查看更多>>摘要：? 2022 Elsevier LtdThe paper addresses the analysis of the failure detected during a routine service inspection in an overhead porticoed structure for traffic signaling installed across the major north–south Spanish highway. The failure, which occurred after more than 30 years of service, consisted of the partial or full loosening of the bolts from the middle-span bolted joint and warned of a structural collapse. The failure analysis is based on the structural design data provided by the Spanish supervising authority for road and transportation and on exhaustive research regarding the structural integrity condition of the bolts removed from the dismantled joint. The experiments performed with the bolt material involve mechanical properties, fracture behavior with respect to the failure criterion of Eurocode 3 and fatigue resistance determination. These are accompanied by fractographic study and microstructural analysis of the bolts broken in-service. The analysis indicates that failure originated from environmentally induced fatigue initiators due to the environment aggressiveness and the galvanized condition of the bolts. The combination of these two factors caused local damage and weakening at the steel interface, after dissolution and microcracking of the Zn-coating protection.
查看更多>>摘要：? 2022 Elsevier LtdThe planet gear crack induced speed fluctuation is fully considered in the three effect factors of vibration signal like path weighting function, meshing forces and the measured-direction projection function. A series of phenomenon models of the vibration AM-FM signals of planet gear with tooth root crack are then developed by introducing three effect factors. The vibration AM-FM sidebands of cracked planet gear are finally obtained from the models, which are classified into two clusters that respectively locate at whole frequency range and harmonics of the meshing frequency. Harmonics of the fault feature frequency in the whole frequency range are modulated by the rotation frequency of carrier, which is obvious in the resonance ranges. Besides, harmonics of the meshing frequency are modulated by the fault feature frequency to form fault modulation sidebands, which are further modulated by the rotation frequency of carrier. The experimental results agree well with those obtained from the phenomenon models. The vibration signal models considering the cracked fault induced speed fluctuation perfect the models only containing the fault AM effect. The improved models clearly explain the sources of complicated vibration modulation sidebands even with small amplitudes, which provide a reliable theoretical basis for the detection of planet gear with tooth root crack.
查看更多>>摘要：? 2022 Elsevier LtdFretting wear is surface damage caused by repeated slight relative slips between two contact surfaces. In railway applications, the fretting wear may occur between the inner ring and the backing ring of an axle journal tapered roller bearing. The authors found that a nonuniform pressure distribution between the inner ring and the backing ring deteriorates the fretting wear; a backing ring grooved on its oil seal sliding surface has been proposed to attain a uniform distribution in the radial direction. In this paper, to further reduce the fretting wear, we have conducted a rotation test on a full-scale railway axle bearing with the backing ring both coated its contact surface to the inner ring with diamond-like carbon (DLC) film and grooved its outer surface, and investigated the combined effect of these two approaches on the fretting wear prevention. We have found that the wear prevention effect is superior to the backing ring with only DLC film, but partial decohesion of the DLC film occurs. It is conceivable that the DLC film delaminated from the contact surface of the backing ring due to the locally increased contact pressure between them, even though the grooved backing ring relaxed the contact pressure. We, therefore, conclude that the combined effect of the above approaches is not very apparent. To improve the combined effect of “the grooving” and “the conventional continuous DLC coating,” preventing the decohesion of the DLC film is a challenge. Additionally, we recommend that a continuous structured film be selected as hard film coating the grooved backing ring, which has higher bonding strength than DLC film and a lower friction coefficient.
查看更多>>摘要：? 2022 Elsevier LtdExperimental and numerical studies are performed to reveal an interrelation between mesoscale deformation-induced surface roughening and in-plane plastic strain in an aluminum alloy. Experimentally, roughness evolution in selected subsections of a uniaxially loaded specimen is examined using a stop-and-study technique. The experimental analysis is complemented by the micromechanical simulations for deformation-induced surface roughening in model polycrystals, with special attention being given to the texture effect on roughness characteristics. The experimental and numerical roughness patterns are analyzed in terms of a relative roughness parameter calculated as a ratio of the rough profile length to the profile evaluation length. This parameter is found to correlate exponentially with in-plane plastic strain with the coefficient of determination 0.99, which implies a strong interrelation between the two quantities. The results prove the assumption that in-plane plastic strains accumulated in a loaded material can be evaluated from the estimations of mesoscale surface roughness.
查看更多>>摘要：? 2022 Elsevier LtdMechanical performance and durability of CFRP/aluminum joints in accelerated corrosion environment have to be considered before designing composite-metallic hybrid structures. In this work, the corrosion behavior and mechanical properties of CFRP/aluminum stacks and riveted joints were evaluated by cyclic salt spray tests to simulate marine environments. The rivet head and aluminum substrate in coupled region experienced severe galvanic corrosion with heavy formation of corrosion products. CFRP laminate suffered substantial matrix swelling and even resin hydrolysis after continuously exposing to moisture environments. Joint strengths fluctuated very slightly while failure displacement gradually increased when interfacial corrosion between CFRP/Al stacks occurred. Corrosion products were identified by several characterization techniques with the corresponding corrosion mechanisms. In general, this work is expected to bring new knowledge to understand corrosion behavior and durability of rivet joints for the CFRP/Al stacks in accelerated corrosion environments and provide experimental results for benchmarking in particular designing CFRP-strengthened aluminum structures.
查看更多>>摘要：? 2022 Elsevier LtdIn recent years, ultra-high-performance concrete (UHPC) has been extensively used in orthotropic steel decks (OSDs) to improve their structural characteristics and extend their fatigue lives. In the present study, an experimental investigation was conducted on three full-scale rib-to-floorbeam welded connections to study the influence of utilizing UHPC overlay on fatigue behavior of such welded connection in OSDs. Two rear axle loads of HL-93 fatigue truck codified in the AASHTO specification were applied in the tests and the effect of longitudinal flexural were considered. Fatigue tests were conducted with full fatigue performance including the failure modes, crack initiation and propagation paths, fatigue lives, and vertical rigidity degradations fully reported. The obtained fatigue test results demonstrated that the application of UHPC overlay remarkably extended the fatigue life of the studied rib-to-floorbeam connections; the fatigue lives at the test end (Nf) were extended by 74.6% under the effect of the same hot spot stress range. The vertical rigidity of the two UHPC reinforced specimens were degraded by 12.3% and 7.3% compared to 15.1% for the unreinforced specimen, indicating that the UHPC reinforced specimens still have considerable load-carrying capacities until the fatigue failure. Moreover, it is demonstrated that the FAT100 fatigue curve provided in IIW fatigue design recommendations could be employed to predict the fatigue resistance of rib-to-floorbeam welded joints in OSDs.
查看更多>>摘要：? 2022 Elsevier LtdThis paper dealt with the mechanical property and failure mechanism of the dieless clinched joints of AL5052, AL5182 and AL6061 aluminum alloys. The cross-tensile test and lap-shear test were executed to assess the mechanical properties of various aluminum joints. Detailed fracture surface analyses were also performed to reveal the failure mechanisms of various aluminum alloy joints in different failure tests from both macro and micro perspectives. The forming curves, key geometrical parameters, static loads, absorbed energy, and fracture morphology of various aluminum alloy joints were obtained and analyzed. From the results, the AL6061 joint exhibits the most superior mechanical properties, i.e., the optimum static load and energy absorption, whereas the AL5182 joint exhibits the worst mechanical properties. Besides, although the macroscopic failure mode of various aluminum joints is the same, i.e., neck fracture mode, the joint microscopic failure mechanism varies with the types of sheet material and failure test.
Henrique de Souza Lima E.Manoel Pereira Carneiro A.
18页
查看更多>>摘要：? 2022 Elsevier LtdPrestressed concrete sleepers are being increasingly used for modern railways worldwide. The main advantages of this type of sleeper are its high mechanical strength, stability, and durability. However, there are challenges in ensuring that the prestressed concrete sleepers meet expected performance standards, as many concrete sleepers fail prematurely and need to be replaced every year. Such failures have already been responsible for large-scale railway accidents which have caused financial losses and endangered the safety of rail transport users. This paper proposes to review the current literature on the main deterioration mechanisms of prestressed concrete sleepers, discuss their causes and consequences, and suggest the main corrective and preventive measures that can be taken to minimize each problem. For ease of understanding, the failures have been separated into two groups: intrinsic failures, such as failures due to internal concrete deficiencies, and extrinsic failures, such as those associated with the high impact loads of railways and freeze–thaw cycles. In general, prestressed concrete sleeper failures manifest as cracking; the position and form of which is a good indication of the type of degradation. The causes of sleeper failures are almost always related to the poor maintenance of railroad tracks, poor conditions of the rolling stocks, and the use of inappropriate materials in the production of concrete, such as reactive aggregates.
查看更多>>摘要：? 2022The present study focuses on fracture mode of Zr-Sn-Nb cladding material under simulated LOCA condition. The results reveal that the oxidation share between 15% and 20% has little influence on the tensile strength. Microstructure analysis of cross-sectional and fracture morphology demonstrate that the fracture mode of Zr-Sn-Nb alloy oxidized at high temperature includes the brittle rupture of ZrO2, the cleavage fracture of α-Zr(O) layer, and a mixed ductile-brittle fracture of prior-β layer. Zr-Sn-Nb coupons exhibit brittle fracture features with the elongation below 0.34% at room temperature, while the plastic strain increases to ～10% at 350 °C in vacuum. The coupons cooled by water quenching have better tensile strength and worse elongation than those cooled by other modes. It is also found that the prior-β layer is composed of α-Zr phase, δ-Zr1.6 and γ-ZrH precipitates, and the composition can be greatly affected by the cooling modes.
查看更多>>摘要：? 2022 Elsevier LtdThe purpose of this study is to explore the influences of working temperatures on mechanical properties and the short circuit of cylindrical lithium-ion cells. A series of compression and three-point bending experiments of a typical 18,650 cylindrical lithium-ion battery is implemented during the discharging process in different working temperatures. The experimental results show that the working temperature presents a negative correlation with the onset of short-circuit in compression loading but non-significant effects on mechanical properties in three-point bending. For the discharging rate, there are non-significant effects on mechanical properties and short circuits of battery cells in both bending and compression loading experiments. In summary, the working temperature effects cannot be neglected in cylindric lithium-ion battery failure, and combined simulation and experimental results indicate that the short circuit criteria for a highly efficient FE battery cell modeling can be established based on internal stress in a specific direction.
NSTL
Elsevier