Test Results

Tensile Test Results—Table 2 shows results of tensile and shear tests that include the relationship between the stress and the amount of displacement for each sealant modulus, as well as the fracture mode for each test specimen. Figure 3 shows the relationship between tensile stress and the modulus of the different types of sealant for both two – and three-sided adhesion joints; for each of these types of joints, the fracture mode of each test set is identified. For the two-sided adhesion joints, sealant products No. 1 and No. 2 showed thin layer cohesion failure (TCF), in which a thin layer of sealant remained on the sub­strate. In contrast, sealant products Nos. 3 through 5 showed a mixture of cohe­sion failure (CF) and material failure (AF) of the ALC substrate. Thus the results show a difference in fracture mode between products No. 1 and No. 2 and prod­ucts No. 3 through No. 5. The maximum tensile stress at which a change in the fracture mode was observed was around 0.7 N/mm2. When the maximum ten­sile stress is less than 0.7 N/mm2, the strength of the ALC substrate is greater than that of the sealant and the sealant fractures, given that the tensile stress is dependent on the sealant. In contrast, when the maximum tensile stress is greater than 0.7 N/mm2, the sealant has a greater strength than the ALC

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FIG. 3—Fracture mode of sealed joint against tensile deformation.

substrate. At this stress level fracture is initiated in the ALC substrate and the sealant is thereafter damaged as the fracture in the ALC substrate progresses. When the maximum tensile stress exceeds 0.7 N/mm2, the tensile strength of the sealed joint is governed by the tensile strength of the ALC substrate. There­fore, the maximum tensile stress that can be attained in tests is that of the ten­sile strength of ALC substrate, which attains a maximum level of around 0.7 N/mm2; this is irrespective of the value for the sealant modulus.

As for the values for the sealant modulus of products No. 1 and No. 2, the test specimens that had fractures with sealant had 50 % modulus values of 0.2 N/mm2 or below, as recommended for exterior wall watertightness design. Specimens for products No. 3 through No. 5 had a 50 % modulus of 0.2 N/mm2 or above, and the specimens had fracture modes that corresponded to the rec­ommended value for avoiding causing ALC fracture of 0.2 N/mm2 or less for the 50 % modulus of the sealant.

The test specimens having the three-side adhesion configuration had simi­lar results, in which a mixture of sealant CF and ALC AF was shown with a max­imum tensile stress of 0.7 N/mm2 or above. These test results also showed a trend of tensile stress and fracture similar to that shown for the specimens in two-sided adhesion tests.

The differences between two – and three-sided adhesion joint specimens with respect to the values achieved for tensile stress and percent elongation arise because three-sided adhesion joints bring about greater internal stress in the joint as compared to two-sided joints. In essence, three-sided joints are ca­pable of accommodating less movement than two-sided joints, and for the same degree of movement they give rise to both higher bond and internal stress.

Shear Test Results—Figure 4 shows the relationship between shear stress and the modulus of the different types of sealant for both two – and three-sided adhesion joints; the fracture mode for each sealantproduct is also given. For two-sided adhesion, specimens of product No. 1 showed TCF at the interface between sealant and substrate, and the sealant remained on the ALC panel

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FIG. 4—Fracture mode of sealed joint against shear deformation.

substrate. Sealant product Nos. 2 to 5 had significant fractures that started at the edge of ALC; this led to CF of the sealant or AF of the ALC. The fracture mode was differentiated by sealant fractures and ALC fractures at maximum shear stresses of 0.6 to 0.7 N/mm2. For three-sided adhesion, all test specimens showed sealant fractures.