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Understanding the mechanical behavior of jointed-rock masses is of critical importance to designing and predicting the performance of a potential nuclear waste repositiry. To this end we have studied the frictional sliding between simulated rock joints using phase shifting moirk interferometry. Preliminary calibration models were made from stacks of Lexan plates that were sand-blasted to provide a uniform frictional interface. Load was applied monotonically and phase shifted moird fringe patterns were recorded at three different load states. Plots of slip along the interfaces for the model are presented to demonstrate the ability of the photomechanics technique to provide precise measurements of in-plane displacement, and ultimately the slip between the plates.

To obtain a well-determined constitutive database for the Alaskan frozen soil at confining pressures up to 100 MPa and temperatures down to -25°C, a series of laboratory tests was conducted using a unique high-pressure, low-temperature apparatus and the split Hopkinson pressure bar (SHPB). Quasi-static compression tests and indirect tension (or Brazilian) tests, are required to constrain the variabilities of material properties of frozen soil. The SHPB tests are required to obtain dynamic compression properties and the strain rate dependency of the frozen soil. The results from laboratory material testing showed that Alaskan frozen soil exhibits pressure and temperature dependence, rate sensitivity, anisotropy, brittle and ductile behavior, volumetric compaction, and dilation. The rate-sensitive and anisotropic version of a plasticity model, being developed by Fossum and Fredrich (2000), was able to represent the deformation behavior of such a complex material very well. This model includes high strain-rate sensitivity and anisotropy in both the elastic and plastic regimes. The model is defined through a continuous yield and loading surface for unified dilation and compaction phenomena. It is envisioned that this model will be used to predict the deformation and failure of frozen soil under the dynamic loading conditions resulting from projectile penetration into frozen soil targets.

Presto is a Lagrangian, three-dimensional explicit, transient dynamics code that is used to analyze solids subjected to large, suddenly applied loads. The code is designed for a parallel computing environment and for problems with large deformations, nonlinear material behavior, and contact. Presto also has a versatile element library that incorporates both continuum elements and structural elements. This user's guide describes the input for Presto that gives users access to all the current functionality in the code. The environment in which Presto is built allows it to be coupled with other engineering analysis codes. Using a concept called scope, the input structure reflects the fact that Presto can be used in a coupled environment. The user's guide describes how scope is implemented from the outermost to the innermost scopes. Within a given scope, the descriptions of input commands are grouped based on functionality of the code. For example, all material input command lines are described in a chapter of the user's guide for all the material models that can be used in Presto. 3 AcknowledgmentsThis document is the result of the collective effort of a number of individuals. The development team responsible for Adagio and Presto, the SIERRA Solid Mechanics codes, includes Manoj

The inner wall of a nuclear pressure vessel can become embrittled during service due to irradiation effects. As a result, a small flaw could become critical during the thermal shock that would accompany a loss-of-coolant-accident. To assess the consequences of this possibility, elastodynamic computations were performed on the subsequent rapid unstable crack run-arrest events. One difficulty is the lack of reliable dynamic fracture toughness data as a function of crack speed and temperature. However, using plausible estimates, computational results were obtained for comparison with conventional quasi-static analyses. These indicate that the neglect of the dynamic effects is mildly anticonservative for this application.