Issue 38

T. Sawada et alii, Frattura ed Integrità Strutturale, 38 (2016) 92-98; DOI: 10.3221/IGF-ESIS.38.12 93 comparing experimental and simulation results. Although some additional papers [4-7] have focused on investigating the multiaxial strength for SFRP, little attention has been paid to the effect of manufacturing process on that property. This study is concerned with the multiaxial fatigue evaluation in short-glass-fibre reinforced phenolic resin (SGP) among various volume fractions. Round-bar specimens molded by injection and compression processes were subjected to static and fatigue tests in room temperqature to clarify the effect of molding processes on the multiaxial strength. Tension - torsion combined tests were conducted with various stress ratio parameters described as the ratio of torsion and tension stress as α = τ / σ . E XPERIMENTAL DETAILS ab. 1 details the configuration of SGP. Thermosetting phenolic resin was used as the matrix. The reinforcement was a short E-glass fibre 10 mm long and 10 μm in diameter. 0.0 V f , 0.2 V f , and 0.5 V f described at the first row means that the fiber volume fraction V f is 0%, 20%, and 50%. Test specimens with three-types V f were molded by compression (C-SGP) and injection (I-SGP) respectively. In the compression molding, 300-mm-square and 30-mm-thick bulk plates were manufactured, and then test pieces were cut from the bulk plate to the dimensions as shown in Fig. 1. Edges of the sample surface were not polished. A machining surface roughness was confirmed by using a roughness tester to be approximately the same in each specimen. Compression molding temperature was 160 °C, press pressure was 20 MPa, and curing time was 250 seconds. In contrast, in injection molding, test specimens were directly manufactured to specimen shapes described as Fig.1. Injection mold temperature was 140-160 °C, injection pressure was 80 MPa, and curing time was 20 seconds. Component 0.0 V f 0.2 V f 0.5 V f Glass Fibre [%] 0 20 50 Phenolic resin [%] 70~85 55~65 30~35 Phenol [%] 1 1 1 Hexamethylene etramine [%] 3 3 3 Rock wool [%] 10~20 10~20 10~20 Zinc stearate [%] 1.0~2.0 1.0~2.0 10~20 Table 1 : Configuration of SGP material.  6  9 50 127 Axial force Torsion torque Figure 1: Tension-torsion test specimen dimensions. Multiaxial test procedure In this study, we conducted multiaxial static and fatigue tests at room temperature to compare strength properties in different manufacturing processes. All the tests were performed by combining tension-torsion electro-hydraulic servo systems under axial-loads up to ± 25 kN with standard displacements of ± 50 mm and torsion-torques up to 220 N ･ m with total rotations of 270°. Tension-torsion combined tests were performed by using the specimen as shown in Fig. 1. Tension stress σ 1 is given by Eq. 1, where F is tension load and D is diameter at the gauge section. Torsion stress τ 12 is given by Eq. 2, where T is torque.