The use of carbon-fiber-reinforced plastic (CFRP) parts is limited because of their high price and long manufacturing time, although CFRP are among of the lightest and stiffest materials in the world. We propose a method of stamping solidified CFRP sheets, in which CFRP sheets are sandwiched by dummy metallic sheets during stamping. The dummy metallic sheets act as heating media, as well as protective materials for CFRP sheets. In this investigation, the results of applying the proposed process to cold and warm V-bending are presented for investigating the characteristics of the fracture and bending of CFRP sheets.
A TiCN-based cermet die was applied to the ironing of stainless steel and aluminum alloy drawn cups to improve the ironing limit. In the TiCN-based cermet die, an additional surface coating is not required because of making of hard TiCN having a low friction without WC and Co. For comparison, TiC-coated WC-Co, non-coated WC-Co and tool steel dies were employed for the ironing. For all the stainless steel and aluminum alloy drawn cups, the cermet die exhibited the largest seizure resistance for single ironing due to the low friction. For the continuous ironing of the SUS430 and A3003 cups using the cermet die, the seizure was prevented up to 100 and 50 times, respectively. The height of the ironed stainless steel drawn cups for the WC-Co die was the largest due to reduction in the extent of elastic deformation of the die at the highest Young's modulus. It was found that a cermet die with a low friction is effective in ironing stainless steel and aluminum alloy drawn cups.
The scale formed on the surface of steel during hot rolling causes surface defects. Thus, controlling scale adhesion is important; however, there have been few reports on quantitative investigations of scale adhesion at high temperature. In this study, a method of measuring scale adhesive strength at high temperature is investigated. The effect of the external stress on the oxide scale is also investigated. The adhesive strength is on the order of 1 MPa. The adhesive strength increases proportionally as axial stress applies on the scale. The scale/steel interface analysis shows that there are many voids at the interface after the oxidation, however, the number of voids decreases and a rough interface is formed after axial compression stress is applied on. It is found that the adhesive strength of the scale depends on the contact area and the rough interface between the scale and the steel.
There must be some differences in deformation characteristics between thin- and thick-walled tubes in tube forming. Experimental results using copper tubing of 8 mm outer diameter (D) are discussed. 0.5- and 0.8-mm-thick specimens were used in cross-shaped-tube hydroforming. Long protruding branches were formed under a constant fluid pressure range and a relatively large amount of axial feeding of approximately 4D. It was revealed that the 0.8-mm-thick specimens have a wider range of faultless forming conditions than the 0.5-mm-thick ones. It seems that there is a thickness threshold between 0.8 mm (0.10 D) and 0.5 mm (0.06 D). In addition, the conditions for contact between the tubular specimen and the die strongly affected the forming results. A MoS2 spray and PTFE sheets were used as lubricants to examine the effects of friction on axial feeding force and tube deformation. The highest axial feeding force was recorded under the forming condition of the 0.8-mm-thick tubing and MoS2 spray without PTFE sheets. Forming pressure had a small effect on feeding force. The length of the formed branches depended on forming pressure and the type of lubrication.
A method for accurately predicting ductile fracture is desired to achieve efficient process optimization. The critical value of the Cockcroft & Latham equation as a typical model of uncoupled damage criteria is formulated taking into consideration the stress triaxiality and microstructural anisotropy. The medium-carbon steel S45C is used as a specimen material. Notched bar tensile test, taper anvil compression test, and torsion test are designed and conducted so as to represent different stress triaxiality states. These material tests are carried out while changing the direction of specimen relative to the rolling direction. Furthermore, tensile-compressive combined loading test is performed to confirm the applicability of the formulated critical value. The result shows that the proposed damage critical value has an advantage over the constant critical value in predicting the occurrence of fracture accurately.
Recently, bars for office automation and automobile industry have been required to achieve high fatigue strength. Generally, tensile residual stress is generated at the surface layer of a drawn bar after the drawing process. The tensile residual stress at the surface layer reduces fatigue strength. Therefore, decreasing in tensile residual stress is required. In this study, the effects of approach geometry and bearing length on the residual stress were investigated. Next, the residual stress of the bar drawn using a new die, which had a protrusion in the bearing area, was investigated. Consequently, the effective approach geometry for decreasing tensile residual stress was determined. Tensile residual stress decreased with increasing bearing length. Additionally, it was clarified that the compressive residual stress is generated during drawing with a protrusion die.
To improve the strength of sintered parts, it is important that the density of green compacts should be as high as possible. In the present work, the possibility of achieving a higher density of green compacts by applying compression and shear combined loadings simultaneously than by uniaxial compaction is investigated. The effect of shear loading on powder compact density and the effect of cylindrical specimen size are investigated by compressive and rotational loadings. The internal density distributions are also examined. The improvement in density by applying shear loading was clearly observed. The effects of shear loading on specimen diameter and height were observed, and the gradient of density was decreased by applying shear load.