Abstract: In this study, an experimental method has been studied to measure the residual stresses
on a specimen with I-groove weldment. The specimens were extracted from I-groove weldment
which was joined by SAW (Submerged Arc Welding) with CO2 shield gas. A FEA (Finite Element
Analysis) model was developed for the estimation of the residual stresses for the specimen.
Measurements were carried out using ESPI(Electronic Speckle Pattern Interferometry) system
which can measure the strain distribution on the surface of specimen. The residual stresses were
estimated by the value of strain measured by ESPI system. Strain gages were added to evaluate the
accuracy of ESPI system. In addition, a three-dimensional FE model was used to estimate the
residual stresses generated by the welding procedure. A thermal elasto-plastic analysis was
performed by the FEA. The stresses measured by the experiments were compared with the results of
FEA. Also, discussed are the difference and agreement between the stresses obtained by
experiments and FEA, respectively.
Abstract: The paper presents the results of a continued study of curved fatigue crack growth in a
multiple arbitrarily pre-cracked isotropic sheet under plane stress loading. The predictor-corrector
method (PCM) was extended in order to analyse the growth of multiple crack systems in a finite 2D
structure. Together with the recently proposed improved modified virtual crack closure integral
(MVCCI) method we can obtain accurate SIF values also for interacting cracks, and furthermore we
can simulate fatigue crack growth of multiple crack systems in plane sheets under proportional
mixed mode loading conditions. As a result, the program PCCS-2D is written to run within ANSYS
to simulate interacting curved cracks. In order to check the accuracy and efficiency of the proposed
method several example problems are solved. Especially curved cracks emanating from loaded fastener
holes in sheets are analysed.
Abstract: This paper presents an experimental study on the anchorage behaviour of long
high-strength steel rebars embedded in high-performance concrete (HPC) under both static loading
and fatigue loading. The HPC was designed as C60 with its cube compressive strength larger than 60
MPa, and the high-strength steel bar was adopted as HRB500 with its characteristic yield strength
equals 500 MPa. Under 3×106 fatigue loading cycles and then followed by a monotonous static
loading, the strain and the stress state of the reinforcement bar, and the bond stress between the
concrete and the 700 mm-long bar were investigated. Based on the test results and the ANSYS finite
element analysis, the bond behaviour between HPC and long high-strength steel bars is discussed.
Abstract: In order to calculate the fracture parameters (Stress intensity factor) in a complicated 3-
dimention aircraft model with damage in the aircraft panel, a new two steps global-local
hierarchical analysis strategy is used. This paper primarily describes the development and
application of advanced computational analysis techniques to determine stress intensity factors for
the damaged panels based on the two steps hierarchical analysis strategy from global to 3-D local
model, the bulging deformation of crack can be considered in the local model. A fracture parameter
calculation programme based on automated global-local procedure to simulate cracked aircraft
panel tests is developed for the hierarchical strategy. This programme may create models of two
stages, transfer boundary conditions, calculate and obtain fracture parameter automatically. Finally,
this paper presents some of the experimental data and the calculated fracture parameters are
compared with the experimental results.
Abstract: In engineering reliability analysis, the limit state equation is generally implicit and
nonlinear, and large number basic random variables and small failure probability are associated. For
this kind of reliability analysis, a novel numerical simulation is presented based on the combination
of Markov Chain Simulation and line sampling. In the presented method, Markov Chain Simulation
is used to draw samples in the failure domain rapidly, and important direction for the line sampling
is determined by these samples. Then the line sampling technique is employed to take samples
according to the important direction, and failure probability can be evaluated by line sampling with
high efficiency. Comparing to the finite differential method for obtaining the important direction,
higher accuracy and higher robustness of the important direction are obtained by the presented
method. The application in the reliability analysis of low cycle fatigue life of aeronautical engine
turbine disc structure, which is applied by multiple cyclic loads, shows that the presented line
sampling combining with the Markov Chain Simulation is efficient and feasible.
Abstract: The effect of undissolved ferrite amount on bending fatigue properties and failure
mechanism were studied by using 42CrMo steel with subcritical quenching process The amount of
undissolved ferrite were 0%, 10% and 15%, respectively. The hardness of the specimen was treated
to medium hardness. The experimental results show that the existence of undissolved ferrite can not
only change the microstructure, but also increase the bending fatigue life. The bending fatigue life
elongates with increasing of amounts of undissolved ferrite. The grains can be fined by using
subcritical quenching process and the area of phase boundaries can also be greatly increased
because of undissolved spheroidal carbide. The martensite and carbide can also be changed using
subcritical quenching process. Stress relaxation due to the move of dislocations inside the ferrite
and the promotion of strength due to occurring of plastic deformation and enwinded dislocations are
main reasons of improving the bending fatigue life. The bending fatigue life elongates with the
increase of amounts of undissolved ferrite before the amount of undissolved ferrite reaches 10%.
Under the experiment conditions, when the amount of undissolved ferrite is 10%, the bending
fatigue life will be the longest.
Abstract: In the present paper, singular stress fields at the vertex on the interface in three-dimensional
bonded joints are analyzed using BEM. The order of stress singularity is determined solving an eigen
equation based on FEM formulation and the stress distribution is expressed using the result of the
eigen-value analysis. A simple relationship between the thickness of layer and a value of stress is
introduced. Then, stress distributions for various thicknesses of layer are unified using the
relationship, and the unified intensity of stress singularity is determined.
Abstract: The dynamic fracture properties of polypropylene/nylon-6 (PP/PA6) blends, with different
weight fractions and different compatibilizars, are investigated by reflected dynamic caustics
experiments. According to the shadow spot patterns around a moving crack tip, which are recorded
during the dynamic fracture process, dynamic fracture toughness and crack growth velocity can be
estimated to evaluate the fracture properties of polymer blends. Moreover, combined with
microscopic observation, the damage mechanism of the polymer blends is discussed.
Abstract: Most of existing studies on rock damage are focused on investigating the macroscopic
stress-strain relationship, and only limited research is available on analyzing the microscopic crack
propagation due to measurement difficulty, cumbersome data reduction procedures, and complexity
of damage in micro-level. In this study, a powerful image-processing program is developed to extract
the microscopic crack distribution from the digital image of microscopic crack status of red sandstone,
and the microscopic crack propagation of red sandstone under single-axial pressure is then evaluated
by the technique of multifractal. It demonstrates that the microscopic crack distribution possesses the
multifractal character, and the capacity dimension of multifractal singular spectrum can be used to
quantitatively characterize the microscopic crack propagation of red sandstone. By comparing the
stress-strain relationship with the one of stress-capacity dimension, the capacity dimension is capable
of acting as a physical quantity to effectively reflect the damage of red sandstone by the means of
characterizing its microscopic crack propagation.
Abstract: Temperature field is formed due to heat dissipation when material is subjected to
irreversible deformation. In this paper, the heat dissipation in the crack-tip plastic zone was
considered. By considering the propagating crack-tip plastic zone as a running heat source and
constructing a reasonable heat source density distribution function, the temperature field around a
steady running crack was obtained. It is shown that temperature rise is dependent on the crack
growth speed and the material parameters. The maximum temperature rise reaches to >50 oC in
our example calculations for a steady running crack in PMMA.