查看更多>>摘要：Mixed-mode crack growth is here investigated through experiments and computations for 34X and P2M steels, 7050 aluminium, and Ti-6A1-4V alloys in a compact tension shear (CTS) specimen. In this study, we use the mechanism-based strain gradient (MSG) plasticity theory to evaluate both crack tip dislocation density behaviour and the coupled effect of the material plastic properties and the intrinsic material length on local stress distributions. The constitutive relations are based on Taylor's dislocation model, which allows to gain insights into the role of the increased dislocation density associated with large gradients in plastic strain near cracks. The material model is implemented in a commercial finite element (FE) software package using a user subroutine, and the nonlinear stress intensity factors (SIFs) are evaluated as a function of the intrinsic material length. As a result of the FE calculations of dislocation density distributions, the effects of both the fracture mode and the stress-strain state are determined. Strain gradient effects associated with dislocation hardening mechanisms elevate crack tip stresses relative to conventional plasticity. Dislocation densities, stress fields and nonlinear SIF solutions are determined for experimental curvilinear crack paths by taking into account the transition from the initial Mode II crack to the mixed-mode fracture.
查看更多>>摘要：This paper presents laboratory and numerical analysis of vertical cut failure due to rainfall-induced landslide resulting in building failure that led to the death of nine people in Kerala, India, on August 15, 2018. The residual shear strength parameters are evaluated by the ring shear test. The soil water characteristics curve (SWCC) is developed by unsaturated soil strength parameters. The slope stability and infiltration analysis are carried out with limit equilibrium and finite element methods, respectively. The infiltration analysis is carried out by considering three different rainfall patterns on the slope as low, medium, and high intensities. The study includes a two-stage numerical analysis of vertical cut. Firstly, vertical cut analysis with and without rainfall effects and second, the analysis of vertical cut using coir geotextile as reinforcement with rainfall effects. The study emphasized the utilization of locally available coir geotextiles as a reinforcement for slope stabilization.
查看更多>>摘要：Numerous technical systems are modeled to identify dependability and safety measures. The modeling approach here is a real data driven approach. We work with the results obtained by assessing a progressive material-natural fibers reinforced laminate composites. The knowledge of certain properties, namely reliability performance, has not been sufficiently studied. Our approaches include the Wiener diffusion process, parametric and non-parametric estimations and mainly a hazard function which is estimated parametrically and non-parametrically by kernel estimators. We also demonstrate the significance between parametric and non-parametric estimations, the way they influence the selection of a resulting model and prospective practical applicability.
查看更多>>摘要：The wire arc additive manufacturing (WAAM) technology is a promising fabrication technique which has been proven to have many advantages for producing large structures; however, the fatigue and corrosion-fatigue performance of WAAM steel components for application in the marine environments is still unexplored. In this study, the WAAM technique was employed to fabricate four specimens made of ER100S-1 steel, which were then tested under cyclic loading conditions in seawater to assess the corrosion-fatigue crack growth (CFCG) behaviour and hence suitability of this fabrication technology for offshore renewable energy applications. The test duration, cracking mechanisms and CFCG rate were investigated for each specimen and the material's behaviour was investigated by considering the microstructural examinations. Furthermore, the obtained results were compared with the BS7910 standard recommended trends and experimental data available in the literature for conventionally built weldments made of different grades of steel which are commonly used for offshore applications.
查看更多>>摘要：? 2022Two industrial examples are described which demonstrate how environmental stress cracking (ESC) can give rise to unexplained, apparently random and catastrophic in-service part failures. In the two case studies, the companies could not identify the cause of failure through normal quality control procedures. Mild environmental stress cracking (ESC) was suspected and this project aimed to investigate and replicate the failures in a laboratory setting. The first case study involved ABS (acrylonitrile butadiene styrene) consumer parts which were exposed to an ester-based lubricant/glue during assembly. Samples were exposed to this product and aged at a range of temperatures (18–80 °C and at elevated humidity) for 6 months. The second case study involved medical grade LDPE (Low-density polyethylene) tubing for use in medical ventilators which was exposed to isopropanol as an assembly aid. The aim was to investigate whether adding an elastomer poly(ethylene–vinyl acetate), or if using an alternative solvent (methyl ethyl ketone) would reduce the likelihood of failure. In both case studies it was found that the failures were due to mild ESC. In the ABS parts it was due to the combination of the polymer, lubricant and residual stress from injection moulding. In the medical tubing, the failures were also determined to be as a result of ESC. It was found that blending the LDPE with an elastomer and using an alternative solvent reduced the likelihood of failure.
查看更多>>摘要：? 2022The failure of drill pipe occurs frequently in oil and gas wells and seriously affects the safety and efficiency of drilling operations. Therefore, this paper clarifies the main failure patterns and reasons of drill pipes, and puts forward the analysis process and method of pipe failures. The case of failure S135 drill pipe was investigated through a series of experimental tests and mechanical simulation. The results showed that the physical and chemical performance of pipe material met the requirements of API Spec 5DP-2020, and the fracture of pipe body belonged to overload ductile fracture. The drill pipe Ni-plating was damaged and the exposed matrix was corroded and scoured. The crack originated from the corrosion pit on the inner wall because of stress concentration, and extended along the circumference during the operation of lifting drill pipe for many times, and finally led to fracturing suddenly. In addition, some suggestions are given to prevent similar failures.
查看更多>>摘要：? 2022 Elsevier LtdWith the increase on the power density of diesel engine, the looseness of connecting rod small end bushing becomes one of the main faults. In order to solve this engineering problem, the swing friction test bench was utilized to investigate the bushing friction temperature increase under different working conditions. The results show that the highest temperature of the bushing can be close to 300 °C. To further analyze the influence of temperature increase on bushing looseness, bushing looseness tests were carried out at 25 °C, 25 → 100 → 25 °C(Heat from 25 °C to 100 °C, hold for 1 h, and then cool to 25 °C), 25 → 200 → 25 °C, and 25 → 300 → 25 °C. The test results show that the bushing looseness was greatly affected by the temperature increase, especially when the temperature was 25 → 300 → 25 °C. The maximum pressing force of QSn7-0.2 bushing was reduced by 83.9% at 25 → 300 → 25 °C compared with 25 °C. The anti-loosening ability of the bushing can be improved by replacing the CuNi6Sn6 bushing material with higher strength ones as the maximum pressing force of the bushing was higher even though the temperature increased to 300 °C.
查看更多>>摘要：? 2022 Elsevier LtdThe failure investigation of a thermocouple protective sheath tube made of UMCo-50 cobalt base alloy exposed to SO2-bearing hot gas in a sulfur refining furnace was systematically conducted. Various microstructural examination techniques were employed in order to clarify a root cause of failure. A tip portion of protective sheath tube remarkably revealed its severe material degradation after exposure to SO2-bearing hot gas in service for approximately 6 months. From the investigation, it turned out that the alloy was significantly prone to sulfidation attacks due to the formation of undesired chromium-rich carbides in its structure, which was accelerated by temperature fluctuation between 550 and 1100 °C during service. As a result, the protective sheath tube could not last for approximately 3 years as its design life.
查看更多>>摘要：? 2022 Elsevier LtdIn order to study the dynamic response similarity law of concrete gravity dam under explosive load, the theoretical similarity model of gravity dam under explosive load was established, and the air explosion similarity law experiments with scaling coefficients of 0.01, 0.0075, 0.005 and 0.0025 were carried out. The shock wave characteristic parameters of air explosion and the similarity of structural dynamic response were analyzed. The simulation calculation was used to verify and extrapolate the experimental results. The comparison results showed that there is a similarity law between the explosion dynamic response parameters of each scaling model obtained by simulation calculation and experimental fitting data, which meets the theoretical results of similarity law. The method of expanding the dynamic parameters of small scale scaling model to large scale model is reasonable and reliable.
查看更多>>摘要：? 2022The potential uplift failure of rock masses above a high-pressure gas storage tunnel is a serious concern for engineering designers, particularly when the burial depth of the tunnel is relatively small. To predict the uplift failure in such tunnels, two curved failure mechanisms for a single rock layer and multiple rock layers are proposed respectively in this paper. In the mechanisms, the influences of the ground load and arbitrary tunnel profiles are incorporated. Then the analytical solutions of the critical uplift pressure and the corresponding failure surfaces are derived on the basis of the upper bound theorem and variational principle. Further, the numerical simulation technique is utilized to validate the proposed method. An elliptical storage tunnel in two-layer rock strata is selected as a specific example for parametric investigation. The change laws of the critical gas pressure and uplift failure range corresponding to varying parameters are obtained. These results may practically provide theoretical references for the design and construction of gas storage tunnels in layered rock strata.
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