Reuleaux plasticity : improving Mohr-Coulomb and Drucker-Prager.

The yielding of soil exhibits both a Lode angle dependency and a dependency on the intermediate principal stress. Ignoring these leads to a loss of realism in geotechnical analysis, yet neither of the widely used Mohr-Coulomb (M-C) or Drucker-Prager (D-P) models include both. This paper presents a simple pressure-dependent plasticity model based on a modified Reuleaux (mR) triangle which overcomes these limitations and yet (like the M-C and D-P formulations) allows for an analytical backward-Euler stress integration solution scheme. This latter feature is not found in more sophisticated (and computationally expensive) models. The mR deviatoric function is shown to provide a significantly improved fit to experimental data when compared with the M-C and D-P functions. Finite deformation finite-element analysis of the expansion of a cylindrical cavity is presented, verifying the use of the mR constitutive model for practical analyses

The Effect of Ballistic Training on Punch Kinetics and Endurance in Trained Boxers

Strength and conditioning coaches are becoming increasingly aware of the importance of sport-specific movements when designing and implementing training programs for power development. The use of ballistic training (BT) for combat athletes, such as boxers, is growing in popularity, however there is a paucity of research on the effect of this method on punching kinetics and endurance. This study examined changes in punch kinetics and endurance following a six-week BT intervention. Forty-five participants (male n = 28, female n = 17; mean age = 28 ± 6.0 years, height = 1.8 ± .1 m, mass = 83.4 ± 15.2 kg) with a mean boxing experience of 11.3 ± 7.9 months were recruited for the study. Participants were sorted by self-reported boxing experience and then randomly assigned to either a control (CONTR) or experimental (BT) group. Participants in the BT group completed supervised training involving loaded ballistic exercises twice per week for six weeks. CONTR group participants completed supervised training twice per week for six weeks, with unloaded exercises performed at a slow and controlled tempo. Participants’ punch kinetics and endurance were examined before and after the 6-week training period using force plates. Results’ showed a 30% increase in maximum punch force (PFmax; p \u3c 0.001) and a 44% increase in rate of force development (RFD; p \u3c 0.001) in the BT group, throughout the 6-week training period. In contrast, CONTR group participants showed no change in PFmax and RFD over the course of the study. Increases in PFmax occurred despite no significant change in lead and rear foot forces. Although PFmax, the average of the PFmax across all punches within the first and third minutes, was shown to significantly increase in the BT group, a similar decrement in force output was observed between both groups post-intervention. Thus, BT exhibited little effect on punching endurance. The ability to produce high power outputs has been identified as a key variable in boxing performance. Consequently, power development should be a priority for strength coaches working with combat athletes. These coaches should consider how punch kinematics relates to force transmission. A distinct advantage of BT is its versatility as a training stimulus, whereby exercises aim to enhance force characteristics while replicating the movement patterns of the sporting task. The present data supports this notion and the inclusion of BT within a speed-strength phase prior to competition should be considered by coaches working with combat athletes

A Compact Geometrically Nonlinear FE Shell Code for Cardiac Analysis: Shell Formulation

There are few free open-source FE programs for 3D geometrically nonlinear shell elements that allow users to modify or extend the code. This paper presents such a MATLAB code which draws heavily on the work of Coombs and Coombs et al

Algorithmic issues for three-invariant hyperplastic Critical State models

Implicit stress integration and the consistent tangents are presented for Critical State hyperplasticity models which include a dependence on the third invariant of stress. An elliptical deviatoric yielding criterion is incorporated within the family of geotechnical models first proposed by Collins and Hilder. An alternative expression for the yield function is proposed and the consequences of different forms of that function are revealed in terms of the stability and efficiency of the stress return algorithm. Errors associated with the integration scheme are presented. It is shown how calibration of the two new material constants is achieved through examining one-dimesional consolidation tests and undrained triaxial compression data. Material point simulations of drained triaxial compression tests are then compared with established experimental results. Strain probe analyses are used to demonstrate the concepts of energy dissipation and stored plastic work along with the robustness of the integration method. Over twenty finite element boundary value problems are then simulated. These include single three-dimensional element tests, plane strain footing analyses and cavity expansion tests. The rapid convergence of the global Newton–Raphson procedure using the consistent tangent is demonstrated in small strain and finite deformation simulations

A One-dimensional Analysis of the Distribution of Temperature, Stress and Strain in the co-axial Laser Cladding Process

The co-axial Laser Cladding (LC) is one of the most advanced surface treatment processes where generally a superior powder or wire material is deposited on the substrate to improve surface properties by using laser heat source. In this work, a physical model of the clad and the substrate has been presented. An attempt has been made to describe the simplified relation of temperature, stress and strain with time by using the established theoretical knowledge of generation of stress and strain after thermal treatment. The simplified relation of temperature, stress and strain with time has been explained with the help of schematic diagrams. The finding of this study will help to understand the temperature, stress and strain behaviour with time in the Laser Cladding process

On the use of Reuleaux plasticity for geometric non-linear analysis.

Three dimensional analyses including geometric and material non--linearity require robust, efficient constitutive models able to simulate engineering materials. However, many existing constitutive models have not gained widespread use due to their computational burden and lack of guidance on choosing appropriate material constants. Here we offer a simple cone-type elasto-plastic formulation with a new deviatoric yielding criterion based on a modified Reuleaux triangle. The perfect plasticity model may be thought of as a hybrid between Drucker-Prager (D-P) and Mohr-Coulomb (M-C) that provides control over the internal friction angle independent of the shape of the deviatoric section. This surface allows an analytical backward Euler stress integration on the curved surface and exact integration in the regions where singularities appear. The attraction of the proposed algorithm is the improved fit to deviatoric yielding and the one--step integration scheme, plus a fully defined consistent tangent. The constitutive model is implemented within a lean 3D geometrically non-linear finite-element program. By using an updated Lagrangian logarithmic strain--Kirchhoff stress implementation, existing infinitesimal constitutive models can be incorporated without modification

70-line 3D finite deformation elastoplastic finite-element code.

Few freeware FE programs offer the capabilities to include 3D finite deformation inelastic continuum analysis; those that do are typically expressed in tens of thousands of lines. This paper offers for the first time compact MATLAB scripts forming a complete finite deformation elasto–plastic FE program. The key modifications required to an infinitesimal FE program in order to include geometric non–linearity are described and the entire code given

Progress in Numerical Simulation of the Laser Cladding Process

Laser Cladding is one of the developing manufacturing techniques used for diverse applications such as coating, repairing and prototyping. Complex processing phenomena and the formation and growth of thin clad of few micrometers to millimeters range in most cases are yet to be fully understood. However, in recent past, several numerical models have been reported to get some understanding of physical, dynamic and metallurgical phenomena of this process. This article reviews the progress of numerical simulations spanning over three distinct stages of the process to model powder flow dynamics, melt pool and clad properties. For each stage, the governing equations, the effect of process variables and experimental validation techniques have been discussed. Specifically, we have outlined some of the underlying assumptions in the current numerical models which can act as pointers for further improvement of the existing numerical models. Authors recommend that numerical simulation results have to be complemented with experimental results to achieve better clad properties

Modeling uncertain and dynamic casualty health in optimization-based decision support for mass casualty incident response

When designing a decision support program for use in coordinating the response to Mass Casualty Incidents, the modelling of the health of casualties presents a significant challenge. In this paper we propose one such health model, capable of acknowledging both the uncertain and dynamic nature of casualty health. Incorporating this into a larger optimisation model capable of use in real-time and in an online manner, computational experiments examining the effect of errors in health assessment, regular updates of health and delays in communication are reported. Results demonstrate the often significant impact of these factors

Online optimization of casualty processing in major incident response: An experimental analysis

When designing an optimization model for use in mass casualty incident (MCI) response, the dynamic and uncertain nature of the problem environment poses a significant challenge. Many key problem parameters, such as the number of casualties to be processed, will typically change as the response operation progresses. Other parameters, such as the time required to complete key response tasks, must be estimated and are therefore prone to errors. In this work we extend a multi-objective combinatorial optimization model for MCI response to improve performance in dynamic and uncertain environments. The model is developed to allow for use in real time, with continuous communication between the optimization model and problem environment. A simulation of this problem environment is described, allowing for a series of computational experiments evaluating how model utility is influenced by a range of key dynamic or uncertain problem and model characteristics. It is demonstrated that the move to an online system mitigates against poor communication speed, while errors in the estimation of task duration parameters are shown to significantly reduce model utility