Detection and Analysis of Barely Visible Impact Damage and its Progression on a Composite Overwrapped Pressure Vessel
PRESENTER: Valentina Dolci
INTRODUCTIONSpacecraft are highly complex systems composed of various structural,hydraulic, propulsion, electronic and avionic elements.Such complex systems require extensive maintenance.A widely recognized definition of Structural Health Monitoring statesthat Health Monitoring (as subsystem of the network of technologies andprocesses known as Integrated Vehicle Health Management) is the processof nondestructively identifying the main characteristics related to thefitness of space component (or system) as it operates.
The test will be simulated with the help of the Altair FEsolver RADIOSS. Afterward there will be a post-processingphase during which we will analyse displacements andcontact forces. We choose an analytical test from Abrate’s work, ‘Impact oncomposite structures’: Es. 3.22.It deals with slow speed impacts causing BVID - BarelyVisible Impact Damage.PHASE ONE: ANALYTICAL COMPARISON The FEA solver RADIOSS will be a really satisfyingtool. The error in comparison with the analyticalsolution will be less than 7.5 %.
- COPV of CFRP FILAMENT WINDING MATERIAL + Al 6061 LINER:Cylindrical coordinate system, need to reproduce the adhesion between linerand composite materialP11_SHELL_SANDWICH- Composite made of 11 layers,Stacking sequence:[ 904 / -12 / +12 / 902 / -12/ +12/ 90 ]:No symmetries!M25_COMPSH
One of the more complex aspects of the numerical simulation is themodelling of the rupture behaviour of the composite material.## Material Law No 25. COMPOSITE SHELL/MAT/COMPSH/1 This card is based on the TSAI-WU ELASTIC-PLASTIC MODELand is used with composite shells with at least one orthotropic layer. Material law COMPSH (25) describes orthotropic elasticity, has twoplasticity models and brittle tensile failure. The best description of our composite material is made by theLAW 25 - CRASURV FORMULATION.
ε t1 Tensile failure strain in direction 1 ε m1 Maximum strain in direction 1 ε f1 Total tensile failure in direction 1: when reached the element isdeleted ε t2 Tensile failure strain in direction 2 ε m2 Maximum strain in direction 2 ε f2 Total tensile failure in direction 2: when reached the element isdeletedThe damage and failure behaviour is defined by the introduction ofthe following SIX INPUT PARAMETERS :
OUTLINE OF THE AUTOMATIC PROCEDURE- Finally the damaged COPV is loaded again with the samepressure of step 1 to verify the REDUCED STRENGTHCAPABILITY of the structure.- During the simulation the model of the tank will besubjected to a first PRESSURE ANALYSIS, to obtain astrength criterion of the structure.- The stress state is recorded and we will proceed to thesecond step: the BARELY VISIBLE IMPACT DAMAGE.
M10/T1000 Resin-Fiber compositeThanks to experimental characterizations we provide the solver with thefollowing mechanical properties:𝑬 𝟏𝟏 188 [GPa]𝑬 𝟐𝟐 9 [GPa]𝑬 𝟑𝟑 9 [GPa]𝑮 𝟏𝟐 4.3 [GPa]𝑮 𝟐𝟑 4.3 [GPa]𝑮 𝟑𝟏 4.3 [GPa]ν 𝟏𝟐 0.3ρ 1100 [Kg/m3]PROPERTIES OF THE COMPOSITE MATERIALThe deformations of the compositeinserted in the solver through thematerial law 25_COMPSH are:ε f1 3e-3ε m1 2.7e-3ε t1 2,4e-3ε f2 2e-3ε m2 1.9e-3ε t2 1.8e-3
Caused to the fact that we have to model a composite obtained byfilament winding, we have to impose different cylindrical coordinatesystems to the two segments of the tank.DEFINITIVE FEM MODEL The cylinder is 500 [mm] height, with a radius of 416 [mm]. The impact occurs at 0° to avoid the complication of modelling afilament wound dome.
STEP 1) PRESSURE ANALYSISPressure Load 50 [MPa]The pressure load is imposed by a curveIn the postprocessing phase wewill have to control the absence ofunacceptable oscillations on thevariation of the internal energywith time.
σxxmax = 387 [MPa]Medium Tensional State = 200 [MPa]RESULTS
CHECK OF THE CORRECT APPLICATION OF THE PRESSURE LOADThe variation of the internal energy with time is regular,showing that the load is applied in an appropriate lapse oftime during the explicit analysis.
STEP 2) BVIDEnergetic Level: 4.56 [J]Sphere Mass: 7.7 [Kg]Sphere Diameter: 12.7 [mm]Impact Position: 0°TENSIONAL STATE CAUSED BY THE IMPACTInitial Velocity of the Sphere: 1.088 [m/s]
- The delamination depth obtained on the experimental results is 1.5[mm]. Considering that each composite layer has a thickness of 0.2 [mm],we can say that the damage touches 7 plies and a half.- The impact area is 4 [mm]FAILED LAYERS- The post-processing software HyperView is able to show damage’sdepth providing the number of the impacted layers.
The numerical simulation overstate depth and area of the damage.In fact we can see that it concern with the 8th ply. Because each finite element has an edge of 2 [mm], the impact area isoverstated too.
STEP 3) PRESSURE ANALYSIS OF THE DAMAGEDSTRUCTUREA pressure load of 50 [MPa] is applied to the damaged tank.The strength capability of the tank is reduced. The COPV is no more able to resistto the applied load after the impact.
CONCLUSIONSThe FEM simulation is able- To show the damage occurred to the structure after a Barely Visible Impact,- To provide the stress state and an overstate of the geometrical parameters of thedamage (dimensions and depth),- To verify the reduction of the mechanical properties of the material.FORESEEN IMPROVEMENTS To avoid the actual overstate of the damage with respect to the experimentalresults making the mesh thickness more consistent and refining thedescription of the material. To make a better simulation of the failure behaviour of the composite givingmore information about the amount of plastic work absorbed before therupture.
 R.M. Jones, Mechanics of Composite Materials, McGraw-Hill, Washington,D.C., 1975.  Hashin,Zvi, The Elastic Moduli of Heterogeneous Materials, J. Appl. Mech.,March, 1962.  Hashin,Zvi e B. Walter Rosen, The Elastic Moduli of Fiber-ReinforcedMaterials, J. Appl. Mech., June, 1964.  Tsai, Stephen Structural Behaviour of Composite Materials, The Netherlands,1953.  Abrate Impact on Composite Structures, Cambridge University Press, 1998.  Thimoshenko Zur Frage Nach der wirkung eines Stosses auf einen Balken,ZAMP 62, 1913.  RADIOSS THEORY MANUAL, Large Displacement Finite Element AnalysisPART2 10.0 version, january 2009BIBLIOGRAPHY
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