Many analyses relating to shearing of sheet products have already been reported. Elasto-plastic analyses to evaluate residual stress inside the sheet have also been increasing. However, only a few papers have shown measured residual stress distributions, so very few in-depth comparisons between calculated stress levels and experimental results are available. In this study, considering ductile fracture conditions of thin steel sheets, two simulations of the shearing process have been carried out. The results of the simulations agree well with experimental ones, such as cut surface shape and residual stress distribution in the vicinity of the cut surface measured using synchrotron radiation. As another example, after punching a round hole to about half the sheet thickness, i.e., extruding a cylindrical protrusion, a round interlock is formed by subsequently laying of a sheet on the others. A simple four-layer interlock simulation model predicts accurate residual stress distributions compared with X-ray diffraction data. The above-mentioned simulations would be promising tools benefitting the performance of steel products by reducing residual stress levels.
The previous study revealed that the new double thread bolts composed of a coarse single thread and coarse multiple threads (called DTB-II) have poor thread rolling formability and insufficient tensile strength. In this study, we developed two modified types of 3-thread DTB-II called 3-1 thread DTB-IIB and DTB-IIC: one thread was removed from the triple threads for both DTBs and the height of the multiple thread root-diameter was raised by half in the latter case at the point where a single thread was traversed by the bottom of multiple threads. The FEM thread rolling simulations were first performed using dedicated dies having a groove that followed the same outline as the thread profile of the modified DTBs. Both modified DTBs were rolled precisely and the thread heights reached the target level at any cross section. The actual forming states in the thread rolling experiments well reproduced the FE-simulation results. The performance evaluation tests demonstrated that the 3-1 thread DTB-IIC, even with a single-nut structure, has a practically sufficient tensile strength, and the fatigue strength and the antiloosening performance of both DTBs clearly exceed that of the conventional DTB-I composed of a coarse single thread and a fine single thread.
An experimental procedure for the hot compression test for Ni-based alloy was proposed and evaluated in order to obtain an appropriate stress-strain curve for numerical analysis. The effect of various parameters, i.e., top and bottom shapes of specimen, lubricant and jig/tool, on the deformation tendency was systematically studied. Ni-based alloy (CMSX-4), which has a higher strength than the specimen, was used as die for preventing temperature gradient. This improved the uniformity of temperature distribution in the specimen. The combination of a specimen having concentric circles on the end surface and a glass sheet as lubricant was the most appropriate to gain stable and low-friction condition of the specimen end. The proposed procedure of the hot compression test is applicable for the temperature range of 1173－1423 K and strain rate range of 0.01－5 s-1. The effectiveness of the obtained stress-strain curve was discussed from the viewpoint of the value and tendency of characteristic features observed in the flow stress curve. The maximum stress exhibited normal temperature and strain rate dependence. Related activation energy for deformation was similar in value to those in other reports.
Research works on the joining of shaft and plate are summarized and the features of the conventional caulking process are discussed. Maximum caulking force is limited by the occurrence of shaft buckling and plate warping. The joining force in upset caulking mainly results from press fit force between the hole wall of the plate and the enlarged shaft diameter, while the joining force in shear caulking mainly results from press fit force at the flange portion of the caulked head. To improve joint efficiency, a two-step process in which upset caulking is combined with shear caulking, is newly proposed. Optimum working conditions are examined and experimental results show considerable improvement of joining efficiency, especially in rotational resistance. Some ideas for the practical application of this process are proposed here.
Obtaining cut surfaces with high precision by shearing, including press cutting and punching, of composite materials such as carbon-fiber-reinforced thermoplastic (CFRTP) is difficult because shear characteristics vary among materials. To address this problem, vibratory finish shearing and shaving have been examined. However, conventional vibratory finish shearing requires a dedicated press machine and conventional shaving requires two processes. The authors have proposed a simple punching method for CFRTP sheets involving the low-frequency vibrational motion of a punch using a numerical control (NC) servo press machine that has recently become widespread. The method realizes high-precision punching in a single process using conventional dies. However, it takes a long time to achieve the desired cut surface. Therefore, the time required for punching should be reduced before this method is practically applied. In this study, experiments were carried out to determine the optimal vibrational conditions of the punch for achieving high-precision cut surfaces of holes within a short period of time. The conditions required for vibro-punching to be completed within ~16 s, which is the allowable time for deep drawing of CFRTP sheets using a hot press, were determined.