Nondestructive testing of defects in adhesive joints

found to be 80.51 and 77.31, respectively. The crystalline material in the total cellulose was
expressed by crystallinity index, which is an empirical measure of relative crystallinity.
Crystallinity index of flax was found to be 0.7580 whereas, in case of flax-g-poly(MA),
crystallinity index has been found to be 0.7065. The incorporation of monomer chains to the
back-bone of flax had impaired the crystallinity of flax fiber. Therefore, grafting decreased the
crystallinity of flax with reduction in its stiffness and hardness.
Mechanical properties of Original flax and Graft Copolymers Reinforced Phenol-
Formaldehyde Composites
Wear Test
In case of phenol-formaldehyde composites, material loss takes place by the mechanism of
abrasion and frictional heat generated due to sliding. Moreover, reinforcement with graft
copolymer improves the wear resistance as compared to reinforcement with original flax. Wear
rate with original flax reinforced composites was much more at all loads. The wear rate was
further enhanced with increase in load. In case of reinforcement of the phenol-formaldehyde
matrix with graft copolymer, a reduced wear rate has been obtained. Maximum weight loss has
been found in case of phenol-formaldehyde matrix followed by reinforcement with original flax.
Graft copolymer reinforced PF composites showed better wear resistance in comparison to
original flax reinforcement and PF matrix [9-13]. Results have been depicted in Table 3.
Tensile Strength
Composites reinforced with original flax can bear load upto 162 N and showed more extension
(2.37 mm), whereas composites reinforced with graft copolymer showed 1.92 mm extension at
load 235 N and PF matrix showed less extension (1.88 mm) and gets failure at load 125 N [9-13]
(Table 3).
Compressive Strength
It is evident from Table 3 that pure phenol-formaldehyde matrix blocks have been observed
with least compressive strength and could not withstand beyond 212 N with compression of 1.62
mm. Composites reinforced with graft copolymer showed less compression (0.78 mm) and can
bear load upto 814 N, whereas composite reinforced with original flax showed 1.32 mm
compression and gets failure at 372 N [9-13].
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