Nobukazu Ogura

Surface fatigue crack life and penetration behavior of stress concentration specimen

Abstract Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. Most structural bodies have a part where stress concentration exists, such as welded joints, corner parts, etc. The analysis on the crack growth and penetration from these defects may, therefore, be one of the most important subjects on the reliability of the LBB design. The authors have analysed the fatigue crack propagation from the surface defect on the stress concentration part. The crack growth behavior can be explained quantitatively using Newman-Raju equation and the stress partitioning method proposed by ASME Boiler and Pressure Vessel Code Section XI. The stress concentration has little effect on the crack growth rate after penetration. Using the K -value proposed by the authors, a particular crack growth behavior and a crack shape after the penetration can be estimated quantitatively.

On the ductile unstable failure of steel control-rolled in two phase regions.

On the Ductile Unstable Failure of Steel Control-Rolled in Two Phase Regions by Kotoji ANDO*, Kazunari MOGAMI**, Shinpei FUJIBAYASHI***, Hisao MATSUSHITA**** and Nobukazu OGURA** Ductile unstable failure test has been made on the high strength control-rolled steel over a wide temperature range. The effects of separation, compliance of the loading system and also temperature on the ductile unstable failure features have been investigated in detail by using compact specimens. The test results were mainly analysed with respect to material and applied tearing moduli. The main conclusions are as follows. (1) Stable-unstable behavior is in good agreement with theoretical prediction except that material tearing modulus at instability is larger than 300. (2) Even at the low temperature range where separation is notable, the specimen showed high resistance to tearing instability. (3) Separation which initiated before the maximum load point, did not induce brittle fracture and also tearing instability. On the contrary, it prevents the initiation of brittle fracture by decreasing the plastic constraint. キ ー ・ワー ド:J積 分,破 壊 じん性,制 御 圧 延 材,延 性不 安 定 破 壊,セ パ レ ー シ ョン

EXPERIMENTAL STUDY ON SEPARATION FRACTURE WITH A HIGH COMPLIANCE TESTING MACHINE FOR GRADE 50 KG-CLASS HIGH STRENGTH STEEL

ABSTRACT The characteristics of separation generation using 50 kg-class high strength steel (JIS SM50A) were studied. Using springs in the loading system, fracture behavior under high compliance-loading was also investigated. The results are as follows: (1) The separation generation depended on the temperature. It occurred above -100°C and attained a maximum at roughly –50°C. (2) Specimens thicker than 15 mm behaved as if consisting of two pieces due to the generated separations. (3) In some instances under high compliance-loading, the separation generated beyond the maximum load induced ductile unstable fracture. No particular compliance dependence was observed.