In recent years Japanese researchers have been active in studies of crack growth behavior, but the findings have often been presented only in the Japanese language. This publication in English is intended to present the important recent results of selected works of some of the leading Japanese researchers in an effort to promote wider dissemination of these findings and thereby contribute to worldwide progress in science and technology. It is well to be aware of these contributions which are distinguished by insight, exactitude in experimental work, and novel experimental procedures. However the editors are a bit modest, for in fact many of the authors of the papers in this volume are highly respected outside of Japan for their contributions to research. Three topics are treated, namely, short fatigue cracks, fatigue crack growth and the threshold, and corrosion fatigue ''cracks. H. Nisitani discusses the behavior of small cracks and related phenomena, K. Yamada, M. Shimizu, and T. Kunio treat the threshold behavior of small cracks, M. Jono and J. Song write on the growth and closure of short cracks, K. Ogura, Y. Miyoshi and I. Nishikawa discuss small cracks at notch roots, K. Tanaka describes short crack fracture mechanics, and S. Usami discusses short cracks and component life estimation. A. Otsuka, K. Mori, and K. Tohgo write on Mode II fatigue crack growth in aluminum alloys, A. Ohta, E. Sasaki, M. Kosuge and S. Nishijima discuss the threshold for welded joints, K. Asami deals with fatigue crack growth in high strength steel, H. Kobayashi and H. Nakamura analyze plasticity induced closure, and M. Kurihara, A. Katoh and M. Kawahara discuss the effects of stress ratio and step loading on the rate of fatigue crack growth.

An extensive set of stress relaxation and constant strain rate tests for characterizing the mechanical responses of a medium density polyethylene and a high density polyethylene that are commonly used in natural gas distribution piping is described and analyzed. The development of coherent master curves for the relaxation modulus, maximum stress, and the time‐to‐failure for pressurized pipes through a combination of both horizontal and vertical shifting is presented. The relaxation data are used to develop a nonlinear Viscoelastic material model. The model is assessed by making comparisons of the predicted stress‐strain response with the measured response in the constant strain rate tests.

Many polymeric materials, including structural adhesives, exhibit a nonlinear viscoelastic response. The nonlinear free volume approach is based on the Doolittle concept that the “free volume” controls the mobility of polymer molecules and, thus, the inherent time scale of the material. It then follows that factors such as temperature and moisture, which change the free volume, will influence the time scale. Furthermore, stress-induced dilatation will also affect the free volume and, hence, the time scale. However, during this investigation dilatational effects alone were found to be insufficient in describing the response of near pure shear tests performed on a bisphenol A epoxy with an amido amine hardener. Thus, the free volume approach presented here has been modified to include distortional effects in the inherent time scale of the material. In addition to predicting the global response under a variety of multiaxial stress states, the modified free volume theory also accurately predicts the local displacement fields, including those associated with a localized region, as determined from geometric moire´ measurements at various stages of deformation.

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