Evaluation of the transverse response of fiber-reinforced composites using a cross-shaped sample geometry

Abstract

The present study introduces the single-fiber, cross-shaped specimen for determination of the response of the fiber-matrix interface to transverse tension, in the absence of free-edge effects, which have been suggested to influence the behavior of uniform-gage samples. This test was found to successfully cause interface damage and matrix plasticity in the center section of the cross. A cursory stress analysis and experimental results were presented which indicate that the remotely-applied tensile stresses are uniform (along the x-axis) over a significant width in the center of the cross, and are not significantly different in magnitude from the normal stress in the uniform (vertical) section. This test was used to investigate SCS-6/Ti-6Al-4V and ACMF/Ti-6Al-4V composites. Earlier attempts to characterize the response of different fiber/matrix interfaces in uniform-gage samples by observing the interface at the free surface were unsuccessful; however, tensile tests using cross-shaped samples were able to distinguish between the two different interface responses. A simple method to calculate the interface tensile strength is presented and provides a preliminary value of 130 MPa for the SCS-6/Ti-6Al-4V interface, and 277 MPa for that of ACMF/Ti-6Al-4V. The value for SCS-6 is higher than previous estimates, where a strength of zero was reported to bestmore » fit the observations in straight-sided tests. Further experimental and theoretical studies with these systems are underway to determine the interface debond stress (and the scatter in the measurements) and the failure mechanism of the interfaces.« less