查看更多>>摘要：Present work provides a detailed failure investigation of a hydraulic lathe chuck assembly that comprises a plunger, three jaws, and three jaw-carriers that are made of carburized, tempered and sub-zero treated EN36C steel. The chuck assembly suffered premature failure of the plunger and one of the jaw carriers during the service in a CNC lathe. The investigation comprises a detailed metallurgical failure analysis involving: visual inspection, fractography, metallography, and hardness measurements. The analysis concludes that plunger failed first by fatigue fracture that is originated at a sharp corner of a T-slot. The mating jaw-carrier failed in the next event due to instant misalignment and overstressing during the lathe operation. The investigation concludes that design flaw and improper heat treatment cycle as the reasons for the premature failure of the assembly. Through experimental simulation of the heat-treatment cycles using EN36C specimens, the work suggests that carburizing, cryogenic treatment and then tempering is the proper sequence for achieving the best combination of mechanical properties that should extend the service life of the chuck-assembly.
查看更多>>摘要：Identifying causations and failure analysis at the onset holds a key to ensure LPG (liquefied petroleum gas) tank trailer transport safety state and prevent similar failures. Current study presents an unexpected accident by LPG tank trailer, which triggered a massive LPG dispersion and destructive explosion. After the post-accidental scene reconstruction by computational approach, the occurrence of pressurized tank burst and continuous dispersion were detected as an active failure analysis. Macroscopic investigation of the explosion phenomenon involving LPG tank trailer suggested that the causation was responsible for vapor cloud explosion. Hazardous parameters regarding the LPG release, dispersion, explosion shock wave and thermal radiation were represented to identify the mechanisms of potential damages by obtaining at multi-directional area. The visual graphics of flammable gaseous mixtures dispersion showed that the ambient factors imposed great influence on explosive energy reserve in different areas, which were not in accordance with the actual accident scene. The results revealed that the reflected and disturbed effects significantly increased the shock wave, causing more severe structural damage with dense obstacles and elevated flame. A large amount of released gaseous mixtures accumulated, resulting in much higher thermal intensity formed by fireball. This study proposed a failure analysis and classifications of LPG tank trailer accident by explosive destruction integrated with damage mechanism, which contributes to improve the hazard identifications and emergency response under LPG transportation accident sequences.
查看更多>>摘要：Aiming to better utilize the strength and slip capacity of Circular Openings with Transverse Rebar shear connectors when subjected to concrete confinement, situation in which failure mode is governed by the transverse rebar, an experimental program was specifically designed to isolate the mechanisms that develop locally in each confined opening and the influence exerted by different geometric and material parameters. Based on the experimental observations and analysis drawn from these tests, an analytical model capable of predicting whole load-slip curves was proposed and, with it, a parametric analysis was performed. The analytical model formulation is presented in the part 1/2 of this publication. This paper is the part 2/2 of the publication and presents 1) experimental results, observations, and analysis, 2) experimental validation of the proposed analytical model using experimental data from this work and from literature, and 3) a parametric analysis, in which it was investigated the influence that each of the connection's main geometric and material parameters exert on its strength and slip capacity. This parametric analysis, together with the experimental observations and the analytical model formulation, provide a deep understanding of the connection's behavior under confinement, which can be used for designing composite elements with optimized composite interaction and ductility.
查看更多>>摘要：Separation layer poses a potential threat to safety mining under an unconsolidated aquifer. A dynamic load will be generated when the upper stratum in the separation layer is broken, leading to an abnormal roof water-inrush. To explore this phenomenon, the 7130 coalface in Qidong coalmine is selected as an example, and the dynamic damage analysis is performed for overburden rock during mining by numerical simulation. A model is presented based on the continuum damage mechanics for simulating the failure of overburden rock under the dynamic load. A new dynamic damage variable is introduced into the model. Subsequently, a user-defined (U-D) model is implemented under the C++ language environment in FLAC-3D. The U-D model is applied to study the abnormal roof water-inrush of the 7130 coalface, compared with the MohrCoulomb (M-C) model in FLAC-3D. The research results show that a larger dynamic failed zone than the M-C model under the dynamic load exists. Additionally, the height of water-conducting fractured zone (WCFZ) by the U-D model is 68.6 m and conforms to the in-situ data of 56.9-80.2 m, while the height of WCFZ by the M-C model is only 35.6 m. It can be inferred that the effect of overburden dynamic damage can lead to the upward development of WCFZ, resulting in disasters of roof water-inrush. The study will be helpful to the prevention and control of roof water-inrush.
查看更多>>摘要：Aiming to better utilize the strength and slip capacity of Circular Openings with Transverse Rebar shear connectors when benefited by concrete confinement, situation in which failure mode is governed by the transverse rebar, an innovative analytical model capable of predicting the whole load-slip curve of the shear connection was proposed. This is the first analytical model in the literature capable of predicting the load-slip curve and slip capacity of a shear connector. This development has potential applications in structural ductility evaluation and composite interaction optimization. The model applies plasticity theory and combines different formulations of the literature to describe the different mechanisms that develop as the connection is subjected to slip between steel plate and concrete, including second-order catenary action in the rebar, deformation of concrete inside the opening, shear and friction at the slip interfaces. This paper is the part 1/2 of the work and presents the whole mathematical formulation of the model. In the part 2/2, the model is confronted with experimental results and is applied to perform a parametric analysis of the connection's behavior.
查看更多>>摘要：Engineering design methods based on the assumption of crack growth and the application of fracture mechanics principles are commonly used in aerospace engineering for the design of aluminum structures. In aerospace manufacturing, surface shot peening is one of the most widely used techniques for improving the fatigue performance of structural components. This work reviews the effect of different shot peening coverage on surface integrity and fatigue crack growth (FCG) properties of 7B50-T7751 aluminum alloy. The shot peening was applied to middle-crack tension (MT) specimens with four kinds of peening coverage: 100%, 300%, 600% and 1000%, respectively. The results showed that shot peening treatment reduced specimen surface roughness, moreover, surface shot peening promoted a maximum microhardness increased by 28.1% and induced compressive residual stresses in order of -412 MPa compared to untreated specimens. FCG experiment results showed that the effect of shot peening coverage on da/dN-Delta K curves was quite limited at constant amplitude loading. With the increase of shot peening coverage from 100% to 1000%, the FCG rate decreases first and then increase. At 300% of surface shot peening coverage, the FCG rate is the lowest, which results in the longest fatigue crack growth life.
NSTL
Elsevier