Er. Sadiku et Rd. Sanderson, A study of the pull-out performance of PPTA fibres in composites of ethylene-type ionomer matrices/PPTA fibres, MACRO MAT E, 286(9), 2001, pp. 535-545
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).