Numerical and experimental study of internal pressure behaviour of integrated and non-integrated weft-knitted reinforced composite elbows

This research aims to study the internal pressure behaviour of integrated and non-integrated composite elbows. For this purpose, weft-knitted integrated preforms were produced on the CMC-330-TC Flat knitting machine. Composite elbows reinforced with integrated weft-knitted preform were fabricated using the bladder molding technique. In addition, the non-integrated composite elbows were provided by wrapping the weft-knitted fabric on a plaster mold and hand lay-up impregnation method. To perform the pressure test, a fixture was designed and manufactured. Produced samples were subjected to the internal pressure test. Experimental results show that integrated composite elbow has higher hydrostatic pressure resistant. The internal pressure behaviour of integrated composite was simulated using the multi-scale model. Results showed that integrated composite elbow has a higher resistance against internal pressure than non-integrated composite elbows, so that the integrated elbows failed at 12.5-bar pressure, while the non-integrated elbow failed at 9.5-bar pressure.

Technology of slip casting of celsian-slavsonite ceramics

The article considers the slip casting technology of celsian-slavsonite ceramics with the ratio of raw materials to obtain crystalline phases of ВаAl2Si2O8: SrAl2Si2O8 – 25:75. The manufacture technology of product proceeded in two stages. The first stage of synthesis was performed in a muffle furnace at a rate of temperature of 15 deg / min at a maximum firing temperature of 1200 °C with a holding time of 2 hours. Then the synthesized ceramics were grinded for 10 minutes. The second stage was to obtain a slip with the addition of surfactants (DOLAPIX PC 67). The finished slip was poured into a plaster mold. Drying of the green sample was carried out in an oven at a temperature up to 110 °C for 3 hours. Firing of the dried sample was carried out in a muffle furnace at a rate of set temperature of 15 deg / min, at a maximum firing temperature of 1250 °C for 2 hours. The fired materials were subjected to machining. The obtained data indicate that, the best sample was fired at a temperature of 1250 ° C and had the following properties: dielectric constant — 9.4, water absorption — 5.9 %, open porosity — 14.4 %, apparent density — 2.42 g/cm3, flexural strength — 19 MPa.

Evaluation of reproduction technique of bitemarks printed in chewing gum for human identification

Forensic Odontology is the science that correlates dental and legal principles, used for processes such as human identification. One of the possible acting fields for Forensic Odontologists is the analysis and study of patterns and injuries created by human bite marks. This study aimed to show the applicability of dental marks printed in chewing gum for human identification in forensic investigations. A transversal observational study was carried out. The data was collected from 20 volunteers over 18 years old. Each subject had their upper and lower dental casts and was asked to chew a piece of gum for one minute. The pieces of chewing gum were refrigerated at -20ºC for a week, and reproduced with addition and condensation silicones using an adapted reproduction technique. The analysis of the chewing gum was made by overlays. The ANOVA test showed no significant differences on width and length between the pieces of chewing gum and their reproductions (greatest width p=0.918, and the length p=0.981). The analysis of the reproductions with plaster mold showed that there was no difference when using addition silicone or condensation silicone. During the analysis, various suspects could be excluded from the investigation (up to 11, depending on the technique used), but it was not possible to confirm one of them as the main suspect. The study showed that the reproduction technique of chewing gum is efficient, viable and easily performed; and can be used in cases of human identification in forensic investigations. However, it is necessary to certify that the chewing gum effectively presents a bite mark and that it is correctly handled to avoid alterations. It also became evident that the process of refrigeration is essential for the analysis proposed in this study.

Sacred Substantiations: Lincoln Casts and Statuary in the American Imagination

On March 31, 1860, Abraham Lincoln waited in the studio of Leonard Wells Volk as a plaster mold hardened around his face and head. After one hour, Volk removed the mold; he later repeated the process for Lincoln’s hands. The resulting life casts elicited profound emotional reactions in those who saw them. Augustus Saint-Gaudens recognized and capitalized on their invaluable status as candid indexes of Lincoln’s likeness in his 1887 Chicago monument, Abraham Lincoln: The Man. In the words of sculptor Lorado Taft, “It does not seem like a bronze. . . . One stands before it and feels himself in the very presence of America’s soul.” It was also Saint-Gaudens who amplified the casts’ influence through the manufacture of a prized series of thirty-three bronze replicas. The actual and imagined characteristics of these casts—their sense of possessing a “soul,” and their physical manifestation of Lincoln’s touch—all warrant consideration of their place within the larger tradition of holy relics. This paper posits the Lincoln casts as “contact relics” and establishes the generative potential of such a numinous categorization for American audiences, especially in the wake of the Civil War. Volk’s direct impressions of Lincoln’s visage and hands provided the “blueprints,” so to speak, for an astonishingly wide variety of sculptural manifestations—from the iconic Lincoln Memorial (1920) by Daniel Chester French to Abraham Lincoln (1917) by George Grey Barnard. This essay argues that the cultural impact of this sculptural genealogy is largely indebted to the casts’ material substantiations of Lincoln’s bodily presence and touch. Indeed, by situating these objects between medieval and modern modes of viewing, it will become clear that the casts, as progeny of the original life molds, afforded an affective, even remedial, authenticity for subsequent Lincoln monuments in the American imagination.

Experimental and numerical thermal analysis of open-cell metal foams developed through a topological optimization and 3D printing process

This study focuses on the thermal analysis and comparing a lattice model and an optimized model of open-cell metal foams manufactured thanks to a metal casting process. The topological optimization defines the complex geometry through thermal criteria and a plaster mold reproduces it in 3D printing to be used in casting. The study of the thermal behavior conducted on the two open foam metal structures is performed based on several measurements, as well as numerical simulations. It is observed that the optimized metal foam presented less and non-homogenous local temperature than the lattice model with the gap of about 10 °C between both models. The pore size and porosity significantly affect the heat transfer through the metal foam. The comparison between numerical simulations and experimental results regarding the temperature fields shows a good agreement allowing the validation of the developed three-dimensional model based on the finite element method.

Using Porcelain Replicas for Precision Control in Flintknapping Experiments

ABSTRACTThe experimental replication of lithic artifacts occasionally encounters issues of standardization and control. Two major issues are how to accurately create a large sample population and how to sample from specific stages over the flaking process. Knappable stone is unpredictable due to inclusions, cracks, and differences in size, texture, and fracture toughness. While this aspect of stone is critical to understanding some aspects of human behavior, decision-making, and skill assessment, in some experimental studies it may hinder other areas. Research for a large study assessing the failure of Folsom preforms during the fluting stage required many knappable facsimiles. The process outlined here uses porcelain as a medium for tackling these requirements. The new method presented here illustrates how a 3-D scanner and printer can be used to record and produce a copy of the artifact form. It then describes how to create a plaster mold of the printed artifact form and, finally, how to cast and fire the artifact replica in porcelain.

Depth-of-cure of Bulk-fill Composites Cured in Tooth or Opaque Substrate

ABSTRACT Purpose To determine the effect of substrate on the depth-of-cure determination when using hardness profiles in a covered-slot technique and to introduce a new covered-slot method that uses tooth substrates. Materials and methods Three bulk-fill composites and one conventional composite were tested: Tetric EvoCeram Bulk Fill, Venus Bulk Fill, Filtek Bulk Fill Flowable, Filtek Supreme Ultra. The composites were light-cured in rectangular slots (2 mm deep, 2 mm wide) made in a plaster mold or an extracted tooth. The slots were covered with an orange glass plate during curing, leaving one end exposed for light-curing. After curing, the glass plate was removed and the sample was stored in the dark for 24 hours before Vickers hardness was measured as a function of depth at 0.5-mm intervals. Results were analyzed using two-way analysis of variance (ANOVA) and pairwise comparisons (significance level 0.05). Results The hardness of composites cured in covered-slot molds decreased with increasing depth (p < 0.001). Bulk-filled composites cured in plaster molds had a slightly lower depth-of-cure than those cured in natural tooth substrates. Differences between the tooth and plaster substrates were significant at all depths in the “packable” bulk-fill composite (Tetric EvoCeram Bulk Fill), and were significant at ≥2.5 and ≥3.5 mm in the flowable bulk-fill composites (Filtek Bulk Fill Flowable and Venus Bulk Fill) respectively. Conclusion Using natural tooth substrates in the covered-slot method increased the depth-of-cure of bulk-filled composites in comparison to opaque plaster molds. How to cite this article Church BW, Tantbirojn D, Do T, Wells MH, Versluis A. Depth-of-cure of Bulk-fill Composites Cured in Tooth or Opaque Substrate. Int J Experiment Dent Sci 2017;6(2):68-73.