Issue34

K. Tanaka et alii, Frattura ed Integrità Strutturale, 34 (2015) 309-317; DOI: 10.3221/IGF-ESIS.34.33 310 [1-5]. The path of crack propagation is influenced by the fiber orientation even if the applied load is uniaxial, and cracks often propagate under mixed mode condition. In most of the previous works, the fatigue crack propagation rate has been correlated to the stress intensity factor or the energy release rate which are derived based on isotropic elasticity even though SFRP are anisotropic. In the present paper, the crack propagation behavior was studied with polyphenylenesulphide (PPS) reinforced with 30wt% carbon fibers. Specimens with single edge notch were cut at different orientation angles with respect to the molding flow direction from plates made by injection molding. Fatigue crack propagation tests were conducted at stress ratios of 0.1 and 0.5. The influences of fiber orientation on the crack path and the crack propagation rate was studied from a viewpoint of fracture mechanics based of anisotropic elasticity. E XPERIMENTAL PROCEDURE Specimens he materials is short-fiber reinforced brittle thermoplastics, polyphenylene sulphite (PPS), reinforced with carbon fibers. The amount of fiber content was 20 wt%. Fatigue specimens were cut from an injection-molded plate (IMP) with the in-plane dimensions of 80×80 mm and the thickness of 1 mm. Fig. 1 shows the shape of test specimens which has a single edge notch of length 2 mm, the length of 80mm, and the width of 20mm. The region of length 15mm was used for chucking to the testing machines through aluminium tabs. A fatigue crack was started from the initial notch. The angle between molding direction and longitudinal direction of specimens was set to be five values:  = 0° (MD), 22.5°, 45°, 67.5°, 90° (TD). Since the fiber direction on the skin layer of injection-molded plates is nearly along the molding flow direction (MFD), the angle  means the angle between the fiber direction and the loading axis. In the following, the angle   is called the fiber angle. Injection-molded plates have a three-layer structure where two skin layers sandwich the core layer [5]. The thickness of the core layer of the present plates was about 0.15 mm. Experimentally measured values of anisotropic elastic constants of IMP are summarized in Tab. 1. Young’s modulus for various fiber angles are given in Tab. 2. Specimens made of only the matrix resin PPS were also made from the injection-molded plate with thickness 1mm. They are isotropic having Young’s modulus of 4.45GPa, and Poisson’s ratio of 0.368. E 1 (GPa)  12 E 2 (GPa) (  21 ) G 12 (GPa) 22.78 0.378 10.84 (0.177) 4.86 Table 1 : Elastic constants of IMP. Fiber angle 0° (MD) 22.5° 45° 67.5° 90°(TD) Matrix Young’s modulus E (GPa) 22.8 18 12.9 11.1 10.8 4.45 Table 2 : Young’s modulus for various fiber angles. T Figure 1 : Single edge notched plate.