EXPERIMENTAL STUDY ON TENSILE FATIGUE PROPERTIES OF CARBON / Aramid Mixed Orthogonal Three - Way Composites

Carbon/Kevlar hybrid three-dimensional (3D) orthogonal composite materials not only can make full use of the advantages of 3D orthogonal structure, such as good structural integrity and stability, high delamination resistance and flexible tailor-ability, but also can take advantages of different fiber materials, overcoming some shortcomings of single fiber reinforced composite materials, leading to the wide application in structural engineering industry. In the process of service, most of the composite materials will be subjected to different forms of cyclic loading which can cause fatigue damage. The accumulation and expansion of damage will cause the sharp loss of material strength and rigidity, greatly reducing the mechanical properties and fatigue life of materials, bringing safe troubles and even having catastrophic consequences. Therefore, in this paper, the mechanical response, fatigue property, structural effect and damage mechanism of carbon/Kevlar hybrid 3D orthogonal composites under in-plane quasi-static tensile loading tensile fatigue loading are studied by means of experimental method, and compared with the mechanical properties of the non-hybrid carbon fiber and non-hybrid Kevlar 3D orthogonal composites, expecting to provide theoretical basis for the design and application of the hybrid composites and components.The tensile properties of four kinds of 3D orthogonal composite materials are tested and analysed using digital image correlation (DIC) method based on full field displacement. The results show that the in-plain tensile modulus and strength of hybrid 3D orthogonal composites made of carbon fiber in warp and weft, Z yarn with Kevlar fiber are biggest, break elongation and Poisson’s ratio are higher. The tensile strength and modulus following composites are from high to low non-hybrid carbon fiber composites, hybrid composites with Kevlar fiber and carbon fiber being interval arranged, non-hybrid Kevlar fiber composites. Hence, the reasonable arrangement of carbon fiber and Kevlar fiber at the proportion for hybrid 3D orthogonal composites can achieve the compromise in the strength and toughness in design.The fatigue performances of two kinds of carbon/Kevlar hybrid 3D orthogonal composites under tensile fatigue loading are studied. It was revealed that the fatigue life were inversely proportional to the stress level. Under a lower stress level, the fatigue life of non-hybrid carbon fiber 3D orthogonal composites is highest. Under the high stress level, the fatigue life of hybrid 3D orthogonal composites with Kevlar fiber and carbon fiber being interval arranged is highest. The peak displacement curves and the stiffness degradation curves of hybrid and non-hybrid 3D orthogonal composites presented typical "three stages". The fatigue damage modes mainly included the matrix cracks,debonding between fiber and resin interface, fiber pull-out and fiber breakage. The existence of Z yarns promote the emergence and development of cracks.According to the practical engineering application, this work investigates tensile fatigue properties of carbon/Kevlar hybrid 3D orthogonal composites,providing the preliminary experimental data and theoretical basis for improving the tensile properties and fatigue performance, optimizing fatigue life of hybrid composites.