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Item Design and Analysis of a Composite Monocoque for Structural Performance : a Comprehensive Approach(2019-08) Kamble, Meghana P.; Dalir, Hamid; Tovar, Andres; El-Mounayri, HazimLately numerous studies have been performed to design composite monocoques with high strength and low weight for various student level racing contests. The objective of this paper is to develop an insightful methodology to design and de veloped a light-weight composite monocoque. The monocoque is designed to pass the mandatory static load tests laid down by the International Automobile Feder ation (FIA)Formula 3. These Formula 3 tests are considered the baseline of the desired structural integrity of the composite monocoque. The presented design tech nique emphasises on a monocoque developed for Sports Car Club of America (SCCA) races. The three standard load tests performed on the monocoque are Survival Cell Side test, Fuel Tank test and Side Intrusion test. A sandwich layup of bi-directional woven carbon/epoxy prepreg and aluminium honeycomb is optimized for minimum weight while predicting the unknown properties of layup and ensuring the mono coque doesnt experience failure. The approach intends to achieve minimum weight with high torsional rigidity and is capable of being used for the design and analysis of any kind of formula type composite monocoque.Item Effect of Gap Geometry on Secondary Caries in Vitro(2009) Nassar, Hani M.; Cabezas, Carlos Gonzales, 1966-; Chu, Tien-Min Gabriel; Fontana, Margherita Ruth, 1966-; Gregory, Richard; Matis, Bruce; Cochran, MichaelObjective: To investigate the effect of the size of the space between the restoration and the dentinal wall of the tooth (i.e. the dentinal portion of the gap) on the development of secondary caries. Methods: Tooth-resin-matrix composite specimens were mounted on custom-made gap-model stages. Specimens were divided into four groups (n=10). Group 1 had a uniform gap size of 30μm throughout both enamel and dentin. Group 2 had a 30μm enamel gap size with a 530μm dentinal gap. Group 3 had 525μm gaps in both enamel and dentin. Group 4 had 525μm and 1025μm gaps in enamel and dentin, respectively. Specimens were attached to plastic Petri plates, gas-sterilized and then incubated in a microbial caries model with S. mutans TH16 in (1% sucrose tryptic soy broth for 1 h, 4 times/day, and with a buffer solution for the rest of the day). After 8 days of incubation, tooth specimens were sectioned and stained with a rhodamine B solution. Digital images were taken under a confocal microscope and analyzed for lesion size at the enamel outer lesion (EOL), enamel wall lesion (EWL), dentin wall lesion next to the DEJ (DWL-A) and dentin wall lesion at 750µm from the DEJ (DWL-B). Results: No difference in EOL size was found between the groups. DWL-A and -B were larger in group 3 than groups 1and 2. Larger DWL-B was found in group 3 than group 4. Group 4 had marginally significant larger EWL than groups 1 and 2 (p=0.0652 and p=0.0648, respectively). Also, group 4 had marginally significant (p=0.0607) larger DWL-B than group 1. Conclusions: Based on the results of this study, it can be concluded that the presence of additional space at the dentinal wall area did not affect secondary caries development as long as the enamel gap was small. However, with enamel gaps of ≈500 µm, the presence of the additional gap space at the dentinal wall led to the development of smaller dentinal wall lesions at the deeper parts of the simulated cavity. Also, in uniform gaps, the size of the interface was positively correlated with size of the dentinal wall lesions.Item In vitro evaluation of polymerization energy for bulk fill composites(2016-05) AlRasheed, Rawan S.; Platt, Jeffery A.; Wallace, Joseph; Matis, Bruce A.; Cook, Norman Blaine; Chu, Tien-Min GabrielRecently, the concept of “bulk-fill” resin-based composites (RBCs) has been re-emphasized, with claimed improvements in depth of cure (DOC) with similar mechanical properties and comparable adaptation to walls and margins relative to conventional composite. More research is needed to carefully examine the properties of these new materials. The objective of this study was to measure the light energy, microhardness (VHN), and elastic modulus across the depth of one conventional and three bulk-fill RBCs. Materials and Methods: Three commercially available bulk-fill RBCs (Tetric EvoCeram Bulk Fill [TE], SonicFill [SF], X-tra fill[XF]) and one conventional RBC (Premise [PR]) were evaluated (n = 10). DOC (using Vickers’s microhardness), elastic modulus (using atomic force microscopy), and the mean irradiance and total light energy transmitted through different thicknesses of RBC were measured by a spectrometer. The effects of group, location, and curing depth on VHN were analyzed using mixed-model ANOVA. Elastic modulus and light energy comparisons were made using two-way ANOVA, with a significance level of 5 percent. Results: There was a significant difference in the depths for the mean irradiance and total energy between different depths in all materials. All materials achieved the manufacturers’ claimed DOC. XF had the highest DOC with 7 mm and a light energy of 0.56± 0.02 J/cm2 at 7 mm. PR had the lowest DOC with 3 mm and a light energy of 0.84 ±0.12 J/cm2 at 3 mm. The elastic modulus showed significant variation in depth profiles that were different than the DOC. Significance: The manufacturers’ claims for bulk-fill DOC were achieved using a microhardness method. However, this method failed to detect the quality of the polymerization. Assessment of the elastic modulus using AFM is a promising method for greater understanding of the polymerization.