Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.39 No.452 September 1998)
Influence of Temperature on FLD of Steel-Plastic Laminates
―Formability of Steel Sheets under Chill Working Conditions V ――
Tetsuro OHWUE, Satoshi ITOH, Kouji HASHIMOTO and Takeo NAKAGAWA
(Received on May 12, 1997)
Hemispherical punch stretching tests for forming limit diagram (FLD) and uniaxial tensile tests are carried out at temperatures from −30 Cels. to 100 Cels., in order to investigate the relationship between FLD and mechanical
properties of steel-plastic laminates. As a result, it was found that major strain under plane strain deformation increases with an increase in the elongation of skin steel, if the elongation of core resin is greater than that of skin steel. On the other hand, if the relation between these elongations is reversed, which occurs in steel-plastic laminates with brittle core resin like nylon 6 (polyamide), FLD decreases when using a chill working condition.
Key words : uniaxial tensile test, composite materials, temperature dependence, steel-plastic laminates, chill working, FLD, tensile strength, elongation.
Effect of Ambient Temperature on Guided Bending of Honeycomb Panel
Hidetoshi KOBAYASHI and Masashi DAIMARUYA
(Received on July 14, 1997)
Using an ordinary aluminum honeycomb sandwich panel manufactured with epoxy resin, a series of guided bending tests were carried out at a number of different temperatures from room temperature to 70 Cels.. The three-point-bending tests were also performed for comparison. The effect of ambient temperature during bending upon the deflection ratio and the strength of bent panels was examined to find the optimum temperature for bending of honeycomb panels. The principal results obtained are as follows. (1) When cooling was performed under loading, the deflection ratio, delta1/delta0, (delta1:the deflection at the center of the panel after unloading, delta0:the gap at the center of the die used for guided bending) obtained at temperatures greater than 50 Cels. was much higher than that obtained at room temperature. (2) The panels bent at 50 Cels. showed the same strength as those bent at room temperature, therefore, the bending at 50 Cels. and cooling under loading was the best condition in our experiments, because of a relatively higher deflection ratio. (3) Shear buckling of core occurred near the two side supports in guided bending at room temperature, although local plastic buckling around the center of the panel as observed in three-point-bending can be avoided.
Key words : guided bending, shear buckling, aluminum honeycomb panel, ambient temperature
Effects of Lubricant and Shape of Die Corner on Superplastic
Blowformability of 7475 Aluminum Alloy Sheet
Masatoshi ARAMAKI, Takanori KIMURA, Masayoshi MORIWAKI,
Tatsuo YOKOTE and Ryuuta ONODERA
(Received on August 4, 1997)
Blowforming by using gas pressure is one of the most suitable methods for the sheet forming of superplastic alloy which exhibit low flow stress. This study is carried out on the assumption that blowforming is applied in the formation of a heat exchanger. The blowformability of 7475 aluminum alloy during superplastic deformation is investigated by changing both the lubricants and the shape of the die corners. The maximum bulge height varied considerably with the lubricant at 520 Cels. under 5.0MPa, and its value increased in the following ascending order:MoS2, graphite and BN. The shapes of specimens and strain distributions as functions of time can be shown by using marking-off. In the strain distributions, the value of the strain at the part which contacted with the wall of the die was greater than that at the part of the bulge top. Furthermore, the rate of deformation, particularly during the early period of sheet forming, was raised by changing the die of C1 to R1.7. However, in the case of MoS2, the fracture strain was observed to be smaller than that expected under tensile test.
Key words : superplasticity, blowforming, die, lubricant, marking-off, strain distribution, 7475 aluminum alloy, formability test
Development of Die Necking Technique for Thinner Wall of DI Can
―― Study on Decreasing the Weight of DI Beverage Cans T ――
Hideki UTSUNOMIYA and Hisashi NISHIMURA
(Received on September 5, 1997)
The die necking technique which enables the reduction of the wall thickness of steel DI (drawn and ironed) cans was experimentally investigated. Although the wall thicknesses of the conventional DI cans have been reduced dramatically since the first developed DI cans, thinning is still very important both for reduction of cost and metal use and is therefore environmentally friendly. The influence of the clearance on wrinkles and buckling at body was investigated and a suitable value was determined. The effect of a necking die inlet radius on the occurrence of wrinkles was studied and it was demonstrated that with a smaller radius the wrinkle was prevented and it enabled the reduction of the thickness of the wall to be necked. Since the reduction of the thickness of neck, the necking load was reduced, reduction of the thickness of body was possible too. It was found that an inlet radius of 3.00mm was suitable. About 8% reduction of the side wall thickness was possible by using the newly developed necking technique.
Key words : tube forming, nosing, die design, DI can, lightweighting
Proposal and Use of a Micromodel
for the Simulation of Ductile Fracture Behavior
Kazutake KOMORI
(Received on October 13, 1997)
The objective of the present work is to clarify the mechanism of ductile fracture in bulk metal forming by means of analysis and experiment. We have developed a computer program based on a conventional FEM program by means of which crack propagation after ductile fracture can be analyzed. In the present work, we have proposed a micromodel which evaluates ductile fracture first. Next, analysis is performed after the model is incorporated into the computer program. The following results are obtained. First, we have proposed a method of evaluating ductile fracture using a micromodel. The relationship between void volume fraction and fracture strain predicted by the model agrees well with that obtained from Thomason's model. Second, the analysis and experiment of multipass drawing are performed for various reductions in area and die angles. The inner diameter of die at the pass where the material is fractured and the material density after drawing at the pass prior to the pass at which the material is fractured are obtained. The results obtained from the analysis agree with the experimental results. Third, it was observed that the inner defect appears periodically in the drawing direction from the analysis of drawing at the pass where the material is fractured. Hence, the validity of the proposed model is clarified.
Key words : drawing, upper bound method, rigid plastic FEM, forming limit, ductile fracture, chevron crack
Yield Improvement by Partial Welding of Rolled Flat Bars
―Reducing Crop Loss by Welding of Different Width Bars with Plasticine Test―
Hiroyuki HINO and Hiroyuki KOTANI
(Received on November 17, 1997)
In hot strip rolling, the head and tail ends of a single transfer bar undergo overlap, flare, tongue or fishtail deformations, which result in numerous problems in terms of quality, yield and threading stability. Endless hot strip rolling, namely, joining the head and tail ends of each bar, is performed to obtain a steady-state condition which prevents the occurrence of these problems. To investigate the effect of partial welding on the crop loss of the rolled flat bar, a miniaturized model test using plasticine slabs has been carried out. As a result of the investigation, the followings can be concluded:1) the width-edges weld is greatly effective for reducing the
crop loss or improving yield(previous report), 2) the smaller the width difference, the better the yield, 3) the rolling schedule with increasing width is more effective than one with decreasing width.
Key words : hot strip rolling, transfer bar, partial welding, different width, crop loss, yield, plasticine, model
mill
Effect of Hydrostatic Stress on Fracture Ductility of an
Aluminum-Alloy and Iron-Base Sintered Powders in Torsion
Misao ITOH, Satoshi SUZUKI,
Yoshihiro ITOH, Masanobu OHMORI and Tamotsu MAJIMA
(Received on January 13, 1998)
Cylindrical specimens from an aluminum-alloy and iron-base sintered materials with second-phase particles were examined for fracture ductility which occurs in torsion tests with axial compression and under hydrostatic pressure. The results obtained are summarized as follows. (1) The fracture ductility increases with decreasing hydrostatic stress. The rate of increase of ductility is especially large in the ductile sintered materials without particles and with soft particles. (2) At a given hydrostatic stress, the ductility of the material with the hard particles and aluminum-alloy is larger in the case of torsion with axial compression than in the case of torsion under hydrostatic pressure. (3) The growth rate of cracks on the cylindrical surfaces of the less ductile specimens, aluminum-alloy and the material including the hard particles, markedly decreases with decreasing hydrostatic stress in torsion with an axial load. (4) The results (2) and (3) reflect the following fact. The compressive axial stress applied to the torsion specimen retards not only the occurrence and growth of internal cracks and voids but also the surface cracking, while the hydrostatic pressure retards only the internal defects.
Key words : fracture ductility, hydrostatic stress, crack growth, torsion test, aluminum-alloy, iron-base sintered materials