SYMPOSIA PAPER Published: 01 January 1975
STP32319S

Reducing Variability in Composite Tensile-Strength Properties

Source

Variability in composite tension-test values limits the application of advanced composite materials to structural design loads far below the capabilities inherent to the reinforcing fibers. Failure probabilities of boron and graphite filaments on the low-strength side of the skewed distribution contribute to composite fracture initiation early in the loading cycle. Dispersion in composite test values at these low levels imposes restrictions on allowable design values to conform to the minimum in the test data population. Prestressing the prepreg materials affects a fiber strength property improvement by prebreaking the filaments at the defect sources of low load failure. Increases in “B” design allowable levels for boron and graphite-epoxy material systems are shown to relate to reductions in fiber strength dispersions accompanied by increases in the average values. Projections of composite “B” allowables to 297 ksi are made for defect-free filaments.

Author Information

Mills, GJ
Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.
Brown, GG
Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.
Waterman, DR
Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.
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Details
Developed by Committee: D30
Pages: 352–363
DOI: 10.1520/STP32319S
ISBN-EB: 978-0-8031-4660-0
ISBN-13: 978-0-8031-0309-2