Issue 45

C. Bellini et alii, Frattura ed Integrità Strutturale, 45(2018) 173-182; DOI: 10.3221/IGF-ESIS.45.15 177 Fig. 3 shows the trend of the temperatures in the respective environment of the three groups. The heating transient for the two groups in water was completed within two hours. Subsequently, the group aged in air was placed in the oven and, having a much lower thermal inertia, reaches the operating temperature within a few minutes. Even in the cooling phase, the different thermal inertia between the three groups involves different cooling speeds: specifically, the cooling rate of the samples in air was an order of magnitude higher than the cooling speed of the samples in water. Once the ageing phase was completed, the specimens were removed from the containers and left to dry at room temperature for one week; then they were tested. The test conditions were performed according to ASTM D5868 using an INSTRON 5586 with a maximum capacity of 300kN and setting a crosshead speed of 1.3 mm/min. R ESULTS AND DISCUSSIONS he reference values of failure loads for the unaged adhesives are taken from a previous work of the authors [13]. The results obtained from the lap shear tests are reported in Fig. 4. For the purpose of being able to state if there are significant differences between the results obtained when the selected factors are changed, an analysis of variance was performed on the entire population of specimens produced. The results are reported in Tab. 3. Figure 4 : Results of the lap shear tests on the single lap joints. Source Contribution Mean Square F-value P-value Adhesive 49.94% 71.817 48.33 0.000 Ageing 15.91% 8.932 6.01 0.004 Interaction (Adhesive*Ageing) 16.5% 9.263 6.23 0.004 Residual 17.65% 1.486 Table 3 : Analysis of Variance: results obtained from all the specimens tested. The p-values below 0.05 indicate that there are significant differences between the results obtained with the related factor. Therefore, it is possible to observe that the factor most characterizing the resistance of the joint is the type of adhesive: it has a greater influence on the process, which can be estimated through the contribution value of 49.94%. From the analysis carried out, ageing generally results in a very low influence (15.91% contribution) on the strength of the bonded joint. However, the complexity of the experimental campaign does not allow to be able to give conclusions about T