Taylor impact test is the simplest experimental approach for characterizing plastic behaviour of metals under high strain rate (up to 105 s−1). Herein, a cylindrical rod is impacted upon a rigid ...stationary anvil and the dynamic yield strength is estimated by comparing the experimentally obtained rod deformation with its theoretical counterpart. Despite being simple and potent concept, the lack of a comprehensive theoretical model (which relates the material constitutive with the deformation pattern of the rod) has so far restricted the use of the Taylor impact test in material characterization. In the present study the Taylor impact test is revisited and an attempt is made to formulate an inverse framework for efficient determination of constitutive parameters for metals. The inverse analysis is performed via the Extended Kalman Filter technique where the forward model is constituted based on the derivation given in Chakraborty et al. (2015). Unlike the common practice, for better estimation of material constants, the deformation time histories are also included in the present inverse formulation. For demonstration five different plasticity models viz Johnson–Cook model, Zerilli–Armstrong model, Steinberg–Cochran–Guinan–Lund model, Mechanical Threshold Stress model and Preston-Tonks-Wallace model are considered. The estimated parameters are found to be in good agreement with their reference values. It is shown that the most distinguished feature of the present attempt is that a single Taylor test is sufficient to determine the parameters with reasonable accuracy.
Leverage the power of basic Windows PowerShell scripts to manage your Exchange messaging environment About This Book * Get to grips with Windows PowerShell and how it can be used to manage various ...aspects of the operating system and applications * Become proficient in PowerShell and apply it to manage Exchange infrastructure on-premise or via Exchange Online as part of Office 365 * Learn to create Windows PowerShell scripts to do administrative tasks with this step-by-step, easy-to-follow guide Who This Book Is For This book is for administrators with a basic or limited understanding of Windows PowerShell and who want to increase their skill set in managing both the Exchange On Premise and Online environments. What You Will Learn * Deep dive into the Windows PowerShell basics * Create and manage Recipients and permissions * Manage Distribution Group members, permissions, and group types * Understand Certificates and Role-Based Access Control using real-world examples * Review the usage of email address, address book, and retention policies with examples * Learn to manage Exchange Client Access and Mailbox Server roles * Use PowerShell for auditing and risk management in your Exchange organization * Manage a highly available Exchange environment using PowerShell * Interact with Exchange through the use of the Exchange Web Services-managed API In Detail PowerShell has become one of the most important skills in an Exchange administrator's armory. PowerShell has proved its mettle so widely that, if you're not already starting to learn PowerShell, then you're falling behind the industry. It isn't difficult to learn PowerShell at all. In fact, if you've ever run commands from a CMD prompt, then you'll be able to start using PowerShell straightaway. This book will walk you through the essentials of PowerShell in Microsoft Exchange Server and make sure you understand its nitty gritty effectively. You will first walk through the core concepts of PowerShell and their applications. This book discusses ways to automate tasks and activities that are performed by Exchange administrators and that otherwise take a lot of manual effort. Microsoft Exchange PowerShell Essentials will provide all the required details for Active Directory, System, and Exchange administrators to help them understand Windows PowerShell and build the required scripts to manage the Exchange Infrastructure. Style and approach This book is written with its target audience in mind; concepts are explained and followed by real-life examples. A comprehensive script is provided in each chapter to give you hands-on practice with all the major commands used in it.
This paper explores the effect of evolutionary-type nonlinear energetic higher order stress inside the strain gradient plasticity framework that allows nonlinearity in dissipation. Based on the ...fundamental principles of thermodynamics, a multi-term Chaboche-type model has been formulated to describe the evolution of energetic moment stresses that depend on strain gradient and effective plastic strain. The derived evolutionary relation shows a coupling between energetic and dissipative length scales. The energetic part of the higher order stress, related to the GND formation, saturates as effective plastic strain increases during plastic flow. Higher order stress update equation and material tangent are derived using implicit time discretization. The proposed nonlinear energetic moment stress model confirms its applicability compared to experimentally observed responses. Our study demonstrates the importance of incorporating a nonlinear kinematic hardening rule to accurately represent the Bauschinger effect in samples with a thickness of less than 1μm. The cyclic bending experiment with a single slip sample shows that the nonlinear kinematic hardening rule can effectively capture nonlinearity in the experimental observation. Compressed shear layer simulation reveals that consideration of thickness-dependent relaxation coefficient accurately models the experimental observations. Thus, it makes further relevant consideration of a more advanced kinematic hardening rule through the proposed approach.
•A proposal for nonlinear energetic higher order stresses within the SGP framework.•Higher order stress evolution is similar to Chaboche-type evolution.•Higher order stress depends on plastic strain gradient and effective plastic strain.•Stress update and material tangent are derived using implicit time discretization.•The proposed model confirms its applicability compared to experimental responses.
The microwire torsion experiment holds significant importance in assessing the size effect at the micron and submicron scales. This paper introduces a model that examines the torsion of a microwire ...within a higher-order phenomenological strain gradient plasticity framework. The energetic consequences of plastic strain gradient are captured through a multi-term Chaboche-type nonlinear higher-order energetic stress evolution. This higher-order stress is linked to the formation of geometrically necessary dislocations (GNDs) and reaches saturation as effective plastic strain increases during plastic flow. The thermodynamically consistent framework demonstrates additional dissipation in the dissipation inequality. To simulate microwires, a comprehensive three-dimensional mixed finite element with displacement and plastic strain as variables is proposed. Subsequently, an axisymmetric version of the general 3D theory is derived for circular cross-sections using the micro-force balance equation, which takes into account both energetic and dissipative higher-order stress. A procedure for identifying hardening parameters from experimental torque-twist data is suggested. Comparative analysis between numerical responses and experimental observations highlights the effectiveness of saturation term(s) in the higher-order energetic stress evolution equation, as well as the influence of radius-dependent hardening parameters. The torsional behavior of a non-circular section indicates that the warping of the non-circular section diminishes with an increased strain gradient effect. Surface passivation enhances the wire’s strength by preventing GNDs from escaping the surface. However, non-uniform surface passivation disrupts the symmetry of the cross-section and leads to more warping.
•Proposal to assess size-dependent 3D torsion using a novel kinematic hardening rule.•An semi-analytical formulation is proposed and compared with the 3D FEM solution.•Proposal for identifying multi-term kinematic hardening parameters from experiment.•Kinematic hardening with equal L/R ratio can better predict the experiment.•Assessing torsion of non-circular section with nonuniform surface passivation.
•Proposal for full-field residual stress identification procedure from partially measured and corrupted measurement without eigenstrain information.•A mixed finite element approach, of ...Hellinger-Reissner type, is proposed within an inverse problem framework.•An energy based penalized least square approach is adopted to solve optimization problem.•Non-iterative reconstruction procedure is validated against a few problems of engineering interest.
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In this paper a full-field residual stress identification procedure is proposed and explored from partially measured residual elastic strain or stress within a PDE constrained optimization framework. At first, we have constructed a penalized least-square cost functional with an appropriate regularization term. We have taken data discrepancy term in energy norm while the regularization term is a complementary strain energy functional. We then construct an appropriate Lagrangian to impose the optimization constraint. It turns out that using first order optimality condition leads to standard two field mixed, of Hellinger-Reissner type, variational formulation with residual stress and Lagrangian variable as independent field variables. This allows us to use standard two and three dimensional mixed finite elements for approximation of the stress and Lagrangian variable. Using mixed finite element set-up, we then solved these equations to obtain full-field residual stress distribution. One key issue of the proposed formulation, as in case of any inverse problem, is the choice of penalization parameter. In this context, we have used modified L-curve based approach to choose optimal penalty parameter. Finally, we assess the numerical effectiveness of the proposed procedure against a few problems of engineering interest.
We have explored hyperelastic material parameter identification problem via minimizing trace of the error in constitutive relation function from partial and corrupted displacement measurements under ...quasi-static loading. The inverse problem is posed as an optimization problem where the cost function measures the error in constitutive relation due to a constitutively incompatible pair of stress and strain field. Incompatibility of stress and strain arises due to dissimilar constraints is imposed in generating these fields. An alternating approach is adopted to solve the optimization problem. A simple, yet effective, penalty based approach is adopted to generate strain field that weakly satisfy available measurements. While the regularization due to illposedness is achieved through the penalization parameter, this also allows us to consider partial and corrupted data map in our reconstruction strategy. After generating incompatible fields, desired reconstruction is obtained via minimizing the constitutive disparity. In the process we obtain explicit parameter update formula. Finally, we show the applicability and computational capabilities of the proposed method via limited number of numerical experiments.
•An ECE based parameter estimation technique for hyperelastic material is proposed.•Incompatible stress–strain pair is generated via two forward problems.•Penalty approach is adopted to generate strains that weakly satisfy measurements.•An alternating strategy is followed to solve the underlying optimization problem.•Explicit material parameter update formula is derived.
In this paper, a variant of constitutive equation error based material parameter estimation procedure for linear elastic plates is developed from partially measured free vibration sig-natures. It has ...been reported in many research articles that the mode shape curvatures are much more sensitive compared to mode shape themselves to localize inhomogeneity. Complying with this idea, an identification procedure is framed as an optimization problem where the proposed cost function measures the error in constitutive relation due to incompatible curvature/strain and moment/stress fields. Unlike standard constitutive equation error based procedure wherein a solution of a couple system is unavoidable in each iteration, we generate these incompatible fields via two linear solves. A simple, yet effective, penalty based approach is followed to incorporate measured data. The penalization parameter not only helps in incorporating corrupted measurement data weakly but also acts as a regularizer against the ill-posedness of the inverse problem. Explicit linear update formulas are then developed for anisotropic linear elastic material. Numerical examples are provided to show the applicability of the proposed technique. Finally, an experimental validation is also provided.
The scientific and intellectual Renaissance of Bengal in the late nineteenth and early twentieth century had acted as a major force in the triumph of independence of India and its progress towards a ...modern civilization. In the history of this new scientific awakening Acharya Prafulla Chandra Ray (1861-1944) occupies a significant position who realized the importance of science as integral to nationalist consciousness and nation building. Ray envisioned science to be a common concern of all humankind which was to be integrated with the development of a public use of reason and the emergence of Indian Nationalism through the establishment of national industry. In this paper my endeavour will be to locate Acharya Prafulla Chandra, not only as a scientist but also as an industrialist, a social thinker, an educationist and a cultural theorist who played a significant role in the social reformation, moral regeneration, economic development and political emancipation of India. In scrutinizing the corpus of Ray's writings on science, industry and society, I shall try to trace a consistent postcolonial strain in Ray that used the tools of mimicry and imitation to challenge the colonial apparatus.
A modified error in the constitutive equation-based approach for identification of heterogeneous and linear anisotropic elastic parameters involving static measurements is proposed and explored. ...Following an alternating minimization procedure associated with the underlying optimization problem, the new strategy results in an explicit material parameter update formula for general anisotropic material. This immediately allows us to derive the necessary constraints on measured data and thus restrictions on physical experimentation to achieve the desired reconstruction. We consider a few common materials to derive such conditions. Then, we exploit the invariant relationships of the anisotropic constitutive tensor to propose an identification procedure for space-dependent material orientations. Finally, we assess the numerical efficacy of the developed tools against a few parameter identification problems of engineering interest.
A modified error in the constitutive equation-based approach for identification of heterogeneous and linear anisotropic elastic parameters involving static measurements is proposed and explored. ...Following an alternating minimization procedure associated with the underlying optimization problem, the new strategy results in an explicit material parameter update formula for general anisotropic material. This immediately allows us to derive the necessary constraints on measured data and thus restrictions on physical experimentation to achieve the desired reconstruction. We consider a few common materials to derive such conditions. Then, we exploit the invariant relationships of the anisotropic constitutive tensor to propose an identification procedure for space-dependent material orientations. Finally, we assess the numerical efficacy of the developed tools against a few parameter identification problems of engineering interest.
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