Papers by Keyword: Elevated Temperature

Abstract: This study focuses on the role of Mo addition on the mechanical properties of an Al-Si-Cu-Mg alloy in as-cast and heat-treated condition at ambient and elevated temperature. Addition of 0.4 to 0.6 wt.% Mo forms Mo-bearing dispersoid particles which have a relatively high melting point and improve high temperature tensile strength. Ductility suffered in the presence of Mo-bearing particles. Trace addition of Mo up to 0.6 wt.% has a negligible influence on the yield strength and hardness of Al-Si-Cu-Mg alloy in as-cast and heat-treated conditions at ambient temperature and 250 °C.

Abstract: Components of gas turbines must be extremely resistant to high temperatures, high stresses, high-temperature corrosion, and erosive environments. The materials used in these environmental conditions are mainly nickel-based superalloys. In this study, the low-cycle fatigue of the nickel-based superalloy Inconel 792 was examined. The total strain range of a gas turbine between 760 °C and 870 °C was considered as the parameter representing the actual gas turbine operation. In addition, tests were performed using a trapezoidal waveform of the total strain to reflect the operation-stop conditions of a gas turbine with frequent shutdowns. The results of the fatigue test were compared with the Coffin–Manson method and energy method. The fractured surface was analyzed using a scanning electron microscope (SEM).

Abstract: Power MOSFETs operate at elevated temperatures due to self-heating and hot ambient temperatures. This paper analyzes the increase in on-resistance with temperature for 1.2 kV rated 4H-SiC planar MOSFETs. The impact of various structural parameters are studied using analytical models supported by experimental data. This work defines how to achieve a low ratio [R_on(150°C)/R_on(25°C)] by structural optimization of 1.2 kV SiC planar MOSFETs for the first time. It is found that the inversion mode MOSFETs, fabricated by us in a 6 inch commercial foundry, have a lower ratio [R_on(150°C)/R_on(25°C)] than the accumulation mode MOSFETs, due to a better balance of change in channel and bulk mobility with temperature. Compared with typical commercially available MOSFETs, our fabricated accumulation mode and inversion mode MOSFETs exhibit a lower ratio [R_on(150°C)/R_on(25°C)], resulting in superior HF-FOM [R_onxQ_gd] at 150°C.

Abstract: This paper presents the experimental test results on mechanical properties of steel plate grade SS400 at elevated temperatures. The steel is often used as structural steel due to its weldability and machinability. The steel plates were heated by a high frequency heating system to reach specific temperatures before being tested on a tensile testing machine. Five different temperature conditions were used, namely room temperature, 100°C, 300°C, 500°C and 600°C. The data of mechanical properties measured for SS400 steel plates at various temperature conditions were recorded and analysed. The research showed that when the temperature is increased, the force in tensile test is decreased while the strain is increased. The observation and the data were then used to setup the stress – strain – temperature relation for formability study of SS400 steel plates. The same method can be used to establish the mechanical properties at elevated temperatures.

Abstract: This paper presents some experimental results of tensile properties of reinforcing bars spliced by grout-filled coupling sleeves after exposed to fires to identify the effect of temperature histories on tensile properties of spliced reinforcing bars, which provide a useful base for assessing structural behaviors of precast reinforced concrete buildings damaged by fires. A spliced rebar system investigated in this paper consists of two equal-diameter steel reinforcing bars with 25mm diameter and a straight coupling sleeve with 55mm outer and 42mm inner diameters. As a result, the thickness of grout between internal steel bars and outer sleeves are 8.5mm. Five test specimens are manufactured in identical technology and divided into three groups. First group is reference group consist of just one specimen which is not exposed to fire. Second and third groups consist of two specimens that are exposed to ISO 834 standard fire in furnace for 15 and 25 minutes respectively. The temperature-time curves of grout between rebars and sleeves are measured via thermocouples embedded in grout. Subsequently, a universal testing machine is used to test the ultimate load bearing capacities of five specimens. Test results demonstrate that ultimate load bearing capacities of steel rebars spliced by grout-filled sleeves are considerably reduced due to fire damaged grout.

Abstract: The present research focuses onto sliding wear of novel plasma transferred arc welded (PTAW) hardfacing with the stainless steel (DIN X3CrNiMo18-13-3) matrix, reinforced with WC/W₂C, under the room and elevated temperature. The hardfacing was produced, applying the optimized set of parameters (current – 55 A, reciprocating speed – 1.0 mm/s, oscillation frequency – 0.6 Hz). The average reinforcement content was 29.3 ± 4.0 vol %. The reinforcement consisted of W₂C and WC, while M₇C₃- and M₂₃C₆-type (M = Fe, Cr, Mo, W) carbides were the main phases in the matrix. Universal hardness and Young’s modulus were approximately 5.3 and 1.9 times higher, than those of the reference steel (DIN X2CrNiMo18-14-3). The sliding wear of the hardfacing was 4.9 times lower under 20 °C and 3.1 times lower under 300 °C, but 1.8 times higher under 500 °C than the wear of the reference steel. Galling was the wear mechanism of the hardfacing under 20 °C, scoring – under 300 °C and combination of scoring and binder extrusion – under 500 °C

Abstract: In this paper tensile properties at elevated temperature of extruded AZ91 magnesium alloy and the same alloy further processed by ECAP (exECAP) are compared. The tensile tests were performed at room temperature and for the temperature range of 100 to 300 °C. Loading speed 2 mm/min was used for the tests. At room temperature mechanical properties except elongation were slightly higher for extruded material yet still very similar to properties of exECAPed material. Overall trend of properties evolution with increasing temperature was also similar but the decrease of strength or the increase of elongation and reduction of area respectively is more intensive for exECAPed material. Elongation of exECAPed material exceeded elongation of extruded material more than twice at 300 °C and with value of ~260% this alloy exhibited pseudosuperplastic behavior.

Abstract: Nowadays, mass reduction is the most often used term in the automotive industry. Car manufacturers are continuously working on getting ever lighter models than the previous ones, because of the global competition and the rigorous emission rules. A light car has many advantages: lower consumption, better handling, longer operating distance, etc. The emission rules forced the car brands to start new researches to find new solutions for mass reduction. The formula is relatively simple, using lighter or less materials or both and the car will be lighter. In the recent solutions there are three different ways: application of high strength steels, aluminum alloys, and carbon-composite elements. Our investigations are focusing mainly on aluminum, because of its high mass reduction potential. The biggest problem with the aluminum is its low formability. The formability of aluminum is lower than the steel, and it causes problems for the manufacturers. To increase the formability of the aluminum is a hot topic in the research and development area. Forming at elevated temperatures is one of the best solutions to increase the formability of aluminum. The relation between the formability and the forming temperature is not linear, furthermore beyond the optimum forming temperature the formability decreases. We need dozens of investigations to describe the perfect relation, but sometimes a good approximation is enough to form sheet products safely. In our work we investigated the EN AW 5754 aluminum alloy sheet at room temperature, 130°C, 200°C and 260°C. From these tests we could obtain FLC curves of the alloy at different temperatures. Using these curves, the process engineers could find the optimum parameters of their forming process.

Abstract: In order to evaluate the safety and integrity of piping with local wall-thinning at elevated temperature, a numerical method for plastic limit load of modified 9Cr-1Mo steel piping is proposed in the present paper. The limit load of piping at high temperature is defined as the load-carrying capacity after the structure has served for a certain time period. The power law creep behavior with Liu-Murakami damage model is implemented into the commercial software ABAQUS via CREEP for simulation, and the Ramberg-Osgood model is modified to consider the material deterioration effect of modified 9Cr-1Mo steel by introducing the creep damage factor into the elasto-plastic constitutive equation. For covering the wide ranges of defect ratios and service time periods, various 3-D numerical examples for the piping with local wall-thinning defects, and creep time are calculated and analyzed. The limit loads of the defected structures under high temperature are obtained through classic zero curvature criterion with the modified Ramberg-Osgood model, and the typical failure modes of these piping are also discussed. The results show that the plastic limit load of piping containing defect at elevated temperature depends not only on the size of defect, but also on the creep time, which is different from the traditional plastic limit analysis at room temperature without material deterioration.

Abstract: In this research, conjugated thermal and fluid dynamics simulations are presented on a modern hollow clay slab blocks filled pre-stressed reinforced concrete beam slab construction. The simulation parameters were set from Eurocode standards and calibrated using data from standardized fire tests of the same slab construction. We evaluated the temperature distributions of the slabs under transient conditions against standard fire load. Knowing the temperature distribution against time at certain points of the structure, the loss of load bearing capacity of the structure is definable at elevated temperatures. The results demonstrated that we could pre-establish the thermal behavior of complex composite structures exposed to fire using thermal and CFD simulation tools. Our results and method of fire resistance tests can contribute to fire safety planning of buildings.