Browsing by Author "Jarratt, Nicholas"

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    An efficient three-dimensional database driven approach for multi scale homogenization
    (2019) Jarratt, Nicholas; Skatulla, Sebastian
    The two-scale homogenization theory, commonly known as the FE2 method, is a well-established technique used to model structures made of heterogeneous materials. Capable of capturing the microscopic effects at the macro level, the FE2 method assigns a representative volume element (RVE) of the materials microstructure at points across the macroscopic sample. This process results in the realization of a fully nested boundary value problem, where macroscopic quantities, required to model the structure, are obtained by homogenizing the RVEs response to macroscopic deformations. A limitation of the FE2 method though is the high computational costs, whereby its reduction has been a topic of much research in recent years. In this research, a two-scale database (TSD) model is presented to address this limitation. Instead of homogenizing the RVEs response to macroscopic deformations, the macroscopic quantities are now approximated using a database of precomputed RVEs. The homogenized results of an RVE are stored in a macroscopic right Cauchy-Green strain space. Discretizing this strain space into a finite set of right Cauchy-Green deformation tensors yields a material database, where the components of each tensor represent the boundary conditions prescribed to the RVE. A continuous approximation of the macroscopic quantities is attained using the Moving Least Squares (MLS) approximation method. Subsequent attention is paid to the implementation of the FE2 method and TSD model, for solving structures made of hyperelastic heterogeneous materials. Both approaches are developed in the in-house simulation software SESKA. A qualitative comparison of results from the FE2 method to those previously published, for a laminated composite beam undergoing material degradation, is presented to verify its implementation. To assess the TSD models performance, an evaluation into the numerical accuracy and computational performance, against the conventional FE2 method, is undertaken. While a significant improvement on computational times was shown, the accuracies in the TSD model were still left to be desired. Various remedies to improve the accuracy of the TSD model are proposed.
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    Effect of anti-corrosive coatings on the bond between corrosion-damaged rebar and concrete repair materials
    (2022) Moolla, Muhammad Ameen; Beushausen, Hans; Jarratt, Nicholas
    Reinforcement corrosion is the largest contributor to the deterioration of existing RC structures worldwide. The aggressive electrochemical process causes destruction to the steel by a loss in cross section and rib height, which in turn affects the bond between steel and concrete and consequently the structural performance of reinforced concrete structures. During a repair strategy, when the patch repair method is considered, one of the steps usually involves the application of a protective coating to the corroded and subsequently cleaned steel. It is well accepted that protective coatings offer corrosion resistance to the steel in reinforced concrete repaired elements. However, information on how well the coated rebar bonds to the new surrounding repair concrete is limited. Hence, developing an understanding on the bond performance of repaired coated rebar is important for engineers in the construction repair industry. One commercially available epoxy-modified, cementitious coating material was considered in this study, Sika ® Armatec ® -110- EpoCem, and applied with one or two coats of 0.6 mm each. Rebar corrosion damage levels of 0%, 10% and 20% (of steel mass loss) were simulated by mechanical grinding of sound rebar samples, attempting to represent the condition of cleaned corroded rebar. Two steel bars, Y12 and Y16, of different diameters were considered. Three repair materials with CEM I 52.5N were considered in this study, which included one concrete with a w/b ratio of 0.45 and two mortars with w/b ratios of 0.47 and 0.65, referred to as C45, M45 and M65, respectively. Pull-out testing was conducted on a total of 108 specimens to assess the effect of coating thickness on the bond with respect to the different parameters of this study. The results indicate that the w/b ratio of the mortars had a significant influence on the bond and the addition of stone showed no difference on the failure loads obtained. There was no significant effect of the rebar diameter on the pull-out force for uncorroded rebar, although with cleaned corroded rebar the effect was significant. Specimens with 10% mass loss had larger reductions in pull-out force compared to those with 20% mass loss. While coatings reduced the bond of uncorroded and cleaned corroded rebar, the thickness of the coating had practically no influence on the pull-out force. Using C45-12 with two coats on 20% corroded steel, the pull-out force was 80% compared to before corrosion. Failure of uncorroded specimens was dominated by splitting, and slip was mostly seen for cleaned corroded specimens. With coatings applied to uncorroded bars, slip coating failure was evident with uncorroded steel while splitting with coating failure was evident especially with Y16. From the corroded coated specimens, there appeared to be good contact between the cleaned corroded steel and repair material.