有限要素法による熱弾塑性拳動の解析

抄録

It is well known that welding produces thermal stresses which cause distortion of structures and residual stresses which influence buckling strength and brittle fracture strength of welded structures. Cold cracking of the weldment has beem investigated from a mechanical point of view with special attention paid to thermal stresses induced during the cooling stage of a welding thermal cycle.
For a better analysis on these subjects, it is necessary to obtain more accurate information on the entire histories of stresses and strains to which the material is subjected during the process of welding. At the instant of welding, a limited portion of the welded joint such as the weldment and the base metal in its vicinity is heated to a very high temperature and therafetr cooled down to room temperature. The thermal cycle proceeds, the temperature distribution changes with time and the mechanical properties of the metals depend on temperature. In order to perform a more reliable analysis, the above mentioned factors should be taken into account. However, there are many difficulties in analysing theoretically practical models, including these effects, by classical methods, and there are only a few reports of their analysis based on simplified assumptions, such as regarding the problem as one dimensional problem or neglecting most of tempe-rature-dependent factors.
The authors developed a method of theoretical analysis on this problem based on the finite element method, with consideration of the effects of changes in modulus of elasticity, yield stress and coefficient of expansion of the metal which are dependent on temperature under the assumption that problem is regarded as quasi-static, so that there is no interaction between temperature distribution and stress one. Accordingly, the temperature analysis is carried out independently before the stress analysis. As both analyses take incremental procedure, they can take into consideration of the effects of experience of the material before a stage at the following step of computation. if necessary, such as the rate of cooling on phase transformation, peak temperature on the mechanical properties, etc. in addition to the above mentioned temperature dependent properties. Examples of calculation given here are thermal stresses induced in butt welded joint under a moving electorode and local stresses and strains in RRC specimens during thermal cycle, and they show the usefulness of the method to general cases of welding.