Residual strength and fatigue life of woven composite under compression after impact loading

The paper investigates the influence of preliminary low-velocity loading on the change in residual strength and fatigue characteristics of a fabric composite using modern testing and diagnostic equipment. A new testing method for layered composites is proposed, which consists of a preliminary low-velocity impact with a drop-weight load followed by cyclic compression. A series of tests were conducted on impact with a drop-weight in a wide energy range followed by a quasi-static and cyclic compression of damaged laminated fiberglass plates. Experimental dependences of residual static strength and fatigue life on the energy of preliminary low-velocity impact were obtained. We revealed the existence of a threshold value of the energy of a preliminary impact with a drop-weight load, below which the preliminary dynamic impact does not affect the residual mechanical characteristics. Based on previously developed models and their modifications, an approximation of the experimental data on the residual properties of the composite was carried out. The high descriptive ability of the proposed models was noted. The kinetics of the destruction process under quasi-static compression is analyzed based on data obtained using the VIC-3D contactless optical video system and the digital image correlation method. The non-uniform nature of the distribution of deformation fields on the surface of the damaged samples was noted. Ultrasonic scanning data made it possible to assess the development of the operational damage caused by preliminary low-speed transverse impacts. A relationship was established between the energy of the dynamic impact, residual mechanical characteristics and the characteristic size of the damage zone. The nonlinearity of the obtained dependencies was revealed. A conclusion is made about the need to study the mechanical behavior of polymer composites under conditions of combined effects to ensure the reliability and safety of critical structures.