An experimental/analytical investigation of combined shear/end loaded compression strength testing of unidirectional composites
The Illinois Institute of Technology Research Institute (IITRI) composite compression test method is probably the most widely accepted as producing accurate results. Difficulties associated with the application of this method, however, have fueled continued research into alternate methods. <p>...
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Format: | Others |
Language: | en |
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Virginia Tech
2014
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Online Access: | http://hdl.handle.net/10919/46404 http://scholar.lib.vt.edu/theses/available/etd-12232009-020534/ |
Summary: | The Illinois Institute of Technology Research Institute (IITRI) composite
compression test method is probably the most widely accepted as producing
accurate results. Difficulties associated with the application of this method,
however, have fueled continued research into alternate methods.
<p>In this study, the Wyoming End-Loaded Side-Supported (ELSS) test scheme was
investigated in a combined shear/end loaded mode. This system was examined
experimentally and analytically to establish the method as a reasonable
alternative to IITRI testing. Combined shear/end loading was accomplished by
applying a controlled amount of clamping force to the stabilizing blocks,
allowing them to transmit shear force to the coupon faces through friction.
<p>The fabrication of test specimens from a BASF graphite IBMI material system
is described in detail, including the application of a novel "press-clave"
processing system developed at Virginia Tech. This system allows for cost-effective
manufacture of flat panels under conditions similar to autoclave
processing. For the material system employed in this study, this process
proved superior to conventional hot press processing.
<p>Experimental results include strengths and failure modes for both tabbed and
untabbed coupons tested by the combined loading ELSS method, and these data
are compared to the results by the IITRI method. Strength was found to
increase with increasing clamping, but reached a maximum with both
untabbed and tabbed specimens. The maximum strength achieved with
untabbed specimens was still significantly below the IITRI value, but the
tabbed specimens reached strengths comparable to the IITRI data. The failure
mode also changed with increased clamping, from end crushing to brooming
with untabbed specimens, and from end crushing to shear failure with tabbed
specimens. As the strength and failure mode achieved with the combined
loading ELSS method using tabbed specimens are both similar to those seen in
the IITRI tests, this modified technique can be considered equivalent to the
IITRI method. Preliminary data from tests using novel nonbonded tabs were
also similar to those given by the IITRI method.
<p>The finite element method was used to analyze the effect of increasing the
clamping force. Competing effects of locally complex and severe stresses at
the coupon end and a stress concentration which develops at the end of the
gage section were shown to limit the maximum strength. Tabs appear to
reduce the stress concentration while further decreasing the stresses at the
end, allowing results comparable to those given by the IITRI method to be
achieved. === Master of Science |
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