Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.40 No.456 January 1999)
Influence of Temperature on Formability of Steel-Plastic Laminates
――Formability of Steel Sheets under Cold Working Temperatures W――
Tetsuro OHWUE, Satoshi ITOH, Kouji HASHIMOTO and Takeo NAKAGAWA
(Received on May 12, 1997)
Uniaxial tensile tests, square cup deep drawing tests and spherical punch stretching tests for
FLD (forming limit diagram) are carried out at temperatures ranging from −30℃ to 100℃.
The bonding strength of resin under shear deformation is increased with decreasing ambient temperature.
Under the chill working temperatures from −30℃ to 0℃, if the elongation of core resin is larger than
that of skin steel, the high bonding strength is very effective for increasing deep drawability. On the other hand,
if the reverse relationship of these elongations, which occurs in steel-plastic laminates
with brittle core resin such as nylon 6 (polyamide), deep drawability and
FLD decrease in the above chill working temperaure range,
even though the core resin has high bonding strength.
Key words : uniaxial tensile test, composite materials, temperature dependence, steel-plastic laminates, chill working, deep drawability, FLD, tensile strength, elongation
Effect of Inclusions on Initiation and Propagation of Crack
in Small-Hole Punching of Fe‐42%Ni Alloy
―― Mechanism of Burr Formation in Punching of Metal Sheet T――
Norio YUKI, Nobuhiro KOGA, Hiroshi AZUMA and Masao MURAKAWA
(Received on November 28, 1997)
The mechanism of burr formation in punching has been investigated with laboratory-produced Fe‐42%Ni alloys
which contain different amounts of sulfur, 0.001 and 0.008mass%. Cold-rolled 0.4mm-thick sheets were punched
to form 0.4mm-diameter holes with tools mounted in an instron-type universal testing machine.
The cross sections of the specimens which were removed from the tools at various stages of punching
were investigated by optical microscopy. Cracks are always initiated near the corner of the die and propagate
toward the corner of the punch. In the alloy which contains 0.001mass% S,
cracks do not propagate steadily and the material flow near the corner of the die
after the initiation of the first crack results in a final large burr of the hole.
In the alloy which contains 0.008mass% S, however, cracks rapidly propagate via MnS inclusions
and only a small burr is formed. The geometric position at which the crack is initiated is predicted
well from the distribution of hydrostatic stress analyzed by visioplasticity.
Key words : shearing, punching, small-hole punching, burr, inclusion, fracture, visioplasticity, ferrous metal (Fe‐42%Ni)
Consolidating and Particle Dispersing Process in Compressive
Torsion Forming of SiC/Aluminum Powder Mixture
Eiji MAEDA, Naoyuki KANETAKE and Takao CHOH
(Received on January 13, 1998)
Compressive torsion forming, which simultaneously utilizes hydrostatic pressure and
shear stress to directly consolidate metal powder, was applied for the fabrication
of cylindrical specimens of SiC-particle reinforced aluminum matrix, of 25mm diameter
and 30mm height. To clarify the consolidating and particle dispersing process,
the changes in tensile strengths, microstructures and fracture surfaces were examined
at various torsion cycles. The compacted and consolidated area spread
from the twisted side to the rigid side with increase in the number of torsion cycles
at 773K. The powder specimen near the twisted side was severely stirred and resulted
in a fine microstructure with homogeneously dispersed SiC particles
and broken alumina films, but the area did not spread. The powder
near the twisted side was consolidated at only 573K, and this part had a satisfactory
microstructure and high strength resulting from work hardening.
Key words : powder forming, consolidation process, mixing process, composite material, shear stress
Deformation Process of Metal Powder in Compressive Torsion Forming
Eiji MAEDA, Naoyuki KANETAKE and Takao CHOH
(Received on January 21, 1998)
To clarify the consolidation process of metal powder in compressive torsion forming,
which simultaneously utilizes hydrostatic pressure and shear stress, the distributions
of shear strain in the formed powder were measured and discussed in terms
of the distributions of microstructure, tensile strength and fracture surface.
Cylindrical specimens of 25mm diameter and 30mm height composed of a combination
of different powders were formed using various torsion cycles at 773K
to visualize the deformation during the forming. A relatively small shear strain
was desirable for compacting and consolidating the powder. The small shear strain
was propagated and the partially consolidated area spread gradually from the twisted side
to the rigid side with increase in the number of torsion cycles. The powder near the twisted side
was severely stirred by gigantic shear strain, but this strain did not spread very far.
Key words : powder forming, consolidation process, shear strain, torsion loading, aluminum composite
Superplastic Working of Hybrid Metal Matrix Composites
Reinforced with SiC Particles
Hirokuni YAMAMOTO, Hisashi NISHIMURA and Yu DUAN
(Received on February 2, 1998)
Hybrid metal matrix composites, which made of SiCp/Al metal matrix composites
and monolithic superplastic aluminum alloy and fabricated by hot pressing,
can be very useful in practical usage where more lightening or partial machining
is required. Cylindrically hybridized rods and layer-hybridized blanks
were used to investigate the workability of the hybrid metal matrix composites
under compressive and tensile stress. The results revealed that precise and partially
strong machine parts can be satisfactorily produced by this process.
Key words : forging, bulging, metal matrix composites, workability, superplasticity
Analysis of Tube Bending Processes Using Rigid Plastic FEM
Shinji TANAKA, Shota IWAKURA, Yuji YOSHITOMI,
Takashi NAGANAWA and Toshimi SATOU
(Received on March 18, 1998)
A novel algorithm is proposed to calculate a 3‐D problem of tube bending
using rigid plastic FEM. That is, when a hollow tube is bent with imaginary ring dies,
the radius of which varies during the bending process, the deformation
of the tubular cross section can be calculated. By quasiaxisymmetric formulation,
it is considered that theta-strain rate in polar coordinates depends on theta.
The bending problems of circular and rectangular tubes are analyzed. Then,
hydraulic pressure in a circular tube prevents the progress of tube flattening
during the bending process. On the other hand, in bending a rectangular tube,
the outer surface is depressed and the side wall is expanded. It seems that
these results are in good agreement with experimental results. Using the present method,
tube bending problems can be calculated within less time and less computer capacity
than a conventional method.
Key words : tube bending, rigid plastic finite element method, circular tube, rectangular tube
Initial Strain Formulation for Meshless Elastoplastic Analysis
by Improved Multiple-Reciprocity BEM
Yoshihiro OCHIAI and Tadashi KOBAYASHI
(Received on April 8, 1998)
In general, internal cells are necessary to solve elastoplastic problems
using a conventional boundary element method. In that method, however, the merit of BEM,
which is easy preparation of data, is lost. The conventional multiple-reciprocity
boundary element method cannot solve the elastoplastic problem, because the distribution
of initial strain or initial stress cannot be determined analytically. In this paper
we show that two-dimensional elastoplastic problems can be solved without using internal
cells, using the improved multiple-reciprocity boundary element method.
An initial strain formulation is adopted and the distribution of initial strain
is interpolated using boundary integral equations. A new computer program was developed
and applied to several problems.
Key words : numerical analysis, BEM, elastoplasticity, initial strain method, computational mechanics, meshless method, strain hardening, forging, multiple-reciprocity method
Influence of the Extension of Negative Clearance Condition
in Push-back Blanking Method
Kenji HIROTA and Kazuyoshi KONDO
(Received on April 9, 1998)
Push-back blanking is one of the burr-free shearing methods derived from reciprocating
blanking. In this method, a partially sheared material at the first step is pressed
between two platens and pushed back for separation. However, it is difficult
to apply this method to brittle materials or convex contour shaped ones because
of the small negative clearance condition at the first step. On the other hand,
when a large negative clearance is adopted, shear deformation proceeds
in a manner similar to cutting, which has been observed in the “Opposed dies
shearing process”. This technique will be effective for increasing the applicability
of push-back blanking. The influence of the extension of the negative clearance condition
on push-back blanking was investigated, and it was found that in the case of a large
negative clearance condition, the product part was separated from the stock part not
by “virtual shearing” but by stretching where necking fracture occurred. The difference
in separation mechanism was explained from the viewpoint of relative clearance
at the second step. Applicable range and dimensional accuracy were studied in detail
for semihard aluminum and some advantages of the large negative clearance condition
were clarified.
Key words : shearing, accuracy, burr-free shearing, negative clearance, necking fracture
Admissible Velocity Field and Energy Dissipation Rate for
Differential Speed Roll Compaction of Metal Powder
――Analysis of Differential Speed Roll Compaction of Metal Powder (1st)――
Tetsuya HIROHATA, Saiji MASAKI and Susumu SHIMA
(Received on April 10, 1998)
An admissible velocity field involving arbitrary variables for differential speed roll
compaction of metal powder is determined under some basic assumptions. The main
assumption is that the plane perpendicular to the rolling direction about the powder
position where densification starts advances toward the exit by gradually changing
its inclination. The total energy dissipation rate, which is the sum of the energy
due to compaction of powder and to friction at high and low speed roll / powder
interfaces, is calculated using the mechanics of powder compaction and the admissible
velocity field proposed.
Key words : powder forming, powder rolling, differential speed rolling, mechanics of powder compaction, admissible velocity field, energy dissipation rate
Analysis of Differential Speed Roll Compaction of Metal Powder
by Upper Bound Method
――Analysis of Differential Speed Roll Compaction of Metal Powder (2nd)――
Tetsuya HIROHATA, Saiji MASAKI and Susumu SHIMA
(Received on April 10, 1998)
An analysis of the differential speed roll compaction of metal powder is carried out
using the upper bound method to clarify process characteristics. An electrolytic copper
powder is used for which the material constants in the constitutive equation are well
determined. The total energy dissipation rate obtained for differential speed roll
compaction of metal powder in the 1st report is utilized. A minimization technique
of the total dissipation energy rate involving arbitrary variables is presented under
given rolling conditions. The effects of influential factors such as roll speed ratio,
initial roll gap and powder feed rates on rolling load, strip thickness and relative
density are discussed. By combining with mill spring, we can predict rolling load,
thickness and relative density of the compacted strips. The predicted results agree
well with experimental results obtained under carefully controlled powder feed rate.
The availability of the proposed admissible velocity field is thus confirmed.
Key words : powder forming, powder rolling, differential speed rolling, upper bound method, electrolytic copper powder, rolling load, relative density, strip thickness