Biaxial Mechanical Fatigue using Cruciform Composite Specimens

Due to the complex anisotropic behaviour of composite materials more advanced experimental testing is needed. Multiaxial testing under complex loading conditions will improve the understanding of their mechanical behaviour and allow the validation of analytical and numerical predictions. For biaxial mechanical testing various techniques have been proposed [1]. At the Free University of Brussels (V.U.B), at the department of mechanics of materials and constructions a special test bench was designed and created in order to realize biaxial mechanical testing. Near to the design of a cruciform specimen for the determination of strength properties under static biaxial loading, a special cruciform specimen geometry and clamps were developed in order to actualise biaxial fatigue tests on the existing test bench (see Fig.1). In this study the mechanical behaviour of glass epoxy composite laminates under biaxial mechanical fatigue loading is investigated and compared with uniaxial test data. The latter data were obtained from exactly the same material during the European project 'Optimat blades'. Cruciform specimens were loaded just uniaxially in order to check whether results would match with those obtained from uniaxially loaded beam specimens (as an evaluation of the cruciform geometry). The material has the typical lay-up of wind turbine blades. During the whole test duration the Digital Image Correlation technique (DICT) was used in order to get full field displacement measurements.

Publication year:2008

Keywords:biaxial testing, fatigue