Issue 38

T. Sawada et alii, Frattura ed Integrità Strutturale, 38 (2016) 92-98; DOI: 10.3221/IGF-ESIS.38.12 92 Focussed on Multiaxial Fatigue and Fracture Effect of molding processes on multiaxial fatigue strength in short fibre reinforced polymer Takahiko Sawada, Hiroshi Aoyama Research & Development Group, Hitachi, Ltd., takahiko.sawada.dy@hitachi.com, hiroshi.aoyama.ra@hitachi.com A BSTRACT . This study concerns the multiaxial static and fatigue strength properties. Short-glass-fibre-reinforced phenolic-resin composites (SGP) molded by injection and compression processes were subjected to tension- torsion combined static and fatigue tests at room temperature under various test conditions. Tension – torsion combined static strength well agreed with Tsai-Hill failure criteria without depending on processes. Relationships between the maximum principal stress, σ p1, max , and the number of fracture cycles, N f , were approximately linear in the whole range of up to 10 6 cycles. For a unified evaluation of multiaxial fatigue life for SGP, non-dimensional effective stress, σ * , defined by modifying Tsai-Hill failure criteria was applied. The slopes of σ * - N f curves according to Baskin’s law were almost identical to the injection ( n = 26.3) and compression ( n = 26.2). We finally confirmed that the multiaxial fatigue life of SFRP could be predicted by using σ * with a unique Wöhler curve without relying on molding processes. K EYWORDS . Short-fibre reinforced plastics; Multiaxial; Fatigue; Tsai-Hill. Citation: Sawada, T., Aoyama, H., Effect of molding processes on multiaxial fatigue strength in short fibre reinforced polymer, Frattura ed Integrità Strutturale, 38 (2016) 92- 98. Received: 27.06.2016 Accepted: 26.07.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION hort fibre reinforced thermo-set plastic (SFRP) has been mainly applied to automobiles and electrical industries owing to its superior mechanical properties and lower weight. However, a machine designer often faces difficulties using SFRP or predicting its mechanical properties. SFRP generally shows complex fracture behaviours combined with a matrix crack, fibre break, fibre pull-out, and others, and these make product design difficult. Therefore, a machine designed using SFRP often requires a production test and a strength test to be repeated until its reliability is confirmed. Because reducing the number of test repetitions decreases the cost of development, high-reliability strength evaluation methods will be required to meet the increase in products that will use SFRP in the future. Further, multiaxial stress generally occurs in a structure subjected to an external force. In the literature, Moosbrugger et al. [1, 2] experimentally investigated and calculated the multiaxial fatigue behaviour of SFRP. They conducted some tension- torsion combined fatigue tests and estimated the fatigue life on the basis of the failure criterion of laminate. Gaier et al. [3] established a simulation process for the multiaxial fatigue life prediction of orthotropic SFRP. They combined the resin flow simulation, finite element analysis, and fatigue analysis. The fatigue damage of a belt pulley was predicted by S