Key Engineering Materials
Vols. 334-335
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Vols. 321-323
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Vol. 319
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Vols. 315-316
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Key Engineering Materials Vols. 321-323
Paper Title Page
Abstract: The Ni-based superalloy GTD-111DS has been widely used as the material of the first stage
blade of gas turbine. But there are little data available on the microstructure and mechanical property.
The strength and ductility of GTD-111DS decrease more rapidly due to the acceleration of its
microstructure degradation under high temperature. The results of study showed that the shape of γ'
did not change with increased aging time but the amount and volume fraction of the deposition of
secondary γ' increased and secondary γ' grew among primary γ'. Also there was difference of yield
strength and tensile strength in room temperature according to heat treatment and collecting region.
632
Abstract: Used pipes in various mechanisms and structures are produced from raw material by
extruding and drawing. The properties such as yield strength, tensile strength, and elongation of a
pipe produced by these methods are different from the properties of their raw material. But
designers use the properties of the raw material because the actual properties of the pipes are
difficult to obtain from testing. Also, the pipe is used after it has been bent in a complex manner and
cut to fit it to mechanisms and structures. The bending process, especially, induces deformation of
the pipe’s section and residual stress, which are involved in the plastic deformation of the bended
pipes. This residual stress affects the pipe’s properties, including its fatigue life. Therefore, it is very
important to understand the residual stress of a material. But, the distribution of residual stress of a
U-shaped pipe, which is examined in this study, is very complicated and cannot be measured
exactly.
636
Abstract: Railway wheels and axles have been one of the most critical components in a railway
vehicle. The service conditions of railway vehicles have became more severe in recent years due to the
increase of the speed. It is very important to evaluate the reliability of wheels with regard to safety,
because wheel failure can cause derailment with loss of life and property. One of the major reasons of
the railway wheel damage is the contact zone failure by wheel/rail contact. One of the methods for
preventing the failure and increasing the fatigue life is to grind periodically the contact surface before
reaching the failure. The increase or decrease of the contact fatigue life by the surface removal of the
contact surface were shown by many researchers. However, the reason why fatigue life increases or
decrease has not been investigated obviously. In this study, the effect of the surface removal depth on
the contact fatigue life for a railway wheel is evaluated through the employment of rolling contact
fatigue tests and the finite element analysis. It is found that the contact fatigue life increased with the
removal depth. But in the case that the removal depth is greater than the optimal depth, the contact
fatigue life decreased. It seems to be obvious that the residual strain is the main factor determining the
fatigue life according to the removal depth
640
Abstract: Nondestructive evaluation of tightly closed small cracks in carbon steel has been
investigated under no load conditions. The investigation has been carried out by using a new
ultrasonic method of testing, which has the capability of dealing with smaller tight cracks
sensitively. Tight closure of small fatigue cracks in carbon steel plates is realized when the
measured responses are compared with the calculated responses of the identical open cracks. Highly
sensitive characteristic of the present method is verified through the comparison of the results with
those obtained by the standard ultrasonic method of testing.
644
Abstract: The majority of catastrophic wheel failures are caused by surface opening fatigue cracks
either in the wheel tread or wheel flange areas. The inclined cracks at railway wheel tread are initiated
and the cracks are caused by wheel damage-spalling after 60,000 km running. Because the failured
railway wheel is reprofiled before regular wheel reprofiling, the maintenance cost for the railway
wheel is increased. Therefore, it is necessary to analyze the mechanism for introduction of crack. In
the present paper, the combined effect on railway wheels of a periodically varying contact pressure
and an intermittent thermal braking loading is investigated. To analyze damage cause for railway
wheels, the measurements for replica of wheel surface and effect of braking application in field test
are carried out. The result shows that the surface cracks in railway wheel tread are due to combination
of thermal loading and ratcheting.
649
Abstract: In this study, dynamic penetration phenomena of high-velocity impact of magnesium alloy
were investigated. The surface hardness of magnesium alloy (AZ31B-O) and the heat-treated
magnesium alloy (AZ31B-200°C, AZ31B-300°C, and AZ31B-430°C) were examined using Micro
Vickers, and the influence of the heat treatment temperature was observed. We analyzed the metal
organization using a microscope. We also used a ballistic range (two-stage light gas gun), and the test
specimens were set at 0°obliquity at room temperature. A high-speed camera allowed us to capture
and analyzed the dynamic penetration phenomena of the test specimen.
654
Abstract: In this paper the life extension of automobile drive plates will be investigated. The material
of specimen is a high carbon steel treated by shot peening, which is most important in the
manufacturing process of drive plates. The optimum shot peening condition was investigated by
changing the feeding speed and exposure time. The fatigue crack was observed at the fracturing
surface of specimens by using scanning electron microscopy (SEM). The distribution of compressive
residual stress induced by shot peening process was investigated by using X-ray diffraction. The
number of cycles to failure increases at the beginning of exposure. The life cycle decreases after
passing some interval of exposure, which will be called as optimum peening zone. Experimental
results show that the residual stress distribution and the number of cycles to failure of a drive plate are
greatly affected by peening process.
658
Abstract: In this paper the fatigue life of spur gear was investigated by changing the shot peening
condition. From bending fatigue test depending on various shot peening intensity, fatigue
characteristics were investigated. The causes of reduction in fatigue life were analyzed by observing
the surface of gear with Scanning Electron Microscope(SEM), and impact of residual stress to fatigue
characteristics was identified by measuring compressive residual stress depending peening intensity
by depth. The results show that the optimum shot ball velocity is 65 m/s and optimum peening time is
8 minutes. From SEM image, the micro-crack was observed at the surface in case of over peening.
This seems to be the factor which reduces fatigue life by decreasing compressive residual stress of
surface.
662
Abstract: During the past couple of decades, several limit load solutions have been proposed to
resolve steam generator (SG) tube integrity issue. However, for estimation of specific load carrying
capacity under different conditions, these solutions have to be modified by using lots of experimental
data. The objective of this paper is to introduce a new burst pressure estimation scheme based on
fracture mechanics analyses for SG tubes with a crack. In this context, closed-form equations were
derived to get relevant parameters from three dimensional elastic-plastic finite element analyses and,
then, a series of structural integrity analyses were carried out using the predicted J-integrals from the
equations. Finally, in comparison with the experimental data as well as corresponding estimation
results from conventional limit load solutions, it was proven that the proposed estimation scheme can
be used as an efficient tool for integrity evaluation of cracked SG tubes.
666
Abstract: The wall thinning due to erosion, corrosion and flow accelerated corrosion is one of critical
issues in nuclear industry. To secure against loss of integrity of pipes with a flaw, ASME Code
Section III and Code Case N-597 etc have been used in design and operating stages, respectively.
However, despite of their inherent conservatisms, it may reach unanticipated accidents due to
degradation at local region. In this paper, a new evaluation scheme is suggested to estimate
load-carrying capacities of wall thinned pipes. At first, computational fluid dynamics analyses
employing steady-state and incompressible flow are carried out to determine pressure distributions in
accordance with conveying fluid. Then, the discriminate pressures are applied as input condition of
structural finite element analyses to calculate local stresses at the deepest point. A series of combined
analyses were performed for different fluid flow velocities as well as d/t, Rm/t and l/t ratios. The
efficiency of proposed scheme was proven from comparison with conventional analyses results and it
is recommended to consider the fluid structure interaction effect for exact integrity evaluation.
670