Susumu Shima

Plasticity theory for porous metals

Abstract A plasticity theory for porous metals is proposed. From the stress-strain curves for sintered copper with various apparent densities, the stress-strain curves for pore-free copper is calculated by utilizing the basic equations. The equations are applied to frictionless closed-die compression and the stress in the direction of compression is evaluated in relation to the relative density and is compared with experimental results.

Criteria for ductile fracture and their applications

Abstract Criteria for ductile fracture of pore-free materials and porous materials are described. A method of estimating material constants in these criteria is also given. Applications of the criteria to prediction of the fracture strain in several types of metal working processes for pore-free materials and porous materials are described. These processes involve various strain paths and stress paths; in other words, various paths of hydrostatic stress component — which has a great effect on fracture strain — are involved. The fracture strain in one process differs from that in another. Although many studies of ductile fracture have already been undertaken, these are not applicable to estimate formability in various metal working processes. In this study, an attempt is made to predict the fracture strain in actual processes using the basic criterion. The calculated fracture strains are in adequate agreement with experimentally measured values.

Densification behaviour of ceramic powder

Abstract A three-dimensional compaction device has been developed to carry out compaction of a ceramic powder. The details of the device, which provides compaction with various stress ratios, are described. A densification criterion for the powder is proposed; this is similar to that for the case for metal powders, but the role of the hydrostatic stress component appears to be different. Stress-strain rate relations are then derived using the concept of plastic potential; experimental results show that the normality of the strain rate vector to the surface which corresponds to the criterion almost holds.

Simulation of pyramid type three-roll bending process

Abstract A simulation of the deformation of a workpiece with a U-shaped cross section in a three-roll bending process is performed. Based on the properties of the workpiece, the distribution of curvature and bending moment are calculated in accordance with the displacement and the rotation of the rolls. The relationship between the position of the rolls and the final curvature of the workpiece is obtained. An experiment is performed and the accuracy of the simulation is confirmed.

Consideration of basic equations, and their application, in the forming of metal powders and porous metals

Abstract 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.

Piezoresistive property of CVD diamond films

Abstract Electrical and piezoresistive properties of chemical vapor-deposited boron-doped p-type polycrystalline diamond films were investigated. The p-type polycrystalline diamond films of about 2 μm thickness were grown on a flat insulating polycrystalline diamond substrate using a conventional microwave plasma CVD system. The optimized p-type polycrystalline CVD film exhibited similar quality to homoepitaxial single crystalline diamond film with activation energy of 0.31–0.33 eV and small effects of grain boundaries. Piezoresistors (500 μm long and 50 μm wide) constituted from the optimized p-type polycrystalline diamond films were fabricated on diaphragm structure using photolithography and reactive-ion etching in an oxygen plasma. Relative change of the electrical resistance (ΔR/R0) of the p-type diamond piezoresistor was almost proportional to the applied strain. Gauge factor K for the p-type diamond piezoresistor was derived to be ∼ 1000 at room temperature and > 700 even at 200°C.

Experiment on metal powder compaction by differential speed rolling

Abstract When differential speed rolling is applied to powder roll compaction, the state of stress in the powder or strip between the rolls may be different from that found in conventional powder rolling. Differential speed rolling of electrolytic copper powder is conducted under the condition of carefully controlled powder feed rate. Roll speed ratios are changed in the range 1.00–1.33 by choosing combinations of the number of roll revolutions. The rolling load increases on increasing the ratio of powder feed volume to strip speed and is slightly smaller compared with that of conventional rolling. The decrease in the rolling load is about 25% of what is found in conventional rolling, when the roll speed ratio is 1.33. The relative density of the strip is about 15% larger than that of conventional rolling under the same rolling load. The strip thickness increases with an increase in the rolling load for each roll gap, regardless of the roll speed ratio.

Shape Optimization To Perform Prescribed Air Lubrication Using Genetic Algorithm

A shape optimization of magnetic head for magnetic recording device with rotating drum was studied. An optimization algorithm was developed based on genetic algorithms in conjunction with finite element method which analyzed interface phenomena between a magnetic tape and a magnetic head. The head shape was defined by a second order spline function. Three reference points and first order derivatives at a origin point were coded by the genetic algorithm. As a result, an applicability of genetic algorithms to the given optimization problem was verified. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

3-D simulation of magnetic particles' behaviour during compaction in a magnetic field

The alignment of anisotropic magnetic particles, each of which has its own easy axis for magnetization, has a great influence on the magnetic performance of the permanent magnet produced. It is, therefore, of great importance to study the behaviour of particles, how they move or rotate, during compaction in an applied magnetic field. We develop and employ a non-spherical axi-symmetric particle model. Magnetic polarization is given to each particle when a magnetic field is applied. The particles are subjected to various types of compaction in a magnetic field. They are translated and rotated by not only mechanical forces but also magnetic forces. The rotation and alignment of the easy axis are studied for various aspect ratios of the particle. They are significantly influenced by the application of the magnetic field and type of compaction. The results are discussed comparing with existing experimental data.

Simulation of rubber isostatic pressing and shape optimization of rubber mold

Abstract An elastic–plastic FEM is developed to study the fundamental features of rubber isostatic pressing of powder with a view to performing a net-shape process. Experiments are also performed. It is thus shown that the properties of the rubber, in particular Poissons ratio, give a great influence on the shape of compact and density distribution. The thickness of the rubber mold is also influential; the thicker the mold, the closer is the shape of compact to the cavity shape. An optimization scheme is also developed, so that one is able to determine the cavity shape that gives a desired shape of compact.