Movement Of Front Research Articles

Experimental study on enhanced heat transfer during rapid cooling of modified and oxidized rods

This research investigates the effects of surface modification and surface oxidation on pool boiling heat transfer performance. An experimental facility was designed and built to perform vertical quenching testings at atmospheric pressure and close to the saturation water pool. Three surface structures (smooth, threaded, and knurled) were fabricated to study the effect of surface area variation and surface oxidation on minimum film boiling temperature (Tmin). A visualization study was performed using a high-speed camera to capture the thermohydraulic behavior of the generated vapor around the heated sample. The results showed that surface features have a significant impact on the enhancement in heat transfer as the knurled surface exhibited a strong impact on increasing Tmin, quenching time, and heat transfer coefficient (HTC). The visualization study displayed different behaviors of the vapor layer breakage where the smooth and the threaded samples experienced larger bubbles and smoother movement of the quench front. Whereas smaller and intense bubbles were generated around the knurled sample at Tmin point. The successive experiments resulted in oxidation layers on the test samples, which proved that the oxidation mechanism depends on the surface finish that caused the surface to experience different heat fluxes. The comparison between the experimental results and available correlations in literature showed the importance of incorporating the surface characteristics effect in Tmin correlations due to its significant impact on pool boiling heat transfer performance.

Hydraulic characteristics of plow pan constructed sandy paddy soil by adding fly ash

The feasibility of mixing fly ash to sandy soil to build the artificial plow pan of paddy soil in the Yellow River beach was explored. Water infiltration characteristics, saturated hydraulic conductivity, saturated water content and water storage capacity of the artificial plow pan were measured by using laboratory column tests. The results showed that under the same bulk density, when the amount of fly ash increased, the movement rate of the plow pan wetting front, the infiltration rate and the saturated hydraulic conductivity were decreased, then the water content and water storage of the soil layer increased. When the application amount of the fly ash was the same, and when the compaction weight decreased, the wetting front movement rate and saturated hydraulic conductivity increased and the soil water content and water storage capacity decreased. Mixing of fly ash with sand at a ratio of 1:3 (by weight) was found to be ideal for making an artificial of plow pan having bulk density of 1.7 g/cm3. Bangladesh J. Bot. 50(3): 993-1002, 2021 (September) Special

Hydrodynamics, Hydrochemistry, and Stable Isotope Geochemistry to Assess Temporal Behavior of Seawater Intrusion in the La Yarada Aquifer in the Vicinity of Atacama Desert, Tacna, Peru

The La Yarada aquifer is the primary water resource for municipal, irrigation, and industrial uses in the semi-arid Tacna, Peru. Presently, over-pumping has caused severe groundwater management problems, including the abandonment of saline water wells. This study presents multivariate analysis and chemical–isotopic trends in water to investigate seawater intrusion and hydrogeological processes affecting water quality. The chemical and isotopic analysis of water samples, collected in two campaigns in the dry (August 2020) and wet (November 2020) seasons, together with the 1988 data, were evaluated with a mixing model, cluster, and factor analysis. The hydrochemical and isotopic mixing model suggested the formation of a wedge with 20% seawater intrusion. The heterogeneity of piezometric map isolines corroborates the wedge formation associated with the groundwater movement. The spatial distributions of factors, FA1 and FA2, suggest two processes of seawater front movement: dispersion (diffusion) of chemical elements and different types of water mixing, respectively. At the edge of the La Yarada aquifer, the water head was relatively low, permitting seawater and freshwater mixing. On the other hand, along the sea-land boundary, the water head of the La Yarada aquifer was relatively high, avoiding seawater and freshwater mixing; however, the chemical species were migrating from the seawater to the groundwater due to the diffusion processes. The cluster 4 samples are in the region corresponding to the isotopic mixing process represented by the FA2, while cluster 4 describes the chemical diffusion process represented by the FA2. Thus, the integrated approach is helpful to assess the seawater intrusion mechanisms in coastal aquifers in a semi-arid region.

Kinematics of steam film wetting while quenching cylindrical samples in thermal oils

The paper presents the determination of the velocity of the vapor front along the outer wall of a cylindrical specimen in the process of two-dimensional axisymmetric quenching of the samples in thermal oils. One thermal oil is Isorapid 277 HM heated to 40°C and the other thermal oil is Marquench 722 heated to 90°C. The experimental setup of the work consists of heating to a temperature of 850°C, then quenching three dimensionally different cylindrical probes. The dimensions of the probe were: ϕ25x100 ϕ50x150 and ϕ75x225 mm. All quenchings were done in strictly controlled conditions of the flow rate of the quenchant around the cylinder as well as maintaining the temperature of the quenchant within the maximum 40±2.5°C or 90d3°C, during the quenching of the samples. The velocity of movement of the steam front on the outer surface of the cylinder was determined from the time-measured values of temperatures at the marked points of each sample. The analysis of the steam front movement velocity along the cylinder wall starts from the moment the lower base of the probe touches the quenchant. During the process of immersing the test probe in the quenchant, in addition to measuring the temperatures in time, the time of lowering the probe to contact with the quenchant sample was also measured. The approximate average velocity of the vapor front was determined based on the indications of the lower and middle thermocouples located 1.5 mm below the outer surface of the cylinder wall. Based on the distance of one half the height of each probe and time, the velocity of the steam film movement or the kinematics of the steam film wetting was obtained. The obtained results were compared with the results of quenching in water and aqueous solutions of the same probes under the same strictly controlled conditions.

Biomechanical Analysis of the Joint and Muscle Forces of the Lower Extremities in Walking of Rheumatoid Arthritis Patient

Summary. Rheumatoid arthritis (RA) is an immunomodulated, chronic inflammatory disease, accompanied by the proliferation of the inflamed synovium and destruction of the articular cartilage, which leads to the formation of contracture of lower extremities joints and disability. Understanding the values of biomechanical loads on the articular surfaces with contracture of the joints of the lower extremities in patients with RA and the muscle forces (MF) participation in this process with the formation of adaptation and compensation mechanisms can contribute to the development of new views and approaches to the tactics of therapeutic measures specific to each stage of the disease.
 Objective: to analyze the behavior of the musculoskeletal system of an RA patient in his walking pattern by calculating the forces acting in the main muscle groups and joints of the lower extremities.
 Materials and Methods. Initial data were obtained from the examination of a female patient K., who was diagnosed with stage 2 phase 3 RA with a predominant lesion of the hip and knee joints and severe pain in the left hip joint. A video system of 6 cameras, reflective markers and a force platform were used for motion capture of the walking. A simulation musculoskeletal model of the gait of the RA patient using the AnyBody Modeling System 6.0 software (Denmark) was created. Joint reaction forces (JRF) and MF were calculated.
 Results. Normal mode of loading of the lower extremities was altered to compensate for structural disorders in joints of RA patients. The peaks of vertical component of the ground reaction force (GRF) are lower compared to the normal population; the gait is static and asymmetric, sparing. MF increase in m. gluteus (maximus, medius, minimus) with increasing amplitude of movements in the frontal plane. JRF of both hips increase in all planes.
 Conclusions. Walking of RA patients with limitation of active extensions in the hip and knee joints occurs due to an increase in the amplitude of the frontal plane compensatory movements. Postural muscle imbalance increases the m. gluteus, m. biceps femoris, m. semitendinosus and m. semimembranosus MF. Other lower extremities muscles decrease their MF. The MF redistribution is compensatory and aimed to keep the RA patient in the upright position and optimize the biomechanics of walking due to less painful movements. Biomechanical overloading of the hip and knee articular surfaces can serve as a factor in maintaining the inflammatory response, the development of degenerative processes, or the further progression of arthrosis and stiffness of the joints of the lower extremities in this category of patients.

Highly scalable numerical simulation of coupled reaction–Diffusion systems with moving interfaces

A combination of reaction–diffusion models with moving-boundary problems yields a system in which the diffusion (spreading and penetration) and reaction (transformation) evolve the system’s state and geometry over time. These systems can be used in a wide range of engineering applications. In this study, as an example of such a system, the degradation of metallic materials is investigated. A mathematical model is constructed of the diffusion-reaction processes and the movement of corrosion front of a magnesium block floating in a chemical solution. The corresponding parallelized computational model is implemented using the finite element method, and the weak and strong-scaling behaviors of the model are evaluated to analyze the performance and efficiency of the employed high-performance computing techniques.

Meteorological Analyses of the Tri-State Tornado Event of March 1925

Severe thunderstorms occurred across portions of the central United States on 18 March 1925. The deadly, long-track Tri-State tornado was the most publicized storm event of 18 March and remains the most significant single tornado in the nation’s history. There has been only one formal paper regarding the Tri-State tornado and its meteorological setting. Results are presented from a recent study of the event that was done drawing upon all relevant Weather Bureau data that could be obtained. The storms of 18 March were associated with a rapidly moving, synoptic cyclone that was not unusually intense. There appear to be no outstanding aspects of the meteorological setting that would explain the extreme character of the Tri-State tornado. Surface analyses indicate: a) the tornado was produced by a long-lived supercell that developed very near the center of the cyclone, possibly at the intersection of a warm front and a distinct dryline; b) the south-to-north temperature gradient ahead of the cyclone was very pronounced due to cooling produced by early morning storms and precipitation; c) the tornadic supercell tracked east-northeastward very rapidly at about 60 to 65 mph (~28 ms-1), moving farther away from the cyclone with time; and d) the storm remained very close to the surface warm front. Previous reports concerning the tornado and its setting had inaccurate surface analyses and surface pressures, and incorrectly stated that the tornado had formed in cold air well west of the surface cyclone. As the supercell and dryline moved rapidly eastward, the northward movement of the warm front kept the tornadic supercell within a very favorable storm environment for several hours. Apparently, this consistent, time and space concatenation of the supercell, the warm front, and the dryline for more than three hours was extremely unusual.

Soaking in CO2 huff-n-puff: A single-nanopore scale study

CO2 Huff-n-Puff is a promising method for enhancing the oil recovery from unconventional reservoirs and sequestering CO2. Optimizing the operation of Huff-n-Puff requires a fundamental understanding of the thermodynamic and transport phenomena of CO2 and oil in nanopores. Here, we investigate the soaking step of CO2 Huff-n-Puff in a single, 4 nm-wide calcite pore using molecular dynamics simulations. We show that the CO2 molecules entering the pore can become adsorbed on pore walls and diffuse along with walls or are transported into the pore's interior as free CO2 molecules. Decane molecules are displaced from the pore walls and out of the bulk zone in the pore. Before reaching the pore's end, the movement of the density fronts of adsorbed and free CO2 molecules inside the pore obeys a t1/2 scaling law with effective diffusion coefficients ∼50% smaller than that of bulk CO2. Except at the very beginning period of soaking, the accumulation of adsorbed and free CO2 molecules occurs at a similar rate and follows the diffusive scaling law. These pore-scale results highlight the importance of surface adsorption in the storage and transport of CO2 during the soaking process in unconventional oil reservoirs.

Lower extremity energy absorption strategies at different phases during single and double-leg landings with knee valgus in pubertal female athletes

Dynamic knee valgus (DKV) malalignment affects the biomechanical characteristic during sports activities. This cross-sectional study was conducted to evaluate mechanical energy absorption (MEA) strategies at initial contact (IC) and total landing (TL) phases during single-leg landing (SLL), and double-leg landing (DLL). Twenty-eight female athletes with DKV (age 10–14) were invited. MEA analysis of lower extremity joints was done in sagittal and frontal motion planes employing 8 Vicon motion capture cameras and 2 Kistler force plates. Statistical analysis was done using IBM Statistics (version24) by Bivariate Pearson Correlation Coefficient test. Knee extensors MEA during SLL (IC: P = 0.008, R = 0.522/TL: P < 0.001, R = 0.642) and DLL (IC: P < 0.001, R = 0.611/TL: P = 0.011, R = 0.525), and knee abductors during SLL (IC: P = 0.021, R = 0.474) were positively correlated with increased DKV angle. Ankle plantar flexors during SLL (TL: P = 0.017, R = − 0.477) and DLL (TL: P = 0.028, R = − 0.404), and hip extensors during SLL (TL: P = 0.006, R = − 0.5120) were negatively correlated with increased DKV angle. Compensated MEA in knee extensors was correlated with less ankle plantar flexion MEA during SLL (IC: P = 0.027, R = − 0.514/TL: P = 0.007, R = − 0.637) and DLL (IC: P = 0.033, R = − 00.412/TL: P = 0.025, R = − 0.485). These outcomes indicated a knee-reliant MEA strategy in female athletes with DKV during puberty, putting them at higher risks of ACL injuries during landing.

Closed‐form analysis of undetected range errors due to ionospheric impacts for GBAS category I operations

Ionospheric anomalies may cause large differential range errors in Ground-Based Augmentation System (GBAS) users. To mitigate those integrity threats, worst-case ionosphere-induced position errors for potentially usable satellite geometries must be bounded by the GBAS ground facility. This mitigation method requires us to compute the worst-case range error for each satellite affected by a hypothetical ionospheric front. This paper presents a simulation-based method for deriving a closed-form expression of undetected ionosphere-induced range errors. Two types of ionospheric impact scenarios are defined in terms of the motion of an ionospheric front. Explicit expressions for outputs of the code-carrier smoothing filter and the code-carrier divergence monitor are derived to reduce the computational load of ionospheric impact simulations. An exhaustive search algorithm is applied to generate the worst undetected range error among all possible ionospheric impact conditions. Finally, a closed-form expression that bounds the maximum ionospheric range errors is determined as a linear function of the magnitude of gradient and the relative speed of the ionospheric front.

New insights into the dissociation of mixed CH4/CO2 hydrates for CH4 production and CO2 storage

Recent but limited studies have shown that multistep slow depressurization based on mixed CH4/CO2 hydrate dissociation can enhance CH4 recovery and increases CO2 storage after CO2 injection into CH4 hydrate [1,2]. For the first time, the resistivity variation and gas recovery and storage variation was investigated to study the change in hydrate saturation and production/storage yield. Lab-scale CH4 and CO2 rich mixed hydrates were synthesized to mimic the production and injection well scenario. The mixed hydrates were synthesized in sandstone with moderate to high water saturation using two different CH4/CO2 gas mixtures. Furthermore, mixed CH4/CO2 hydrates were dissociated three to six steps based on cyclic depressurization. Pressure, resistivity and gas chromatography data were collected. The presence of two thermodynamic stability zones provided an opportunity for additional CH4 recovery and CO2 storage during mixed hydrate dissociation. Gas and water migration between the injection and production well caused CO2 hydrate reformation, improvement in CO2 sweep area and movement of the CO2 hydrate front toward the production well. Multiple peaks in CH4 recovery and CO2 storage suggest major dissociation and reformation. Peak values were independent of mixed hydrate type. Peaks values of CH4 rich hydrates occurred at high pressure than peak values of CO2 rich hydrates. The slight change in resistance during depressurization below pure CH4 hydrate stability pressure confirms the loss of CH4 hydrate mass recovered by the formation of CO2 hydrate mass. This study discusses the correlation between the change in resistivity and type of guest molecule and its concentration and initial water saturation. The results of this study will be useful to explore the application of slow depressurization for the dissociation of CH4/CO2 mixed hydrates to improve CH4 recovery and CO2 storage.

Cellulase as an “active” excipient in prolonged-release HPMC matrices: A novel strategy towards zero-order release kinetics

Hydrophilic matrices are of utmost interest for oral prolonged release of drugs. However, they show decreasing release rate over time, mainly due to lengthening of the diffusional pathway across the gel formed upon glass-rubber transition of the polymer. Therefore, achievement of zero-order release kinetics, which could reflect in constant drug plasma levels, is still an open issue. With the aim of improving the release performance of hydroxypropyl methylcellulose (HPMC) systems, the use of cellulolytic enzymes was proposed to aid erosion of the swollen matrix, thereby counteracting the release rate decrease particularly toward the end of the process. The effectiveness of this strategy was evaluated by studying the mass loss and drug tracer release from tableted matrices consisting of high-viscosity HPMC (Methocel® K4M), Acetaminophen and increasing amounts (0.5–10% on HPMC) of a cellulolytic product (Sternzym® C13030). A faster erosion and progressive shift to linearity of the overall release profiles were observed as a function of the enzyme concentration. Release was markedly linear from matrices containing 5 and 10% Sternzym® C13030. In partially coated matrices with these cellulase concentrations, such results were in agreement with data of erosion and swelling front movement, which exhibited early and long-lasting synchronization.

Experimental Analysis of NiTi Alloy during Strain-Controlled Low-Cycle Fatigue.

The interaction between the stress-induced martensitic transformation and resistivity behavior of superelastic NiTi shape memory alloy (SMA) was studied. Strain-controlled low-cycle fatigue up to 6% was monitored by in situ electrical resistivity measurements. The experimental results show that a great motion of martensite fronts results in a significant accumulation of defects, as evidenced by transmission electron microscopy (TEM), before and after the tensile cycles. This gives rise to an overall increase of the resistivity values up to the maximum deformation. Therefore, the research suggests that shape memory alloy wire has great potential as a stress sensor inside bulk materials.

On the Propagation of Reaction Fronts in a Sandy Aquifer Over 20+ Years: Lessons From a Test Site in Northwestern Germany

AbstractDespite reduction measures, nitrate and aluminum concentrations remain high in aquifers in northwestern Europe. To evaluate the effectiveness of groundwater protection policies, the long‐term fate of these contaminants in groundwater needs to be understood. The groundwater catchment of the Haren water works, NW Germany, was characterized hydrogeochemically in the late 1990s, which provides an opportunity to study the solute fronts over a two‐decade period and conduct a post‐audit of the predicted front movement. Results indicate that, despite a significant reduction of the atmospheric acid loads, the acidification of soil and groundwater at the forest site persists. Removal of sorbed aluminum is required to induce a noticeable improvement, which will take at least several decades. The unexpected appearance of nitrate at the site, caused by a land use change in 1998, highlights the need for long‐term monitoring. Core data at the agricultural site show that the denitrification front has moved very little between 1998 and 2017, in accordance with previous forecasts. Denitrification by‐products, mainly sulfate and nitrogen, have migrated from the upper into the lower aquifer. A reactive transport model demonstrated how the link between the regional groundwater flow, pyrite oxidation, and the temporal variability of the nitrate concentration in recharge water, as reconstructed from age tracers, result in the observed vertical distribution of sulfate and nitrogen. This study demonstrates how long‐term monitoring, aided by model‐based data interpretation, can be used to successfully study and predict the fate of contaminants in groundwater.

Liquid crystal thermography based study on melting dynamics and the effect of mushy zone constant in numerical modeling of melting of a phase change material

Melt front tracking is vital in a solid–liquid phase change process to understand the melting process and quantify the system’s liquid faction, sensible and latent energies. This study presents a method to track the solid–liquid interface during the melting of a phase change material using liquid crystal thermography. The melt front movement is captured simultaneously through temperature influenced color variation in Thermochromic Liquid Crystal (TLC) sheet and direct visualization. Experiments have been performed for the cases of (i) heating from the bottom and (ii) heating from the top. Further, three-dimensional numerical simulations have been performed to validate the mushy zone temperatures and understand the effect of the mushy zone constant in the mushy zone temperature and liquid fraction. The results show that the TLC easily captures the dynamic motion of the solid–liquid interface during melting. From numerical simulations, it is found that the mushy zone constant affects the numerical prediction of melting in the bottom heating case with the low and high mushy zone constants, respectively, over predicting and under predicting the mushy zone temperatures during melting. Additionally, in this case, it is seen that the Rayleigh–Benard convection creates a wavy interface and accelerates the melting rate of the PCM. In the case of heating from the top, the numerical prediction of melting is independent of the mushy zone constant. Besides, a flat interface is observed in this case due to the absence of convection in the PCM during melting. Additionally, in the case of heating from the top, the combination of the PCM’s low thermal conductivity and heat diffusion through conduction leads to the self insulation effect of the PCM during melting. The convection-driven melting of PCM maintains the heater temperature lower by up to 35%, reduces the melting thermal resistance up to 78%, and increases the average volumetric melting to 92% over the case of melting without convection in the PCM.

Directional movement of consumer fronts associated with creek heads in salt marshes.

Consumers often deplete local resources and aggregate along edges of remaining resources, forming "consumer fronts." We examined the factors that promote Sesarma reticulatum crab aggregations at saltmarsh creek heads to explain the directional but slow movement of these fronts. We also created artificial creek heads to test the hypothesis that hydrological conditions at creek heads create superior habitat for crabs. Soil temperatures were ˜11-12% cooler, hydrogen sulfide concentrations lower (0.0 vs. ˜0.58mg/L), and dissolved oxygen concentrations twofold higher at the creek head versus the marsh platform. In the artificial creek-head experiment, altering hydrological conditions led to lower dissolved sulfide levels, higher dissolved oxygen levels, and increased densities of crab burrows and Sesarma crabs. Moreover, the elevation of the soil surface declined rapidly at artificial creek heads versus controls, suggesting that crabs were increasing erosion. Our results suggest that abiotic conditions for crabs are better at the leading edge of the creek head than the trailing edge, explaining the directional movement of the front. Moreover, the speed at which the front propagates appears to be limited by the rate at which the creekhead erodes, rather than by crab mobility. The directional and slow movement of Sesarma fronts compared to consumer fronts of other invertebrates appears to result from the inextricable link between Sesarma and marsh geomorphology, whereas other consumer fronts are associated mostly with food resources.

Methodology for the nonlinear coupled multi‐physics simulation of mineral dissolution

AbstractThis article presents a numerical methodology for the simulation of mineral dissolution which couples brine flow, dissolved mineral transport, and cavity evolution. The proposed model considers both (1) the varying density brine flow within the cavity governed by the compressible Navier‐Stokes equations and (2) the evolution of the cavity boundary using a sharp interface model with a physically‐derived dissolution rate equation. The proposed nonlinear multi‐physics model can capture complex flow patterns such as the generation of a vortex in the cavity. The impact of those complex flow patterns on the cavity development can be studied because of the coupling of brine flow and dissolution front movement. The model employs a new strategy to explicitly track the dissolution front, which results in low computational cost for long‐term dissolution simulations. The proposed model is verified through a convergence analysis, showing both spatial and temporal convergence. Numerical simulations of mineral dissolution in horizontal cavities are conducted to investigate the flow velocity, mass fraction of dissolved mineral, cavity shape evolution, and dissolution rate over time. Additionally, a discussion on the effect of Peclet number on mineral dissolution in the cavity is undertaken.

Prediction of solute concentration gradients during growth of discontinuous precipitates in a Fe-13.5 at.% Zn alloy

The influence of Zn-concentration gradient on the occurrence of discontinuous precipitation has been analyzed in a Fe-13.5 at.% Zn alloy using the simulation method and Cahn′s diffusion model. The results have shown that the reaction front (RF) movement takes place by go- and -stop fashion accompanied by appropriate changes of Cahn′s parameter reaching maximum values, Cmax at the end of go- period. Then, the value of C decreases enabling relaxation of the RF and beginning of the next go- event. In this way, the simulation is the only one source of data showing how the solute concentration across the α phase lamella changes during the stop- period of the growth of discontinuous precipitates.The smaller thickness of the α phase lamellae and larger Cmax, the longer whole go- and –stop cycle, but not exceeding few seconds. The distance of RF movement is characterized by certain optimum value which is close to v = 45 nm/s regardless of the value of α phase lamella thickness.

A comprehensive investigation of the influence of clay minerals on oxidized and pyrolyzed cokes in in situ combustion for heavy oil reservoirs

Coke is the most important intermediate product during an in situ combustion for maintaining the combustion front stability. Coke is classified as oxidized and pyrolyzed based on the reaction mechanism. The clay minerals exhibit a catalytic effect on the formation and reaction of coke. In this study, a comprehensive experiment was performed to investigate the influence of four clay minerals on oxidized and pyrolyzed cokes. Results showed that these clay minerals exhibited a catalytic effect on the generation and reaction of coke at different levels. In the oxidation process montmorillonite and kaolinite exhibited an excellent catalytic effect on the generation of oxidized coke. In the pyrolysis process, montmorillonite, kaolinite, and illite could promote the breakage of C–S, C–N, and C–O bonds and reduce the number of heteroatoms. In the reaction process, the catalytic effect of montmorillonite induced the aggravation of the polymerization of hydrocarbon derivative with a large molecular weight, resulting in a low activity of the oxidized coke. Moreover, the montmorillonite can induce coke reaction in a low-temperature range, whereas the others exert only suppression effects on coke decomposition. The pyrolyzed coke achieves lower activation energy than the oxidized coke, proving that the pyrolyzed coke can be easily ignited under the reservoir condition. All clay minerals investigated herein can promote the reaction of pyrolyzed coke to different degrees. The montmorillonite achieves the lowest activation energy at 35 °C–100 °C and 350 °C–600°C stages, which benefits the movement of the combustion front.

Asymmetrical superelastic behavior of thermomechanically processed semi-equiatomic NiTi alloy in tensile and compressive modes of deformation

In the present work two different cold working and annealing schemes were utilized, and the asymmetric superelastic response of thermomechanically processed materials were then assessed through cyclic tensile and compressive modes of deformation. The values of transformation stress, transformation strain, and pseudoelastic strain were measured for each treated and solutionized specimens and the asymmetric response was compared. In the solution annealed state, the difference of these parameters at different deformation modes was negligible due to the weak texture of the material, while for thermomechanically treated ones, development of specific deformation and recrystallization texture components was identified to be one of the underlying reasons of intensified asymmetry. The evolved substructure during the thermomechanical processing also played a substantial role in determining the asymmetric response. The presence of fine grains and dense dislocation substructure could hinder the movement of the transformation front, thus limiting the range of transformation. In tensile mode, the transformation stress was lower, but higher transformation strain was achieved, which was discussed relying on the slip activity in specified oriented grains. The lower transformation strain in compression mode led to lower pseudoelastic strain due to the narrow transformation range which finally degraded superelastic response of the material.