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We developed an active forceps using shape memory alloy pipes for laparoscopic surgery. The temperature of Ti-Ni shape memory alloy is controlled by electric heating, so that the response is improved. This paper describes a design and characteristics of the active forceps.

An experimental set-up for cold butt welding is developed. Before conventional upsetting of two specimens to be bonded, surfaces of the specimens are shaved off by an edge to bring out the virgin metal which is essential to cold pressure welding. Since the bulk deformation to form the virgin surfaces is smaller compared with the conventional process without using the edge, complete bonding is accomplished with a small strain in upsetting of the specimens. This result leads the following advantages of the present process. (1) Waste of the material which is used as a flash is reduced. (2) The upsetting load, i.e., the bonding load is lower.

Axisymmetric deformation of anisotropic porous materials caused by geometry of pores or by distribution of pores is analyzed. Two models of the materials are proposed: one consists of spherical cells each of which has a concentric ellipsoidal pore; and the other consists of ellipsoidal cells each of which has a concentric spherical pore. The velocity field in the matrix is assumed and the upper bound approach is attempted. Yield criteria are expressed as ellipses on the σm σ3 plane which are longer in longitudinal direction with increasing anisotropy and smaller with increasing volume fraction of the pore. Furthermore, the axes rotate about the origin at an angle α from the σm-axis, while the axis for isotropic porous materials is on the σm-axis.

Axisymmetric deformation of an anisotropic porous material is analyzed. A model of the material is proposed ; the material consists of ellipsoidal cells each of which has an ellipsoidal pore in the center of the matrix. The velocity field in the matrix is assumed and the upper bound approach is attempted. The yield criterion of the porous materials with various volume fractions of pore Vf is represented as ellipses on the σm-σ3 (the hydrostatic and principal stresses) plane. Their axes become smaller with increasing Vf and rotate clockwisely or counter clockwisely at an angle δ from the σm axis. The angle δ increases with increasing anisotropy. The direction of the rotation is dependent upon the aspect ratio of pore.

Yield criteria and stress—incremental strain relations for compressible materials, such as metal powders and sintered porous metals, are described and experimental verification of these basic equations is then given. The application of slip-line field theory, upper-bound theory, the finite-element method and the visio-plasticity method based on the above equations is described and some results are presented. When powders are compacted, or sintered metals are plastically deformed, they undergo a change in density and also density variations occur within the product. Since the change in density and the density variation have a great effect upon the properties of the product, it is important to be able to evaluate them. Loads to cause densification or plastic deformation, and pressures exerted on the die-walls, are also important in tool design. Using the above theories or methods, it is possible to predict the working load, the pressures exerted on the die walls and the density variation within the product. Whereas these important factors have not been treated theoretically in the past, a rational basis can now be introduced into the forming of metal powders and sintered metals.

Indentation of sintered metals with square-based pyramids is performed and the relationship between the hardness and the compressive flow stress of the sintered metals in obtained. When the semi-angle α of the pyramid is 68°, which corresponds to the semi-angle of a Vickers hardness indenter, the ratio of the hardness to the flow stress is dependent upon the relative density. However, when α is 45°, the ratio is a constant value of 2.7 without influence of the relative density. Therefore, the flow stress of the sintered metals can be estimated from the hardness measured by using the indenter with the semi-angle of 45°.

Deformation behavior of laminated sheet metals is estimated by the upper bound method based on Hill’s plasticity theory for anisotropic materials. The r-value and the stress-strain curve are theoretically derived for the laminated sheet metals whose component metals are combined at arbitrary angles to the rolling direction. Tension tests of the laminated sheet metals which are made by bonding in combinations of mild steel, brass, and aluminum sheet metals are carried out. The experimental results are compared with the theoretical ones. They are in good agreement.

The relationship between the Brinell hardness HB and the flow stress σe of sintered porous metals is examined considering the ratio d/D ; the diameter of indentation to that of the indenter. When d/D=0.4, at which the Brinell hardness test is usually done, the ratio c=HB/σe varies from 2 to 3 with a relative density ρ of 0.70 to 0.97. However, when d/D=0.7 to 0.9, the ratio c is almost constant at 2.5 to 2.8 without influence of the relative density. Therefore, the flow stress of porous metals can be estimated from the Brinell hardness test at a ratio d/D of 0.7 to 0.9.

Triaxial deformation of a porous material is analyzed. A material model is proposed where the material consists of spherical cells each of which has a spherical pore in the center of the matrix. The velocity field in the matrix is assumed and the upper bound approach is attempted. The yield surfaces of the porous materials with various volume fractions of pores vf are obtained as ellipsoids whose axes become smaller with increasing vf.They coincide with the yield surfaces which have been proposed by the authors earlier.

An analysis of indentation of a porous material with square-based pyramids is made. The analysis is based on an approximate energy method using a velocity field which is constructed with the slip line field for the wedge indentation of the porous material. The hardness, that is, the indentation pressure is expressed as a function of the yield stress and the relative density of the porous material. Experiments on the indentation with square-based pyramids are also carried out using workhardened and annealed specimens of sintered copper powder. The experimental results are compared with the theoretical results.