Abstract: In the present paper, a micromechanical based damage model and corresponding
permeable coefficient tensor are developed for rocks under tensile stress and hydraulic pressure
loading based on the concept of the domain of microcrack growth (DMG) . After choosing an
appropriate fracture criterion for microcracks, we obtain the equations from which the DMG under
a monotonically increasing proportional plane stress and an invariable hydraulic pressure loading is
obtained. Then the overall effective stress-strain relations and the permeable coefficient tensor of
damaged rocks are calculated. The theory is verified by test.
Abstract: This study gives the problem of a crack in the film oriented perpendicular to the
film-substrate interface with the crack tip terminating at the interface. Based on Beuth’s theory,
three-dimensional model is simplified to plane strain problems, which obtains fracture mechanisms
of a cracked film-substrate medium by applying the boundary element method(BEM). The method
aptly resolves the problem involving stress concentration and, further, that this study develops the
multi-region boundary element method and applies it to evaluate the cracked film-substrate
medium. It shows that the stress intensity factor is affected by the different elastic mismatches and
the thickness ratio of the film and the substrate. These results indicate: 1) The stress intensity factor
has remarkable increased with the decrease of the thickness ratio of the film and the substrate. The
effect of the fracture behavior of film is negligible when the thickness ratio of the film and the
substrate is above 10, therefore, it is treated as thin film; 2) The stress intensity factor will decrease
with the increase of α ( −1 pα p +1) for β = 0 and β =α / 4 , where α and β are called
Dundurs parameters. What’s more, this paper studies the special condition of the film-substrate
medium, which is the analysis of the fracture of the absence of any elastic mismatch between the
film and the substrate, i.e.α=β=0, and revision of the formula of Xia and Hutchinson is put forward
for the stress intensity factor of the deep crack problems by comparing to the former conclusions of
Abstract: A ultrahigh carbon steels (UHCS) containing 1.6 wt pct carbon was studied. Through
spheroidizing process by divorced-eutectoid transformation (DET), the forged microstructure was
spheroidized and the microstructure was fine carbide particles distributed in ferrite matrix.
Second-time heat treatment included two kinds of technologies: normalizing and quenching +
tempering. Finally, the UHCS obtained ideal mechanical properties. The yield strength and tensile
strength of the UHCS were higher than that of 40CrNiMo, moreover plasticity of the UHCS was
equal to that of 40CrNiMo. So the UHCS was an excellent structural material.
Abstract: It is very important to detect fiber orientation error in orthotropic composite laminates
because the layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the
properties of the laminate, including stiffness, strength and thermal behavior. In this study, an
investigation of shear wave ultrasonic technique was carried out in order to detect stacking
orientation error for the orthotropic composite laminates. During testing, the most significant
problem is that the couplant conditions do not remain the same because of changing the viscosity
of the couplant. Therefore, the design and use of a shear wave transducers would greatly aid in
alleviating the couplant problem. A pyramid with an isosceles triangle with two 45o was made of
aluminum to generate shear waves using two longitudinal transducers based on ultrasonicpolarized
mechanism. Also, the signal splitter was connected to the pulser jack on the
pulser/receiver and to the longitudinal transducers which were mounted with mineral oil. The shear
transducer was mounted on the bottom as a receiver with burnt honey. It is found that the shear
wave was generated at a maximum and a minimum based on the ultrasonic-polarized mechanism.
Finally, test results with model data were compared for a fiber orientation of the laminates.
Abstract: The present study shows a new idea for investigating characteristics of stress singularity
field around a vertex associated with elasto-plastic properties of materials. FEM formulation for
elasto-plastic stress singularity analysis is expressed to investigate an eigenvalue and the intensity of
singularity.The elasto-plastic stress singularity in a flip chip joint was investigated using the FEM
formulation. After that, the possibility of delamination on the flip chip joint was discussed.
Abstract: In the present work, the fracture toughness of a NiTi pseudoelastic alloy has been
obtained by experiments on CT specimens, which is KIC =39.38MPa·m1/2. Then the stress induced
phase transformation behavior in front of the crack tip of the CT specimen is simulated by a
micromechanical model considering the different elastic properties between martensite and
austenite. The results show that the pre-crack promotes phase transformation at the crack tip. And
the phase transformation is localised near the crack tip. It is also shown that phase transformation
reduces the Mises stress around the crack tip.
Abstract: In order to study the behavior of fatigue crack propagation under random overloads, a
Monte Carlo simulation scheme is proposed. Overloads of Poisson flow with uniform distribution
on base-line constant-amplitude cyclic loads are considered. The retardation effect of overload is
taken into account using crack closure model and the crack opening stress level is assumed to vary
linearly in the yield zone produced by the overload. The fatigue crack growth curve from initial
crack size till fatigue failure is simulated step by step. Through the large number of the simulated
samples, the average fatigue crack propagation life is calculated. Finally, the influence of overload
intensity and magnitude on fatigue crack propagation life is studied.
Abstract: Many military aircraft have reached or exceeded their original design life, and have been
subject to significant increase in maintenance and repair cost due to multiple site damage (MSD). In
order to assessing the effects of MSD on the structural integrity of aircraft lap joints, the wing lap
joint of certain model military aircraft with MSD was analyzed using special code FRANC2D/L. The
rivet holes along the top row of the outer skin of lap joint were considered as the independent
structural unit for the simulated MSD cracks. The stress intensity factors (SIFs) at each crack tip with
different distribution loads at the rivet holes were computed and show that the analysis results have
good coherence with the available literature data. It also shows that the SIF at each crack tip s a
function of crack length can be calculated by the crack growth simulation capability of FRANC2D/L.
The SIF values are not sensitive to the rivet load distribution manner, which has seriously influence
on MSD crack growth direction. Rivet loading can be best molded quadratic load distribution over
one half of rivet hole relative to uniform load distribution and point load. As a result of this analysis,
it is postulated that for MSD in aircraft lap joints, compliance measurements may provide a useful
tool for assessing the structural integrity of the lap joints.
Abstract: Ductile tearing of brittle solid with initial crack is studied numerically. This work is
focused on the simulation and analysis of crack path deviation for the respective configuration and the
study of relation between crack length and the fracture resistance, and that the configuration of
fracture surface is also observed. The simulating tool is a novel numerical code, 3D Realistic Failure
Process Analysis code (abbreviated as RFPA3D). The simulating investigation has shown that the
fracture resistance decreases with the increase of the angle between the crack ends and horizontal
direction. Due to heterogeneity of materials distribution, crack path deviation towards the softer zone
or elements is observed. The topography of the non-planar fracture surface has plotted. Concluding
the simulation made in the present study, the problem of crack extension in the brittle solid can be
handled by RFPA3D. Fracture resistance can be predicted and the crack path deviation be simulated,
if the model parameters have been carefully identified and the mesh design is adequate. So this work
is beneficial to choose safe load-spots and predicate the direction of the crack path deviation.