Shape Of Flow Curves Research Articles

Investigation of predictive factors for the presence of voiding dysfunction after transvaginal mesh surgery-Can the flow curve shape on uroflowmetry be a predictor?

This study established the prognostic significance of the uroflowmetry flow curve shape in the presence of voiding dysfunction following transvaginal mesh surgery. This is a retrospective study of 439 symptomatic cystocele patients who underwent anterior wall repair with transvaginal mesh surgery. Uroflowmetry and postvoid residual were used to evaluate voiding function both preoperatively and 12 months postoperatively. The patients were divided into two groups: those with and without postoperative voiding dysfunction, and the predictors of postoperative voiding dysfunction were analyzed. The shape of the urine flow curve was analyzed for its influence on the presence of postoperative voiding dysfunction. Thirty-five participants were in the voiding dysfunction group, while 404 were in the nonvoiding dysfunction group. Multivariate analysis was conducted by adding an interrupted-shaped curve to age, Qmax, and postvoid residual, which showed significant differences in univariate analysis, found that age 68 years or older (odds ratio [OR]: 7.68, 95%CI 1.02-58, p=0.048), postvoid residual ≥110 mL (OR: 2.8, 95%CI 1.25-6.29, p=0.013) and interrupted-shaped curve (OR: 2.47, 95%CI 1.07-5.69, p=0.034) were discovered to be independent risk factors for the presence of voiding dysfunction after transvaginal mesh surgery. Following transvaginal mesh surgery for cystocele, three variables were found to be predictive of voiding dysfunction: the old age, excessive postvoid residual, and an interrupted-shaped flow curve. The uroflowmetry flow curve shape has the potential to be a new predictor of postoperative voiding dysfunction.

Effect of tartaric acid on the hydration of oil well cement at elevated temperatures between 60 °C and 89 °C

In order to study the abnormal viscosity evolution behavior of oil well cement slurries containing tartaric acid, the influence of tartaric acid on the early-age hydration of oil well cement at high temperatures was investigated by isothermal calorimetry (IC), thermogravimetric analysis (TGA) and quantitative XRD (QXRD) analysis in the temperature range of 60 °C to 89 °C. Results show that, a high dosage of tartaric acid can fundamentally change the typical shape of the cement hydration heat flow curve - two additional exothermic peaks associated with aluminate phase hydration (C3A and C4AF) appear before the main hydration peak. The unsynchronized hydration of the aluminate phases and the silicate phases was found to be the cause of premature setting. Additionally, long-term curing study (up to 28 d) showed that increasing the dosage of tartaric acid decreased the ultimate hydration extent of C2S while it increased the ultimate hydration extent of C4AF.

Evolution of Annealing Twins in a Hot Deformed Nickel-Based Superalloy.

The hot deformation characteristics of a GH4169 superalloy are investigated at the temperature and strain rate ranges of 1193–1313 K and 0.01–1 s−1, respectively, through Gleeble-3500 simulator. The hot deformed microstructures are analyzed by optical microscopy (OM), transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD) technology. The effects of deformation parameters on the features of flow curves and annealing twins are discussed in detail. It is found that the shapes of flow curves are greatly affected by the deformation temperature. Broad peaks appear at low deformation temperatures or high strain rates. In addition, the evolution of annealing twins is significantly sensitive to the deformation degree, temperature, and strain rate. The fraction of annealing twins first decreases and then rises with the added deformation degree. This is because the initial annealing twin characters disappear at the relatively small strains, while the annealing twins rapidly generate with the growth of dynamic recrystallized grains during the subsequent hot deformation. The fraction of annealing twins is relatively high when the deformation temperature is high or the strain rate is low. In addition, the important role of annealing twins on dynamic recrystallization (DRX) behaviors are elucidated. The obvious bulging at initial twin boundaries, and the coherency of annealing twin boundaries with dynamic recrystallized grain boundaries, indicates that annealing twins can motivate the DRX nucleation during the hot deformation.

Milkability traits across milk flow curve types in Sarda sheep

A temporary interruption of the milk flow is observed between alveolar and cisternal fraction in ewes for the peculiar anatomy of the mammary gland. Often during milking a physiological delay in milk excretion between the cisternal and the alveolar fraction occurs. However, long delays may indicate suboptimal pre-stimulation of teats and/or insufficient oxytocin release in the bloodstream, resulting in undesired protracted interruptions between the 2 milk peaks. Moreover, a clear distinction between the fractions may be undetectable in high-producing ewes, particularly in early lactation. Based on both milk flow curve shape and duration of different excretion phases during milking, 3 curve types can be identified: single-peak (P1), double-peak (P2), and long plateau (PL). The aim of the present study was to compare milkability traits across the 3 milk flow curve types using data recorded in Sarda sheep breed; for this scope, 10 features were measured with a milkmeter in 568 ewes belonging to different parities, lactation stages, and commercial farms. After editing, data of 544 ewes reared in 17 farms were available for the analysis. The P1 curves were the most frequent (57.5 %), but ewes with a PL curve were significantly more productive than those with a P1 curve (0.61 ± 0.03 vs 0.53 ± 0.02 kg of milk/milking). Milk yield of P2 ewes was intermediate (0.58 ± 0.03 kg of milk/milking) and in all curves the majority of milk was excreted in the first 60 s of milking. The highest milk flow rate and the shortest milk emission time were estimated for the P1 curves; moreover, the blind time, indicator of overmilking, was the minimum in PL curves and the maximum in P1 curves. Based on such findings, farmers are recommended to pay more attention to milk emission curves in their herd in order to avoid overmilking, particularly in the presence of P1 curves. Considering the large herd size of Sarda breed farms (170.3 ewes per farm in 2020), part of milking routine could be slightly modified and customized according to milk flow curve type and lactation stage. Ideally, this will allow optimal milking practices to be adopted within groups of ewes with similar milkability. Monitoring milk emission curves and adopting less-standard and more adjusted milking practices is useful to meet the ewe’s individual milking ability and in the long term would limit mammary gland stress, reduce antimicrobial use due to udder issues, and improve the udder health in Sarda sheep.

MP51-06 A CALL TO DISCONTINUE THE USE OF FLOW SHAPES IN PEDIATRIC UROFLOWMETRY

You have accessJournal of UrologyPediatric Urology IV (MP51)1 Sep 2021MP51-06 A CALL TO DISCONTINUE THE USE OF FLOW SHAPES IN PEDIATRIC UROFLOWMETRY Jason Van Batavia, Hans Pohl, Walid Farhat, George Chiang, Ahmad Bani Hani, Therese Collett-Gardere, and Israel Franco Jason Van BataviaJason Van Batavia More articles by this author , Hans PohlHans Pohl More articles by this author , Walid FarhatWalid Farhat More articles by this author , George ChiangGeorge Chiang More articles by this author , Ahmad Bani HaniAhmad Bani Hani More articles by this author , Therese Collett-GardereTherese Collett-Gardere More articles by this author , and Israel FrancoIsrael Franco More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002077.06AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Uroflow curves are read on a regular basis and are considered an essential tool in the evaluation and management of patients with voiding dysfunction. Unfortunately, the actual inter-rater reliability is poor in many instances. Our aim was to investigate what the inter-rater reliability (IRR) is among 5 disparate reviewers without any relationship in their training pedigree. METHODS: We obtained deidentified uroflow curves from 5 centers which were read by 5 seasoned pediatric urologists with different training backgrounds. 1 reviewer and his NP reviewed studies separately to assess the effect of similar pedigrees. All flow data was recorded, and the readings were all recorded for each curve and then a Fleiss inter rater kappa was generated for the group. The similar pedigree 2 person readers also were scored as well using the fleiss IR kappa. Descriptive statistics were generated on all the data along with subgrouping based on the flow curve shapes along with the sex. RESULTS: We reviewed 405 studies from females who averaged 9.3 yrs and 121 studies from males who were 10.6 yrs. When shapes are defined by the Q avg flow index based on the cutoffs of <=0.67 for plateau and >=1.33 for tower we see the following rates of agreement. We saw very low IRR as evidenced by the Fleiss Kappa for these studies as outlined in the tables above. The best result was obtained by using the Qavg flow index to describe the flow characteristics where we were able to obtain a kappa of 0.773. This finding clearly demonstrates what we learned from discriminant analysis which picks Qavg FI as the dominant characteristic to define shapes as well. CONCLUSIONS: It is quite clear that a kappa of 0.156 is indicative of very poor IRR between disparate seasoned pediatric urologists who all have different pedigrees with regards to training. These findings contradict other studies where personnel trained in the same center have relatively good kappa’s and substantiates the finding of the recent paper by Netto et al where in a global survey the IRR was poor. The fact that the kappa for the shape based on a cut off of 1 S.D. below and above the Q avg flow index has a kappa of 0.773 represents a much better way to define uroflowmetry and substantiates our call to abandon the use of the arbitrarily defined flow shapes which are incapable of consistent reading across disparate readers. Source of Funding: None © 2021 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 206Issue Supplement 3September 2021Page: e898-e898 Advertisement Copyright & Permissions© 2021 by American Urological Association Education and Research, Inc.MetricsAuthor Information Jason Van Batavia More articles by this author Hans Pohl More articles by this author Walid Farhat More articles by this author George Chiang More articles by this author Ahmad Bani Hani More articles by this author Therese Collett-Gardere More articles by this author Israel Franco More articles by this author Expand All Advertisement Loading ...

Clinical validation of an audio-based uroflowmetry application in adult males.

Uroflowmetry is a common test to evaluate lower urinary tract symptoms. Audio-based uroflowmetry is a novel, alternative approach that determines urine flow by measuring sound. Available as a smartphone application, it has potential for screening and monitoring common urological pathologies, particularly in out-of-office environments. This study is the first to evaluate audio-based uroflowmetry in a clinical setting against the gold standard. Adult male patients (n=44) attending a general urology clinic were recruited. Audio-based uroflowmetry and conventional uroflowmetry were performed concurrently. Pearson correlation and Bland-Altman analysis were used to compare performance with respect to max flow, time to max flow, and total voiding time. Symmetric mean absolute percentage error (SMAPE) was used to compare curve shapes. Repeatability was evaluated separately in three healthy volunteers using repeat measures correlation. Among urology clinic patients, the correlation for max flow was 0.12. Correlation for time to max flow was 0.46, with limits of agreement of -120-165%. Correlation for total voiding time was 0.91, with limits of agreement of -41-38%. The SMAPE for curve shape was 32.6%, with corresponding accuracy of 67.4%. Among healthy volunteers, the repeat measures correlation for max flow was 0.72. Audio-based uroflowmetry was inconsistent in evaluating flow rate, attributable to high variability and difficult standardization for acoustic signals. Performance improved with respect to temporal variables, as well as flow curve shape. Further work evaluating intra-patient reliability and pathology-specific performance is required to fully evaluate audio-based uroflowmetry as a screening or monitoring tool.

FepiM: A Novel Inverse Piecewise Method to Determine Isothermal Flow Curves for Hot Working

In forming simulations, flow curves are cardinal inputs to predict features, such as forming forces and material flow. The laboratory-scale experiments to determine them, like compression or tensile tests, are affected by deformation heating, restricting direct flow curve determination. In principle, the current analytical and inverse methods determine flow curves from these tests, but while the analytical methods assume a simplified temperature profile, the inverse methods require a closed-form flow curve equation, which mostly cannot capture complex material behavior like multiple recrystallization cycles. Therefore, the inverse piecewise flow curve determination method “FepiM” previously developed and published by the current authors is extended by introducing a two-step procedure to obtain isothermal flow curves at elevated temperatures and different strain rates. Thereby, the flow curve is represented as tabular data instead of an equation to reproduce complex flow curve shapes while also compensating the effect of inhomogeneous temperature profiles on the flow stress. First, a flow curve at the highest temperature is determined. In the second step, using this first flow curve as a reference, the flow curves at lower temperatures are obtained via interpolation. Flow curves from conventional compression tests for aluminum and copper in the temperature range of 20–500 °C are predicted, and it is shown that these flow curves can reproduce the experimental forces with a maximum deviation of less than 1%. Therefore, the proposed new piecewise method accurately predicts isothermal flow curves for compression tests, and the method could be further extended to highly inhomogeneous methods in the future.

Flow Curve and Microstructure Analysis of a ZK60 Magnesium Alloy during Hot Compression Tests

In this work, a commercial extruded Mg-6Zn-0.5Zr (ZK60) magnesium alloy was compressed to investigate the correlations among flow curve shape, microstructure evolution and loading parameters in terms of strain rate and deformation temperature. According to the results, twinning played an important role during deformations below 250 °C and the number of twinning bands increased with the increase in strain rate. Twinning caused initially softening followed by hardening. The flow curve shape before peak stress was determined by the number of twinning bands that were initiated. Dynamic recrystallization (DRX) was initiated during deformations at temperatures higher than 150 °C, and the DRX grain size decreased with strain rate and increased with deformation temperature. At 400 °C, twinning was not initiated and the microstructure of the specimens was composed of both DRX and SRX (static recrystallization) grains.

Hot deformation behavior and microstructure characteristic of 2055 Al-Li alloy during uniaxial compression

The hot deformation behavior of as-extruded 2055 Al-Li alloy at T6 state has been investigated by uniaxial hot compression test in a Gleeble-3800 thermal simulation machine at the temperature of 320 oC, 380 oC, 440 oC, 500 oC with strain rate ranging from 0.001 s−1 to 1 s−1. Deformation instability occurred under the deformation condition of 380 oC/5 s−1 and at the deformation temperature of 500 oC via the shape of flow curve and the side view observation of the compressed samples. The serration in flow curve of the low strain rate suggests occurring of DSA. The constitutive equation based on Arrhenius equation were established with the deformation activation energy of 174.6 kJ mol−1. The microstructures of the compressed samples were analyzed by OM and TEM, the DRXed grains could be observed in the compressed samples at 440 oC with strain rate of 1 s−1 and 0.001 s−1. The dominated precipitates in the alloy were plate-shaped T1 phase and spherical β1 phase. The precipitates-dislocations interaction was analyzed by HRTEM. The dislocations could be pinned by both the T1 phase and β1 phase, and the precipitates and dislocations around them divided the grain into small zones, and the misorientation across the dislocation was about 0.8o.

Hot Deformation Behavior and Processing Map of a Cu-Bearing 2205 Duplex Stainless Steel

The hot deformation behavior and processing map of Cu-bearing 2205 duplex stainless steel (2205-Cu DSS) were investigated at temperatures of 950–1150 °C and strain rates of 0.01–10 s−1. The effects of Cu addition and different deformation parameters on deformation behavior were, respectively, characterized by analyzing flow curves, constitutive equations and microstructures. The results indicated that the shapes of flow curves strongly depended on the volume fraction of two phases. When deformed at low strain rate, DRV in ferrite was prompted with increase in the temperature and was further developed to continuous DRX. At high strain rate, flow localization preferentially occurred in ferrite at low deformation temperature due to the strain partitioning and relatively less fraction of ferrite. The activation energy for 2205-Cu DSS was 452 kJ/mol and was found to connect with the variation of strain, strain rate and deformation temperature. The optimum hot deformation parameters for 2205-Cu DSS were obtained in the temperature range of 1100–1150 °C and strain rate range of 0.1–1 s−1 with a peak power dissipation efficiency of 41%. Flow localization was the main way to lead to flow instability. Meanwhile, the Cu-rich precipitates were generated within a few ferrite grains when deformed at temperature lower than 1000 °C. The interaction between dislocations and Cu-rich precipitates at high strain rate, as well as the limited DRV in ferrite and DRX in austenite, contributed to the complex microstructure and flow behavior.

Thermal decomposition characteristic and kinetics of DINA

N-Nitrodihydroxyethyl dinitrate (DINA) is a useful energetic plasticizer in double-base propellant. To analyze the potential hazards of its thermal decomposition, the differential scanning calorimetry (DSC) was used to test the thermal behavior of DINA under non-isothermal and isothermal conditions. It is found from the non-isothermal DSC results, that the melting point of DINA is about 50 °C, the initial exothermic decomposition temperature (T onset) is between 177.46 and 189.60 °C with the heating rate 2, 4, 8 and 10 °C min−1, and its decomposition enthalpy (ΔH d) is about 3235.63 J g−1. Both the shapes of heat flow curves and activation energy curves, calculated by Friedman method, indicate the exothermic decomposition of DINA contains at least four reactions (P1–P4), which were separated into four curves by AKTS software according to the four peaks. The relatively constant E(α) of P1, P2, P3 and P4 verifies this four peaks are likely to be described by a single reaction model. The method proposed by ICTAC was used to determine the most suitable reaction function and kinetic parameters of DINA decomposition, the results show that P1 and P2 follow the Z–L–T model and the Avrami–Erofeev model, respectively, both of them are autocatalytic models, which is consistent with the isothermal DSC results. The reaction model of P3 cannot be obtained, while P4 corresponds to n-order reaction, f(α) = (1 − α)1.67.

The experimental modeling of gas percolation mechanisms in a coal-measure tight sandstone reservoir: A case study on the coal-measure tight sandstone gas in the Upper Triassic Xujiahe Formation, Sichuan Basin, China

Tight sandstone gas from coal-measure source rock is widespread in China, and it is represented by the Xujiahe Formation of the Sichuan Basin and the Upper Paleozoic of the Ordos Basin. It is affected by planar evaporative hydrocarbon expulsion of coal-measure source rock and the gentle structural background; hydrodynamics and buoyancy play a limited role in the gas migration-accumulation in tight sandstone. Under the conditions of low permeability and speed, non-Darcy flow is quite apparent, it gives rise to gas-water mixed gas zone. In the gas displacing water experiment, the shape of percolation flow curve is mainly influenced by core permeability. The lower the permeability, the higher the starting pressure gradient as well as the more evident the non-Darcy phenomenon will be. In the gas displacing water experiment of tight sandstone, the maximum gas saturation of the core is generally less than 50% (ranging from 30% to 40% and averaging at 38%); it is similar to the actual gas saturation of the gas zone in the subsurface core. The gas saturation and permeability of the core have a logarithm correlation with a correlation coefficient of 0.8915. In the single-phase flow of tight sandstone gas, low-velocity non-Darcy percolation is apparent; the initial flow velocity (Vd) exists due to the slippage effect of gas flow. The shape of percolation flow curve of a single-phase gas is primarily controlled by core permeability and confining pressure; the lower the permeability or the higher the confining pressure, the higher the starting pressure (0.02–0.08 MPa/cm), whereas, the higher the quasi-initial flow speed, the longer the nonlinear section and the more obvious the non-Darcy flow will be. The tight sandstone gas seepage mechanism study shows that the lower the reservoir permeability, the higher the starting pressure and the slower the flow velocity will be, this results in the low efficiency of natural gas migration and accumulation as well as low gas saturation. The laboratory modeling on gas migration accumulation mechanism in coal-measure tight sandstone can provide a theoretic foundation to reveal the tight sandstone gas enrichment regularity, evaluation of prospecting area, and the study of development mechanism.

Compressive mechanical behavior of Al/Mg composite rods with different types of Al sleeve

In the present study, mechanical behavior of two types of Al/Mg composite rods, Mg AZ31 core/soft Al 1100 sleeve and Mg AZ31 core/hard Al 7050 sleeve, under compression along the extrusion direction (ED) was systematically studied, with a great emphasis on the effect of different Al sleeves and Al fractions. The rule of mixtures for flow curve was also addressed. Our results show that the strength and fraction of Al sleeve greatly affect the shape of flow curves of Al/Mg rods. A plateau shape that often exists in flow curve of compression along the ED of a monolithic Mg extruded rod also appears in that of the Al/Mg rods. This plateau completely disappears with the fraction of Al 7050 up to 78.7%, but is still visible with Al 1100 86%. A fluctuation exists in the flow curves of composite with the soft Al 1100 sleeve, but is absent in those with the hard Al 7050 one. Different types of Al sleeve hardly affect the {101¯2} twinning fraction in Mg core during ED compression. Compared to the soft Al 1100 sleeve, a hard 7050 one contributes to a homogeneous deformation of the whole composite and, hence, reduces the propensity for cracking at Al/Mg interface. The measured yield strengths of Al/Mg rods slightly deviate from the predicted ones by the rule of mixtures (about 4–36 MPa), while the rule of mixtures for the compressive flow curves does not work. It is found for the first time that the quite different strain hardening behaviors between the Mg core and the Al sleeve result in the large deviation of the experimental curves from the predicted ones.

Determination of the optimizing operating procedure for DSC test of wax-solvent samples with narrow and sharp wax peak and error analysis of data reliability

Differential scanning calorimetry (DSC), as a convenient and reliable thermal analysis technique, is widely used to analyze wax precipitation characteristics. This paper studies the optimizing operation conditions in DSC test for wax-solvent mixtures characterized by a narrow and sharp wax peak to promote the test reliability. The influences of cooling rate and isothermal time on the wax precipitation characteristics of wax-solvent samples are investigated through DSC experiments. The shape of heat flow curve, wax precipitation temperature and measured wax content are all affected. According to the stability and repeatability of test results, the optimizing procedure is determined for this kind of oil samples. What is more, this paper analyzes the applicability of the optimizing procedure on a crude oil sample with broad and mild wax peak. Experiment errors in the parallel experiments conducted under the determined procedure are checked, and all of them are in acceptable error ranges. This study may provide a meaningful reference for DSC application and a rethink of the test standard in practical operation for particular waxy mixtures.

Determination of the first normal stress difference from viscometric data for shear flows of polymer liquids

New equation for determination of the primary normal stress difference from viscosity curve is proposed, and the methods of calculations with the use of adequate viscosity models are discussed. Comparison of calculated and measured values of primary normal stress difference has shown that the proposed equation describes quite well experimental data but the calculations are not stable. For this reason, the proposed equation along with other equations of this type known from the literature was transformed into shear stress-dependent form. It was shown that such transformation makes it possible to represent the normal stress-to-shear stress ratio (Weissenberg number) as a unique function of the local slope of the flow curve, which is simultaneously temperature invariant. Such representation was confirmed using experimental data for eight systems comprising linear polymers and various measurement temperatures. It was found that new equation in the shear stress-dependent form is numerically stable and provides excellent description of experimental data. The general structure of expressions, which may be used for description of the elasticity of polymer liquids based on the flow curve shape, was discussed from the point of view of dimensional analysis. Obtained results made it possible to modify other expressions known from the literature in such way that they also provide an excellent fit to experimental data.

The flow behavior and the deformation mechanisms of Ti–6Al–2Zr–2Sn–2Mo–1.5Cr–2Nb alloy during isothermal compression

The effects of the processing parameters on the shapes of flow curves, the microstructural evolution and the strain rate sensitivity are analyzed via the isothermal compression tests of Ti–6Al–2Zr–2Sn–2Mo–1.5Cr–2Nb alloy. The isothermal compression is performed on a Gleeble-1500 thermal simulator in the deformation temperature range of 1103–1243 K, strain rate range of 1.0 × 10−2 to 5.0 s−1 and strain range of 0.2–1.2. The softening mechanisms are investigated thoroughly in the α+β phase region and β phase region through the experiments of optical microscopy, scanning electron microscopy and transmission electron microscopy. Then, the correlation between the flow behavior and the microstructural evolution is discussed. The results show that more noticeable flow softening at a high strain rate (5.0 s−1) in the α+β phase region arises from the thermal softening, the dynamic recovery and the dynamic recrystallization of alpha phase. However, the thermal softening can no longer be considered to be the major softening mechanism at a low strain rate (1.0 × 10−2 s−1). In the β phase region, the dynamic recovery and the dynamic recrystallization of β phase are main softening mechanisms. Moreover, the maximum m value of 0.3 occurs at a deformation temperature of 1163 K, a strain rate of 0.1 s−1 and a strain of 0.7, in which the microstructure is equiaxed and uniform.

Microstructural evolution and constitutive equations of Inconel 718 alloy under quasi-static and quasi-dynamic conditions

The deformation behavior of IN718 superalloy was investigated using the hot compression tests in the temperature range of 950–1100°C, and strain rates covering the quasi-static to the quasi-dynamic regions (0.001–10s−1). The shape of flow curves as well as the corresponding work hardening rates analysis was utilized to reveal the dynamic recrystallization (DRX) phenomena. DRX was the dominant restoration mechanism in the whole temperature and strain rate domains, which was characterized by the optical and EBSD images. Extended flow softening was observed at high strain rates due to the adiabatic heating and dislocations interaction. In addition to the assessment the capability of Sellars equations, a new constitutive equation based on the multiple variable regression analysis was proposed for modeling the peak stress as a function of strain rate and temperature. Besides the simple form of the proposed model, it has a good accuracy for predicting the peak stress.

The correlation between the flow behavior and the microstructure evolution during hot working of TC18 alloy

The effects of processing parameters on the flow stress, the strain rate sensitivity and the strain hardening exponent of TC18 alloy are investigated in present study. The isothermal compression is performed in the deformation temperature range of 993–1203K, strain rate range of 0.01–5.0s−1 and strain range of 0.5–1.2. The micro-mechanisms that might control flow behavior are analyzed using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results demonstrate that the shapes of flow curves are dependent on the competing processes of the work-hardening, the thermal softening and the microstructure-related softening. The maximum m-value of 0.45 occurs at a deformation temperature of 993K, a strain rate of 0.01s−1 and a strain of 0.5. At 0.1s−1, the m-value is approximately 0.20–0.27, implying that controlling deformation mechanism is dislocation glide/climb. At a deformation temperature of 1053K and a strain of 0.5, the levels of n-value decrease from 0.01s−1 and 1.0s−1, respectively, to 0.1s−1. The more significant softening effect at 0.1s−1 is attributed to the medium thermal softening and the microstructure-related softening.

Effect of the alpha grain size on the deformation behavior during isothermal compression of Ti–6Al–4V alloy

Abstract The effects of alpha grain size on the flow stress, the apparent activation energy for deformation (Q) and the processing maps of Ti–6Al–4V with an equiaxed microstructure are thoroughly investigated using isothermal compression tests, and detailed explanation is given based on the microstructure observation and quantitative analysis. The shapes of flow curves are dependent on the microstructure characteristic of the alloy before deformation and during the deformation process. The flow stress increases with increasing equiaxed alpha phase, but decreases with increasing alpha grain size. The Q-values for d r1 and d r2 are smaller than those for d r3 and d r4 , respectively, which is possibly attributed to that Ti–6Al–4V alloy for d r1 and d r2 which exhibits a very strong grain-boundary sliding (GBS) mode besides dominant dislocation glide/climb mechanism. The local efficiency maxima and unstable regions in processing maps change with the alpha grain size, which implies that proper hot-working domains should be modified in different grain size range so as to meet the precision forging process.

Correlation between grain size and flow stress during steady-state dynamic recrystallization

The mechanical behaviour and microstructure evolution during hot deformation remain a fundamental industrial topic for metallic materials. In the present paper, the correlation between grain size and flow stress during steady-state dynamic recrystallization (DRX) has been investigated from an internal-variable perspective. From the competition between work-hardening and recrystallization softening, a dynamic model of DRX evolution has been generalized by proposing an identification criterion on DRX continuity or periodicity. The dependence of grain size on deformation parameters under the DRX steady state has been obtained from the dynamic balance. An Arrhenius constitutive model for the DRX steady state has also been constructed from the Estrin-Mecking formula, and the stress exponent has been fixed as a constant equal to 6. The correlation between grain size and flow stress has been validated as an inverse proportion with the relevant exponent n=1/2. In addition, the influence of deformation parameters on flow curve shapes and grain coarsening/refinement has been characterized correspondingly.