Search results

The purpose of this paper is to assess the hydrogen embrittlement sensitivity of carbon gradient heterostructure materials and to verify the reliability of the scratch method.

The surface-modified layer of 18CrNiMo7-6 alloy steel was delaminated to study its hydrogen embrittlement characteristics via hydrogen permeation, electrochemical hydrogen charging and scratch experiments.

The results showed that the diffusion coefficients of hydrogen in the surface and matrix layers are 3.28 × 10⁻⁷ and 16.67 × 10⁻⁷ cm²/s, respectively. The diffusible-hydrogen concentration of the material increases with increasing hydrogen-charging current density. For a given hydrogen-charging current density, the diffusible-hydrogen concentration gradually decreases with increasing depth in the surface-modified layer. Fracture toughness decreases with increasing diffusible-hydrogen concentration, so the susceptibility to hydrogen embrittlement decreases with increasing depth in the surface-modified layer.

The reliability of the scratch method in evaluating the fracture toughness of the surface-modified layer material is verified. An empirical formula is given for fracture toughness as a function of diffused-hydrogen concentration.

The purpose of this paper is to investigate, the effects of residual stress and microstructure on the corrosion behaviour of carburised 18CrNiMo7-6 steel in a 3.5% NaCl aqueous solution.

The electrochemical tests were conducted using an electrochemical workstation with a three-electrode system in a 3.5% NaCl aqueous solution, the residual stress of each working face was measured by a high-speed residual stress analyser, and microstructure of different carburised layers were observed scanning electron microscopy. Finally, the effect of carbon content, microstructure and residual stress on the corrosion behaviour of the steel was discussed.

The results showed that the residual compressive stress in the carburised layer initially increased and subsequently decreased with increasing depth of the carburised layer, reaching stability in the matrix layer. The electrochemical tests before and after stress reduction showed that the electrochemical impedance and the electrochemical potential increased with the reduction of residual compressive stress.

The residual compressive stress in the carburised layer initially increases and subsequently decreases with increasing carburised layer depth. The electrochemical impedance and the electrochemical potential increased with the reduction of residual compressive stress. The general relationship between electrochemical potential and residual stress was established.

The purpose of this paper is to find a new method to evaluate the hydrogen embrittlement performance of heterogeneous materials and thin film materials.

The changes of hydrogen embrittlement properties of steel were studied by electrochemical hydrogen charging test and scratch test. The microstructure and properties of the alloy were analyzed by hardness tester, scanning electron microscope and three-dimensional morphology. The fracture toughness before and after hydrogen charging was calculated based on the scratch method.

The results showed that the hydrogen-induced hardening phenomenon occurs in the material after hydrogen charging. The scratch depth and width increased after hydrogen charging. The fracture toughness obtained by the scratch method showed that hydrogen reduces the fracture toughness of the material. The comparison error of fracture toughness calculated by indentation method was less than 5%.

The results show that the scratch method can evaluate the hydrogen embrittlement performance of the material. This method provides a possibility to evaluate the hydrogen embrittlement of thin-film and heterogeneous materials.

The purpose of this paper is to find the best solver for parallelizing particle methods based on solving Pressure Poisson Equation (PPE) by taking Moving Particle Semi-Implicit (MPS) method as an example because the solution for PPE is usually the most time-consuming part difficult to parallelize.

To find the best solver, the authors compare six Krylov solvers, namely, Conjugate Gradient method (CG), Scaled Conjugate Gradient method (SCG), Bi-Conjugate Gradient Stabilized (BiCGStab) method, Conjugate Gradient Squared (CGS) method with Symmetric Lanczos Algorithm (SLA) method and Incomplete Cholesky Conjugate Gradient method (ICCG) in terms of convergence, time consumption, parallel efficiency and memory consumption for the semi-implicit particle method. The MPS method is parallelized by the hybrid Open Multi-Processing (OpenMP)/Message Passing Interface (MPI) model. The dam-break flow and channel flow simulations are used to evaluate the performance of different solvers.

It is found that CG converges stably, runs fastest in the serial way, uses the least memory and has highest OpenMP parallel efficiency, but its MPI parallel efficiency is lower than SLA because SLA requires less synchronization than CG.

With all these criteria considered and weighed, the recommended parallel solver for the MPS method is CG.

As a response to the growing operational and disruptive threats to water distribution networks (WDNs), researchers have developed a vast array of methods for the reliability analysis of WDNs. In order to follow this growing number of methods, this paper reviews and documents in one place the historical developments in the reliability analysis of WDN.

A systematic literature review (SLR) is carried out to summarize the state-of-the-art research on reliability analysis of WDNs. In conducting this systemic literature review, the authors adopted an iterative approach to define appropriate keywords, analyze and synthesize data and finalizing the classification results.

First, the hydraulic approach to reliability analysis is currently pervasive, and relatively little academic research has addressed the topological reliability analysis of WDNs. Second, in order to provide a comprehensive picture of the network reliability, a different approach that integrates topological and hydraulic attributes seems a more effective method. Third, the conventional reliability analysis methods are only effective for demonstrating a snapshot of these networks at a given point in time. The availability of methods that enable researchers to evaluate the reliability in response to changes in its variables is still a major challenge.

The present paper facilitates future research in the reliability analysis of WDNs by providing a source of references for researchers and water utilities. Further, this article makes a contribution to the literature by offering a roadmap for future reliability analysis of WDNs by reviewing the evolution of the current reliability analysis methods throughout history.