PSI - Issue 2_A

Keisuke Tanaka et al. / Procedia Structural Integrity 2 (2016) 058–065 Author name / Structural Integrity Procedia 00 (2016) 000–000

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Fig. 9. SEM micrographs of fatigue fracture surface of MD and TD specimens at RT and 403K.

4. Conclusion The crack propagation behavior was studied at RT, 343K, 373K, and 403K with center-notched specimens which were cut from an injection-molded short fiber reinforced plastic plate at two fiber angles relative to the loading direction, i.e. θ = 0° (MD) and 90° (TD). The obtained results are summarized as follows: (1) Macroscopic crack propagation path was nearly perpendicular to the loading axis for both MD and TD. Microscopically, cracks in MD were blocked by fibers and circumvented fibers, and rarely broke fibers, showing zigzag path. For TD, the crack path was less tortuous following fiber interfaces. (2) The relations between crack propagation rate, da/dN , and stress intensity factor range, ∆ K , at RT and 373K were similar for both MD and TD, while da/dN increased much with increasing temperatures above glass transition temperature, T g , by two to three orders. At each temperature, da/dN of MD was about two orders lower than that of TD. (3) At temperatures above T g , inelastic deformation took place; the relation between load and displacement became nonlinear, accompanied by hysteresis loop expansion. When da/dN is correlated to the J -integral range, ∆ J , the relation at each temperature came closer for each case of MD and TD. Especially for the case of TD, the relations at different temperatures merged together. At each temperature, da / dN of MD was lower than that of TD, even though the difference between MD and TD was smaller. (4) Many fibers pulled out from the matrix were seen on fatigue fracture surface of the skin layer of MD and parallel fibers were observed on the fracture surface of TD. High temperature environment increased matrix deformation both in MD and TD, but did not change the fracture path or the micromechanism of fatigue crack propagation. References Akiniwa, Y., Harada, S., Yagyu, Y., Nakano, M., 1992. Effect of fiber content and fiber orientation on fatigue strength of short-fiber reinforced plastics. Journal of Materials Science, Japan 41, 1285-1291 Dowling, N. E., 1976. Geometry effects and J integral approach to elastic plastic fatigue crack growth. In: ASTM STP 601, Cracks and Fracture, Edited by Swedlow, J. L., Williams, M. L., American Society for Testing and Materials, Philadelphia, pp. 19-32. Karger-Kocsis, J., Friedrich, K., Bailey, R.S., 1991. Fatigue crack propagation in short and long glass fiber reinforced injection-molded polypropylene composites. Advances in Composite Materials 1, 103-121. Pegoretti, A., Ricco, T., 2000. Fatigue fracture of neat and short glass fiber reinforced polypropylene; Effect of frequency and material orientation. Journal of Composite Materials 34, 1009-1027. Rybicki E. F., Kanninen M. F., 1977. A finite element calculation of stress intensity factors by a modified crack closure integral. Engineering Fracture Mechanics 9, 931-938. Sih, G.C., Liebowitz, H., 1968. Mathematical theory of brittle fracture, in: H. Liebowitz (Ed.), Fracture, Vol. 2 Mathematical Fundamentals, Academic Press, New York, pp. 67-190. Tada, H. , Paris, P. C., Irwin, G. R., 2000. The Stress Analysis of Cracks Handbook, Third Edition. ASME, New York, p.41. Tanaka, K., Kitano, T., Egami, N., 2014. Effect of fiber orientation on fatigue crack propagation in short-fiber reinforced plastics. Engineering Fracture Mechanics 123, 44-58. Tanaka, K., Oharada, K., Yamada, D., Shimizu, K., 2015. Fatigue crack propagation in short-fiber reinforced plastics. Frattura ed Integrita Strutturale 34, 345-355. Wyzgoski., M. G., Novak, G. E., 1990. Fatigue fracture of nylon polymers, Part I Effect of frequency. Journal of Materials Science 25, 4501 4510.