“…The apparent density is used for cellular materials because their density is calculated with the volume of the expanded material and not only the volume of the solid polymer. 38 The cost of the sandwich composite manufacturing process usually represents an important part of the total cost 37 ; thus, the analysis of the overall density and the weight/m 2 are important data to build economical and high-performance panels (Figure 5). Figure 5.Relation of cost, weight and density of the panels studied.…”
Sandwich composites are materials that have superior properties including low weight, high impact energy absorption and high thermal insulation features, compared to conventional materials. In this study, four different sandwich samples were explored for use in cold storage chambers. The composites were created using an injection molding process with polyurethane foam as the core and different materials (glass fiber reinforced polyester, galvanized steel, aluminum sheets and crimped aluminum) as face materials. Morphological, physical and mechanical properties were evaluated. An inexpensive and nondestructive method was used to determine the thermal behavior of the sandwich panels, and the surface temperature evolution was thermally monitored during the tests. In general, results showed that polyurethane had a homogeneous distribution of size and shape with closed cells, which can improve the retention of the insulating gas. Additionally, the compressive strength of polyurethane within the composites exhibited typical values to be used in specific applications. Thus, the sandwich with galvanized steel exhibited lower flexural strength, which provides more freedom in panel design. The overall heat transfer coefficient of the panels in the form of cubes presented values below the maximum limit requested by ABNT NBR-15457. Finally, the composite galvanized steel/polyurethane/galvanized steel achieved the best performance for use as a thermal insulation material in a cold storage chamber.
“…The apparent density is used for cellular materials because their density is calculated with the volume of the expanded material and not only the volume of the solid polymer. 38 The cost of the sandwich composite manufacturing process usually represents an important part of the total cost 37 ; thus, the analysis of the overall density and the weight/m 2 are important data to build economical and high-performance panels (Figure 5). Figure 5.Relation of cost, weight and density of the panels studied.…”
Sandwich composites are materials that have superior properties including low weight, high impact energy absorption and high thermal insulation features, compared to conventional materials. In this study, four different sandwich samples were explored for use in cold storage chambers. The composites were created using an injection molding process with polyurethane foam as the core and different materials (glass fiber reinforced polyester, galvanized steel, aluminum sheets and crimped aluminum) as face materials. Morphological, physical and mechanical properties were evaluated. An inexpensive and nondestructive method was used to determine the thermal behavior of the sandwich panels, and the surface temperature evolution was thermally monitored during the tests. In general, results showed that polyurethane had a homogeneous distribution of size and shape with closed cells, which can improve the retention of the insulating gas. Additionally, the compressive strength of polyurethane within the composites exhibited typical values to be used in specific applications. Thus, the sandwich with galvanized steel exhibited lower flexural strength, which provides more freedom in panel design. The overall heat transfer coefficient of the panels in the form of cubes presented values below the maximum limit requested by ABNT NBR-15457. Finally, the composite galvanized steel/polyurethane/galvanized steel achieved the best performance for use as a thermal insulation material in a cold storage chamber.
“…The porcine spine could not be a totally representative model for the human spine, but we believe that for biomechanical studies emphasizing in insertional locations of lateral vertebral body and effect of cortical purchase, the porcine spine still could be an alternative model. To increase the reproducibility and reliability of the pullout data, the screws were pulled out along the same axis as the pullout arm by using a custom-made grip equipped with two universal joints on the upper and lower side of Instron wedge grip, respectively, to achieve coaxial alignment of the screw and the pullout arm 40 , 41 .…”
Although an anterior approach with anterior lateral screw fixation has been developed for stabilizing the thoracolumbar spine clinically, screw loosening still occurs. In this novel in vitro study, we attempted to elucidate the optimal screw position in the lateral lumbar vertebra and the effect of bicortical fixation. A total of 72 fresh-frozen lumbar vertebrae from L1–6 were harvested from 12 mature pigs and randomly assigned to two modalities: bicortical fixation (n = 36) and unicortical fixation (n = 36). Six groups of screw positions in the lateral vertebral body in each modality were designated as central-anterior, central-middle, central-posterior, lower-anterior, lower-middle, and lower- posterior; 6 specimens were used in each group. The correlations between screw fixation modalities, screw positions and axial pullout strength were analyzed. An appropriate screw trajectory and insertional depth were confirmed using axial and sagittal X-ray imaging prior to pullout testing. In both bicortical and unicortical fixation modalities, the screw pullout force was significantly higher in the posterior or middle position than in the anterior position (p < 0.05), and there was no significant differences between the central and lower positions. The maximal pullout forces from the same screw positions in unicortical fixation modalities were all significantly lower, decreases that ranged from 32.7 to 74%, than those in bicortical fixation modalities. Our study using porcine vertebrae showed that screws in the middle or posterior position of the lateral vertebral body had a higher pullout performance than those in the anterior position. Posteriorly positioned lateral vertebral screws with unicortical fixation provided better stability than anteriorly positioned screws with bicortical fixation.
“…The densities of each group may vary slightly (up to ± 10% according to the manufacturer). To obtain reproducible results, recommendations for sample preparation were followed 27 . The apparent density was determined for each foam block according to ASTM D1622 28 .…”
Threads of modern pedicle screws can vary greatly in design. It is difficult to assess which interplay of design features is particularly advantageous for screw anchorage. This study aims to increase the understanding of the anchorage behaviour between screw and cancellous bone. Pull-out tests of six pedicle screws in two sizes each were performed on three densities of biomechanical test material. More general screw characteristics were derived from the screw design and evaluated using the test data. Selected screws were tested on body donor material. Some screw characteristics, such as compacting, are well suited to compare the different thread designs of screws with tapered core. The combination of two characteristics, one representing bone compacting and one representing thread flank area, appears to be particularly advantageous for assessing anchorage behaviour. With an equation derived from these characteristics, the pull-out strength could be calculated very accurately (mean deviation 1%). Furthermore, findings are corroborated by tests on donor material. For screws with tapered core, the design demands for good anchorage against pull-out from cancellous bone change with material density. With sufficient bone quality, screws with a high compacting effect are advantageous, while with low bone density a high thread flank area also appears necessary for better screw anchorage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
