Numerical Modeling of Shear Banding and Dynamic Fracture in Metals

Understanding the failure of metals at high strain rate is of utmost importance in the design of a broad range of engineering systems. Numerical methods offer the ability to analyze such complex physics and aid the design of structural systems. The objective of this research will be to develop reliable finite element models for high strain rate failure modelling, incorporating shear bands and fracture. Shear band modelling is explored first, and the subsequent developments are extended to incorporate fracture. Mesh sensitivity, the spurious dependence of failure on the discretization, is a well known hurdle in achieving reliable numerical results for shear bands and fracture, or any other strain softening model. Mesh sensitivity is overcome by regularization, and while details of regularization techniques may differ, all are similar in that a length scale is introduced which serves as a localization limiter. This dissertation contains two main contributions, the first of which presents sev- eral developments in shear band modeling. The importance of using a monolithic nonlinear solver in combination with a PDE model accounting for thermal diffusion is demonstrated. In contrast, excluding one or both of these components leads to un- reliable numerical results. The Pian-Sumihara stress interpolants are also employed in small and finite deformation and shown to significantly improve the computational cost of shear band modelling. This is partly due to the fact that fewer unknowns than an irreducible discretization result from the same mesh, and more significantly, the fact that convergence of numerical results upon mesh refinement is improved drastically. This means coarser meshes are adequate to resolve shear bands, alleviating some of the computational cost of numerical modelling, which are notoriously significant. Since extremely large deformations are present during shear banding, a mesh to mesh transfer algorithm is presented for the Pian Sumihara element and used as part of a remeshing strategy. A practical application of the numerical formulation developed is modelling the shear band failure of a friction stir welded aluminum joint under high rate loading. The energy absorption capacity of these joints are subse- quently analyzed and found to be significantly weaker than untreated aluminum due to the nonhomogeneous material properties of the joint. The second contribution is extending the shear band model described previously to account for fracture by way of the phase field method. The phase field method is modified to account for the contribution of inelastic deformation to the creation of fracture surfaces, which results in a rate and temperature dependent theory for fracture, due to the rate and temperature dependence of plasticity. The combined fracture and shear band model is shown to be capable of representing a wider spectrum of strain rates than either the phase field model or the shear band model alone

A study of a group career development intervention based on social learning and decision-making principles.

EducationDoctor of Education (Ed.D.

Human punishment is motivated by inequity aversion, not a desire for reciprocity

Humans involved in cooperative interactions willingly pay a cost to punish cheats. However, the proximate motives underpinning punitive behaviour are currently debated. Individuals who interact with cheats experience losses, but they also experience lower payoffs than the cheating partner. Thus, the negative emotions that trigger punishment may stem from a desire to reciprocate losses or from inequity aversion. Previous studies have not disentangled these possibilities. Here, we use an experimental approach to ask whether punishment is motivated by inequity aversion or by a desire for reciprocity. We show that humans punish cheats only when cheating produces disadvantageous inequity, while there is no evidence for reciprocity. This finding challenges the notion that punishment is motivated by a simple desire to reciprocally harm cheats and shows that victims compare their own payoffs with those of partners when making punishment decisions.Human Evolutionary Biolog

Advising From a Constructive Developmental Perspective

Advisors can enhance development by, first, identifying student\u27s meaning-making assumptions and, second, challenging those assumptions while offering support as students struggle to increase the complexity of meaning making. Constructive developmental theory is offered as a useful framework from which to encourage greater student ownership of the educational planning process. Methods of assessing and enhancing development are suggested. Two cases that depict advising from the constructive developmental perspective are offered

KNEE TORQUE KINETICS DURING HIGHLAND DANCING

The purpose of the study is to measure torque variations in the knees of malaligned Highland dancers during the early and late stages of a six step Highland Fling. A secondary objective is to measure variations in knee malalignment at impact, maximum flexion and extension. The most frequently occurring injuries in dance involve the knee (Arnheim, 1980; Schafle, Requa & Garrick, 1990; Solomon & Micheli, 1986). More specifically, knee injuries in dance develop largely from knee malalignrnent (Arnheim, 1980; Clarkson & Skrinar, 1988; Clippinger-Robertson, 1987; Ende & Wickstrom, 1982; Reid, 1988; Solomon & Micheli, 1986; Teitz, 1987; Watkins & Clarkson, 1990). Quantifying knee torque due to malalignment provides a measure to better understand malalignment and the prevention of injury due to incorrect dance technique. Seven subjects, dancing a six step Highland Fling, were video taped from both a frontal and oblique view (45 degrees to the frontal view) while performing on a force platform. Video analysis provided knee displacement measures from both frontal and oblique views. Ground reaction forces (GRF) provided the force component for knee torque calculations. Knee malalignment displacements at impact, maximum flexion and extension were measured from the oblique view. Results were analyzed using a single subject baseline design and indicated mixed trends in knee torque, knee malalignment, and knee flexion from early to late stages of the dance. The decrease in knee torque is explained by a decrease, therefore, malalignment could have increased to aid in the absorption of shock. Maximum knee malalignment occurred at maximum knee flexion in the last step for all subjects and for five subjects in the first step. Increased knee malalignment measures, in the oblique plane, demonstrate potential for injury unless the dancer's technique and lower extremity alignment is corrected. The research utilizes Highland dancers, however the research concentration is on dancing in the turned-out position, a position common to other dance forms, such as ballet, jazz, and modern dance

THE EFFECTS OF PRACTICE ON THE KINETICS OF VERTICAL AND HORIZONTAL JUMPING

INTRODUCTION The purpose of this study is to determine the effects of practice onthe kinetics of vertical and horizontal jumping. A sub purpose of this study is to determine the relationship between peak power and distance jumped. The focus of this research is interdisciplinary in that an attempt will be made to understand vertical and horizontal jumping from both a Biomechanical and a Skill Acquisition perspective. The relationship between force and velocity is important in determining the peak power produced in vertical and horizontal jumping movements. Peak power is realized at the point in which the force time curve intercepts the velocity time curve (Dowling and Vamos, 1993). To understand the mechanics of jumping it is necessary to determine the relationship between force, velocity and peak power on the distance jumped. In terms of skill acquisition, practice isan important variable (Schmidt, 1988). As the learner performs a number of practice trials, they develop a memorial representation for the movement pattern. The kinetic components of the movement pattern may be importantdetenninants of skillful performance. Therefore, it is important to take into account the relationships between movement kinetics and movement outcome (i.e. distanceheight jumped), as a function of practice, to more fully understand the processes involved in the acquisition of a jumping skill. METHOD lkenty volunteer subjects were randomly assigned to either anexperimental or a control group. Subjects in the experimental group performed five maximal vertical and horizontal jumps daily for ten days. Pre and post tests were conducted on day one and day ten. Subjects performed three maximal vertical and horizontal jumps on an AMTI force plate. Power, force and velocity data was computed using the AMTI Power software. In addition, movement outcome (i.e., distance or height jumped) was measured. RESULTS AND DISCUSSION The prdpost mean differences in the temporal and kinetic variables were used to determine the effect of practice on the 'kinetics of jumping. In addition, multiple regression and correlation were used to determine the relationship between the temporal and kinetic variables and the distance jumped. The results are discussed in terms of the changes in time to peak power as a function of practice. In addition, the relationship between peak power and distance jumped is discussed in terms of the learning process. Implications for the role of practice in skill acquisition and efficiency as a determinant of skill acquisition are discussed. REFERENCES Dowling, J.J. & Vamos, L. (1993). Identification of kinetic and temporal factors related to vertical jump performance. Journal of Applied Biomechanics, 9,95-110. Schmidt, R.A. (1988). Motor Control and Learning: A Beehavioral Emphasis. (2nd ed.). Champaign, 11: Human Kinetics

Using Art-Based Multicultural Interventions to Reduce Counselor Trainees\u27 Ethnocentrism

This qualitative research explored the use of the Cultural De-Centering Activity-Visual (CDCA-V) as a means of challenging culture-centrism in a graduate-level multicultural counseling course. Results indicated that the CDCA-V provoked students to question their received norms about religion, ethnicity, gender, sexual orientation, and/or social class

Using Art-Based Multicultural Interventions to Reduce Counselor Trainees\u27 Ethnocentrism

This qualitative research explored the use of the Cultural De-Centering Activity-Visual (CDCA-V) as a means of challenging culture-centrism in a graduate-level multicultural counseling course. Results indicated that the CDCA-V provoked students to question their received norms about religion, ethnicity, gender, sexual orientation, and/or social class