Results for 12,000 impacts on a wide range of materials were studied to determine the reproducibility of the liquid oxygen impact test method. Standard deviations representing the overall variability of results were in close agreement with the expected values for a binomial process. This indicates that the major source of variability is due to the go - no go nature of the test method and that variations due to sampling and testing operations were not significant

Gayle, J. B.

English

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NASA TN D-7905 NASA TECHNICAL NOTE 
I-
REPRODUCIBILITY OF LIQUID OXYGEN 
IMPACT TEST RESULTS 
J. B. Gayle 
John F. Kennedy Space Center 	 0UTI0,, 
Kennedy Space Center, Fla. 32899
'76i91 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. • MAY 1975
https://ntrs.nasa.gov/search.jsp?R=19750014413 2020-03-22T21:33:42+00:00Z
I .	 Report No. 2.	 Government Accession No. 3.	 Recipients	 Catalog No. 
NASA_TN_D-_7905 
4.	 Title and Subtitle 5.	 Report Dote 
REPRODUCIBILITY OF LIQUID OXYGEN IMPACT May 1975 
6.	 Performing Organization Code TEST RESULTS 
7.	 Author(s) 8.	 Performing Organization Report No. 
J. B. Gayle  
9.	 Performing Organization Name and Address 10. Work Unit No. 
NASA John F. Kennedy Space Center
11. Contract or Grant No. 
Support Operations - Laboratories Division 
Kennedy Space Center, Florida 32899 13. Type of Report and Period Covered 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration Technical Note 
Washington, D. C.
	
20546 14. Sponsoring Agency Code 
15. Supplementary Notes 
16. Abstract 
Results for 12 000 impacts on a wide range of materials were studied to 
determine the reproducibility of the liquid oxygen impact test method.. 
Standard deviations representing the overall variability of results were 
in close agreement with the expected values for a binomial process.
	 This 
indicates that the major source of variability is due to the "go - no go" 
nature of the test method and that variations due to sampling and testing 
operations were not significant. 
17. KeyWords 18. Distribution Statement 
Statistical Analysis Unclassified - Unlimited 
19. Security Classif.(of this report) .20. Security Clossif.(of this page) 21. No. of Pages 22. Price 
Unclassified Unclassified 6 $3.25
*For sale by the National Technical information Service, Springfield, Virginia 22151 
REPRODUCIBILITY OF LIQUID OXYGEN IMPACT TEST RESULTS 
By J. B. Gayle 
John F. Kennedy Space Center 
INTRODUCTION 
Under suitable conditions, oxygen reacts violently with a wide range of materials. 
Methods for assessing the hazard of any given oxygen/material combination are there-
fore essential for the design and operation of equipment and facilities used in the 
manufacture, storage, transportation, and utilization of oxygen. 
Although many testing methods have been developed, probably the most widely 
accepted is the liquid oxygen (LOX) impact test in which specimens are subjected to 
mechanical impact while submersed in LOX. The most common version of this test, 
developed by Lucas and Riehl (ref. 1), was originally known as the Army Ballistic 
Missile Agency (ABMA) Impact Sensitivity Test. Today, three similar test methods 
are widely used: (1) NASA MSFC-SPEC-106-B, (2) AF Specification Bulletin 
527, and (3) ASTM Test for Compatibility of Materials with Liquid Oxygen, 
D-2512-70. 
As an aid to the reader, where necessary the original units of measure have been 
converted to the equivalent value in the Systeme International d'Unit 's (SI). The SI 
units are written first, and the original units are written parenthetically thereafter. 
DISCUSSION 
During the past 16 years, approximately 250 000 individual test drops on 
more than 2000 different materials have been conducted by NASA in accordance with 
MSFC-SPEC-106-B. This test procedure consists of imparting a known amount of 
energy from an essentially free falling plummet to a striker pin that rests directly on 
a test specimen immersed in LOX. The test is relatively simple, and the impact 
energy is easily controlled by varying the drop heights of the plummet. In most 
1
instances, a 9.09-kilogram plummet (20 pounds) is dropped from a height of 1.1 
meters (3.7 feet) onto a striker pin with a 1.27-centimeter diameter (0.5 inch), 
thereby imparting an impact energy of 7.72 x 10 J/m 2 (10 kilogram-meters) to 
the test specimen immersed in LOX. The occurrence of a reaction is indicated by 
(1) an audible report, (2) a visible flash (in a darkened room), or (3) burning or 
charring of the specimen, or any combination of these three. Because each drop or 
trial either results in a reaction or does not, impact tests belong to the general 
category of "all-or-none" or "go - no go" type tests that can result in only one of two 
possible outcomes. The test is normally repeated several times, and the percent of 
total trials yielding a particular outcome is reported. 
The impact and other "all-or-none" type tests possess the characteristic 
features of a binomial process. The observed reproducibility of results should 
therefore reflect the inherent variability of a binomial process and any contributions 
associated with the sampling and testing operations. This inherent variability may 
be represented by the standard deviation of a binomial process which depends on 
the distribution of outcomes and the number of trials as follows: 
cJiiom i a I	 =	 (1) 
where
p = percent of one outcome 
q = (100-p) = percent of other outcome 
n = number of trials 
cTbinomial = expected standard deviation of a binomial process
To obtain direct experimental information on the variability of the test, 
results were pooled for 121 groups of data, each including five sets of 20 impacts 
on replicate samples of a single material in LOX. Approximately one-third of these 
data was supplied by the Director of the Materials and Processes Laboratory at 
Marshall Space Flight Center. Results were included for a wide range of materials 
such as titanium alloys, plastics, elastomers, and lubricants. The percent reactions 
ranged from 0 to 100, but most values were well below 50. Because the amount of 
data for materials giving more than 50 percent reactions was small, the definitions 
of success and failure for thes&few tests were interchanged before pooling. Thus, 
a set of data giving 60 percent reactions was treated like a set giving 40 percent 
reactions and was pooled with other sets giving approximately 40 percent reactions.* 
The resulting pooled data that corresponds to a binomial type process with up 
to 50 percent reactions is presented in table I and figure 1. 
TABLE I. - COMPARISON OF OBSERVED STANDARD DEVIATIONS FOR 
LOX IMPACT TEST RESULTS WITH EXPECTED VALUES FOR 
CORRESPONDING BINOMIAL PROCESS 
Standard Deviation, Percent 
Number Average Pooled Range of Pooled Pooled Binomial 
of Sets Values, Percent Values, Percent Values Process 
10 1.00 1.00-	 1.00 2.2 2.2 
7 2.00 2.00-	 2.00 2.7 3.1 
15 3.00 3.00-
	 3.00 3.4 3.8 
10 4.00 4.00- 4.00 4.5 4.4 
11 5.00 5.00-	 5.00 4.7 4.9 
9 6.56 6.00-
	 7.00 6.0 5.5 
13 9.08 8.00-10.00 6.6 6.4 
16 15.62 11.00-20.00 7.9 8.1 
10 25.60 21.00 - 30.00 8.5 9.8 
20 40.00 31.00-50.00 12.5 11.0
* The basis for this procedure is equation (1), which indicates that interchanging 
the definitions of success and failure has no effect on the binomial standard deviation. 
3 
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Inspection of the data indicates close agreement between the observed standard 
deviations and the expected values for a binomial process, and F tests on the 
corresponding variances failed to indicate significant differences. 
Any contributions to the variability of test results due to sampling errors or 
to testing variations would be expected to increase the observed standard deviations 
in accordance with the following relation: 
std dev =	 std dev2 + std dev2 + std dev2
	 (2) (observed)	 (binomial)	 (sampling)	 (testing) 
where std dev is standard deviation. 
CONCLUDING REMARKS 
The fact that the observed standard deviations did not significantly exceed the 
expected values for a binomial process indicates that for these data, sampling and 
testing errors were not significant. It therefore appears that the binomial model can 
be used as a close approximation for impact test results for most applications. 
John F. Kennedy Space Center 
National Aeronautics and Space Administration 
Kennedy Space Center, Florida, November 25, 1974 
5
REFERENCE 
1. Lucas, W. R.; and Riehi, W. A.: An Instrument for Determination of Impact 
Sensitivity of Materials in Contact with Liquid Oxygen. ASTM Bulletin, 
No. 244, Feb., 1960, pp. 29-38. 
6	 NASA-Langley, 1975
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Reproducibility of liquid oxygen impact test results

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