Issue34

K. Tanaka et alii, Frattura ed Integrità Strutturale, 34 (2015) 309-317; DOI: 10.3221/IGF-ESIS.34.33 316 C ONCLUSION he influences of fiber orientation on the crack propagation behavior was studied with single edge-notched specimens which were cut from an injection-molded short fiber reinforced plastic plate at five fiber angles relative to the loading axis, i.e.  = 0° (MD), 22.5°, 45°, 67.5°, 90° (TD), under the stress ratio R =0.1 and 0.5. Fracture mechanics parameter determined by FEM based on anisotropic elasticity were used to correlate the crack propagation rate. The obtained results are summarized as follows: (1) Macroscopic crack propagation path was nearly perpendicular to the loading axis for the cases of MD and TD. For the other fiber angles, the crack path was inclined because the crack often propagated along fibers. (2) For mode I crack propagation in MD and TD, the resistance to crack propagation is improved by fiber reinforcement, when the crack propagation rate is correlated the range of stress intensity factor. The crack propagation rate, d a /d N , was slowest for MD and fastest for TD. For each material, the crack propagation rate is higher for larger R ratio. The effect of R ratio on d a /d N diminished in the relation between d a /d N and the range of energy release rate,  G I . (3) Difference among MD, TD and matrix resin becomes small when d a /d N correlated to a parameter corresponding the crack-tip radius, H I  G I , where H I is compliance parameter. (4) Fatigue cracks propagated under mixed loading of mode I and II for the fiber angles other than 0° and 90°. The data of crack propagation rate correlated to the range of total energy release rate,  G total lie between the relations obtained for MD and TD. (5) All data of crack propagation rates tend to merge a single relation when the rate is correlated to the range of total energy release rate divided by Young’s modulus for various fiber angles and R ratios. A PPENDIX EM analyses were conducted using Marc Ver. 2005 to determine the energy release rate of mode I for MD and TD, and of mixed mode of I and II for the other fiber angles. The crack was assumed to propagate at the angle,  , determined by experiments. Two-dimensional isoparametric eight-node rectangular elements were used under the condition of plane stress. The modified crack closure integral was adapted to determine the energy release rate. The orthotropic elastic constants used for FEM is given in Tab. 1. A load was applied to the edges of the central region of 20×50 mm 2 shown in Fig. 1 under constant displacement condition in the longitudinal direction. The calculated values of energy release rates were inserted in Eq. (1) and the correction factor, Y I and Y II were determined. For MD and TD, the stress intensity factor was determined by using Eq. (2) from the energy release rate. T F Figure 10 : Correction factors of mode I energy release rate and stress intensity factor. (a) Correction factor for mode I energy release rate. (b) Correction factor for mode I stress intensity factor.