Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.40 No.461 June 1999)

Simulation of Texture Development in Cold Rolling for Al-Mg Alloy

Yasushi MAEDA, Shigeo HATTORI and Takashi ISHIKAWA

(Received on February 18, 1998)

The present study aims to predict the texture distribution of FCC metals (Al-2.5%Mg alloys) in the rolling process by using full constraints and a rate-sensitive model with high-speed calculation and high accuracy. In this model, two major improvements were ontroduced. First, the phenomenon of cross-slip was introduced into the model using the equation , where is the strain rate after cross-slip and is the cross-slip ratio. Using this model, „0.3 shows good agreement with the experimental results. Second, the deformation gradient history obtained from three-dimensional FEM is incorporated into this model. Using this model, the effects of rolling conditions on the texture distribution were studied. In the case of friction, the textures near the surface change from compression type to shear type with increasing friction coefficient. In the case of geometry h/ld, at medium friction (0.2), the textures near the surface change to shear type with increasing h/ld.
Key words : cold rolling, aluminum alloy sheet, crystallographic texture, numerical simulation, cross-slip model, friction

Influence of Strain Rate on Yield Stress of Polymers

Tetsuya AYA & Toshio NAKAYAMA

(Received on May 25, 1998)

Yield conditions of polymers are important not only from a technological point of view, but for comprehension and prediction of the polymer yield behavior. We performed tension tests on polymers with various strain rates from 10|3 to 1s|1. The polymers studied are high-density polyethylene (HDPE), poly (vinylidene fluoride) (PVdF), polyoxymethylene (POM), polyamideimide (PAI) and polyetheretherketone (PEEK). The relation between the yield stress and strain rates is understood by consideration that the strain rate causes a dissipation of energy, a sort of viscous force, not a conservative force. We tried to describe this behavior based on an activated rate process developed by Eyring and a standard linear solid model composed of a spring and a dashpot. The former is more useful for explaining the behavior.
Key words : high polymer materials, material testing, tensile properties, strain rate, tensile speed, yield behavior, yield stress, yield strain, activated rate process, standard linear solid model

Influence of Hydrostatic Pressure on Yield Stress of Polymers

Tetsuya AYA and Toshio NAKAYAMA

(Received on May 25, 1998)

Uniaxial tension tests under hydrostatic pressure from atmospheric pressure to 392MPa are carried out on five types of polymers (high-density polyethylene (HDPE), poly (vinylidene fluoride) (PVdF), polyoxymethylene (POM), polyamideimide (PAI) and polyether-etherketone (PEEK). Yield stress increases with increasing pressure in all of the polymers tested. In some polymers, a break in the yield stress-pressure curve is found; similar to that reported by other authors. A yield condition which takes the influence of hydrostatic pressure into consideration has been proposed by Hu, Pae and other authors. This condition was used for the results obtained in this paper, and proved useful in describing yield stress under hydrostatic pressure. Also, the stress-strain model proposed by us extends current understanding of the influence of pressure on yield stress.
Key words : high polymer materials, material testing, tensile properties, hydrostatic pressure, yield behavior, yield stress, yield strain, potential theory

Estimation of Welding Defect Criterion by Using Irregular Front Surface Model in Ceramic Injection Molding

Kazunori KATO, Yongho CHUNG and Naoto OTAKE

(Received on July 29, 1998)

In injection molding of ceramic composites, voids or pores that remain in the welded part play a key role in the occurrence of a crack, starting at the weld line. In this study, an experimental method for examining welding property is proposed. A block specimen, on the surface of which grooves of various sizes are machined as the model of rough asperity of flow front, is compressed to an other block specimen with no grooves under various injecting conditions, and the remaining voids are measured. Consequently, it was found that the void size in the welded part is reduced with increasing welding pressure (PW) and material temperature (TM) and that the final void size (dV) is independent of the initial void size and shape when the void size becomes sufficiently small, say dV…50 micro meter. The void vanishing criterion is obtained as a function of PW and TM. Finally, voids at the welded part in actual injection molding are examined under various conditions of PW and TM, and the applicability of the criterion to actual injection molding was confirmed.
Key words : ceramic injection molding, welding property, flow front, groove machined specimen, void vanish- ing criterion