The extrusion force and the mean strain rate during the extrusion of strain rate sensitive materials

The constitutive relation for the Reynolds stress tensor is considered for turbulence developing in axisymmetric strain fields. It is confirmed that the Reynolds stress tensor is aligned linearly with the mean strain rate. In contrast to the Prandtl-Kolmogorov, hypothesis, the effective viscosity is found to grow in proportion to the anisotropy of turbulence and the length scale based on the magnitude of the mean strain rate. Using invariant theory the effective viscosity is determined for the limiting states of turbulence. Additional analysis of the constitutive relations is supplemented for the dissipation and pressure-strain correlations. It is shown that analytical derivations are in excellent agreement with the data obtained from direct numerical simulations. [S0098-2202(00)02801-7]

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Inertial particle acceleration in strained turbulence

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.579 ◽

2015 ◽

Vol 785 ◽

pp. 31-53 ◽

Cited By ~ 6

Author(s):

C.-M. Lee ◽

Á. Gylfason ◽

P. Perlekar ◽

F. Toschi

Keyword(s):

Particle Acceleration ◽

Strain Rate ◽

Probability Density ◽

Energy Dissipation Rate ◽

Distribution Functions ◽

Inertial Particles ◽

Inertial Particle ◽

Mean Flow ◽

The Mean ◽

Mean Strain

The dynamics of inertial particles in turbulence is modelled and investigated by means of direct numerical simulation of an axisymmetrically expanding homogeneous turbulent strained flow. This flow can mimic the dynamics of particles close to stagnation points. The influence of mean straining flow is explored by varying the dimensionless strain rate parameter $Sk_{0}/{\it\epsilon}_{0}$ from 0.2 to 20, where $S$ is the mean strain rate, $k_{0}$ and ${\it\epsilon}_{0}$ are the turbulent kinetic energy and energy dissipation rate at the onset of straining. We report results relative to the acceleration variances and probability density functions for both passive and inertial particles. A high mean strain is found to have a significant effect on the acceleration variance both directly by an increase in the frequency of the turbulence and indirectly through the coupling of the fluctuating velocity and the mean flow field. The influence of the strain on the normalized particle acceleration probability distribution functions is more subtle. For the case of a passive particle we can approximate the acceleration variance with the aid of rapid-distortion theory and obtain good agreement with simulation data. For the case of inertial particles we can write a formal expression for the accelerations. The magnitude changes in the inertial particle acceleration variance and the effect on the probability density function are then discussed in a wider context for comparable flows, where the effects of the mean flow geometry and of the anisotropy at small scales are present.

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The Influence of Specimen Geometry and Strain Rate on the Portevin-Le Chatelier Effect and Fracture in an Austenitic FeMnC TWIP Steel

Metals ◽

10.3390/met10091201 ◽

2020 ◽

Vol 10 (9) ◽

pp. 1201

Author(s):

Jidong Kang ◽

Liting Shi ◽

Jie Liang ◽

Babak Shalchi-Amirkhiz ◽

Colin Scott

Keyword(s):

Strain Rate ◽

High Speed ◽

Twip Steel ◽

Image Correlation ◽

Specimen Geometry ◽

Dynamic Strain ◽

Mean Flow ◽

Chatelier Effect ◽

The Mean ◽

Mean Strain

We studied the Portevin-Le Chatelier effect and fracture behavior of a FeMnC TWIP steel using high speed digital image correlation by varying the specimen geometry (flat vs. round) and test strain rate (0.001 vs. 0.1 s−1). The results show that the mean flow stress, the mean strain hardening rate and the mean strain rate sensitivity parameters are all independent of the specimen geometry and are uncorrelated with the presence or not of Portevin-Le Chatelier (PLC) bands, the type of PLC bands observed or the critical strain for band formation. However, both the fracture strains and stresses and the PLC behavior are highly geometry and/or strain rate dependent. Dynamic strain aging (DSA) and in particular the presence of PLC instabilities appears to play an important but as yet unclear role in promoting premature necking and final fracture.

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Investigation of Changes in Fatigue Damage Caused by Mean Load under Block Loading Conditions

Materials ◽

10.3390/ma14112738 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2738

Author(s):

Roland Pawliczek ◽

Tadeusz Lagoda

Keyword(s):

Fatigue Life ◽

Fatigue Damage ◽

Strain Curve ◽

Mean Value ◽

Fatigue Properties ◽

Stress Strain ◽

Reference Case ◽

Block Loading ◽

The Mean ◽

Mean Strain

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads.

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Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions

Metals ◽

10.3390/met11020307 ◽

2021 ◽

Vol 11 (2) ◽

pp. 307

Author(s):

Matthias Bruchhausen ◽

Gintautas Dundulis ◽

Alec McLennan ◽

Sergio Arrieta ◽

Tim Austin ◽

...

Keyword(s):

Surface Roughness ◽

Fatigue Life ◽

Elevated Temperature ◽

Strain Rate ◽

Power Plants ◽

Research Effort ◽

Hold Time ◽

Strain Range ◽

Austenitic Steels ◽

Mean Strain

A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

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Abstract 14768: Echocardiographic Strain Outcomes of Cardiac Resynchronization Therapy in Patients With Chemotherapy Induced Cardiomyopathy

Circulation ◽

10.1161/circ.142.suppl_3.14768 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Fatima M Ezzeddine ◽

Antoine N Saliba ◽

Vaibhav Jain ◽

Hector R Villarraga ◽

Joerg Herrmann ◽

...

Keyword(s):

Cardiac Resynchronization Therapy ◽

Strain Rate ◽

Left Ventricular ◽

Cardiac Resynchronization ◽

Control Group ◽

Resynchronization Therapy ◽

Control Groups ◽

Left Ventricular Strain ◽

The Mean ◽

And Control

Introduction: Several chemotherapy agents, especially anthracyclines, are associated with the development of non-ischemic cardiomyopathy. When chemotherapy-induced cardiomyopathy (CHIC) is associated with left bundle branch block (QRS >150 ms) and a left ventricular ejection fraction (LVEF) of 35% or lower, cardiac resynchronization therapy (CRT) is often utilized to improve cardiac function and relieve symptoms. Hypothesis: CRT is associated with improvement in left ventricular strain in patients with CHIC. Methods: The study included 22 patients with CHIC and 44 age- and gender-matched controls with other types of NIC who underwent CRT implantation between 2004 and 2017. LVEF, left ventricular global longitudinal strain (GLS), systolic strain rate (SRS), and early diastolic strain rate (SRE) were assessed at baseline and 6-18 months after CRT. CRT response was defined as LVEF improvement by >5% after CRT. Results: CRT responders had a significant improvement in left ventricular GLS as compared to CRT non-responders in the control group, but not in the CHIC group (Table 1). The mean change in LVEF after CRT was similar between the CHIC and control groups (10 ± 10% versus 11 ± 11%, p= 0.67). The mean change in GLS after CRT was also similar between the two groups (-2.15 ± 4.32 versus -3.57 ± 4.02, p= 0.19). The proportion of patients whose LVEF increased by more than 5% was similar between the two groups (59% in the CHIC group versus 68% in the control group, p= 0.46). The mean changes in LV myocardial systolic and early diastolic strain rates were similar between the CHIC and control groups. Mean SRS decreased by 0.13 ± 0.14 in the CHIC group and by 0.34 ± 1.28 in the control group (p=0.45). Mean SRE increased by 0.06 ± 0.18 in the CHIC group and by 0.07 ± 0.22 in the control group (p=0.86). Conclusions: CRT is associated with improvement in left ventricular strain in patients with CHIC. Prospective studies are needed to further evaluate the echocardiographic strain outcomes of CRT in CHIC.

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Measurements and Characterization of Turbulence in the Tip Region of an Axial Compressor Rotor

Journal of Turbomachinery ◽

10.1115/1.4037773 ◽

2017 ◽

Vol 139 (12) ◽

Cited By ~ 4

Author(s):

Yuanchao Li ◽

Huang Chen ◽

Joseph Katz

Keyword(s):

Strain Rate ◽

Shear Layer ◽

Turbulent Flows ◽

Reynolds Stress ◽

Suction Side ◽

Stress And Strain ◽

Spatial And Temporal Variability ◽

Mean Flow ◽

The Mean ◽

Stress And Strain Rate

Modeling of turbulent flows in axial turbomachines is challenging due to the high spatial and temporal variability in the distribution of the strain rate components, especially in the tip region of rotor blades. High-resolution stereo-particle image velocimetry (SPIV) measurements performed in a refractive index-matched facility in a series of closely spaced planes provide a comprehensive database for determining all the terms in the Reynolds stress and strain rate tensors. Results are also used for calculating the turbulent kinetic energy (TKE) production rate and transport terms by mean flow and turbulence. They elucidate some but not all of the observed phenomena, such as the high anisotropy, high turbulence levels in the vicinity of the tip leakage vortex (TLV) center, and in the shear layer connecting it to the blade suction side (SS) tip corner. The applicability of popular Reynolds stress models based on eddy viscosity is also evaluated by calculating it from the ratio between stress and strain rate components. Results vary substantially, depending on which components are involved, ranging from very large positive to negative values. In some areas, e.g., in the tip gap and around the TLV, the local stresses and strain rates do not appear to be correlated at all. In terms of effect on the mean flow, for most of the tip region, the mean advection terms are much higher than the Reynolds stress spatial gradients, i.e., the flow dynamics is dominated by pressure-driven transport. However, they are of similar magnitude in the shear layer, where modeling would be particularly challenging.

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LES Investigation of Boussinesq Constitutive Relation Validity in a Corner Separation Flow

Volume 2C: Turbomachinery ◽

10.1115/gt2018-75792 ◽

2018 ◽

Author(s):

Jean-François Monier ◽

Nicolas Poujol ◽

Mathieu Laurent ◽

Feng Gao ◽

Jérôme Boudet ◽

...

Keyword(s):

Strain Rate ◽

Stress Tensor ◽

Reynolds Stress ◽

Constitutive Relation ◽

Strain Rate Tensor ◽

Separation Flow ◽

Compressor Cascade ◽

Corner Separation ◽

Reynolds Stress Tensor ◽

Mean Strain

The present study aims at analysing the Boussinesq constitutive relation validity in a corner separation flow of a compressor cascade. The Boussinesq constitutive relation is commonly used in Reynolds-averaged Navier-Stokes (RANS) simulations for turbomachinery design. It assumes an alignment between the Reynolds stress tensor and the zero-trace mean strain-rate tensor. An indicator that measures the alignment between these tensors is used to test the validity of this assumption in a high fidelity large-eddy simulation. Eddy-viscosities are also computed using the LES database and compared. A large-eddy simulation (LES) of a LMFA-NACA65 compressor cascade, in which a corner separation is present, is considered as reference. With LES, both the Reynolds stress tensor and the mean strain-rate tensor are known, which allows the construction of the indicator and the eddy-viscosities. Two constitutive relations are evaluated. The first one is the Boussinesq constitutive relation, while the second one is the quadratic constitutive relation (QCR), expected to render more anisotropy, thus to present a better alignment between the tensors. The Boussinesq constitutive relation is rarely valid, but the QCR tends to improve the alignment. The improvement is mainly present at the inlet, upstream of the corner separation. At the outlet, the correction is milder. The eddy-viscosity built with the LES results are of the same order of magnitude as those built as the ratio of the turbulent kinetic energy k and the turbulence specific dissipation rate ω. They also show that the main impact of the QCR is to rotate the mean strain-rate tensor in order to realign it with the Reynolds stress tensor, without dilating it.

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CORRELATIONS OF THE MEAN TIME AND MEAN MAGNITUDE OF ACCELERATING PRESHOCKS WITH THE ORIGIN TIME AND MAGNITUDE OF MAINSHOCK

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11406 ◽

2017 ◽

Vol 43 (4) ◽

pp. 2154

Author(s):

E. M. Scordilis

Keyword(s):

Standard Deviation ◽

South America ◽

Strain Rate ◽

Central Asia ◽

Earthquake Prediction ◽

Critical Region ◽

Origin Time ◽

The Mean ◽

Benioff Strain ◽

Mean Time

Forty-five preshock sequences preceding corresponding strong (M≥6.4) mainshocks which occurred recently (since 1980) in a variety of seismotectonic regimes (W. Mediterranean, Aegean, Anatolia, California, Japan, Central Asia, South America) have been examined to identify new predictive properties. It has been observed that the mean origin time, , and the mean magnitude, of the accelerating preshocks of each sequence are correlated with the origin time, tc, and the magnitude, M, of the mainshock, respectively. The following relations have been derived: where sa (in Joule ½ /yr.104 Km2 ) is the Benioff strain rate in each preshock (critical) region and σ is the corresponding standard deviation. The possibility for using these relations as constraints in attempts for intermediate term earthquake prediction is discussed.

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