   thicker	
   wing	
   root,	
   adding	
   a	
   stiffener	
   spar	
   or	
   spreading	
   the	
   loads	
   through	
   the	
   cantilever	
   over	
   a	
  
larger	
  root	
  chord	
  distance	
  if	
  possible.	
  In	
  actuality	
  the	
  structural	
  integrity	
  of	
  the	
  wind	
  tunnel	
  will	
  be	
  fine	
  
as	
  the	
  safety	
  factor	
  will	
  not	
  cause	
  the	
  part	
  to	
  fail	
  during	
  testing,	
  however	
  the	
  wing	
  plate	
  will	
  need	
  to	
  be	
  
checked	
   regularly	
   if	
   left	
   as	
   is,	
   there	
   will	
   be	
   some	
   permanent	
   deformation	
   which	
   could	
   progressively	
  
worsen.	
  	
  
	
  
Non-­‐strength	
  related	
  issues	
  identified	
  with	
  the	
  FEA	
  is	
  with	
  the	
  use	
  of	
  constrains.	
  Use	
  of	
  nodal	
  elements	
  
to	
  constrain	
  the	
  root	
  of	
  the	
  wing	
  has	
  identified	
  and	
  amplified	
  a	
  potential	
  highly	
  stressed	
  region	
  as	
  stated	
  
previously.	
  Material	
  is	
  said	
  to	
  be	
  failing	
  by	
  surpassing	
  the	
  steel’s	
  elastic	
  yield	
  limit.	
  This	
  indicates	
  a	
  high	
  
stress	
   concentration	
   when	
   in	
   actual	
   fact	
   more	
   information	
   is	
   required	
   on	
   the	
   part.	
   A	
   static	
   deflection	
  
experiment	
  can	
  be	
  conducted	
  to	
  prove	
  or	
  disprove	
  the	
  FEA	
  and	
  is	
  usually	
  what	
  is	
  done	
  on	
  actual	
  aircraft	
  
skins.	
  The	
  use	
  of	
  strain	
  rosettes	
  and	
  bonded	
  strain	
  gauges	
  on	
  aircraft	
  test	
  skins	
  can	
  identify	
  experimental	
  
strains	
  which	
  can	
  be	
  later	
  input	
  back	
  into	
  the	
  FEA	
  model	
  for	
  comparison.	
  
	
  
Checking	
   by	
   analytical	
   methods	
   is	
   a	
   lengthy	
   task	
   and	
   the	
   solution	
   will	
   not	
   always	
   be	
   accurate	
   as	
   the	
  
number	
   of	
   iterations	
   can	
   never	
   be	
   matched	
   to	
   that	
   carried	
   out	
   by	
   FEA.	
   Some	
   analytical	
   methods	
   are	
  
shown	
  above	
  and	
  their	
  limitations	
  on	
  the	
  real	
  geometry	
  of	
  the	
  plate.	
  
	
  
The	
  objective	
  of	
  this	
  FE	
  investigation	
  was	
  to	
  determine	
  the	
  structural	
  integrity	
  of	
  a	
  test	
  wing	
  to	
  be	
  tested	
  
at	
  supersonic	
  speeds	
  in	
  a	
  wind	
  tunnel.	
  The	
  analysis	
  shows	
  that	
  further	
  investigation	
  is	
  required	
  as	
  the	
  
material	
  would	
  be	
  prone	
  to	
  yielding	
  in	
  some	
  areas.	
  Therefore	
  simply	
  based	
  on	
  that	
  evidence,	
  justification	
  
for	
  FEA	
  is	
  complete	
  as	
  it	
  avoids	
  potential	
  damage	
  to	
  the	
  wind	
  tunnel,	
  saves	
  on	
  costs	
  for	
  development	
  as	
  
components	
   can	
   be	
   sized	
   to	
   withstand	
   the	
   loads	
   imparted	
   on	
   them	
   without	
   testing.	
   For	
   the	
   case	
   of	
  
Cantilever	
  thin	
  plates,	
  analytical	
  methods	
  exist	
  for	
  rectangular	
  shapes	
  however	
  the	
  boundary	
  conditions	
  
for	
   simply	
   supported	
   plates	
   cannot	
   be	
   applied	
   in	
   this	
   application	
   directly.	
   Cantilever	
   beam	
   bending	
  
theory	
  can	
  be	
  used	
  to	
  determine	
  the	
  maximum	
  Bending	
  Moment	
  (BM)	
  at	
  the	
  root;	
  however	
  often	
  in	
  most	
  
cases	
  the	
  faster	
  and	
  accurate	
  solution	
  will	
  be	
  by	
  FEM	
  methods.	
  
	
  
The	
   maximum	
   deflection	
   of	
   this	
   plate	
   during	
   peak	
   loading	
   conditions	
   was	
   approximately	
   1.6mm	
   as	
  
shown	
  in	
  Table 5.	
  Which	
  means	
  it	
  has	
  a	
  deflection	
  ratio	
  of	
  approximately	
  2%	
  over	
  the	
  span	
  of	
  80mm.	
  This	
  
is	
  a	
  reasonable	
  deflection	
  and	
  can	
  be	
  calculated	
  with	
  cantilever	
  beam	
  bending	
  functions.	
  (A	
  clamped	
  15	
  
cm	
  steel	
  rule	
  will	
  also	
  help	
  to	
  understand	
  the	
  static	
  mechanics	
  of	
  this	
  wing	
  loading	
  problem).	
  To	
  improve	
  
deflection	
  the	
  real	
  wing	
  is	
  given	
  a	
  thickness,	
  with	
  reinforcement	
  stringers,	
  spars	
  and	
  ribs,	
  thus	
  provides	
  a	
  
larger	
   Second	
   Moment	
   of	
   Area	
   (I)	
   and	
   enables	
   the	
   skins	
   to	
   be	
   in	
   pure	
   tension	
   or	
   compression.	
  
Composites	
  can	
  therefore	
  be	
  introduced	
  in	
  order	
  to	
  use	
  this	
  geometry	
  and	
  loading	
  condition	
  to	
  one’s	
  
advantage.	
  
Amit Ramji – A4 – University of Hertfordshire
11
Discussion	
  
The	
  direction	
  of	
  pressure	
  loads	
  as	
  described	
  in	
  the	
  Finite Element Analysis (FEA) Procedure	
  section	
  of	
  this	
  
report	
  explains	
  how	
  direction	
  is	
  important.	
  However	
  for	
  this	
  simplification	
  of	
  a	
  thin	
  cantilever	
  plate,	
  the	
  
mid	
  plane	
  symmetry	
  and	
  combination	
  of	
  not	
  considering	
  weight	
  means	
  this	
  analysis	
  is	
  valid	
  if	
  a	
  +ve	
  or	
  –
ve	
   pressure	
   is	
   applied.	
   Other	
   investigations	
   including	
   sinusoidal	
   loading	
   due	
   to	
   shock	
   waves,	
   ground	
  
interference,	
  weather	
  gusts	
  or	
  microbursts	
  may	
  be	
  considered	
  for	
  wing	
  loading	
  along	
  with	
  frequency	
  
analysis	
  of	
  sustained	
  engine	
  imbalance	
  and	
  its	
  effects	
  on	
  fatigue.	
  
	
  
Plate	
   modelling	
   can	
   be	
   used	
   for	
   fuselage	
   and	
   wing	
   skin	
   loading	
   analysis	
   alongside	
   other	
   applications	
  
using	
  composite	
  structures	
  and	
  sandwich	
  panels	
  [15-­‐18].	
  Consideration	
  of	
  cantilever	
  plate	
  methods	
  have	
  
also	
   been	
   made	
   in	
   gear	
   tooth	
   analysis	
   as	
   reported	
   by	
   Wellauer	
   et	
   al	
   [19].	
   Composite	
   modelling	
   with	
  
isotropic	
  properties	
  can	
  also	
  be	
  made	
  simple	
  with	
  thin	
  plate	
  analogies	
  where	
  minimum	
  strength	
  values	
  
are	
   input	
   into	
   the	
   model	
   to	
   identify	
   stress	
   hot-­‐spots,	
   delamination	
   and	
   surface	
   effects	
   for	
   further	
  
consideration	
  and	
  fibre	
  orientation	
  and	
  design	
  sizing.	
  [16,	
  18,	
  20,	
  21]	
  
	
  
From	
  Table 1,	
  one	
  can	
  see	
  how	
  the	
  pressure	
  loading	
  is	
  increasing	
  as	
  the	
  angle	
  of	
  attack	
  is	
  increased	
  and	
  at	
  
lower	
  Mach	
  No’s.	
  The	
  benefit	
  of	
  FEM	
  methods	
  is	
  that	
  one	
  can	
  input	
  all	
  these	
  complex	
  combinations	
  into	
  
the	
   model	
   as	
   separate	
   load	
   cases	
   and	
   run	
   the	
   analysis	
   in	
   a	
   very	
   short	
   amount	
   of	
   time.	
   Therefore	
   the	
  
sizing	
  and	
  analysis	
  can	
  be	
  carried	
  out	
  on	
  the	
  components	
  with	
  consideration	
  to	
  a	
  wide	
  range	
  of	
  input	
  
variables/cases.	
  The	
  same	
  applies	
  for	
  frequency	
  and	
  vibration	
  analysis,	
  a	
  range	
  band	
  can	
  be	
  set	
  for	
  each	
  
load	
  case	
  and	
  studied	
  further	
  in	
  the	
  post-­‐processor	
  or	
  numerically	
  through	
  direct	
  output	
  files.	
  It	
  may	
  be	
  
interesting	
  to	
  investigate	
  increases	
  in	
  aircraft	
  pitch	
  angle,	
  thus	
  Mach	
  No	
  decreases,	
  meaning	
  from	
  the	
  
range	
  considered	
  in	
  Table 1,	
  the	
  combination	
  of	
  these	
  flight	
  characteristics	
  could	
  worsen	
  the	
  loading	
  on	
  
the	
  wing.	
  
	
   	
  
Amit Ramji – A4 – University of Hertfordshire
12
References	
  
[1] Young, W., Budynas R. Roark’s formulas for stress and strain. 7. 2002, McGraw-Hill.
[2] Jaehwan, K., et al., Finite-element modeling of a smart cantilever plate and comparison with experiments. Smart
Materials and Structures, 1996. 5(2): p. 165.
[3] Clough, R.W. and C.A. Felippa, A refined quadrilateral element for analysis of plate bending. 1968, DTIC
Document.
[4] Batoz, J.L., An explicit formulation for an efficient triangular plate-bending element. International Journal for
Numerical Methods in Engineering, 1982. 18(7): p. 1077-1089.
[5] Batoz, J.L., K.J. Bathe, and L.W. Ho, A study of three-node triangular plate bending elements. International
Journal for Numerical Methods in Engineering, 1980. 15(12): p. 1771-1812.
[6] Hughes, T.J.R., R.L. Taylor, and W. Kanoknukulchai, A simple and efficient finite element for plate bending.
International Journal for Numerical Methods in Engineering, 1977. 11(10): p. 1529-1543.
[7] Megson, T.H.G., Chapter 7 - Bending of thin plates, in Aircraft Structures for Engineering Students (Fifth
Edition), T.H.G. Megson, Editor. 2013, Butterworth-Heinemann: Boston. p. 233-266.
[8] Wang, W. and M.X. Shi, Thick plate theory based on general solutions of elasticity. Acta mechanica, 1997.
123(1): p. 27-36.
[9] Arnold, D.N. and R.S. Falk. Edge effects in the Reissner-Mindlin plate theory. in Presented at the winter annual
meeting of the American Society of Mechanical Engineers. 1989.
[10] Karam, V.J. and J.C.F. Telles, On boundary elements for Reissner's plate theory. Engineering Analysis, 1988.
5(1): p. 21-27.
[11] Fo-van, C., Bending of uniformly cantilever rectangular plates. Applied Mathematics and Mechanics, 1980. 1(3):
p. 371-383.
[12] Reissner, E. and M. Stein, Torsion and transverse bending of cantilever plates. 1951: National Advisory
Committee for Aeronautics.
[13] Reissner, E., On bending of elastic plates. Quart. Appl. Math, 1947. 5(1): p. 55-68.
[14] Pilkey, W.D. and D.F. Pilkey, Peterson's stress concentration factors. 2008: John Wiley & Sons.
[15] Thomsen, O.T. and W. Rits, Analysis and design of sandwich plates with inserts—a high-order sandwich plate
theory approach. Composites Part B: Engineering, 1998. 29(6): p. 795-807.
[16] Lu, P., et al., Thin plate theory including surface effects. International Journal of Solids and Structures, 2006.
43(16): p. 4631-4647.
[17] Barbero, E.J., J.N. Reddy, and J. Teply, An accurate determination of stresses in thick laminates using a
generalized plate theory. International journal for numerical methods in engineering, 1990. 29(1): p. 1-14.
[18] Barbero, E.J. and J.N. Reddy, Modeling of delamination in composite laminates using a layer-wise plate theory.
International Journal of Solids and Structures, 1991. 28(3): p. 373-388.
[19] Wellauer, E.J. and A. Seireg, Bending strength of gear teeth by cantilever-plate theory. Journal of Engineering
for Industry, 1960. 82: p. 213.
[20] Newman Jr, J.C. and I.S. Raju, Analyses of Surface Cracks in Finite Plates Under Tension or Bending Loads.
1979, DTIC Document.
[21] Reddy, J.N., E.J. Barbero, and J.L. Teply, A plate bending element based on a generalized laminate plate theory.
International Journal for Numerical Methods in Engineering, 1989. 28(10): p. 2275-2292.

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AmitRamji10241445FEA Report

  • 1. Amit Ramji – A4 – University of Hertfordshire 1 COURSEWORK ASSIGNMENT Module Title: Mechanics and Properties of Materials Module Code: 6ACM0003 Assignment Title: Finite Element Analysis of a Wind Tunnel Model Individual Tutor: Dr Y Xu/Dr A Chrysanthou Internal Moderator: Dr. Yong Chen ASSIGNMENT SUBMISSION Students, this section must be completed before your work is submitted. Please print your forename and surname in capitals, provide your student registration number, your study year code (e.g. ASE1, EE1), and your signature in the spaces provided below. For Group work, each team member must complete this information. You may add or delete rows as required. Copyright Statement By completing the information below, I/we certify that this piece of assessment is my/our own work, that it is has not been copied from elsewhere, and that any extracts from books, papers, or other sources have been properly acknowledged as references or quotations. Forename: Family Name: SRN: Year Code: Signature: Amit Ramji 10241445 A4 Marks Awarded %: Marks Awarded after Lateness Penalty applied %: Penalties for Late Submissions • Late submission of any item of coursework will be capped at a minimum pass mark if received up to one week late. Any submission received more than one week late will be awarded a mark of zero. • Late submission of referred coursework will automatically be awarded a mark of zero. Guidance on avoiding academic assessment offences such as plagiarism and collusion is given at the URL: http://www.studynet.herts.ac.uk/ptl/common/LIS.nsf/lis/citing_menu
  • 2. Amit Ramji – A4 – University of Hertfordshire 2 ASSIGNMENT BRIEF Students, you should delete this section before submitting your work. This Assignment assesses the following module Learning Outcomes: 4. Examine existing designs and actual components in engineering situations, using methods such as finite element analysis, photoelasticity, non-destructive testing and fractography. 5. Limit the occurrence of failure in materials by appropriate modelling, design and materials selection. 6. Apply analytical methods to structural components subjected to complex stress/strain fields. Assignment Brief: In this assignment, you will create a finite element model of a wind tunnel model of a wing to be tested at supersonic speeds in order to assess its structural integrity. You should carry out the modelling and write a short report on your findings. Further details are provided on the attached sheets. Submission Requirements: Submission shall be through StudyNet This assignment is worth 50 % of the overall in- course assessment for this module. Marks Awarded for: Validity of the FE results - 40%; Extent to which reporting requirements are met - 20%; concluding remarks section – 20%; presentation of report - 20%. A note to the Students: 1. For undergraduate modules, a score above 40% represent a pass performance at honours level. 2. For postgraduate modules, a score of 50% or above represents a pass mark. 3. Modules may have several components of assessment and may require a pass in all elements. For further details, please consult the relevant Module Guide or ask the Module Leader. Typical (hours) required by the student(s) to complete the assignment: 15 hours Date Work handed out: 7 th November 2013 Date Work to be handed in: 29 th November 2013 Target Date for the return of the marked assignment: 7 th January 2014 Type of Feedback to be given for this assignment: General feedback on StudyNet and individual feedback for each report.
  • 3. Amit Ramji – A4 – University of Hertfordshire 3 Finite Element Analysis ANSYS Report Group E Amit Ramji 10241445 University of Hertfordshire - Aerospace Engineering Year 4 – Mechanics and Properties of Materials - 6ACM0003 26th November 2013
  • 4. Amit Ramji – A4 – University of Hertfordshire 4 Contents   Introduction .......................................................................................................................................................................... 5   Preliminary Analysis............................................................................................................................................................ 5   Finite Element Analysis (FEA) Procedure........................................................................................................................... 5   Analysis:............................................................................................................................................................................... 8   Alternative methods of analysis ........................................................................................................................................... 9   Conclusions:....................................................................................................................................................................... 10   Discussion .......................................................................................................................................................................... 11   References .......................................................................................................................................................................... 12   Table  of  Figures   Figure 1 – Cantilever Plate geometry....................................................................................................................................... 5   Figure 2 – Material Properties Input ........................................................................................................................................ 6   Figure 3 - Uniform stiffness properties.................................................................................................................................... 6   Figure 4 - Uniform thickness properties .................................................................................................................................. 6   Figure 5 - Selection of fine mesh ............................................................................................................................................. 6   Figure 6 - Post meshing operation............................................................................................................................................ 6   Figure 7 - Boundary conditions (Fix all DOF between Node ID’s E to F).............................................................................. 7   Figure 8 - Applying Pressure Loading onto wind surface ....................................................................................................... 7   Figure 9 – Nodal Displacements stating Max Deflection at Wing Tip (CD) is 1.596mm....................................................... 7   Figure 10 - Stress Intensity Showing Highest Stress at Node F, lowest at Node A as expected. ............................................ 8   Figure 11 - Von-Misses Stress peak at Node F as expected. ................................................................................................... 8   Data  Tables   Table 1 - Provided Parameters and calculated pressures ......................................................................................................... 5   Table 2 - Cantilever Plate Coordinates .................................................................................................................................... 5   Table 3 - Summary Material Properties ................................................................................................................................... 6   Table 4 - Raw material properties from sample tests............................................................................................................... 6   Table 5 - Post Processor Output Summary Table of results .................................................................................................... 8   Table 6 - Roark's Stress and Strain simplification into Rectangular Plate............................................................................... 9  
  • 5. Amit Ramji – A4 – University of Hertfordshire 5 Introduction   This   study   considers   a   single   edge   cantilever   plate   bending   for   interpretation   and   simplification   of   a   model   aircraft   wing   at   supersonic   speeds   for   wind   tunnel   testing.   The   objectives   are   to   evaluate   the   pressure  loads  and  analyse  the  structural  integrity  of  the  wing  model  to  be  tested.  The  relation  to  a  real   wing   allows   for   identification   of   stress   concentration   centre   and   maximum   stress   regions   which   attention   can   be   paid   in   more   detail   by   further   analysis,   reinforcement   or   alternative   modelling   techniques.   The   Finite   Element   methods   used   in   this   report   provide   a   basis   for   understanding   the   properties  of  thin  plates  under  uniform  pressure  loads,  however  in  reality  the  loading  conditions  and   boundary  conditions  are  very  complex.  Simple  analytical  methods  do  not  exist  for  complex  shapes  such   as  a  wing  plan-­‐form,  hence  a  comparative  study  is  shown  using  rectangular  cantilever  plates  to  display   that  the  theory  agrees  but  the  values  obtained  are  non  comparable.  Thus  providing  further  significance   to  Finite  Element  Modelling  (FEM)  methods  in  order  to  analyse  the  part  geometry  chosen  for  design  in   haste,  compared  to  non-­‐conservative  approximations  such  as  rectangular  plate  methods  described  later   in  this  report.   Table 1 - Provided Parameters and calculated pressures   Preliminary  Analysis   Sample  Calculation  of  Pressure  Loads   ∆𝑝 = 𝑞! 4 𝑀! ! − 1 𝛼 Calculation  of  Max  Pressure  Loading  from  Mach  No:   𝑀!" = 1.5     ∴   𝑞!" = 260  𝑀𝑃𝑎     ∴    Δ𝑝!" = 𝑞!" 4 𝑀!" ! − 1 8! 360 2𝜋 = 129.881  𝑀𝑃𝑎 𝑀!" = 2.5     ∴   𝑞!" = 275  𝑀𝑃𝑎   ∴    Δ𝑝!" = 𝑞!" 4 𝑀!" ! − 1 8! 360 2𝜋 = 67.032  𝑀𝑃𝑎 ∴    Δ𝑝!"# = 𝑆. 𝐹  ×  𝑀𝐴𝑋 Δ𝑝!" Δ𝑝!" = 𝟏𝟗𝟒. 𝟖𝟐𝟐  𝐌𝐏𝐚                              (𝑊ℎ𝑒𝑟𝑒  𝑆. 𝐹 = 1.5  𝑔𝑙𝑜𝑏𝑎𝑙) Finite  Element  Analysis  (FEA)  Procedure   Initially   set   up   the   geometry   of   a   flat   plate   with   the   dimensions   as   shown   in   Figure 1   and   tabulated   coordinates  in  Table 2.  Later  set  up  the  plate  geometry  by  selecting  the  points  and  creating  the  lines  as  in   Figure 1.   Table 2 - Cantilever Plate Coordinates Figure 1 – Cantilever Plate geometry Given  Parameters    Angle  of  attack,  𝛼  (deg)   8.0   7.0   6.0   5.0   4.0   3.0   2.0   1.0   Angle  of  attack,  𝛼  (rad)   0.13963   0.12217   0.10472   0.08727   0.06981   0.05236   0.03491   0.01745   M01   1.5   M02   2.5   S.F  (Safety  Factor)   1.5   Δ𝑝!"For  M01   129881.0   113645.9   97410.8   81175.6   64940.5   48705.4   32470.3   16235.1   Δ𝑝!"  For  M02   67031.7   58652.8   50273.8   41894.8   33515.9   25136.9   16757.9   8379.0   Node  ID   X  (m)   Y  (m)   A   0   0.180   B   0   0   C   0.080   0.080   D   0.030   0.080   E   0   0.150   F   0   0.025  
  • 6. Amit Ramji – A4 – University of Hertfordshire 6 Secondly  set  up  the  linear  elastic  isotropic  material  properties  as  shown  below  in  Figure 2  and  Table 3,   where  the  steel  plate  is  assumed  to  perfectly  manufactured  with  uniform  (isotropic)  properties  in  all   directions,  perfectly  elastic,  and  without  consideration  of  thermal  expansion  as  the  plate  dimensions  are   relatively  small.   Table 3 - Summary Material Properties Table 4 - Raw material properties from sample tests Figure 2 – Material Properties Input Next   set   up   the   thickness   properties   of   the   plate   to   account   for   the   stiffness   properties,   again   this   assumes  the  material  stiffness  is  uniform  in  all  directions,  which  isn’t  the  case  for  all  material  scenarios.   Figure 3 - Uniform stiffness properties Figure 4 - Uniform thickness properties Subsequently  set  up  a  Fine  4  Node  quadrilateral  mesh  using  the  surface  selection  tool.  This  type  of  mesh   can   be   used   for   analysis   of   plane   stress   or   strain,   thin   plate   bending   and   for   shear   analysis   of   plates.   Other  mesh  types  are  explained  in  Table  5.1  of  literature  [1],  also  in  [2]  and  new  approaches  found  in  [3-­‐ 6].  Package  specific  FEA  guides  also  explain  the  use  and  types  of  mesh’s  and  their  applications  whereas   tools  such  as  Abaqus,  Hypermesh  and  MSC  PATRAN  can  allow  specific  mesh  optimisation  in  key  areas,   however  is  out  of  the  scope  in  this  application  of  simple  cantilever  plate  bending.         Figure 5 - Selection of fine mesh Figure 6 - Post meshing operation   Steel  Plate     [Rolled:  tmin<3mm<tmax]     Units   Young’s  modulus,  E   200   Gpa   Poisson’s  Ratio,  v   0.30   -­‐   Tensile  strength  (Yield),   𝝈 𝑻𝒀𝑺   600   Mpa   Tensile  strength  (Ultimate)   𝝈 𝑼𝑻𝑺   800   Mpa  
  • 7. Amit Ramji – A4 – University of Hertfordshire 7 Following  meshing,  apply  boundary  conditions  and  load  cases  into  the  pre-­‐processor  menu,  where  the   wing  root  is  treated  as  fixed  in  all  Degrees  of  Freedom  (DOF)  and  apply  the  uniform  maximum  pressure   load  (Δp!"#)  as  calculated  in  the  Preliminary Analysis  section  of  this  report.  The  direction  of  the  pressure   load  is  to  be  applied  normal  to  the  wing  surface,  however  as  the  analysis  is  linear,  geometry  above  and   below  the  mid-­‐plane  is  symmetric,  weight  direction  is  not  considered,  therefore  the  loading  direction   does  not  affect  the  results.   Figure 7 - Boundary conditions (Fix all DOF between Node ID’s E to F) Figure 8 - Applying Pressure Loading onto wind surface Finally  proceed  with  simulation  of  the  load  case  and  view  the  solution  as  nodal  for  Displacements,   Stress  intensity  and  Von-­‐Misses  stress.       Figure 9 – Nodal Displacements stating Max Deflection at Wing Tip (CD) is 1.596mm  
  • 8. Amit Ramji – A4 – University of Hertfordshire 8 Figure 10 - Stress Intensity Showing Highest Stress at Node F, lowest at Node A as expected. Figure 11 - Von-Misses Stress peak at Node F as expected. Post  Processor  Outputs   Output  (unit)   Output  (Required  unit)   Displacement  (Normal  to  Wing  surface)   0.001596  (m)   1.596  (mm)   Stress  Intensity  (Node  F)   729,000,000  (Pa)   729  (MPa)   Von-­‐Misses  (Node  F)   694,000,000  (Pa)   694  (MPa)   Table 5 - Post Processor Output Summary Table of results Analysis:     From   the   Finite   Element   method   above,   the   results   state   that   the   maximum   stress   is   seen   at   Node   F,   which   agrees   with   classical   static   mechanics.   Node   F   is   the   point   that   is   surrounded   by   most   of   the   perpendicular  area  from  the  root  chord  therefore  will  have  the  highest  stress  concentration.  Additionally   the  method  of  constraint  for  the  FE  modelling  means  that  this  area  is  showing  to  fail  and  go  beyond  the   elastic  region  of  the  material,  however  the  truth  may  be  that  the  part  will  not  fail  in  this  region  and  is  a   property  of  the  constraint  method  used  in  modelling.     Furthermore  the  stress  distribution  will  become  smaller  as  the  leading  edge  (AC)  is  approached  until  the   stress  is  the  same  as  the  wing  loading  pressure.  In  the  lateral  direction  moving  from  the  root  to  the  tip,   the  stress  levels  will  decrease  as  the  constraint  is  moved  further  away  from  the  area  of  interest.  Thus  the   stress  distribution  in  the  lateral  direction  will  decrease  to  the  pressure  loading  value  (wing  tip)  as  this   case  is  considering  a  cantilever  solution.  The  maximum  deflection  nodes  are  also  as  expected  as  the  wing   tip   is   furthest   from   the   support   of   the   root   structure,   hence   will   be   prone   to   relatively   high   levels   of   deflections.  The  slope  of  deflection  at  the  root  will  be  greatest  as  once  again  the  constraint  is  present  in   this  region  from  EF.    
  • 9. Amit Ramji – A4 – University of Hertfordshire 9 Overall   the   FE   model   does   correctly   describes   what   is   true   regarding   cantilever   plate   bending   and   justifies  a  reason  to  conduct  further  analysis  in  the  constraint  region  at  Node  F.  The  possibility  of  gradual   increased  cross  section  can  be  justified  or  a  reinforcement  wing  spar  added.  However  for  this  analysis,   the   Von   Misses   stress   is   shown   to   be   694   MPa   (Table 5),   the   material   Tensile   Yield   Strength   (σ!"#)=600MPa  (Table 3),  therefore  suggests  this  cantilever  plate  has  exceeded  its  elastic  limits  and  could   potentially  fail  rapidly  under  plastic  fast  fracture.  This  is  the  most  extreme  case,  judging  from  the  stress   difference   between   beginning   of   plastic   region   and   maximum   Von-­‐Misses   stress,   the   difference   is   94   MPa,  therefore  requires  further  investigation  if  reinforcement  is  not  to  be  carried  out.   Alternative  methods  of  analysis     There  can  be  many  methods,  which  attempt  to  calculate  the  stress  for  a  non-­‐rectangular  cantilever  plate   to  calculate  the  stress  at  different  locations.  Using  integration  methods  to  work  out  the  areas  in  different   locations  over  the  wing  and  discretizing  the  areas  into  dy  and  dx  of  which  the  product  is  a  small  element   area.  The  slope  of  the  leading  edge  and  trailing  edge  will  lead  one  to  encounter  a  function  of  geometry  for   the   integration   limits.   Later   the   pressure   loading   is   multiplied   to   acquire   a   loading   function   per   dydx   area.   Subsequently   a   function   for   moment   arm   is   required   which   cantilever   beam   bending   theory   provides  for  uniform  load  distribution.  However  this  is  the  exact  same  as  discretising  the  problem  into  4   Node  Quad  Elements,  which  FEA  has  provided  a  solution  for  in  a  shorter  time.     Other  methods  found  in  chapter  7  of  reference  [7]  by  Megson,  considers  a  pure  analytical  approach  is   methods   using   Kirchhoff-­‐Love   plate   representation,   Navier   Solutions,   Mildlins   methods   for   thicker   plates,  or  the  most  appropriate  for  the  current  case  would  be  to  utilise  Reissner-­‐Stein  Cantilever  plates.   [1,  7-­‐13]   Rectangular  plate  approximation   An  attempt  to  show  the  trend  has  been  made  below  which  utilises  methods  based  on  stiffness  constants   of  flat  plates  through  experimental  means  and  problem  simplification  into  a  rectangular  plate.  The  same   solution  is  not  reached,  as  the  real  solution  would  require  an  iterative  and  element  wise  approach  as  FE   provides   and   is   explained   above.   This   does   however   provide   a   justification   of   classic   mechanics   of   perpendicular   moment   arms   being   kept   constant   and   the   wing   root   (parameter   “a”   below)   being   increased.     Table 6 - Roark's Stress and Strain simplification into Rectangular Plate. From  the  above,  increasing  root  length  has  very  shallow  stress  climb  rate  compared  with  perpendicular   distance  (Span)  increase,  thus  confirming  classic  beam  bending  theory.       Roarks  [Table  11.4]  (Simplification  of  wing  into  Flat  Rectangular  Cantilever  Plate  to  observe  trend)  [1]   t  (mm)   3   a  (mm)   50   80   120   160   240   b  (mm)   80   a/b   0.625   1   1.5   2   3   Δ𝑝!"#  (MPa)   -­‐0.194821529   𝛽!   0.38   0.665   1.282   1.804   2.45   𝛽!   0.386   0.565   0.73   0.688   0.434   𝛾!   0.541   0.701   0.919   1.018   1.055   𝛾!   0.526   0.832   1.491   1.979   2.401   𝜎 = −𝛽!Δ𝑝!"# 𝑏! 𝑡!   (at  centre  of  fixed  edge)  (MPa)   52.6451   92.1289   177.6080   249.9257   339.4224   𝑅 =   𝛾!Δ𝑝!"# 𝑏   (at  centre  of  fixed  edge)  (mm)   8.4319   10.9256   14.3233   15.8663   16.4429   𝜎 = −𝛽!Δ𝑝!"# 𝑏! 𝑡!   (at  centre  of  free  edge)  (MPa)   -­‐53.4763   -­‐78.2750   -­‐101.1340   -­‐95.3154   -­‐60.1263   𝑅 =   𝛾!Δ𝑝!"# 𝑏   (at  end  of  free  edge)  (mm)   8.1981   12.9673   23.2383   30.8441   37.4213  
  • 10. Amit Ramji – A4 – University of Hertfordshire 10 Conclusions:     By  observing  the  Maximum  Von  Misses  stress  of  694  MPa  from  Table 5,  one  can  observe  that  some  areas   have   indeed   surpassed   the   elastic   limit   of   steel   with   the   current   geometry   of   which   the   yield   limit   is   shown  in  Table 3  of  600  MPa.  This  may  be  due  to  modelling  constraints  as  discusses  earlier,  where  the   maximum  stressed  area  is  amplified  by  the  presence  of  constraint  features.  This  has  the  same  effect  as   stress   concentration   factors   where   stresses   are   amplified   based   on   geometry,   further   reading   can   be   found  in  Petersons  et  al  [14]  for  stress  concentrations  factors  (Kt)  based  on  geometry.     The   structural   integrity   of   the   plate   wing   model   in   the   wind   tunnel   will   be   effected   as   the   stressed   material  would  yield  in  some  places  as  indicated  by  FEA,  therefore  may  exhibit  fast  fracture.  To  reduce   the  chances  of  failure  and  damage  to  the  wind  tunnel,  this  case  should  be  investigated  further  by;  Non-­‐ Linear  FEA,  a  better  representation  of  constraints,  possible  structural  improvements  such  as  a  thicker   plate,   thicker   wing   root,   adding   a   stiffener   spar   or   spreading   the   loads   through   the   cantilever   over   a   larger  root  chord  distance  if  possible.  In  actuality  the  structural  integrity  of  the  wind  tunnel  will  be  fine   as  the  safety  factor  will  not  cause  the  part  to  fail  during  testing,  however  the  wing  plate  will  need  to  be   checked   regularly   if   left   as   is,   there   will   be   some   permanent   deformation   which   could   progressively   worsen.       Non-­‐strength  related  issues  identified  with  the  FEA  is  with  the  use  of  constrains.  Use  of  nodal  elements   to  constrain  the  root  of  the  wing  has  identified  and  amplified  a  potential  highly  stressed  region  as  stated   previously.  Material  is  said  to  be  failing  by  surpassing  the  steel’s  elastic  yield  limit.  This  indicates  a  high   stress   concentration   when   in   actual   fact   more   information   is   required   on   the   part.   A   static   deflection   experiment  can  be  conducted  to  prove  or  disprove  the  FEA  and  is  usually  what  is  done  on  actual  aircraft   skins.  The  use  of  strain  rosettes  and  bonded  strain  gauges  on  aircraft  test  skins  can  identify  experimental   strains  which  can  be  later  input  back  into  the  FEA  model  for  comparison.     Checking   by   analytical   methods   is   a   lengthy   task   and   the   solution   will   not   always   be   accurate   as   the   number   of   iterations   can   never   be   matched   to   that   carried   out   by   FEA.   Some   analytical   methods   are   shown  above  and  their  limitations  on  the  real  geometry  of  the  plate.     The  objective  of  this  FE  investigation  was  to  determine  the  structural  integrity  of  a  test  wing  to  be  tested   at  supersonic  speeds  in  a  wind  tunnel.  The  analysis  shows  that  further  investigation  is  required  as  the   material  would  be  prone  to  yielding  in  some  areas.  Therefore  simply  based  on  that  evidence,  justification   for  FEA  is  complete  as  it  avoids  potential  damage  to  the  wind  tunnel,  saves  on  costs  for  development  as   components   can   be   sized   to   withstand   the   loads   imparted   on   them   without   testing.   For   the   case   of   Cantilever  thin  plates,  analytical  methods  exist  for  rectangular  shapes  however  the  boundary  conditions   for   simply   supported   plates   cannot   be   applied   in   this   application   directly.   Cantilever   beam   bending   theory  can  be  used  to  determine  the  maximum  Bending  Moment  (BM)  at  the  root;  however  often  in  most   cases  the  faster  and  accurate  solution  will  be  by  FEM  methods.     The   maximum   deflection   of   this   plate   during   peak   loading   conditions   was   approximately   1.6mm   as   shown  in  Table 5.  Which  means  it  has  a  deflection  ratio  of  approximately  2%  over  the  span  of  80mm.  This   is  a  reasonable  deflection  and  can  be  calculated  with  cantilever  beam  bending  functions.  (A  clamped  15   cm  steel  rule  will  also  help  to  understand  the  static  mechanics  of  this  wing  loading  problem).  To  improve   deflection  the  real  wing  is  given  a  thickness,  with  reinforcement  stringers,  spars  and  ribs,  thus  provides  a   larger   Second   Moment   of   Area   (I)   and   enables   the   skins   to   be   in   pure   tension   or   compression.   Composites  can  therefore  be  introduced  in  order  to  use  this  geometry  and  loading  condition  to  one’s   advantage.  
  • 11. Amit Ramji – A4 – University of Hertfordshire 11 Discussion   The  direction  of  pressure  loads  as  described  in  the  Finite Element Analysis (FEA) Procedure  section  of  this   report  explains  how  direction  is  important.  However  for  this  simplification  of  a  thin  cantilever  plate,  the   mid  plane  symmetry  and  combination  of  not  considering  weight  means  this  analysis  is  valid  if  a  +ve  or  – ve   pressure   is   applied.   Other   investigations   including   sinusoidal   loading   due   to   shock   waves,   ground   interference,  weather  gusts  or  microbursts  may  be  considered  for  wing  loading  along  with  frequency   analysis  of  sustained  engine  imbalance  and  its  effects  on  fatigue.     Plate   modelling   can   be   used   for   fuselage   and   wing   skin   loading   analysis   alongside   other   applications   using  composite  structures  and  sandwich  panels  [15-­‐18].  Consideration  of  cantilever  plate  methods  have   also   been   made   in   gear   tooth   analysis   as   reported   by   Wellauer   et   al   [19].   Composite   modelling   with   isotropic  properties  can  also  be  made  simple  with  thin  plate  analogies  where  minimum  strength  values   are   input   into   the   model   to   identify   stress   hot-­‐spots,   delamination   and   surface   effects   for   further   consideration  and  fibre  orientation  and  design  sizing.  [16,  18,  20,  21]     From  Table 1,  one  can  see  how  the  pressure  loading  is  increasing  as  the  angle  of  attack  is  increased  and  at   lower  Mach  No’s.  The  benefit  of  FEM  methods  is  that  one  can  input  all  these  complex  combinations  into   the   model   as   separate   load   cases   and   run   the   analysis   in   a   very   short   amount   of   time.   Therefore   the   sizing  and  analysis  can  be  carried  out  on  the  components  with  consideration  to  a  wide  range  of  input   variables/cases.  The  same  applies  for  frequency  and  vibration  analysis,  a  range  band  can  be  set  for  each   load  case  and  studied  further  in  the  post-­‐processor  or  numerically  through  direct  output  files.  It  may  be   interesting  to  investigate  increases  in  aircraft  pitch  angle,  thus  Mach  No  decreases,  meaning  from  the   range  considered  in  Table 1,  the  combination  of  these  flight  characteristics  could  worsen  the  loading  on   the  wing.      
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