Managing director, Analysis and Design Consultants, Newport Pagnell,
Materials engineer, Ruston Gas Turbines, New Products Division, Lincoln,
Research officer, Materials and Structures Department, Royal Aircraft Establishment, Farnborough, Hampshire
Pages: 14 Published: Jan 1988
An experimental evaluation of the ASTM D 4255 two-rail shear test has been carried out for the fatigue of unidirectional E-glass/913 epoxy. Results from the standard configuration were unsatisfactory with scatter on fatigue life of three orders of magnitude. A close examination of specimens revealed the presence of longitudinal cracks from the specimen free edge caused by the transverse loading component from rail bending. Specimens with such cracks had long lives while specimens without had short lives. The coupon configuration was thus modified with the inclusion of small slots at the location of the longitudinal cracks. This modification greatly decreased scatter of both static strength and fatigue life. Finite-element work showed a consistent shear field in the gage area of the slotted coupon. Experimental work showed a slightly lower value of stiffness from the modified coupon. An effective gage length for the slotted coupon was deduced. A useful S-N curve for unidirectional glass/epoxy in shear has been produced from a simple modification to an existing static shear test method. Its applicability to other materials and layups has been commented upon.
composite materials, fatigue, shear, glass/epoxy
Paper ID: STP26138S