查看更多>>摘要：? 2022The presented paper aims to characterize the damage and fracture behavior of HX340LAD Micro-Alloyed steels using small punch test. Variations with respect to punch geometries and cutting clearance are made to describe the damage behavior of the material under different loading conditions. Experimental investigations are conducted to identify the crack initiation in the specimens. Furthermore, the numerical FEM simulations are performed to identify the stress state at crack initiation. It is shown that different stress states from shear to biaxial tension can be achieved by changing the geometries of punch and varying the cutting clearance. Moreover, it is presented how changing the configurations can influence the stress state variables: Triaxiality and lode angle parameter.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, an analytical model for evaluating the durability life of reinforced concrete (RC) piles subjected to localized corrosion under chloride attack is proposed. The localized corrosion process is divided into three stages, and a predictive method is presented to predict the durability life of the pile by calculating the time of each stage. The time of each stage is determined based on the chloride diffusion model, the pitting corrosion model and the crack propagation model. The effects of the water-cement ratio, concrete cover thickness, pile concrete quality, relative humidity, chloride threshold level, pitting factor, corrosion current density and initial surface chloride ion concentration on the various stages of localized corrosion and the durability life of the pile are investigated. The analysis results show that the effects of the water-cement ratio and concrete cover thickness on the durability life of the pile are the most significant in the corrosion initiation stage. The durability life is increased by a reasonable choice of both concrete water-cement ratio and concrete cover thickness with constant concrete quality. The durability life of the pile increases with increasing concrete cover thickness, concrete quality, chloride threshold value and limit crack width, while it decreases with increasing water-cement ratio, relative humidity, corrosion current density and initial surface chloride concentration. The influence of the pitting factor is minimal and is mainly in the pit nucleation stage.
查看更多>>摘要：? 2022In order to investigate the effect of surface indentation size on the corrosion behaviour of MAO coated AZ80 magnesium alloy, the laser confocal microscope, scanning electron microscope, X-ray diffractometer and electrochemical test were carried out to study the corrosion process of MAO coated AZ80 and the coatings damaged with different impact heights. The results display that when MAO coating was damaged with the impact height of 400 mm, the corrosion current density of the specimen increased to 8.0 × 10?1 μA/cm2 from 3.2 × 10?1 μA/cm2 for MAO without indentation. After immersion for 72 h, the corrosion resistance of the damaged specimens decreased sharply because of the defects on the surface. Moreover, the corrosion mechanism for the coatings with different indentation sizes was clarified.
查看更多>>摘要：? 2022The knowledge of the mechanical behavior and deformation characteristics of lining structure of super-large section tunnels with a small clearance can help to optimize the tunnel lining design and reduce the construction costs. Based on Xinwu twin tunnels with eight lanes in China, a reduced-scale model experiment was carried out to investigate the deformation characteristics, the crack behaviors, the ultimate bearing load and internal force of the super-large section tunnels under different clearances. The results show that the positions in order (from largest to smallest deformation) are as follows: crown, right spandrel, left spandrel, invert, springs. 12 m (about half the width of tunnel) can be considered as the smallest reasonable spacing for large section tunnels in grade IV surrounding rock. With the increase of loading level, the cracks mainly appeared at the invert and the springs of the two tunnels. After the secondary lining was damaged, the deformation of each measuring point did not decrease but gradually increased with the clearance. These findings can provide significant reference data for the design optimization and safety assessment of super-large section tunnels with a small clearance.
查看更多>>摘要：? 2022The corrosion mechanism of the overhead pipeline of the H2S stripper tower was studied by macro examination, metallography, SEM and EDS analysis. The primary reason for the corrosion is the unsuitable material selected for the inhibitor injection pipe. In a H2S + HCl + NH3 + H2O environment, first dew point corrosion occurs. Then oil and gas erosion corrosion causes the injection tube to perforate and break, which directly alters the flow pattern and temperature in the overhead pipeline. Eventually, the tube is broken by erosion and acid corrosion. A computational fluid dynamic tool has been used for the simulation of the multiple phases inside the corroded pipe. The numerical simulation proves our conclusion of the development of corrosion in multiple locations.
查看更多>>摘要：? 2022 Elsevier LtdThe blasting impact poses a serious threat to the safety of temporary support structures in tunnel blasting construction, such as a temporary middle wall. Thus, this study investigated and explored these problems. First, the dynamic response results of the temporary middle wall after the explosion were studied according to the field monitoring data. Subsequently, the damage characteristics of the temporary middle wall near the blasting source were investigated on field, and the development stages of the failure evolution were summarized. Furthermore, combined with the explicit finite element software LS-DYNA, the fluid–solid coupling algorithm was used to simulate the vibration response and the failure modes of the temporary middle wall under the condition of different charge weight and blasting distances. According to the field investigation, the closest blasting holes away from the temporary middle wall had a much more significant impact on its damage than other holes. The failure reason of the sprayed concrete of the supporting structure is caused by the excess high peak tension or compression stress. The failure process of supporting structure can be divided into four development stages with the reduced distance away from the blasting source: the appearance of the cracks, the cracks interconnect to form large X-shaped cracks, structural bending-shear coupling failure, and instability failure. The displacement values of the steel arch in the temporary middle wall continuously exceed 7 cm, 20 cm, 28 cm, and 34 cm, respectively, corresponding to the above four failure stages. The relation function containing the blasting tensile stress (BTS) parameter is obtained through dimensional analysis, which can be directly used to design and the damage evaluated of temporary support structures subjected to blasting at close range.
查看更多>>摘要：? 2022 Elsevier LtdThis paper presents the failure analysis of an engine mounting bracket. During the proving ground testing, the right brackets of the three testing cars get broken or cracked at the mileage about 7,000 km. In order to determine the causes of the failure, a nonlinear finite element method (FEM) and failure morphology analysis together with mechanical properties, chemical components and micro-structural analyses of the specimen s material have been performed. The metallographic observation shows the precipitates observed at the inner and outer surfaces, which reduces the strength of inter-granular and then causes the fatigue fracture initiation at the inter-granular. The FEM results show that, the max mises stress is right just at the fillet of bracket, where is the initiation of the crack, and it is a little higher than the yield stress of SAPH400. An optimized structure is proposed, the max tress reduces 20%, and the following tests show the optimized bracket achieving the test mileage more than18,000 km and meets the test requirement.
查看更多>>摘要：? 2022 Elsevier LtdThe fatigue failure behavior and fatigue strength prediction were performed on a Ni-based superalloy for the turbine blade in 750 °C elevated temperature environment. The asymmetric load tests with the stress ratios R = -1 and 0.1 were tested, followed by microstructure characterization and fracture mode analysis via two & three-dimensional microscopic observation and electron-backscattering diffraction, etc. Results show that as stress level decreases, fatigue failure is less likely to be induced by pore, while the possibility of grain cracking induced failure increases. The larger roughness of the fracture surface is attributed to the geometric incompatibility of grains and the plastic deformation at the crack tip. For the grain related failure, crack nucleation is mainly in Goss grain along the direction of the maximum Schmid factor. Moreover, the threshold values of small & long cracks, the transition crack size from small to long, are all lower for interior failure due to the effect of vacuum environment. Finally, based on El-Haddad model, a new fatigue strength prediction model is proposed, and the predicted results are in good agreement with the experimental ones.
查看更多>>摘要：? 2022 Elsevier LtdSCC and electrochemical behaviour of selective laser melted 316L stainless steel was studied under the combined effect of surface residual stresses (RS) and energy input variation. A significant correlation was found between columnar subgrains width and pore size with the electrochemical response and SCC susceptibility. There existed a critical pore size affecting local corrosion behaviour which decreased with an increase in RS magnitude. The critical RS needed for SCC occurrence was lower compared to wrought counterpart and the SCC mechanism was hypothesized as the synergistic effect of exceptional selective corrosion attack at subgrains and mechanical rupture of subgrain boundaries.
查看更多>>摘要：? 2022 Elsevier LtdThe application of back propagation neural network (BP neural network) in very-high cycle fatigue life evaluation of centrifugal impeller to explore the effect of internal inclusion and granular bright facet (GBF) region on the fatigue life is a key and potential issue. Numerical simulation analysis of centrifugal impeller is carried out in this study to clear the mechanical state of centrifugal impeller in operation condition. Then, the designed very-high cycle fatigue test is conducted out; the test data and fracture morphology are analyzed to reveal the effect of internal inclusion and GBF region on the fatigue failure and life distribution. Then, with the comprehensive application of BP neural network, the fatigue life with different input parameters are predicted. In the case of different input parameters, the prediction changed and the very-high cycle fatigue life with the consideration of both internal inclusion and GBF region is very satisfactory. Study on neural network fatigue life prediction approach of centrifugal impeller in VHCF affected by internal inclusion and GBF region is novel for the further fatigue study in theoretical research and engineering practice for mechanical component and engineering metallic material.
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