Effects Of Fiber Microstructure And Interface On Tensile Behaviors Of Short Plant Fiber Reinforced Composites

Random short natural fiber reinforced composites,such as spruce/PP and sisal/PP are a kind of green environmentally friendly material.They have many advantages such as light-weighted and high fracture toughness.They are also environmentally friendly,recyclability and widely used in automotive,high-speed trains and aircraft for load bearing component.It is significant in theory and engineering applications to the optimized design of this material and its structural members to investigate the influence of microstructures of fibers and properties of interface on the effective properties of composites.The influence of scale of material on effective properties of random short natural fiber reinforced composites is investigated by homogenization method.The three-dimensional variable scale representative volume element finite element models of random short natural fiber reinforced composites are established.In these models,the influence of randomness of fiber volume fraction,aspect ratio,location,posture and principal direction of fibers are taken into consideration.Nine kinds of periodic boundary conditions are constrained on representative volume element by in-house program,the effective moduli of orthotropic materials are calculated.It is found that the effective properties of random short natural fiber reinforced composites appear to be randomly anisotropy in meso-scale.The effective properties of materials gradually tend to be isotropic with the increasing of scale.The influence of properties of interface on tensile behavior of random short natural fiber reinforced composites is investigated.The mechanical behavior of interface between fibers and matrix is characterized by cohesive zone model(CZM).The two-dimensional representative volume element finite models including interface of random short natural fiber reinforced composites are established.The elements of interphase are inserted in finite element models by own program.The influence of interface stiffness,the displacement of initial damage and complete damage are taken into consideration.The influence of randomness of fiber volume fraction,aspect ratio,location,posture and principal direction of fibers are also considered.The tensile curves of composites are simulated and the parameters of cohesive element are determined.It is found that the effective modulus is influenced by interface stiffness.By numerical tensile experiment of several specimens and method of statistical average,the curves of relationship between fiber/matrix interface stiffness and effective modulus,which are also called Ec-Ki curves,are achieved.The numerical formula of prediction of Ec-Ki curves is also proposed.It is found that there exists a critical intersection between the Ec-Ki curves of composites with different fiber volume fraction.On hard interface stiffness side of the intersection,the effective modulus of composites increases as the fiber volume fraction increases.On weak interface stiffness side of the intersection,the effective modulus of composites decreases as the fiber volume fraction increases.The location of intersection is influenced by properties of fiber and matrix.The influence of shear interface stiffness on the effective modulus of composites is also investigated.