Fig. 1. Relation between fatigue crack propagation rate and stress intensity factor range. Fig. 2. Effect of stress ratio on fatigue crack opening rat

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1 Fatigue Crack Propagation and Fracture Surface in Polyvinyl Chloride by Tetsuro SHIRAISHI The fatigue crack propagation behavior and the fracture surface appearance under several load conditions in polyvinyl chloride were investigated. The crack closure behavior was also examined. The fatigue crack propagation rate, da/dn, under constant amplitude loading increased with increasing stress ratio in the relationship of da/dn versus the stress intensity factor range, ƒ K. This effect of stress ratio on da/dn was closely related to the crack closure behavior when the stress ratio was not so high. Discontinuous growth bands (D.G.B.) on the fracture surface seemed to be difficult to be formed when the stress ratio was very high. The width of D.G.B. was found to be dominated by the effective stress intensity factor range, ƒ Keff. The crack extension during loading a single peak overload was very large and so it could be clearly identified on the fracture surface. This region of the crack extension on the fracture surface revealed granular markings containing many voids, which was similar to that found in D.G.B.. The amount of this crack extension was about equal to the size of the plastic zone at the crack tip formed by the overload under a plane strain condition. Key words: Polyvinyl chloride, Fatigue crack propagation, Fracture surface, Crack closure, Discontinuous growth bands, Single peak overload

2 Fig. 1. Relation between fatigue crack propagation rate and stress intensity factor range. Fig. 2. Effect of stress ratio on fatigue crack opening ratio. Fig. 3. Relation between fatigue crack propagation rate and effective stress intensity factor range.

(a) Optical micrograph Fig. 4. Optical micrograph of typical discontinuous growth bands (D.G.B.) at R=0 (ƒ K=1.1MPa49 ãm). (b) Scanning electron micrograph Fig. 6. Incomplete D.G.B. at R=0.5 (ƒ K=0.

3 (a) Optical micrograph Fig. 4. Optical micrograph of typical discontinuous growth bands (D.G.B.) at R=0 (ƒ K=1.1MPa49 ãm). (b) Scanning electron micrograph Fig. 6. Incomplete D.G.B. at R=0.5 (ƒ K=0.56MPa ãm). (a) Initial part of the band (b) Final part of the band Fig. 5. Scanning electron micrograph of typical D.G. B. at R=0 (ƒ K=1.2MPa ãm). Fig. 7. Relation between the band size of D.G.B. and stress intensity factor range.

$Scanning electron micrograph of fracture surface of crack extension by a single peak overload Fig. 9.$

4 Fig. 8. Relation between the band size of D.G.B. and effective stress intensity factor range. Fig. 10. Scanning electron micrograph of fracture surface of crack extension by a single peak overload Fig. 9. Optical micrograph of fracture surface of crack extension by a single peak overload (Ko.L.=2.6 MPa ãm). (Ko.L.=1.9MPa ãm). The arrow indicates the void.

5 2) W. Elber, ASTM STP 486, 230 (1971). Fig. 11. Relation between the amount of crack extension by a single peak overload and stress intensity factor. 3) R.W. Hertzberg, M.D. STP 675, 471 (1979). Skibo and J.A. Manson, ASTM 4) C.M. Rimnac, R.W. Hertzberg and J.A. Manson, J. Mater. Sci., 19, 1116 (1984). 17) H. Tsukuda, H. Ogiyama and T. Shiraishi, Fatigue Fract. Engng Mater. Struct., 18, 503 (1995). 18) R.W. Hertzberg and J.A. Manson, gfatigue of Engineering Plastics h, p. 110 (1980) Academic Press. 19) M.T. Takemori and R.P. Kambour, J. Mater. Sci., 16, 1108 (1980). (1981). 20) J.A. Sauer and G.C. Richardson, Int. J. Frac.,

The Effect of the Circumferential Temperature Change on the Change in the Strain Energy of Carbon Steel during the Rotatory Bending Fatigue Test by Ch

The Effect of the Circumferential Temperature Change on the Change in the Strain Energy of Carbon Steel during the Rotatory Bending Fatigue Test by Chikara MINAMISAWA, Nozomu AOKI (Department of Mechanical