Deformation Micromechanics in Model Carbon Fiber Reinforced Composites Part II: The Microbond Test

Abstract

Raman spectroscopy is used to study the deformation micromechanics of the microbond test for a carbon fiber epoxy resin system using surface-treated and untreated PAN-based fibers, and the results are compared with those of the conventional microbond test. Fiber strain and interfacial shear stress (ISS) are mapped along the embedded regions of fibers during the test using the Raman technique, and the maximum value of ISS, τ_max, is determined. The maximum τ_max value can be used to characterize the strength of the fiber matrix interface, and it is higher for specimens with surface-treated fibers. The apparent value of interfacial shear strength, τ _a , determined from conventional analysis of the microbond test, is a function of the embedded fiber length. However, the value of τ _a extrapolated to zero embedded length, τ _i , is comparable to the maximum ISS value, τ_max, determined from the Raman analysis. The influence on the results of radial compression and geometric factors, such as droplet shape and size and separation of the knife edges, is also discussed.