Experimental study on basalt FRP/steel single-lap joints under different loading rates and temperatures

In this work, basalt FRP/steel single-lap joints were tested under various temperatures (−25, 0, 25, 50, 100 °C) and dynamic loading speeds (0.625, 1.25, 2.5, 5.0 m/s), using a servo-hydraulic high-rate testing machine with an environmental chamber. The deformation and failure behavior of the sample in the overlap region were captured by a Phantom v7.3 high speed digital camera at a sampling rate of 20,000 fps, and analyzed using a digital image correlation (DIC) method. Experimental results presented in this paper include average bond strength, toughness, bond strength-displacement curves and FRP strain distributions in the overlapping areas. In aspect of the loading rate effect, both the bond strength and shear stiffness increase with the increasing loading rate. Most specimens showed a mixed failure mode under dynamic tensile loads. On the other hand, the average bond strength increases in the temperature range of −25 to 50 °C, while decreases significantly from 50 to 100 °C as the glass transition temperature Tg is exceeded. The observed typical failure mode in most specimens at low temperature is debonding at adhesive-steel interface, whereas samples rupture at the adhesive-BFRP interface at elevated temperature with lower load-bearing capacity.