Detection of nonlinear behaviour of composite components before and after endurance trials

Composite components are being studied by many researchers due to complex nature of their nonlinear dynamic behaviour. This behaviour can be a function of several factors, such as lay-up configuration and/or visco-elastic material properties etc. Recent studies on failure criteria of composite structures under endurance testing have shown that vibration forced responses can be nonlinear because of structural modification occurring during a test. Typically, endurance testing can cause initiation and propagation of a delamination(s) of the test structure, shifting dynamics of composites from quasi linear to non-linear regime. This transition was observed during laboratory experiments but very little effort was made to generate an understanding of the phenomenon. The aim of this paper is to focus on the study of nonlinear behaviour of composites before and after endurance trials. Recently, tools capable of addressing detection, characterisation, localisation and quantification aspects of nonlinearity have been developed. Some of these tools will be used in this exercise with an overall objective of quantifying the level of nonlinearity.