查看更多>>摘要：? 2022 Elsevier LtdThe damage caused by impact of hard particles on aircraft components is called Foreign object damage (FOD) and it may cause premature failure. 7075-T6 is one of the alloys frequently used for manufacturing aircraft parts and components. In this paper, the failure mechanism of a damaged 7075-T6 specimen subject to rotating bending was explained from a phenomenological point of view using the Finite Element (FE) method and the fracture surface observation. The results showed that the crack initiation occurred in the locations of the highest residual tensile axial stresses after the impact, where also the tensile axial stresses in the simulated fatigue cycle are the highest, and at the surface of the FOD dent. A discontinuity was observed under the dent, in the area subject to compression after the impact and in the fatigue cycle. The damage induces a 30 ± 10% reduction in fatigue strength compared to undamaged specimens.
查看更多>>摘要：? 2022 Elsevier LtdAccelerated vibration fatigue, using the inverse power law model (IPL), is effective to evaluate the durability of materials. However, for 6061-T6 and AZ31B-F with two-stage S-N curves, the prediction error exceeds orders of magnitude. Therefore, an improved inverse power law model (IIPL) is proposed. The results obtained from the vibration fatigue experiments show that the fatigue life prediction accuracy of IIPL is more acceptable than IPL. For two-stage S-N curves, the error of IIPL is between ?61.8% – ?0.8%, better than that of IPL (8.68 × 101% – 2.42 × 105%). Even without accelerated fatigue tests, the error by IIPL is also reasonable (-69.1% – 23.2%).
查看更多>>摘要：? 2022 Elsevier LtdWith the improvement of computational capability, finite element simulation is an increasingly practical method to accurately predict the ultimate capacity and ductile fracture behavior of high-strength bolts. However, the mesh size affects the results of FE simulations but related research on mesh size effects is relatively limited. In the present contribution, the mesoscale critical equivalent plastic strain (MCEPS) is used as a failure index for calibrating the parameters of ductile fracture locus of high-strength bolts with different mesh sizes. The identified fracture locus is compared with a large bulk of experimental data taken from the previously published literature. The results showed that mesh size can have high effects on the calibrated parameters of the plastic constitutive relationship after necking and ductile fracture locus of high-strength bolts.
查看更多>>摘要：? 2022 Elsevier LtdTunneling in fault zone presents considerable challenges to the engineer, including the unexpected failure of supporting structures and the unpredictable geohazards. This paper provides a case study about the structural failures and treatment measures during the construction of the Shengli tunnel crossing the fault fracture zone. During the fault fracture zone construction, structural failures and geohazards such as large deformation of primary lining, water inflow, and collapse were encountered. Before the collapse, the maximum displacement rate of the surrounding rock was 71.7 mm/d, and the extreme deformation of the lining was characterized by the large vault settlement and asymmetric deformation. Combined with on-site monitoring, laboratory tests, and meteorological investigations, the mechanism of structural failures was analyzed. Rocks with low bearing capacity and strong softening, extremely broken rock mass, and abundant groundwater were the main factors leading to the tunnel structural failures. To reduce the adverse effect of fault fracture zone, a series of comprehensive treatment measures were put forward from the aspects of the treatment of collapse body, advanced support, reinforcement of lining, and adjustment of the construction method. Through the field monitoring data of the processing section, the effectiveness of the adopted countermeasures was verified. Based on the monitoring data and field investigations, the process of failures and the rationality of treatment measures were discussed. These results can provide theoretical and technical experience for future similar projects.
查看更多>>摘要：? 2022 Elsevier LtdThis paper reports a collapse accident of slope instability at the entrance of Taizhen Tunnel in Qujiang Section of Hangxinjing Expressway in China. The landslide instability mechanism was studied by field observation and testing. Considering the stability of the landslide and the disturbance effect of secondary tunneling construction, comprehensive reinforcement measures were proposed. The monitoring data showed that good results were achieved. In addition, the effectiveness analysis of the treatment scheme was further examined via numerical simulation. The analysis results show that slope reinforcement before tunnel excavation can not only prevent slope failure but also reduce the deformation of the supporting structure. The improved double side-wall heading method has less disturbance to the slope and is more conducive to the overall stability of the slope. Finally, the lessons learned were summarized, providing insights for preventing future similar incidents from reoccurring.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the root cause of an uncommon coating adhesion failure of hot-dip galvanized boron added low carbon steel was investigated. Metallurgical characterizations were performed by GDOES, SEM, AES, FIB and EDS. It was found that the coating adhesion failure was caused by the enrichment of boron at the coating/steel interface, which significantly prevented the formation of Fe-Al inhibition layer. The root cause of boron enrichment was further attributed to the external oxidation of boron during the annealing process. The vaporization of B2O3 and the formation of BN in the annealing furnace polluted the rollers and the inner furnace walls, which caused further boron contamination on the following steel surface. The suppression of boron external oxidation by dew point increasing effectively improved the coating adhesion of hot-dip galvanized boron added steel.
查看更多>>摘要：? 2022 Elsevier LtdFerromagnetic materials exhibit a stress-magnetic coupling effect, where mechanical and magnetic energy are converted to each other. This effect is known as the effect of stress-magnetization. The effect of stress-magnetization of 304 austenitic stainless steel after the occurrence of martensitic phase transformation to produce ferromagnetic phase is not clear. To clarify the effect of stress-magnetization of alpha'-martensite and its mechanism. A tensile loading test is designed to evaluate the effect. X-ray diffraction (XRD) and Lorentz transmission electron microscopy (LTEM) methods are used to investigate the evolution of microstructures and clarify the mechanism. Furthermore, an analytical expression model is established on the basis of martensitic transformation dynamics and a magneto-mechanical model. The accuracy of the model is validated from perspectives of martensitic transformation, the effect of stress-magnetization of alpha'-martensite, and their combination. Results showed that the effect of stress-magnetization of alpha'-martensite is significant and increases magnetic signal collected by fluxgate sensor. The mechanism is the increase of magnetization of the material due to stress by assimilating the orientation of magnetic domains. The proposed model demonstrates satisfactory accuracy and provides theoretical bases for evaluating mechanical damage in 304 austenitic stainless steel.
查看更多>>摘要：? 2022 Elsevier LtdThis paper presents an advanced submodelling methodology for local stress analysis of complex details of existing metallic railway bridges. The fatigue assessment of connections of large structures based on local methods leads inherently to a multiscale problem that can only be solved by adopting efficient numerical procedures. Aiming to overcome such limitations that influence the analysis process, submodelling techniques and modal superposition principles are combined to fully represent numerically the local geometrical, material and contact properties of the fatigue-critical details. The results of experimental in situ tests are proposed to characterise the numerical models and respective multiscale relation, implementing optimisation and validation procedures. In this work, the suggested efficient multiscale methodology for stress analysis aims to allow the subsequent local fatigue assessment, according to the real mechanism of loading transference, reducing sources of conservatism. All numerical procedures and respective validation thru experimental techniques are illustrated using a real case study.
查看更多>>摘要：? 2022 Elsevier LtdThe thermal buckling behaviors of oil-filled tanks subjected to heat radiation of a burning tank are investigated considering the effect of isopentane on the heat transfer. The effects of the height-to-diameter ratio, fluid level, and wall thickness on the thermal buckling behavior and fire resistance of oil-filled tanks are studied, and the failure mechanism of the steel tank is analyzed based on the temperature and stress distributions. The results indicate that the buckling area is located at the upper part of the tank which is exposed to air. The oil-filled tank has a similar thermal buckling mode to the empty tank. Moreover, the height-to-diameter ratio, fluid level, and wall thickness hardly affect the thermal buckling mode of the oil-filled tank. This study can be used to optimize the design of steel oil tanks to resist fire accidents and lessen the loss triggered by fire accidents in tank farms.
查看更多>>摘要：? 2022 Elsevier LtdThe material microstructure of plays an important role in crack initiation of rolling contact fatigue. To address crack initiation of tapered roller bearings, the inhomogeneous characteristic of material is considered. The random distribution of material grains is simulated with Voronoi graph, and a Voronoi finite element model of rolling contact fatigue is given. Numerical analysis of damage-life constitutive relation is carried out with finite element analysis. The effect of material microstructure inhomogeneity on initiation life of fatigue crack is studied. Researches show that the smaller the grain size, the more difficult the fatigue crack appearing. The larger the difference of elasticity modulus between non-metallic inclusions and matrix material, the greater the impact on fatigue life of crack initiation. The angular and sharp non-metallic inclusions reduce fatigue life more than rounded shape inclusions. Initiation life of fatigue crack has a minimum value on a critical depth of nonmetallic inclusion. The longer distance between two laterally arranged inclusions, the greater it affect the initiation life of fatigue crack. The effect of distance between two vertically arranged inclusions on fatigue crack initiate depends on the depth of inclusions.
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