Ultrasonic vibration is applied to the extrusion process. When ultrasonic vibration is applied on the die in the backward extrusion of pure aluminum at room temperature, the load is reduced to 40% of that without ultrasonic vibration. The plastic deformation zone appears concentrated just under the die compared with that in the extrusion without ultrasonic vibration. On the other hand, the reduction in the load was small in the case in which ultrasonic vibration is applied to the stem in the forward extrusion. It is estimated that in the backward extrusion, the material just under the die is easily deformed and flowed out to the die exit because the free exit space is just on the side of the vibrating die.
The authors have performed static compression tests on lead zirconate titanate (PZT) ceramics, and the variation in material properties and the development of internal damage in these materials during compression tests have been clarified. In the present study, the development of internal damage was used to formulate an evolution equation for a damage variable on the basis of continuum damage mechanics. On the other hand, the variation in material properties was related to the damage variable, and thus was used to formulate a material function of the damage variable. In the present paper, the elastic coefficient was newly evaluated from stress-strain relations in order to describe stress-strain curves, and the dependence of the elastic coefficient on the evaluation method used was discussed. Using the material functions and damage evolution equation, stress-strain relations for static compression tests were simulated, and the validity of the formulations was verified by comparing their results with experimental results.
The theory and application of plastic anisotropy have extensively developed in the main field of sheet metal forming. Round tubes and bars are generally used for tube forming and forging; they exhibit plastic anisotropy similarly to sheets. In this paper, assuming that these materials show anisotropy with three cylindrical orthogonal symmetry axes, r, θ and z, we used the simple anisotropic criterion proposed by Hill in 1948 as follows: 2C2 = F (σθ- σz)2 + G (σz- σr)2 + H (σr- σθ)2. In the tube materials, the ratios εθ/εr = F/G and εθ/εz = H/G are not necessarily equal to unity. For a tube of A6063 in JIS as an example, F/G = 0.55 and H/G = 0.69 were determined by a tube tensile test and a tube wall compression test, respectively. In the bar materials, we theoretically showed that anisotropy affects the mean stress in the tensile/compression test. Also, by a semi-cylinder compression test, for a round bar of A2017-F in JIS as an example, F/G = 0.37 was determined. Moreover, in the ring compression test for determining frictional coefficient, we found using FE analysis that anisotropy and friction affect the reduction in internal diameter.
A hot spline forming process of an ultra high strength steel gear drum was developed to manufacture high tensile strength steel spur gears. Since the cross-sectional area of a side wall of a cup formed by cold deep drawing and ironing was uniform, the side wall formed put between the upper and lower electrodes was uniformly heated by the electrification in the axial direction. The uniformity of the temperature was improved by inserting a copper foil between the electrode and the side wall, and by decreasing the area of contact. Although the high strength steel cup was fractured by cold spline forming, a spur gear was successfully manufactured by the hot spline forming. The load for a hot spline forming of the high strength steel gear drum is similar to that for the cold forming of a mild steel gear drum, and the accuracy of teeth was improved. In addition, the formed gear drum was hardened by die quenching.
A method of determining stress measurement error in biaxial tensile tests using a cruciform specimen is proposed. The cruciform specimen is assumed to be fabricated from a flat sheet by laser machining and to have uniform thickness and slits in its arms. Using finite element analysis with the von Mises yield function, the optimum dimensions of the cruciform specimen and the strain measurement point that minimize the stress measurement error are determined. The following conclusions are drawn. (i) When the side length of the test area of the cruciform specimen is B, the thickness of the test material should be less than 0.08 B. (ii) The dimensions of the cruciform specimen should be N≥7,L≥B,ωS≤0.01B and 0.0034≤R/B≤0.1, where N is the number of slits, L is the length of slits in the arms, ωS is the width of slits and R is the corner radius at the junction of the arm and test area. (iii) Strain components in the test area should be measured on the centerline of the specimen parallel to the maximum principal stress direction at a position approximately 0.35B from the center of the specimen. The stress measurement error is estimated to be less than 2% when the optimum conditions above are adopted.
We have developed model materials using which the forming simulation of a metallic material could be carried out at a low stress at room temperature. In a previous paper, we explained that the flow curves of the model materials could be controlled to be the same as those of the work softening type, steady state deformation type and work hardening type by adjusting the powder content of the model materials. Then, a procedure for the application of the model materials to the physical forming simulation of a metallic material was developed in this work. As application examples, the forming simulations of plane strain upsetting were carried out using the aluminum A1050, representing the flow curve of the work hardening type, the magnesium alloy AZ31B, representing the flow curve of the work softening type and these model materials. As the results, we confirmed that the forming simulation using the model materials provides almost the same outer profile, material flow and strain condition in a forming product as those observed by the forming simulation using an actual metallic material with sufficient accuracy for engineering purposes.