Residual stress is the stress present in a fixed reference configuration in which the body is at rest in the absence of external forces. In this investigation, residual stress is viewed as constitutive information in order to develop nondestructive mechanical tests that lead to the residual stress fields in bodies of various shapes that respond in a linearly elastic manner to small deformations from the residually stressed state. Energy theorems are being used to bound the residual stress in terms of experimental data and solutions to associated classical problems.

Martensitic alloys exhibit metastable equilibria involving microstructures consisting of different phases and their variants. Particular microstructural features may, depending on context, enhance or inhibit performance of such alloys. This research is intended to increase understanding of the manner in which various microstructures are created and altered during the course of phase transitions in martensitic alloys.

Recently, nematic liquid crystalline polymers have been crosslinked to form rubber-like solids that display highly novel behavior. Experimentally observed phenomena include spontaneous shape changes accompanying phase transitions, orientational memory effects, strain-induced optical transitions, and nonlinear elastic behavior such as discontinuous stress-strain relations and ``softening'' in which there is little resistance to large loads along certain directions. The coupling between deformation and order in these materials is due to their solid nature, as opposed to their liquid crystal counterparts. This research focuses on developing a thermomechanically consistent continuum framework for the study of such orientable elastomers.

The independence of the loading path of a wire rope is investigated. The existing load-deformation theory is slightly path dependent. This study is concerned with a determination of the factors that can be used to make the theory path independent. Plots are made showing the path dependence.

The load-deformation response of cord-reinforced cylindrical shells is being studied. The deformations of an axially loaded circular cylindrical shell with a single layer of equally spaced cords at an angle relative to the axis of the shell are found analytically. Cord-reinforced cylindrical shells are found to have extension-twist coupling. This extension-twist coupling is taken into account in the theory.

External fixators are bar-and-pin frames that are often used to set broken bones in animals (including humans). Currently there are no mechanics-based methodologies for selecting the number, size, and spacing of the pins to achieve a desired frame stiffness. The ultimate goal of this project is the development of an easy-to-use com- puter program that can be run by the operating surgeon to help design an appropriate fixator geometry during the operation. A two-dimensional frame model seems to capture some, but not all, of the features of overall frame compliance.

Spatial bands of intense plastic deformation may nucleate, intensify, and propagate in a variety of engineering materials under favorable conditions. A model of a shear band embedded in an infinite sheet of a thermal viscoplastic material is used to derive the asymptotic fields in the vicinity of the band tip for a power-law thermal and rate-dependent material model. Models for both static and dynamic band-tip fields are sought. Such derivations are expected to provide a rationale for the development of a so-called ``band strain intensity factor'' which may be used to characterize the local deformation fields in the vicinity of a band tip.

We examine the failure mechanics associated with railroad crossings made of austenitic manganese subject to impact loading. We account for the dynamic nature of the loading as well as for the elastic-viscoplastic material response. A parametric computational study is underway to help us better understand the effects of geometry and material properties on damage evolution.

The final shape of a continuous cast slab is not always uniform, or even rectangular. Of particular concern is the great variation in final slab width of certain grades, such as 409 ferritic stainless steel. Width variations, which occur during slow-downs in operation, create production and logistic problems due to uncertain tonnage, in addition to quality concerns. Models are being developed to simulate heat flow, creep bulging, and associated distortion throughout the secondary cooling zone, in order to understand and quantify the mechanism for slab width variations. Model predictions are being compared with data collected from plant trials. The calibrated models eventually will be applied as a tool to predict and control slab shape.

A coupled, 2-D, transient finite-element model has been developed to predict temperature, shrinkage, and stress development in a solidifying shell as it moves down through a continuous caster. The model features a robust, efficient algorithm to integrate the highly temperature- and stress-dependent constitutive equation for the inelastic-creep strain rate. Efforts are currently devoted to applying the model to understand the development of shape and residual stress in a vertical section through a low carbon steel shell during the early stages of solidification near the meniscus. The results show that during a sudden change in liquid level, thermal stress causes the thin shell to bend toward the liquid.

Generally, in internally constrained nonlinear thermoelasticity, it is hypothesized that the dependent fields are given by constitutive functions of appropriate independent fields to within indeterminate reaction fields. The assumption that the reactions do not contribute to the rate of entropy production in processes that satisfy the internal constraints leads to the form of the reactions. Here, we show that by a slight reorganization of the conventional development, it is possible to infer the existence of the reaction fields (except for the one corresponding to the heat flux). Furthermore, the forms of the reactions are obtained, as are the usual results for the constitutive functions.

* Denotes principal investigator.