Abstract A test specimen which is particularly suitable for testing the tensile strength of high strength, but brittle fibers incorporated in a resin matrix in unidirectional laminates. Each test specimen comprises a flat, unidirectional laminate with integrated loading pads at each end of the unidirectional laminate. The loading pads are made integral with the unidirectional laminate by: (1) employing substantially the same resin in the pads as is present in the flat laminate; (2) employing different reinforcing within each pad with the fibers on the inner side of each pad being the same as those present in the unidirectional laminate and with the fibers on the outer side of each pad being formed from generally high strength, nonbrittle material to withstand the crushing action of test machine jaws; and (3) by assembling the uncured components of the specimen and curing them in a single curing step without an additional adhesive. The ratio of brittle/non-brittle fibers in the pads is between about 1:2 and about 2:1.
The tensile specimen of claim 1 wherein said brittle fibers are selected from the group consisting of graphite and boron.
Claim 2
Dependent Claim
15 words
The tensile test specimen of claim 2 wherein said high-strength, non-brittle fibers are glass fibers.
Claim 3
Dependent Claim
13 words
The tensile test specimen of claim 1 wherein said ratio is about 2:1.
Claim 4
Dependent Claim
17 words
The tensile test specimen of claim 1 wherein each said pad is formed from six fiber-reinforced plies.
Claim 5
Dependent Claim
21 words
The tensile test specimen of claim 5 wherein the thickness of said laminate is about 0.04 in. to about 0.05 in.
Claim 6
Dependent Claim
205 words
A tensile test specimen for use in testing high-strength brittle fibers comprising: a unidirectional laminate comprising a plurality of fiber-reinforced resin plies, said fiber being selected from the group consisting of graphite and boron fibers and said laminate having width-defining surfaces of a width greater than its thickness; and discrete pads formed integral with said laminate for gripping by the jaws of a tensile test machine with a pair of said pads being disposed on each said laminate surface adjacent the ends thereof to leave exposed sections of said surfaces between said pads on each of said surfaces for fracturing when subjecting said specimen to tensile loading, each of said pads comprising a plurality of plies of substantially the same resin as in said laminate reinforced with one of said graphite and boron fibers and with glass fibers, the ratio of said graphite/boron-reinforced plies to said glass-reinforced plies being between about 1:2 and about 2:1, said graphite/boron-reinforced plies being disposed between said laminate and said glass-reinforced plies, the plies in each of said pads having differing surface areas and being arranged in order of size with the ply having the largest area in each pad being disposed on the unidirectional laminate to minimize stress concentration.
Claim 7
Dependent Claim
22 words
The tensile test specimen of claim 7 wherein the total number of said graphite/boron reinforced plies and said glass-reinforced plies is six.
Claim 8
Dependent Claim
13 words
The tensile test specimen of claim 8 wherein said ratio is about 2:1.
Claim 9
Dependent Claim
21 words
The tensile test specimen of claim 8 wherein said laminate has a thickness of about 0.04 in. to about 0.05 in.