Test motor in which high initial pressure can be reduced suddenly provides a method of testing stress effects in the throat of a rockets nozzle. Motors operating pressure is increased to aggravate tensile stresses in a submerged throat. Opposing compression stresses are limited by control of the operating pressure

Estes, E. G.

English

NASA Technical Reports Server

September 1969	 Brief 69-10358 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Stress-Testing of the Throat of a Rocket's Nozzle 
Test Motor
Typical Service Motor 
800 
0 
C 
- 600 
U, 
U) 
U)
°-	 400 
200 
01 
0
	
4	 8	 12	 16	 20
	
24	 28	 32 
Seconds 
Fig. 1 Chamber Pressure Versus Time 
1200 
1000 
The problem: 
To develop a method of testing the effects of stresses 
in the throat of a rocket's nozzle. Tensile stresses are 
developed in the material of the throat by great tem-
perature differentials; when the throat is submerged 
within the motor's chamber, the throat itself is corn-
time, the opposing compression stresses had to be 
limited by control of the operating pressure. 
The solution: 
A test motor in which high initial pressure can be 
reduced suddenly. 
pressed by the pressure in the chamber. A method How it's done: 
was needed whereby the motor's operating pressure
	 Initially the motor is operated at a pressure higher 
could be increased to aggravate the thermally induced
	 than normal in order to create a higher-than-normal 
tensile stresses in a submerged throat; at the same
	 heat flux to the material of the throat. When the ther-
-•	
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19690000356 2020-03-16T18:15:22+00:00Z
C 
.0 
'-C 
-0 ) 0)0, 
11
Thermal Stress
- 
(Overtest) Net	 tress 
(Over test) 
N 
//YNet Stress N (Flight)
N 
2	 3	 4 5If
Time (Seconds)
_ 
Pressure Stress 
(Overtest)
Fig. 2. Stresses at a critical point in the throat 
material versus time; net stress is thermal 
stress plus pressure stress. 
mally induced tensile stress is at maximum, pressure 
in the chamber is dropped suddenly to a level well 
below normal so that the tensile stresses are dominant 
(figs. 1 and 2); the stress-inducing temperature dif-
ferential falls much more slowly than the pressure. 
The time at which maximum tensile strength occurred 
was established by three-dimensional thermostruc-
tural analysis; the drop in chamber pressure was 
effected by designing a step in the propellant-grain 
burning-surface area. The analysis and propellant-
grain designs were based on complete characteriza-
tion of all involved materials, up to the maximum 
expected operating temperatures. 
Earlier methods used either (I) test motors operat-
ing at pressures higher than normal in order to produce 
great heat flux, without consideration of the opposing 
pressure stresses; (2) propellants burning at extremely 
high temperatures to effect a great heat flux; or (3) 
heat-shock tests of samples of throat material in the 
laboratory. The new method has several advantages: 
it is selective, permitting testing of the throat for the 
critical stresses of concern; it is economical in that 
normal propellant and reusable hardware are used; 
by exaggeration (overtesting) of the critical stress, a 
high level of confidence in design of the throat is
established by very few tests; and it is realistic, the 
throat being tested in its normal chemical environ-
ment. 
Notes: 
I. The method may interest manufacturers of rocket 
nozzles or pneumatic components or systems. 
2. No further documentation is available. Inquiries 
may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B69-10358 
Patent status: 
This invention is owned by NASA, and a patent

application has been filed. Royalty-free, nonexclusive

licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546.

Source: E. G. Estes of 
McDonnell Douglas Corporation

under contract to

NASA Pasadena Office

(N PO- 1031 1) 
Brief 69-10358	 Category 05 


Stress-testing of the throat of a rocket's nozzle

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server