PSI - Issue 45

Kentaro Yamauchi et al. / Procedia Structural Integrity 45 (2023) 125–131 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

127

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2.2. Measurement of contact angles Contact angle measurements are necessary to obtain the surface free energy, as detailed in Subsection 2.3. A contact angle measurement device, namely, Excimer Smart Contact Mobile 5, was used to measure the contact angles of water and methylene iodide on the samples in accordance with the theory provided by Owens and Wendt (1969), as recommended by the ISO standard (2017). These two types of liquid were selected because the dominant surface free energy components differed between them, as presented in Table 2. The contact angles were measured at five different points for each sample, and the average values were considered as the contact angles.

Table 2. Surface free energy and components of water and methylene iodide (mN/m). γ L d : Dispersion component, γ L p : Dipole-hydrogen bonding component, γ

L : Surface free energy of liquid

Ref.

γ L

γ

γ

d

p

L

L

Water

21.8 50.8

51.0

72.8 50.8

ISO (2017) ISO (2017)

Methylene iodide

0.0

2.3. Surface free energy Owens and Wendt (1969) reported a method to calculate the surface free energy of a solid sample, as expressed below. According to the theory by Owens and Wendt, the adhesion work W is expressed as follows: = (1 + cos ) = 2√ ∙ + 2√ ∙ (1) Here, is the surface free energy of the liquid; θ is the contact angle of the liquid; and are the dispersion and dipole-hydrogen bonding components of the surface free energy of solid, respectively; and and are the dispersion and dipole-hydrogen bonding components of the surface free energy of the liquid, respectively. In Equation (1), γs d and γs p are unknown. By using the values of γ L d and γ L p with θ from the two types of liquid with different surface free energies, two simultaneous equations were obtained. By solving these equations, the values of γs d and γs p were obtained. The sum of these values is the surface free energy of the solid. 2.4. Shear tensile test A shear tensile test was performed using a desktop tensile tester (A&D MCT-2150). The shear tensile test was conducted using the epoxy resin adhesive and the individual adherends in accordance with the JIS K 6850 standard. The shapes of the test pieces are shown in Fig. 2 and Table 3.

Fig. 2. The shapes of the shear tensile test pieces.