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This paper is devoted to developing an experimental/theoretical procedure for identifying yield criteria for powder materials. The experimental part includes several compression tests. The variation of the loading paths in these tests is achieved by deforming a plastically incompressible ring and powder material together. The description of the ring’s material behavior is not required to interpret experimental results, which is an advantage of the proposed method. The theoretical description of the test is provided using an analytical solution, which is also an advantage of the proposed method. The method is adopted for identifying Green’s yield criterion for aluminum powder. Comparison with other predictions of the yield criterion for this material is made.

Copyright of Eurasian Physical Technical Journal is the property of E.A. Buketov Karaganda University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Introduction. Being an integral part of the modern construction, concrete is a complex nonlinear material. The behaviour of concrete depends to a large extent on stress–strain state and loading history. Among the structures of newly constructed and reconstructed buildings, there are a large number of elements operating in the conditions of the triaxial stress–strain state, alternating and cyclic loading. A phenomenological material model used in the numerical methods can serve as a universal tool that allows to describe the behavior of concrete under such conditions. The aim of the research is to develop the concrete model that allows to simulate material behavior with sufficient accuracy under static short-term loading. The model should reflect the key features, which characterizes the behaviour of concrete and have an algorithm for regularizing the problem of localization of irreversible deformations.Materials and methods. This research is based on the analytical generalization and systematization of the data received from domestic and foreign sources devoted to the plasticity theory and fracture mechanics of concrete and reinforced concrete.Results. The model was implemented in the ANSYS finite-element software package, with the help of which it is possible to apply custom material models. Comparison of the laboratory and numerical results for concrete and reinforced concrete was made.Conclusions. The presented model allows to simulate behavior of concrete with substantial accuracy within the static short-term loading and reflects main features of the material behavior. To regularize the problem of localization of irreversible deformations, the model uses an approach based on the crack band theory. The values of all parameters required for the utilisation of the material model are presented.

This paper presents a novel plasticity-based formulation for three-dimensional (3D) topology optimization of continuum structures. The proposed formulation addresses the optimization problem by combining mixed rigid-plastic analysis with density-based topology optimization, resulting in a volume minimization approach. Unlike conventional stress-constrained topology optimization methods that rely on linear elastic structural analysis, our developed formulation focuses on enhancing the loading capacity of the designed structures based on the plastic limit theory, leading to more cost-effective designs. To improve computational efficiency, we employ the smoothed finite element technique in our proposed method, enabling the utilization of linear tetrahedral elements for 3D mesh refinement. Moreover, the final formulation of our developed method can be efficiently solved using the advanced primal–dual interior point method, eliminating the need for a separate nonlinear finite element structural analysis. Numerical examples are presented to demonstrate the effectiveness of the proposed approach in offering enhanced design possibilities for continuum structures. [ABSTRACT FROM AUTHOR]

The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years. However, how and to what extent the cement-enhanced soil influences the ultimate lateral resistance has not been fully investigated. In this paper, the ultimate lateral resistance of the composite pile was studied by finite element limit analysis (FELA) and theoretical upper-bound analysis. The results of FELA and theoretical analysis revealed three failure modes of laterally loaded composite piles. The effects of the enhanced soil thickness, strength, and pile-enhanced soil interface characteristics on the ultimate lateral resistance were studied. The results show that increasing the enhanced soil thickness leads to a significant improvement on ultimate lateral resistance factor (NP), and there is a critical thickness beyond which the thickness no longer affects the NP. Increasing the enhanced soil strength induced 6.2%–232.6% increase of NP. However, no noticeable impact was detected when the enhanced soil strength was eight times higher than that of the natural soil. The maximum increment of NP is only 30.5% caused by the increase of interface adhesion factor (α). An empirical model was developed to calculate the NP of the composite pile, and the results show excellent agreement with the analytical results.

Studies of language acquisition have shown that language learning ability declines with age. It has been documented that the overwhelming majority of learners who begin the process of second language (L2) learning after passing the critical period -- after a certain age - cannot attain native-like competence (underlying knowledge of language) at the end state. There is a universal folk belief, shared by almost all psycholinguists, that at an early age, the brain is plastic; it can modify its own structure, organization and function as a direct consequence of experiences and learning. According to this belief, the plasticity of the brain fades with age and with the increasing specialisation of the different hemispheres and areas of the brain. However, recently neuroscientists, equipped with the complementary aid of brain neuroimaging, have discovered that mature brain is far from being fixed as previously thought; it has the ability to continuously adapt its structure and function based on internal and external environmental changes and/or input such as experience, ageing, illness, injury and learning, meaning that the brain remains plastic throughout life. The purpose of this article, therefore, is to illustrate that the theory about the loss of brain plasticity during natural maturation is not valid in explaining the question why L2 learning is affected by delayed exposure to a language? It should be mentioned here that until now, the overwhelming majority of L2 researchers tend to think of plasticity as a phenomenon confined to early development; and therefore, evidence supporting plasticity is generally ignored. [ABSTRACT FROM AUTHOR]

The comprehensive determination of mechanical properties of heterogeneous objects such as welding joint remains challenging in various scientific fields. This paper develops a Local-micro-zone-wise Time-resolved Integrated Digital Image Correlation (LTIDIC) method, which can self-divide different regions of the material and get the multiple elastic–plastic parameters of each region through parameter inversion simultaneously, including elastic modulus, yield strength, hardening coefficient, and hardening exponent. First, the principle and process of the LTIDIC method are demonstrated, and the method of automatically dividing regions is introduced. Then, the reliability of the LTIDIC is analyzed and optimized, based on evaluating the influence of the correlation criteria, the area size, the noise type, and the number of pictures on the results of parameter inversion. Finally, a uniaxial tensile test was performed on the friction stir welding joint of aluminum alloy 6061T6 thin plate sample, and the distribution of multiple mechanical parameters was measured by the LTIDIC method. The results show that the modulus in the weld zone ranges between 30 and 70 GPa, with the lowest modulus in the thermo-mechanical affected zone and the highest modulus in the heat affected zone. The yield strength in the weld zone ranged from 75–115 MPa. The elastic modulus distribution shows an asymmetric W-shape, and the plastic parameters generally show a decreasing trend from the weld nugget to both sides. The feasibility and accuracy of the LTIDIC method were verified by comparing the consistency with the localized DIC method. The proposed method can obtain multiple elastic–plastic parameter distributions in different areas of material simultaneously through a single tensile experiment and provide important experimental data for the evaluation of mechanical properties of heterogeneous materials similar to welding joints. Highlights: 1. The developed LTIDIC method can obtain multiple elastic–plastic parameter distributions including elastic modulus, yield strength, hardening coefficient, and hardening exponent simultaneously through a single tensile experiment. 2. Automatically identify areas of heterogeneous materials with different mechanical properties. 3. The parameter inversion error is less than 1% by analyzing the factors that affect parameter identification. It can effectively reduce the influence of random noise on the inversion and improve the accuracy of the results. [ABSTRACT FROM AUTHOR]

The shear strength of prestressed concrete girders with a low amount of web reinforcement is an ongoing subject of research, in particular with regard to the assessment of existing concrete bridges. In this paper, a series of experiments is presented that addresses this question and at the same time significantly lowers the degree of longitudinal reinforcement in line with efficiently designed bridge cross‐sections and contrary to the vast majority of representative scaled test series. The limit case observations allow for a shear failure of the system even in the case of yielding longitudinal reinforcement due to the incremental strain in the tendons that could be activated. The focus of the presented analysis lies within the load‐dependent crack kinematics of the beam elements on the basis of the digital image correlation. It is shown that, depending on the longitudinal strain of the cross‐section, load‐bearing components associated with aggregate interlock do not seem to be mechanically reasonable and an extent of plasticity‐theoretical ideas through a compression chord component appears to be more consistent. [ABSTRACT FROM AUTHOR]

The residual stress generated during the welding process affects the mechanical properties of the material. In this study, a measurement method of residual stress fields in the friction stir welded zone is developed based on the plastic strain increment and Mises yield criterion. First, the relationship among the residual stress, the measured local yield strength, and the plastic strain increment is derived according to the Mises yield criterion. Then, through uniaxial tensile tests, the stress–strain curve of any point in the friction stir welded zone is obtained using the digital image correlation method. Finally, the distribution of residual stress around the friction stir welded zone is characterized by the derived relationship on the basis of accurately obtaining the local yield strength. The feasibility of the method developed in this paper for measuring residual stress is verified by comparison with the results of the mechanical method combined with the charge coupled device Moiré method. Additionally, other material parameters such as modulus and yield strength can also be measured at the same time. The proposed method is applied to a mechanical properties evaluation of the friction stir welded joint of an aluminum alloy 6061T6 thin plate. The results show that the residual stress around the weld is tensile, showing a bimodal distribution, and the peak value of the residual stress is located in the thermomechanical affected zone. The strength has a double-valley distribution, and the local yield strength of the thermomechanical affected zone is the lowest. The mechanical properties of the thermomechanical affected zone are relatively poor, and it is the location that is prone to fracture. [ABSTRACT FROM AUTHOR]

abstract: This paper analyses the behaviour of reinforced concrete beams subjected to progressive loads. Although this topic is addressed in recent works through tri-dimensional finite elements, the present study adopts a simpler alternative, using Euler-Bernoulli’s beam finite element. The evolution of the generalized cracking is addressed by Damage Mechanics theory, and the nonlinear constitutive models of concrete and steel are considered, including plasticity and post-peak ‘. The laminated approach permits not only to ascertain the damage evolution but, in practical aspects, makes easy to define vertically symmetrical transversal sections and to distribute the reinforcement as desired, even if the steel rebars have different lengths. It is highlighted the changing of the neutral axis during the damage evolution process, which is updated automatically by the developed numeric-computational code. To validate the proposed methodology, two examples are detailed, both based on experimental tests found in the literature. The results obtained are close to the experimental ones and confirm the applicability of the proposed approach.

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper analyzes the properties of the constitutive relations of the theory of plasticity for a continuum, which plastic properties depend on the type of stress state. The plasticity condition presented in the corresponding generalized form is used, where the parameter of the type of stress state is introduced, which is the ratio of the hydrostatic stress component to the equivalent von Mises stress, named in the literature the stress triaxiality. For a particular type of plasticity condition, an analytical solution of the problem for a solid with a circular hole under plane strain is obtained. The stress distributions corresponding to the obtained solution are compared with the ones for a solid whose plastic properties are invariant to the stress state using the Huber – Mises plasticity condition. The influence of the degree of sensitivity of materials properties to the type of stress state on the stress distributions in plastic areas are studied.

A plane closed problem of theory of plasticity has been formulated and solved. Generalizing factors of the problem solution are the argument functions for which differential dependencies are obtained in a form of Cauchy-Riemann and Laplace's equations. It is shown that differential equations with different purposes and with different physical quantities have the same solution formats, which allows using them to establish the connection between the mechanical characteristics of the process. Closed solution allows determining this connection. A multicomponent model of a plastic medium, depending on integral characteristics of a deformed state of the medium and its temperature, i.e. on thermomechanical processing parameters, is presented in the analytical form. Stress state calculations have been carried out for various methods of metal forming with pressure. Their comparability with a real distribution of contact stresses under symmetrical and asymmetric loading, determined by technological factors of production is shown. [ABSTRACT FROM AUTHOR]

Understanding of the mechanics of the brittle‐ductile transition (BDT) in porous limestone is significantly more challenging than for sandstone because of the lack of consistent acoustic emission activity in limestone, meaning that one must rely on alternative techniques. In this paper, we investigate systematically the failure modes in Indiana limestone using X‐ray microComputed Tomography imaging (μCT) and Digital Volume Correlation (DVC). Our new mechanical data show that the envelope for the onset of shear‐enhanced compaction can be well approximated by an elliptical cap. The DVC analysis revealed the development of shear bands through the BDT, but no evidence of compaction bands. The shear band angles were between 29° and 46° with respect to the maximum principal stress. Compiling these new results with published data on Purbeck and Leitha limestones, we showed that inelastic compaction in each of these dual porosity allochemical limestones was in a good agreement with the normality condition, as defined in plasticity theory. Comparison of the observed failure modes with predictions based on bifurcation analysis showed that the shear band angles are consistently smaller than the theoretical predictions. Plain Language Summary: A fundamental understanding of the brittle‐ductile transition (BDT) in porous sedimentary rocks is important in many geophysical and geological applications. In porous sandstone, a lot of our current understanding of both brittle and ductile behaviors is based on acoustic monitoring. In limestone however, the lack of consistent acoustic emission activity obliges us to rely on alternative techniques. In this paper, we investigated systematically deformation and failure in compression in Indiana limestone using X‐ray Computed Tomography imaging, a technique used to image density contrasts. Samples were scanned pre‐ and post‐deformation and image correlation was used to study the various failure modes. Our analysis revealed the development of shear bands through the BDT but no evidence of compaction bands. The shear band angles were between 29° and 46° with respect to the maximum principal stress. Compiling our new results with published data on Purbeck limestone, we showed that inelastic compaction in these allochemical limestones with double porosity (micro‐ and macro‐pores) was in a good agreement with the normality condition, as defined in plasticity theory. Comparison of the observed failure modes with theoretical predictions showed that the shear band angles are consistently smaller than the predicted ones. Key Points: New triaxial and CT data are presented on Indiana limestone of porosity 16%Digital Volume Correlation reveals several complex failure modes involving shear bands through the brittle‐ductile transitionThe onset of inelastic compaction in dual porosity allochemical limestones is in agreement with the normality condition [ABSTRACT FROM AUTHOR]

Based on the analysis of the results of experimental studies of 12Х18Н10Т stainless steel specimens under a rigid (controlled deformation) process of deformation, which includes a sequence of monotonic and cyclic loading modes, some features and differences in isotropic and anisotropic hardening processes under monotonic and cyclic loading are revealed. To describe these features within the framework of the theory of plasticity in the space of the plastic strain tensor, a criterion for changing the direction of plastic deformation and a memory surface are introduced, which made it possible to separate the processes of monotonic and cyclic deformation. To describe the transient processes, evolutionary equations are formulated for the parameters of isotropic and anisotropic hardening. The calculated and experimental changes in the stress-strain states are compared for the process of monotonic and cyclic loading. [ABSTRACT FROM AUTHOR]

This paper presents an appreciation of the importance of the paper “On the generalised stress-strain behaviour of ‘wet’ clay” by Roscoe and Burland (1968), which sets out the Modified Cam Clay (MCC) framework for understanding the behavior of clays. In the last 50 years MCC has become one of the most important theoretical tools for understanding and modelling soil behaviour. Here I present a number of different aspects of the influence of MCC, as a simple conceptual model which allows hand calculations, as the basis of numerical modelling software, as the starting point for some of the most sophisticated of constitutive models developed today, and as a vehicle for discussion of fundamental features of soil behavior as a scientific topic. [ABSTRACT FROM AUTHOR]

Based on experimental studies of specimens of 12Kh18N10T stainless steel under a rigid (strain-controlled) deformation process, which includes a sequence of monotonic and cyclic loading modes, some features and differences between isotropic and anisotropic hardening under monotonic and cyclic loading are found. To describe these features in terms of the theory of plasticity (the Bondar model), the criterion of change of plastic deformation direction and a memory surface are introduced in the space of the plastic strain tensor, which allow one to separate the processes of monotonic and cyclic loading. To describe the transitional processes, evolutionary equations for isotropic and anisotropic hardening parameters are formulated. The change in the stress-strain state during monotonic and cyclic loading, obtained by calculation and experiment, is compared. [ABSTRACT FROM AUTHOR]

The paper provides results of the study of correctness of the mathematical model that includes the influence of stresses on irradiation-induced swelling of metal in the problems of elastic-plastic deformation mechanics. The present-day approaches to modeling irradiation-induced swelling, which take into account a damaging dose, irradiation temperature, and the effect of the stress state on the swelling deformation, are discussed. The constitutive equations that describe the elasticplastic deformation processes allowing for the influence of a stress mode on the irradiation-induced swelling in metal are put forward. Analysis of these equations has made it possible to find the conditions that ensure correctness of the plasticity equations considered and to make a lower-bound estimate of the maximum permissible value of free swelling and irradiation dose. A priori estimates of the maximum permissible value of free swelling and damaging dose are given for 08Kh18N10T steel under various irradiation temperatures. In the practice of strength design such estimates are needed at the stage of problem formulation in order to analyze adequacy of input data, for they enable one to assess a prior the possibility of solving the problem for a given temperature and irradiation dose. The boundary-value problem that describes non-isothermal processes of elasticplastic deformation including swelling strains has been defined in the form of a nonlinear operator equation. Based on the findings regarding the correctness of the constitutive equations, we have established the existence and uniqueness of the generalized solution and its continuous dependence on applied loads, thermal strains and swelling strains. The convergence of the method of elasticity solutions and the method of variable elasticity parameters has been studied as applied to a thermoplasticity problem including irradiation-induced swelling strains. [ABSTRACT FROM AUTHOR]

In this article, the work of H. Hencky: "On the theory of plastic deformations and the residual stresses caused by them in the material" (Zur Theorie plastischer Deformationen und der hierdurch im Material hervorgerufenen Nachspannungen), which he presented in April 1924 at the first International Conference for Applied Mechanics in Delft and which in the same year appeared at ZAMM, is explained, commented on and placed in the context of the further development of plasticity theory. [ABSTRACT FROM AUTHOR]

This article proposes two constitutive models to describe the nonlinear, elastic-plastic behavior of unidirectional fiber-reinforced composites at the meso-level. Key ingredients are the formulation of two anisotropic yield functions with the aid of representation theorems (invariant formulation), and the set-up of governing equations for plastic variables with respect to associative and non-associative flow response. The governing equations are solved using an elastic predictor-plastic corrector algorithm which imposes the constraint posed by the yield condition. Both the models are evaluated qualitatively and quantitatively by comparison to micromechanics simulations as well as to experimental data. [ABSTRACT FROM AUTHOR]

Personal growth is not only a central individual need but also a key requirement for organizational success. Nevertheless, workplace interventions aimed at stimulating the personal growth of employees are still scarce. In this study, we investigated the effectiveness of an intervention that aimed at the identification, development, and use of employee strengths in stimulating personal growth initiative. We conducted a field experiment with a sample of 84 educational professionals who were either assigned to a strengths intervention or a wait‐list control group. In a 1‐month follow‐up study, we found that the intervention had a direct effect on general self‐efficacy (GSE) and an indirect effect on personal growth initiative. Moreover, in line with plasticity theory we found that the intervention was especially effective for participants with low to medium initial levels of GSE. We conclude that a strengths intervention may provide a brief and effective tool for organizations that aim for self‐directed learning among their staff, in particular when offered to employees who lack confidence in their own abilities. Practitioner points: In a 1 month follow‐up study, we found that a strengths intervention had a positive direct effect on general self‐efficacy and an indirect effect on personal growth initiative.In line with plasticity theory, we found that the strengths intervention was especially effective for participants with low to medium initial levels of general self‐efficacy. [ABSTRACT FROM AUTHOR]

Abstract Fracture process is investigated using finite-difference simulations with a new constitutive model. It is shown that both geometry and fracture mechanism itself depend on the preexisting heterogeneities that are stress concentrators. In the brittle regime (low pressure, P), Mode-I fractures propagate normal to the least stress σ 3 from the imposed weak zones. At high P , shear deformation bands are formed oblique to σ 3. At intermediate values of P , the fracture process involves both shear banding and tensile cracking and results in the initiation and propagation of pure dilation bands. The propagating band tip undulates, reacting on the failure mechanism changes, but its global orientation is normal to σ 3. The σ 3 -normal fractures are joints. There are thus two types of joints resulting from Mode-I cracking and dilation banding, respectively. The obtained numerical results are in good agreement with and explain the results from previous similar experimental study. [ABSTRACT FROM AUTHOR]

Existing approaches to cutting are analyzed. The advantages and disadvantages of each model are considered in detail. [ABSTRACT FROM AUTHOR]

Uniaxial compression tests in the grain (longitudinal) direction of solid wood were conducted using specimens of Sitka spruce and Japanese birch. The nonlinear stress-strain behavior was analyzed using plasticity theory, which is typically applied to ductile materials such as metals. The relationship between the longitudinal and tangential directions obtained from the experimental results showed nonlinearity, as predicted based on plasticity theory. Nevertheless, it was more pronounced in the experimental results than in the plasticity analysis.

In this study, a generic formulation for constitutive modelling of engineering materials is developed, employing theories of plasticity and continuum damage mechanics. The development of the proposed formulation is carried out within the framework of thermodynamics with internal variables. In this regard, the complete constitutive relations are determined by explicitly defining a free energy potential and a dissipation potential. The focus is put on the rigour and consistency of the proposed formulation in accommodating the coupling between damage and plasticity, while keeping its structure sufficiently generic to be applicable to a wide range of engineering materials. In particular, by specifying the coupling between damage and plasticity in the dissipation function, a single generalised loading function that controls the simultaneous evolution of these dissipative mechanisms is obtained. The proposed formulation can be readily used for either enriching existing plasticity models with damage, or for the developments of new coupled damage-plasticity models. The promising features and the applications of the proposed formulation for describing the behaviour of different engineering materials are discussed in details. [ABSTRACT FROM AUTHOR]

In this research, a discrete modelling approach employing a new cohesive model is proposed to investigate the failure response of cemented materials. A cohesive model considering mixed-mode fracture is developed based on a generic thermodynamic framework for coupling damage mechanics and plasticity theory. Discrete Element Method (DEM), a well-known computational method for simulating large deformation and cracking issues, is utilised as a numerical platform to facilitate the implementation of the proposed cohesive model. The nature of discrete modelling is analogous to the internal structure of cemented materials, making it more efficient compared with conventional continuum methods to characterise the failure behaviour of cemented materials. This combined cohesive-discrete modelling approach is then employed to simulate four experimental tests under different boundary conditions. Simulation results show excellent agreements with the experiments in terms of both macro force-displacement responses and cracking patterns, suggesting the effectiveness of the proposed modelling approach for conducting numerical experiments and exploring the failure mechanisms in cemented materials. [ABSTRACT FROM AUTHOR]

A constitutive model with an enhanced strain field is developed in this study for predicting the behaviour of unidirectional fibre reinforced composite materials. The different deformation modes introduced in the enhanced strain field take into account of both the variation of strains and internal equilibrium conditions across the fibre-matrix interfaces in unidirectional composites. This opens rooms to accommodate the difference in the responses of fibre and matrix and allows both fibre and matrix to be represented separately by their own constitutive responses. The enriching deformation modes and internal equilibrium conditions lead to a combination of both upper and lower bound solutions on different components of the stress/strain tensors, resulting a homogenised macro response that compares well with experimental data and sophisticated homogenisation approaches in the literature. In addition, the key feature of the proposed approach is that the macro homogenised behaviour can be written in terms of incremental responses of both constituents and their interactions, facilitating the applications in both linear and nonlinear regimes of behaviour of both fibre and matrix. In parallel with this, a new coupled damage-plasticity model is also developed for the matrix behaviour and validated against experimental data of two resins, before being used in the proposed approach. The performance of the model and its promising features are demonstrated through verification with existing benchmarking models and validation with experimental data in both elastic and inelastic regimes. [ABSTRACT FROM AUTHOR]