A study on prediction method for low cycle fatigue strength of steel welded members

点击翻译按钮获取中文摘要

A new low cycle fatigue testing system has been developed, in which strains of the specimen are measured by image technique. The low cycle fatigue tests of steel plain material and welded portion under constant and variable strain amplitude, particularly the fatigue life less than ten cycles, was conducted by using the newly developed testing system. The test results indicated that the fatigue life of welded portion, such as deposit metal and heat affected zone (HAZ), was much shorter than that of plain material. Particularly, HAZ was the weakest spot, of which fatigue life was about 30% of the plain material. And fatigue strength curves for the plain material, the deposited metal and the HAZ were proposed, individually.As an estimation method of low cycle fatigue strength of "welded joint", peak strain based fatigue assessment method was verified. T-shape welded joints were employed for the verification test. The specimen was analyzed by elasto-plastic finite element method in order to quantify the local strain field around welded portion and the peak strain at the cracked point. On the other hand, fatigue life of the specimen was experimentally obtained by low cycle fatigue tests. The relationship between the peak strain and the fatigue life was consistent with the fatigue strength curve for the deposited metal. Consequently, it was demonstrated that the fatigue assessment method by peak strain approach was available even in low cycle fatigue region. And the improvement of fatigue strength of welded joints by TIG dressing was investigated. T-shape welded joint specimens of which weld toes were finished by TIG dressing were tested. The fatigue test results were compared with that of as-welded specimens tested in the same conditions. The test results indicated that TIG dressing could substantially increase the low cycle fatigue strength of welded joints.