Experimental study of postcritical deformation stage realization in layered composites during tension using digital image correlation and acoustic emission

Creating conditions to implement equilibrium processes of damage accumulation under a predictable scenario enables control over the failure of structural elements in critical states. It improves safety and reduces the probability of catastrophic behavior in case of accidents. Equilibrium damage accumulation in some cases leads to a falling part (called a postcritical stage) on the material’s stress-strain curve. It must be taken into account to assess the strength and deformation limits of composite structures. Digital image correlation method, acoustic emission (AE) signals recording, and optical microscopy were used in this paper to study the deformation and failure processes of an orthogonal-layup composite during tension in various directions to orthotropy axes. An elastic-plastic deformation model was proposed for the composite in a plane stress condition. The evolution of strain fields and neck formation were analyzed. The staging of the postcritical deformation process was described. AE signals obtained during tests were studied; characteristic damage types of a material were defined. The rationality and necessity of polymer composites’ postcritical deformation stage taken into account in refined strength analysis of structures were concluded.