SEDL / STP / STP787-EB / STP28492S

Strain Rate Characterization of Unidirectional Graphite/Epoxy Composite

Daniel, IM
Professor and Director, Experimental Stress Analysis Laboratory, Illinois Institute of Technology, Chicago, Ill.

Hamilton, WG
Assistant Research Engineer, IIT Research Institute, Chicago, Ill.

LaBedz, RH
L. J. Broutman & Associates, Chicago, Ill.

Pages: 21    Published: Jan 1982

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Abstract

Unidirectional graphite/epoxy was characterized at various strain rates ranging from quasi-static to over 500 s⁻¹. Properties were obtained by testing thin rings 10.16 cm (4 in.) in diameter, 2.54 cm (1 in.) wide, and 6 to 8 plies thick under internal pressure. Unidirectional 0, 90, and 10-deg off-axis rings were tested to obtain longitudinal, transverse, and in-plane shear properties. In the dynamic tests internal pressure was applied explosively through a liquid, and the pressure was measured with a calibrated steel ring. Strains in the calibration and specimen rings were recorded with a digital processing oscilloscope. The data were processed and the equation of motion solved numerically by a minicomputer attached to the oscilloscope. Results were obtained and plotted in the form of a dynamic stress-strain curve. Times to failure were as short as 30 μs. The 0-deg properties which are governed by the fibers do not vary much with strain rate with only a moderate increase in modulus. The 90-deg properties show a marked increase in modulus and strength with strain rate. In-plane shear properties follow a similar trend, although less pronounced than transverse properties. In all cases ultimate strains do not vary much with strain rate.