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Ozen Engineering Inc.
1210 E. Arques Ave, Suite 207
Sunnyvale, CA 94085
info@ozeninc.com
Can Ozcan (can@ozeninc.com)
Fract...
Design Philosophies
• It is critical to decide on a design philosophy
– Safe-Life
– Fail-Safe
– Damage-Tolerant
22
What is Fracture Mechanics?
• It is the study of flaws and cracks in materials
• Can be seen as a special case among diffe...
Why is Fracture Mechanics important?
• Strength of Material approach does not anticipate the
presence of a crack or does v...
Why is Fracture Mechanics important?
• Flaw Size (a) is an important parameter in
fracture mechanics approach
• Fracture T...
Industries
• Probably encountered in any industry dealing
with structures
– Automotive
– Electronics
– Healthcare
– Aviati...
Historical Background
• Comet Airplanes
7
[1] “The DeHavilland Comet Crash | Aerospace Engineering Blog.” [Online]. Availa...
Historical Background
• Liberty Ships
• ~1,500 instances of
brittle fracture during
WWII
• Studies revealed ships in
North...
Effect of Temperature on Fracture Toughness
• Fracture Toughness of materials are affected
by temperature
• Ships experien...
Historical Background
• Aloha Flight #243 in 1988:
• German Train ICE Accident in 1998:
10
• Life span definition:
Crack Initiation & Propagation
11
• Life span definition for fatigue analysis:
Crack Initiation & Propagation
The initiation stage
can represent a large
par...
CRACK INITIATION
• Physically, cracks initiate from;
– An imperfection
– An already existing crack
– A damaged (locally we...
Theoretical Developments
• A. Griffith (1893-1963)
published the results of his
studies on brittle fracture
• He found the...
15
Three Modes of Fracture
• Mode I denotes a symmetric opening (opening or tension mode)
• Mode II denotes an antisymmetric ...
Fracture Mechanics Parameters
• J-Integral
• Energy-Release Rate
• Stress-Intensity Factor
• T-Stress
• Material Force
• C...
Energy Release Rate and J-Integral
 Energy release rate can be calculated from stress intensity
factors
 The J-integral ...
Stress Intensity Factor
• The magnitude of stress field in the immediate vicinity of the crack tip is measured
by the “Str...
T-Stress
• Is the stress acting parallel to the crack faces
• Unlike J-integral, it can have both negative and
positive va...
Material Force
• “Material Force” method provides parameters for
global material and dissipation forces that yield
near-ti...
C*-Integral
• Creep crack growth becomes a concern when
structural components are operated at high
temperatures (ie Nuclea...
UMM Method
• The unstructured mesh method (UMM) is a
numerical tool used for evaluating fracture
mechanics parameters on u...
Fracture Mechanics Table
• Which parameters is applicable for which assumptions:
24
Method Material Behavior
J-Integral Li...
Crack-Growth Simulation
• VCCT-Based Interface Element Method
• Cohesive Zone Method
• XFEM-Based Method
25
Fracture Mechanics Meshing & Element Support
 KSCON command is used to skew
mid-side nodes around the crack tip.
 This w...
Fracture Mechanics Meshing & Element Support
27
2-D Edge Crack Propagation
 2 D Edge cracked plate
analysis
 can be solved both using
fracture mechanics tools
and cohes...
2-D Edge Crack Propagation
Crack Propagation Animation, β =15° (a) Crack Propagation Path, (b) SIF, FI; β =15°
• Fracture ...
Interface modeling
Problem Geometry Finite Element Model
 Edge crack propagation in a thin film-substrate(SiO2/Si) is stu...
3-D Edge Crack Analysis
In Thin Film-Substrate Systems
(a) Propagation Animation; Cut
Length=150
(b) Propagation Path; Cut...
Industrial Example: Pump Housing Fracture
• Pump housing subjected to internal pressure with a through
crack
Crack
0
0.04
...
Industrial example: Cracked helicopter flanged plate
• Automatic crack growth simulation under variable loading
33
Following Week Schedule
• March 26th: 10AM-10:45AM PT How to Perform
Fracture Mechanics Analysis in Workbench
• April 2nd:...
END
Thanks for your attention !!!
Questions ?
CONTACT:
Attention: Can Ozcan
OZEN ENGINEERING, INC.
1210 E. ARQUES AVE. SUI...
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01_INTRODUCTION_TO_FRACTURE_MECHANICS_linkedin

  1. 1. Ozen Engineering Inc. 1210 E. Arques Ave, Suite 207 Sunnyvale, CA 94085 info@ozeninc.com Can Ozcan (can@ozeninc.com) Fracture Mechanics in Ansys R16 Session-01 Introduction to Fracture Mechanics
  2. 2. Design Philosophies • It is critical to decide on a design philosophy – Safe-Life – Fail-Safe – Damage-Tolerant 22
  3. 3. What is Fracture Mechanics? • It is the study of flaws and cracks in materials • Can be seen as a special case among different design philosophies • Mostly deals with crack growth and life-time estimation 23
  4. 4. Why is Fracture Mechanics important? • Strength of Material approach does not anticipate the presence of a crack or does via concentration factors • Presence of cracks can significantly decrease the structural strength and reliability 4 𝜎 = 𝐹 𝐴 𝜎 ≫ 𝐹 𝐴 4
  5. 5. Why is Fracture Mechanics important? • Flaw Size (a) is an important parameter in fracture mechanics approach • Fracture Toughness replaces strength of material 5 𝜎 ≫ 𝐹 𝐴 a – For Linear-Elastic Fracture Mechanics (LEFM), fracture toughness of a material is determined from “Stress Intensity Factor” – For Elastic-Plastic Fracture Mechanics(EPFM), fracture toughness is determined via energy required to grow a crack 𝑲 𝑰𝑪 𝑱 𝑰𝑪 5
  6. 6. Industries • Probably encountered in any industry dealing with structures – Automotive – Electronics – Healthcare – Aviation – Civil – Nuclear – Defense – Maritime 6
  7. 7. Historical Background • Comet Airplanes 7 [1] “The DeHavilland Comet Crash | Aerospace Engineering Blog.” [Online]. Available: http://aerospaceengineeringblog.com/dehavilland-comet-crash/. [Accessed: 17-Mar-2015].
  8. 8. Historical Background • Liberty Ships • ~1,500 instances of brittle fracture during WWII • Studies revealed ships in North Atlantic were exposed to cold temperatures were subject to brittle fracture 8
  9. 9. Effect of Temperature on Fracture Toughness • Fracture Toughness of materials are affected by temperature • Ships experiencing cold weather conditions may be prone to fracture type failures 9
  10. 10. Historical Background • Aloha Flight #243 in 1988: • German Train ICE Accident in 1998: 10
  11. 11. • Life span definition: Crack Initiation & Propagation 11
  12. 12. • Life span definition for fatigue analysis: Crack Initiation & Propagation The initiation stage can represent a large part of the life span During the stable propagation stage the crack speed grows exponentially with the crack size The crack grows unstably until the ductile fracture Simulation context 12
  13. 13. CRACK INITIATION • Physically, cracks initiate from; – An imperfection – An already existing crack – A damaged (locally weakened) area • A failure analysis must include; – Stress analysis – Failure criterion 13
  14. 14. Theoretical Developments • A. Griffith (1893-1963) published the results of his studies on brittle fracture • He found the strength of glass depended on the size of microscopic cracks CONSTANTaS  14
  15. 15. 15
  16. 16. Three Modes of Fracture • Mode I denotes a symmetric opening (opening or tension mode) • Mode II denotes an antisymmetric separation (In-plane shear mode) • Mode III denotes an antisymmetric separation (out-of-plane shear or tearing mode) • Crack growth usually takes place in mode I or close to it. • The crack “adjusts” itself such that the load is perpendicular to the crack faces. 16
  17. 17. Fracture Mechanics Parameters • J-Integral • Energy-Release Rate • Stress-Intensity Factor • T-Stress • Material Force • C*-Integral – UMM Method (Unstructured Mesh) 17
  18. 18. Energy Release Rate and J-Integral  Energy release rate can be calculated from stress intensity factors  The J-integral can be defined as a path-independent line integral that measures the strength of the singular stresses and strains near a crack tip. Ozen Engineering, Inc. confidential information 18
  19. 19. Stress Intensity Factor • The magnitude of stress field in the immediate vicinity of the crack tip is measured by the “Stress Intensity Factor” • Stress Intensity Factor is a quantity determined analytically and varies as a function of the crack configuration and the external loads are applied • Critical stress intensity factor is independent of the crack geometry and loading and may be regarded as a material constant. • Typical critical stress intensity factor values are; Ultimate Critical Stress Strength Intensity Factor • AL 7075-T651 83 ksi 26 ksi in1/2 • AISI 4340 280 ksi 40 ksi in1/2 19
  20. 20. T-Stress • Is the stress acting parallel to the crack faces • Unlike J-integral, it can have both negative and positive values • Positive T-stress values promotes fracture, where negative T-stress values results in larger plastic zones) 20
  21. 21. Material Force • “Material Force” method provides parameters for global material and dissipation forces that yield near-tip crack-driving force • Can be applied to all kind of material models (elastic, visco-elastic, plastic…) 21
  22. 22. C*-Integral • Creep crack growth becomes a concern when structural components are operated at high temperatures (ie Nuclear Industry) • C*-Integral can be used to evaluate the crack tip fields under creep deformation • C*-Integral is a path-independent integral, which is the steady-state creep analogue of J integral. 22
  23. 23. UMM Method • The unstructured mesh method (UMM) is a numerical tool used for evaluating fracture mechanics parameters on unstructured hex or tet element meshes. • Unstructured mesh method supports: – J-integral – Stress-intensity factor 23
  24. 24. Fracture Mechanics Table • Which parameters is applicable for which assumptions: 24 Method Material Behavior J-Integral Linear isotropic elasticity Isotropic plasticity Energy-Release Rate (VCCT Method) Linear isotropic elasticity Orthotropic elasticity Anisotropic elasticity Stress-Intensity Factor Linear isotropic elasticity T-Stress Linear isotropic elasticity Isotropic plasticity Material Force Various (including plasticity, viscoelasticity) C*-Integral Creep
  25. 25. Crack-Growth Simulation • VCCT-Based Interface Element Method • Cohesive Zone Method • XFEM-Based Method 25
  26. 26. Fracture Mechanics Meshing & Element Support  KSCON command is used to skew mid-side nodes around the crack tip.  This way the crack tip 1/(r1/2) singularity is captured. PLANE183 SKEWED NODES SOLID186 PLANE183 26
  27. 27. Fracture Mechanics Meshing & Element Support 27
  28. 28. 2-D Edge Crack Propagation  2 D Edge cracked plate analysis  can be solved both using fracture mechanics tools and cohesive zone elements in ANSYS. Ozen Engineering, Inc. confidential information
  29. 29. 2-D Edge Crack Propagation Crack Propagation Animation, β =15° (a) Crack Propagation Path, (b) SIF, FI; β =15° • Fracture parameters can be calculated directly using KCALC and CINT command in ANSYS. • Crack initiation angle and energy release rate can be calculated from stress intensity factors. • Cracks propagate straight (parallel to loading direction) to attain pure mode-I conditions. Ozen Engineering, Inc. confidential information 29
  30. 30. Interface modeling Problem Geometry Finite Element Model  Edge crack propagation in a thin film-substrate(SiO2/Si) is studied.  Effect of interface layer on crack propagation path is examined using cohesive zone elements. Ozen Engineering, Inc. confidential information 30
  31. 31. 3-D Edge Crack Analysis In Thin Film-Substrate Systems (a) Propagation Animation; Cut Length=150 (b) Propagation Path; Cut Length=150  Crack propagation is performed quasi-statically. Fracture parameters are calculated at each propagation step and the geometry is updated for the next propagation step.  Cohesive zone elements are placed between thin film and substrate to model interface. Ozen Engineering, Inc. confidential information 31
  32. 32. Industrial Example: Pump Housing Fracture • Pump housing subjected to internal pressure with a through crack Crack 0 0.04 0.08 0.12 0.16 0 1 2 3 4 Path 1 Path 2 Path 3 Path 4 Path 5 Inner surface Outer surface J Integral Calculations 32
  33. 33. Industrial example: Cracked helicopter flanged plate • Automatic crack growth simulation under variable loading 33
  34. 34. Following Week Schedule • March 26th: 10AM-10:45AM PT How to Perform Fracture Mechanics Analysis in Workbench • April 2nd: 10AM-10:45AM PT XFEM Method – Meshless Fracture Mechanics • April 9th: 10AM-10:45AM PT Fracture Mechanics with Cohesive Zone and Delamination • April 16th: 10AM-10:45AM PTFatigue Crack Propagation 34 www.ozeninc.com
  35. 35. END Thanks for your attention !!! Questions ? CONTACT: Attention: Can Ozcan OZEN ENGINEERING, INC. 1210 E. ARQUES AVE. SUITE: 207 SUNNYVALE, CA 94085 (408) 732-4665 info@ozeninc.com www.ozeninc.com

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