Strain-gradient effect on the crack tip dislocations density

In this study, the influence of a material’s plastic properties on the crack tip fields and dislocation density behavior is analytically and numerically analyzed using the conventional mechanism-based strain-gradient plasticity (CMSGP) theory established using the Taylor model. The material constitutive equation is implemented in a commercial finite element code by a user subroutine, and the crack tip fields are evaluated with novel parameters in the form of the intrinsic material length, characterizing the scale over which gradient effects become significant. As a consequence of the strain-gradient contribution, FE results show a significant increase in the magnitude of the stress fields of CMSGP when the material length parameter is considered. It is found that the density of geometrically necessary dislocations (GND) is large around the crack tip, but it rapidly decreases away from the crack tip. On the contrary, the density of statistically stored dislocations (SSD) is not as large as geometrically necessary dislocations around the crack tip, but it decreases much slower than GND away from the crack tip. A couple effect of material work hardening and the crack tip distance is identified.

Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).

Prediction of Chip Morphology and Formation in High Speed Milling of Hardened Steels

A P20 steel are machined in the milling speed range of 200 to 942m/min. The morphology and formation of the chips are investigated at various speeds. The serrated chips with adiabatic shear band are observed at a high milling speed. The transition from continuous to serrated chip formation is favored by the increase in work material hardness and milling speed. The study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. Based on adiabatic shear theory, using the JC and the power material constitutive equation, the modified material model which takes into a strain softening is developed for prediction of the serrated chip formation. Experimental measurements are compared with the simulation results.

The Simulation of Stem Cutting and Parameter Optimization for Power Station Valve

We expound the finite element simulation and the key points of metal turning by the material properties of the stem in this paper, and select the proper material constitutive equation, then use the adaptive meshing technique, and then finite element modeling was carried out on the valve stem in the professional finite element software Advantedge FEM. The optimization scheme we designed of finite element simulation for the valve stem through the finite element software Advantedge FEM, and we research the influence of the amount of feed and speed cutting process about the cutting force and the cutting temperature.

Nonlinear Constitutive Equation and Elastic Constant of Rubber Material

In-depth study of compressible material constitutive equation, using incompressible condition, the nonlinear incompressible elastic solid’s complete irreducible constitutive equation and strain energy function expressed in invariants are derived in this essay. The elastic constants of rubber material are given by fitting the experiment data that was carried out by Treloar with the equation. Then we got evelen exact value of the elastic constants.

Flow Stress Determination of Aluminum Alloy 7050-T7451 Using Inverse Analysis Method

In the present study, two-dimensional orthogonal slot milling experiments in conjunction with an analytical-based computer code are used to determine flow stress data as a function of the high strains, strain rates and temperatures encountered in metal cutting. By using this method, the flow stress of Al7050-T7451 is modeled. Through the comparison of cutting forces between FEM and experiment, the FEM model using predicted flow stress can give precise cutting forces. The work of this paper provides a useful method for material constitutive equation modeling without doing large number of cutting experiment or expensive SHPB tests.

A New Optimization Method of Constitutive Equation for Hot Working Based on Physical Simulation and Numerical Simulation

This paper advances a new optimization method about material constitutive equation on the basis of physical simulation and numerical simulation results which basic thinking can be described as the following: through comparing the results of the material deformation process under actual experimental conditions and virtually simulated by the finite element numerical simulation method with the constitutive equation established on the basis of the physical simulation, the constitutive equation established by the experimental data is optimized in turn. Based on it, this paper advances a visco/plastic constitutive equation to depict the semi-solid thixo-forming and the constitutive equation is analyzed and optimized through coupling of the physical simulation and numerical simulation. It is observed that this method can effectively eliminate the influence of the factor outside material itself on the constitutive equation. So, it can exactly depict the deformation behavior of the materials and improve the accuracy and reliability of the numerical simulation.

Characterizing the Effect of 319 Aluminum Microstructure on Machinability: Part 2 — Model Validation

In Part 1 of this paper, a machining force model was developed based on an enhanced version of Zheng’s Continuum Mechanics model that incorporates microstructural effects. Machining experiments identified Secondary Dendrite Arm Spacing (SDAS) as a significant microstructure feature of 319 aluminum in terms of machinability. A new material constitutive relationship that incorporates SDAS microstructure effects on the flow stress was proposed. In this part of the paper, disk turning tests are performed to simulate the orthogonal cutting process. The cutting forces obtained from some of these tests are used in concert with an inverse form of the continuum mechanics machining model to estimate the parameters in the material constitutive equation. The enhanced continuum mechanics orthogonal cutting model is then applied to predict cutting forces when machining Al319. Comparison of the model predicted and experimentally acquired cutting forces is demonstrated to show good agreement.

An Orthogonal Cutting Model Based on Finite Deformation Analysis: Part I — Model Development

Based on the finite deformation theory of continuum mechanics, the velocity, Eulerian strain, Eulerian strain rate, and deformation rate distributions along a family of assumed streamlines are analytically obtained for an orthogonal cutting operation. An iterative incremental method is used to predict the temperature on the shear plane. The total power in orthogonal cutting may be expressed in terms of three parameters, which are predicted by minimization of the total power. This model allows a general form for the material constitutive equation, which, in general, is a function of strain, strain rate, and temperature. The rotation effect of streamlines on the strain and strain rate calculations is automatically considered using the finite deformation theory of continuum mechanics. In Part I of this paper, the theoretical underpinning for the orthogonal cutting model is established. The verification of the model, including determination of the material constitutive equation using the Hopkinson bar technique, is presented in Part II of this paper.

Measurement of Wall Deformation and Flow Limitation In a Mechanical Trachea

A mechanical model of the human trachea is investigated experimentally. A modified version of an earlier model, it consists of a square sectioned rigid tube in which part of one wall is removed, and replaced by a prestretched flat latex membrane. Air is drawn from atmosphere through an inlet into the rigid upstream tube; it then flows through the flexible section and finally through a rigid section Into a plenum chamber where suction is applied. As the membrane collapses in response to flow, the transmural pressure and deflection are measured at the mid-point. These values are used in conjunction with a finite deformation membrane wall theory to determine the elastic constant in a nonlinear material constitutive equation. This equation is used to predict the tube law. Results show that the flow limits at the long wave speed predicted by this law. Thus it behaves as a conventional collapsible tube while having the advantage of a rational wall model.