Specimen designs for accurate tensile testing of unidirectional composite laminates

Tensile testing of unidirectional composites based on standardized test methods nearly always leads to premature failure in the end tab region. The material near the tab section is under a complex loading state, including longitudinal, transverse, and shear stress components. The present work examines different conventional designs for tensile testing along with novel ones to find the method that minimizes the geometric discontinuity and yields the highest failure strain. Finite element (FE) models are utilized to predict the stress concentrations for all end tab designs with representation of the actual grip components. The simulation reveals that the stress concentration near the edge of the end tabs can vary significantly with end tab design. FE models are used to further optimize the geometry of end tabs. The experimental results reveal that specimens with novel arrow-shaped tabs and continuous tabs yield the highest failure strain, and hence are best at avoiding premature failure.