Flow Stress Distribution Research Articles

Validation of Multi-scale Model Describing Microstructure Evolution in Steels

Properties of deformed steels depend on various microstructure parameters such as distribution of grain size and precipitates. Strain, strain rate and temperature inhomogeneities make quantitative prediction of microstructure difficult but the Finite Element method is able to model these inhomogeneities. Different scales of phenomena occurring in deformed materials are another difficulty in modelling. Microstructure evolution can be described by more realistic methods (e.g. Cellular Automata CA, Monte Carlo), which, on the other hand, are unable to simulate larger samples. Therefore, development of the methods capable of spanning multiple scales became a current challenge. CAFE modelling, which couples FE and CA methods, is the objective of the paper. The model consists of two layers. The micro-scale layer, simulated by CA, represents microstructure evolution including nucleation and growth of the grains. Evolution of a dislocation density is described for every grain separately by solving differential equation. The FE thermal-mechanical model is used as a macro-scale part. Multistage plane strain compression tests for niobium steel are considered. Distributions of initial and final grain size are measured during the tests. The results from the CAFE model are compared to the measurements and to the predictions by a conventional model. The comparisons confirm the capability of the CAFE method to predict flow stress, recrystallized fraction and grain size distribution. Conventional approach gives a good agreement with experiments for an average grain size only.

Finite-element analysis of V-ring indenter mechanism in fine-blanking process

In fine-blanking process, V-ring indenter is very important in increasing the edge quality of the blanked part. Previous research in this field was mainly experiment-based; therefore, the theoretical mechanism was not clarified. In this study, the V-ring indenter mechanism was investigated using the finite element method. The mechanism and effects of the V-ring indenter could be theoretically clarified on the basis of material flow analysis and stress distribution. The application of the V-ring indenter increased compressive stress before the cutting phase, and significantly suppressed the increased rotation of material flow during the cutting phase. This, in turn, caused increased hydrostatic compressive stress, resulting in a larger smooth cut surface.

Investigation of spring-go phenomenon using finite element method

Bending is an application used in the sheet metal forming processes in many industries. One of the main problems of the bending process is the occurrence of spring-back/spring-go. Past research has investigated the spring-back problem. However, the spring-go problem was rarely investigated. In this study, the spring-go phenomenon was investigated using the finite element method (FEM) on the V-bending process. The FEM simulation results clearly and theoretically clarified the spring-go phenomenon on the material flow analysis and stress distribution. The comparison between the spring-back and spring-go phenomena was also clarified.

Flow Characteristics in a Rotating Circular Flume

Increased construction activity and associated receiving water concerns in the Greater Toronto Area has prompted this study to advance our knowledge on cohesive sediment transport processes in rivers and lake environments. Flow characteristics in a rotating circular flume at the National Water Research Institute (NWRI), Burlington, Ontario were studied using a computational fluid dynamics (CFD) model. The objective of this study was to use a CFD model to predict the complex 3D turbulent flow characteristics, including the tangential flow velocity distribution, turbulent secondary flow circulation patterns, and the bed shear stress distributions. The numerical model was calibrated using experimental data collected using a Laser Doppler Anemometer for velocity profiles and measurements obtained by a Preston tube for bed shear stress distributions. Tangential velocity profiles and bed shear velocity distributions across the rotating circular flume were used to evaluate the accuracy of the model predictions. When compared with experimental smooth bed shear stress data, the model performed reasonably well for the range of flume speeds examined. The calibrated CFD model was then used for simulating a series of 210 scenarios using varying ring operating speeds over a range of flow depths and bed roughness heights. The numerical simulation results were then used to study the complex 3D turbulent flow conditions in the circular flume at NWRI, including velocity profiles, turbulence characteristics of flow and bed shear stress distributions.

Flow Characteristics in a Rotating Circular Flume

Increased construction activity and associated receiving water concerns in the Greater Toronto Area has prompted this study to advance our knowledge on cohesive sediment transport processes in rivers and lake environments. Flow characteristics in a rotating circular flume at the National Water Research Institute (NWRI), Burlington, Ontario were studied using a computational fluid dynamics (CFD) model. The objective of this study was to use a CFD model to predict the complex 3D turbulent flow characteristics, including the tangential flow velocity distribution, turbulent secondary flow circulation patterns, and the bed shear stress distributions. The numerical model was calibrated using experimental data collected using a Laser Doppler Anemometer for velocity profiles and measurements obtained by a Preston tube for bed shear stress distributions. Tangential velocity profiles and bed shear velocity distributions across the rotating circular flume were used to evaluate the accuracy of the model predictions. When compared with experimental smooth bed shear stress data, the model performed reasonably well for the range of flume speeds examined. The calibrated CFD model was then used for simulating a series of 210 scenarios using varying ring operating speeds over a range of flow depths and bed roughness heights. The numerical simulation results were then used to study the complex 3D turbulent flow conditions in the circular flume at NWRI, including velocity profiles, turbulence characteristics of flow and bed shear stress distributions.

An investigation of step taper-shaped punch in piercing process using finite element method

Abstract Nowadays, the technology on sheet metal forming has rapidly grown especially in the automotive and electrical industry. Furthermore, the strong concern is to obtain better product quality with lower cost. Therefore, in this study, the piercing process using the step taper-shaped punch was investigated in order to improve the pierced surface quality. Although past research has been studied on this process, most of them were studied with experiments. Therefore, the theoretical mechanism has not been clarified. In this study, the authors focused on the theoretical explanation of the piercing process using step taper-shaped punch (STSP) by using the finite element method (FEM) and also verified these FEM simulation results with experiments. As a result, the mechanism and effects of the taper angle could be theoretically clarified on the material flow analysis and stress distribution in FEM. Moreover, the suitable taper angle of approximately 6° obtained in this study corresponded well with past research done with experiments. Finally, the correspondence of the FEM simulation and experiment results indicated that the FEM simulation could be a useful tool to predict the pierced surface features of the piercing process using the STSP.

Finite element analysis of heat generation from different light-polymerization sources during cementation of all-ceramic crowns

Exothermic composite resin chemical reactions and visible light generators can produce heat during a restorative polymerization process. These thermal changes in restored teeth may cause pain and irreversible pulpitis. The purpose of this study was to analyze the temperature distribution and heat flow patterns of a crowned mandibular second premolar tooth model using 3 different light-polymerization technologies and a finite element technique. A 2-dimensional finite element model was used to simulate a clinical condition. Heat flow and thermal stress distribution in a tooth during cementation of an all-ceramic crown using 4 commercially available light-polymerization units (LPUs), each with different wavelengths (Elipar TriLight, Elipar Freelight, Apollo 95 E, and ADT 1000 PAC), were investigated. The temperature values were measured at 3, 10, 12, and 40 seconds for each light-polymerizing unit (LPU) at 6 different finite element nodes. Two-dimensional temporal and spatial distribution of the thermal stress within the tooth, including the thermal coefficients and boundary conditions of the dental materials, were obtained and evaluated. The temperature at the nodal points did not exceed 42 degrees C, which is a threshold value for tissue vitality within the recommended operating periods at the dentin and pulp surface for all LPUs, except for Elipar TriLight. In the case of Elipar TriLlight, the temperatures at the dentin and pulp surfaces were 47 degrees C and 42 degrees C, respectively. When the light-polymerization units were used according to the manufacturers' operating procedures and without prolonged operating periods, with the exception of Elipar TriLight, the investigated LPUs did not produce significant heat. However, when the operating periods were prolonged, unacceptable temperature increases were observed, especially with the high-intensity LPUs.

Stress and Flow beneath Island Arcs

The flow pattern, stress distribution, topography, and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the Aleutian arc. The results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench. In models with simple distributions of rheological parameters, the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc. Material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab. Models with the resistance to flow thus reduced had outer rises, deep trenches, horizontal tension seaward of the trench, horizontal compression under the trench, and downdip tension in the slab. Free air gravity anomalies, which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow, were not fit excellently by any of the models, in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc. An alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models. Shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench. This is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism.

PIV and CFD assessment of flow and shear stress distribution in central vein hemodialysis catheters

PIV and CFD assessment of flow and shear stress distribution in central vein hemodialysis catheters

Tubular heart valves: A new tissue prosthesis design—Preclinical evaluation of the 3F aortic bioprosthesis

It was hypothesized that native heart valves function as if they were simple tubes with sides that collapse when external pressure is applied. Because "form follows function," this hypothesis could theoretically be confirmed by implanting a simple tube into the anatomic position of any native heart valve and documenting that under the same anatomic constraints and physiologic conditions as the native valve, the tube would assume the form of that native valve. If the hypothesis were thus proved, it would follow that a tissue valve based on a tubular design would have superior flow dynamics and stress distribution and would therefore be expected to outlast currently available tissue valves. Such a tubular tissue valve, the 3F Aortic Bioprosthesis (3F Therapeutics, Inc, Lake Forest, Calif) was designed and tested in vitro against a commercially available stentless aortic bioprosthesis. With the use of state-of-the-art testing equipment, some of which had to be developed especially to test this truly stentless bioprosthesis in vitro, transvalvular gradients, effective orifice areas, degree of transvalvular laminar flow, finite element analysis of the distribution of leaflet stress, and accelerated wear testing for long-term durability were evaluated for the new 3F Aortic Bioprosthesis in comparison with the St Jude Medical Toronto SPV aortic bioprosthesis (St Jude Medical, Inc, St Paul, Minn). The valve gradients were lower and the effective orifice areas were greater for the 3F Aortic Bioprosthesis at all valve sizes and under all test conditions, including cardiac outputs ranging from 2.0 to 7.0 L/min, mean perfusion pressures from 40 to 200 mm Hg, and aortic compliances of 4% and 16%. The transvalvular flow across the 3F Aortic Bioprosthesis in vitro was qualitatively smooth, with a minimum of surrounding vortices. Maximum stress occurred in the belly of the leaflets of the 3F Aortic Bioprosthesis, with minimum stress at the commissural posts. The 3F Aortic Bioprosthesis was superior to the Toronto SPV valve in accelerated wear tests. These in vitro studies show that a tissue aortic valve designed on the basis of the proved engineering principle that form follows function has better hemodynamics, flow dynamics, stress distribution, and durability when compared under identical in vitro conditions with an excellent commercially available tissue aortic valve.

Prediction of Flow Stress and Microstructural Evolution during Hot Forging of Three Microalloyed Medium Carbon Steels

A constitutive relation is proposed in this study by introducing a function prescrbing the volume fraction of dynamically recrystallized grains into the Voce’s equation to predict the stress-strain relations for three microalloyed medium carbon steels. We performed hot torsion test in temperature range of 900-1100 and strain rate range of 0.05-5.0s-1 to obtain the flow stress-strain curves. The calculated flow stresses are in good agreement with the measured ones. We have then applied the equations in FE analysis to predict the distribution of dynamic recrystallization volume fraction and flow stress for hot forging.

Modelling of plane strain compression (PSC) test for aluminium alloys using finite elements and fuzzy logic

A semi-physical hybrid model has been developed for the prediction of material properties (i.e. stress/strain, recrystallisation behaviour and the internal states) for aluminium alloys. The model input variables are the temperature, strain-rate and strain. It predicts the material behaviour and properties under plain-strain compression (PSC) tests using a hybrid structure of intelligent models (neuro-fuzzy) and constitutive equations. An integration process incorporating both the hybrid and the finite element models has been undertaken, where the hybrid model is embedded into the finite element model and utilised for calculating the flow stress distribution for the PSC tests. The paper discusses the model developments and its integration into the final finite element model. This is demonstrated via some selected results when modelling plane strain compression tests of an Al–1%Mg alloy.

Modelling of plane strain compression (PSC) test for aluminium alloys using finite elements and fuzzy logic

A semi-physical hybrid model has been developed for the prediction of material properties (i.e. stress/strain, recrystallisation behaviour and the internal states) for aluminium alloys. The model input variables are the temperature, strain-rate and strain. It predicts the material behaviour and properties under plain-strain compression (PSC) tests using a hybrid structure of intelligent models (neuro-fuzzy) and constitutive equations. An integration process incorporating both the hybrid and the finite element models has been undertaken, where the hybrid model is embedded into the finite element model and utilised for calculating the flow stress distribution for the PSC tests. The paper discusses the model developments and its integration into the final finite element model. This is demonstrated via some selected results when modelling plane strain compression tests of an Al–1%Mg alloy.

くさび形工具によるアルミニウム円板の切断加エシミュレーション

Cutting of the circular aluminum sheets (1100P-H14, 1100P-O) by indentation of wedge shape punches was investigated as a process to achieve burr-free-cutting. Numerical simulations of the cutting process were conducted using a rigid plastic finite element code developed by the authors. The Jeong expression is used as a fracture criterion and was linked with the simulation. Metal flow and mean normal stress distributions at the deformation region of the sheet were calculated. The effects of nose angle and radius of the wedge shape punch on the cut edge profile are discussed based on the calculated results. To confirm the results of the finite element simulations, cutting experiments were also carried out. Cutting force with punch penetration depth was measured. And the shape of the cut edge was observed using an optical microscope. These experimental results can be explained well by the simulation results. From simulational and experimental results, it was clarified that the cutting process of the circular aluminum sheets of the burr-free was possible with wedge shape punch.

On establishing uniform channel flow with tail gate

Steady uniform flow is a basic reference condition for hydraulic analyses of water surface profiles, resistance, velocity and pressure distributions, and channel geometry effects for open-channel flows. In laboratory experiments uniform flow is often generated by adjusting tail and entrance gates such that the flow depth remains constant along the channel. This note shows that the constant depth criterion is necessary, but insufficient, to obtain a true uniform flow for which cross-sectional flow velocity and stress distributions should also remain unchanged for a short reach around the measurement section.

On establishing uniform channel flow with tail gate

Steady uniform flow is a basic reference condition for hydraulic analyses of water surface profiles, resistance, velocity and pressure distributions, and channel geometry effects for open-channel flows. In laboratory experiments uniform flow is often generated by adjusting tail and entrance gates such that the flow depth remains constant along the channel. This note shows that the constant depth criterion is necessary, but insufficient, to obtain a true uniform flow for which cross-sectional flow velocity and stress distributions should also remain unchanged for a short reach around the measurement section.

Effect of Weissenberg number on the flow structure: DNS study of drag-reducing flow with surfactant additives

A second-order finite difference scheme was employed for the DNS study of drag-reducing flow with surfactant additives. We focus on the effect of Weissenberg number (nondimensional relaxation time) on the flow structures. The instantaneous flow structures and stress distribution at different elasticities are compared. The effects of Weissenberg number on turbulence statistics such as turbulence intensities, Reynolds shear stress and two-point correlation coefficients are also presented.

Finite element simulation of warm deep drawing of aluminium alloy sheet when accounting for heat conduction

The deformation behaviour and the temperature change in cylindrical deep drawing of an aluminium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and the heat conduction finite element methods. The comparison with the experimental results shows that the forming limits and the necking sites are successfully predicted by the simulation. It is clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher limiting drawing ratio. The numerical as well as the experimental results show that the limiting drawing ratio in the warm deep drawing increases with the die profile radius.

A numerical study of blood flow patterns in anatomically realistic and simplified end-to-side anastomoses.

Recently, some numerical and experimental studies of blood flow in large arteries have attempted to accurately replicate in vivo arterial geometries, while others have utilized simplified models. The objective of this study was to determine how much an anatomically realistic geometry can be simplified without the loss of significant hemodynamic information. A human femoral-popliteal bypass graft was used to reconstruct an anatomically faithful finite element model of an end-to-side anastomosis. Nonideal geometric features of the model were removed in sequential steps to produce a series of successively simplified models. Blood flow patterns were numerically computed for each geometry, and the flow and wall shear stress fields were analyzed to determine the significance of each level of geometric simplification. The removal of small local surface features and out-of-plane curvature did not significantly change the flow and wall shear stress distributions in the end-to-side anastomosis. Local changes in arterial caliber played a more significant role, depending upon the location and extent of the change. The graft-to-host artery diameter ratio was found to be a strong determinant of wall shear stress patterns in regions that are typically associated with disease processes. For the specific case of an end-to-side anastomosis, simplified models provide sufficient information for comparing hemodynamics with qualitative or averaged disease locations, provided the "primary" geometric features are well replicated. The ratio of the graft-to-host artery diameter was shown to be the most important geometric feature. "Secondary" geometric features such as local arterial caliber changes, out-of-plane curvature, and small-scale surface topology are less important determinants of the wall shear stress patterns. However, if patient-specific disease information is available for the same arterial geometry, accurate replication of both primary and secondary geometric features is likely required.

The prediction of the hot strength in steels with an integrated phenomenological and artificial neural network model

Abstract The hot torsion data of a commercial 304 stainless steel has been analysed with an integrated phenomenological-artificial neural network model (IPANN), developed from the Estrin–Mecking (EM) phenomenological model and a back-propagation artificial neural network (ANN) model. In order to predict the flow stress in this model, the work-hardening coefficient and its product with the stress were used as inputs, along with strain, temperature and strain rate. The Pearson correlation coefficient was used to evaluate the performance and terminate the simulation of the IPANN model, whilst the standard errors were employed to quantitatively compare the accuracy of different models. The IPANN model is able to predict the distribution of flow stress more accurately in the work-hardening and dynamic recrystallisation regimes in comparison with the original EM and ANN models. The training speed is significantly improved and the test of the model is satisfactory, if reasonable training data is provided. In addition, by using the phenomenological model as training data, the IPANN model may be used for extrapolation.