Issue 46

A. Akhavan-Safar et alii, Frattura ed Integrità Strutturale, 46 (2018) 266-274; DOI: 10.3221/IGF-ESIS.46.24 270 Barbosa et al. [14] established that the mechanical properties of the adhesive change with the presence of cork. For tensile tests, the volume fraction having the highest strength is 1%, showing an increase relative to the neat resin (see Fig. (7)). Figure 5 : Typical load-displacement curves of bulks with different amounts of corks. Figure 6 : Fracture surface of bulk tensile specimens at room temperature with (a) no-cork, (b) 1 vol% cork and (c) 5 vol% cork. SLJs were tested varying the overlap length and the cork volume fraction. Micrographs of fracture surfaces of the SLJs with neat adhesive and with 1 vol% of cork are shown in Fig. (8). Fig. (9) shows the average shear stresses of SLJs with different overlap lengths and as a function of cork volume fraction. As shown in Fig. (9), the strength of the SLJs increase with cork volume fraction. A possible reason for the higher energy absorption of the cork modified adhesive is the deviation of crack path due to the presence of cork particles. The deviation of the crack path during the failure process cause an increase of the crack surface area. This phenomenon is one of the main sources of energy absorption which resulted in higher fracture energy of the modified adhesive joints. Acting as a crack stopper and consequently stabilizing the crack propagation prevents developing large and unstable cracks which is another source of energy consumption which increases the fracture energy of the tested material. However, it should be noted that further increase of the volume fraction of the micro cork particles leads to lower static strength of the joints and bulk specimens. The failure analysis showed that higher volume fractions of cork increases the presence of voids and raise the possibility of weak adhesion