查看更多>>摘要：Electromagnetic high-speed nailing (E-HSN) has wide application prospect due to the advantage of high flexibility, unilateral operation and excellent performance. In this paper, the fatigue behavior of E-HSN joints with the aluminum alloy 5052 (Al)/high-strength steel DP590 (HSS) structure was systematically studied. The fatigue tests were conducted and Basquin equation was used to fit the fatigue data. Fatigue fracture were observed. The results showed that the joint had two typical fatigue failure modes. The cyclic stress of 253 MPa was the critical point of two failure modes. The rivet shank fractured under a higher cyclic stress (mode 1, over or equal to the critical point) and rivet head fractured under a lower cyclic stress (mode 2, below the critical point). Moreover, the fracture appearance was analyzed to reveal the failure mode and mechanism of the joints. The quasi-cleavage fracture in the fatigue fracture mode 1 was characterized by ductile and brittle mixed fracture. For the fatigue fracture mode 2, cleavage cracks appeared cleavage fan shape due to the large-angle grain boundary. Finally, based on the damage evolution model, the fatigue life prediction values of E-HSN joints were obtained. The predicted results were basically distributed within 2 times error band, which showed good accuracy and consistency.
查看更多>>摘要：An underground gas storage company adopted bimetallic composite pipes for gas transmission. The pipelines were inspected with industrial camera, it was found that a large number of pipelines had liner collapsed, and some of collapsed liner had suspected cracks. In order to analyze the reasons for the collapse and cracking of the liner, visual inspection, non-destructive testing, material examination, crack analysis, bend fatigue test and pressure test were conducted. The results showed that the material properties of the bimetal composite pipe meet standard requirements. The external pressure test was imposed on phi 168 composite pipe, the liner collapse under the pressure of 1.76 MPa which is lower than the calculated value. The cause of collapse was analyzed from manufacturing process and service condition. There are micro-cracks around the main crack of the liner, the fracture showed fatigue striations and thickness thinning characteristic. The root cause of the liner collapse is that the water enters the interlayer during the manufacturing of bimetallic composite pipe, and the thermal expansion coefficient of base pipe and lining pipe is different. When external anti-corrosion coating was manufactured and temperature changed during operation, collapse tendency of the liner increased. The root cause of the crack of the liner is bending fatigue, and the load originates from pressure fluctuations during operation. In order to avoid such incidents, the online inspection should be performed for the effusion part of the pipeline to check whether the remaining wall thickness of the base pipe meets the requirements for safe operation. The carbon steel pipe with regular pigging was recommended for this application situation.
查看更多>>摘要：This article examines the failures of cabin sheet metal panels in depth. The truck cabin segments' failures are examined in relation to one another. The failure distributions are evaluated to determine their correlation coefficients and then classified. The frequency of failures in cabin-in white (CiW) structural panels and cabin mount elastomeric bushings was determined in this investigation. Later investigation of the elastomer mount's stiffness fluctuation during field operation established that the fractures in the cabin panels were caused by the elastomer bush rotating out of position and resulting changes in transmissibility. Experiments conducted in a variety of working conditions established the existence of high stress zones predicted by finite element modeling. Finally, preventative measures are offered to avert such failures.
查看更多>>摘要：SA508Gr.4N steel is a novel Ni-Cr-Mo low-alloy steel for the new-generation reactor pressure vessel. Herein, a coarse-grained heat-affected zone (CGHAZ) in a P-doped SA508Gr.4N steel is simulated using Gleeble thermal cycling simulation with a peak temperature of 1320 degrees C under a heat input of 100 kJ cm(-1). For the as-simulated specimen, due to the synergistic effect of high residual stress and P grain-boundary segregation, the fracture appearance changes in the order of ductile fracture to intergranular fracture, and then to cleavage fracture with decreasing impact temperature. With the residual stress relieved by annealing at 620 degrees C, the specimen toughens to a certain extent even after ageing at 560 degrees C, causing a decrease in ductile-to-brittle transition temperature (DBTT), although the boundary cohesion declines to a certain degree owing to the increase of P segregation. Simultaneously, the intergranular-to-cleavage fracture transition temperature (ICFTT) shifts to a lower temperature below -190 degrees C, enabling the specimen to exhibit intergranular fracture even at -190 degrees C. With the ageing temperature lowered to 500 degrees C, the boundary segregation of P is raised to a high level, leading to a large increase in DBTT and a further decrease in ICFTT. Accordingly, the synergistic effect of residual stress and P boundary segregation affects the fracture nature of CGHAZ, thereby making fracture appearance have different characteristics. A mechanism diagram for the above effect is proposed based on the experimental results.
查看更多>>摘要：Based on the practical application requirements, the weld rotor was chosen as a preferable candidate to adapt to the higher steam temperature. In this study, the rupture behavior and fracture mode for the 9% Cr-CrMoV dissimilar welded joints are investigated. The specimens both rupture in the heat affected zone of CrMoV steel with a ductile rupture mode. The rupture time of the specimen under lower stress at higher temperature is shorter than that under higher stress at lower temperature. Additionally, the microstructure observation shows that the increased temperature can accelerate the precipitation and growth of the second phase particles. The microvoids caused by these particles can reduce the ductility of the welded joint and resultantly lead to the premature fracture.
NSTL
Elsevier