A study of the pull-out performance of PPTA fibres in composites of ethylene-type ionomer matrices/PPTA fibres

The mean frictional shear stresses of six ionomer resins and sized Kevlar f ibre were determined from fibre pull-out tests. A study of the failure mech anisms occurring during pull-out revealed that fibre delamination and fibre resin adhesion were factors which increased the measured frictional shear stresses and that there,was a definite grouping of high and low frictional shear stress values. The low frictional shear stress values were used to ca lculate the mean frictional shear stress values, <(<tau>)over bar>(B), beca use these were uncomplicated by fibre delamination and fibre resin adhesion , since these factors (delamination and adhesion) are certainly not unexpec ted in an ionomer/Kevlar composite. From these shear stress values, it was determined that critical fibre lengths should be between 35 and 72 mm far t he high tensile strength Kevlar fibres within ionomer matrix, for the compo site to be used effectively. The ratio of the debonding force (F-B) to the frictional shear force (F-F), theta, did not vary significantly with the le ngths of the embedded reinforcing fibres. Both debonding and frictional for ces indicate increasing trends with the interfacial contact areas. The rati o of the interfacial bonding strength (<(<tau>)over bar>(B)) to the frictio nal shear stress (tau (F)), phi, for the resin PEA-6 compared to the surfac e modified polyp-phenylene terephthalamide) (PPTA) fibre ranged from 2 to 2 4. These ratios were grouped into two, viz: those where phi > 11 and those with phi < 7. Using only the tau (F) where phi > 11 provided a mean frictio nal shear stress of 0.94 MPa and a standard deviation, s, of 0.23 MPa (the number of test samples, n, was 9). This value is little different from the frictional shear stresses measured for sized PPTA (0.84 MPa). The decrease in the values of phi is attributed to the decrease in <(<tau>)over bar>B, d ue to the surface modification reaction, without necessarily affecting the frictional shear stress, tau (F).