Nondestructive testing of defects in adhesive joints

in comparison to that of the base resin was due to the high degree of compatibility arising from
the polar groups of HTPB and UPR. The tensile strength of maleated HTPB blends gradually
decreases on adding progressively larger amounts of rubber due to the higher flexibility of
maleated HTPB.
The elongation at break increases with increase in elastomer concentration as shown in Fig.3.
The addition of MA-g-HTPB produced the greatest increase in elongation at break compared to
HTPB due to the higher flexibility and compatibility of maleated HTPB. The elongation at break
of MA-g-HTPB/UPR is about 219 % of UPR
The energy absorption of the cured resin as a function of rubber concentration is
shown in Fig.4. At 3-wt % MA-g-HTPB concentration, the energy absorption of the blend was at
a maximum (about 305 % of the energy absorption of UPR). The energy absorption is related to
the toughness of the sample. Higher elongation at break values increases the toughness of MA-g-
HTPB. The performance of MA-g-HTPB was far superior to HTPB, due to better dispersion of
the rubber phase as particles in the continuous polyester phase.
Flexural properties
Fig. 5 shows the variation of flexural strength with rubber content. The flexural strength of
MA-g-HTPB/UPR blend decreases with elastomer concentration due to the higher flexibility and
compatibility of maleated HTPB.
Water absorption
Water absorption of HTPB and maleated HTPB modified resins is shown by Fig.6.
The maleated HTPB has slightly higher water absorption compared to HTPB due to the higher
functionalisation.
CONCLUSIONS
The study reveals the effect of incorporating functional elastomers into UPR at low
concentrations by a physical method. Toughness and tensile/flexural properties show maximum
improvement at about 2-3 wt % HTPB concentrations. Interestingly, the increase in toughness (76
% of the energy absorption of UPR) has been observed with simultaneous increase in tensile and
flexural properties for HTPB.
Maleation increases the toughness and elongation at break of HTPB. At 3-wt % MA-g-
HTPB concentration, the energy absorption of the blend was at a maximum (about 305 % of the
energy absorption of UPR) with marginal lowering of tensile and flexural properties.