AliAkbar Allahdadian

Grade:  Ph.D.

Ph.D. Thesis:

Experimental and numerical study of the mode I interlaminar behavior of the carbon nanotube reinforced glass-epoxy composite: the multiscale approach

Year:  Sept.  2015 -Feb. 2023.

Abstract:

The effect of adding carbon nanotubes (CNTs) between glass-epoxy composite laminate in the mode I interlaminar behavior was investigated by experimental and numerical methods. By using the double cantilever beam (DCB) test, the weight ratios of 0.5%, and 1%, the weight of CNTs were compared with the case without CNTs. By adding the CNTs, the mode I interlayer fracture toughness increases by about 50%. A multiscale approach was used for modeling the DCB test. At the micro-scale, toughness mechanisms, including CNT pull-out, its breaking and bridging, and the separation of the nanotube from the surrounding resin were modeled. The separation of the nanotube from the surrounding resin was modeled with a cohesive element. The cohesive element around the nanotube was embedded in the three-dimensional elements of the resin and according to the weight percentage of the nanotube to the resin, a representative volume element (RVE) was created. The orientation, length, and diameter of CNT were considered randomly in the RVE. In the meso-scale, according to the percentage of glass fibers to resin, an RVE was created randomly. By using the damage model whose parameters were extracted from the micro-scale, crack growth was simulated. According to the Hill-Mendel conditions, the relationship between the meso and macro scale was established and the number of effective quantities of traction and separation from the micro-scale was used as the parameter of the cohesive element in the macro-scale. To consider the bridging effect of glass fibers and its effect on interlayer fracture toughness, random distribution of interlayer beam elements  was created. At the macro-scale, the DCB test simulated and cohesive elements were considered for modeling lower-scale mechanisms and beam elements for fiber bridging simultaneously. A favorable agreement between the experimental and simulation results was obtained.

Keywords: Glass-epoxy/CNT Nanocomposites, Cohesive element method, multiscale approach, interlaminar behavior.