Experimental method and evaluation for interlaminar shear properties of randomly oriented strand thermoplastic composites based on modified double-notch specimen and two dimensional digital image correlation

Abstract

A new interlaminar shear test method has been proposed based on the double-notch compression test method, in which the test specimen shape with a modified overlap length of the notches is proposed, and the interlaminar shear strain is measured by two-dimensional digital image correlation (2D-DIC) analysis. In order to obtain the interlaminar shear properties in the elastic and non-linear regions of randomly oriented strand thermoplastic composites, we adopted a 2D-DIC analysis system using a bi-telecentric lens, which can accurately measure the strain in a small field of view, and a test system including an interlaminar shear test jig, which can apply a compressive load to the end face of the specimen at high perpendicularity. It is necessary to provide an overlap of the double-notch of 1 mm or more in order to simultaneously obtain the strain in the elastic region and the non-linear region from the actual test results. When numerical analysis by finite element method (FEM) was carried out on four types of test specimen with different shapes used in this research, by using the interlaminar shear property data obtained from actual tests on the optimum test specimen, there was a high level of agreement with the 2D-DIC analysis results for the shear stress – strain diagrams and the interlaminar shear strain distribution. Therefore, the benefits of the test specimen shape and dimensions in the new test method and the validity of the interlaminar shear property values that can be obtained using this method have been confirmed.