Understanding limitations of through thickness test methods

Abstract

Through thickness properties are increasingly important for the detailed analysis of complex composite structures. Recent papers and research have proposed a variety of test method solutions for the determination of through thickness properties. A comprehensive experimental evaluation has led to the drafting of standards for through thickness tension, compression, and shear test methods. A detailed comparison of the mechanical test methods, data, and failure modes is presented. An assessment is made of their utility, applicability, and limitations, highlighting sensible test precautions. In selected cases, comparisons with elastic constant data obtained using ultrasonic techniques are provided.Despite a number of difficulties, tension and compression specimens are relatively easy to design, provided the test material is of sufficient thickness (e.g. 20 mm). Shear test methods are not so easily defined, such that none is applicable to all materials or all directions, and failure modes may be neither initiated nor dominated by shear.