Device includes load cell attached to rigid structure. Crosshead directly beneath cell is connected to constant-speed electrical motor. Crossarm supported by crosshead serves as platform on which bodies are tested. Test data are recorded on X-Y recorder which is connected to load cell and motor

Haehner, C. L.

Tarpley, J. L.

English

NASA Technical Reports Server

October 1975
	 B75-10214 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Apparatus for Measuring Static Coefficient of Friction

Under Compressive Loads 
A standard conventional test apparatus that 
measures the static coefficient of friction between two 
bodies is shown in Figure 1. This mechanism is 
satisfactory for testing under low stress conditions. 
For testing under high stress conditions, a new 
apparatus has been designed and built, employing the 
design shown in Figure 2. This new apparatus has 
been used to measure the static coefficient of friction 
of bodies under compressive stress of up to 600 psi 
(4.1x106
 N/rn2). 
The new apparatus includes a load cell attached to 
a rigid structure. A crosshead directly beneath the cell 
is connected to a constant-speed electrical motor. A 
crossarm supported by the crosshead serves as a 
platform on which the bodies are tested. Test data are 
recorded on an X-Y recorder which is connected to the 
load cell and the motor. 
Before measurements are initiated, the body (test 
specimen) is placed between the two mounting plates 
Upper 
Body ...
	
Weight 
Lower 
Body
which have been machined to the proper surface 
finish from material to be tested. The four bolts on 
top of the plate/spring assembly are then adjusted 
until the desired compressive load is reached. A 
special index mounted on the side of the assembly 
shows how much the spring must be compressed to 
obtain the desired load. 
The test procedure for both the conventional and 
the new apparatus is the same: The crosshead motor 
is switched on, and this allows the crosshead to move 
down, away from the load cell. The resulting tension 
on the filament applies horizontal force to the upper 
body. After this force reaches sufficient magnitude to 
overcome friction between the two bodies, the upper 
body begins to translate toward the pulley. This 
translation comes in spurts because, as the upper 
body .
 moves, the filament tension is temporarily 
relaxed and then is applied again bythe crosshead. 
Load 
Cal I 
F Rigid Structure
Recorder 
Y
X 
Filament 
Pulley
Crossarm 
To Be	 Powero—. 
Friction	
Swlt:_j,JTarrT	 CrossheadDC 
Input	 Moto 
Measured
Figure 1. Apparatus for Measuring Static Coefficient of Friction
(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=19750000214 2020-03-19T20:26:47+00:00Z
Spring 
Mountin 
Plat
Magnified View 
To Load
Cell 
Body	 Crossarm
Plates 
Crosshead 
Figure 2. Use of Spring To Provide Compressive Force 
The force F necessary to overcome the friction is 	 Patent status: 
recorded continuously on the X-Y recorder. The 	 This invention is owned by NASA, and a patent 
coefficient of friction IA is obtained from the following 	 application has been filed. Inquiries concerning 
equation:	 nonexclusive or exclusive license for its commercial 
= F/N	 development should be addressed to: 
Patent Counsel 
where F is obtained from the recorder and N is the 	 Goddard Space Flight Center 
normal force supplied by the compressive load.	 Code 204 
Greenbelt, Maryland 20771 
Note: 
Requests for further information may be directed 	 Source: Carl L. Haehner and 
to:	 John L. Tarpley 
Technology Utilization Officer 	 (GSC-11893)
Goddard Space Flight Center 
Code 704.1 
Greenbelt, Maryland 20771 
Reference: TSP75-10214 
B75-10214	 Category: 06 (Mechanics)


Apparatus for measuring static coefficient of friction under compressive loads

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server