The Automated Composites Laboratory

Thermal and Mechanical Analyses of Dental Composites for Class II Cavity Restoration in a Molar Tooth: A Finite Element Study

Abstract: Flowable dental resin composites have substituted mercury-based amalgam as dental restorations over the past decade due to amalgam’s biological adverse effect. The flowable dental resin composites are more preferred due to their material properties, aesthetics, and minimal invasiveness. Therefore, the effect of thermal and mechanical stimuli on resin dental composites is an area of active research. This study describes the construction of three-dimensional finite element models of a posterior molar tooth based on data obtained from micro-CT. The scanned tooth consisted of 872 slices that were segmented and meshed in Mimics Innovation Suite software to obtain separate geometric models of enamel, dentine, and pulp. The segmentation process involved mask creation through threshold sets, followed by manual inputs through multiple slice editing. Geometric models were imported to a commercial finite element analysis (FEA) software and conditions such as an intact, cavitied, and filled tooth were simulated for Class II dental cavity restoration. The material properties of each model were assumed to be homogenous and isotropic with elastic behaviour. Transient thermal analysis was conducted to determine the temperature change within each model. The ambient tooth temperature was assumed to be 37℃ with extremities in thermal stimuli to be 2℃ and 50℃. Moreover, the models were subjected to loading of 400N on the occlusal surface to imitate a bite force at ambient tooth temperature. The strain and stress distributions in the tooth, and tooth restoration, due to thermal and mechanical loading, were studied to optimise the Class II dental cavity restoration. The finite element simulations showed that restorative filling materials with higher Young’s modulus and larger coefficient of thermal expansion independently results in higher stress levels. The regions of higher stress on the tooth model were detected and the effects of temperature and mechanical load variations on restoration microleakage were discussed. This study investigated the potential application of three-dimensional finite element modelling for optimizing restorative materials.

Authors: Jerrin Thadathil Varghese, Behzad Babaei, Raju, Paul Farrar, Gangadhara Prusty
Year: 2020
Presented in: ANBUG-AINSE Neutron Scattering Symposium, AANSS 2020
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CF/PEEK 3D printed materials microstructure characterisation by X-RAY computed tomography

Abstract: In this study, we have utilised a state-of-art 3D X-ray micro-computed tomography (micro- CT) technique to investigate and characterise the microstructure of a 3D printed CF/PEEK sample and the commercial feedstock material used to produce it. Unique helical scanning and iterative reconstruction technologies have been employed to acquire high-resolution, high-quality images on both the feedstock material and printed sample. Reconstructed 3D images have been processed and thoroughly investigated and samples micro-structure analysed and characterised. Material constituents (main: fibre fragments, polymer matrix, voids; minor: high density impurities) have been identified and their distribution mapped and visualised in 3D. In addition, voids and impurities have been segmented and their individual total amounts quantified as volume %. Our images unequivocally show that the feedstock filament contains a large quantity of macro (i.e. above image resolution) voids randomly and heterogeneously distributed. Within the volume imaged we observe the occurrence of fibre fragments and large voids in cluster-like accumulations. Analysis of the 3D printed sample indicates an overall slight decrease in voids content compared to the feedstock material. Within the printed sample micro-structure, voids density and distribution are still clearly heterogeneous with the majority of voids preferentially distributed in rows parallel to the printing direction.

Authors: Sommacal, S., Matchinski, A., Dreschler, K., Compston, P.
Year: 2020
Presented in: Society for the Advancement of Material and Process Engineering
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Machine learning-based process monitoring and characterisation of automated composites

Abstract: There has been a huge uptake by industry groups to adapt automated fibre placement (AFP) based manufacturing due to it’s high level of productivity, accuracy and reliability. The AFP technology merges through several manufacturing stages like cutting, curing and consolidation. The high level of productivity, accuracy and reliability in automated fibre placement (AFP) have opened new markets and applications for high value laminated composite structures. However, from a system engineering perspective, manufacturing of composites using AFP is a complex, high-dimensional nonlinear multivariable process that involves large number of variables and parameters. The quality and integrity of the structure is critically dependent on the choice of these parameters, which are typically extracted by conducting several lab-based experiments with varied processing parameters. Appropriate selection of these parameters would provide optimal result. Artificial neural network (ANN), a Machine Learning technique has been gaining popularity in various engineering applications including prediction, control, fault diagnosis etc. In this study, a multi-layer perceptron-based ANN has been trained to accurately represent the complex relationship between various processing parameters in AFP that would give optimised outcome. The ANN model will subsequently be used to obtain the optimised parameters that can be integrated in AFP based manufacturing of laminated composite structures.

In-vitro investigation of S-2 glass fibre aspect ratio on flexure strength, hardness and wear performance of fibre reinforced flowable dental composites

Abstract: With the continuous increase in the life expectancy and changing food habits, studying the wear of human tooth is of primary importance. Fibre reinforced composites are gaining major market share among various restorative dental materials. The current experimental investigation on the flexure strength, hardness and wear performance of dental restorative composites is to understand the effect of S-2 glass fibres of low volume (5%) and aspect ratio (AR 50, 70 and 100) embedded dental resins. Specimens with nine dental systems were manufactured and tested. Flexural strength is characterised as per ISO-4049 standards and hardness by Vickers hardn ess. Wear investigation is carried out with a fixed load during a single test providing steady condition. Wear pattern is also analysed and micro-mechanical behaviour is investigated using laser Microscope and SEM. It is observed that inclusion of processed AR 70 S-2 glass fibres increases the mechanical properties of resin by 10.3%, 34.1% and 54.1% respectively for flexure modulus, flexure strength and Vickers hardness. Coefficient of friction for composite samples was evaluated to be around 0.65 compared with resin samples at 0.35. Fibre length of 0.35 mm (aspect ratio = 70) provided the best results which is also the critical fibre length.

Authors: Raju, R., Rajan, G., Ellakwa, A., Hoffman, M., Shouha, P., Farrar, P., Prusty, G.
Year: 2017
Presented in: 9th Australasian Congress on Applied Mechanics (ACAM 9)
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Investigation on the surface treatment of short S2-glass fibre for dental composites

Abstract: Low aspect ratio S2-glass fibres serve as excellent load carrying members along with conventional fillers and additives. Untreated surface of the glass fibre results in poor bonding with the monomer reducing the strength, stiffness, stability and life of the structure. The current study focusses on analysing different methods of chemical surface treatments on glass fibre so as to augment the bonding strength with the monomer or polymer. A strategy for the surface treatment of glass fibres is introduced to improve the interfacial bonding between fibres and monomers. Enhanced dispersibility of low aspect ratio glass fibre in high viscosity resins will contribute to the generation of extremely stable local shear strength. Short glass fibres with the aspect ratio between 50-100 are cut and then treated in acid etching solutions which can produce an increased surface energy, surface roughness and dispersion ability. Uniformly distributed glass fibres within the resin will work as the key to reinforce the light cured dental composites that can be validated by analytical and experimental methods such as interfacial shear strength and flexural strength, thereby broadening the performance of dental restoration materials.

Authors: Cho, K., Wang, G., Raju, R., Rajan, G., Ellakwa, A, Stenzel, M.H., Shouha, P., Farrar, P., Prusty, G..
Year: 2017
Presented in: 9th Australasian Congress on Applied Mechanics (ACAM 9)
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Failure analysis of dental restorative composites in class II (MOD) cavity using FEM

Abstract: Fracture of restored posterior premolars is a common clinical challenge, which is generally caused by large mastication forces onto the occlusal surface of the tooth. Although, different restorative materials with enhanced mechanical properties have been introduced into the market with an aim of improving their fracture resistance, still an ideal restoration remains a distant dream. The current investigation focuses on the numerical analysis of commercially available composite resins with elastic modulus ranging from 8.5 GPa to 19 GPa (low to high) using Finite Element Method. Four contact bodies (enamel, dentin, cement and restorative material) are modelled and are subjected to a static load on the occlusal surface of the restored tooth. Mohr-Coulomb failure criterion is used to identify the location of failure and to determine the maximum load carrying capacity of the restored tooth.

Authors: Kamboj, S., Raju, R., Rajan, G., Farrar, P., Prusty, G.
Year: 2017
Presented in: 9th Australasian Congress on Applied Mechanics (ACAM 9)
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Hydrofoil Manufacture with Automated Fibre Placement

Abstract: With the recent progress being made in the optimisation of lay-up schemes for composite propellers, an automated method of manufacturing those propellers is currently being investigated as the next step towards realising the potential of composite propeller technology. As a reduced problem, the manufacture of a composite hydrofoil is considered first. The nature of the curved surfaces of a composite hydrofoil requires a new tooling and manufacturing methodology to produce such hydrofoils using an Automated Fibre Placement (AFP) robot. This paper details the optimisation and fabrication of a small-scale shape-adaptive hydrofoil as a preliminary trial before attempting larger-scale productions. By using a mould originally designed for resin transfer moulding (RTM), insight is gained in the requirements and design limitations of purpose-built AFP tooling.

Authors: White, J.M., Maung, P., Prusty, B.G., David, M., Phillips, A.W., St John, N.A.
Year: 2017
Presented in: 9th Australasian Congress on Applied Mechanics (ACAM 9)
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Investigation of the effects of heating bias and placement head angle on the short beam strength of CF/PEEK laminates manufactured in a laser tape placement process

Abstract: This paper investigates the effects of heating bias and placement head angle on the short beam strength (SBS) of unidirectional CF/PEEK laminates manufactured in a laser tape placement process. Placement trials were performed with constant laser power at 400 mm/s. The effect of heating bias was studied by changing the bias angle of the laser by ±0.5° from the default position where the surface temperature on the tape and substrate are equal. The angle of the placement head relative to the tooling was also varied by ±6.0° from the default position. The process was instrumented with a long wave infra-red thermal camera. The SBS of the samples was determined following the ASTM D 2344 standard. Increasing the laser bias +0.5° towards the tape had no effect on the SBS, however increasing the bias towards the substrate by -0.5° resulted in a 26% decrease in SBS. This was attributed to the substrate acting as a heat sink, combined with insufficient heating of the tape. Decreasing the angle between the placement head and the tooling by 6.0° lead to a 10% decrease in SBS. This was attributed to the increased angle of incidence, leading to decreased laser absorptance and therefore lower bond interface temperatures. Increasing the angle of the placement head by 6.0° revealed no significant difference in strength.

Authors: Stokes-Griffin, C.M., Kollmannsberger, A., Drechsler, K.
Year: 2017
Presented in: 9th Australasian Congress on Applied Mechanics (ACAM 9)
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Machine learning based process monitoring and characterisation of automated composites

Abstract:

Authors: Oromiehie, E., Prusty, B.G., Rajan, G., Wanigasekara, C., Swain, A.
Year: 2017
Presented in: International SAMPE Technical Conference
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Distributed strain measurement using fibre optics in a high performance composite hydrofoil

Abstract: With rapidly advancing composite manufacturing industry in recent years, advanced composites have become favourable alternative materials to conventional alloys in marine propeller production. However, composite structures are very susceptible to failure and thus strain monitoring in multiple locations throughout the structure will be essential to prevent catastrophic failure. In this experiment, composite hydrofoil was manufactured using resin transfer moulding (RTM) and embedded with a standard single mode optical fibre along the trailing and leading edges for distributed strain sensing. Distributed sensing with continuous fibre can be implemented in complex composite structures such as a high performance composite hydrofoil or propeller for structural monitoring purposes. Quasi-static loads were applied to the instrumented composite hydrofoil achieving deflections of up to 11 mm to monitor strains in multiple locations through distributed fibre sensing using a high sensitivity optical backscatter reflectometer (OBR). The strain field within the layered hydrofoil was produced, and the experimental result was validated using finite element analysis. The combined numerical and experimental validation demonstrates that fibre optic distributed sensing is reliable and can be utilised for structural health monitoring of high performance composite hydrofoils.

Authors: Maung, P.T., Prusty, B.G., Rajan G., Li, E., Phillips A.W., John, NA.S.
Year: 2017
Presented in: 21st International Conference on Composite Materials (ICCM-21)
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The influence of consolidation force on the performance of AFP manufactured laminates

Abstract: With the increasing use of carbon/glass fibre reinforced polymer composites for large components like wing skins, fuselages and fuel tanks in aircrafts and next generation of spacecraft, utilization of advanced automated manufacturing is critical for mass production. In-situ consolidation in automated fibre placement (AFP) technology through merging several manufacturing stages like cutting, curing and consolidation has opened up a wider range of applications as well as new markets for composite materials in several sectors including aerospace and automobile in large scale. Nevertheless, the quality and integrity of AFP manufactured composites is heavily dependent on large number of variables and parameters like lay-up speed, curing/melting temperature and consolidation force. In order to establish and understand a correlation between the key parameters in AFP and the mechanical properties, several parametric experiments were performed. This is done through manufacturing uni-directional carbon fibre reinforced polymer laminates and identifying some of their main mechanical properties at different location along the length of samples. It was found that, the strength of laminates at different locations is critically dependent on the effect of those parameters.

Authors: Oromiehie, E., Prusty B., G., Paul, C., Ginu, R.
Year: 2017
Presented in: 21st International Conference on Composite Materials (ICCM-21)
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Robotic manufacture of advanced composites- current trends and opportunities