Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

Computer Methods in Applied Mechanics and Engineering

A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.

A review on high-pressure torsion (HPT) from 1935 to 1988

Using finite element modeling to examine the temperature distribution in quasi-constrained high-pressure torsion

Experiments and finite element simulations were conducted to measure the temperature increase in processing disc samples by high-pressure torsion. Aluminum, copper, iron and molybdenum were selected as model materials. The temperature increases at the early stages of straining but saturates to steady-state levels at large strains. The increase of temperature is proportional to the hardness and rotation speed and is higher at higher imposed pressures and is somewhat higher at larger distances from the disc center.

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Significance of temperature increase in processing by high-pressure torsion

https://www.witpress.com/Secure/elibrary/papers/RISK08/RISK08040FU1.pdf

Numerical simulation of leaking hydrogen dispersion behavior in a partially open space

The balancing domain decomposition (BDD) method is a well-known preconditioner due to its excellent convergence rate The BDD method includes the Neumann-Neumann preconditioner and a coarse grid correction Several studies have considered applications of the BDD method to various phenomena and improvement of its convergence rate However, in applying the BDD method to large-scale problems, it is difficult to solve the coarse problem of a coarse grid correction since the size of the coarse problem increases in proportion to the number of subdomains (ie, the size of the original problem) Other preconditioners with a coarse grid correction have the same problem To overcome this problem, use of a new preconditioner, namely, incomplete balancing domain decomposition with a diagonal-scaling (IBDD-DIAG) method is proposed in this study The method is based on the BDD method, and constructed by an incomplete balancing preconditioner and a simplified diagonal-scaling preconditioner Moreover, it is parallelized by the hierarchical domain decomposition method To evaluate this new approach, some computational examples of large-scale problems are demonstrated

Hiroshi Kanayama

Papers

Significance of temperature increase in processing by high-pressure torsion

Numerical simulation of leaking hydrogen dispersion behavior in a partially open space

An Inexact Balancing Preconditioner for Large-Scale Structural Analysis

Similarity consideration of the buoyant jet resulting from hydrogen leakage

A possible explanation for the contradictory results of hydrogen effects on macroscopic deformation