Nondestructive testing of defects in adhesive joints

weight of the resin respectively to obtain a reasonable gel time. The resin was then poured into
the tensile mould. Samples for impact test and flexural strength were cast separately in
appropriate moulds. Curing was done at room temperature for 24 hrs, followed by post curing at
80 0 C for 3 hrs
The blends were prepared by the following procedure. Varying amounts (0-5 wt %) of the HTPB
were added to the resin. The mixture was stirred well using a mechanical stirrer to give a
homogeneous liquid. Curing of the blend was done as per the procedure employed for UPR.
Thereafter, post curing was done at 80 0 C for 3 hrs.
The samples after post curing were tested for tensile strength, elongation at break,
modulus, flexural strength and flexural modulus taking six trials in each case. The tensile and
flexural properties were tested on a universal testing machine (ASTM D 638-89).
Modification of UPR with MA grafted HTPB
Maleated HTPB is prepared by mixing HTPB with 5% MA and 0.5% benzoyl
peroxide in a Brabender at 100 0 C and 50 RPM speed for 10 min. The reaction of MA with HTPB
was confirmed by FTIR spectroscopy and titration. The amount of maleic anhydride reacted is
determined by refluxing a solution of maleated HTPB in xylene saturated with water for 1 hr and
then titrating with a solution of 0.05N ethanolic KOH using 1 % thymol blue as an indicator.
Varying amounts of MA modified HTPB containing 0-5 weight percentage of
elastomers were blended and cast with the UPR by the same procedure adopted earlier. The
tensile and flexural properties and water absorption were determined in accordance with ASTM
standards.
Test methods
Tensile testing
machine.
Tensile tests were carried out according to ASTM D 638-89 using a universal testing
Flexural properties (ASTM D 790-99)
Flexural strength is a measure of the load required to break a material
when it is subjected to bending Flexural modulus is the ratio of stress to corresponding strain
and is expressed in MPa. It is calculated by drawing a tangent to the steepest initial straight line
portion of the load- deflection curve
Water absorption
Water absorption of the sample was measured according to ASTM 570-81.
RESULTS AND DISCUSSIONS
Mechanical Properties of UP resin modified by Functional elastomers
Tensile Properties
Referring to Fig.1, tensile strength values obtained by adding HTPB were
significantly higher than that obtained by adding maleated HTPB. Tensile strength values reached
a maximum on adding progressively larger amounts of HTPB, but addition of more rubber
beyond this point resulted in a reduction of tensile strength. The improvement in tensile strength,