Elasto-plastic Material Properties Research Articles

Study on postbuckling of axial compressed elastoplastic functionally graded cylindrical shells

ABSTRACTPostbuckling of plates and shells is an important and cumbersome problem in the structural stability field. Presently, postbuckling behaviors of elastoplastic functionally graded cylindrical shells are investigated by a numerical simulation. The elastoplastic material properties are assumed to be of a multilinear hardening type, according to the constituent distributions, and are modeled using the laminate method. The Riks algorithm is used to obtain the equilibrium path. The postbuckling deformation and stain history of elastoplastic functionally graded cylindrical shells are investigated and various effects of the shell thickness and the constituent distributions are discussed. The results show material unloading effects in the postbuckling state.

Buckling and postbuckling of elastoplastic FGM plates under inplane loads

Elastoplastic buckling behaviors of rectangular plates made from functionally graded materials (FGMs) are investigated in this paper. The elastoplastic material properties are assumed to vary smoothly through the thickness of the plates. The three dimensional material constitutive relation of FGMs is found by introducing the material homogenization method, named Tamura-Tomota-Ozawa(TTO) model, into J2 deformation theory or J2 flow theory. The uniform strain hypothesis helps to simplify the prebuckling state and derive the analytical expression of the position of the material elastoplastic interface. The buckling governing equations and the buckling critical condition of the structures are formulated under the framework of the classical plate theory. An iterative algorithm is designed to obtain the elastoplastic buckling critical load, a converging result between the prebuckling and the buckling critical internal forces. ABAQUS simulation well verifies the present theoretical predictions from J2 flow theory, and is resorted to investigate the postbuckling behaviors of FGM plates. Discussions are addressed for the effects of the constituent distribution, the material plastic flow, the preloaded states of the plates, and the regions of buckling types are plotted as well.

Measuring elasto-plastic properties of solid wall materials of metallic foams at elevated temperatures by using indentation hardness technique

To evaluate or design metallic foams at the meso-level for applications at high temperatures, an indentation method is extended to measure the Young’s moduli, the yield strengths and the strain hardening exponents of the cell wall materials. The method was verified against a type of aluminum foam and the elasto-plastic properties of the aluminum cell walls were measured at various temperatures up to 400 °C. An approximate linear temperature dependence is observed for the hardness, the Young’s modulus and the yield strength. The present study provides a feasible way to investigate the meso-mechanical behavior of foam materials at high temperatures.

Improvement of squeezing ground prediction and monitoring capabilities for Mount Isa Mines Northern 3500 orebody

This paper investigates readily incorporable improvements to the identification of squeezing ground conditions and the determination of the depth of movement for Mount Isa Copper Operations’ Northern 3500 (MICO N3500) orebody. Numerical modelling using the boundary element method (BEM) indicated that the current use of elastic material properties to calculate the rockwall condition factor and predict tunnel squeezing is appropriate, as no apparent benefit was gained by employing elastoplastic material properties or including the tunnel void geometry. Further analysis using the finite element method indicated that complex, large-scale models would be required to make meaningful improvement on the elastic BEM model. However, due to large time and computational overheads such models are not practical within the site’s engineering workflow. In conjunction with numerical modelling, a prototype monitoring device was also developed to address the problem of rigid instrument shear and inspection camera obstruction when determining the depth of movement in a squeezing rockmass. The reverse downhole probe device will allow distance measurement and a live video feed to be returned to the excavation surface by taking advantage of stable ground beyond the excavation zone of influence and using a thin, flexible cable to transmit power and data.

Buckling resistance assessment of thin-walled open section element under pure compression

The paper deals with the problem of buckling resistance determination in case of perforated thin-walled elements. Depending on element slenderness the limit load in compression mode may be determined taking into account elastic (LBA analysis), elasto-plastic and plastic material properties (GMNA analysis). The limit load value is determined on the basis of thin-walled open section beam theory in case of elastic buckling and using Johnson-Ostenfeld approximation for elasto-plastic buckling. Obtained results are compared with finite element solutions derived using shell modelling and large deformation theory with Huber-Mises elasto-plasticity constitutive model without any geometrical imperfections. Some results of the carried out experiments are also shown.

Material property evaluation of particle reinforced composites using finite element approach

In this work, the elasto-plastic material properties of particle reinforced composites are evaluated using three-dimensional finite element approach. Effective properties of the composite are evaluated using representative volume element and numerical homogenization for kinematic and static boundary conditions. A computer program is developed to generate non-overlapping spherical particles of arbitrary size in an representative volume element. The numerical modeling of representative volume element containing the randomly distributed spherical particles of different sizes is performed by finite element method. Convergence study is performed to determine the suitable size of representative volume element. Homogenization is carried out for two cases i.e. matrix with soft and hard particles for reinforcement volume fraction up to 25%. A numerical comparison of 2-D and 3-D results is presented in terms of material behavior for matrix with soft particles.

Lagrangian Explicit Finite Element Modeling for Spin-Rolling Contact

Spin in frictional rolling contact can cause significant stress, which is the key to understanding and predicting the wear and fatigue behavior of contact components, such as wheels, rails, and rolling bearings. The lateral creep force arising from spin influences the kinematics of a wheelset and thus of vehicles. The solution that is currently employed in the field of elasticity and continuum statics was developed by Kalker and uses a boundary element method (BEM). In this paper, a new approach based on Lagrangian explicit finite element (FE) analysis is employed. This approach is able to consider arbitrary geometric profiles of rails and wheels, complex material behavior and dynamic effects, and some other factors. The new approach is demonstrated using a three-dimensional (3D) model of a wheel with a coned profile rolling along a quarter cylinder and can be easily adapted to apply to wheels and rails of arbitrary profiles. The 3D FE model is configured with elastic material properties and is used to obtain both normal and tangential solutions. The results are compared with those of the Hertz theory and the Kalker's model. The 3D FE model is then configured with elastoplastic material properties to study the spin-rolling contact with plasticity. The continuum dynamics phenomenon is captured by the FE model, which enhances the ability of the model to mimic reality. This improvement considerably extends the applicability of the FE model. The model can be applied to fatigue and wear analyses at gauge corners or rails as well as to deep groove bearings, where a large geometrical spin is present and plastic deformation may be of importance.

The mechanical properties of ionoplast interlayer material at high strain rates

Abstract Ionoplast material has been recently introduced and extensively used as interlayer material for laminated glass to improve its post-glass breakage behavior. Due to its sound mechanical performance, the applications of laminated glass with ionoplast interlayer have been widely extended to the protection of glass structures against extreme loads such as shock and impact. The properties of this material at high strain rates are therefore needed for properly analysis and design of such structures. In this study, the mechanical properties of ionoplast material are studied experimentally through direct tensile tests over a wide strain rate range. The low-speed tests are performed using a conventional hydraulic machine at strain rates from 0.0056 s−1 to 0.556 s−1. The high strain-rate tests are carried out with a high-speed servo-hydraulic testing machine at strain rates from approximately 10 s−1 to 2000 s−1. It is found that the ionoplast material virtually exhibits elasto-plastic material properties in the strain rate range tested in this study. The testing results show that the material behavior is very strain-rate dependent. The yield strength increases with strain rate, but the material becomes more brittle with the increase in strain rate, with the ultimate strains over 400% under quasi-static loading, and decreasing to less than 200% at strain rate around 2000 s−1. The testing results indicate that simply applying the static material properties in predicting the structure responses of laminated glass with ionoplast interlayer subjected to blast and impact loads will substantially overestimate the ductility of the material and lead to inaccurate predictions of structure response. The testing results obtained in the current study together with available testing data in the literature are summarized and used to formulate the dynamic stress–strain curves of ionoplast material at various strain rates, which can be used in analysis and design of structures with ionoplast material subjected to blast and impact loads.

2013 Bower Award and Prize for Achievement in Science presented to Kenichi Iga, Tokyo Institute of Technology, Tokyo, Japan

The mechanical behavior of materials can be modeled and evaluated across multiple scales that encompass: atomic and molecular rearrangements to create incipient defect nuclei; combination or growth of such nuclei to form micro-scale and subsequently macro-scale defects; and finally development of critical flaw sizes that result in final failure of engineering structures. Through an understanding of the mechanisms governing these processes, which depend on the loading conditions and the specific materials, new or modified materials systems designs can be integrated with advanced structural concepts to advance our energy, civil, transportation and healthcare infrastructures, among others.Subra Suresh׳s research includes development of novel experimental techniques and the discovery of new mechanistic processes that are broadly applicable to essentially every major class of natural and synthetic materials, including metals, ceramics, polymers, composites, biomolecules and biological cells. Beginning in the 1970s, he elucidated mechanisms of near-threshold fatigue crack growth in steels and aluminum alloys, contributing to improved alloy design for nuclear pressure vessels, fossil plants, offshore structures and aircraft. Subsequent work identified mechanisms for toughening brittle ceramics against fatigue crack growth under cyclic compressive loads. Turning to the microscale and the study of thin films, he developed new methods for extracting elastoplastic and functional properties of materials from small-volume contact probing. This led to new theories, computation and experiments on material and surface design through controlled gradients in composition and properties, and applications to coatings. At the nanoscale, he experimentally discovered nanocrystallization of bulk amorphous alloys during nanoindentation, and also showed how nanoscale twins could optimize the strength and ductility of fine grained metals. Most recently, he is noted for demonstrating the effects of disease-induced changes to human red blood cell deformability and biorheology, and for linking these changes to human diseases such as malaria.

2013 Benjamin Franklin Medal in Mechanical Engineering presented to Subra Suresh

The mechanical behavior of materials can be modeled and evaluated across multiple scales that encompass: atomic and molecular rearrangements to create incipient defect nuclei; combination or growth of such nuclei to form micro-scale and subsequently macro-scale defects; and finally development of critical flaw sizes that result in final failure of engineering structures. Through an understanding of the mechanisms governing these processes, which depend on the loading conditions and the specific materials, new or modified materials systems designs can be integrated with advanced structural concepts to advance our energy, civil, transportation and healthcare infrastructures, among others.Subra Suresh׳s research includes development of novel experimental techniques and the discovery of new mechanistic processes that are broadly applicable to essentially every major class of natural and synthetic materials, including metals, ceramics, polymers, composites, biomolecules and biological cells. Beginning in the 1970s, he elucidated mechanisms of near-threshold fatigue crack growth in steels and aluminum alloys, contributing to improved alloy design for nuclear pressure vessels, fossil plants, offshore structures and aircraft. Subsequent work identified mechanisms for toughening brittle ceramics against fatigue crack growth under cyclic compressive loads. Turning to the microscale and the study of thin films, he developed new methods for extracting elastoplastic and functional properties of materials from small-volume contact probing. This led to new theories, computation and experiments on material and surface design through controlled gradients in composition and properties, and applications to coatings. At the nanoscale, he experimentally discovered nanocrystallization of bulk amorphous alloys during nanoindentation, and also showed how nanoscale twins could optimize the strength and ductility of fine grained metals. Most recently, he is noted for demonstrating the effects of disease-induced changes to human red blood cell deformability and biorheology, and for linking these changes to human diseases such as malaria.

OS2-1 Identification of Elasto-plastic Material Properties from Measured Displacement Fields Using the Virtual Fields Method with Total Strain Theory(Digital image correlation and its applications (1),OS2 Digital image correlation and its applications,MEASUREMENT METHODS)

OS2-1 Identification of Elasto-plastic Material Properties from Measured Displacement Fields Using the Virtual Fields Method with Total Strain Theory(Digital image correlation and its applications (1),OS2 Digital image correlation and its applications,MEASUREMENT METHODS)

Alternative methods to determine the elastoplastic properties of sintered hydroxyapatite from nanoindentation testing

• The direct and inverse FE-models for nanoindentation tests are done. • A semi-empirical method is presented to calculate the hardening parameters of HA. • We examine the effect of sintering temperature on the mechanical properties. • An algorithm for the inverse technique is used to obtain elastoplastic material model. This study introduces alternative methods to determine the elastoplastic properties of bovine-derived Hydroxyapatite (HA) porous bone graft through a set of nanoindentation tests with a Berkovich indenter. Generally, experimental data obtained from nanoindentation tests are force displacement, hardness and elastic modulus. However, to determine plastic properties such as strength coefficient and work hardening exponent of bovine HA, analytical or inverse finite element models are required. In this paper, the effect of sintering temperature on these properties of HA is studied for the range of 1000–1400 °C. The direct and inverse Finite Element (FE) simulation models for nanoindentation tests were written in MSC, MARC ® software. A special algorithm for the inverse technique was developed to infer the most suitable elastoplastic material model for HA. A semi-empirical method was adapted to calculate the elastoplastic material properties of HA. The numerical results of harder hydroxyapatite showed better agreement with the experiments while the work hardening exponent, or n -value, and strength coefficient k of hard HA were found to be 0.23 and 8.05 GPa respectively. A comparison between the experimental and predicted load–displacement curves showed that the proposed inverse technique is effective in predicting the elastoplastic material properties from the nanoindentation test with error below 4% at maximum load.

Buckling of elastoplastic functionally graded cylindrical shells under combined compression and pressure

Buckling behaviors of elastoplastic functionally graded material cylindrical shells under combined axial compression and external pressure are investigated with classical shell theory. The material properties vary smoothly through the thickness, and a multi-linear hardening elastoplasticity is used in the analysis. By extending TTO model of functionally graded materials into J2 deformation theory, the elastoplastic constitutive relation of FGMs is founded. The buckling governing equations are solved by Galerkin method, and the expression of the critical condition under combine in-plane loads is given. Numerical results are given through an iterative procedure between the prebuckling state and the critical condition. Numerical results give the interactive curves of the stability regions and the exact elastoplastic interface of the materials. It is interesting to find that, material plastic flow is of significant effects on the stability region, and the effects of the constituent distribution and the elastoplastic material properties are discussed as well.

Identification of Elasto-plastic Material Properties with Full-field Surface Displacement Measurements

Identification of Elasto-plastic Material Properties with Full-field Surface Displacement Measurements

Investigation on buckling behaviors of elastoplastic functionally graded cylindrical shells subjected to torsional loads

In the present work, a semi-analytic solution is presented to analyze buckling behaviors of elastoplastic functionally graded circular cylindrical shells under torsional loads. The material properties vary smoothly through the shell thickness according to the power law distribution and a multi-linear hardening elastoplasticity of materials is included in the analysis. The Ritz energy method and both the flow and deformation constitutive theories help to develop the buckling government equation and the buckling critical condition. An iterative algorithm is resorted to derive the critical load and the buckling mode parameters. Numerical results reveal various effects of the constituent distribution of FGMs, dimensional parameters, and elastoplastic material properties. Meanwhile, the influences of material flow effect on buckling of elastoplastic FGM cylindrical shells are discussed.

MODEL ANALYSIS OF ELASTIC PROPERTIES OF COATING

The article describes a method of solving the problem of designing the friction surfaces withcomposite coatings. Despite the fact that many scientists have investigated the effect of coatings on theproperties of the items during the exploitation, however, has not yet been carried out a detailed study ofelastoplastic properties of the coating to the copper-containing material with different concentrations ofultrafine additions of copper, nickel, molybdenum disulfide. Elastoplastic properties of such materials isusually described by the relations of the deformation theory of plasticity.It is proved that the modeling of physical and mechanical properties, and varying the coatingcomposition can achieve a favorable combination of properties of the surface and the substrate. Proposed ofdesigning friction surface with composite coating, development an adequate model of the interaction ofsurfaces, which makes it possible to judge which components need to enter into the coating to obtain thedesired properties.

Composite structure modeling and mechanical behavior of particle reinforced metal matrix composites

The present work aims to investigate the relationship between the mechanical behavior and composite structure of silicon carbide (SiC) particle reinforced aluminum matrix composites. On account of newly developed particle size analysis technique, a large number of SiC particles are experimentally measured to provide statistical particular structural information. According to the statistical analysis and physical observations of SiC particles, the composite structures of SiC/Al composites are numerically reproduced in line with their actual microscopic structures, in which a developed structural modeling program can build the randomly dispersions of the particle sizes, the particle shapes, the particle positions and the volume fractions of SiC particles. Elastoplastic material properties, strengthened matrix properties and particle–matrix interfacial behaviors are introduced to simulate the mechanical behavior of SiC/Al composites. Enough fine meshes and reasonable loads and boundaries conditions can efficiently guarantee the computing accuracy and reduce the computing cost. A lot of simulating results of SiC/Al composites are provided and verified with the related experimental results. This work makes an effective attempt to establish the relationship between the actual composite structures and the mechanical behaviors within the particle reinforced metal matrix composites.

Numerical analysis of fatigue cracks growth in flexible pavements with the elastoplastic fracture mechanics method

In this paper the elastoplastic fracture mechanics method to analyse the fatigue damage of the flexible pavement has been applied. This approach is an appropriate alternative for analysing the fatigue cracking damage of a road pavement, with respect to traditional methodologies based on the use of the experimental fatigue laws of the bituminous mixtures. In this regard, a numerical method to evaluate the stress intensity factor at the edge of the crack has been used and the Paris' law to analyse the crack propagation into bituminous layer has been applied. Then, a comparison with the linear elastic fracture mechanic method and with the traditional approach based on the use of the fatigue laws has been carried out. A numerical example has shown the influence of the elastoplastic properties of the bituminous materials in the phenomenon of propagation of the fracture.

Estimation of the elasto-plastic properties of metallic materials from micro-hardness measurements

Although hardness testing is a cost-effective and reliable technique to quickly estimate the overall mechanical properties of materials, hardness is not a fundamental mechanical parameter and it is rarely used in constitutive modeling or in engineering design. This work proposes a procedure to derive the elasto-plastic properties of metallic materials from the Vickers and the Knoop hardness measurements. Through dimensional analysis and finite-element simulations, relationships between hardness testing variables and mechanical parameters (Young’s modulus, yield strength, and strain hardening exponent) are built up. An inverse procedure is developed to derive the mechanical parameters within the framework of genetic algorithm. The method is verified against two bulk steel materials and it is shown the derived stress–strain curves are in good accord with those measured by tensile tests. Then the method is successfully applied to measure the elasto-plastic properties of the pore walls of a metallic foam material. The present method can achieve a performance as good as those based on the instrumented indentation test and it is more readily accessible to the industry considering all the measurements can be performed on a cost-effective micro-hardness tester.

Characterization of stress-strain relationships of elastoplastic materials: An improved method with conical and pyramidal indenters

The load-displacement curve in indentation is widely used to extract elastoplastic properties of materials. It is believed that such a measurement is non-unique and a full stress-strain curve cannot be obtained with a sharp indenter or even plural and spherical indenters. By introducing a ratio of the additional residual area to the area of a profile indenter, we proposed a new set of dimensionless functions. Based on these functions and finite element simulations, analytical expressions were derived between indentation data and elastoplastic properties. It is shown that this method can effectively distinguish highly elastic and plastic solids (Cheng and Cheng, 1999) and mystical materials (Chen et al., 2007), which provides a useful guideline for properly using the indentation technique to measure elastoplastic properties of materials with conical and pyramidal indenters.