Effect Of Thermal History Research Articles

Individual thermal comfort prediction using classification tree model based on physiological parameters and thermal history in winter

Individual thermal comfort models based on physiological parameters could improve the efficiency of the personal thermal comfort control system. However, the effect of thermal history has not been fully addressed in these models. In this study, climate chamber experiments were conducted in winter using 32 subjects who have different indoor and outdoor thermal histories. Two kinds of thermal conditions were investigated: the temperature dropping (24–16 °C) and severe cold (12 °C) conditions. A simplified method using historical air temperature to quantify the thermal history was proposed and used to predict thermal comfort and thermal demand from physical or physiological parameters. Results show the accuracies of individual thermal sensation prediction was low to about 30% by using the PMV index in cold environments of this study. Base on the sensitivity and reliability of physiological responses, five local skin temperatures (at hand, calf, head, arm and thigh) and the heart rate are optimal input parameters for the individual thermal comfort model. With the proposed historical air temperature as an additional input, the general accuracies using classification tree model C5.0 were increased up by 15.5% for thermal comfort prediction and up by 29.8% for thermal demand prediction. Thus, when predicting thermal demands in winter, the factor of thermal history should be considered.

Effect of Thermal History on Hot Workability of Fe–Cr Multiphase Steel during Hot Working

In the hot working of multiphase steels, the thermal history before hot working affects the phase balance. The aim of this study is to investigate the effect of the thermal history immediately before hot working on hot workability by performing hot uniaxial tensile tests. Duplex stainless steel was chosen as the test material, as this material has a typical dual-phase structure consisting of δ ferrite and austenite, and its phase balance changes with the working temperature. The phase ratio of δ ferrite is higher at high temperatures, and the ratio of the austenite phase increases as the temperature decreases. To clarify the effect of the cooling rate immediately before hot working on hot workability, a hot tensile test was carried out with two extremely different cooling rates (0.3°C/s, 10.0°C/s) from the heating temperature of 1250°C. The hot working test temperature was in the range of 650°C to 1150°C. Hot workability was higher under the rapid cooling condition than under the slow cooling condition in the hot working temperature range of 850°C to 1150°C, but this tendency was eliminated or reversed at temperatures below 750°C. The reason for this change was clarified by investigating both the phase balance immediately before hot working, which depends on the cooling rate, and the strength of each single phase. Therefore, in order to accurately measure the hot workability of a multiphase material, it is important to consider the thermal history immediately before hot working.

Importance of experienced thermal history: Effect of acclimation temperatures on the high-temperature tolerance and growth performance of juvenile marbled flounder.

Experienced thermal history often affects the temperature tolerance of fish; however, the effect of thermal history on growth performance is unclear. To contribute to effective stocking (release of hatchery-reared juveniles in the field), we conducted four laboratory experiments using juvenile marbled flounder (Pseudopleuronectes yokohamae, around 30mm standard length and 0.3g body wet weight) acclimated at 12°C and 24°C for approximately 2 weeks to investigate the effects of acclimation temperature on high-temperature tolerance, food consumption, and growth performance. The acclimation to 24°C increased tolerance to high temperatures, as shown in a 24-h exposure experiment and in a temperature elevation experiment. The 50% lethal temperature (upper incipient lethal temperature) was estimated to be 25.9°C and 29.0°C for the 12°C and 24°C acclimation groups, respectively. In subsequent experiments, we tested the effects of high and low temperature acclimation on the food consumption and growth performance of two size groups of juveniles (28.7±2.0 and 34.5±2.9mm, mean±SD), that were reared at temperatures ranging from 14°C to 23°C. The optimal temperature for growth was 20°C and did not differ between the acclimation temperatures or between the size groups. However, food consumption and growth performance were suppressed by acute temperature changes. Specifically, feeding and growth were lower in the 24°C-acclimated group than in the 12°C-acclimated group when exposed to 14°C, which is close to the natural water temperature at release in the field. These results suggest that experienced thermal history does not affect the optimal temperature but can affect the growth performance of juveniles. To maximize the post-release growth of hatchery-reared juveniles, the influence of thermal history should be taken into consideration and acute thermal changes before release should be avoided.

Sirtuin-dependent recovery from aerial heat shock: The effects of food ration, thermal history, and sirtuin inhibition on clearance rates and valve gape activity of the California mussel, Mytilus californianus (Conrad)

Intertidal mussels regularly experience seasonal fluctuations in food availability and heat stress over the course of a tidal cycle, yet little is known about the biochemical mechanisms linking food ration and thermal tolerance, despite evidence that food enhances stress tolerance at the organismal level. We hypothesized that sirtuins (food-dependent protein regulators of cellular homeostasis), which may regulate the cellular stress response of mytilids during heat stress, also affect organismal performance during recovery from heat stress. As part of a broader study, we investigated the effects of acclimation food ration, acclimation emersion (air) temperature, and sirtuin inhibitors on the feeding behavior of the California mussel, Mytilus californianus, during recovery from acute aerial heat shock. Mussels were acclimated for 3 wk. to either a low (0.25% algae·g mussel dry wt−1) or high (1.5% algae·g mussel dry wt−1) algal ration and low (20 °C) or high (30 °C) emersion temperatures, in tidal simulator tanks capable of maintaining standard circadian and circatidal rhythms. Following acclimation, mussels were exposed to two sirtuin inhibitors (nicotinamide and suramin) or no inhibitors for one high tide cycle. During the subsequent low tide cycle, all mussels were exposed to an acute aerial heat shock (33 °C) and then allowed to recover in their respective acclimation conditions. Every 12 h during the 48 h before sirtuin inhibition and 48 h following acute heat shock (in the corresponding high tide periods), we recorded clearance rates and valve gape activity. Mussels acclimated to a low food ration significantly reduced clearance rates with heat shock and sirtuin inhibition, but not with heat shock alone, relative to pre-treatment values regardless of emersion temperature. Mussels acclimated to a low food ration and high emersion temperature showed significant reductions in valve gape activity following an acute heat shock following sirtuin inhibition, but not in any of the other acclimation groups. Unexpectedly, heat shock alone reduced clearance rates of mussels acclimated to high food and high emersion temperatures only, without any additional effect by heat shock and sirtuin inhibition. Together, these findings suggest an important role for sirtuins at the organismal level during recovery from heat shock following acclimation to a low food ration.

Directed energy deposition additive manufacturing of a Sc/Zr-modified Al–Mg alloy: Effect of thermal history on microstructural evolution and mechanical properties

Recently, laser additive manufacturing (LAM) of Al–Mg–Sc–Zr alloys has been considered an important method for developing a new generation of high-performance Al alloys. However, one of the key differences between LAM and conventional casting/wrought processes is that it has a unique combination of rapid solidification and in-situ solid-state transformation induced by repeated thermal cycling during deposition. In addition, owing to its near-net shape characteristics, subsequent plastic deformation processing is typically not an option to improve the as-built microstructure. To gain insight into the effect of the complex thermal history during LAM on the microstructural evolution and mechanical properties of the novel alloy systems, an Al–Mg–Sc–Zr alloy was processed via laser-directed energy deposition (L-DED) using a substrate with air cooling (AC) or water cooling (WC). The results show that the solidification microstructure was closely related to the dynamic solidification conditions in the molten pool, which promoted the transition from an equiaxed grain structure at low cooling rate (AC) to a heterogeneous grain structure at high cooling rate (WC). Furthermore, in-situ precipitation occurred during the repeated high-temperature thermal cycling in the AC sample, while it was effectively suppressed in the WC sample by lowering the peak temperature during thermal cycling. After aging, the yield strength of the WC sample was enhanced to ~2 times that of the AC sample, while the uniform elongation was still comparable to that of the AC sample. To achieve good mechanical properties for L-DED-processed Al–Mg–Sc–Zr alloys, it is crucial to conduct integrated control of the thermal history during both rapid solidification and in-situ precipitation.

Interactive effect between long-term and short-term thermal history on outdoor thermal comfort: Comparison between Guangzhou, Zhuhai and Melbourne

Thermal history can influence human thermal comfort through physiological (short-term) and psychological (long-term) aspects. However, the nature of the interaction between long-term and short-term thermal history is unclear. To investigate the interactive effects of long-term and short-term thermal history on outdoor thermal comfort, we conducted summer thermal comfort surveys in Melbourne (n = 3293, January–February 2014), Guangzhou, and Zhuhai (n = 4304, September 2018). The mean thermal sensation of residents of Guangzhou was higher than that of Melbourne and Zhuhai residents under a similar Universal Thermal Climate Index (UTCI) range. The preferred UTCI was the highest for Melbourne residents (19.62 °C). When UTCI was 25.6–38.4 °C, respondents' mean thermal sensation from Köppen climate zones A, B, and C was significantly higher in Guangzhou than those of Zhuhai and Melbourne. A three-way ANOVA test revealed that peoples' thermal sensations depended on a significant interaction among UTCI thermal stress levels, climate zones, and prior exposure environment. The prior exposure environment could affect the difference in thermal perception between climate zones. However, there was no significant interaction between climate zones and activity engaged in before taking the survey on thermal sensation. The difference in the thermal perception of various climate zones diminished under universally uncomfortable conditions for specific prior exposure environments and activities. The socio-ecological system model, environmental perception theory, climatocultural adaptation, and alliesthesia are useful for understanding the interactive effect of long- and short-term thermal history on outdoor thermal comfort. By revealing how people adapt to different climatic environments, our results can help ensure that people with diverse climatic backgrounds can experience thermal comfort outdoors.

Thermal and nutritional environments during development exert different effects on adult reproductive success in Drosophila melanogaster.

Environments experienced during development have long‐lasting consequences for adult performance and fitness. The “environmental matching” hypothesis predicts that individuals perform best when adult and developmental environments match whereas the “silver spoon” hypothesis expects that fitness is higher in individuals developed under favorable environments regardless of adult environments. Temperature and nutrition are the two most influential determinants of environmental quality, but it remains to be elucidated which of these hypotheses better explains the long‐term effects of thermal and nutritional histories on adult fitness traits. Here we compared how the temperature and nutrition of larval environment would affect adult survivorship and reproductive success in the fruit fly, Drosophila melanogaster. The aspect of nutrition focused on in this study was the dietary protein‐to‐carbohydrate (P:C) ratio. The impact of low developmental and adult temperature was to improve adult survivorship. High P:C diet had a negative effect on adult survivorship when ingested during the adult stage, but had a positive effect when ingested during development. No matter whether adult and developmental environments matched or not, females raised in warm and protein‐enriched environments produced more eggs than those raised in cool and protein‐limiting environments, suggesting the presence of a significant silver spoon effect of larval temperature and nutrition. The effect of larval temperature on adult egg production was weak but persisted across the early adult stage whereas that of larval nutrition was initially strong but diminished rapidly after day 5 posteclosion. Egg production after day 5 was strongly influenced by the P:C ratio of the adult diet, indicating that the diet contributing mainly to reproduction had shifted from larval to adult diet. Our results highlight the importance of thermal and nutritional histories in shaping organismal performance and fitness and also demonstrate how the silver spoon effects of these aspects of environmental histories differ fundamentally in their nature, strength, and persistence.

Modeling and Simulation of Void Closure during Steckel Mill Rolling for Steel Plate

Internal void defects as shrinkage porosity, gas bubble, and thermo‐mechanical cracks are usually formed during steel casting processes. These defects have critical impact on the quality and service life of hot‐rolled products. Study of the possibility of self‐healing of existing internal defects during hot‐rolling process has been of interest to industry and researchers. Prediction of void closure is extremely useful in relation to better product design and manufacturing process optimization. Herein, a 3D finite element model of the slab hot‐rolling process is developed to simulate and analyze the healing of internal voids in hot‐rolled steel plate. The material model for the steel plate is developed based on Johnson–Cook constitutive relation to accurately represent its viscoplastic behavior at high temperatures as well as account for strain rate sensitivity. The study evaluates the thermal and mechanical response of low‐carbon steel slabs having pre‐existing voids during multi‐pass strands reverse hot‐rolling process. Through thickness plastic strains within the slab are found to influence void closure. Results show that variation in void size and locations also affect the healing possibilities. Finally, the effect of thermal history and thermo‐mechanical stresses on void closure is studied.

Unravelling thermal history during additive manufacturing of martensitic stainless steel

In-situ thermal cycling neutron diffraction experiments were employed to unravel the effect of thermal history on the evolution of phase stability and internal stresses during the additive manufacturing (AM) process. While the fully-reversible martensite-austenite phase transformation was observed in the earlier thermal cycles where heating temperatures were higher than Af, the subsequent damped thermal cycles exhibited irreversible phase transformation forming reverted austenite. With increasing number of thermal cycles, the thermal stability of the retained austenite increased, which decreased the coefficient of thermal expansion. However, martensite revealed higher compressive residual stresses and lower dislocation density, indicating inhomogeneous distributions of the residual stresses and microstructures on the inside and on the surface of the AM component. The compressive residual stresses that acted on the martensite resulted preferentially from transformation strain and additionally from thermal misfit strain, and the decrease in the dislocation density might have been due to the strong recovery effect near the Ac1 temperature.

Control effects of temperature and thermal evolution history of deep and ultra-deep layers on hydrocarbon phase state and hydrocarbon generation history

Deep and ultra-deep layers in the petroliferous basins of China are characterized by large temperature difference and complicated thermal evolution history. The control effects of temperature and thermal evolution history on the differences of hydrocarbon phase states and the hydrocarbon generation history in deep and ultra-deep layers are researched less and unsystematically. To deal with this situation, based on a large number of temperature and pressure data of deep layers and combined with the complicated historical situation of deep layer evolution in the oil and gas basins of China, the effects of temperature, heating time and pressure on the hydrocarbon formation temperature and phase state were analyzed, and the types of temperature and pressure relationships were classified. Finally, based on the classification of thermal evolution history of deep and ultra-deep layers, We discussed the control effects of basin thermal evolution history on the hydrocarbon generation and phase state, and the following research results were obtained. First, the hydrocarbon phase states of deep layers in different basins and regions are greatly different, and they are mainly affected by temperature, heating time, heating rate, pressure, source rock types and other factors. And temperature is the most important factor controlling hydrocarbon generation and phase state distribution. Second, under the conditions of rapid temperature increasing and short heating time, there still may be oil reservoirs and condensate gas reservoirs in deep and ultra-deep layers in the case of high temperature. Third, overpressure inhibits hydrocarbon generation and pyrolysis. Fourth, there is a close relationship between temperature and formation pressure of deep layers, which can be divided into three types, i.e., low–medium temperature and high pressure type, high temperature and high pressure type, and medium temperature and low–medium pressure type. Fifth, the thermal evolution history of deep and ultra-deep layers can be divided into four types, namely the late rapid subsidence, heating and low geothermal gradient type, the late rapid subsidence, heating and high geothermal gradient type, the middle–late rapid heating and late uplifting and cooling type, and the early great subsidence and rapid heating and middle–late great uplift erosion and cooling type. In conclusion, deep and ultra-deep layers in the basins with different types of thermal history are different in hydrocarbon phase states, accumulation stages and prospects.

Influences of molecular weight and thermal history on partial melting of polyethylene: Existence of non-lamellar crystallite

The effects of molecular weight and thermal history on the partial melting of polyethylene (PE) were investigated by in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. In the partial melting process, both surface melting and melting of small lamellae were found to play prominent roles. However, in some cases that could not be explained by these mechanisms, the concept of “non-lamellar crystalline” (NLC) was proposed. We argue that melting of the NLC domains can also contribute to the partial melting, especially at low temperatures. The event would decrease the crystallinity but does not perturb the lamellar structure, which are not seen in surface melting and melting of small lamellae. Upon further heating, structural changes, including the extension of lamellar length and reduction of lamellar width, were also observed. The experimental results in the temperature range dominated by the surface melting mechanism could be described by the model proposed by Albrecht and Strobl.

Roles of phase separation and crystallization in the structure formation of new segmented polyurethane ureas and their nanocomposites with single-walled carbon nanotubes

Crystal structure and supramolecular organization of new segmented thermoplastic polyurethane ureas and their nanocomposites with ultra-small additives (less than 0.1 wt.%) of single-walled carbon nanotubes (SWCNTs) have been been investigated using DSC and X-ray diffraction analysis. Taking into account the Avrami model, effects of physical aging and thermal history of the samples on the crystallization rate was described. It was demonstrated that the introduction of ultra small amounts of SWCNTs does not decrease the crystallinity, but decreases the crystallization rate.

Effect of water vapor and thermal history on nuclear waste feed conversion to glass

AbstractWater affects the glass melting process by interacting with the foam layer at the glass melt surface and by influencing the batch conversion reactions. Nuclear waste aqueous slurry feed maintains a high water vapor pressure in the melter atmosphere. To investigate to what extent water vapor affects the foaming during vitrification of nuclear waste in joule‐heated cold‐top melters, a series of feed expansion experiments were performed under humid and dry atmospheres using samples of low‐activity waste (LAW) melter feed simulants. Melting of feed pellets in the presence of water vapor slightly decreased the temperature of primary foam onset for an extensively foaming feed, but did not significantly affect the feed volume expansion by foaming or the foam‐collapse temperature. Sets of feed expansion experiments and evolved gas analyses were also performed to check the effect of thermal history on conversion behavior of LAW feed samples. The thermal history was varied by testing feed samples prepared as direct slurry, loose powder, and slow‐ and fast‐dried pellets. The sample preparation methods and the sample shape were not found to influence foaming parameters, except for the direct slurry where the low‐temperature swelling prevented the foam onset and collapse temperatures to be determined.

Effect of Thermal History and Mass Scale on the Thermal Safety of 1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazocane

AbstractThe effect of thermal history and mass scale on the thermal safety of Octogen (HMX) were explored by microcalorimetric and differential scanning calorimetry. The autocatalytic properties were verified by isothermal experiments, and the thermal decomposition kinetics was analyzed by Kissinger, Ozawa and Friedman methods. The results indicated that the thermal decomposition process was accomplished under solid state conditions with the heating rates in the range of 0.1–1 °C/min, and the apparent activation energy calculated by isothermal experiment was basically consistent with that calculated by dynamic method. Thermal history experiments presented that the thermal decomposition had autocatalytic properties, which was verified by isothermal experiments. Moreover, thermal history which had great influence on the thermal decomposition kinetics made the apparent activation energy decrease significantly, resulting in safety risk augmentation. Additionally, mass scale had a salient effect on the thermal stability. With the increase of sample mass, the degree of hazard augmented. It is necessary to keep the heat source off and avoid the large mass storage in the industrial production.

Effect of long-term thermal history on physiological acclimatization and prediction of thermal sensation in typical winter conditions

Thermal history plays an important role in thermal comfort of occupants. In this study, climate chamber experiments were conducted in winter using two groups of total 32 subjects who have different indoor thermal histories. The cold-adapted (CA) group consisted of subjects who long lived in naturally ventilated buildings (approximately 11.8 ± 3.4 °C in winter) in the hot summer and cold winter climate zone of China. The warm-adapted (WA) group consisted of subjects who long lived in heated space in winter. Two kinds of thermal conditions were investigated: the temperature dropping (24-16 °C) and constant severe cold (12 °C) conditions. Results show the thermal sensation vote and heart rate of the CA group were significantly different from that of the WA group in a short period when temperature just dropping to 16 °C and in most time of severe cold condition of 12 °C. However, there were no difference in skin temperatures and blood pressure between the CA and WA groups during the whole experiment period in both conditions. Thus, a cold-adapted basal heart rate was proposed to calculate metabolic rate for the CA group. Results show the accuracy of predicted thermal sensation model could be improved while considering the factor of cold acclimatization.

Thermal Decomposition Behavior and Thermal Hazard of Benzoyl Peroxide under Different Environmental Conditions

AbstractThermal decomposition characteristics of benzoyl peroxide (BPO) were preliminary studied by differential scanning calorimetry (DSC), microcalorimeter (C600) and high‐pressure calorimeter (DSC 204 HP). DSC and C600 were used to research the effect of thermal history on the thermal decomposition characteristics of BPO. The time to maximum rate under adiabatic conditions (TMRad) and the self‐accelerating decomposition temperature (SADT) were calculated by combining with the thermal equilibrium equation. The results reveal that the initial decomposition temperature, the highest decomposition temperature and the decomposition completion temperature of BPO increased with the increase of heating rate. The mass scale and thermal history have significant effects on its thermal decomposition. The apparent activation energy of the BPO was calculated by the Kissinger method to be 146.8 kJ mol−1, the apparent activation energy calculated by Friedman method presents that BPO has different apparent activation energy at different stages of the reaction. TD2, TD4, TD8 and TD24 were gained to be 83.5, 80.2, 77.0 and 72.2 °C, respectively. With the increase of the packing quality, the SADT gradually decreased, resulting in a further increased in the risk. To prevent accidents, the initial temperature of BPO should be well governed and massive storage should be avoided.

Investigating the Effects of Lithium Phosphorous Oxynitride Lamination on PEO/PPC Blended Hybrid Electrolytes

Solid-state electrolytes play an important role in the development of new generations of technology including lithium metal batteries. Lithium conducting solid materials offer a solution to the safety issues that are present in lithium-ion batteries (LIBs). Conventional LIBs typically use highly flammable organic solvents as a transport medium for lithium ions, potential risks that arise due to these solvents include fire, volatilization, and explosions. Solid polymer electrolytes (SPEs) are great as electrolyte material because fabrication of the electrolyte films is cheap, and processing is simple. However, SPEs can have stability issues when in contact with lithium metal for extended periods which is a problem for cells required to offer long lifetimes. Poly (ethylene oxide) (PEO) has been extensively studied since the conception of SPEs, due to its ability to solvate ions due to its polar ether groups. However, PEO, being a semi-crystalline polymer, exhibits thermal history effects due to recrystallization behavior. Amorphous SPEs are highly desirable because there are no recrystallization kinetics at play, and the properties are consistent regardless of the thermal history. Poly(propylene carbonate) (PPC), an amorphous, biodegradable polymer, can offer high ionic conductivities. Blending PEO and PPC offers a solution to resolve the thermal history effects of PEO by interfering with the crystalline structures in blended electrolyte systems with the salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Inorganic solid electrolytes (ISEs) can offer better chemical stability and excellent mechanical properties compared to SPEs; however, brittleness may decrease the structural stability over time. Thin films ISE’s also tend to cost much more than SPEs due to the fabrication methods required such as electron beam evaporation, and chemical vapor deposition. Lithium phosphorous oxynitride (LiPON), produced through RF magnetron sputtering, was developed in the 1990s at Oakridge National Laboratories and offers great electrochemical stability against lithium and relatively high ionic conductivities on the order of 10-6 S/cm at room temperature. A new bilayer lithium-ion conducting hybrid solid electrolyte (HSE) consisting of a blended polymer electrolyte (BPE) coated with a thin layer of the ISE LiPON, has been prepared. PEO and PPC are blended in a 1:1 mass ratio, then the salt LiTFSI is incorporated. BPE films are then produced through a facile solution casting method using acetonitrile as the solvent. Structure-property relationships are then systematically evaluated to understand the effects of molecular weight and mass loading of LiTFSI on the BPE systems. Influences of molecular weight and salt loading on crystallinity is observed though X-ray diffraction and optical microscopy of the BPE films. Ionic conductivity is evaluated through impedance spectroscopy between two stainless steel blocking electrodes, thermal history measurements were taken by heating and cooling the SPE while recording EIS at specified temperatures. The best BPE based on ionic conductivity, consists of 100k molecular weight PEO, 50k molecular weight PPC, and 25(w/w)% LiTFSI, (denoted as PEO100PPC50LiTFSI25) and exhibits an ionic conductivity of ~2x10-5S/cm. Temperature dependent EIS shows that the lowest molecular weight polymers offer lower activation energies as a result of the higher degree of free volume and molecular motion of the polymer chain. The optimized BPE system is then coated with various thicknesses of LiPON. The effects of LiPON coating are evaluated and show promise for the development of lithium stable solid electrolytes. Linear sweep voltammetry (LSV) is used to assess the anodic voltage stability against lithium metal. Incorporating very thin layers of LiPON down to 20nm on the BPE shows an increase in the voltage window of the electrolyte system from 5.2 to 5.5V (vs Li/Li+). However, the incorporation of LiPON decreases the ionic conductivity of the BPE. Thinner layers of LiPON show the ionic conductivity approaches that of the BPE, with thicker LiPON layers offering lower ionic conductivies. To assess the stability against lithium metal over time, impedance spectroscopy is used. Cells consisting of the solid electrolyte against lithium metal are prepared, and impedance measurements are taken over a 20-day period to assess the changes in charge transfer resistance. From these measurements, it has been shown that only a 30nm thin layer of LiPON is required to improve the stability of the resulting HSE. Therefore, coating BPEs with a thin layer of LiPON is shown to be an effective strategy to improve the long-term stability of solid-state lithium ion conductors.

Investigation on the functionality of laser-welded NiTi to NiTiCu shape memory wires

NiTi shape memory wires are widely used in several markets, mainly for medical and aerospace applications, due to their excellent properties including superelasticity and shape memory effect. The combination of NiTi alloys with other alloys can provide high flexibility in the design of various smart structures. Nevertheless, the joining of NiTi alloys is really challenging because of the effect of thermal history on the functionality of welded joints. In fact, the temperature can change the microstructure and the balance of the material composition in the welding area, and, consequently, it leads to some alterations in the transformation temperature of the welded zone. The present study reports the effect of laser parameters, namely, laser power and scan speed, on the functionality of laser-welded NiTi to NiTiCu wires. The experimental findings allowed us to identify the best operational windows of the laser parameters, stating welding by high-power diode laser as an extremely promising technique in joining of dissimilar NiTi wires.

An Investigation into Thermal History and Its Correlation with Mechanical Properties of PA12 Parts Produced by Selective Laser Sintering Process

Thermal history is a key factor affecting mechanical properties of polymeric parts made by the selective laser sintering (SLS) process. In this research, the effect of thermal history on the mechanical properties of PA12 parts produced by the SLS process has been investigated. It is hypothesized that different cool-down methods (normal to very slow cooling) and built orientations, resulted from flat and edgewise layouts fabrication, could be influencing factors on the thermal history during the SLS process. The temperature changes at different points inside the powder bed were recorded during the fabrication of specimens. Afterward, the morphology of fabricated samples was examined using scanning electron microscopy. In addition, the degree of crystallinity and melting point of the parts were studied by differential scanning calorimetry analysis. It was found that the built orientation was more effective than the cooling methods on ultimate tensile strength (UTS) and elongation at break (EaB), so that UTS and EaB of the edgewise parts were 10%, 50% greater than the flat parts. On the other hand, the variation of crystallinity with cooling methods has been found to be much less than might be expected from the implemented various fabrication conditions. However, the applied slowest cool-down method slightly increased the edgewise parts crystallinity to 23%, compared to 19.2% for the normal cooled down samples, leading to greater UTS than the normal cooled specimens. The morphology observation of specimens fracture surfaces suggests that better mechanical performance of the edgewise samples is likely connected to fewer defects such as pores and un-melted powder particles remained in their cross sections due to experiencing higher temperature during fabrication. The work is relevant to attempts to build high mechanical performance parts by selective laser sintering.

Effects of superheating magnitude on olivine growth

Magmatic superheating is a condition with relevance to natural systems as well as experimental studies of crystallization kinetics. Magmas on Earth and other planetary bodies may become superheated during adiabatic ascent from the mantle or as a consequence of meteorite impact-generated crustal melting. Experimental studies of igneous processes commonly employ superheating in the homogenization of synthetic starting materials. We performed 1-atmosphere dynamic crystallization experiments to study the effects of superliquidus thermal history on the morphologies and compositions of subsequently grown olivine crystals. An ultramafic volcanic rock with abundant olivine was fused above the experimentally determined liquidus temperature (1395 °C), held for 0, 3, or 12 h, cooled at 25 °C h−1, and quenched from 200 °C below the liquidus, all at constant fO2, corresponding to FMQ-2 ± 0.2 log units. An increase in olivine morphologic instability is correlated with superheating magnitude, parameterized as the integrated time the sample is held above the liquidus (“TtL”; °C h). We infer that a delay in nucleation, which intensifies monotonically with increasing TtL, causes crystal growth to be increasingly rapid. This result indicates that the structural relaxation time scale controlling the formation of crystal nuclei is (a) far longer than the time scale associated with viscous flow and (b) exceeds the liquidus dwell times typically imposed in crystallization experiments. The influence of magmatic superheating on crystal morphology is similar in sense and magnitude to that of subliquidus cooling rate and thus, both factors should be considered when interpreting the thermal history of a volcanic rock containing anhedral olivine.