Engineering topics

Orphal, D. L.

Publications and source records attributed to Orphal, D. L..

8 records

NASA NTRS1981

Z-model analysis of impact cratering - An overview

The Maxwell Z-Model has been applied to two continuum mechanics computer calculations: (1) a laboratory-scale impact of an aluminum projectile into plasticene clay, and (2) a planetary-scale impact of an iron meteor into gabbroic anorthosite. The material flow in the cratering flow field may be well approximated by incompressible flow for most of the excavation stage of crater growth. The center of the flow field is located beneath, not at, the surface. Soon after energy partitioning is complete, Z can assume values less than 2.0 associated with the initial directedness of the projectile's momentum. The Z-Model parameters are time dependent during a significant portion of the crater growth time, and Z increases steadily with time from about 2.0 or slightly less at the beginning of the excavation stage to level off at values in the neighborhood of about 3.0 before the excavation stage is half-over.

Austin, M. G.↗

NASA NTRS1980

Computer code simulations of the formation of Meteor Crater, Arizona - Calculations MC-1 and MC-2

It has been widely accepted that hypervelocity impact processes play a major role in the evolution of the terrestrial planets and satellites. In connection with the development of quantitative methods for the description of impact cratering, it was found that the results provided by two-dimensional finite difference, computer codes is greatly improved when initial impact conditions can be defined and when the numerical results can be tested against field and laboratory data. In order to address this problem, a numerical code study of the formation of Meteor (Barringer) Crater, Arizona, has been undertaken. A description is presented of the major results from the first two code calculations, MC-1 and MC-2, that have been completed for Meteor Crater. Both calculations used an iron meteorite with a kinetic energy of 3.8 Megatons. Calculation MC-1 had an impact velocity of 25 km/sec and MC-2 had an impact velocity of 15 km/sec.

Roddy, D. J.↗

NASA NTRS1980

Impact melt generation and transport

The results from the first two calculations in a series of continuum mechanics computer code calculations, investigating the effects of variations in impactor mass and velocity on the generation and transport of impact melt, are reported. In the present calculations, the impactor is modeled as a spherical iron projectile with a mass of one trillion grams, and the target as a gabbroic anorthosite (GA) half-space, where the cases calculated have impact velocities of 5 and 15.8 km/sec. Early-time ejection velocities are 1-2 km/sec in both cases. The first calculation results in 0.07 projectile masses of GA being partly or completely melted, with all the melted GA being ejected from the crater, and a maximum impact range for the ejected melted material of 30 km. The second calculation yields 10.4 projectile masses of melted GA, 50% of which is ejected from the crater to ranges of up to about 130 km. Peak shock pressure attenuation with depth is reported for both cases, and transient cavity dynamics are described and compared to that for surface and near-surface explosions.

Orphal, D. L.↗

NASA NTRS1980

Calculational investigation of impact cratering dynamics - Material motions during the crater growth period

The considered investigation was conducted in connection with studies which are to provide a better understanding of the detailed dynamics of impact cratering processes. Such an understanding is vital for a comprehension of planetary surfaces. The investigation is the continuation of a study of impact dynamics in a uniform, nongeologic material at impact velocities achievable in laboratory-scale experiments conducted by Thomsen et al. (1979). A calculation of a 6 km/sec impact of a 0.3 g spherical 2024 aluminum projectile into low strength (50 kPa) homogeneous plasticene clay has been continued from 18 microseconds to past 600 microseconds. The cratering flow field, defined as the material flow field in the target beyond the transient cavity but well behind the outgoing shock wave, has been analyzed in detail to see how applicable the Maxwell Z-Model, developed from analysis of near-surface explosion cratering calculations, is to impact cratering

Austin, M. G.↗

NASA NTRS1979

Impact cratering calculations. Part 1: Early time results

Early time two dimensional finite difference calculations of laboratory scale hypervelocity impact of 0.3 g spherical 2024 aluminum projectiles into homogeneous plasticene clay targets were performed. Analysis of resulting material motions showed that energy and momentum were coupled quickly from the aluminum projectile to the target material. In the process of coupling, some of the plasticene clay target was vaporized while the projectile become severely deformed. The velocity flow field developed within the target was shown to have features similar to those found in calculations of near surface explosion cratering. Specific application of Maxwell's analytic Z-Model showed that this model can be used to describe the early time flow fields resulting from the impact cratering calculations as well, provided the flow field centers are located beneath the target surface and most of the projectile momentum is dissipated before the model is applied.

Thomsen, J. M.↗

NASA NTRS1979

Calculational investigation of impact cratering dynamics - Early time material motions

Early time two-dimensional finite difference calculations of laboratory-scale hypervelocity (6 km/sec) impact of 0.3 g spherical 2024 aluminum projectiles into homogeneous plasticene clay targets were performed and the resulting material motions analyzed. Results show that the initial jetting of vaporized target material is qualitatively similar to experimental observation. The velocity flow field developed within the target is shown to have features quite similar to those found in calculations of near-surface explosion cratering. Specific application of Maxwell's analytic Z-Model (developed to interpret the flow fields of near-surface explosion cratering calculations), shows that this model can be used to describe the flow fields resulting from the impact cratering calculations, provided that the flow field center is located beneath the target surface, and that application of the model is made late enough in time that most of the projectile momentum has been dissipated.

Thomsen, J. M.↗

NASA NTRS1978

Floor-fractured craters on the moon and Mars

Impact craters on the moon provided primary pathways for volcanic eruptions through shock-induced fractures that immediately or subsequently tap magma reservoirs. Evidence for this process includes unbreached lava-filled craters and fractured crater floors with associated eruptives. Over 200 craters with floor fractures have been identified on the moon. They commonly occur along the margins of irregular maria, thereby suggesting a link to this important phase of lunar volcanism. Topographic data reveal small elevation differences between the summit of the remnant central peaks and crater rim, and in many cases suggest that floor fracturing resulted from a tabular intrusion localized beneath the crater with uplift of the crater floor. A comparison of lunar and Martian crater photographs shows that some Martian craters also exhibit similar highly localized endogenic modifications.

Schultz, P. H.↗

NASA NTRS1978

An alternative model for the Manicouagan impact structure

Geologic evidence suggests that the 210 million year old Manicouagan impact structure of eastern Quebec is an endogenically altered crater analogous to many lunar floor-fractured craters. According to this hypothesis, the impact at Manicouagan formed a transient cavity 80 km in diameter, generating melted target material which created a pool about 65 km in diameter in the bottom of the crater. Collapse of the transient crater rim and formation of a central peak-ring complex about 15 km in diameter subsequently occurred. Intrusion of a tabular magmatic body into the fractured and brecciated rock below the crater took place before recent glaciation; the intrusion caused an outer ring fracture around the crater.

Orphal, D. L.↗