Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

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Friction Stir Welding and Processing

Explicit finite element and finite difference methods are used to solve a wide variety of transient problems in industry and academia. Unfortunately, explicit methods are rarely discussed in detail in finite element text books. This paper reviews the basic explicit finite element and finite difference methods that are currently used to solve transient, large deformation problems in solid mechanics. A special emphasis has been placed on documenting methods that have not been previously published in journals.

Computational methods in Lagrangian and Eulerian hydrocodes

A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets

Natural impacts in which the projectile strikes the target vertically are virtually nonexistent. Nevertheless, our inherent drive to simplify nature often causes us to suppose most impacts are nearly vertical. Recent theoretical, observational, and experimental work is improving this situation, but even with the current wealth of studies on impact cratering, the effect of impact angle on the final crater is not well understood. Although craters' rims may appear circular down to low impact angles, the distribution of ejecta around the crater is more sensitive to the angle of impact and currently serves as the best guide to obliquity of impacts. Experimental studies established that crater dimensions depend only on the vertical component of the impact velocity. The shock wave generated by the impact weakens with decreasing impact angle. As a result, melting and vaporization depend on impact angle; however, these processes do not seem to depend on the vertical component of the velocity alone. Finally, obliquity influences the fate of the projectile: in particular, the amount and velocity of ricochet are a strong function of impact angle.

Understanding oblique impacts from experiments, observations, and modeling.

CTH is a family of codes developed at Sandia National Laboratories for modelling complex multi-dimensional, multi-material problems that are characterized by large deformations and/or strong shocks. A two-step, second-order accurate Eulerian solution algorithm is used to solve the mass, momentum, and energy conservation equations. CTH includes models for material strength, fracture, porosity, and high explosive detonation and initiation.

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CTH: A software family for multi-dimensional shock physics analysis

CTH: A three-dimensional shock wave physics code

CTH is a software system under development at Sandia National Laboratories Albuquerque to model multidimensional, multi-material, large deformation, strong shock wave physics. One-dimensional, two-dimensional, and three-dimensional Eulerian meshes are currently available. CTH uses tabular or analytic equations of state that model solid, liquid, vapor, plasma, and mixed-phase materials. CTH can model elastic-plastic behavior, high explosives, fracture, and motion of fragments smaller than a computational cell. CTH was carefully structured to vectorize and multitask on the CRAY X-MP. Three-dimensional databases reside on the CRAY solid state disk with only five planes in core at once. The input/output to the solid state disk is overlapped with computations so there is no penalty for using the solid state disk. This allows very large problems to be run effectively. A sophisticated post-processor, CTHED, has been developed for interactive analysis using color graphics. This paper describes the architecture, database structure, models, and novel features of CTH. Special emphasis will be place on the features that are novel to CTH or are not direct generalizations of two-dimensional models. 8 refs., 1 fig.

M.G. Elrick

Papers

CTH: A three-dimensional shock wave physics code

CTH: A three-dimensional large deformation, strong shock wave physics code