53 research outputs found

    Experimental and numerical studies on forming and failure of woven thermoplastic composites

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    Fuel efficiency, weight reduction, and sustainability are major global challenges fuelling research into advanced material systems. There is an urgent necessity to manufacture light weight products from highly recyclable, lightweight materials. Woven thermoplastic composites are attractive light weight candidates for the replacement of metallic parts in a wide range of industries from automotive to aerospace. They offer attractive benefits such as high specific strength, balanced thermomechanical properties, improved fatigue and wear resistance, and recyclability. However, there are two major concerns needed to be addressed properly before they can be adopted into mainstream manufacturing industries: forming and failure. This thesis investigates formability and failure behaviour of a woven self-reinforced polypropylene composite (SRPP) using a custom-built press, an open die configuration, and a real time 3D photogrammetry measurement system (ARAMIS). Specimens with novel geometries having different aspect ratios and fibre orientations were formed until catastrophic failure. Deformations and strains were measured to construct a strain-based path dependant failure envelope in a principal strain space. Optical microscopy investigations were conducted to reveal the relation between incorporated failure mechanisms and deformation modes of the composite. Then, experimental forming and failure behaviours of SRPP were benchmarked against a woven glass-fibre reinforced polypropylene composite (GRPP). Characterisation experiments were conducted on SRPP composite using a universal testing machine and a real time strain measurement system to elucidate mechanical behaviours of the composite at room temperature. The highly nonlinear behaviour of SRPP necessitated adopting an incremental deformation theory to develop constitutive stress-strain relations and construct an orthotropic material model. Material and failure models were coded in FORTRAN and implemented into a finite element analysis using the Abaqus-Implicit solver. A finite element model with a nonlinear contact condition was developed to predict formability and failure behaviours of the SRPP during stamp forming process. Comparison between experimental and finite element analysis results proved high accuracy and reliability of the developed numerical model in predicting formability and failure of a woven self-reinforced polypropylene composite. The finite element analysis predictions demonstrated the potential of the developed numerical model to accurately predict strain path, evolution of surface strains, and failure initiation in woven composites. Finally, wrinkling behaviour of the SRPP composite was investigated through a novel Modified Yoshida Buckling Test (MYBT). The inadequacy of the current wrinkling measures to predict compressive instability in woven composites was shown. A more reliable, wrinkling-sensitive criterion, based on gradient of principal strains, was proposed. An important conclusion drawn from this study indicates that proper selection of forming path, fibre orientation and specimen dimensions facilitates manufacturing complex parts from woven thermoplastic composites. The developed numerical model showed the potential to predict failure of the thermoplastic composites experiencing complicated loading conditions. This process eliminates the need to conduct expensive, time consuming trial and error manufacturing processes to achieve flawless products made of woven thermoplastic composites

    Effect of Thermocycling and Type of Restorative Material on Microleakage of Class II Restorations

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    Objectives: Microleakage is a major cause of failure of dental restorations and results in development of secondary caries, tooth hypersensitivity and pulp pathosis. This study aimed to compare the microleakage of class II cavities filled with two types of composite resins and a compomer and subjected to thermocycling.Methods: In this in vitro experimental study, class II cavities with a gingival margin below the cementoenamel junction (CEJ) and beveled enamel margins were prepared in proximal surfaces of 60 molar teeth. The teeth were randomly divided into three groups of 20 and restored with Spectrum TPH3 and Esthet X composites and Dyract eXtra compomer. Each group was randomly divided into two subgroups (n=10) of control and thermocycling (1000 thermal cycles). Dye penetration in occlusal and cervical margins was scored under a stereomicroscope. Data were analyzed using the Kruskal Wallis test and Mann Whitney U test (P<0.05).Results: No significant difference was noted in microleakage of the three groups neither in the occlusal nor in the cervical margins in presence or absence of thermocycling (P>0.05). But, the microleakage in the cervical margins of compomer restorations was slightly higher than that of other groups especially after thermocycling.Conclusion: Microleakage of composite restorations was not significantly different from that of compomer restorations in the occlusal or gingival margins in presence or absence of thermocycling

    Comparison of Compressive Strength of Five Hydraulic Cements

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    Objectives: Maintaining pulp vitality is a main goal in restorative dentistry. Introduction of pulp capping agents paved the way to eliminate the shortcomings of these materials and obtain successful restorations. On the other hand, nanotechnology is an emerging field of science with increasing use in dental materials. This study sought to assess the effect of addition of nano-TiO2, nano-SiO2 and nano-Al2O3 on compressive strength of five hydraulic cements.Methods: In this in vitro, experimental study, three experimental formulations of nano hybrid MTA, MTA Angelus and MTA Angelus+ nano-oxide particles cements were placed in molds measuring 4±0.1mm in internal diameter and 6±0.1mm in height made of stainless steel (ISO9917-1). Ten samples were fabricated for each of the five groups of materials. Sound samples were stored at 37°C and 95±5% humidity and were subjected to compressive strength testing in a universal testing machine at a crosshead speed of 0.5mm/minute after 24 hours and one month. Two-way ANOVA, one-way ANOVA and independent samples t-test were used for comparison of compressive strength of groups at different time points.Results: The highest compressive strength belonged to MTA Angelus+ nanohydroxyapatite and nano-hybrid MTA C at 24 hours and 30 days, respectively. The lowest compressive strength belonged to nano-hybrid MTA B and MTA Angelus at 24 hours and 30 days, respectively (P<0.05).Conclusion: Addition of nanoparticles affected the compressive strength of cements. Compressive strength significantly increased over time in all groups

    Effect of Composite Color and Thickness on Correction of Tooth Discoloration

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    Objective: Selection of an appropriate shade of composite is critical in achieving an esthetic restoration. Different systems are used to assess and describe color parameters. This study aimed to assess the effect of color and thickness of Filtek Supreme (FS) and Premise (P) composite resins on correction of tooth discoloration.Methods: In this in vitro experimental study, 10 anterior teeth with Vita A2 color shade were selected. Composite specimens were fabricated in 0.5 and 0.75 mm thicknesses of FS and P composites. Intact teeth, prepared teeth, prepared teeth with enamel and dentin composite discs on their buccal surfaces, stained teeth and stained teeth with composite discs were photographed using a digital camera under standard conditions and color change (ΔE) at different phases was calculated.Results: The L*, a* and b* color parameters in prepared and unstained teeth were not significantly different from those of intact teeth. In stained teeth, the L* parameter only in prepared and stained teeth with 0.75mm P composite was not significantly different from the L* parameter in intact teeth. Significant differences were seen in other stained teeth. The a* and b* parameters only in prepared and stained teeth with 0.5 mm FS composite were significantly different from those in intact teeth. By increasing the thickness of composite, the color change in comparison with intact teeth decreased in both groups.Conclusion: The results showed that the effect of type of composite, its thickness and their interaction on the color change was significant when using FS and P composites in 0.5 and 0.75mm thicknesses in comparison to intact teeth and the lowest color difference with intact teeth was achieved using 0.75mm thickness of P composite (enamel and dentin)

    Disseminated Aspergillosis as the Herald Manifestation of Chronic Granulomatous Disease in an Adult Patient

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    Chronic granulomatous disease is an inherited defect in intracellular killing of ingested microorganisms characterized by recurrent life threatening bacterial and fungal infections including invasive aspergillosis in early childhood. We report  a  disseminated aspergillosis as  the  representative  of  adult  onset  chronic granulomatous disease without previous infection, with dramatic response to combination of antifungal and interferon therapy

    Stretch Forming Simulation of Woven Composites Based on an Orthotropic Non-Linear Material Model

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    Characterisation experiments have been conducted on a woven self-reinforced polypropylene composite (SRPP) including uniaxial and bias extension tests. Outcomes of these experiments were employed to develop a non-linear orthotropic material model within an incremental deformation framework. The material model of the woven composite was implemented into a finite element simulation to predict stretch forming behaviour of SRPP specimens. The predicted strain paths at the pole of specimens were verified against experimental outcomes. It was shown that specimens possessing different aspect ratios deform under a wide range of deformation modes from uniaxial extension to biaxial stretch modes. Finally, the effect of different forming parameters on the strain path evolution of the woven composite was elucidated through numerical simulations. It was shown that the aspect ratio of the samples plays an important role in forming behaviour of woven composites. Development of a reliable and accurate numerical model for predicting forming behaviour of woven composites and understanding their main forming mechanisms promote and encourage the extensive application of these materials systems in a wide range of mass producing industries. Adopting woven composites in manufacturing industrial components facilitates addressing environmental concerns such as recyclability and sustainability issues

    A Comparison between Forming Behaviours of Two Pre-Consolidated Woven Thermoplastic Composites

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    This paper presents the results of an investigation on stretch forming behaviour of two consolidated woven thermoplastic composites: a self-reinforced polypropylene (SRPP) and a glass-fibre reinforced polypropylene (GRPP) composite. A custom-built press with a hemispherical punch was employed to deform composites’ specimens possessing different aspect ratios into an open die. The induced strains on the outer surface of specimens were measured continuously through two high speed, high resolution CCD cameras by employing a Digital Image Correlation (DIC) technique. The strain paths at three different locations on the surface of specimens were compared to elucidate the effect of fibre and matrix on the formability of a woven composite. The fractured surface of specimens was investigated to reveal the effect of fibre mechanical properties on failure morphologies in woven composites. It was found out that the main mode of failure in GRPP is fibre fracture while observed failure morphologies in SRPP were a complex combination of different failure mechanisms. It was revealed that the combination of applied boundary conditions and specimen’s width determines the effective forming mechanisms
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