Singular Fields in Plane-Strain Penetration

1991 ◽  
Vol 58 (4) ◽  
pp. 910-915 ◽  
Author(s):  
David Durban ◽  
Omri Rand
Keyword(s):  
Boundary Layer ◽  
Strain Rate ◽  
Plane Strain ◽  
Constitutive Relation ◽  
Solid Material ◽  
Material Behavior ◽  
Wall Friction ◽  
Friction Factors ◽  
Hardening Parameter ◽  
Strain Rate Hardening

Local singular fields are investigated in the vicinity of the vertex of a sharp wedge that penetrates a viscous solid. Material behavior is modeled by the usual powerlaw constitutive relation. Wall friction is accounted for by imposing friction factors along the walls of the wedge. The case of a Newtonian fluid is investigated analytically, and sample numerical results are presented for nonlinear strain rate hardening. It is shown that the exponent of strain rate singularity increases as the wedge becomes sharper and smoother. Increasing the hardening parameter also results in a stronger strain rate singularity. High levels of wall friction induce an intensive shear boundary layer near the wall.

Numerical Analysis of Plane-Strain Tension Test for Rate-Dependent Solids

1992 ◽  
Vol 59 (3) ◽  
pp. 485-490 ◽  
Author(s):  
P. Tugˇcu
Keyword(s):  
Numerical Analysis ◽  
Strain Rate ◽  
Plane Strain ◽  
Rate Sensitivity ◽  
Tension Test ◽  
Engineering Strain ◽  
Plane Strain Tension ◽  
Rate Dependent ◽  
Strain And Strain Rate ◽  
Strain Rate Hardening

The plane-strain tension test is analyzed numerically for a material with strain and strain-rate hardening characteristics. The effect of the prescribed rate of straining is investigated for an additive logarithmic description of the material strain-rate sensitivity. The dependency to the imposed strain rate so introduced is shown to have a significant effect on several features of the load-elongation curve such as the attainment of the load maximum, the onset of localization, and the overall engineering strain.

Verification of a Thermoviscoplastic Constitutive Relation for Brass Material Using Taylor's Test

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Farid Abed ◽  
Tomasz Jankowiak ◽  
Alexis Rusinek
Keyword(s):  
Strain Rate ◽  
Dynamic Behavior ◽  
Constitutive Relation ◽  
Split Hopkinson Pressure Bar ◽  
Constitutive Relations ◽  
Strain Curve ◽  
Material Behavior ◽  
Experimental Results ◽  
Face Centered Cubic ◽  
Test Technique

This paper presents a methodology to define and verify the dynamic behavior of materials based on Taylor's test. A brass alloy with a microstructure composed mainly of two pure metals that have two different crystal structures, copper (face-centered cubic (fcc)) and zinc (hexagonal closed-packed (hcp)), is used in this study. A combined approach of different principal mechanisms controlled by the emergence and evolution of mobile dislocations as well as the long-range intersections between forest dislocations is, therefore, adopted to develop accurate definition for its flow stress. The constitutive relation is verified against experimental results conducted at low and high strain rates and temperatures using compression screw machine and split Hopkinson pressure bar (SHPB), respectively. The present model predicted results that compare well with experiments and was capable of simulating the low strain rate sensitivity that was observed during the several static and dynamic tests. The verified constitutive relations are further integrated and implemented in a commercial finite element (FE) code for three-dimensional (3D) Taylor's test simulations. A Taylor's test enables the definition of only one point on the stress–strain curve for a given strain rate using the initial and final geometry of the specimen after impact into a rigid surface. Thus, it is necessary to perform several tests with different geometries to define the complete material behavior under dynamic loadings. The advantage of using strain rate independent brass in this study is the possibility to rebuild the complete process of strain hardening during Taylor's tests by using the same specimen geometry. Experimental results using the Taylor test technique at a range of velocity impacts between 70 m/s and 200 m/s are utilized in this study to validate the constitutive model of predicting the dynamic behavior of brass at extreme conditions.

Steady Penetration of a Rigid Cone With a Rough Wall Into a Power-Law Viscous Solid

1991 ◽  
Vol 58 (4) ◽  
pp. 872-880 ◽  
Author(s):  
N. A. Fleck ◽  
D. Durban
Keyword(s):  
Boundary Layer ◽  
Strain Rate ◽  
Power Law ◽  
Eigenvalue Analysis ◽  
Rough Wall ◽  
Wall Friction ◽  
Stress Fields ◽  
Wall Roughness ◽  
Perfectly Plastic ◽  
Special Cases

Singular strain rate and stress fields are examined at the tip of a rigid conical indentor penetrating an incompressible viscous solid. Attention is focused on friction effects induced by wall roughness. The problem is formulated within the usual framework of eigenvalue analysis of locally singular fields. Some special cases are investigated further with emphasis on a boundary layer expansion for the rigid/perfectly plastic solid sliding along the perfectly rough wall. It has been found that the level of singularity increases as the cone becomes sharper and the wall friction decreases. Numerical results, presented for a variety of cases, suggest a boundary layer build up for sharp cones with rough walls.

Constitutive Relation of Yunjialing Anthracite Under Medium Strain Rate

2007 ◽  
Vol 17 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Wen-jiao GAO ◽  
Ren-liang SHAN ◽  
Gong-cheng WANG ◽  
Rui-qiang CHENG
Keyword(s):  
Strain Rate ◽  
Constitutive Relation ◽  
Medium Strain Rate

Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures

2010 ◽  
Author(s):  
Christian Eichler ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Wall Friction ◽  
Evaluation Procedure ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Flame Flashback ◽  
Turbulent Wall

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.

scholarly journals Rate-dependent ductile fracture under plane strain tension: experiments and simulations

2018 ◽  
Vol 183 ◽  
pp. 02022
Author(s):  
Vincent Grolleau ◽  
Vincent Lafilé ◽  
Christian C. Roth ◽  
Bertrand Galpin ◽  
Laurent Mahéo ◽  
...  
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Plane Strain ◽  
Static Loading ◽  
High Strain ◽  
Fracture Initiation ◽  
Surface Strain ◽  
Experimental Program ◽  
Loading Conditions ◽  
Plane Strain Tension

Among all other stress states achievable under plane stress conditions, the lowest ductility is consistently observed for plane strain tension. For static loading conditions, V-bending of small sheet coupons is the most reliable way of characterising the strain to fracture for plane strain tension. Different from conventional notched tension specimens, necking is suppressed during V-bending which results in a remarkably constant stress state all the way until fracture initiation. The present DYMAT talk is concerned with the extension of the V-bending technique from low to high strain rate experiments. A new technique is designed with the help of finite element simulations. It makes use of modified Nakazima specimens that are subjected to V-bending. Irrespective of the loading velocity, plane strain tension conditions are maintained throughout the entire loading history up to fracture initiation. Experiments are performed on specimens extracted from aluminum 2024-T3 and dual phase DP450 steel sheets. The experimental program includes quasi static loading conditions which are achieved on a universal testing machine. In addition, high strain rate experiments are performed using a specially-designed drop tower system. In all experiments, images are acquired with two cameras to determine the surface strain history through stereo Digital Image Correlation (DIC). The experimental observations are discussed in detail and also compared with the numerical simulations to validate the proposed experimental technique

Lyon-Type Integral Forms of Wall Friction, Heat- and Mass Transfer Closure Relationships for Non-Equilibrium Two-Phase Flows: Generalization for Annular and Rod Cluster Geometries

2013 ◽  
Author(s):  
Yuri Kornienko
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Constitutive Relations ◽  
Wall Friction ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Friction Heat ◽  
Integral Forms ◽  
Substance Transfer

The main goal of this paper is to describe new approach to constructing generalized closure relationships for pipe, annular and sub-channel transfer coefficients for wall friction, heat and mass transfer. The novelty of this approach is that it takes into account not only axial and transversal parameter distributions, but also an azimuthal substance transfer effects. These constitutive relations, which are primordial in the description of single- and two-phase one-dimensional (1D) flow models, can be derived from the initial 3D drift flux formulation. The approach is based on the Reynolds flow, boundary layer, and substance transfer generalized coefficient concepts. Another aim is to illustrate the validity of the “conformity principle” for the limiting cases. The method proposed in this paper is founded on the similarity theory, boundary layer model, and a phenomenological description of the regularity of the substance transfer (momentum, heat, and mass) as well as on an adequate simulation of the flow structures. With the proposed generalized approach it becomes possible to develop an integrated in form and semi-empirical in maintenance structure analytical relationships for wall friction, heat and mass transfer coefficients.

An Investigation of the Dynamic Recrystallisation Behaviour of Magnesium AZ31 Alloy at 450°C Using Plane Strain Compression Testing as a Tool

2012 ◽  
Vol 715-716 ◽  
pp. 164-169
Author(s):  
Bradley P. Wynne ◽  
R. Bhattacharya ◽  
Bruce Davis ◽  
W.M. Rainforth
Keyword(s):  
Strain Rate ◽  
Plane Strain ◽  
Testing Machine ◽  
Az31 Alloy ◽  
Plane Strain Compression ◽  
Strain Rates ◽  
Basal Texture ◽  
Magnesium Az31 ◽  
Dynamic Recrystallisation ◽  
Double Hit

The dynamic recrystallisation (DRX) behaviour of magnesium AZ31 is investigated using a plane strain compression (PSC) testing machine at 450°C. The variables included strain rate, double hit including intermittent anneal and double hits with different strain rate at each hit. The alloy shows higher peak stress and strain with increasing strain rates. Predominant basal texture with different intensities are observed at different strain rates. The annealing treatment between double tests leads to strong basal texture. Reversal of strain rate during double hit results in similar flow curves. This shows that in AZ31 alloy, DRX mechanism is independent of the initial microstructure and only depends on the test condition viz. temperature, strain rate and total equivalent strain.

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