MODIFIED TENSILE TEST SETUP FOR HIGH-MODULUS MULTIFILAMENT YARNS

Existing numerical and experimental approaches for the micromechanical characterization of high modulus yarns necessitate a more detailed description of high modulus yarns especially for the novel application to use these yarns as reinforcement in concrete. Crucial for the bearing load of the composite elements is the tensile strength of a yarn in a cracked state of the matrix. This type of stress is fundamentally different compared to applications in fibre-reinforced plastics where composite action is consistent in the yarn length and cross-section. The assembly of the yarn with a brittle matrix provides new and more complex demands to the yarn behaviour and requires a detailed knowledge of local support and failure mechanisms. Compared to other applications, the fundamental difference is that the yarn is strained differently, depending on the location of the filaments, both in extremely short effective lengths (in a crack of the matrix) as well as in extremely long effective lengths (inside the yarn). Stress concentrations with short effective lengths (cracks and direction changes) occurring during the failure processes in the yarn and their interactions cannot be described sufficiently. This paper recapitulates existing test methods and describes an improved test method to measure the tensile strength of shorter test length and to achieve a better yarn characterization.