Open-Hole Compression and Digital Image Correlation based Method for Measuring Interlaminar Tensile Strength of Composites

摘要

Advanced polymeric composites are increasingly used in high-performance aircraft structures to reduce weight and improve efficiency. However, a major challenge delaying the implementation of the advanced composites is the lack of accurate methods for material characterization. Accurate measurement of three-dimensional mechanical properties of composites, stress-strain response, strength, fatigue, and toughness properties, is essential in the development of validated analysis techniques accelerating design and certification of composite structures. Certain key properties are typically assumed in the analysis as they cannot be currently measured using standard test methods. The objective of the Composite Airframe Life Extension (CALE) program is to evaluate the applicability of advanced computational progressive damage and failure (PDFA) methods to assess the durability and damage tolerance of composite structures within the United States Air Force (USAF) fleet for service life extension. As part of this Task, a significant effort has been performed to accurately, reliably, and efficiently determine the required input properties and parameters for the methods. In particular, accurate measurement of the interlaminar tensile (ILT) strength is needed to capture delamination failure, which is one of the primary failure modes in composite aircraft structures. A major technical challenge to accurate measurement of ILT properties is their strong sensitivity to manufacturing defects including porosity that could lead to unacceptable scatter in the test results. Unacceptable failure mode in standard test methods that use transverse tension specimens is another challenge to accurate measurement of the ILT properties. In this work, an alternative methodology based on unidirectional open-hole compression (OHC) specimens is proposed and investigated as a viable alternative method to assessing ILT strength, fatigue, and stress-strain constitutive properties.