General Disclaimer

One or more of the Following Statements may affect this Document

This document has been reproduced from the best copy furnished by the 

organizational source. It is being released in the interest of making available as 

much information as possible.

This document may contain data, which exceeds the sheet parameters. It was 

furnished in this condition by the organizational source and is the best copy 

available.

This document may contain tone-on-tone or color graphs, charts and/or pictures, 

which have been reproduced in black and white.

This document is paginated as submitted by the original source.

Portions of this document are not fully legible due to the historical nature of some 

of the material. However, it is the best reproduction available from the original 

submission.

Produced by the NASA Center for Aerospace Information (CASI)
5

6

BOEWG AEROSPACE COMPANY

A Dart& n of T^.e Soe ng Company

PC Box 3999

Seare Aa9vVion 96124-2499

tj1ksA-Ch- 17b392) EYPERIMENZAL INVESTIGATION N8b- 142 12

GF CeaTEb GhOkTh [YNAMICS jEceir,q Aerospace

Co., Seattle, flash.) 5 p HC A02 /MF A31

CSCL 038 Unclas

63/91 J4939

rian Stop IF-72

November 15, 1985

Dr. David H. Scott

Discipline Scientist

Planetary Geology and Geophysics Program

CODE E L

NASA Headquarters

600 Independence Avenue S. W.

Subject: Semiannual report (Contract NASW-3291 )

Dear David,

arr, enclosing a copy of the Program Abstract forwarded under separate

cover for use in the NASA Technical Memorandum. This summarizes our

current progress and results under contract NASW-3291 .

Please note the change in my mail stop. It is now H/S 1F-12. Please

wdate my address file for NASA mailings. The correct mail stop is quite s

necessary for timely receipt of incoming mail. Note that phone number has

also changed to (206) 655-2167. r

Thank You.

Sincerely,

Dr. Robert M. Schmidt

Shock Physics org 2-3647

M/S IF-72

Boeing Aerospace Co.

Seattle WA 98124

(206)655-2167
Experimental Investigation of Crater Growth Dynamics

Robert M. Schmidt, Kevin R. Housen, Michael D. Bjorkman and Keith A. Holsapple

Boeing Aerospace Co., M/S IF-72, P. 0. Box 3999, Seattle WA 98124.

This work is a continuation of an ongoing program whose objective is to perform experiments and to

develop scaling relationships for large-body impacts onto planetary surfaces. The centrifuge technique is used to

provide experimental data for actual target materials of interest. With both powder and gas guns mounted on the

rotor arm, it is possible to match various dimensionless similarity parameters, which have been shown to

govern the behavior of large-scale impacts. The development of the centrifuge technique has been pioneered by

the present investigators and is documented by numerous publications, the most recent of which are listed

below.

Understanding the dependence of crater size upon gravity has been shown to be key to the complete

determination of the dynamic and kinematic bchavior of crater formation as well as ejecta phenomena. (See

Table I in ref. 7). We have identified three unique time regimes in the formation of an impact crater. 2.5 The

"early" time regime represents the initial contact during which the target material is overdriven by the impactor.

The particle velocity in the target, initially one dimensional, is determined by the high pressure material

properties of the impactor and the target.

As the process continues into the "intermediate" time regime, the flow becomes two dimensional and a.

length scale based upon impactor size evolves. The specific characteristics of the impactor such as size,

velocity, and density can no longer be identified in the flow field. In their place an overall size scale evolves

which then holds out to much later times. The properties of the flow field depend only upon a particular product

of powers of the impactor size a, and impactor velocity U. This quantity a0μ is referred to as a coupling

parameters In particular cases the flow field in the intermediate regime has very special motions. For example.

if subsequent to the early-time regime, crater growth is independent of gravity, material strength and wave speed,

then crater dimensions should g ► -ow as a simple power-law in time with exponent equal to μi1+μ.

"Late" tine refers to the final stage when retarding forces due to gravity or material strength arrest the

decaying flow field to form the final crater or maximum transient crater. For this stage, we have shown that the

final crater should depend only upon the coupling parameter product aU U, gravity and/or strength 6,10

The existence of a coupling parameter for water was previously demonstrated by showing that the time

of formation could be simply related to the maximum transient crater volume and gravity. 9,11,15 Data for rate

of crater growth spanning over two orders of magnitude, were also presented. Those data are now supplemented

with microsecond resolution results which show that the power-law growth regime extends over a range of 5

orders of magnitude from a size scale on the order of source dimensions to approximatly 70% of the maximum

transient crater vclume. 18 This was true for all the different test conditions, which covered a range of gravities

from 1 to 5006 and produced final formation times on the order of 100 inset for the largest of the 1G tests and

less than 4msec for the 5006 tests.

An ultra high speed framing camera has now been used to obtain very early time explosion crater

growth in water. Framing rates up to 1.4 million pictures/sec provided interframe times on the order of source

relaxation times. However, no definitive observation of early-time growth has been observed for the types of

sources tested to date. Higher-velocity impacts should extend the duration of the early time regime and will be

pursued next. The complete growth curve for crater volume is shown below. Comparable curves for crater

depth and radius also show power-law growth. Both are in good agreement with the expected value of the

exponent equal to μ13(l+g).
G

O.O 1

m

E

7

\0 

1 0 ­4

Q

C d

4

OF POOR QUALITY

12:34:10 1 4—NOY-65

0

II C^

^^ Fgaern^a^

0 as.o .s so

e ]41 —ran

1 .74R 75.71k

0 .74.7 7.70

1 .744 14.00

.740 14.00

1 440 -440

1 J4N 17.40

v a.^..o^ ^ .ne7

♦ ^•.-tea <>•.00

O —4

—O 1 O-4D. (3 1

Mrne^T

r1w.4^

Other ongoing data analysis of high-G experiments in saturated sand also are in good agreement with the

appropriate power-law growth behavior as was seen for the water experiments above. 12,14 Detailed

examinadon l6,17 of previous data for explosions in dry sand obtained by Piekutowski8 and more recent impact

data in both dry and wet sand obtained at Ames by Schmidt and Piekutowski 13 indicates that these data have

many of the same growth features also. While there are still individual detai'.s that are not completly

understood, it appears that the radius follows the expected growth rule in most of the shots. However,

especially for the dry Flintshot sand, the depth has already "flattened out" by the earliest times observed

(200-600psec). We suspect that the effects of gravity occur earlier in time for depth than for radius, since the

latter is at zero depth. The volume, which depends more strongly on the radius tends to be in resonable

agreement with the expected power-law behavior. Another explanation now being examined is that the effective

origin of the flow field does not coincide with the center of the explosive charge, but seems to be at the bottom

of the charge as observed by Piekutowski. 8 For the impact experiments, it very clearly depends upon the

impact conditions and for the lower velocities into water the effective origin was on the order of 10 diameters

below the surface.

These experiments to record dynamic data for crater growth provide a very detailed and critical test of a

complete and unified scaling theory for impact cratering. They provide very important information that is

required to apply and extend the scaling to planetary problems currently under investigation by the technical

community.

1)Bjorkman, M. D. (1984) Feasibility of determing impact conditions from total melt volume (abstract). In

Lunar Planteary Science XV, 64-65.

2) Holsapple, K. A. (1984) On crater dynamics: Comparisons of results for different target and impactor

conditions (abstract). In Lunar Planetary Science XV, 367-368.

I
3) Holsapple, K. A. and K. R. Housen (1985) Cratering estimates for rock and ice (abstract). Lunar Plant. Sci.

XVI, Houston.

4) Holsapple, K. A. and K. R. Housen (1985) Scaling of catastrophic impacts. Memoirs of Italian

Astronomical Society (in press).

5) Holsapple, K. A. and R. M. Schmidt (1985) Point-source solutions and coupling parameters in cratering

mechanics. Submitted for publication to J. Geophys. Res.

6) Housen, K. R. (1984) Cratering flow fields: A general form and the Z-model (abstract). In Lunar Plantary

Science XV, 377-378.

7) Housen, K. R., R. M. Schmidt, and K. A. Holsapple (1983) Crater ejects scaling laws: Fundamental forms

based upon dimensional analysis. J. Geophys. Res. 88(B3), 2485-2499.

8) Piekutowski,A. J.(1980) Formation of bowl-shaped craters. Proc. Lunar Sci. Conf. I1 th, 2129-2144.

9) Schmidt, R. M. (1981) Scaling crate: time of formation (abstract). EOS (Trans. Amer. Geophys. Union) ,

62, 944.

10)Schmidt, R. M. (1983) Strength-gravity transition for impact craters in wet sand(abstract). In Lunar

Planetary Science XIV, 666-667,

11)Schmidt, R. M. (1983) Centrifuge quarter-space cratering results: A gravity criterion for kinematic

similarity (abstract). EOS (Trans. Amer. Geophys. Union) , 64,747.

12)Schmidt, R. M. (1984) Transient crater motions: Saturated sand centrifuge experiments (abstract). In Lunar

Planetary Science XV, 722-723.

113) Schmidt, R. M. and A. J. Piekutowski (1982) Quarter-space impact experiments: Particle-motion and

crater-growth measurements (abstract). EOS (Trcm. Amer. Geophys. Union) , 63, 1020.

14) Schiridt, R. M. and A. J. Piekutowski (1983) Development of the quarter-space technique for cratering

experiments on a centrifuge (abstract). In Lunar Plantary Science XIV, 668-669.

15)Schmidt, R. M. and K. A. Holsapple (1984) Explosively generated water waves (abstract). EOS (Trans.

Amer. Geophys. Union) 65,221.

16)Schmidt, R. M., K. R. E:ousen, M. Luke, and A. J. Piekutowski (1984) Scaling consistency tests for

cratering experiments (abstract). EOS (Trans. Amer. Geophys. Union) 65, 983.

17)Schmidt, R. M., K. R. Houser., and A. J. Piekutowski (1985) Experimental observations on crater growth

regimes (abstract). EOS (Trans. Amer. Geophys. Union) 66, 296.

18)Schmidt, R. M., K. R. Housen, and V. T. Webbeking (1985) Growth of water cavities over a range of 105

in time (abstract). EOS (Trans. Amer. Geophys. U.) 66.
Experimental Investigation of Crater Growth Dynamics

Robert M. Schmidt, Kevin R. Housen, Michael D. Bjorkman and Keith A. Holsapple

Boeing Aerospace Co., MIS 1F-72, P. O. Box 3999, Seattle WA 98124.

A Centrifuge has been used to investigate large-body impacts onto planetary surfaces.

At elevated gravity, it is possible to match various dimensionless si •-Hilarity parameters which

have been shown to govern large-scale impacts. Observations of crater growth and target flow

fields have provided detailed and critical tests of a complete and u .tied scaling theory for

impact cratering.

The scaling theory has also been applied to the problem of coLisional fragmentation.

This exercise has shown that current methods of scaling laboratory experiments up to asteroidal

size scales may be incorrect. In particular, asteroids may be considerably easier to shatter than

predicted by current models of fragmention.