Static and fatigue analysis of bolted/bonded joints modified with CNTs in CFRP composites under hot, cold and room temperatures

The present study evaluated for the first time, the tensile and fatigue properties of bolted/bonded scarf adhesive joints (SAJs) in carbon fiber reinforced polymer (CFRP) composites at room temperature of +25 °C, +50 °C and −70 °C. The adhesive layer of the SAJs was modified with multi-walled carbon nanotubes (CNTs) and the results are compared with respect to neat adhesive and adhesive thickness. A new simple approach was developed to measure bolt-hole elongation, which successfully differentiates between bearing failure and interfacial shear failure modes and loads. Results from tensile tests showed that the bolted/bonded SAJs can perform well at −70 °C with maximum loss in strength of 9.6% and stiffness improvement of 30%. Incorporation of CNTs into the adhesive layer improved fatigue lives, at +25 °C, by about 72.1%-97.8% compared with that of neat-adhesives. Interfacial shear failure, cohesive failure and CNTs pull-out are the dominated failure modes in the SAJs, whereas bearing, shear-out, longitudinal splitting and bolt fracture are observed for the bolted joints. Considerable attention was given to analyze the scatter in the tensile strength and fatigue life results.