Showing papers on "Shock (mechanics) published in 1993"

Review of chemical-kinetic problems of future NASA missions, II: Mars entries

Abstract: A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.

A simplified theory of kinematic waves in highway traffic, part I: General theory

Abstract: In the theory of “kinematic waves,” as described originally by Lighthill and Whitham in 1955, the evaluation of the shock path is typically rather tedious. Instead of using this theory to evaluate flows or densities, one can use it to evaluate the cumulative flow A ( x , t ) past any point x by time t . It is shown here how a formal solution for A ( x, t ) can be evaluated directly from boundary or initial conditions without evaluation at intermediate times and positions. If there are shocks, however, this solution will be multiple-valued. The correct solution, which is the lower envelope of all such formal solutions, will automatically have discontinuities in slope describing the passage of a shock. To evaluate A ( x, t ) at any particular location x , it is not necessary to follow the actual path of the shock. The solution can be evaluated directly in terms of the boundary data by either graphical or numerical techniques.

Direct numerical simulation of isotropic turbulence interacting with a weak shock wave

Abstract: Direct numerical simulations are used to investigate the interaction of isotropic quasi-incompressible turbulence with a weak shock wave. A linear analysis of the interaction is conducted for comparison with the simulations. Both the simulations and the analysis show that turbulence is enhanced during the interaction. Turbulent kinetic energy and transverse vorticity components are amplified, and turbulent lengthscales are decreased. It is suggested that the amplification mechanism is primarily linear. Simulations also showed a rapid evolution of turbulent kinetic energy just downstream of the shock, a behavior not reproduced by the linear analysis. Analysis of the budget of the turbulent kinetic energy transport equation shows that this behavior can be attributed to the pressure transport term. Multiple compression peaks were found along the mean streamlines at locations where the local shock thickness had increased significantly.

Shock/boundary-layer interaction control with vortex generators and passive cavity

Abstract: This paper describes an experimental comparison of two passive approaches for controlling the shock interaction with a turbulent boundary layer: low-profile vortex generators and a passive cavity (porous wall with a shallow cavity underneath). This investigation is the first known direct comparison of the two methods wherein the advantages and disadvantages of both are revealed. The experiments were conducted with a normal shock wave in an axisymmetric wind tunnel. The shock strength (M = 1.56-1.65) was of sufficient magnitude to induce a large separation bubble, thus causing substantial boundary-layer losses. The low-profile vortex generators were found to significantly suppress the shock-induced separation and improve the boundary-layer characteristics downstream of the shock. However, the suppression of the separation bubble decreased the extent of the low total pressure loss region associated with the lambda foot shock system which results in a lower mass-averaged total pressure downstream of the shock. The passive cavity substantially reduced the total pressure loss through the shock system (and thus wave drag) by causing a more isentropic compression over a larger lateral extent. However, the boundary-layer losses downstream of the shock were significantly increased.

Perpendicular transport in 1‐ and 2‐dimensional shock simulations

Abstract: We consider the foundations of 1- and 2-dimensional shock simulations in which the physical quantities are independent of a coordinate which is not parallel to the magnetic field. We show analytically that in such simulations the ions are effectively tied to the convected magnetic lines of force because of the presence of an ignorable spatial coordinate. This conclusion has important consequences. In particular we conclude that the acceleration of energetic charged particles at quasi-perpendicular shocks cannot be properly studied in such simulations because the role of perpendicular diffusion cannot be properly evaluated.

Review of chemical-kinetic problems of future NASA missions. I: Earth entries

Abstract: A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.

Liquid crystal device with an isotropic shock mounting and gasket

Abstract: An isotropic shock mounting to prevent damage to electronic components such as a display mounted in a hand-held signature capture terminal includes a shock gasket which extends around the edges of the display, a carrier in which the display is disposed, a formed metal bezel within which the carrier fits having a cut-out portion through which the display can be viewed, and a plurality of shock grommets positioned at the corners of the carrier to coact with the interior of the housing of the hand-held terminal. This arrangement provides for torsional and beam strength, elastic support of the display, strain relief for TAB and PCB connections, and controlled isotropic deceleration in case of an impact resulting from a fall of the hand-held terminal.

Disk drive and method for minimizing shock-induced damage

Abstract: A disk drive has a fall detection control system that detects when a disk drive is in a free fall, and takes precautionary protective action to minimize physical damage from any resulting shock upon impact. The disk drive includes an accelerometer device that measures acceleration of the disk drive along three mutually orthogonal axes x, y, and z and resolves the measurement into respective vectors a x , a y , and a z . In one embodiment, a processor is programmed to (1) compute a net acceleration a net of the disk drive, (2) compare the net acceleration a net with the selected acceleration threshold level, (3) measure a duration that the net acceleration a net exceeds the acceleration threshold level, (4) compare the measured duration with a selected reference time period, and (5) output the warning signal when the measured duration exceeds the reference time period. Upon receipt of the warning signal, a controller initiates protective routines in preparation for shock.

Influence of Shock-Wave Deformation on the Structure/Property Behavior of Materials

Abstract: While the field of shock-wave physics has provided significant insights into many of the processes related to wave propagation in materials, the exact micromechanisms of deformation during shock loading remain poorly understood. The initial response of a material subjected to explosive or high-velocity impact conditions is to propagate shock waves that rapidly traverse the material. These waves produce dynamic deformations, the extent of strain is dependent on the precise method of loading and the degree to which a hydrostatic stress state is maintained. If we are to develop an understanding of the total response of a material to impact, we must investigate the specific influence of shock waves on microstructure and the corresponding effects on mechanical properties. The severe loading path conditions imposed during a shock induce a high density of defects in most materials, i.e., dislocations, point defects, and/or deformation twins. In addition, during the shock process some materials may undergo a pressure-induced phase transition which will affect the real-time material response. If the phase remains present to ambient conditions (although metastable) the post-mortem substructure and mechanical response will also reflect the high-pressure excursion. Interpretation of the results of shock-wave effects on materials must therefore address all of the details of the shock-induced deformation substructure in light of the operative metallurgical strengthening mechanisms in the material under investigation, and the experimental conditions under which the material was deformed and recovered.

Solar wind conditions in the outer heliosphere and the distance to the termination shock

Abstract: The Plasma Science experiment on the Voyager 2 spacecraft has measured the properties of solar wind protons from 1 to 40.4 AU. We use these observations to discuss the probable location and motion of the termination shock of the solar wind. Assuming that the interstellar pressure is due to a 5 micro-G magnetic field draped over the upstream face of the heliopause, the radial variation of ram pressure implies that the termination shock will be located at an average distance near 89 AU. This distance scales inversely as the assumed field strength. There are also large variations in ram pressure on time scales of tens of days, due primarily to large variations in solar wind density at a given radius. Such rapid changes in the solar wind ram pressure can cause large perturbations in the location of the termination shock. We study the nonequilibrium location of the termination shock as it responds to these ram pressure changes. The results of this study suggest that the position of the termination shock can vary by as much as 10 AU in a single year, depending on the nature of variations in the ram pressure, and that multiple crossings of the termination shock by a given outer heliosphere spacecraft are likely. After the first crossing, such models of shock motion will be useful for predicting the timing of subsequent crossings.

Hybrid simulations of the effects of interstellar pickup hydrogen on the solar wind termination shock

Abstract: Hybrid (kinetic ions/fluid electrons) plasma simulations are used to study the effects of a population of energetic interstellar pickup hydrogen ions on the solar wind termination shock. The pickup hydrogen is treated as a second ion species in the simulations, and thus the effects of the pick-ups on the shock, as well as the effects of the shock on the pickups, are treated in a fully self-consistent manner. For quasi-perpendicular shocks with 10-20 percent pickup hydrogen the pickup ions manifest themselves in a small foot ahead of the shock ramp caused by pickup ion reflection. For oblique shocks with smaller angles between the field and the shock normal, a large fraction of the pickup ions are reflected and move back upstream where they excite large amplitude magnetosonic waves which steepen into shocklets. These backstreaming pickup ions may provide advance warning of a spacecraft encounter with the termination shock.

Impact and explosion : analysis and design

Abstract: Part 1 Accident survey: Introduction, Wind hurricane and tornado generated missiles, Impact and explosion at sea, Car collisions and explosions, Train collisions and impacts, Aircraft and missile impacts, crashes and explosions, Explosions with and without impact, Nuclear explosions and loss-of-coolant accidents, The Gulf War, Recent air crashes - aircraft impact at ground level Part 2 Data on Missiles, Impactors, Aircraft and Explosions: Introduction, Types of conventional missiles and impactors, Military airforce and navy missiles and impactors, Data on civilian and military aircraft, tanks and marine vessels, Types of explosion, Dust explosions, Underwater explosions Part 3 Basic Structural Dynamics: General introduction, Single-degree-of- freedom system, Two-degrees-of-freedom system, Multi-degrees-of-freedom systems Part 4 Impact Dynamics: Introduction, The impactor as a projectile, Aircraft impact on structures - peak displacement and frequency, Aircraft impact - load-time functions, Impact due to drop weights, Impact on concrete and steel, Impact on soils/rocks, Impact on water surfaces and waves, Snow/ice impact Part 5 Explosion Dynamics: Introduction, Fundamental analyses related to an explosion, Explosions in air, Shock reflection, Gas explosions, Dust explosions, Explosions in soils, Rock blasting - construction and demolition, Explosions in water Part 6 Dynamic Finite-element Analysis of Impact and Explosion: Introduction, Finite-element equations, Steps for dynamic non-linear analysis, Ice/snow impact, Impact due to missiles, impactors and explosions - contact problem solutions, High explosions, Spectrum analysis, Solution procedures, Force or load - time function Part 7 Case studies: A Steel and Composites: Steel structures, Composite structures, Impact analysis of pipe rupture, Explosions in hollow steel spherical cavities and domes, Dropped impact analysis of shipping container for radioactive material, Car impact and explosion analysis, Train crash phenomenon B Concrete Structures: Introduction, Concrete beams, Reinforced concrete slabs and walls, Impact/explosion at roadways and runways, Buildings and structures subject to blast loads, Aircraft crashes on containment vessels (buildings) C Brickwork: General introduction, Finite-element analysis of explosion , Bomb explosion at a wall D Ice/snow Impact: Introduction, Finite-element analysis E Nuclear Reactors: PWR - loss-of-coolant accident (LOCA), Nuclear containment under hydrogen detonation, Impact/explosion at a nuclear power station - turbine hall, Jet impingement forces on PWR steel vessel components F Concrete Nuclear Shelters: Introduction, Design of a concrete nuclear shelter against explosion and other loads based on Home Office manual, Design of a nuclear shelter based on the US codes, Lacing bars, Finite-element analysis G Sea Environment: Multiple wave impact on a beach front, Explosions around dams, Ship-to-ship and ship-to-platform - impact analysis, Jacket platform - impact and explosion, Impact of dropped objects on platforms H Soil/rock Surfaces and Buried Structures: General introduction, Soil strata subject to missile impact and penetration

A linearized Euler analysis of unsteady transonic flows in turbomachinery

Abstract: A computational method for efficiently predicting unsteady transonic flows in two- and three-dimensional cascades is presented. The unsteady flow is modeled using a linearized Euler analysis whereby the unsteady flow field is decomposed into a nonlinear mean flow plus a linear harmonically varying unsteady flow. The equations that govern the perturbation flow, the linearized Euler equations, are linear variable coefficient equations. For transonic flows containing shocks, shock capturing is used to model the shock impulse (the unsteady load due to the harmonic motion of the shock). A conservative Lax-Wendroff scheme is used to obtain a set of linearized finite volume equations that describe the harmonic small disturbance behavior of the flow. Conditions under which such a discretization will correctly predict the shock impulse are investigated. Computational results are presented that demonstrate the accuracy and efficiency of the present method as well as the essential role of unsteady shock impulse loads on the flutter stability of fans.

Ion injection and acceleration at parallel shocks : comparisons of self-consistent plasma simulations with existing theories

Abstract: We present a simulation study of particle acceleration by parallel collisionless shocks and compare our results with existing shock acceleration theories, in particular, diffusive and shock drift acceleration. We extend the earlier work in this field by drawing attention to the similarities and discrepancies between the results obtained from the more realistic, self-consistent simulations and these well-established theories

Validation of multi-temperature nozzle flow code NOZNT

Abstract: A computer code NOZNT (Nozzle in n-Temperatures), which calculates one-dimensional flows of partially dissociated and ionized air in an expanding nozzle, is tested against five existing sets of experimental data The code accounts for: a) the differences among various temperatures, ie, translational-rotational temperature, vibrational temperatures of individual molecular species, and electron-electronic temperature, b) radiative cooling, and c) the effects of impurities The experimental data considered are: 1) the sodium line reversal and 2) the electron temperature and density data, both obtained in a shock tunnel, and 3) the spectroscopic emission data, 4) electron beam data on vibrational temperature, and 5) mass-spectrometric species concentration data, all obtained in arc-jet wind tunnels It is shown that the impurities are most likely responsible for the observed phenomena in shock tunnels For the arc-jet flows, impurities are inconsequential and the NOZNT code is validated by numerically reproducing the experimental data

The gradient of galactic cosmic rays at the solar-wind termination shock

Abstract: We report on a study of the expected spatial variation of the galactic cosmic-ray intensity in the outer heliosphere, in the vicinity of the solar-wind termination shock. Model simulations which contain all of the transport effects, including drifts, predict that the radial gradients change abruptly at the shock, and that the nature of the effect varies significantly with particle energy. At low energies, the radial gradient changes abruptly from a lower value inside the shock to a higher value outside, whereas at high energies, the higher value of the gradient is inside the shock. This effect, which is a consequence of the matching conditions at the shock and is closely related to diffusive shock acceleration, is qualitatively the same for both helisopheric magnetic polarity states and remains much the same in one-dimensional, two-dimensional, and three-dimensional models. Hence drifts do not change the nature of this phenomenon, although they change it quantitatively. The effect is, of course, not present in the absence of a terminal shock and may prove to be an important diagnostic tool for the study of the termination of the solar wind.

Temporal variations in the termination shock distance

Abstract: A kinematic analysis is made of solar wind driven temporal variations in the heliospheric termination shock distance. This has become possible because the large-scale dynamics of, and temporal variations in the distant solar wind are now well enough known from a combination of in situ and remote measurements. Conversely, nothing is known of the corresponding properties in the local interstellar medium, and hence these will be ignored. Given specific assumptions for how the termination shock responds to solar wind fluctuations, it is shown that the termination shock is very agile, moving in and out by up to a few AU in a month. This conclusion holds for a broad range of shock response assumptions. Because a spacecraft moves slowly in comparison to the termination shock, the shock will sweep back and forth over the spacecraft once the shock is first encountered.

Computations and experiments for a multiple normal shock/boundary-layer interaction

Abstract: Results from a numerical investigation of a Mach 1.61 multiple normal shock wave/turbulent boundary-layer interaction are compared to wall static pressure and laser Doppler velocimeter measurements. The computations used the explicit, time-dependent, second-order accurate MacCormack scheme to solve the mass-averaged Navier-Stokes equations. Turbulence was modeled by means of the Baldwin-Lomax algebraic model and the Wilcox-Rubesin two-equation model. The computation with the Wilcox-Rubesin model was able to capture the major features of the normal shock train and accurately predicted the flow reacceleration mechanisms which occur between shocks. However, this computation failed to accurately predict the level of flow separation under the first shock. The Baldwin-Lomax computation displayed a more limited ability to capture the features of this shock train flow.

Diffusive Shock Acceleration by Multiple Shocks

Abstract: Diffusive shock acceleration produces a power law momentum distribution f(p)α p −b , with b ≥ 4 for a single shock, and b = 4 for a single strong shock. It has been shown that the distribution for acceleration at a sequence of identical shocks is flatter, approaching f(p)α p −3 below a high energy knee, for an arbitrarily large number of shocks. We show how this flatter distribution arises and discuss the range of momenta over which it extends after a finite number of shocks.

X‐ray radiographic measurements of radiation‐driven shock and interface motion in solid density material

Abstract: Time resolved x‐ray radiographic measurements at high photon energy (∼7 keV) are used to observe radiation‐driven shock propagation and interface motion in solid density plastic samples, produced by indirect drive on the Nova laser. Measurements of x‐ray transmission through the shock compressed material are used to infer a density of approximately three times solid. In addition, by doping a section of a sample with high‐Z material (Br) for radiographic contrast, the shocked particle velocity was measured by observing the motion of the interface between the doped and nondoped materials resulting from acceleration by a shock.

Motion of the heliospheric termination shock - A gas dynamic model

Abstract: A simple quantitative model is presented for the heliospheric termination shock's anticipated movement in response to upstream solar wind condition variations, under the assumption that the termination shock is initially a strong gasdynamic shock that is at rest relative to the sun, and that there is a discontinuous increase or decrease in the dynamical pressure upstream of the shock. The model suggests that the termination shock is constantly in motion, and that the mean position of the shock lies near the mean equilibrium position which corresponds to the balance between the mean solar wind dynamical pressure and the mean interstellar pressure.

Disk drive with accerleration rate sensing

Abstract: A data recording disk drive includes acceleration rate sensing for controlling or modifying one or more disk drive operations in response to external shock or vibration. An acceleration rate sensor is mounted on the disk drive housing and provides direct detection of acceleration rate of the disk drive when subjected to external shock or vibration. The sensor includes two spaced-apart piezoelectric transducers that operate in current mode. The transducers are connected to an interface circuit that generates two voltage signals that are directly proportional to the angular and linear acceleration rates, respectively, when the disk drive is subjected to an external force. The disk drive microcontroller uses the voltage signals to inhibit writing of data or modify the servo control signal to maintain the heads on track during track seeking or following. The microcontroller can also combine the two signals to determine the acceleration rate of an unbalanced rotary actuator, which can then be used to modify the servo control signal. This permits the use of an unbalanced rotary actuator, which makes the disk drive smaller and lighter and reduces power consumption.

The role of magnetic loops in particle acceleration at nearly perpendicular shocks

Abstract: The acceleration of superthermal ions is investigated when a planar shock that is on average nearly perpendicular propagates through a plasma in which the magnetic field is the superposition of a constant uniform component plus a random field of transverse hydromagnetic fluctuations. The importance of the broadband nature of the transverse magnetic fluctuations in mediating ion acceleration at nearly perpendicular shocks is pointed out. Specifically, the fluctuations are composed of short-wavelength components which scatter ions in pitch angle and long-wavelength components which are responsible for a spatial meandering of field lines about the mean field. At nearly perpendicular shocks the field line meandering produces a distribution of transient loops along the shock. As an application of this model, the acceleration of a superthermal monoenergetic population of seed protons at a perpendicular shock is investigated by integrating along the exact phase-space orbits.

Simulations of particle acceleration in parallel shocks: Direct comparison between Monte Carlo and one-dimensional hybrid codes

Abstract: We have made a direct comparison between two different computer simulations of a plane, parallel, collisionless shock including particle acceleration to energies typical of those of diffuse ions observed at the earth bow shock. Despite the fact that the one-dimensional hybrid and Monte Carlo techniques employ entirely different algorithms, they give surprisingly close agreement in the overall shapes of the complete distribution functions for protons as well as heavier ions. Both methods show that energetic ions emerge smoothly from the background thermal plasma with approximately the same relative injection rate and that the fraction of the incoming plasma's energy flux that is converted into downstream enthalpy flux of the accelerated population (i.e., the acceleration efficiency) is similar in the two cases. The fraction of the downstream proton distribution made up of superthermal particles is quite large, with at least 10% of the energy flux going into protons with energies above 10 keV. In addition, an upstream precursor, produced by backstreaming energetic particles, is present in both shocks, although the Monte Carlo precursor is considerably longer than that produced in the hybrid shock. These results offer convincing evidence that, at least in these ways, the two simulations are consistent in their description of parallel shock structure and particle acceleration, and they lay the groundwork for development of shock models employing a combination of both methods.

The Damage and Failure of GRP Laminates by Underwater Explosion Shock Loading

Abstract: This paper examines the development of microstructural damage in a glass reinforced polymer (GRP) laminate when it is subjected to explosive shock loading in water. GRP is commonly used in the small naval vessels, and may be subjected to underwater explosions. In the experiments, the laminates were exposed to increasing levels of shock loading produced by underwater explosions. The laminates were backed with either water or air to modify the amount of bending the GRP laminate experienced under loading, with the air-backed laminates having the higher amount of bending. Examination of the GRP microstructure by optical and scanning electron microscopy after shock testing failed to reveal any damage to either the polymer matrix or glass fibres when the laminate was backed with water. In contrast, when the laminate was backed with air, small cracks were produced in the polymer matrix at low shock pressures. Raising the shock pressure above a threshold limit caused complete failure of the laminate by cracking in the polymer matrix, cracking of the glass fibres, and delamination of the glass fibres from the polymer. The differences in the shock resistance of the water- and air-backed GRP are discussed. Measurements of the residual tensile fracture strength of the laminates after shock loading are also presented. The fracture strength of the water-backed laminate was not affected by shock, but the fracture strength of the air-backed laminate deteriorated with the onset of glass fibre breakage and delamination in the GRP microstructure.

Multi-spacecraft observations of particle events and interplanetary shocks during November/December 1982

Abstract: We present a sample of solar energetic particle events observed between November 18 and December 31, 1982 by the HELIOS 1, the VENERA 13, and IMP 8 spacecraft. During the entire time period all three spacecraft were magnetically connected to the western hemisphere of the Sun with varying radial and angular distances from the flares. Eleven proton events, all of them associated with interplanetary shocks, were observed by the three spacecraft. These events are visible in the low-energy (about 4 MeV) as well as the high-energy (30 MeV) protons. In the largest events protons were observed up to energies of about 100 MeV. The shocks were rather fast and in some cases extended to more than 90% east of the flare site. Assuming a symmetrical configuration, this would correspond to a total angular extent of some interplanetary shocks of about 180%. In addition, due to the use of three spacecraft at different locations we find some indication for the shape of the shock front: the shocks are fastest close to the flare normal and are slower at the eastern flank. For particle acceleration we find that close to the flare normal the shock is most effective in accelerating energetic particles. This efficiency decreases for observers connected to the eastern flank of the shock. In this case, the efficiency of shock acceleration for high-energy protons decreases faster than for low-energy protons. Observation of the time-intensity profiles combined with variations of the anisotropy and of the steepness of the proton spectrum allows one in general to define two components of an event which we term ‘solar’ and ‘interplanetary’. We attempt to describe the results in terms of a radially variable efficiency of shock acceleration. Under the assumption that the shock is responsible not only for the interplanetary, but also for the solar component, we find evidence for a very efficient particle acceleration while the shock is still close to the Sun, e.g., in the corona. In addition, we discuss this series of strong flares and interplanetary shocks as a possible source for the formation of a superevent.

The microstructural response of quartz and feldspar under shock loading at variable temperatures

Abstract: Shock recovery experiments were carried out on Westerly granite and Hospital Hill quartzite targets in the peak pressure range 8 to 25 GPa, preshock temperatures of 25°, 450°, and 750°C and pulse durations of 2 to 7 μs using internally heated momentum traps and explosive plane wave generators. Optical and transmission electron microscopy analyses of quartz and feldspar shocked at 25°C revealed the previously documented progression, with increasing pressure: (1) fracturing; (2) planar fractures and shock mosaicism; (3) shock mosaicism and planar deformation features (PDFs); and (4) isotropization. This same sequence is observed for experiments at elevated preshock temperature but with specific microstructures occurring at lower pressures than those in previous experiments at room temperature. At 750°C, strong shock mosaicism, partially thermally recovered, is characteristic of feldspar shocked to 8 GPa, whereas 15 GPa is required for its development in quartz and for the generation of PDFs in both minerals. The results suggest that threshold pressures for formation of the various microstructures and phases are expected to vary systematically as a function of the preshock temperature of the target material. We suggest that PDFs are generated in the shock transition by progressive, heterogeneous, phase transformation of the crystal structure to form dense glass or high pressure polymorphs. The onset pressures for PDFs in specific crystallographic orientations is not influenced strongly by temperature, but the character of the PDFs does change as preshock temperature is increased at the same peak shock stress. The change from multiple sets of thin PDFs at low temperature to thicker single sets of PDFs at moderate temperature, and finally to complete isotropization at high temperatures, reflects a change in the phase transformation mechanism as a function of temperature. In contrast, development of shock mosaicism in quartz and feldspar occurs throughout the duration of shock loading and is better developed at elevated temperatures where the kinetics are enhanced by the additional thermal energy in the target.