In orthopedic biomaterials, the advantages of porous metals are their improved fixation by bone tissue growing into metal pores and their low modulus resulting in stress shielding prevention. Among various fabrication techniques for porous materials, rapid prototyping is a prospective method of creating directly porous devices with controlled size in the form of a 3D structure. In this study, some types of Ti porous device composed of thin cell walls, which were analogous to human cancellous bone, were prepared by selective laser melting (SLM) and their compressive strength was evaluated in terms of cell wall thickness. A tensile test of a sheet formed by SLM was also carried out. The compressive strength of the porous device decreased with increasing bulk porosity. When the cell wall thickness was less than 1.0 mm, the strength of the device became markedly lower than that in the case of a thicker wall of the same bulk porosity. This is attributed to the decrease in the wall strength caused by incomplete melting at the surface．This speculation was confirmed by the observation that the tensile strength of a sheet decreased in proportion to sheet thickness．
A method for the numerical analysis of the lubricated skin pass rolling of tin plates with bright work rolls is established considering a noncircular deformation of the work rolls. A discontinuous elongation behavior with a rolling load unique to lubricated skin pass rolling of tin plates with bright work rolls, known as the jumping phenomenon, has been simulated with constitutive equations of a rolled material having upper and lower yield stresses. The results of the analysis show good agreement with the experimental results obtained under the same rolling conditions with adequate modeling of the constitutive equations of the rolled material. The hysteresis behavior in the relationship between elongation and rolling load has been explained as a bifurcation phenomenon between two different mechanical states: one has a larger elastic strain energy accumulated in the rolled material and work rolls with a smaller elongation in the rolled material, and the other has a smaller elastic strain energy in the rolled material and work rolls with a larger elongation in the rolled material.
Although the closure of defects at the center of billets on rolling such billets is an important subject, a method of quantity evaluation for such closure has not yet been clarified. Therefore, to establish a method for such quantity evaluation, we study such defects using experiments and finite element analysis including asymmetric rolling, especially with respect to the integration of the hydrostatic stress Gm. The results showed that stress was widely distributed, as determined in the experiment and in the FEM analysis of rolling at the edge around an artificial central hole in which defects were simulated. Therefore, it was suggested that, to evaluate the behavior of defect closure, the size of defects and the shape of the grooved roll used should be taken into account.
Products formed using a conventional cold-roll forming machine have cross-sectional profiles constrained to a single width along the longitudinal axis. Products with cross-sectional profiles varying in width in the longitudinal direction, namely, flexible cross sections, cannot be formed using a conventional cold-roll forming machine. In recent years, research and development of a flexible cold-roll forming machine (FCRFM) controlled by a PLC (Progressive Logic Controller) Unit to form products with flexible cross sections has been carried out in Japan and Europe. In this study, the relations between the motions of the roll stand of the FCRFM and the fluctuations in flange width along the longitudinal direction caused in forming the blank steel sheet are investigated to clarify the mechanism of the occurrence of the faults of flange dimension. It is found that when the forming point of the roll is on the same line as the center line of the rotational spinning shaft of the turntable, the flange width of the product formed becomes narrower at the corner and oblique parts of the blank sheet. The optimum method of forming a constant flange width is to keep both the bending point of the roll and the rotational spinning shaft of the turntable in the same concentric circle, in which the center of the concentric circle is that of the circle making the corner part of the blank sheet.
A focused femtosecond laser pulse induces shock waves at the surface of a target. Laser peen forming is a type of sheet metal forming using plastic deformation induced by shock waves. We adopted laser peen forming using a femtosecond laser for thin-sheet-metal bending. However, this method had unstable forming features, which were easily affected by irradiation conditions and the unstable properties of the femtosecond laser. To improve the accuracy of the bending angle, we adopted a simple detection device, which detected the position of the workpiece free end and adjusted the bending angle. The scanning path also affected the bending angle. An improved scanning path was adopted. The deviations in the bending angle were also estimated. These steps stabilized the bending angle and improved the bending accuracy.
The deformation behavior of high strength steel sheets with a tensile strength of 590 MPa under biaxial tension was investigated for a strain range from initial yielding to fracture. The test material was bent and laser welded to fabricate a tubular specimen with an inner diameter of 44.6mm, a wall thickness of 1.2mm, and an axial length of 200mm. Multiaxial tube expansion tests were performed using a servo-controlled tension-internal pressure testing machine. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the forming limit curve (FLC) and forming limit stress curve (FLSC) of the as-received sheet material, in addition to the contours of plastic work and the directions of plastic strain rates from initial yielding to fracture. Results calculated using the Yld2000-2d yield function with exponents of 6 to 8 provided the closest agreement with the measured work contours and directions of plastic strain rates for a reference plastic strain range of 0.002 ＜ε0p＜ 0.20. It was concluded that the multiaxial tube expansion test is effective for measuring the multiaxial deformation behavior of sheet metals for a wide range of plastic strains.
Magnesium alloys have the highest light-weight among practical metals, and high-specific-strength to weight ratios. However, because wrought magnesium alloys have poor formability and corrosion resistance at room temperature, the manufacture of Mg/Al clad sheets with thin aluminum sheets has been investigated: high corrosion resistance and good formability can be achieved for a Mg/Al combination with an optimum manufacturing process. In this study, we fabricated Mg/Al clad sheets by roll bonding at a rolling temperature of 300℃. Consequently, the following results were obtained. Firstly, the magnesium and aluminum sheets could be bonded by roll bonding at 30% reduction. Secondly, by annealing at 300℃ for 1h for each pass of rolling, the formability of magnesium was improved markedly. Finally, the insertion of titanium foil between the magnesium and aluminum sheets prevented the peeling of the surface aluminum sheet in the V bending test.