Influence of rigid and flexible matrices on ultimate strength and fracture mechanisms of polymer composite materials upon impact and static loading conditions

An universal method “Break upon Impact and Static” (RUS) has been developed for the experimental determination of the ultimate strength properties of polymer composite materials based on multifilament nanocrystalline ultra-high molecular weight polyethylene (UHMWPE) fibers, which differs in the method of fixing the sample in a testing machine.The method is carried out using a uniform BIS-sample with an intermediate matrix at the ends and equipment for its attachment to the platforms of testing machines. The sample is a round composite rod composed of the fibers and matrices under investigation, which is held in the tooling by an additional matrix that fixtures it under various loading rates. The RUS method was used to study the properties and mechanisms of destruction upon impact and in a static situation of anisotropic polymer and hybrid composite materials (PCM and HCM) based on flexible and rigid matrices reinforced with hybrid fibers of carbon, aramid, and UHMWPE-fibers activated by non-equilibrium low-temperature plasma. The breaking loads under low-velocity impact and static bending conditions, relative deformation, specific absorbed-in-fracture energy, work of adhesion, shear strength, and other properties are determined. It was found out that the plasticity of the matrix and the hybrid fiber composition affect the properties and fracture mode of PCM and HCM. For the destruction of HCM with a flexible matrix upon impact, a load twice as large as for composites with a rigid matrix is required. HCMs have the highest strength, in which at all stages of loading up to failure, joint deformation of the matrix and the reinforcing fiber occurs. The mechanism of deformation and destruction of anisotropic HCM upon impact is stepwise, while the nature of the deformation curve is zigzag. In statics, the deformation proceeds smoothly. By changing the ratio of carbon and UHMWPE-fibers during hybridization, it is possible to control the properties of HCM and improve its specific properties. The combination of carbon and UHMWPE-fibers in a hybrid fiber for reinforcing a flexible matrix makes it possible to create a material with a delayed fracture. It has been established that for HCM based on a flexible matrix reinforced with a hybrid fiber combining 20 % carbon and 80 % UHMWPE fiber, the fracture load increases by factor 2, the specific fracture work by 42 %, relative deformation by 68 %.