Backward extrusion was performed on two-layered rotary-cut veneer disks. The angular difference of the fiber orientation between the two disks influenced formability. The earring of the wall was largest when the fiber orientations of the two disks were parallel to each other, whereas it was smallest when the fiber orientations of the two disks were perpendicular to each other. Cups were produced from six-layered rotary-cut veneer disks by backward extrusion. The deformation and formability depended strongly on the arrangement of the disks. To prevent cracking in the wall and mold successfully, it is better to place the disks with the fiber orientation of adjoining disks perpendicular to each other. This enables the fiber cells of the disks to intertwine with each other. Heat treatment was performed on the cups to improve water stability. The cups not subjected to heat treatment failed to keep their shapes in water. On the other hand, the cups subjected to heat treatment (250°C for 60 minutes) had excellent water stability and showed no swelling on exposure to water.
The bore expansion tests of a mild steel sheet and two types of high-strength steel sheets using conical- and flat-headed punches are simulated using the dynamic explicit finite element program LS-DYNA ver. 970 with shell elements. The ductile fracture criterion proposed by Cockcroft and Latham is applied to the prediction of the forming limit in bore expansion processes. In our previous studies, the fracture strains derived from the criterion gave the best fit to the experimental results in biaxial stretching. The comparison of the simulation results with the experimental results in this study shows the possibility of forming limit prediction via the present approach in which we take the work hardening and damage in the blanking process of the bore into consideration.
The term shock wave in solids has been defined only mathematically so far. However, the modern information digital technology enable us to measure thickness and rise time on the wavefront that varies very steeply similar to the shock wave. In this study, the thickness or the rise time on the wavefront is measured using a plate impact test at an impact velocity ca. 600 m/s for a glassy polymer such as PMMA or PC, and yet it is difficult to ensure that the thickness or the rise time is infinitesimal. On the other hand, the longitudinal wave velocity of the wavefront measured using PVDF gauges and also using a modified UWSS (Unsteady Wave Sensing System) is more than the wave velocity associated with corresponding stress. Moreover, the stress-strain relationships on the wavefront are along Rayleigh lines. Thus, this wavefront is considered physically as the shock wavefront.
A circular tube becomes flat when it is bent with a conventional bending apparatus. Typically, a mandrel is used to prevent the tube from flattening. However, the mandrel cannot always be used because of its high cost or the tube design. The objective of this study is to present a valid method involving the application of the axial compressive force of the tube to prevent flatness. A prototype machine was fabricated to change the axial compressive force. The material of the tube was STK490. The bending die radius was threefold the tube-outer diameter. It was concluded that the flatness of the bent tube is directly related to the axial compressive force exerted upon the tube. To apply a satisfactory axial force for the reduction in flatness, the pressure die force is also needed for the prevention of buckling. Consequently, the flatness of the bent tube can be successfully controlled by applying both axial compressive and pressure die forces.
The dynamic friction properties of the extruded AZ31 magnesium alloy of 20 μm grain size were investigated by ring compression test at 523, 548 and 573 K and a rate of 1.0 x 10-2 s-1, where all the initial testing conditions were characterized by the climb-controlled dislocation creep. The MoS2 lubricant maintained lower dynamic friction coefficient (m value) than the oil lubricant. The difference in m values between the machined surface and polished surface was unclear. The m values for WC-Co and diamond-like carbon (DLC) tools were similar in the MoS2 lubricant. The m values for the DLC tool were lower than those for the WC-Co tool in the oil lubricant. The extrusion direction affected the friction properties. The aspect ratio of the inner diameter at 90° to the extrusion direction after testing was almost isotropic; on the other hand, the anisotropy occurred at 0° and 45°. The extent of anisotropy at 548 K was the highest, although the lower the temperature, the higher the critical shear stress of the non-basal plane. The condition at 523 K, where fine grain sizes less than 3 μm could be obtained by dynamic recrystallization during deformation, is suitable for making superplastic at the given strain rate.
The workability in cold pilgering of zirconium-based alloy tube was investigated. In this study, a compression test was proposed as an evaluation method of cold workability. The compression test results showed the effect of heat treatment in the fabrication process as well as the texture of tube on the cold workability of zircaloy-4 tube shell. The cold pilgering test result ascertained that the reduction in height of the circumferential-direction specimen of the tube shell at the initiation of crack in the compression test was a good indication of cold workability. The numerical analysis results of cold pilgering proved the validity of the compression test as an evaluation method of cold workability.