DETERMINATION OF MECHANICAL PROPERTIES OF COMPOSITE SANDWICH PANEL WITH ALUMINIUM HONEYCOMB CORE

This paper deal with comparison of mechanical properties of composite sandwich panel with aluminium honeycomb core which is determined by experimental measurement, analytic calculation and numerical simulation. The goal was to compared four composite sandwich panels. The composite sandwich panels were made of two different aluminium honeycomb cores with density 32 and 72 kg.m-3 and two different layup of skin with 4 and 5 layers. The comparison was performed on a three-point bend test with support span 400 mm. This paper confirms the possibility of a very precise design of a composite sandwich panel with an aluminium honeycomb core using analytical calculation and numerical simulation.

In-vitro Comparative Evaluation of Flexural Strength and Depth of Cure of Bulkfill Composite

Aims and objectives: Bulkfill composite resins have been used for the posterior restorations in an attempt to speed up the restorative process. Here 4 to 5mm thickness of composite resins can be placed andcured in asingle step so that time consuming layering technique can be eliminated. The purpose of this study was to investigate the flexural strength and depth of cure of two bulk fill composites and to compare it with a universal composite. Materials and method: Two bulk fill composites (Sonic fill and Filtekbulkfill) and one universal composite (Filtek Z350 XT) were used. Ten samples per group were made using rectangular split brass mold following ISO standard 4049 to measure the flexural strength. Each sample was then subjected to three point bend test using universal testing machine until failure occurred. For depth of cure measurements, ten samples per group were made using cylindrical brass mold and were subjected to acetone shake test for 30 sec. The dimensions of the samples were measured using Vernier callipers and compared. One-way analysis of variance followed by Tukey’s post-hoc test was used to determine the statistical differences among groups at significance of p<0.05. Results: Sonicfillgave highest flexural strength value and Filtek Z350 XT the least. There was no statistically significant difference between the flexural strength of Filtekbulkfill and Filtek Z350 XT. For depth of cure, Filtekbulkfill showed higher value than other tested groups. Conclusion: All the tested materials showed significantly higher flexural strength values than the minimum flexural strength (80MPa) that is required for use in stress bearing areas. Sonicfill composite produced highest value of flexural strength than other composites, which may bedue to its increased percentage of filler content. For depth of cure, both the tested bulkfill composites showed lesser value of depth of cure than that claimed by manufacturers .

Mechanical Properties of Laser Welded SS316 and SS321

Stainless steel is used in a plenitude of domains from low end applications, like surgical products to high-end applications like aerospace sector. Stainless steels are iron-carbon based alloys with more than 10.5% chromium. The chromium present in stainless steel has greater affinity towards oxygen atom and will result in the formation of chromium oxide film over the surface at molecular level. Stainless steel grades SS321 and SS316 are considered in this work due to its better flexural rigidity, corrosion resistance and maximum temperature withstanding capacity. The laser beam welding was preferred due to high local energy concentration of the laser beam, which makes it more suitable method for stainless steel welding. Chromium precipitation on the grain boundaries is avoided by using a high laser welding speed that diminishes the exposure of the weld to high temperatures. The microstructure of the welded joints are examined using metallurgical microscope to find out the flaws over the weld joint. Three-point bend test was conducted to quantify the mechanical strength of the welded joints.

Gap Test of Crack-Parallel Stress Effect on Quasibrittle Fracture and Its Consequences

In the standard fracture test specimens, the crack-parallel normal stress is negligible. However, its effect can be strong, as revealed by a new type of experiment, briefly named the gap test. It consists of a simple modification of the standard three-point-bend test whose main idea is to use plastic pads with a near-perfect yield plateau to generate a constant crack-parallel compression and install the end supports with a gap that closes only when the pads yield. This way, the test beam transits from one statically determinate loading configuration to another, making evaluation unambiguous. For concrete, the gap test showed that moderate crack-parallel compressive stress can increase up to 1.8 times the Mode I (opening) fracture energy of concrete, and reduce it to almost zero on approach to the compressive stress limit. To model it, the fracture process zone must be characterized tensorially. We use computer simulations with crack-band microplane model, considering both in-plane and out-of-plane crack-parallel stresses for plain and fiber-reinforced concretes, and anisotropic shale. The results have broad implications for all quasibrittle materials, including shale, fiber composites, coarse ceramics, sea ice, foams, and fone. Except for negligible crack-parallel stress, the line crack models are shown to be inapplicable. Nevertheless, as an approximation ignoring stress tensor history, the crack-parallel stress effect may be introduced parametrically, by a formula. Finally we show that the standard tensorial strength models such as Drucker–Prager cannot reproduce these effects realistically.

Numerical modeling of Nomex honeycomb core composite plates at meso scale level

Honeycomb core composite plates are becoming more important in the construction of primary aerospace structures. Nowadays, these types of materials are used for construction of fuselage skins, central and outer wing boxes, engine tail cones, landing gear doors, command surfaces like spoilers and ailerons etc. To determine the stress strain field in loaded honeycomb plates elastic coefficients are required. In the present work, a method for determining all required elastic coefficients for the core and plates is presented. Using experimentally obtained values for Nomex paper (type 410) and phenolic resin material model is presented and FEA model of composite plate with honeycomb core is created and three point bend test is simulated. Numerically obtained stress and strain values are compared to the experiment. Good agreement between proposed material model and experimentally obtained values is observed.

The Combination of CQ-amine and TPO Increases the Polymerization Shrinkage Stress and Does Not Improve the Depth of Cure of Bulk-fill Composites

SUMMARY Objectives: To evaluate the effect of combining camphorquinone (CQ) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the depth of cure and polymerization shrinkage stress of bulk-fill composites. Methods and Materials: Experimental bulk-fill composites were produced containing equal molar concentrations of either CQ-amine or CQ-amine/TPO. The degree of in-depth conversion through each millimeter of a 4-mm-thick bulk-fill increment was evaluated by Fourier transform near-infrared microspectroscopy using a central longitudinal cross section of the increment of each bulk-fill composite (n=3). Light-transmittance of the multi-wave light-emitting diode (LED) emittance used for photoactivation (Bluephase G2, Ivoclar Vivadent) was recorded through every millimeter of each bulk-fill composite using spectrophotometry. The volumetric shrinkage and polymerization shrinkage stress were assessed using a mercury dilatometer and the Bioman, respectively. The flexural modulus was also assessed by a three-point bend test as a complementary test. Data were analyzed according to the different experimental designs (α=0.05 and β=0.2). Results: Up to 1 mm in depth, adding TPO to CQ-based bulk-fill composites increased the degree of conversion, but beyond 1 mm no differences were found. The light-transmittance of either wavelengths emitted from the multi-wave LED (blue or violet) through the bulk-fill composites were only different up to 1 mm in depth, regardless of the photoinitiator system. Adding TPO to CQ-based bulk-fill composites did not affect volumetric shrinkage but did increase the flexural modulus and polymerization shrinkage stress. Conclusion: Adding TPO to CQ-based bulk-fill composites did not increase the depth of cure. However, it did increase the degree of conversion on the top of the restoration, increasing the polymerization shrinkage stress.

Mechanical Performance of Honeycomb Sandwich Structures Using Three-Point Bend Test

In this study, honeycomb sandwich structures were prepared and tested. Facesheets of sandwich structures were manufactured by carbon fiber epoxy matrix composites while Nomex® honeycomb was used as core material. An epoxy-based adhesive film was used to bond the composite facesheets with honeycomb core. Four different curing temperatures ranging from 100oC to 130oC were applied with curing times of 2h and 3h. Three-point bend test was performed to investigate the mechanical performance of honeycomb sandwich structures and thus optimize the curing parameters. It was revealed that the combination of a temperature of 110oC along with a curing time of 2h offered the optimum mechanical performance together with low damage in honeycomb core and facesheets.