Presentation on theme: "Failure Mechanisms in Twill-weave Laminates:"— Presentation transcript:
1Failure Mechanisms in Twill-weave Laminates: FEM Predictions vs. ExperimentsbyGianni Nicoletto and Enrica RivaDipartimento di Ingegneria IndustrialeUniversità di ParmaParma, ItalyCOMPTEST 2003Chalons en Champagne, FranceJan. 28, 2003
2Outline Introduction e motivation Related works COMPTEST Chalons en Champagne G. Nicoletto & E. RivaOutlineIntroduction e motivationRelated worksTwill-weave laminate chacterizationFinite element modelingExperimental observations and computational resultsConclusions
3Motivation Cooperation with Dallara Automobili F3 racing car COMPTEST Chalons en Champagne G. Nicoletto & E. RivaMotivationCooperation withDallara AutomobiliF3 racing carIRL racing carInfinity ProCFRP Chassis
4Woven Composites Definitions Advantages COMPTEST Chalons en Champagne G. Nicoletto & E. RivaWoven CompositesDefinitionsYarns: bundle of thousands fibersWarp yarns: parallel to load directionFill yarns: perpendicular to load directionTexture: plain weave, twill weave, etc.Crimp ratio: degree of yarn curvatureAdvantagesWith respect to unidirectional laminates:Easier handling and shapingImproved impact resistanceSuperior out-of-plane stiffnessBalanced in-plane mechanical propertiesCost competitiveyarn
5COMPTEST 2003 Chalons en Champagne G. Nicoletto & E. Riva Objectives of the workDevelop a finite element-based modeling approach to the mechanics of woven laminate composites.Compare modeling results and experimental observations.Analyze the role of texture on mechanical performance.Develop tools for monitoring damage development in woven laminates.
6Related Modeling Work Analytical approach T.W. Chu et al (1983 - ) COMPTEST Chalons en Champagne G. Nicoletto & E. RivaRelated Modeling WorkAnalytical approachT.W. Chu et al ( )N.K. Naik et al ( )Models, such as mosaic, crimp and bridging models subjected to iso-strain or iso- stress conditions, predict adequately the stiffness of woven laminates.These models are less satisfactory for strength prediction and micromechanical stress determination.Convenient approach for texture design.The plain-weave texture has been mainly considered.
7Finite element approach V. Carvelli and C. Poggi (2001) COMPTEST Chalons en Champagne G. Nicoletto & E. RivaFinite element approachJ. Whitcomb et al. ( )V. Carvelli and C. Poggi (2001)D. Blackketter et al. (1993)Computational prediction of the mechanics of woven laminate composites.The finite element method is used to geometrically model an elementary cell of the woven laminate.Boundary conditions enforcing stress and strain periodicity are imposed to the representative volume (RV) .Stress-based damage and stiffness discount technique to model damage progression.Most studies deal with the plain-weave texture.
8Electrical resistance method applied to unidirectional composites COMPTEST Chalons en Champagne G. Nicoletto & E. RivaRelated Experimental WorkK. Schulte et al ( )J.C. Abry et al. (1998)Electrical resistance method applied to unidirectional composites
9Material and Experiments COMPTEST Chalons en Champagne G. Nicoletto & E. RivaMaterial and Experiments0° directionFiber: Toray T-300 carbon fibersFiber diameter: 7 μmFiber volume fraction Vf: 42%Density ρ: 1.76 g/cm2Strength su= 3200 MPaElastic modulus E: 228 GPaMatrix: Epoxy Hexcel 1990SLaminateLay-up: 8-plyTexture: Twill-weaveYarns: 3k fibersWarp and fill yarns: IdenticalLaminate thickness: 2.4 mmTensile tests according to: ASTM D3039Servo-hydraulic testing machine: MTS 810Resistance strain gages & ExtensometerElectric resistance measuring apparatus
10Geometrical Characterization of Twill-weave Texture COMPTEST Chalons en Champagne G. Nicoletto & E. RivaGeometrical Characterization of Twill-weave TextureYarn shape: circular arcsPly stacking: randomabgRTRL2.040.171.136.116.15All dimensions in mm
11Tensile Tests and Evolution of Electrical Resistance COMPTEST Chalons en Champaign G. Nicoletto & E. RivaTensile Tests and Evolution of Electrical ResistanceStrainNorm. elect. resistance vs. strainStress (MPa)(R-R0)/R0Stress vs. strainTwill-weave laminates
12Damage Observations Fill yarn Tow yarn Epoxy Fiber fracture COMPTEST Chalons en Champagne G. Nicoletto & E. RivaDamage ObservationsFill yarnTow yarnEpoxyFiber fractureFracture in yarn
13Inter-ply delamination Delamination between orthogonal yarns COMPTEST Chalons en Champagne G. Nicoletto & E. RivaDamage Mechanisms: a SummaryInter-ply delaminationCrackin fill yarnDelamination between orthogonal yarnsFinal longitudinal fiber fracture is preceeded by a number of mechanisms.Matrix cracks develop in fill yarns.Delamination occurs between orthogonal yarns.Inter-ply delamination is observed
14Homogeneization Method for Composite Materials COMPTEST Chalons en Champagne G. Nicoletto & E. RivaHomogeneization Method for Composite MaterialsAssumption of periodic microstructures which can be represented by unit cellsAsymptotic expansion of all variables and the average technique to determine the homogeneized (macroscopic) material properties and constitutive relations of composite materialsPrediction of microscopic fields of deformation inside the unit cell through the localization process
15Texture and Representative Volume RV COMPTEST Chalons en Champagne G. Nicoletto & E. RivaTexture and Representative Volume RVMaterial models:Yarn: transverse isotropic, linear elasticMatrix: linear elasticTwill-weaveRV
16Finite Element Modeling of RV COMPTEST Chalons en Champagne G. Nicoletto & E. RivaFinite Element Modeling of RVParametric geometrical model (I-DEAS)Finite element code (ABAQUS)Convergence studyOptimized model: > elementsGeometric nonlinearity includedProgressive damage evolution routine in FORTRAN
17Boundary conditions on RV COMPTEST Chalons en Champagne G. Nicoletto & E. RivaBoundary conditions on RVFree surfaceCarvelli & Poggi (2001)whereu(x) is the displacement field in the RVu0 is a rigid displacement of the RVW is a small rigid rotation of RVE is the average strain (macroscopic)of RVũ(x) is a periodic displacement associated to microscopic strain field within RVPost, Han and Ifju (1994)
18Damage Modes for Fiber Yarn COMPTEST Chalons en Champagne G. Nicoletto & E. RivaDamage Modes for Fiber YarnM. Zako et al (2003)
19Modeling Damage Development COMPTEST Chalons en Champagne G. Nicoletto & E. RivaModeling Damage DevelopmentDiscount methodBlackketter et al (1993)Iterative procedure.Evaluation at each integration point.Normal stress criterion for failure.Elastic modulus is reduced to 1/10 of its initial value.Role of time step and mesh size.
20Effect of Texture on Longitudinal Stiffness COMPTEST Chalons en Champagne G. Nicoletto & E. RivaEffect of Texture on Longitudinal StiffnessPlain weaveTwill weaveLaminaThick laminateStrong influence of crimp ratio on stiffness.Good correlation with experimental results.A thick laminate is stiffer than a single lamina.At high crimp ratios the twill-weave is stiffer than the plain- weave.
21Effect of Crimp Ratio on Stress-Strain Curve COMPTEST Chalons en Champagne G. Nicoletto & E. RivaEffect of Crimp Ratio on Stress-Strain CurveStrong influence of crimp ratio on stress-strain curve.Good correlation with experimental results.Low crimp ratio shows a trend linear to failure.Influence of computational parameters.
22Stresses and Damage Step a a d c b COMPTEST Chalons en Champagne G. Nicoletto & E. RivaStresses and DamageabcdStep aThe critical stress is perpendicular to the fill yarn surface.The wedge elements of the straight portion of the fill yarns fail first.Initial damage occurs near the fill yarns.The critical stress is representative of damage initiation in the matrix.
23Stresses and Damage Step b b d c a COMPTEST Chalons en Champagne G. Nicoletto & E. RivaStresses and DamageabcdStep bThe critical stress direction does not change. It is perpendicular to the fill yarn surface.Damage continues in the fill yarns.Damage now involves the brick elements next to the wedge elements.The damage spreads into the matrix.
24Stresses and Damage Step c c d b a COMPTEST Chalons en Champagne G. Nicoletto & E. RivaStresses and DamageabcdStep cThe wedge elements, where the two perpendicular yarns are close to each other, fail.Fiber failure occurs in the fill yarn.Failure occurs where the yarn is curved to the maximum.
25Stresses and Damage Step d d c b a COMPTEST Chalons en Champagne G. Nicoletto & E. RivaStresses and DamageabcdStep dFailure extends to the neighboring brick elements up to final catastrophic collapse.In this final stage different failure modes are activated such as transverse and longitudinal shear, and transverse direct stress.
26Inter-ply delamination Delamination between orthogonal yarns COMPTEST Chalons en Champagne G. Nicoletto & E. RivaQualitative CorrelationExperimentalInter-ply delaminationCrackin fill yarnDelamination between orthogonal yarnsComputational
27COMPTEST 2003 Chalons en Champagne G. Nicoletto & E. Riva ConclusionsOptical inspection of a twill-weave laminate during tensile testing showed different damage mechanisms.Finite element modelling of an appropriate RV provided the macroscopic stress-strain relation of a woven laminate that were compared to experimental results.The finite element model of the RV provided the microscopic stresses and strains within matrix and reinforcements.An iterative procedure based on a damage routine has been developed to simulate damage evolution.A first correlation between experimental observations and computed damage evolution in a twill-weave laminate is encouraging.