Localization analysis of variationally based gradient plasticity model

The paper presents analytical or semi-analytical solutions for the formation and evolution of localized plastic zone in a uniaxially loaded bar with variable cross-sectional area. A variationally based formulation of explicit gradient plasticity with linear softening is used, and the ensuing jump conditions and boundary conditions are discussed. Three cases with different regularity of the stress distribution are considered, and the problem is converted to a dimensionless form. Relations linking the load level, size of the plastic zone, distribution of plastic strain and plastic elongation of the bar are derived and compared to another, previously analyzed gradient formulation.Comment: 42 pages, 11 figure

Localization Analysis of an Energy-Based Fourth-Order Gradient Plasticity Model

The purpose of this paper is to provide analytical and numerical solutions of the formation and evolution of the localized plastic zone in a uniaxially loaded bar with variable cross-sectional area. An energy-based variational approach is employed and the governing equations with appropriate physical boundary conditions, jump conditions, and regularity conditions at evolving elasto-plastic interface are derived for a fourth-order explicit gradient plasticity model with linear isotropic softening. Four examples that differ by regularity of the yield stress and stress distributions are presented. Results for the load level, size of the plastic zone, distribution of plastic strain and its spatial derivatives, plastic elongation, and energy balance are constructed and compared to another, previously discussed non-variational gradient formulation.Comment: 41 pages, 24 figures; moderate revision after the first round of review, Appendix A re-written completel

Analysis of size effect on strength of quasi-brittle materials using integral-type nonlocal models

The influence of the averaging operator of nonlocal continuum damage models near specimen boundaries on the size effect on strength of quasibrittle materials is investigated. Two phenomenological approaches, namely standard rescaling and distance-based models, are considered. The numerical results are compared to data from three-point bending tests of notched and unnotched beams recently reported in the literature. It is shown that both approaches can reproduce the experiments well for one type of geometry with one set of input parameters. However, only the distance-based model provides a good agreement for both unnotched and notched beams with the same set of parameters

Evaluation of nonlocal approaches for modelling fracture near nonconvex boundaries

Integral-type nonlocal damage models describe the fracture process zones by regular strain profiles insensitive to the size of finite elements, which is achieved by incorporating weighted spatial averages of certain state variables into the stress-strain equations. However, there is no consensus yet how the influence of boundaries should be taken into account by the averaging procedures. In the present study, nonlocal damage models with different averaging procedures are applied to the modelling of fracture in specimens with various boundary types. Firstly, the nonlocal models are calibrated by fitting load-displacement curves and dissipated energy profiles for direct tension to the results of mesoscale analyses performed using a discrete model. These analyses are set up so that the results are independent of boundaries. Then, the models are applied to two-dimensional simulations of three-point bending tests with a sharp notch, a V-type notch, and a smooth boundary without a notch. The performance of the nonlocal approaches in modelling of fracture near nonconvex boundaries is evaluated by comparison of load-displacement curves and dissipated energy profiles along the beam ligament with the results of meso-scale simulations. As an alternative approach, elastoplasticity combined with nonlocal or over-nonlocal damage is also included in the comparative study

Nonlocal Theories in Continuum Mechanics

The purpose of this paper is to explain why the standard continuum theory fails to properly describe certain mechanical phenomena and how the description can be improved by enrichments that incorporate the influence of gradients or weighted spatial averages of strain or of an internal variable. Three typical mechanical problems that require such enrichments are presented: (i) dispersion of short elastic waves in heterogeneous or discrete media, (ii) size effects in microscale elastoplasticity, in particular with the size dependence of the apparent hardening modulus, and (iii) localization of strain and damage in quasibrittle structures and with the resulting transitional size effect. Problems covered in the examples encompass static and dynamic phenomena, linear and nonlinear behavior, and three constitutive frameworks, namely elasticity, plasticity and continuum damage mechanics. This shows that enrichments of the standard continuum theory can be useful in a wide range of mechanical problems.

Financial Performance Feedback and R&D: A Comparison of Different Models

Purpose: Performance feedback either supports or undermines a firm’s current strategy. R&D is one of the most favoured proxies for a firm’s response to performance feedback and this relation complements the commonly studied influence of innovation (R&D) on a firm’s performance with a backward loop. The performance feedback literature works with a number of models used to empirically test these propositions and this study aims to compare the most common measures and models to locate potentially preferred alternatives for further research. Methodology/Approach: The research uses panel data with 1,558 observations. The sample consists of 208 US stock exchange listed firms followed over the years 2001-2015. Findings: The research suggests that models with separate historical and social aspirations may yield a slightly better fit with the data. However, the findings also indicate differences among R&D related dependent measures and their implications for empirical research. These differences arguably also reflect the underlying construct heterogeneity, therefore, researchers should work carefully with them to correctly explain their findings and provide results comparable to the previous literature. Research Limitation/implication: The limitations of the research rose mainly from the limited number of performance factors studied, which stems from an emphasis on standard financial performance indicators. Originality/Value of paper: The research contributes to the performance feedback literature by complementing a previous study that compared different aspiration models (Bromiley and Harris, 2014). By focusing on financial performance and R&D variables, the research offers the first concise entry point for researchers considering empirical studies on financial performance feedback and R&D relationship

The Organizational Life Cycle: Review and Future Agenda

Purpose: The review summarizes major research that contributed to the organizational life cycle theory, discusses major issues and contradictions of the theory and offers additional assumptions about the organizational life cycle. Based on that, it attempts to offer a future research agenda for the theory. Methodology/Approach: The paper uses narrative review; the list of included life cycle models stems from previous summaries of the theory and subsequent snowball search through reference lists of individual reviewed papers. Findings: The theory is rich with various life cycle models that nevertheless converge on some major characteristics. Organizational life cycle can be described with classical five stages: (i) founding, (ii) growth, (iii) maturity, (iv) decline, and (v) revival. However, the stages do not necessarily follow in such an order, and therefore the research establishes likely paths in their development. Also, it appears that growth rate (relative to a market) and change in formalism are major factors distinguishing in the theory individual stages. Research Limitation/implication: Organizational life cycle theory is often neglected based on simplifying presumptions like determinism of organizational development. On the other hand, there is a growing evidence that factors stemming from particular life cycle stages alter organizational behavior and therefore should be considered in behavioral research on an organizational level. Originality/Value of paper: The paper represents up to date review of major theoretical models from the perspective of the current state of the field. Since the theory flourished in 70’s and 80’s it is inevitably limited in some aspects. The new review may spark renewed interest in implications stemming from the theory and enrich analytical tools of management scholars