Infrastructure Engineering - Theses
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ItemDevelopment of fabric-reinforced polyurea structures for ballistic protection( 2016)Textile-reinforced structures have been increasingly applied in personal protective armours due to their blast and impact resisting capabilities. Their enhancement in energy absorption, lightweight, flexibility, and fragments capturing capabilities when subjected to ballistic impact made them the preferable alternative options to traditional metallic materials. However, the recently developed multi-laminate structures with rate-dependent and non-homogeneous materials have substantially increased the complexity in analysing the behaviour of such systems, which renders the traditional experimental-reliant development approach less capable. This research aims at establishing a new development approach for multi-material laminate structures using finite-element modelling, supported by the experimental testing of basic material properties and structural performance. A new polymer-textile laminate structure was investigated by constructing virtual composite laminate models using LS-DYNA® package. Using the third-party software commanded via the custom-developed python code, the ballistic model of the meso-scale single layer Kevlar® 29 woven fabrics was first constructed and validated to study the evolution of kinetic, strain, and frictional energy components of the fabric during the ballistic impact, as well as its damage mechanism. An improved meso-scale solid element model was then developed to resemble the Twaron® fabric properties, in order to study the influence of the woven structures and projectile impact resistance. The results have shown superior performance from the plain weave structure in comparing to other architectures. To simulate the multi-layer fabric structures, further studies using various mesh sizes have led to the development of a hybrid-mesh finite element model, which simulates the inter-yarn and inter-layer contacts of the multi-layer fabrics with enhanced computational efficiency of over 500%. The numerical models of the textile-reinforced polyurea structures were eventually constructed by combining the meso-scale hybrid-mesh Twaron® fabric model with the nonlinear polyurea model. Ballistic impact on the three-section layup structures consist of polyurea sheets and fabric piles of similar areal density was then simulated. Comparison between various multi-material structures provided insights into the criticality of the material layup arrangements. Energy absorption mechanism was compared among all structural arrangements to reveal the contribution and energy absorption capacity (EAC) of each structure.
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ItemDeformation of polyurea-coated steel plates under localised blast loading( 2013)This thesis presents the results of experimental and numerical studies to investigate the effect of polyurea coatings on the deformation of steel plates under localised blast loading. Exploratory experiments and numerical modelling were initially performed to develop an explosive test methodology and provide validation data for preliminary numerical modelling. Using the developed methodology, explosive testing was conducted on bare and polyurea-coated steel plates, where the plate configurations all had the same areal density. It was found that the polyurea-coated plates resulted in higher residual deformations compared to the uncoated plates, with the residual deformations increasing with coating thickness (and hence increasing with thinner steel). High speed video footage of the events revealed that the polyurea coatings debonded and hyper-extended during the events, before coming to rest back against the plate. This resulted in transient deformations of the polyurea coatings which were approximately twice that of the bare steel plates. Following the explosive experiments, numerical modelling of the polyurea-coated plates under blast loading was conducted using AUTODYN®. The dimensions of the numerical mesh were selected through a sensitivity study. De-bonding of the polyurea was reproduced by using a thin layer of elements which failed at a designated principal stress value, which was tuned to fit the experimental measurements. The polyurea was modelled using a two-parameter Mooney-Rivlin relationship, the constants for which were validated in the preliminary simulations. The initial models of the explosive experiments showed excellent agreement with the experimental residual deformations of the plates, but under-predicted the peak transient deformations of the polyurea. To improve the model accuracy, tensile tests were conducted on the polyurea at various strain rates and used to fit new Mooney-Rivlin material model constants. The new material model constants gave improved results for the transient deformations of the polyurea coatings. Parametric studies were conducted using the validated material models to investigate the effect of bond strength, polyurea stiffness, polyurea bulk modulus and the coating location. It was found that the greatest improvement could be achieved by changing the coating location to the front (blast side) face of the steel plate instead of the back face. The coating performance could also be improved by increasing the polyurea stiffness or bulk modulus, or increasing the strength of the bond between the polyurea and the plate. None of the polyurea-coated plates in the parametric studies performed as well as a mass-equivalent steel plate. However, polyurea-coated steel plates may still be preferable for other reasons, for example when the coating is to be applied as an appliqué (add-on) armour.
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ItemPolymeric coatings for enhanced protection of reinforced concrete structures from the effects of blast( 2011)Reinforced concrete (RC) structural systems dominate the construction of buildings and infrastructure in Australia, as well as in most parts of the world. The increase in terrorist activities, accidental explosions and proliferation of weapons in recent years has made these structures more vulnerable to extreme impulsive loadings. Due to these developments, structural and material engineers are seeking to develop innovative and technically feasible protective solutions to protect critical RC infrastructure and to mitigate the damage resulting from such extreme loading events. This research evaluates the potential of using an elastomeric polymer (i.e. polyurea) to develop an innovative structural retrofitting application to enhance the resistance of RC structural elements to blast effects. The polymeric material is applied on to the structure as a protective coating, by using a spray-on procedure. The overall research involved comprehensive experimental, analytical and numerical investigation programs to evaluate the effectiveness and technical reliability of this technique. Experimental investigations were undertaken to evaluate the contribution of enhanced strain rates on the mechanical properties and behaviour of polyurea in comparison to its quasi-static properties. The findings were used to establish the stress–strain characteristics and other dynamic mechanical properties of the polymer in the strain rate ranges of 0.006 to 388 s-1. It was observed that the stress–strain behaviour of polyurea at high strain rates was considerably non-linear and exhibited significant rate dependency. Subsequently, constitutive equations were developed to characterise the dynamic increase factor (DIF) of various mechanical properties of this material at higher strain rates. The second experimental program involved the assessment of several unretrofitted and polyurea coated panels in a series of blast trials. The polyurea coatings applied on each of the retrofitted panels were unique in terms of coating thickness and location combinations. The findings of these trials indicated that polyurea coating contributes significantly in reducing the damage to the structural elements from the blast effects. Furthermore, it was also observed that the location of application of the protective coating play a major role in the level of protection offered by the retrofitting scheme. The experimental findings were also utilised in verifying the finite element (FE) models developed in the numerical analyses stage. The FE analyses were performed using the explicit solver of the non-linear FE code, LS-DYNA. Six different material models available in LS-DYNA were selected to model and simulate the behaviour of the polyurea, and the feasibility of each of this material model in representing the comprehensive strain rate parameters of the polymer were emphasised. The significance of the constitutive equations developed to model the DIF of various mechanical properties of the polyurea was also highlighted in this exercise. Based on the findings of the FE analyses, one of the material models was identified as the most suitable to represent polyurea. The verified FE models were subsequently used as the foundation to perform the parametric analyses to evaluate and identify the main parameters that contribute towards the overall effectiveness of the retrofitting scheme. The influence of location of application of coating, and the coating thickness, as well as various combinations of the two parameters were meticulously assessed in this exercise. Furthermore, the effectiveness of the retrofitting technique was also evaluated on a full-sized structural RC panel. The findings of the parametric studies were used to establish the functional configurations that could be practiced to optimise the level of protection offered by the proposed retrofitting scheme.