PSI - Issue 64

Lingzhen Li et al. / Procedia Structural Integrity 64 (2024) 1318–1325 Author name / Structural Integrity Procedia 00 (2019) 000–000

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When a nonlinear adhesive serves as the bonding agent, noticeable differences exist between CFRP and Fe-SMA joints. The Fe-SMA strip demonstrates a noticeable nonlinear behavior, resulting in a wider wine glass compared to the CFRP wine glass. Consequently, the CFRP joint experiences approximately twice the tensile stress compared with the Fe-SMA strip, leading to a bond capacity that is roughly twice as high as the Fe-SMA joint. On the other hand, the Fe-SMA joint displays greater tensile strain compared against the CFRP joint, indicating significantly higher ductility for Fe-SMA joints. 5.3. Non-prestrained vs. prestrained Fe-SMA lap-shear joints Further phenomena reported by Li et al. (Li et al., 2023b) are that (i) when bonded by the same linear adhesive, the non-prestrained and prestrained Fe-SMA strips exhibit alike bond capacities, while that of the non-prestrained Fe SMA strip is marginally greater; (ii) when bonded by the same nonlinear adhesive, the prestrained Fe-SMA strip demonstrates a greater bond capacity. These phenomena can be visualized via the application of the Wine Glass model as well.

(a) Bonded by a linear adhesive (SikaDur 30). Tensile strain demonstrated up to 4%.

(b) Bonded by a nonlinear adhesive (SikaPower 1277). Tensile strain demonstrated up to 15%.

Fig. 6. Bond capacities of non-prestrained and prestrained Fe-SMA joints. The footnotes "NS" and "PS" represent non-prestrained and prestrained Fe-SMA bonded joints, respectively.

The fracture energy of a linear adhesive is relatively low and insufficient to induce a pronounced nonlinear behavior of Fe-SMA strips. Therefore, only the quasi-linear stage of Fe-SMA strips is utilized, where the non-prestrained Fe SMA wine glass (the red curve in Fig. 6 (a)) is slightly narrower than the prestrained Fe-SMA wine glass (the blue curve in Fig. 6 (a)). Consequently, the tensile stress level (height of the wine) and the resulting bond capacity of the non-prestrained Fe-SMA joint are marginally greater than the joint comprising a prestrained Fe-SMA strip. A nonlinear adhesive, featuring a large fracture energy, is able to induce the stress-strain behavior of Fe-SMA strips to the nonlinear stage, where the prestrained Fe-SMA wine glass (the blue curve in Fig. 6 (b)) has a clearly higher profile than the non-prestrained Fe-SMA wine glass (the red curve in Fig. 6 (b)). Consequently, the tensile stress level (height of the wine) and the resulting bond capacity of the prestrained Fe-SMA joint are clearly greater than those of the joint with a non-prestrained Fe-SMA strip. All these phenomena observed by Li et al. (Li et al., 2023b), though could be quantitatively explained by the analytical model presented by Li et al. (Li et al., 2023a), can be more intuitively demonstrated by the Wine Glass model.