Nondestructive testing of defects in adhesive joints

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Table 1. Raw rubber properties
Parameter ISNR 20 DPSR Skim rubber
Nitrogen content, %w/w 0.37 0.62 2.30
Ash content, % w/w 0.36 0.40 0.53
Initial plasticity, Po 51 38 39
Plasticity retention index, PRI 49 56 17
Acetone extractable, % 2.64 6.78 6.24
o
Mooney viscosity, [ML(1+4)100 C] 86 76 70
Copper content, ppm 6.0 10.0 18.0
Table 2. Formulation of mixes
Ingredient
Mix Nos
1 2 3 4 5 6
ISNR 20 100 100 100 100 100 100
Deproteinized skim rubber - 20 - - 20 -
Skim rubber - - 20 - - 20
Zinc oxide 5 5 5 5 5 5
Stearic acid 2 2 2 2 2 2
HAF black (N300) 30 30 30 30 30 30
Naphthenic oil 1.5 1.5 1.5 1.5 1.5 1.5
Antioxidant TDQ 1
1 1 1 - - -
CBS 2
0.7 0.7 0.7 0.5 0.5 0.5
Sulphur 2.5 2.5 2.5 2.5 2.5 2.5
1
2,2,4-trimethyl 1,2-dihydroquinoline
2
N-cyclohexyl-2-benzthiazil sulphenamide
Table 3. Cure characteristics and mechanical properties
Parameter
Mix Nos
1 2 3 4 5 6
Minimum torque, dN.m 0.39 0.35 0.40 0.24 0.40 0.37
Maximum torque, dN.m 9.43 8.09 8.81 5.97 5.07 5.25
Δ, Rheometric torque, dN.m 9.04 7.74 8.41 5.73 4.67 4.88
Optimum cure time (t 90 ) at
150ºC, min
7.33 8.88 7.08 9.17 10.58 9.54
Scorch time (t s2 ) at 150ºC,
min
2.17 3.09 2.35 3.07 4.91 4.07
Cure rate, dN.m/min 1.47 1.08 1.16 0.48 0.41 0.43
100 % Modulus, MPa 1.1 0.9 1.1 1.2 1.2 1.2
200 % Modulus, MPa 2.1 1.6 2.0 2.4 2.4 2.5
300 % Modulus, MPa 3.5 2.5 3.3 4.9 4.8 5.1
Tensile strength, MPa 28.1 25.1 27.0 23.6 24.7 24.9