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To use distinct element simulation (PFC2D) to investigate the relationships between microparameters and macroproperties of the specimens that are modeled by bonded particles. To determine quantitative relationships between particle level parameters and mechanical properties of the specimens.

A combined theoretical and numerical approach is used to achieve the objectives. First, theoretical formulations are proposed for the relationships between microparameters and macroproperties. Then numerical simulations are conducted to quantify the relationships.

The Young's modulus is mainly determined by particle contact modulus and affected by particle stiffness ratio and slightly affected by particle size. The Poisson's ratio is mainly determined by particle stiffness ratio and slightly affected by particle size. The compressive strength can be scaled by either the bond shear strength or the bond normal strength depending on the ratio of the two quantities.

The quantitative relationships between microparameters and macroproperties for parallel‐bonded PFC2D specimens are empirical in nature. Some modifications may be needed to model a specific material. The effects of the particle distribution and bond strength distribution of a PFC2D specimen are very important aspects that deserve further investigation.

The results will provide guidance for people who use distinct element method, especially the PFC2D, to model brittle materials such as rocks and ceramics.

This paper offers some new quantitative relationships between microparameters and macroproperties of a synthetic specimen created using bonded particle model.

Negative Poisson’s ratio (NPR) material has huge potential applications in various industrial fields. However, lower Young’s modulus due to the porous form limits its further applications. Based on the topology optimization technique, this paper aims to optimize the structure consisting two isotropic porous materials with positive Poisson’s ratio (PPR) and NPR and void.

Under prescribed dual-volume fraction constraints, the structural compliance is taken as the objective. Young’s modulus and Poisson’s ratio are, respectively, interpolated and expressed with Lamé’s parameters for easier programming. Accordingly, the sensitivities can be derived through the chain rule. Several two- and three-dimensional illustrative examples are presented to demonstrate the capability and effectiveness of the proposed approach. The influences of Poisson’s ratios, volume fractions and Young’s moduli on the optimized results are investigated.

For NPR materials having unique load responses, the resulting topologies of PPR and NPR materials have distinct material distributions in comparison of the results from two PPR materials. Furthermore, it is observed that higher structural stiffness can be achieved from the hybrid of PPR and NPR materials than that obtained from the structures made of individual constituent materials.

A topology optimization methodology is proposed to design structures composed of PPR and NPR materials.

The purpose of this paper is to study the effect of the relative density and geometric parameters on the homogenised in-plane elasticity modulus of a cellular honeycomb structure using analytical and numerical approaches.

In this work, the mechanical behaviour of a new design of the honeycomb is analysed through a refined analytical model that is developed based on the energy theorems by considering the shearing and stretching effects in addition to bending.

By taking into account the various deformation mechanisms (MNT), the obtained results show that the values of elasticity modulus are the same for low relative densities, but the difference becomes remarkable for higher densities. Moreover, it is difficult to judge the effect of the relative density and anisotropy of the cellular structure on the values of the homogenised elasticity modulus without considering all the three deformation mechanisms in the analytical model. It is shown that conventional models overestimate the elasticity modulus, especially for high relative densities.

In this paper, a refined model that takes into account the three deformation mechanisms (MNT) is developed to predict the in-plane elasticity modulus of a honeycomb cellular material. It is shown that analytical models that describe the anisotropic behaviour of honeycomb cells can be improved by considering the three deformation mechanisms, which are bending, stretching, and shearing deformations.

This paper aims to simplify a new frequency-independent model to calculate vertical vibration of rigid circular foundation resting on homogenous half-space and subjected to vertical harmonic excitation is presented in this paper.

The proposed model is an oscillator of single degree of freedom, which comprises a mass, a spring and a dashpot. In addition, a fictitious mass is added to the foundation. All coefficients are frequency-independent. The spring is equal to the static stiffness. Damping coefficient and fictitious mass are first calculated at resonance frequency where the response is maximal. Then, using a curve fitting technique the general formulas of damping and fictitious mass frequency-independent are established.

The validity of the proposed method is checked by comparing the predicted response with those obtained by the half-space theory. The dynamic responses of the new simplified model are also compared with those obtained by some existing lumped-parameter models.

Using this new method, to calculate the dynamic response of foundations, the engineer only needs the geometrical and mechanical characteristics of the foundation (mass and radius) and the soil (density, shear modulus and the Poisson’s ratio) using just a simple calculator. Impedance functions will no longer be needed in this new simplified method. The methodology used for the development of the new simplified model can be applied for the resolution of other problems in dynamics of soil and foundation (superficial and embedded foundations of arbitrary shape, other modes of vibration and foundations resting on non-homogeneous soil).

Casing damage problems are increasingly prominent in oil fields, most of which were caused by casing external squeezing loads. The traditional calculation method of casing external squeezing loads is not very accurate now, especially in complex formation. The purpose of this paper is to propose a new calculation method to solve the problem of actual casing loads under above conditions.

Based on Lame’s model of elastic mechanics, a new calculation method of casing external squeezing loads is deduced. Comprehensive influence laws of the loads which caused by in-situ stress, internal pressure, formation parameters, cement annulus parameters and casing parameters are analyzed.

The paper provides a new calculation method of casing external squeezing loads, by which the dispersion effect of internal liquid pressure caused by casing wall material is eliminated. The main influence factors of casing external squeezing loads are in-situ stress and formation elastic modulus.

The model and boundary conditions used in the paper is based on elastic mechanics. The accuracy of the calculation results depends on the quality and accuracy of the input formation parameters.

This paper proposes a new method to calculate casing external squeezing loads. And compared with traditional methods, this method is more practical.

This paper aims to present the results of testing of low-strength concrete specimens exposed to elevated temperatures. These data are limited in the existing literature and do not exist in Pakistan.

An experimental testing programme has been employed. Cylindrical specimens of 100 × 200 mm were used in the testing programme. These were heated at temperatures which were varied from 100°C to 900°C in increment of 100°C. Similar specimens were tested at ambient temperature as control specimens. The compressive and tensile properties of heat treated specimens were determined.

The colour of concrete started to change at 300°C and hairline cracks appeared at 400°C. Explosive spalling was observed in few specimens in the temperature range of 400°C-650°C which could be attributed to the pore pressure generated by steam. Significant loss of concrete compressive strength occurred on heating temperatures larger than 600°C, and the residual compressive strength was found to be 15 per cent at 900°C. Residual tensile strength of concrete became less than 10 per cent at 900°C. The loss of concrete stiffness reached 85 per cent at 600°C. Residual Poisson’s ratio of concrete increased at high temperatures and became nearly six times larger at 900°C as compared to that at ambient temperature.

The parameters of the study included heating temperature and effects of temperature on strength and stiffness properties of the concrete specimens.

Building fire incidents have increased in Pakistan. As a large number of reinforced concrete (RC) buildings exist in the country, the data related to elevated temperature properties of concrete are required. These data are not available in Pakistan presently. The study aims at providing this information for the design engineers to enable them to assess and increase fire resistance of RC structural members.

The presented study is unique in its nature in that there is no published contribution to date, to the best of authors’ knowledge, which has been carried out to assess the temperature-dependent mechanical properties of concrete in Pakistan.

THE main object of this paper is to help bridge the gap that exists between the scientific knowledge of materials and the practical application of that knowledge to the production technique of sheet‐metal forming. During the past year the Production Research Group of Lockheed's engineering department has given special attention to this important problem and has worked closely with the production departments in an effort to put sheet‐metal forming on a scientific basis. The following discussion is based largely on the work of the Production Research Group, as reported in various references and in papers yet to be published. Mr. William Schroeder and Mr. G. A. Brewer of this group have been particularly helpful to the author in the preparation and editing of the technical material. Because of the scope of the present paper, detailed discussion and analysis of new developments cannot be undertaken; however, such information will be made available as soon as possible in the form of individual papers by those directly responsible for the work.

The problems of inelastic instability (buckling) and dynamic instability (resonance) have been the subject of extensive investigation and have received wide attention from the structural mechanics community. This paper aims to tackle these problems in thin-walled structures, taking into account geometrical and/or material non-linearity.

The inelastic buckling mode interactions and resonance instabilities of prismatic thin-walled columns are analysed by implementing the semi-analytical finite strip method (FSM). A scalar damage parameter is implemented in conjunction with a material modelling named rheological-dynamical analogy to address stiffness reduction induced by the fatigue damage.

Inelastic buckling stresses lag behind the elastic buckling stresses across all modes, which is a consequence of the viscoelastic behaviour of materials. Because of the lag, the same column length does not always correspond to the same mode at the elastic and inelastic critical stress.

This paper presents the influence of mode interactions on the effective stresses and resonance instabilities in thin-walled columns due to the fatigue damage. These mode interactions have a great influence on damage variables because of the fatigue and effective stresses around mode transitions. In its usual semi-analytical form, the FSM cannot be used to solve the mode interaction problem explained in this paper, because this technique ignores the important influence of interaction of the buckling modes when applied only for undamaged state of structure

Finite element analysis (FEA) has been carried out utilizing the ANSYS software package to assess the failure of thick and thin‐walled steel cylindrical pressure vessels. A simple experimental stress analysis (ESA) procedure is described to evaluate the stress components on inner and outer surfaces of the vessels under internal pressure from the measured surface strains. The procedure is validated considering the strain values of FEA for the applied pressure as measured quantities and obtained the corresponding stress components considering the stress‐strain data of the material from ESA and compared with those of FEA results. Failure pressure estimates from FEA (based on the global plastic deformation) were found to be in good agreement with test results of thin as well as thick‐walled cylindrical vessels made of ductile steel materials.

Natural gas hydrate (NGH) has been regarded as one of the most important resources due to NGH's large amounts of reserve. However, NGH development still faces many technical challenges, such as low production rate and reservoir instability resulting from NGH decomposition. Therefore, developing a fully coupled THMC model for simulating the hydrate decomposition and studying its mechanical behavior is very important and necessary. The purpose of this article is to develop and solve a multi-phase, strong nonlinearity and large-scale fully coupled thermal-hydro-mechanical–chemical (THMC) model for simulating the multi-physics processes involving solid-liquid-gas flow, heat transfer, NGH phase change and rock deformation during NGH decomposition.

In this paper, a multi-phase, strong nonlinearity and large-scale fully coupled THMC model is developed for simulating the multi-physics processes involving solid-liquid-gas flow, heat transfer, NGH phase change and rock deformation during NGH dissociation. The fully coupled THMC model is solved by using a fully implicit finite element method, in which the gas pressure, water pressure, temperature and displacement are taken as basic unknown variables. The proposed model is validated against with the experimental data, showing high accuracy and reliability.

A multi-phase, strong nonlinearity and large-scale fully coupled THMC model is developed for simulating the multi-physics processes involving solid-liquid-gas flow, heat transfer, NGH phase change and rock deformation during NGH decomposition. The proposed model is validated against with the experimental data, showing high accuracy and reliability.

Some assumptions are made to make the model tractable, including (1) the composition gas of hydrate is pure methane; (2) the gas-liquid multi-phase flow in the pore obeys Darcy's law; (3) hydrate occurs on the surface of soil particles, both of them form the composite consolidation material; (4) the small-strain assumption is applied to composite solid materials, which are treated as skeletons and cannot be moved; (5) momentum change caused by phase change is not considered.

NGH has been regarded as one of the most important resources due to its large amounts of reserve. However, NGH development still faces many technical challenges, such as low production rate and reservoir instability resulting from NGH decomposition. Most of the existing studies decouple the process with solid deformation and seepage behavior, but the accuracy of the numerical results will be sacrificed to certain extent. Therefore, it is very important and necessary to develop a fully coupled THMC model for simulating the hydrate decomposition and studying its mechanical behavior.

NGH, widely distributed in shallow seabed or permanent frozen region, has the characteristics of high energy density and high combustion efficiency (Yan et al., 2020). A total of around 7.5 × 1,018 m³ has been proved to exist around the world and 1 m³ of NGH can release about 160–180 m³ of natural gas (Kvenvolden and Lorenson) under normal conditions. Safely and sustainably extracting NGH commercially can effectively relieve global energy pressure and contribute to achieving carbon reduction goals.

The novelty of the present work lies in mainly two aspects. First, a fully coupled THMC model is developed for studying the multi-physics processes involving solid-liquid-gas flow, heat transfer, NGH phase change and solid deformation during NGH dissociation. Second, the numerical solution is obtained by using a fully implicit finite element method (FEM) and is validated against experimental data.