Abstract: The turbine wheels of a turbocharger are operated at high revolution speed in high
temperature inlet gas. Alloy 713LC blades of the turbine wheel broke in an hour the during a model
test. Two failures and several cracks were found in the turbine blades. Failures in blades are suspected
to occur as a result of thermal mechanical stresses or fatigue load and other cause such as
creep-rupture and resonant vibration. The present study investigates the possible causes of the failure
of these blades. FEM (Finite Element Method) was used to calculate the thermal centrifugal stresses
and natural frequency to find the cause of failures. LCF (Low Cycle Fatigue) life of blades was
roughly estimated by using the stress and strain level calculated by FEM. The investigation indicates
that the failures were associated with resonant forces and HCF (High Cycle Fatigue).
Abstract: In this paper the bridging action of steel fibres on the model I crack propagation has been
studied experimentally for steel fibre reinforced concrete (FRC). From the experimental results three
main conclusions are obtained. First, the bridging action increases with the number of the steel fibres
across the crack surface and the stress intensity factor near the crack tip decreases thereby. Second,
bridging action increases with the strength of the matrix because the matrix with higher strength can
provide stronger interfacial bond with steel fibres. Third, the interfacial bonding gets damaged when
the steel fibres under cyclic loads and the bridging action degrades with the cycle number.
Abstract: Recently, high-performance hybrid composites have been used for various applications
which require the high strength, high stiffness and low weight. There are growing needs in an
automotive, an aircraft, and military applications for composite materials since they have good
structural characteristics. They also have good penetration resistance and structural integrity after
impact. In order to clarify the mechanism of high-speed destruction for composite materials, this
study examined the penetration resistance and the fracture behavior of CFRP (Carbon Fiber
Reinforced Plastic) Laminates by using ballistic range (one-stage light gas gun). Test materials for
investigation are carbon/epoxy laminated composite materials with fiber direction; [0°]8, [0°/45°]4s,
[ 0°/90°]4s, [ 0°/45°/90°]3s and [ 0°/45°/-45°90°]2s. The high speed camera allows us to capture and
analyze the dynamic penetration phenomena of the test materials.
Abstract: The present study was investigated on the melting phenomena and the accelerative factors
of phase change material (PCM) by acoustic streaming induced ultrasonic vibrations. To investigate
the melting phenomena and accelerative factors, the experimental study was measured the liquid
temperature and melting time of PCM and was observed the velocity vectors and thermal fluid flow
induced acoustic streaming to investigate the heat transfer using particle image velocimetry (PIV) and
infrared thermo vision camera, respectively. Also, the numerical study based on a coupled finite
element-boundary element method (Coupled FE-BEM) was performed to investigate the analysis of
pressure field in the PCM. The results of experimental works revealed that acoustic streaming
observed by PIV and infrared thermo vision camera is one of the prime effects accelerating phase
change heat transfer. And, the final temperature of PCM is lower and melting speed is 2.6 times faster
than that without ultrasonic vibrations when ultrasonic vibrations are applied. The results of
numerical work presented that acoustic pressure is higher near the ultrasonic transducer than other
points where no ultrasonic transducer was installed and develops more intensive flow such as acoustic
streaming, destroying the flow instability. Moreover, the profile of acoustic pressure variation is
consistent with that of enhancement of heat transfer.
Abstract: In order to strengthen or repair the welded structural members or fatigue damaged areas,
various surface treatment methods such as grinding, shot peening and/or hammer peening are
commonly employed among other methods available. While the weld toe grinding method is known
to give 3~4 times of fatigue strength improvement, this improvement may significantly vary
according to weld bead shapes and loading modes. In this context, a series of fatigue tests is carried
out for three types of test specimens that are typically found in ship structures. Weld burr grinding is
carried out using an electric grinder in order to remove surface defects and improve weld bead
profiles. The test results are compared with the same type of test specimen without applying the
fatigue improvement technique in order to obtain a quantitative measure of the fatigue strength
improvement. Moreover, structural stress method is employed to evaluate the effectiveness of the
method in evaluating the fatigue strength improvement of welded structures.
Abstract: The objective of this study is to establish a numerical technique applicable for the
assessment of damage characteristics of laminate ceramic. A numerical simulator, which can be used
for the optimal material design, was developed based on the damage mechanics approach. To evaluate
the internal damage evolution behavior within composite material, generalized damage evolution
equation was developed and implemented in way of finite element method. By virtue of an automatic
data interface between the commercial FEA results and damage calculation, a simple and
cost-effective damage evaluation system is constructed. It was found that the developed system can be
used for the evaluation of the material performance of composite.
Abstract: In the present study, numerical work applying a finite element method (FEM) is used to
analyze the characteristics of aluminum (Al) alloy mold for thermal strain control. In the concrete, the
temperature distribution on the inside of Al alloy mold, the contraction rate and stress occurred by
temperature variations are investigated to predict the accurate measurement variation of Al alloy mold
during the cooling process. In addition, the numerical result of the Al alloy mold were compared with
those of mild steel mold in order to obtain the improvement and good quality of mold. In the end, the
numerical results such as temperature distributions, contraction rate and stress are presented to help to
make the effective and the best mold products. Besides, the introduced technique of numerical
analysis applying a FEM is very useful and important things in the fracture and damage mechanics,
especially needs the accuracy improvement such as Al alloy mold products.
Abstract: This paper presents the results of an experimental investigation on surface contact fatigue
of AA6082 aluminium alloy. After testing, microscopy analysis of the specimen contact area shows
plastic deformation at the centre and circumferential cracks at the very edge of the print. Major cracks
develop at a certain depth under the border of the contact area and propagate beneath the surface, in
the direction of both the centre of contact and the lateral free edge of the specimens. No cracks have
been observed at the centre of contact, neither on the surface, nor inside the material.
Tensile properties of the alloy have been measured and a non linear finite element analysis has been
performed in order to calculate the field of deformation and stress in the contact zone. Finally, stress
intensities are correlated with the crack initiation points and an interpretation of the propagation
paths, in regard to stress distribution, is given.
Abstract: This work presents the results of an experimental investigation on the effects of thermal
ageing over the residual fatigue strength of AA2618-T6511 aluminium alloy.
Among others, this kind of light alloy finds practical applications in highly stressed engine
components, such as pistons, that are typically subjected to both thermal and fatigue loads. Thermal
cycles are responsible for ageing phenomena, that involve the precipitation of silicates, with a
corresponding progressive damage of the microstructure and weakening of the mechanical
characteristics of the material.
Artificial ageing has been reproduced in laboratory by means of thermal cycles controlled in time
and temperature. These variables have been correlated to the hardness values measured on the
surface of specimens. Bending fatigue tests have been performed on a rotating machine in a
temperature controlled environment. The experimental S-N diagram is finally presented, as a
function of the tested temperature, in order to provide a design tool for the fatigue life estimation of
Abstract: This paper presents the results of an experimental investigation on the failure behaviour of
power screw linear actuators subjected to very high compressive loads. Quasi-static tests performed
in laboratory have shown the presence of primary and secondary buckling failure modes. On the one
hand the primary buckling is characterized by plane deflection of the inner screw, on the other hand
the secondary buckling involves either spatial buckling, forcing the screw to assume a helical shape,
or plane buckling of the external arm, in relation to the actual slenderness and the position of the
Non linearities of the axial stiffness have been observed during the proportional phase of loading, as a
consequence of the superposition of primary buckling and the lateral constraint effect opposed by the
cylindrical case of the actuator to the bending deformation of the screw.
Maximum deflections and longitudinal deformations have been measured as a function of the applied
compressive load, whose axial and bending components have been calculated.
A mathematical model of the elastic loss of stability has been developed, in order to calculate the
critical load as a function of the actuator geometry.