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The precision machining of metal surfaces and the ductile-regime grinding of ceramic surfaces are examples of fundamental cutting processes used in fabricating high-tolerance parts. Components with dimensional tolerances of a few tens of nanometers are currently being produced by direct machining with single-point diamond tools. Despite the ability to fabricate these parts, little is understood of the basic deformation mechanisms that determine how material is removed and deformed, how a tool-tip interacts with a workpiece, how induced surface and subsurface damage occurs, and how cutting tools wear.The key to solving these problems is a fundamental understanding of basic tribological processes such as surface indentation and scraping. Indentation experiments measure the mechanical response of a surface, the onset of plastic deformation, and material hardness. Macroscopic hardness measurements have been shown to correlate well with observed tensile yield strengths. Microscopic indentation studies, where the indentation size is smaller than the material grain size, show new and interesting phenomena. In the pioneering work of Gane and Bowden, no permanent penetration occurred until a critical load was achieved. They related this critical yielding to the theoretical shear strength in the metal, the strength required to create dislocations. Yielding of this sort has since been observed by many investigators.

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With the first four of its eventual 192 beams now executing shots and generating more than 100 kJ of laser energy at its primary wavelength of 1.06 m, the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is already the world's largest and most energetic laser. The optical system performance requirements that are in place for NIF are derived from the goals of the missions it is designed to serve. These missions include inertial confinement fusion (ICF) research and the study of matter at extreme energy densities and pressures. These mission requirements have led to a design strategy for achieving high-quality focusable energy and power from the laser and to specifications on optics that are important for an ICF laser. The design of NIF utilizes a multipass architecture with a single large amplifier type that provides high gain, high extraction efficiency, and high packing density. We have taken a systems engineering approach to the practical implementation of this design that specifies the wavefront parameters of individual optics to achieve the desired cumulative performance of the laser beamline. This paper provides a detailed look at the causes and effects of performance degradation in large laser systems and how NIF has been designed to overcome these effects. We also present results of spot size performance measurements that have validated many of the early design decisions that have been incorporated in the NIF laser architecture.The optical quality or wavefront specifications for the laser slabs, crystals, windows, lenses, and mirrors that make up the National Ignition Facility ͑NIF͒ beamlines were established by flowdown analysis of those that were needed for these components to meet the primary criteria and functional requirements for the NIF laser system. In this work we summarize the NIF primary system criteria that are influenced by the wavefront quality of a beamline, and then describe how the beamline architecture and specifications for individual optical components have made it possible for NIF to meet its system criteria.The national motive for building the NIF laser centers around providing a laser driver for three missions of national purpose:• inertial confinement fusion ͑ICF͒ • the high-energy-density study of materials of interest to the stockpile stewardship program • the study of materials under very high temperatures and pressures of interest to the scientific community, particularly the astrophysical community.Of these user groups, the one that was most active in establishing the original specifications for NIF was the ICF community; their emphasis for the initial embodiment of NIF was for indirect drive ICF. For this mission, laser light enters a hohlraum through two laser entrance holes ͑LEH͒ to irradiate the walls of the hohlraum, subsequently generating x-rays that drive the implosion of a capsule centrally located within the hohlraum. 1 Thus, the primary wavefront requirement for NIF became its ability to provide focusable energy and power into the laser ...

Non-equilibrium molecular dynamics is used to study the indentation of an ideal metallic surface by a hard spherical ball. The problem is symmetric about the axis of the ball and we choose to study the deformation in two dimensions. We use the simple embedding function F(ρ) = 2eρln ρ along with the Lennard-Jones two body potential to model a material resembling copper. We present a calculation of the st'ress field (from the internal atomistic description) for both elastic and plastic deformations. The material deforms plastically through the creation of edge dislocations and the flow of material around the sides of the indenter. The creation of dislocations is reversible—they return to the surface (anneal out) when the indenter is removed. The plastic flow leads to a permanent indentation in the surface.