Experimental Studies of the Mechanisms of Formation of Residual Strain in Fibrous Composites Under Cyclic Loading

On the example of a unidirectional fibrous composite made from ELUR-P unidirectional carbon fiber reinforced plastic and KhT-118 cold curing binder, tests of test specimens with for \([ \pm 45^{^\circ } ]\) lay-up for cyclic tension were carried out. It is shown that in each loading cycle, a change in the mechanical properties of the material occurs, associated with the restructuring of its microstructure due to the implementation of different-scale buckling forms leading, in particular, to degradation of the material, a change in the secant modulus of elasticity, and stabilization of the magnitude of the strain increment. For various, significantly different loading rates, experimental dependences on the cycle number of the values of the secant moduli of elasticity at the stages of loading and unloading, which differ most from each other in the initial cycles, are obtained. It has been established that under cyclic tension, the loading and unloading branches do not coincide, forming a hysteresis loop.