Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Combustion. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

The spall strength of condensed matter

Abstract: Two conditions are proposed which place constraints on the processes of dynamic spall in condensed media, and determine inequalities which bound the spall strength, fragment size, and failure time. Spall is defined as rupture within a body due to stress states in excess of the tensile strength of the material. The first is a horizon condition which establishes a domain of communication, consistent with the time to failure, within which spall must be independent of the surrounding environment. The second is an energy condition which requires that the potential and kinetic energy associated with the tensile loading process exceed the fracture energy of the material. Equality in the relations established from these conditions corresponds to energy-limited spall and provides specific analytic expressions for the spall properties. Inequality implies flaw-limited spall and requires more detailed material property information before spall can be characterized. Energy-limited spall is determined by the material fracture toughness in brittle solids and the material flow stress in ductile solids. Calculated spall properties, assuming energy-limited spall, compare well with experimental spall data for various materials. Under certain conditions, a transition from brittle to ductile spall (definition in text) with increasing strain rate is predicted. Comparison is made with spall data on 6061-T6 aluminum for which a brittle-to-ductile transition is predicted to occur at a critical strain rate of approximately 4 × 105 s−1. Energy-limited spall in liquids within their range of Newtonian fluid behavior is governed by surface energy and viscosity. Spall is predicted to be dominated by surface energy at low strain rates and viscous dissipation at high rates. Examples of each appear to exist within the scant experimental spall data available for liquids.

Single-shot measurement of the intensity and phase of an arbitrary ultrashort pulse by using frequency-resolved optical gating

Abstract: We introduce a new technique, frequency-resolved optical gating, for measuring the intensity I(t) and the phase ϕ(t) of an individual arbitrary ultrashort pulse. Using an instantaneous nonlinear-optical interaction of two variably delayed replicas of the pulse, frequency-resolved optical gating involves measuring the spectrum of the signal pulse versus relative delay. The resulting trace, a spectrogram, yields an intuitive full-information display of the pulse. Inversion of this trace to obtain the pulse intensity and phase is equivalent to the well-known two-dimensional phase-retrieval problem and thus yields essentially unambiguous results for I(t) and ϕ(t).

The flux of small near-Earth objects colliding with the Earth

Abstract: Asteroids with diameters smaller than approximately 50-100 m that collide with the Earth usually do not hit the ground as a single body; rather, they detonate in the atmosphere. These small objects can still cause considerable damage, such as occurred near Tunguska, Siberia, in 1908. The flux of small bodies is poorly constrained, however, in part because ground-based observational searches pursue strategies that lead them preferentially to find larger objects. A Tunguska-class event-the energy of which we take to be equivalent to 10 megatons of TNT-was previously estimated to occur every 200-300 years, with the largest annual airburst calculated to be approximately 20 kilotons (kton) TNT equivalent (ref. 4). Here we report satellite records of bolide detonations in the atmosphere over the past 8.5 years. We find that the flux of objects in the 1-10-m size range has the same power-law distribution as bodies with diameters >50 m. From this we estimate that the Earth is hit on average annually by an object with approximately 5 kton equivalent energy, and that Tunguska-like events occur about once every 1,000 years.