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## J. Krystek, R. Kottner, L. Bek

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**Comparison of strength behavior of unidirectional HMC and**HSC composite subjected to biaxial loading J. Krystek, R. Kottner, L. Bek 19th Conference on Materials and Technology; 22 and 23 November 2011, Portorož, Slovenia**Outline**Introduction Material model Mechanical properties Failure criteria Experiments Numerical analysis Summary**Currently, the failure of composite is well predictable only**in basic cases • Biaxial tests shown dependence of specimen strength on the ratio of tension and compression Introduction Wrapped pin joint**Tensile test**Compression test – type I Compression test – type II ( E1, E2, ν12, XT, YT ) ( XC, Y C, α0 ) ( YC, α0 ) ASTM D 3039 ASTM D 3410 Mechanical properties Elasticity and strength parameters of composite**Unidirectional composite material**Material model Stiffness matrix of transverse isotropic material • 5 independence components of stiffness matrix (C11, C12, C22, C23, C66) • 5 independence material constants(E1, E2, G12 , υ12 , υ13) • Nonlinear function with constant asymptote was used for shear modulus G12: Force and extension dependencies • This material model is not standard part of used FEM system MSC.Marc, therefore it was implemented into MSC.Marc system.**FIBRE FAILURE**• Maximum stress • Hashin • LaRC04 #3 • adjusted LaRC04 #3 Failure criteria • MATRIX FAILURE • Maximum stress • Hashin • LaRC04 #2 • adjusted LaRC04 #2**Experiments**• Biaxial test • Standard testing machine Zwick/Roell Z050 was supplemented by second loading axis for the localized compression • The second loading axis consisted of power machine vice VMC-130 and HBM C9B compact force transducer Testing machine Schema of biaxial test**Loading steps**• Loading was applied in two basic steps**Specimens**• Specimens were cut using water jet from unidirectional composite plates, which were made from 8 layers of prepreg • Geometry parameters of specimens • HSC composite • b = 5.0 mm, h = 2.2 mm, l = 240 mm • HMC composite • b = 4.8 mm, h = 2.0 mm, l = 240 mm • Geometry parameters of compression element: • w = 20 mm, v = 10 mm, R = 1 mm Geometry parameters • Specimens were supplemented with aluminium pads on both sides. • All pads were bonded on the specimens by Araldit AV 138M + HV 998 adhesive Specimens with aluminium pads**HSC**HMC Experiments - results b = 4.8 mm, h = 2.0 mm b = 5.0 mm, h = 2.2 mm Dependences of specimen strength on the combination of tensile and compression forces Failure of matrix in biaxial test Failure of fibres in biaxial test • Compressive strength (matrix failure) is increasing with the tensile force • Tensile strength (fibre failure) is decreasing with the compressive loading**FEM system: MSC.Marc**• Regarding symmetry of the specimen, only one quarter of the specimen was modelled • Loading was applied in two basic steps which correspond with experiment • Compressive loading was applied by force acting on contact surface which represented compressive element • Friction was neglected Numerical analysis Modeled quarter Boundary condition**HSC composite**Numerical analysis Failure index for Hashin - fibre failure Failure index for LaRC04 #2 - matrix failure Failure index for Maximum stress - matrix failure**Selected stiffness and strength parameters of composites**were identified • Composites had high modulus carbon (HMC) fibres and high strength carbon (HSC) fibres • Strength analysis of the composites subjected to biaxial loading was performed • Experimental specimens were loaded in two perpendicular directions • Specimens were exposed to the combination of the tension in the fibre direction and the localized compression in the transverse direction • Loading was applied in two basic steps • Experiments showed similar dependence of specimen strength of both types of composite on the ratio of tension and compression • Compressive strength is increasing with the tensile force • Tensile strength is decreasing with the compressive force • Predictive capabilities of different failure criteria for composite materials were tested in the failure analysis - Maximum stress, Hashin, LaRC04 Summary