Abstract

One of the failures with significant practical repercussions in structural elements made of laminated composite materials is the formation and growth of interlaminar cracks (delamination) under static and dynamic loading. Although the cracks can be subjected to three different modes of stress, the material toughness in mode III is higher than in the other two, so delamination mainly occurs in modes I or II. This is true when there is more than one fracture mode acting in the element. However, by using a testing methodology that allows testing in pure or nearly pure mode III, such as the Longitudinal Half Fixed Beam (LHFB) method, it is possible to characterize the material against this mode. Therefore, the degree of purity of mode III, compared to the residual modes I and II, will be an important indicator of the adequacy of the testing methodology. In this research work, the degree of purity of mode III in LHFB-type tests has been determined by using a digital image correlation (DIC) system. This technique allowed for the analysis of displacements in the X, Y, and Z directions in specimens with initial crack lengths of 1, 5, 10, 15, 20, 25, and 30 mm, using AS4/8552 and AS4/3501-6 materials. Considering the displacements measured with DIC during the different tests, it has been possible to determine the level of combination of modes I, II, and III achieved during the tests.