Stress Engineering

Expert system RESIsT

The fatigue life of welded elements depends on a number of factors and a complex task should be resolved to find the optimum way for fatigue life improvement of welded structure without the increase in its metal consumption. The Expert System for Fatigue Assessment and Optimization of Welded Elements and Structures – RESIsT was developed to resolve the above-mentioned problem. Major attention was paid to developing the predictive model for analysis of the influence of the residual stresses and their redistribution under the effect of improvement treatments and cyclic loading on the fatigue life of welded elements. Presently, elaborate, time- and labor-consuming fatigue tests of large-scale specimens are required for this type of analysis.

Optimization of welded elements is based on the fatigue assessment of welded joints in the dialog mode. The following important parameters of welded structures with the goal to enhance the fatigue performance are analyzed:

• Material selection
• Preferred design of welded elements
• Weld processes & materials
• Residual stresses
• Application of improvement treatments
• Influence of possible repair technologies
• Realistic service conditions

The RESIsT includes a package of programs allowing to perform storing, classifying and statistical processing of the fatigue testing results and subsequent comparative analysis of the fatigue life of welded joints in the initial condition (after welding) and after application of improvement treatments. Searching for initial data for comparative analysis is carried out according to the selected combination of design and technological parameters of the welded elements, as well as according to the type and parameters of improvement treatments.

The RESIsT includes the possibility to assess through calculation the effect of welding residual stresses and improvement treatments application on the fatigue life of welded elements without having to perform the time and labor consuming fatigue tests. The program package enables to calculate the fatigue strength parameters of welded joints after application of heat-treatment, vibration treatment, overloading, ultrasonic peening and other improvement treatments. The mechanical properties of the used materials, the type of welded elements and stress concentrations, as well as the cyclic loading parameters are taken into account in an explicit form. Detailed analysis of the influence of residual stresses and their redistribution under the effect of cyclic loading in the zones of stress concentration is performed during such assessment.

Effect of Residual Stresses