Fixture and technique have been developed for predicting behavior of stiffened skin panels under biaxial compressive loading. Tester can load test panel independently in longitudinal and transverse directions. Data can also be obtained in combined mode

Hansard, E. T.

English

NASA Technical Reports Server

Compression Test Machine for Biaxial Compression Testing 
S
becember 1975	 B75-10319 
NASA TECH BRIEF 
Lyndon B. Johnson Space Center	
A 
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Biaxial Compression Test Technique 
(continued overleaf) 
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https://ntrs.nasa.gov/search.jsp?R=19750000319 2020-03-19T20:20:00+00:00Z
The problem: 
Sheet aluminum alloy, when used as a load-bearing 
skin or panel, can be stiffened either with integrally 
machined risers or with risers separately attached. 
When such sheets are stiffened primarily in one 
direction, as is often the case, problems with biaxial 
stability result. Studies of biaxial stability (longitudi-
nal versus transverse compression loading) also often 
ignore the problems of longitudinal strength degrada-
tion; sometimes correction factors are arbitrarily 
assigned with inadequate justification to the test 
procedure. 
The solution: 
A fixture and a technique have been developed for 
predicting the behavior of stiffened skin panels under 
biaxial compressive loading. The tester can load the 
test panel independently in the longitudinal and 
transverse directions. Independent data can be 
obtained in either test mode as well as in the 
combined mode. The effect of loading sequence can 
also easily be obtained. Provision is available to 
convert the specimen-simulated frames from a flat to 
a curved configuration. 
How it's done: 
A universal-type compression test machine, as 
shown, applies a longitudinal compression load 
simultaneously with a transverse load. This load is 
applied with a pair of rigid loading beams connected 
by hydraulic cylinders. A uniform loading is ensured 
at the ends by machining the specimen ends flat and 
parallel. The side loading beams are grooved to 
receive the specimen edge skin. Adjustable stops are 
provided to prevent excessive lateral deflection which 
would produce local bending of the edge skin.
A pin-end configuration is provided at the specimen 
ends via a steel adapter plate at each end with a 
knife-edge bearing on the machine heads. The 
adapter plate is segmented to accommodate a curved 
specimen. All bearing surfaces are liberally oiled 
during testing to minimize frictional resistance under 
combined loads. 
Longitudinal loads are controlled through the test 
machine. The transverse loads are applied separately 
by means of a hydraulic pump and are controlled 
through load-cell readouts. Load distributions are 
monitored, using strain gage readouts, in both 
longitudinal and transverse directions. Deflections 
normal to the skin panel are obtained by a pattern of 
transducers and are recorded incrementally during all 
test conditions. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Johnson Space Center 
Code AT3 
Houston, Texas 77058 
Reference: TSP75-10319 
Patent status: 
NASA has decided not to apply for a patent. 
Source: E. T. Hansard of 
General Dynamics Corp.
(MSC-14883)
. 
Categories: 08 (Fabrication Technology)
07 (Machinery) 
B75-10319
	 04 (Materials)


Biaxial compression test technique

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