We find a cracked hook twin tie plate to study. It is clear to know that the welds at the fracture are denser than other parts, and the deformation is relatively large. The structure of the crack part is in the figure1.The transverse weld at the crack source has an R = 4mm circular transition, at the vertical intersection of the side seam of the bottom plate 2, and the V-notch is formed on the welded structure, resulting in stress concentration and localized the stress. It is easy to sprout cracks and expand rapidly, leading to fracture when leveling the hook twin tie plate like the figure 2.
First, we choose a hook twin tie plate from our warehouse to do a room temperature tensile test. The hook twin tie plates were subjected to a room temperature tensile test in the direction of the parallel rolling direction and the vertical rolling direction of the bottom plate. Our product has reached the requirements of the tensile properties.
Second, we do the 180 cold bend tests. We choose a pair of hook twin tie plate to make a comparison. A hook twin tie plate has no cracks on the surface after the 180 cold bend tests. Besides, the plastic deformation of the parts at the bend is uniform.
There are no cracks, undercuts, and stomata near the welds. The longitudinal welds and horizontal welds of the hook twin tie plate are more than 10mm. Compared with others welds, the width will cause the deformation of the hook twin tie plate get bigger and bigger. There are two symmetrical crack sources in the hook twin tie plate, where the first source of the crack occurs at the group of welding arcs and there are some slags.
The fracture analysis results show that the bottom plate is brittle overload fracture because of the local stress and material weakened. The structure of hook twin tie plate exist a gap that intensifies the concentration of local stress. Meanwhile, the gap lies in a welding heat affected position and the multiple solder joints. This position is not beneficial to keep the original shape and destroy the hook tie plate’s performance.
For some problems like this issue, we take measures to solve them based on this study. In order to ensure the quality of our products, we will do more tests in our hook twin tie plate production. As a railroad fasteners supplier, AGICO Rail provides many types of railway products like rail clip, rail joint, rail bolt and etc. Based on a professional attitude and strict quality control, we will do much better to provide high quality service！