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Nanoclay has been a popular kind of nanofiller for polymer-based nanocomposites in industries since adding a small amount of it can effectively enhance the mechanical properties of polymer. In the present study, a suitable sonication time was first found for manufacturing nanoclay/epoxy adhesive. Then, the lap joint shear strengths of nanoclay/epoxy adhesives with different nanoclay content (0, 1, 3, 5 wt%) conditioned at both room temperature and cryogenic temperature environment were investigated. The main failure mechanism of all samples was interfacial failure between the first layer of glass fiber and adhesive due to peeling. Results showed that 1 wt% was the optimal nanoclay concentration for cryogenic temperature. Scanning electron microcopy was used to examine the fracture surfaces of samples. Good exfoliation and dispersion were found in samples containing 1 wt% of nanoclay. Adding nanoclay into epoxy did not greatly affect the lap joint shear strength at room temperature but significantly influence the strength at cryogenic temperature. This was due to a clamping force induced on nanoclay by negative thermal expansion during conditioning from room temperature to cryogenic temperature. With good exfoliation and dispersion, the clamping force can be evenly distributed. Hence, 1 wt% nanoclay/epoxy adhesive is suitable for bonding composite lap joints, which will be servicing at low temperature environment.

Multi-scale modeling method was used to study tensile properties of single-walled carbon nanotube (SWCNT) and double-walled carbon nanotube (DWCNT) reinforced polymer-based composites at room temperature (RT) and cryogenic temperature (like liquid nitrogen temperature 77K) conditions. At RT, Young's Modulus of a SWCNT M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT reinforced polymer composite is 1.88 times of a DWCNT reinforced polymer composite due to a weak interfacial bonding between layers of DWCNT, which is bound by the weak Van der Waal interaction. The Young's Modulus of DWCNT reinforced polymer composite is significantly improved with the decrease of temperature and the difference in Young's Modulus between SWCNT and DWCNT reinforced polymer composites has been largely reduced. The radial stress imposed on an outer surface of nanotubes due to the contraction of polymer at liquid nitrogen environment is examined to explain the stress transfer mechanism in a composite system. The extra stresses imposed on the surface of DWCNT increase bonding forces between outer and inner layers of DWCNT. This tendency agreed well with experimental results found in other literatures.