Effects of loading rate, temperature, and thickness on the tensile strength of precision adhesive joints

The influences of the micron bondline thickness, temperature, and loading rate on the tensile strength of adhesive joints were studied for the precision adhesive structures, and the fractured surfaces were analyzed by the infrared imaging and SEM methods. The testing results show that the tensile strength increases and then linearly decreases with the increase of bondline thickness; the peak tensile strength is always acquired at the bondline thickness of around 30 μm; the maximum tensile strength increases up to 28.6% as the thickness increases from 10 to 30 μm at the loading rate of 1 mm/min; the strength decreases by more than 33% and finally reaches a closed value at different bondline thicknesses as the temperature rises from −30 to 110 °C. The results indicate that reducing the bondline thickness, less than about 10 μm, could result in a weak bonding interface; the tensile strength increases with the increase of the loading rate, exhibiting the strain-rate hardening effect below the T_g; the plastic-damage characteristic appears and becomes clearer on the fractured surface as the temperature increases. Under the tested conditions, the temperature shows the most significant effect on the tensile strength, then the bondline thickness followed by the loading rate.