A study of nanomaterials enhanced epoxy as adhesives for CFRP-steel bonding

2017-01-31T04:34:34Z (GMT) by Faleh, Haydar
The successful retrofitting of steel structures by using CFRP significantly depends on the performance and integrity of the CFRP-steel joints, and the effectiveness of the adhesive used. However, the adhesives are usually much weaker than the adherents they join. To improve bonding performance, one possibility is to consider toughened adhesives. It is a common practice to enhance the epoxy by adding nanoparticles to it. This thesis reports a detailed investigation of infusing different types and amounts of nano-particles onto different adhesives used in CFRP-steel joint. It is a common practice to use nanoparticles to strengthen polymers in general and adhesives in particular. Literature review shows that sonication is widely used technique to infuse nanoparticles onto composites. A series of coupons tests was carried out to study the effect of adding different types and percentages of multi wall carbon nan-tubes (MWCNT) and SiC nano-powder on the properties of Araldite-420 and Sikadur-30 adhesives. Scanning electron microscope was used to evaluate the dispersion of the nanoparticles inside the epoxy. Sonication alone increased the homogeneity of the epoxies and enhanced Sikadur-30 properties with no effect on Araldite-420. MWCNT increased the strength and elastic modulus for Araldite-420 in different percentages depending on nanoparticles amounts. SiC nanoparticles had no or minor effect on strength and elastic modulus for Araldite-420. Adding nanoparticles to Sikadur-30 had no, or even negative effect, on strength and elastic modulus. The transition glass temperature does not affected by adding nanoparticles. Also, test to find the properties of steel and CFRP plates were carried out Same results were repeated when enhanced epoxies used to attach CFRP plates on steel with single lap joint. 2% MWCNT was the optimum percentage for Araldite-420 joint strength. As the nanoparticles percentages reach the optimum values, the failure mode changed from epoxy failure to a delamination failure. Photogramatry technique were used to calculate strains on the top of CFRP bond length and compared with classical strain gages. Due to its simplicity and efficiency, photogramatry was adopted to collect the strain along bonding length. The delamination failure type of the CFRP-steel joint, which include full separation of particles, made simulation process ,using classic finite element simulation method , handicap. A mesh-less simulation method called material point method, easily simulates the exact shape of failure with reasonably good prediction of experimental results. The simulation method was verified with the results from experimental tests carried out in this research as well as tests available in the literature. The model predicts the ultimate load, displacements and strain distribution reasonably well. Also, using this method provide the ability to study the effect of loading rate on CFRP-steel joints. Finally, a bond slip model and bond stress values for different percentages and types of nanoparticles were calculated for better understanding of bonding mechanism.