Thermal Curves Research Articles

Molecular Dynamics Simulations of HPr Proteins from a Thermophilic and a Mesophilic Organism: A Comparative Thermal Study.

The histidine-containing phosphocarrier (HPr) is a monomeric protein conserved in Gram-positive bacteria, which may be of mesophilic or thermophilic nature. In particular, the HPr protein from the thermophilic organism B. stearothermophilus is a good model system for thermostability studies, since experimental data, such as crystal structure and thermal stability curves, are available. However, its unfolding mechanism at higher temperatures is yet unclear at a molecular level. Therefore, in this work, we researched the thermal stability of this protein using molecular dynamics simulations, subjecting it to five different temperatures during a time span of 1 μs. The analyses of the structural parameters and molecular interactions were compared with those of the mesophilic homologue HPr protein from B. subtilis. Each simulation was run in triplicate using identical conditions for both proteins. The results showed that the two proteins lose stability as the temperature increases, but the mesophilic structure is more affected. We found that the salt bridge network formed by the triad of Glu3-Lys62-Glu36 residues and the salt bridge made up of Asp79-Lys83 ion pair are key factors to keep stable the thermophilic protein, maintaining the hydrophobic core protected and the structure packed. In addition, these molecular interactions neutralize the negative surface charge, acting as "natural molecular staples".

Microwave dielectric characterization and thermal analysis of B2O3-La2O3-ZnO glass-ceramic/Al2O3 composites for LTCC applications

High frequency performance and the content of glass are the direct factors affecting the performance of LTCC. In order to reduce the content of glass and improve the performance, we conducted a systematic study on the composition regulation of B2O3-La2O3-ZnO (BLZ) glass. Glass with low softening point is helpful for LTCC to achieve compact structure. DSC shows that the softening point of BLZ glass can be reduced from 580 ℃ to 537 ℃ by adjusting the composition. XRD analysis indicate that the glass and Al2O3 formed ZnAl2O4 interfacial phases. Combined with the thermal shrinkage curve, it can be proved that the softening of glass and the formation of interfacial phases are the reasons for the shrinkage and densification of LTCC. The lowest coefficient of thermal expansion of 2.878 ppm/℃ was obtained, and the minimum loss of LTCC is 0.00277 at 15 Ghz. These properties are making LTCC more suitable for high-frequency applications.

Challenges in correlating oxygen stable isotope ratios of hydrates on uranium ore concentrates to process waters

Abstract Exchange of oxygen stable isotopes (δ18O values) between precipitation waters and uranium oxides is governed by thermodynamics or kinetics. It has been assumed that meteoric waters can be related to precipitation waters in uranium ore concentrates and their calcined and reduced uranium oxide products. With this assumption, the δ18O values of uranium materials could provide forensic signatures that identify the production history and geolocation of nuclear materials. To further exploit the potential of δ18O values in nuclear material analysis, this study examines the oxygen stable isotope exchange in two UOCs, magnesium diuranate (MDU) and sodium diuranate (SDU). MDU and SDU were synthesized from solutions of uranyl nitrate hexahydrate using precipitation waters with unique oxygen isotope compositions. The structures of the MDU and SDU were analyzed using powder X-ray diffraction (p-XRD) and thermal mass loss curves, while the δ18O values of waters generated during thermal decomposition were analyzed using a thermogravimetric analyzer coupled to an isotope ratio infrared spectrometer (TGA-IRIS). By p-XRD, the MDU was uniform and amorphous across all syntheses with residual crystalline material incorporated as a minor component. Combined with the TGA results, all of the MDU is likely amorphous MgU2O7·3H2O with MgO impurities present throughout. In contrast, the SDU synthesis resulted in multiple phases with many samples exhibiting crystalline phases including a combination of Na(UO2)4O2(OH)5·5H2O and Na2(UO2)6O4(OH)6·8H2O with a Na2U2O7 minor phase. A small fraction of the SDU samples were amorphous with no crystalline XRD peaks observed. Mass loss curves of the SDU samples revealed that the amorphous samples contained inclusions of similar crystalline phases compared to the crystalline materials. The uniformity of the MDU samples enabled highly reproducible measurements of δ18O values of the water vapor yielded from two dehydration events at 170 °C and 500 °C. In contrast, the multiphase composition of the SDU samples resulted in poor reproducibility in δ18O values. Neither system revealed any correlation between the δ18O values of precipitation water and the waters released during dehydration of the UOCs.

An investigation of the MHD Cu-Al2O3/H2O hybrid-nanofluid in a porous medium across a vertically stretching cylinder incorporating thermal stratification impact

The thermal aspects of 𝐶𝑢 − 𝐴𝑙2𝑂3/𝑤𝑎𝑡𝑒𝑟 hybrid nanofluid in a porous medium across a ver-tically stretched cylinder with the incorporation of heat sink/source impact are investigated in this numerical study. A magnetic field along the transverse direction of the stretching cylinder and the thermal buoyancy effect is considered in the flow problem. A pertinent similarity vari-able has been employed to simplify the boundary layer equations which govern the flow and convert the coupled nonlinear partial differential equations into a set of non-linear ordinary differential equations. The numerical results are computed using the 3-stage Lobatto IIIa tech-nique, Bvp4c. The impacts of non- dimensional parameters, including Prandtl number, heat source/sink parameter, magnetic parameter, porosity parameter, curvature parameter, ther-mal stratification parameter, and thermal buoyancy parameter on the velocity curve, thermal curve, skin-friction coefficient, and Nusselt number, are illustrated graphically and numeri-cally portrayed in tables. The important results demonstrate that hybrid nanofluids are more thermally conductive than nanofluids. Therefore, the hybrid nanofluid has a considerable im-pact on improving thermal developments. It has been found that the absolute skin friction of the hybrid nanofluid is up to 31% higher compared to the nanofluid. The heat transport rate of the hybrid nanofluid is 7.5% enhanced in comparison to the nanofluid. The influence of heat stratification of the hybrid nanofluid flow is appreciably significant.

A Theoretical Thermal Tolerance Function for Ectothermic Animals and Its Implications for Identifying Thermal Vulnerability across Large Geographic Scales

The time-to-thermal-death curve, or thermal death curve, seeks to represent all the combinations of exposure time and temperature that kill individuals of a species. We present a new theoretical function to describe that time in lizards based on traditional measures of thermal tolerance (i.e., preferred body temperatures, voluntary thermal maximum, and the critical thermal maximum). We evaluated the utility of this function in two ways. Firstly, we compared thermal death curves among four species of lizards for which enough data are available. Secondly, we compared the geography of predicted thermal vulnerability based on the thermal death curve. We found that the time to loss of function or death may evolve independently from the critical thermal limits. Moreover, the traditional parameters predicted fewer deleterious sites, systematically situated at lower latitudes and closer to large water bodies (lakes or the coast). Our results highlight the urgency of accurately characterizing thermal tolerance across species to reach a less biased perception of the geography of climatic vulnerability.

Bell-shaped tree-ring responses to air temperature drive productivity trends in long-lived mountain Mediterranean pines

We investigated the dendroclimatic response of a Pinus heldreichii metapopulation distributed over a wide elevation interval (from 882 to 2143 m a.s.l.), spanning from low mountain to upper subalpine vegetation belts in the southern Italian Apennines. The tested hypothesis is that wood growth along an elevational gradient is non-linearly related to air temperature. During three years of fieldwork (2012–2015) at 24 sites, we collected wood cores from a total of 214 pine trees with diameter at breast height from 19 to 180 cm (average 82.7 ± 32.9 cm). We used a combination of tree-ring and genetic methods to reveal factors involved in growth acclimation using a space-for-time approach. Scores from canonical correspondence analysis were used to combine individual tree-ring series into four composite chronologies related to air temperature along the elevation gradient. Overall, the June dendroclimatic response followed a bell-shaped thermal niche curve, increasing until a peak around 13–14 °C. A similarly bell-shaped response was found with previous autumn air temperature, and both dendroclimatic signals interacted with stem size and growth rates, generating a divergent growth response between the top and the bottom of the elevation gradient. Increased tree growth in the upper subalpine belt was consistent with the consequences of increasing air temperature under no drought stress. A positive link was uncovered between pine growth at all elevations and April mean temperature, with trees growing at the lowest elevations showing the strongest growth response. No elevational genetic differences were found, hence long-lived tree species with small geographical ranges may reverse their climatic response between the lower and upper bioclimatic zones of their environmental niche. Our study revealed a high resistance and acclimation capability of Mediterranean forest stands, and such low vulnerability to changing climatic conditions highlights the potential to store carbon in these ecosystems for the coming decades.

Exergetic efficiency prediction of roughened solar air heater

Energy losses of flowing air through solar air heater (SAH) duct does not consider in the ther-mal performance. Therefore, thermohydraulic performance based on exergetic efficiencies is a tool to assess the performance by considering energy losses in propelling the air simul-taneously to identify the best ribs configuration. This paper presents the thermohydraulic performance of SAHs exploiting various ribs roughness’s. The performance of SAHs is based exergetic evaluation based on IInd law of efficiency is most suitable for design of artificial-ly roughened SAH as it includes both requirement of pumping power and effective energy output. In this paper exergetic evaluation of differently roughened SAH has been done. The exergy efficiency of roughened SAH was calculated analytically with the help of correlations developed by researchers and the results also compared with conventional SAH under same operating parameters. The thermal and exergy efficiency curve as a function of temperature rise parameter (ΔT/I) has been plotted. As a results, hybrid ribs configuration exhibited the highest exergetic efficiencies when temperature rise parameters greater than 0.01 K.m/W, however, smooth duct also showed a significant exergetic efficiency when temperature rise parameters had low values.

Performance of Thermal-Oxidative Aging on the Structure and Properties of Ethylene Propylene Diene Monomer (EPDM) Vulcanizates.

A thermal-oxidative aging test at 120 °C was conducted on ethylene propylene diene monomer (EPDM) vulcanizates of the semi-efficient vulcanization system. The effect of thermal-oxidative aging on EPDM vulcanizates was systematically studied by curing kinetics, aging coefficient, crosslinking density, macroscopic physical properties, contact angle, Fourier Transform Infrared Spectrometer (FTIR), Thermogravimetric analysis (TGA) and thermal decomposition kinetics. The results show that the content of hydroxyl and carbonyl groups as well as the carbonyl index increased with increasing aging time, indicating that EPDM vulcanizates were gradually oxidized and degraded. As a result, the EPDM vulcanized rubber chains were crosslinked with limited conformational transformation and weakened flexibility. The thermogravimetric analysis demonstrates that the thermal degradation of EPDM vulcanizates had competitive reactions of crosslinking and degradation, and the thermal decomposition curve can be divided into three stages; meanwhile, the thermal stability of EPDM vulcanizates gradually decreased with increasing aging time. The introduction of antioxidants in the system can promote the crosslinking speed and reduce the crosslinking density of EPDM vulcanizates while inhibiting the surface thermal and oxygen aging reaction. This was attributed to the fact that the antioxidant can reduce the thermal degradation reaction level, but it is not conducive to the formation of a perfect crosslinking network structure and reduces the activation energy of thermal degradation of the main chain.

Microstructure characteristics under varying solidification parameters in different zones during CMT arc additive manufacturing process of 2319 aluminum alloy

The microstructure affects the performance of the formed component during the wire arc additive manufacturing (WAAM) process of aluminum alloy. The present research utilized a finite element model to investigate the temperature field, thermal cycle curve, temperature gradient and cooling rate curve of the deposition layer at different positions in the WAAM process. The microstructure distribution and grain size variation of the deposition layer at different positions were examined according to the experimental results. The microstructure evolution of the deposition layer in the WAAM was simulated using a macro-micro coupled grain growth model. The variation law of solid phase and liquid phase distribution with solidification time steps of molten pool under varying temperature gradients is analyzed. The results indicated that the average length and width of the grains continuously decrease from right to left in the top zone of the deposition layer. When the temperature gradient increases to a certain extent, both the liquid phase area difference and the solid phase area ratio difference within the same time step gradually decrease with the development of the temperature gradient. This research supplies a reference for optimizing the microstructure of WAAM aluminum alloy by adjusting the heat input and solidification parameters.

Coupling effect on the thermal hazard assessment of hazardous chemical materials via calorimetric technologies and simulation approaches

The coupling effect of heat absorption and release exists in the thermal decomposition of a few chemical materials. However, the impact of the above coupling on thermal hazard assessment is not considered in the literature studies. In this work, nitroguanidine (NQ) and 1,3,5-trinitro-1,3,5-triazine (RDX) are selected as representative materials to explore the influence of the coupling effect on the thermal hazard assessment of chemical materials. The linear heating experiments of NQ and RDX are carried out by a microcalorimeter and synchronous thermal analyser. The thermal decomposition curves are decoupled by advanced thermokinetics software. The thermal decomposition and kinetic parameters before and after decoupling are calculated. The results of TG experiment show that both NQ and RDX began to lose mass during the endothermic stage. The endothermic melting and exothermic decomposition of NQ and RDX are coupled within this stage. The coupling effect has different degrees of influence on its initial decomposition temperature and safety parameters. Compared with the parameters in the coupling state, the initial decomposition temperature and adiabatic induction period after decoupling decrease. The self-accelerating decomposition temperature increases, and internal thermal runaway time decreases. In the thermal hazard assessment of chemical materials with coupling effects, the calculated parameters after decoupling should be taken as an important safety index.

Calibration Experiment and Temperature Compensation Method for the Thermal Output of Electrical Resistance Strain Gauges in Health Monitoring of Structures

Electrical resistance strain gauges are widely used in asymmetric structures for measurement and monitoring, but their thermal output in changing temperature environments has a significant impact on the measurement results. Since thermal output is related to the coefficient of thermal expansion of the strain gauge’s sensitive grating material and the measured object, the temperature self-compensation technique of strain gauges fails to eliminate the additional strain caused by temperature because it cannot match the coefficient of thermal expansion of various measured objects. To address this problem, in this study, the principle of the thermal output of electrical resistance strain gauges was analyzed, a calibration experiment for thermal output in the case of a mismatch between the coefficient of linear expansion of the measured object and the strain gauge grating material was conducted, and the mechanism for temperature influence on thermal output was revealed. A method was proposed to obtain the thermal output curves for different materials by using thermostats with dual temperatures to conduct temperature calibration experiments. A linear regression method was used to obtain a linear formula for the thermal output corresponding to each temperature. The thermal output conversion relationship was derived for materials with different coefficients of linear expansion. An in situ temperature compensation technique for electrical resistance strain gauges that separates the measured strain into thermal and mechanical strains was proposed. The results showed that the thermal output curve for the measured object can be calibrated in advance and then deducted from the measured strain, thus reducing the influence of temperature-induced additional strain on the mechanical strain. In addition, a new method was provided for the calculation of the thermal output among materials with similar coefficients of linear expansion, providing a reference for the health monitoring of asymmetric structures.

A new methodology for optimization of overcurrent protection relays in active distribution networks regarding thermal stress curves

In this paper, a novel method for optimizing and coordinating directional overcurrent relays in active distribution networks considering thermal equivalent short-circuit current is proposed. A modified genetic algorithm is used as a tool in order to simultaneously minimize the operating times of the primary relays and maximize the time delay between the operation of backup relays and their respective protected elements’ thermal stress curves. In other words, the objective function to be minimized is defined as the sum of the operating times of all primary relays and the reciprocal sum of the thermal violation check. The latter part is necessary because a protection engineer needs to be sure that the operation of a backup relay is as far as possible from the thermal stress curve of the protected element. Needless to say, for every solution, the algorithm ensures the proper coordination between primary and backup relay pairs throughout the network. The simulation is carried out for a closed loop medium voltage distribution network and the results are presented to demonstrate the effectiveness of the proposed approach. The main benefit of this optimization process is that it indicates whether the existing protection system can operate safely below the thermal stress curves of the protected elements’ or whether additional measures are required.

A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curve.

There are no planets intermediate in size between Earth and Neptune in our Solar System, yet these objects are found around a substantial fraction of other stars1. Population statistics show that close-in planets in this size range bifurcate into two classes on the basis of their radii2,3. It is proposed that the group with larger radii (referred to as 'sub-Neptunes') is distinguished by having hydrogen-dominated atmospheres that are a few percent of the total mass of the planets4. GJ 1214b is an archetype sub-Neptune that has been observed extensively using transmission spectroscopy to test this hypothesis5-14. However, the measured spectra are featureless, and thus inconclusive, due to the presence of high-altitude aerosols in the planet's atmosphere. Here we report a spectroscopic thermal phase curve of GJ 1214b obtained with the James Webb Space Telescope (JWST) in the mid-infrared. The dayside and nightside spectra (average brightness temperatures of 553 ± 9 and 437 ± 19 K, respectively) each show more than 3σ evidence of absorption features, with H2O as the most likely cause in both. The measured global thermal emission implies that GJ 1214b's Bond albedo is 0.51 ± 0.06. Comparison between the spectroscopic phase curve data and three-dimensional models of GJ 1214b reveal a planet with a high metallicity atmosphere blanketed by a thick and highly reflective layer of clouds or haze.

Nano additives-enhanced PEG /AlN composites with high cycle stability to improve thermal and heat storage properties

The low thermal conductivity and easy leakage of phase change materials are the shortcomings that hinder their further application for thermal energy storage. It is crucial how to properly match skeleton materials and phases to improve heat transfer in order to solve the above problem. Here, we systematically investigate the effects of nano additives on the phase change and thermal properties of bionic hierarchical porous aluminum nitride-polyethylene glycol (PEG/AlN) composites. Alumina (Al2O3) nanoparticles were found to have the largest enhancement effect for the thermal conductivity of PEG (84% for 4 wt% addition) compared to silica, titanium dioxide, and boron nitride. For these additives, the thermal conductivity and stability of the nano additives-enhanced PEG increase with the increase of their mass fraction. After 100 heating/cooling cycles, the thermal response curve shows that the Al2O3-enhanced PEG can maintain the phase transition behavior, and the measured phase transition temperature agrees well with the differential scanning calorimeter results. The thermal conductivity of the PEG/AlN enhanced with 4 wt% Al2O3 is 20.41 W/m·K, and the melting point and phase change enthalpy are 55.93 °C and 81.05 J/g. In addition to the great improvement in thermal response, the heat storage rate also increases by 36.10%.

ClinoformNet-1.0: stratigraphic forward modeling and deep learning for seismic clinoform delineation

Abstract. Deep learning has been widely used for various kinds of data-mining tasks but not much for seismic stratigraphic interpretation due to the lack of labeled training datasets. We present a workflow to automatically generate numerous synthetic training datasets and take the seismic clinoform delineation as an example to demonstrate the effectiveness of using the synthetic datasets for training. In this workflow, we first perform stochastic stratigraphic forward modeling to generate numerous stratigraphic models of clinoform layers and corresponding porosity properties by randomly but properly choosing initial topographies, sea level curves, and thermal subsidence curves. We then convert the simulated stratigraphic models into impedance models by using the velocity–porosity relationship. We further simulate synthetic seismic data by convolving reflectivity models (converted from impedance models) with Ricker wavelets (with various peak frequencies) and adding real noise extracted from field seismic data. In this way, we automatically generate a total of 3000 diverse synthetic seismic datasets and the corresponding stratigraphic labels such as relative geologic time models and facies of clinoforms, which are all made publicly available. We use these synthetic datasets to train a modified encoder–decoder deep neural network for clinoform delineation in seismic data. Within the network, we apply a preconditioning process of structure-oriented smoothing to the feature maps of the decoder neural layers, which is helpful to avoid generating holes or outliers in the final output of clinoform delineation. Multiple 2D and 3D synthetic and field examples demonstrate that the network, trained with only synthetic datasets, works well to delineate clinoforms in seismic data with high accuracy and efficiency. Our workflow can be easily extended for other seismic stratigraphic interpretation tasks such as sequence boundary identification, synchronous horizon extraction, and shoreline trajectory identification.

A new approach based on off-design R-curve and thermal load duration curve for the design and optimization of bioresources driven cogeneration Rankine cycle: Application on industrial site in Nova Scotia, Canada

Decarbonization objectives in industrial processes impose major changes for industrial energy supply. The combination of decarbonization of heat and electric load can be achieved by cogeneration plant driven by clean energy resources. Despite of new innovative cogeneration cycle being investigated, Rankine cycle cogeneration plant driven by biomass or biofuels stills the most attractive solution in low solar irradiance countries. The aim of this study is to establish a new original method combining a steady state and dynamic approach to solve and link optimal conceptual design problem and operation strategies of the plant. This approach is applied also to evaluate the worthiness of adopting a thermal energy storage solution. Breakdown of electricity and thermal cost of cogeneration plant is established for the first time for the sake of mapping energy prices of different decarbonization solutions. A thermodynamic and economic model to predict the performances of the cogeneration plant at design and off-design conditions was developed.Three off-design operation strategies are identified: the first engenders steam throttling, the second induces part-load operation of the condensing turbine, and the third requires an auxiliary boiler to meet peak thermal demand. A new R-curve named off-design R-curve is developed to predict cycle performances during these operations, and then combined with the thermal load duration curve to predict energy consumption. Subsequently, an optimization procedure combining the R-curve tool and cost break-down of electricity and thermal energy is carried out. The energy prices and the annualized capital cost R-curves are summed up to optimize the design of power to heat ratio.A case study in an industrial site in Nova Scotia (Canada) is considered. The method proves its simplicity and effectiveness in the conceptual design of the plant, as well as predicting different costs of energy and the optimization of the R ratio. Case study results show that biomass energy cost saving rises with power production to achieve its maximum at Rd equal to 1.23, while biofuel energy cost saving decreases with Rd and was achieved only when Rd is lower than 0.7. Combining the annualized cost with the energy cost reveal that the optimal Rd is at 1.07 for biomass and 0.21 for biofuel, respectively. Moreover, with the introduction of the off-design R curve, it was found that the cogeneration efficiency drops down to 18 % (from 0.52 to 0.34 at Rd equal to 1.23) and the power production down to 60 % when the process load is double the average load. Hence, more accurate energy cost-saving values and optimal on-site power production are achieved. Energy cost saving drops by 7 %, which lowers the value of Rd where biofuel cost saving is achieved to 0.3, while the optimal value stays the same for biomass. Besides, the maximum potential of thermal energy storage in energy saving is accounted. The saving in the case study is low at 5–6 %, but generally it is dependent on the frequency at which the thermal load occurs. The method developed proves its effectiveness in solving conceptual design problems, and can used to rigorously evaluate new innovative configurations of cogeneration plants. Challenges and future works to improve this method are also addressed.

Numerical simulation of the temperature field of T2 copper/304 steel dissimilar metal electron beam welding

ANSYS workbench finite element analysis software was adopted to simulate and study the thermal process of electron beam welding of T2 copper and 304 steel heterogeneous materials in this paper. A solid model was established according to the size of the specimens, and a double ellipsoidal moving heat source model of the temperature field of the specimens of the three-dimensional dynamic simulation was imposed. Copper and steel welding transient temperature field distribution pattern and molten pool morphology were studied, and the temperature field welding thermal cycle curve was analyzed. The results show that the peak temperature of the steel side is higher than the copper side, the morphology of the welding pool is basically biased toward the steel side, and the highest temperature during the welding process appears in the center of the weld on the steel side about 0.5 mm.

Skin microvascular reactivity in patients with diabetic retinopathy.

Early detection of microangiopathic complications of diabetes mellitus (DM) is necessary to analyze the patient's condition and prevent disease progression. The study was aimed to investigate the relationship between the presence of retinopathy and decreased reactivity of the microcirculatory bed in patients with diabetes. The study involved 130 subjects: healthy volunteers (n=48), DM patients without retinopathy (n=53) and with retinopathy (n=29). Skin microvascular reactivity was assessed on the forearm using laser Doppler flowmetry with a local heating test combined with occlusion. The slope of local thermal hyperemia curve (Slope-120) and other parameters of microvascular reactivity showed difference in pairwise comparisons between the groups. Slope-120 had the highest sensitivity (0.759) and specificity (0.717) in detection of diabetic retinopathy. The decrease of Slope-120 was associated with retinopathy (odds ratio (OR) - 8.3 (2.9-24.1), p<0.001), even after adjusting for other factors (OR - 11.0 (1.6-77.2), p=0.016). Thus, assessment of skin microvascular reactivity may be a useful test for detecting signs of microangiopathic complications and for screening patients in risk group. Decreased microvascular reactivity has been shown to be prospective as an independent indicator of retinopathy in type 1 DM.

Alkaline Treatment Investigation for Sedge Fibers (Cyperus malaccensis): A Promising Enhancement.

Natural fibers have some advantages in comparison to synthetic fibers, especially because they are more environmentally friendly. For this reason, using them as a reinforcement for polymeric matrices is growing exponentially. However, they present the disadvantage of having the hydrophilic nature, which strongly reduces the interface interaction. Sedge fibers have been investigated when reinforcing an epoxy matrix in terms of ballistic properties and mechanical performance. Aiming to enhance the fiber-matrix interface, an alkali treatment was proposed. The group conditions were divided into three NaOH concentrations (3%, 5%, and 10%), as well as the three periods of immersion (24, 48, and 72 h). Therefore, nine different conditions were investigated in terms of their thermal behaviors, chemical structures, physical structures, and morphological aspects. Based on TGA curves, it could be noticed that treatments related to 3% NaOH for 24 h and 48 h exhibited better thermal stability properties. For the time of 48 h, better thermal stability with for a decay of the thermal DSC curve was shown for all treatment conditions. The FTIR spectra has shown a reduction of waxes for higher NaOH concentrations. The XRD diffractogram exhibited an increase in the crystallinity index only for 5% NaOH and an immersion time of 48 h. The morphological aspects of fibers treated with 5% and 10% of NaOH have shown that the treatments have damaged the fiber, which highlighted the crystallinity index reductions.

Investigation on residual stress of EQ56 high strength steel butt weld

In the welding process of high-strength steel (HSS), the intense temperature change in joints induces the formation of welding residual stress (WRS), which increases the fatigue crack growth rate. Developing an effective finite element (FE) model for accurately predicting the WRS distribution is critical to improve the quality of welded structures. Experimental tests and numerical simulations were carried out to investigate the WRS distribution of EQ56 HSS. The thermal expansion curves at various heating and cooling rates were measured through thermal simulation experiments for achieving the continuous cooling transformation (CCT) diagram of EQ56 HSS. Based on the CCT diagram, the thermo-metallurgical-mechanical (TMM) FE model was developed to consider the influence of solid-state phase transformation (SSPT) on distribution and magnitude of WRS for welded EQ56 HSS joints, as well as material hardening law. Comparison of predicted WRS distribution and experimental data shows that plastic hardening laws of materials significantly affect the precision of WRS distribution, and combined hardening law gives most reliable prediction. The FE model considering SSPT behavior provides more accurate estimation of WRS distribution than those without considering SSPT behavior.