This study clarifies and quantifies factors which increase the ductility of a low‐molecular‐weight propylene homopolymer having an intrinsic viscosity of 0.89 dl/g. The tensile behavior of homopolymer/ethylene‐propylene rubber (EPR) blends was studied from the viewpoint of the associated molecular structure of EPR and its compatibility with the homopolymer. When EPR is “dissolved” in a homopolymer, the glass transition temperature (Tg) of the amorphous phase of a homopolymer was found to shift to a lower temperature, with homopolymer/EPR compatibility being subsequently evaluated using this shift, i.e., Δtg. Results show two conditions are required to improve the ductility of the low‐molecular weight propylene homopolymer: ΔTg must be ≥ 3°C and ≥ 30 wt% EPR must be blended with the homopolymer.

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The objective of the present paper is to evaluate the fatigue crack growth behavior in press-fitted axles using a fracture mechanics approach and to predict the fatigue strength regarding crack propagation (σw2). The relationship between nominal bending stress (σn) and non-propagating crack length in press-fitted axles is also discussed. Rotating bending fatigue tests were conducted on the induction hardened and quench-tempered axles of 38 and 40 mm in diameter. The equation for ΔK was formulated from the result of FEM analyses in which the micro-profile at the contact edge was taken into consideration. The threshold stress intensity factor range ΔKth for small cracks was estimated from the crack size measured after the fatigue tests by using a modified stress ratio effect at fully compressed stress reversals due to high compression residual stress. σw2 and the relationship between σn and non-propagating crack length were predicted by using the above mentioned ΔK and ΔKth. The predicted σw2 and non-propagating crack length were in good agreement with the experimental values.

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