Although a scratch test is commonly used for evaluating the strength of adhesion between a thin film and substrate, the relationship between indentation load and interfacial stress state has not been directly derived. In the present study, three dimensional finite element analyses on a scratch test were performed to clarify the interfacial stress state. DLC-Si and TiN were employed as the film materials. As the substrate material, SUS440 was used. The calculated result was in good accordance with the result of the actual test on the geometry of the scratched groove. From the results of interfacial stress states, the interfacial normal and shear stresses took the maximum at an area inside the lip of the groove where the delamination may first occur in the actual tests. Then, the effect of film material on the interfacial stress state was discussed using this model. The interfacial shear stress was more sensitive to the change in the film material. Finally, the effect of friction between the indenter and the thin film on the interfacial stress is also discussed. The result shows that the interfacial stress state was highly affected by the change in frictional conditions. This indicates that the critical indentation load will fluctuate unless the friction conditions are properly controlled.
The kinematic hardening model proposed by Yoshida et.al was applied to the prediction of springback of stainless steel sheet part. From the experiments for the determination of material constant, the anisotropy of plastic-strain-dependent Young's modulus was observed. The prediction accuracy of springback was examined by comparing the calculated results with the experimental results. To take the anisotropy of the plastic-strain-dependent Young's modulus into account, calculations using different material constants at angles of 0°, 45° and 90° from the rolling direction were performed. It was found that the most accurate prediction can be obtained when using the material constant at an angle of 90°, along which the springback occurs. Therefore, the consideration of the anisotropic property of the plastic-strain-dependent Young's modulus was found to be effective for the improvement of prediction accuracy of the springback for stainless steel sheet.
The static and fatigue strengths of mechanically clinched, self pierce riveted and resistance spot welded joints in aluminium alloy A5052-H34 sheets were investigated. In the static tension-shearing test, self pierce riveted, resistance spot welded and mechanical clinched joints were tested in order of the maximum load. The endurance ratio of the sheets joined by the mechanical clinching and self pierce riveting were larger than that of the sheets joined by resistance spot welding owing to the work-hardening and slip at the interface between the sheets, i.e. the fatigue characteristic of mechanical joining processes was better than that of the welding processes involving metallurgical bonding. To increase the maximum joint load for mechanical clinching, a step punch was proposed. In the mechanical clinching using the step punch, the wall thickness in the side wall of the punch was increased by the compression of the step. The maximum static load and endurance ratio for mechanical clinching using a step punch were increased by 21% and 45%, respectively.
In this study, high-tensile steel plates are pierced with a press working (PW) punch and a right-angle (RA) punch in incremental steps. The difference between the hole surfaces formed by these punches is observed to explain why the roughness of fracture surfaces of pierced holes varies with the type of punch used, despite the fact that punches do not come in contact with the fracture surfaces directly. The main results are as follows: (1) For the RA punch, a crack emanating from the corner of the punch and one emanating from the corner of the die meet each other. (2) The fracture surfaces of holes pierced with the RA punch show maximum roughness at the center, or at the junction of the two cracks. (3) The PW punch absorbs the stress at its corner, so cracks do not emanate from the punch side.
The drawbead technique is very important for sheet metal forming in order to control defects such as springback, cracking, wrinkling. Therefore, approximation calculation models of drawbead force have been proposed in the past. However, such calculation models were applied to mild steel or aluminum alloy. In this paper, we propose an approximation calculation model of high-strength steel using the energy method and taking into account the Bauschinger effect. The calculation results were compared with the experiment results obtained under several drawbead shape conditions, and it was confirmed that the prediction value of drawbead force has good accuracy. Also, the through-thickness strain after passing through a drawbead was in good agreement with what obtained using stress reduction parameter due to Bauschinger effect. Moreover, it was found that the strain decreases effectively when the drawbead width is larger than the drawbead height. As a conclusion, the approximate calculation model discussed here is a practical and effective means of designing what tools.
A high-speed large-reduction forging technology has been developed to improve the hot strip production process. This technology can be used to produce fine-grained steel by enhancing the dynamic recrystallization caused by high strain. And it has specific features in width deformation caused by intermittent and large deformation. In this paper, laboratory-scale experiments and FE analysis are carried out to clarify the fundamental characteristics of the deformation and stress field. Large reduction results in a large width spread, and intermittent working causes periodic width deviation. The influences of die shape, the amount of feed per pass and the aspect ratio of the width against the thickness of the initial works on width spread and deviation are discussed. Large forging load results in a chevron-like indentation profile of the die surface and produces a thickness profile of the work.
In this paper, we describe the occurrence of stringlike paper dust in the shearing of a heightwise corrugated paperboard (Cpb). To determine the effect of blade position together with the apex position of a corrugated medium (CM) wave on the deformation behavior of CM, a pair of asymmetric upper/lower cutting blades was quasi-statically indented to Cpb and the side view of Cpb was observed using a CCD camera. Through the experiment, the following were revealed: (1) The deformation behavior of CM during the blade indentation was classified into three groups: M-like form (apex crushing), Z-like form (doubly folded), and W-like form (back side liner and root crushing). (2) The Z-like form was subdivided into the three modes: ZC, ZOV, ZDR. Here, ZC is blade just cut off the Z-form, ZOV is the blade moved aside from the Z-form due to surplus folding, and ZDR is the blade moved aside from the Z-form due to insufficient folding. (3) The asymmetric structure of CM wave affects the distribution of deformation modes of CM with respect to a certain X range. (4) The asymmetric structure of the upper/lower blades and the asymmetric constraint of specimen affect the occurrence probability of the deformation modes.