Effect Of Service Temperature Research Articles

Effect of service temperature and hygrothermal aging coupling on mechanical properties of adhesively bonded BFRP-Aluminum alloy joints

To study the coupled effect of hygrothermal aging and service temperature on the mechanical properties of adhesively bonded basalt FRP-aluminum alloy joints (BFRP-Al joints), the mechanical properties and failure mechanism of BFRP-Al joints at different temperatures before and after aging were analyzed in this paper. The accelerated aging test of the adhesively bonded joint was performed under the hygrothermal condition (80 °C&95% relative humidity), and the hygroscopic property of the joint were analyzed by the water absorption test. Then, the mechanical properties of the aged joints were measured at 80 °C, room temperature (RT 25 °C), and −40 °C. The failure mechanism of the joints under the coupling effect of hygrothermal aging and service temperature was analyzed based on the Differential Scanning Calorimetry (DSC) results. The results reveal that the BFRP-AL joint reaches moisture saturation after exposure to hygrothermal environment for 200 h, and the moisture absorption behavior complies with Fick's law. Due to the decrease of material Tg caused by hygrothermal aging, the mechanical properties of the joint at 80℃ decrease more obviously after aging. Moreover, the failure modes of joint are altered as a result of hygrothermal aging and temperature coupling. A methodology for predicting the performance of bonded joints was established based on the variation laws in Tg and failure load, taking into consideration the effects of hygrothermal aging and service temperature which can provide guidance for the lifetime design of the hygrothermal aged adhesive structures within the entire service temperature range.

Activation strategies for glass-to-iron-based shape memory alloy adhesively bonded joints

Previous research has demonstrated the potential of improving the performance of glass beams through pre-stressed bonded iron-based shape memory alloy (Fe-SMA) tendons. The pre-stressing of bonded Fe-SMA tendons significantly enhanced both the initial glass cracking load and the residual load-bearing capacity of glass beams, compared with unstrengthened ones. To achieve the desired pre-stress level, the Fe-SMA should be activated, which involves controlled heating and natural cooling of the Fe-SMA. The achieved pre-stress level of the substrates highly depends on the activation strategies for the Fe-SMA, such as activation position, length and temperature. An appropriate activation strategy is essential to achieve a high pre-stress level and to prevent premature failures, such as glass breakage or debonding during activation. This experimental work was carried out on glass-to-Fe-SMA bonded joints. Two activation temperatures (160 ºC and 200 ºC) were considered, aiming to attain high pre-stress levels while avoiding glass breakage and debonding. Afterwards, the effect of service temperature (50 ºC and 80 ºC) on the pre-stress loss was investigated. The findings in this research contribute to the efficient design and application of pres-stressing glass elements using adhesively bonded Fe-SMA tendons.

Effect of Service Temperature on Mechanical Properties of Adhesive Joints after Hygrothermal Aging.

Polyurethane adhesive and aluminum alloy were selected to make adhesive joints. Butt joints tested at different loading angles (0°, 45°, and 90°) using a modified Arcan fixture were selected to represent three stress states (normal stress, normal/shear combined stress, and shear stress, respectively). Firstly, the accelerated aging tests were carried out on the joints in a hygrothermal environment (80 °C/95% RH). The quasi-static tests were carried out at different temperatures (−40 °C, 20 °C, and 80 °C) for the joints after hygrothermal aging for different periods. The variation rules of the joints’ mechanical properties and failure modes with different aging levels were studied. The results show that the failure load of the joints was obviously affected by stress state and temperature. In the low-temperature test, the failure load of the joints decreased most obviously, and the BJ was the most sensitive to temperature, indicating that the failure load decreased more with the increase of the normal stress ratio in the joint. Through macroscopic and SEM analysis of the failure section, it was found that the hydrolysis reaction of polyurethane adhesive itself and the interface failure of the joints were the main reasons for the decrease of joint strength. The failure models were established to characterize the adhesive structure with different aging levels at service temperature.

The effect of service temperature on the impact strength and fracture toughness of GTD-111 superalloy

The study of the impact resistance of gas turbine blades due to exposure to internal and external damage can prevent human and economic disasters. In this study, a GT 13-E2 General Electric gas turbine blade was used, which has been exposed to heating, hot gases, the material to a temperature of 850–900 °C in 10,000 operating hours. Microstructural examinations of the two sections of the airfoil and the root confirmed the microstructural damage of the airfoil due to more severe working conditions. Impact test was performed at temperature 25 and 900 °C for both airfoil and root sections. Impact test results showed that the fracture toughness for blade root in both temperatures of 25 and 900 °C was 4.7 and 6.2 J, respectively. This value was 2.4 and 3.3 for the airfoil blade, respectively. This was the formation of hard phases that were formed during service in airfoil due to unwanted aging. These phases included M23C6 carbide, γ′ nanometer particles and the TCP phase.

Connecting the Microstructure Stability of Ni Based Superalloys to their Chemical Compositions

The degradation of creep resistance in Nickel-based single crystal superalloys is essentially ascribed to their microstructure evolution. Yet there is a lack of work that manages to simulate the effect of alloying element concentrations on microstructure degradation. In this research, a computational model is developed to connect the rafting kinetics of Ni superalloys with their chemical composition, by combining thermodynamics calculation and an energy-based microstructure model. The isotropic coarsening rate and γ/γ misfit stresses have been selected as composition related parameter, and the effect of service temperature, time and applied stress are also taken into consideration to simulate the evolutions of microstructure parameters during creep process. The different generations of commercial Ni superalloys are selected and their chemical compositions are calculated based on this model. The simulated microstructure parameters are validated by the results from experimental results and the existing analytical model. The capability of the model in predicting the microstructure characteristics may provide instructional thought in developing a novel computational guided design approach in Ni superalloys.

Performance of glass fiber‐reinforced cement composites containing phase change materials

The use of solar energy has become a promising method to reach energy efficient solutions throughout the last century. Improving the thermal properties of building members will contribute to the efficient use of energy by preventing heat gain/loss through the building envelope. Phase change materials (PCMs) are favorable materials for thermal applications because of their large contribution to the thermal mass of a building and thus providing “inertia” against temperature fluctuations. In this experimental study, glass fiber‐reinforced cementitious composites were modified using a commercial microencapsulated PCM to improve their thermal performance. The thermal and the mechanical performances of the composites were investigated. With the use of PCMs, the latent heat capacity of the composites increased while the thermal conductivity decreased. Conversely, the mechanical properties of composites declined with increases in PCM amount. The main conclusions of the experimental study are as follows: PCMs provide a great potential to fiber‐reinforced cementitious composites to support the efficient use of energy, thereby enhancing the thermal features of the composites. The performance of PCM composites shows a serious variation according to different service temperatures. Therefore, the effect of service temperature must be considered particularly with respect to safe utilization of these materials. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13061, 2019

Thermal Stability of Zone Melting p-Type (Bi, Sb)2Te3 Ingots and Comparison with the Corresponding Powder Metallurgy Samples

During the past few decades, Bi2Te3-based alloys have been investigated extensively because of their promising application in the area of low temperature waste heat thermoelectric power generation. However, their thermal stability must be evaluated to explore the appropriate service temperature. In this work, the thermal stability of zone melting p-type (Bi, Sb)2Te3-based ingots was investigated under different annealing treatment conditions. The effect of service temperature on the thermoelectric properties and hardness of the samples was also discussed in detail. The results showed that the grain size, density, dimension size and mass remained nearly unchanged when the service temperature was below 523 K, which suggested that the geometry size of zone melting p-type (Bi, Sb)2Te3-based materials was stable below 523 K. The power factor and Vickers hardness of the ingots also changed little and maintained good thermal stability. Unfortunately, the thermal conductivity increased with increasing annealing temperature, which resulted in an obvious decrease of the zT value. In addition, the thermal stabilities of the zone melting p-type (Bi, Sb)2Te3-based materials and the corresponding powder metallurgy samples were also compared. All evidence implied that the thermal stabilities of the zone-melted (ZMed) p-type (Bi, Sb)2Te3 ingots in terms of crystal structure, geometry size, power factor (PF) and hardness were better than those of the corresponding powder metallurgy samples. However, their thermal stabilities in terms of zT values were similar under different annealing temperatures.

<b>Effect of service temperature on shear strength of <i>Pinus</i> wood for roof structures

Temperature in timber roof trusses structures can reach 60°C and significantly affect wood strength, compromising the structural mechanical performance. This study aimed at quantifying the influence of exposure time to the mentioned temperature in wood strength by monitoring shear parallel to grain ( f v0 ) of Pinus taeda and Pinus elliottii from planted forests. Exposure times at 60°C, in controlled oven, consisted of zero, 168, 456 and 720 hours. ANOVA results indicated that temperature (60°C) influences significantly, in the four exposure times, f v0 for both Pinus wood species. For Pinus taeda , slightly more resinous, strength in shear parallel to grain presented successive reductions, related to reference condition (zero hour) for exposure times 168 and 456 hours; and increase for 456 hours to 720 hours. Different behavior was observed for Pinus elliottii , where f v0 successively showed increases from reference condition for the other temperatures. Even with varied behavior of Pinus wood referring to the influence of exposure times at temperature 60°C, shear strength was significantly affected.

The Compositional Dependence of the Microstructure and Properties of CMSX-4 Superalloys

The degradation of creep resistance in Ni-based single-crystal superalloys is essentially ascribed to their microstructural evolution. Yet there is a lack of work that manages to predict (even qualitatively) the effect of alloying element concentrations on the rate of microstructural degradation. In this research, a computational model is presented to connect the rafting kinetics of Ni superalloys to their chemical composition by combining thermodynamics calculation and a modified microstructural model. To simulate the evolution of key microstructural parameters during creep, the isotropic coarsening rate and γ/γ′ misfit stress are defined as composition-related parameters, and the effect of service temperature, time, and applied stress are taken into consideration. Two commercial superalloys, for which the kinetics of the rafting process are selected as the reference alloys, and the corresponding microstructural parameters are simulated and compared with experimental observations reported in the literature. The results confirm that our physical model not requiring any fitting parameters manages to predict (semiquantitatively) the microstructural parameters for different service conditions, as well as the effects of alloying element concentrations. The model can contribute to the computational design of new Ni-based superalloys.

Thermal stability of p-type polycrystalline Bi2Te3-based bulks for the application on thermoelectric power generation

In the present work, the thermal stabilities of p-type polycrystalline Bi0.44Sb1.56Te3 bulks have been investigated at different temperatures in vacuum environment. The effect of service temperature on the microstructure, thermoelectric and mechanical properties of Bi0.44Sb1.56Te3 bulks were investigated in detail. The results showed that the service temperature below 473 K had no obvious influence on the grain size, the crystal lattice constant, the density and the corresponding thermoelectric properties, and p-type Bi0.44Sb1.56Te3 based bulks could maintain good thermal stability below 473 K. Nevertheless, when the service temperature was over 523 K, the volume expansion began to accelerate, the increasingly obvious mass loss presented due to drastic Te volatilization, and the density of the bulks decreased notably, which resulted in the obvious increase of resistivity and a serious decline in the power factor as service temperature increased, although the Seebeck coefficient presented a slight increase. More seriously, the mechanical properties of the Bi0.44Sb1.56Te3 bulks degraded seriously when the service temperature was above 523 K. All evidences implied that the Bi0.44Sb1.56Te3 bulks could be stabilized at service temperature of 473 K, the thermoelectric and mechanical properties would get worse obviously when the service temperature was over 523 K. Therefore, the highest service temperature of Bi2Te3 based thermoelectric power generation modules could not exceed 473 K.

Effect of service temperature on the shear creep response of rigid polyurethane foam used in composite sandwich floor panels

This paper presents an experimental and analytical study about the effect of temperature on the shear creep response of a rigid polyurethane (PUR) foam within the scope of sandwich panel application in building floors. Shear creep tests were carried out on a foam (87.4kg/m3) subjected to shear stress levels of 11%, 22% and 44% of its shear strength at temperatures of 20°C, 24°C and 28°C – a range likely to be found in the envisaged application – for more than 1300h. The results obtained show that the foam’s creep response increases with both stress level and temperature. Findley’s power law, extended to include Arrhenius equations describing the temperature dependency of its viscoelastic parameters, was fitted to the experimental creep curves, thus allowing to model the time-temperature-stress dependent shear creep behaviour of the PUR foam. The proposed model provided a good fit to the experimental creep curves within the linear viscoelastic range. Practical design equations were also derived for the time-temperature dependent (i) shear modulus, (ii) creep coefficient, and (iii) shear modulus reduction factor. Finally, the time-temperature-stress superposition principle (TTSSP) and the time-stress superposition principle (TSSP) were used to yield “master curves” that compared well with the proposed model’s predictions.

Effect of service temperature on the flexural creep of vacuum infused GFRP laminates used in sandwich floor panels

This paper presents an experimental and analytical study about the effect of temperature on the flexural creep of GFRP laminates produced by vacuum infusion. Such laminates are considered for use in the faces of sandwich panels for building floor application. Flexural creep tests were carried out in a three point bending configuration for stress levels of 15%, 25% and 35% of the laminate's flexural strength, and temperatures of 20 °C, 24 °C and 28 °C (a range likely to be found in the envisaged application), with durations between 1000 h and 2215 h. The creep response was observed to increase both with temperature and stress level. Findley's power law was used to model the experimental results, and extended to include an Arrhenius equation for temperature dependence of the creep response. The proposed model provided a good fit to the experimental creep curves, and was used to derive a set of practical design equations for the time-temperature dependent (i) flexural modulus, (ii) creep coefficient, and (iii) flexural modulus reduction factor. Finally, the time-temperature-stress superposition principle (TTSSP) and the time-stress superposition principle (TSSP) were used to obtain “master curves” that compared well with the proposed model's predictions.

Effect of Temperature on Damage Evolution of Cr25Ni35Nb Alloy Subjected to Combined Mechanical and Environmental Degradation

AbstractDue to combined mechanical and environmental degradation, i.e. coupled creep and carburization, Cr25Ni35Nb alloy often fails prior to the expected design life. In the present paper, based on the continuum damage mechanics, the constitutive model of coupled multi-damage factors for computing the damage evolution of Cr25Ni35Nb alloy was proposed. The damage prediction was carried out by using finite element method based on ABAQUS code. And then damage evolution processes at different operating temperatures (950 °C and 1050 °C) were simulated and the effect of service temperature on the damage evolution was discussed. The results showed that the rate of damage increased obviously with operating temperature increasing. The location with maximum damage is along the inner surface of tube, which implies that fracture begins along the inner surface of tube under the action of coupled creep and carburization damage and this is coincident with the actual observation of the failure of furnace tube.

Effect of service temperature on structure and mechanical properties of polyamide 6 & 66 tyre cords

The effect of service temperature on chemical structure and mechanical properties of polyamide 6 & 66 tyre cords was studied over the broad range of 50–200 °C and for a period of 16 h. The heat treatment of cords at below 100 °C and above 120 °C was found to reduce their tensile properties considerably. The changes in properties above 120 °C were caused by increase in width of the molecular weight distribution curve as ascertained by gel permeation chromatography (GPC) studies and increase in irregularity of the polymeric chains as ascertained by birefringence studies; this appears to be due to the fact that, by raising the temperature, both chain folding and chain scission occur. Since there was deformation of the amorphous regions as ascertained by FTIR spectroscopy and birefringence studies, the changes in properties below 100 °C were attributed mainly to the effectiveness of thermal oxidation and annealing in the amorphous phase. In other words, the degree of crystallinity increased, the tyre cord became brittle, and breaking load and elongation at break were decreased. The lower reduction of tensile properties at an intermediate temperatures of 100–120 °C was caused by the lower polydispersity and irregularity in the polymeric chains, in comparison with higher temperatures and less crystallinity than lower temperature treatments.

Service-induced Changes in the Microstructure and Mechanical Properties of a Cr-Mo-Ni-V Turbine Steel.

The effect of service temperature on the degradation of mechanical properties of a low alloy Cr-Mo-Ni-V steel applied for turbine rotor, retired after 15.8 years of service was evaluated and supplemented with the results from microstructural and fractographic examinations. Maximum embrittlement, manifested as decrease in upper shelf energy and increase in ductile-to-brittle transition temperature had occurred at a service temperature of 714 K and the material serviced at 811 K exhibited relatively better toughness. A re-aging treatment at 811 K for 24 h partially recovered the loss in toughness. The dominant carbides identified were M23C6 and M6C, enriched with chromium and iron, and molybdenum and iron, respectively and M2C with molybdenum and vanadium as the major metallic constituents. Coarsening of carbides occurred with increasing temperature through carbide reactions. The embrittled material showed the presence of coarse M23C6 carbides along the prior-austenite grain boundaries. However, material serviced at 811 K contained relatively less coarse grain boundary precipitates. Homogeneous precipitation of fine carbides of M 2 C type also occurred at this temperature through carbide reactions. Re-aging of the embrittled material led to partial dissolution of grain boundary carbides and also to copious precipitation of M2C type of carbide. Observed changes in mechanical properties are partly attributed to the in-service evolution of carbides and partly attributed to segregation of impurities at grain boundary.