Assessment method of COD for a surface flaw at a structural discontinuity

1992 Fiscal Year Final Research Report Summary

• Project/Area Number: 03555095
• Research Category: Grant-in-Aid for Developmental Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: 船舶構造・建造
• Research Institution: KYUSHU UNIVERSITY
• Principal Investigator: TOYOSADA Masahiro KYUSHU UNIV.,FACULTY OF ENGN.,PROFESSOR, 工学部, 教授 (30188817)
• Co-Investigator(Kenkyū-buntansha): MURAI Ryousuke MITUBISHI HEAVY INDUSTRY,HIROSHIMA INSTITUTE, 広島研究所, 研究員 ; KAJIMOTO Katuya MITUBISHI HEAVY INDUSTRY,HIROSHIMA INSTITUTE, 広島研究所, 主務 ; NIWA Toshio KYUSHU UNIV.,FACULTY OF ENGN.,RESEARCH ASSOCIATE, 工学部, 助手 (10208267)
• Project Period (FY): 1991 – 1992
• Keywords: COD for a Surface Crack / Superposition of Elasto-Plastic COD / COD of a Crack in Sheet / T Tubular Joint / CTOD / 誘起曲げ応力

Research Abstract

We invested at first that elasto-plastic COD's for a single edge cracked sheet(SC), which is a cross section of a surface crack, subjected to tension(sigma_m) were given by some superposition of COD's for a center cracked sheet(CC) subjected to tension and COD's for a single edge cracked sheet subjected to bending stress(m*) by eccentricity. As a result, COD's for SC by sigma_m are obtained by superposition of COD's for CC subjected to tens ion which stress is sigma_m plus 0.75m* and COD's for SC subjected to m*. In above treatment,m*/sigma_m is a function of sigma_m/sigma_y(sigma_y:yield stress) and decreases as sigma_m increases to zero when gross yield occurs.
Then working tension stress and bending stress for a cross section of a surface crack are obtained by K value at the deepest point of a surface crack working tension and bending. By adapting a simplified beam theory, aperient yield stress for SC due to bending in case of combined tension and bending is introduced.
This estimating method of COD's is applied to a surface flaw in a crown part of T tubular joint of an offshore structure. Estimated COD's at a center of a surface are in good agreement with experimental ones. As a result, it becomes clear that CTOD defined by the displacement of R end of a notch tip is tend to give smaller value in case of high working stress than CTOD defined by Dugdale model and hinge model for 3 point bending CTOD testing .