Key Engineering Materials Vols. 452-453

Abstract: Due to high centralized instantaneous heat input in the process of the welding, a great deal of residual stresses and distortions should be brought in the welded structures, which can heavily influence the capability and reliability of the structure. Residual stresses and welding fatigue behaviors of stainless steel penetration assembly joined by multi-pass welding are studied in this paper. The distribution of transient temperature field and real-time dynamic stresses field in the welded region must be calculated first. Based on the residual stresses, the random wave load putting on the structure and fatigue factors, according to Miner fatigue damage law, some fatigue behaviors such as fatigue life and remaining life are obtained.

Abstract: Recently, due to increasing popularity of the magnesium alloys, many studies on corrosion resistance of the magnesium alloys have been reported to improve their corrosion resistance. However, it is not clarified yet whether an electrochemical polarization curve or a corrosion rate is a good measure for the corrosion fatigue resistance or not. In the present study, corrosion fatigue tests, the weight loss test, and measurement of the electrochemical polarization curve were performed in 3% sodium chloride solution using both the extruded and the rolled Mg alloys. It was clarified that there are no differences in the corrosion fatigue lives between the extruded and the rolled Mg alloys, though they have different corrosion resistance. So, it was concluded that the corrosion fatigue characteristic does not correspond well with the trend in corrosion resistance.

Abstract: The proposed paper describes fatigue damage evolution in Eurofer 97 reduced activation ferritic-martensitic steel. The short crack growth study was performed on small cylindrical specimens using an MTS 880 servohydraulic machine at constant strain amplitude. Based on the fatigue crack growth data obtained and corresponding 3D finite element analysis Paris law region of the fatigue curve were estimated. The results obtained were compared with standard determination of the fatigue crack growth rate according to ASTM using CT specimens. The presented results can help to transfer experimental data measured on small specimens to large structures and vice versa.

Abstract: In this paper, we study the problems of scattering of out-of-plane line source load by half-space shallow-embedded circular lining structure and a crack in the field of linearly elastic dynamic mechanics. This is an essential solution to the displacement field for the elastic space possessing shallow-embedded circular lining structure and a crack while bearing out-of-plane harmonic line source load at arbitrary point. The wave function of scattering of shallow-embedded circular lining structure impacted by incident steady SH-wave is constructed based on the symmetry of SH-wave scattering and the method of multi-polar coordinates system. Then a crack is made out using the method of “crack-division”. Thus expressions of displacement and stress are established when shallow-embedded circular lining structure and a crack are both in existent. Finally, with two different dimensionless parameters, numerical results of scattering of out-of-plane line source load by half-space shallow-embedded circular lining structure and a crack are obtained and numerical examples are provided to show the influence of wave number ratio, shear modulus ratio, thickness ratio and the ratio of distance between the center of the different cavity and ground surface and the radius of the circular lining structure upon the dynamic stress concentration factor(DSCF) and dynamic stress intensity factor(DSIF) at crack tip.

Abstract: It is well known that the MFS based on the collocation method can be implemented easily and gives good accuracy in most cases[1,2,3]. The stability of the accuracy, however, depends on the source location. Recently, Karageorghis et.al. calculated SIF of a central crack in a rectangle plate using a similar shape of uniformly distributed points[4]. Gorzelanczyk et.al. made some remarks concerning the shape of the source contour with application of the MFS to elastic torsion of prismic rods. It is reported that the accuracy is better when the source contour is geometrically similar to the boundary of the region in comparison to the source contour with a shape of a circle[5].

Abstract: : In this research, some concrete three-point bending specimens (beams) reinforced by FRP are used in numerical simulation to study the influence of the reinforcement on fracture mechanism and the extreme load-bearing capacity of the specimens. The numerical simulation results show the propagation of the crack in concrete is controlled by using FRP. Meanwhile the load-bearing capacity is increased greatly and failure modes are changed.

Abstract: To clarify the instantaneous strain field during the fatigue crack propagation test, an attempt is made to estimate the displacement vector of the small area of the crack tip from the high speed movie. The key theory of the estimation is Particle Image Velocimetry (PIV) which is frequently use in the fluid dynamical data analysis. PIV means the area based correlation matching between the sequential image pair. At first the earlier image divided into the small subareas, and on the later image most correspondent position to the subarea is searched. The each displacement of the subarea position between earlier and later image means the local deformation of the crack tip. Through the numerical simulation, the subarea size and search area size are defined to get the realistic result. To make the instantaneous deformation within a cycle of the fatigue crack propagation test, high-speed camera with high-power camera is used. The frame rate is beyond 1000Hz and shutter speed is 1/8000 second. By using the such camera and optimized PIV algorithm, the instantaneous strain field can be estimated and this will analyze the phenomenon of fatigue crack propagation.

Abstract: Traditionally, applications of fracture mechanics have been mainly focused on cracks growing under the opening or mode I mechanism (three point bend specimen, middle tension specimen, crack tension specimen, etc.). When investigating instability under mixed mode loading conditions, three different alternatives can be envisaged consisting of: a) machining a hole in standard specimens, b) creating a crack oriented under a given angle, and c) using non-standard Arcan-Richard specimens. In this work, finite element calculations are performed to analyze the initial values of the fracture parameters in Arcan-Richard specimens. First, the influence of the normal stress mode to the shear stress mode ratio is analyzed, then the effect of the constraint level is discussed, and finally, the initial propagation angle of the daughter crack is derived.

Abstract: The bearing capacity decreases continuously along with the deterioration of material property under the action of external effects. It is important to evaluate the damage of concrete, and the damage parameter plays an important role in this process. An experimentation method has been designed, which can simulate the initial damage by mixed initiator into concrete. Using the elastic modulus of axial compression experimentation, the initial damage D0 and damage threshold value Df have been gained. The Size effect of concrete compress damage parameters is verified.

Abstract: A common means of facilitating cross welding on the girder flange is to use cope hole on the girder web. This paper presents a study on the fatigue strength of the corrugated web girders with the cope hole using numerical analysis. Typical stress concentration behaviours are discussed relative to reported experimental results, and parameter variations are then used to study the stress gradient on the corrugated web as the influence of the cope hole. Based on the simplified cumulative fatigue summation implemented in fatigue post-processor, fatigue life predictions are presented with codified curves of AASHTO LRFD.