Micro-mechanics modeling of compressive strength and elastic modulus enhancements in unidirectional CFRP with aramid pulp micro/nano-fiber interlays

Compressive strength and elastic modulus of unidirectional carbon fiber reinforced polymer (UD-CFRP) have been enhanced experimentally by using soft micro-length Aramid pulp (AP) micro/nano-fiber interlays. This study presents a micro-mechanics model to prove theoretically such enhancements in the compressive strength and elastic modulus of UD-CFRP are possible. The micro-mechanics model recognizes the importance of in-situ formed graded interfacial region between carbon fiber plies generated from the random distribution and out-of-plane movements of micro-length AP micro/nano-fibers. The micro-mechanics model shows that even an areal density of only similar to 4 g/m(2) of AP micro/nano-fibers (with the interlay thickness < 30 mu m) is sufficient to generate the enhancements in both compressive strength and elastic modulus along the carbon fiber direction of UD-CFRP. The new micro-buckling or shear failure mechanism has been identified to be responsible for the compressive strength enhancement, instead of local delamination in plain UD-CFRP. The theoretical and experimental findings show interfacial microstructural designs at the carbon fiber ply interface can be critical to the bulk properties of CFRP.