Analysis of the Effect of the Direction of Reinforcement of a Fibrous Composite Material on the Inhomogeneity of Localization of Deformations and Stresses Using the Method of Thermoelastic Response

Abstract The objective of the work is to study the influence of the reinforcement direction of a composite material relative to a cyclic load on the heterogeneity of stress distribution using the thermal nondestructive testing method owing to the thermoelastic effect. This method is widely used in all industries to test structural elements and in research. The degree of stress heterogeneity is used to select safety factors required to ensure the safety of technical objects. In the conducted study, the possibility of estimating the local stress distribution over the temperature field of the test object was shown using the thermal method owing to the thermoelastic effect. In this case, the temperature of the elastic body and mechanical stresses are related linearly. The objects of the study are laminates made of a composite material consisting of fibrous filler (fiberglass) with an epoxy matrix. Various options for laying fibers in relation to the load direction were investigated. Four types of laminates were considered: single-layer [0] and [90]; three-layer [0]3 and [90]3. The paper uses statistical data and estimates of variation coefficients, clustering methods and averaging over the length of laminates of the temperature distribution values over the surface of the laminates. Numerical characteristics of the local temperature distribution are obtained. It is established that their more uniform distribution occurs when the material is reinforced in the direction of loading of the part. A comparison of the integral and local characteristics of the temperature distribution in the samples is carried out. Differences in the local temperature distribution depending on the thickness of the laminate (single-layer and three-layer) are visually noted. The load is distributed more uniformly upon reinforcement in its direction, as well as with an increase in the number of reinforcement layers. The results of the study showed that the choice of the safety factor value assessing the level of stress heterogeneity depends on the design features of the laminates. During the operation of composite products in the presence of significant accumulated damage, when the unevenness of its distribution increases, the levels of safety factors should be adjusted.