Papers by Keyword: High Temperature

Abstract: Reinforced concrete exposed to high temperatures, such as in a fire, poses a serious threat to buildings by weakening the concrete and reducing the structure's stiffness. Therefore, the article investigated the structural behavior of reinforced concrete when subjected to elevated temperatures in Peru, where many structures are not designed to withstand high temperatures, leading to irreparable damages such as loss of human lives and changes in material properties. To enhance the heat resistance of reinforced concrete, carbon fibers were added, and a percentage of ultra-high-strength concrete was incorporated. The material was analyzed using the finite element method. Different frames were evaluated, focusing on the use of matrices and nodes. The proposal involved adding new materials; carbon fibers were added at 0.06%, and ultra-high-strength concrete at 20%. These quantities were chosen based on the researched articles. First, the properties of each material were defined and input into the software. Then, a temperature ranges from 100°C to 1000°C was defined. The results were evaluated, and improvement percentages regarding displacements due to applied loads were determined. The findings indicate a 33.05% improvement in distributed load and temperature-induced loads between 100°C to 1000°C, varying between 17% and 6.56% respectively. It was concluded that higher temperatures result in more significant damages such as changes in color, deflections, and loss of stiffness, increasing the probability of collapse in a shorter time frame. In conclusion, the use of the proposed materials enhances resistance and reduces deflections when subjected to various types of loads.

Abstract: The Harmonic Structure (HS) is a recently introduced concept that paves the way for engineering metallic materials to achieve superior mechanical performance. They consist of soft, coarse-grained regions surrounded in three dimensions by an interconnected network of hard, ultra-fine grained regions. In addition, from a structural materials point of view, high entropy alloys have attracted attention due to their unique mechanical properties. In the present study, the HS design was applied to a high entropy CrMnFeCoNi alloy (also called "Cantor alloy"). The HS-designed Cantor alloy was successfully fabricated by mechanical milling, which is one of the surface severe plastic deformation processes, and the subsequent sintering process. The mechanical properties of these HS and homogeneous (Homo) Cantor alloy compacts were investigated by high-temperature compression tests in the temperature range of room temperature (RT) and 1173K, under initial strain rates of 0.01 s^-1, 0.001 s^-1, and 0.0001 s^-1. The stress-strain curves of the HS compacts showed a large initial increase in stress and then a rapid decrease with strain, while that of the Homo compact showed a gentle increase and a gradual decrease. EBSD observation of the deformed compacts revealed that the HS compacts were probably deformed not only by dynamic recrystallization, but also by grain boundary sliding during deformation. The strain rate sensitivity value m of the HS compacts was 0.541 (true strain: 0.2) at 1173 K. In other words, the HS compacts exhibited pseudo-superplastic deformation at these temperatures.

Abstract: Harmonic Structure (HS) materials, a class of heterogeneously structured materials, are known to exhibit unique and superior mechanical properties. The HS consists of soft, coarse-grained regions (Core) that are three-dimensionally surrounded by an interconnected network of hard, ultrafine grained (UFG) regions (Shell). The unique UFG network structure of the Harmonic Structure increases the dislocation density of the core regions in contact with the Shell, resulting in increased strength and work hardening rate in the Core regions. These contribute to the high strength of the HS materials and suppress the plastic instability of the Shell regions, resulting in higher ductility of the HS materials. In the present research, the HS design is applied to a high-entropy CrMnFeCoNi alloy, also known as the Cantor alloy, to study the microstructure change during high temperature deformation at 1073 K and 1173 K. Although the alloy exhibits high strength and high ductility at cryogenic temperature due to the twinning deformation, the high temperature properties are not clear, especially in the case of the HS design. As a result, the alloy with or without HS design did not show twinning deformation at these temperatures, and it is noteworthy that the alloy with HS showed preferential recrystallization in the UFG network region, and thus the recrystallized UFGs played an important role in grain boundary sliding to demonstrate the pseudo-superplastic deformation behavior.

Abstract: The avalanche robustness of 430 V SiC avalanche diodes at high temperatures is investigated. The UIS test was performed with fixed avalanche time in order to avoid the effect of a thermal diffusion time on an avalanche energy. It is found that the avalanche energies at 25 are 10.5 J/cm² for and 12.7 J/cm² for while those at 170 are 8.02 J/cm² and 9.96 J/cm², respectively. Their temperature coefficients are about-0.018 J/cm²K, which are much smaller than those of typical SiC-MOSFETs, indicating that the SiC diodes maintain great avalanche robustness even at high temperatures.

Abstract: It is pertinent to mention here that the high temperature behaviour of CNT-reinforced NiCrAlY with CNT 3%, 5% and 7% with HVOF on T-SA213-T-11 steel at 600°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at high elevated temperatures are underwent low porosity, opaque coatings, they are more viscid in nature and are due to its low porosity, high dense coatings, more adhesive in nature and strong bond. Kinematics hot corrosion, oxidation and erosion are to be analyzed by the attainment of mass gain after each and every progression under thermogravimetric studies (1hour heating and 20 minutes cooling). Results will be achieved by using visual examination, and advanced microscopy like XRD and SEM/EDS analysis. Keywords: High temperature, hot corrosion, Thermal spray coatings HVOF, XRD and SEM/EDS analysis.

Abstract: The article presents the results of research focused on the behavior of composites with a matrix based on alkali-activated materials when exposed to extreme temperatures (up to 1200°C). The behavior of the material based on alkali-activated fly ash, blast furnace slag, metakaolin, their mutual combinations respectively was analyzed in detail. The effect of thermal exposure on the properties of the developed materials was assessed by a complex of physical, mechanical and chemical methods. A specific area of research was the examination of the rheological properties of the developed mixtures in the fresh state.

Abstract: On the worldwide tendency of wight reduction of automobile, aluminum is drawing a large number of researcher’s sights because it’s advantages of low weight, corrosion resistance, flexible and so on. Aimed at understanding high-temperature flow behavior of aluminum alloy A5005, tensile tests were conducted at temperatures 360°C, 430°C, 500°C and strain rates 0.0003s^-1, 0.003s^-1, 0.03s^-1 respectively. For constitutive equation molding, a simplified Johnson-Cook model was adopted to describe high-temperature relationship of A5005 alloy. One of superiorities of this model is the flow stress model can be established more efficiently. What’s more, adiabatic temperature rise is eliminated by introducing development trend of material stress and strain in this model. Finally, the root mean square error (RMSE) was used to check the accuracy of the final model. The results show that the model accuracy increase by temperature increasing and strain rate decreasing, and the simplified Johnson-Cook model can describe stress-strain tendency without losing much accuracy.

Abstract: Material extrusion additive manufacturing (ME-AM) builds 3D models by extruding materials through a nozzle layer by layer. As the development of materials, an increasing demand of the high-temperature extrusion has emerged in additive manufacturing (AM). While the smooth and stable extrusion process at high temperature relies heavily on the nozzle, the optimization study on the metal nozzle is reported in this work. From current brass and steel nozzles, two optimized nozzles (a steel nozzle with brass embedded and a steel nozzle with brass encircled) have been designed and the thermal conductivity has been studied by simulation analysis. Then the thermal deformation of designed nozzles and traditional nozzles have been investigated at the temperature of 410°C. Conducting the extrusion and printing tests, the extrusion performance of the proposed nozzles has been compared to that of traditional nozzles. The results indicate that the proposed nozzles lead to the better thermal distribution as well as the stronger resistance to thermal deformation compared to the traditional brass nozzle. The designed steel nozzle with brass encircled shows the excellent extrusion performance and printing performance.

Abstract: In this work, the effect of high temperature molten KOH wet etching on GaN/AlGaN epilayer has been investigated for different family of dislocations. The high etching temperature (up to 510°C) allows a good definition of the pits, making easy the observation and the counts. Such high temperature will allow a detailed study on the statistical distribution of the dislocations on whole wafer by optical microscope for screw/mixed dislocation. A comparison on dislocation density between AlGaN/GaN structure grown on Si (111) substrate and 4H-SiC substrate has been performed.

Abstract: Polymer-based fiber composites have a number of unique physical and mechanical properties and are widely used in the design of structural elements in rocket and space engineering. However, along with the high characteristics of strength and rigidity, there is a noticeable anisotropy of properties which contributes to occurrence and development of damage leading to degradation of the load bearing capacity of structures and their premature destruction. Along with development of micromechanical and phenomenological models, an important place has the procedure for identifying the basic characteristics of composite materials. Such characteristics, in particular, include those of layer elasticity which are usually used when designing structures. However, even such characteristics depend on the loading conditions and for their identification, computational methods based on statistical analysis should be used. This paper attempts to identify the elastic characteristics based on test results of unidirectional carbon plastic with AS4 carbon fibers and polyetheretherketone thermoplastic matrix. For identification, the least squares method was used for samples tested at off-axis angles of 0, 10, 30, 45, 60 and 90 ° and different values of strain rates.