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In this paper, a longitudinal compression experiment of composites was conducted and the macroscopic failure mode was obtained. Also, the microscopic failure morphologies of longitudinal compression and kink band were observed by using scanning electron microscopy. It can be seen that, under compression, fibers bend and form a kink band, which is the most typical failure mode. Then a micromechanical model of fiber random distribution based on the random collision algorithm, which can reveal the progressive failure mechanism of longitudinal compression considering the kink-band deformation, was established, with two dominant damage mechanisms – plastic deformation and ductile damage initiation of the polymer matrix and interfacial debonding included in the simulation by the extended Drucker-Prager model and cohesive zone model, respectively. Through numerical simulation, the loading and failure procedures were divided into three stages: elastic domain, softening domain and fiber failure domain. It can be concluded that the kink band was a result of fiber instability (micro-bulking), which is caused by the elastic bending of fibers. The fibers rotate and break into two places, forming a kink band. Then the fibers rotate further until the matrix between the fibers fails and the kink-band breaks and, hence, the composite loses its load-bearing capability.

In order to study the mechanical and thermal properties of carbon fiber-reinforced cross-ply laminate, a macroscopic [90/0]8Scross-ply laminate model and a unit cell of fiber regular distribution near the [90/0]8Slaminate interlaminar zone with plastic matrix and interface were created. Then the damage initiation discipline details of [90/0]8Scross-ply laminate are researched, and the effects of interfacial coefficient of thermal expansion on thermal residual stress distribution and damage initiation are researched in detail both based on the macroscopic and microscopic models. It shows that the initial damage of interlaminar interface occurs in macroscopic model and the initial damage in microscopic model occurs both at intralaminar interface and interlaminar cohesive zone. No matter in macroscopic or microscopic model, the residual stress of 6.27 × 10−6/°C interfacial coefficient of thermal expansion is larger than that of 6.27 × 10−7/°C interfacial coefficient of thermal expansion. And the initial damage expands more widely in the first one. [ABSTRACT FROM AUTHOR]

Computational mechanics has been carried out to study the microscopic failure mechanisms of unidirectional fiber-reinforced polymer composites. A representative volume element of fiber random distribution based on molecules random collision model is established, with two dominant damage mechanisms, matrix plastic deformation and interfacial debonding included in the simulation by the extended Drucker–Prager model and cohesive zone model, respectively. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the transverse tension fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation, while the compression failure is dominated by matrix plastic damage. The longitudinal tension and compression are both dominated by fiber breakage, but longitudinal tension initiates as matrix plastic damage and longitudinal compression initiates as fiber microbuckling. Finite element method appropriately simulated the process of progressive damage of the fiber buckling failure, which is consistent with the observed result under scanning electron microscopy. [ABSTRACT FROM AUTHOR]