Abstract: In this paper, via experimental results of ultrasonic wave velocity changes and FEPM
simulations of slip system under the pure shear plastic deformation of a pure Aluminum single
crystal, the authors verify that the ultrasonic longitudinal wave velocity depends upon the
development of point defects caused by intersected cross slip among dislocations and also examine
the correlation of the point defect dependence of the longitudinal wave velocity with the elastic
stiffness degradation due to plastic deformation damage which is closely related to the deformation
Abstract: Representative length scale of ULSI (Ultra Large Scale Integration) cells is going to be at
a nano-meter order, and the atomic level defects, such as uneven oxide films or dislocation
accumulation are becoming more and more important. Among these defects, dislocation
accumulation is known to be caused by thermo-plastic deformation in silicon during the processes
of device fabrication. In this study, we analyse such thermal stress, plastic slip deformation and
accumulation of dislocations in STI (Shallow Trench Isolation) type ULSI devices when the
temperature drops from the initial at 1000 °C to room temperature. For the analysis, we use a
crystal plasticity analysis code CLP, assuming that lattice friction stress for the movement of
dislocations is proportional to the hardness of silicon, which is known to have strong dependency
on temperature. The results show that dislocations are generated between the temperature range
from 880 to 800 °C, and its maximum density is highly dependent on the lattice friction stress in
the temperature range above 800 °C. For example, the difference of 16 MPa in the lattice friction
stress at 1000 °C caused increase in dislocation density more than ten times. It is concluded that
control of lattice friction stress at high temperatures is one of the most promising way for the
suppression of dislocation accumulation.
Abstract: A multiscale model on dislocation patterning of cell structure and subgrain for
polycrystal is newly developed on the basis of reaction-diffusion theory. A FD simulation for
dislocation patterning and a FE one for crystal deformation are simultaneously carried out for a
FCC polycrystal at large strain. Reflecting stress value on stress-effect coefficients, it is numerically
predicted that the evolution of dislocation pattern in a polycrystal is different in response to the
stress condition of each grain.
Abstract: In this study, effects of typical texture components observed in rolled aluminum alloy
sheets (i.e. Copper, Brass, S, Cube and Goss texture components) on plastic flow localization are
studied. The material response is described by a generalized Taylor-type polycrystal model, in which
each grain is characterized in terms of an elastic-viscoplastic continuum slip constitutive relation.
First, forming limits of thin sheet set by sheet necking are predicted using a Marciniak–Kuczynski
(M–K-) type approach. It is shown that only the Cube texture component yields forming limits higher
than that for a random texture in the biaxial stretch range. Next, three-dimensional shear band
analyses are performed, using a three-dimensional version of M–K-type model, but the overall
deformation mode is restricted to a plane strain state. From this simple model analysis, two important
quantities regarding shear band formation are obtained: i.e. the critical strain at the onset of shear
banding and the corresponding orientation of shear band. It is concluded that the Cube texture
component is said to be a shear band free texture, while some texture components exhibit
significantly low resistance to shear band formation. Finally, shear band developments in plane strain
pure bending of sheet specimens with the typical textures are studied.
Abstract: Physical interpretations of the incompatibility tensor are extensively discussed and applied
to model several practically-important dislocation substructures in metallic materials. This paper
firstly performs a tangible decomposition of the incompatibility tensor into the two types of defects by
introducing Nye’s contortion tensor, and also clarifies the interrelationship with expressions given
based on differential geometry. The effects on the evolutions of intra-granular substructures like cells
and geometrically-necessary type bands are examined based on finite element simulations on
multi-grain models under tension and simple shear with several representative orientations.
Abstract: The structural behavior of an old six-span reinforced concrete arch bridge, which has
been in service for about 40 years, is investigated. Field monitoring (inclusive of test of material
property, static and dynamic test of the bridge) was conducted, static and dynamic responses of
the bridge are obtained. Based on the primitive bridge, a scaled one-span bridge model was
fabricated by organic-glasses. Both the static and dynamic tests were executed on the bridge
model in the laboratory. Since the arch rib is the crucial member for the arch bridge, 7 notches
were cut on both arch ribs of the bridge model to simulate different damages of the arch rib.
Mechanical responses of the bridge with different damages on the arch ribs were achieved. FEM
analyses were preformed on the bridge as well. Numerical results show good agreement with the
Abstract: Damage development due to creep under uniaxial tension at elevated temperatures is
assessed using destructive and non-destructive methods in steels, commonly used in power plants or
chemical industry, and in aluminium alloy used in aircrafts for responsible elements. The results
obtained using two different destructive methods for assessments of damage development are
critically discussed. In the first method the specimens of steel after different amounts of creep
prestraining were stretched up to failure and variations of the selected tension parameters were taken
into account for damage identification. In the second one, a damage degree was evaluated by
studying variations of an initial yield locus position in the stress space and by determination of the
yield loci dimensions. The ultrasonic investigations were selected as the non-destructive method for
damage development evaluation.
Abstract: A methodology for evaluating and predicting component lives in creep-fatigue interaction
region was investigated for Waspaloy. A unified viscoplasticity constitutive equation including
multi-back stresses was used to describe cyclic material behaviors. Also, a continuum damage model
coupling with the creep-fatigue damage rules was established based on the analysis of creep and low
cycle fatigue behavior. Multi-axial fatigue and creep equivalent stress concepts were employed to
predict three dimensional component lives. Notched cyclic tests under various stress conditions in the
creep-fatigue interaction region were carried out to validate the life prediction methodology with
FEM simulation based on the continuum damage model. The comparison of experimental data and
prediction results indicates that the continuum damage model is a powerful approach for the
prediction of component lives.
Abstract: An ultralight magnesium alloy AM50A has been investigated for its potential to be used
in aerospace and automotive industry. The dynamic stress strain relation of aluminum 6061 T6 and
the magnesium alloy AM50A have been obtained by using the Hopkinson bar apparatus. The strain
rates range between 600 s-1 and 1300 s-1. The Al 6061 T6 results tally well with those in literature.
The magnesium alloy AM50A displays about 50% higher tensile stress at the strain rate of about
1300 s-1 than at static.