In this paper, recent fatigue tests conducted on welded specimens subjected to high frequency mechanical impact (HFMI) treatment are described, geometry measurements and metallurgical analyses of the tested specimens are presented, and efforts to estimate the test results using a nonlinear fracture mechanics model are discussed. The specimens were fabricated from 9.5-mm-thick (3/8 in.) aluminum (5083-H321) and high-strength steel (ASTM A514) plate. The specimen geometry and preparation followed procedures used in previous studies on mild steel (CSA 350W). Fatigue tests were performed on the as-welded and impact-treated specimens under two loading histories (constant amplitude with and without periodic under-loads) at several equivalent stress ranges. Residual stress distributions were determined by x-ray diffraction. In addition, weld toe geometry measurements were obtained using silicon impressions and microhardness distributions were obtained on polished weld samples for each material type. This information was used to establish parameter values for a nonlinear fracture mechanics analysis. The employed fracture mechanics model is reviewed in this paper, and its benefits as a tool for modelling the fatigue behavior of impact-treated welds are discussed. Following this, the effectiveness of the model in estimating the test results for the three materials is assessed.
The idea of using 3D point clouds obtained with the aid of a handheld 3D laser scanner for the quality assurance of high-frequency mechanical impact (HFMI) treatment is proposed and demonstrated in this paper. The effectiveness of impact treatments for extending the fatigue lives of welded structures has been demonstrated in numerous studies. Guidelines for the proper execution of impact treatments have been developed. A lack of suitable quality assurance (QA) procedures for accepting or rejecting the treatment after completion has been previously identified. In contrast with the existing QA procedures, which are based mainly on controlling inputs and visual inspection, a technology-based, quantitative methodology is developed in this paper. Five welded specimens were subjected to impact treatment at various levels to simulate under-, proper, and over-treatment. A handheld 3D laser scanner was then used to facilitate a point cloud-based method to determine the geometric parameters of the treated weld toe groove, which were then measured manually. The results show that the proposed methodology is successful in identifying the different treatment levels. This approach has a number of advantages over the existing QA methods, including the following: providing quantitative measures, ease of use, and archive-ability.
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