EXFOLIATION THE THIN REINFORCEMENT IN AN ORTHOTROPIC BODY UNDER CYCLIC LOADING

Abstract

Exfoliation of the flexible ribbon-like inclusion in orthotropic composition in conditions of plane problem under cyclic stress loading at infinity are researched. The development of localized zones of prefracture (weakened contact), which may correspond to the area of accumulation of damage, partial rupture of ties, etc. are precedes the exfoliation. We assume that in the vicinity of the ends of the inclusion, with a certain combination of amplitude values and the number of load cycles, there will be sliding delamination, which will advance along the material separation boundary from each edge to the central part. The length of the reinforcement without fragments peeled off at the ends is called the working length of the reinforcement. The coefficient of friction on the exfoliated part is assumed to be zero. Analytical dependences for changing the working length of the inclusion depending on the amplitude of the load and the number of cycles and the parameters of the orthotropic matrix are obtained. An energy criterion was used to construct the delamination equation, which assumes the existence of a critical value of energy necessary for the working length of the inclusion to decrease by a unit of length, which is considered a known characteristic of the composition. For a continuous load, the solution of the problem is reduced to the Cauchy problem for a first-order differential equation, and for a cyclic – to the integration of a given function from the load parameters and the elastic and strength characteristics of the system. For a given load per cycle and a predetermined number of cycles, using the obtained formulas, it is always possible to choose the length of the reinforcing element in such a way that its peeling does not exceed the predetermined value (or does not occur at all). The speed of exfoliation depends significantly on the initial working length of the inclusion (it is longer for a longer one) and the maximum load per cycle. The reinforcing element in the middle part under the conditions of the problem remains connected to the base. The orthotropy parameters of the composite components significantly affect the delamination process. Orientation of the inclusion along the direction of greater matrix stiffness is preferable both for preserving its integrity and for the possibility of protecting it from delamination.