Analysis of creep-induced strains and stresses in notches subjected to a cyclic load

2007 ◽  
Vol 42 (5) ◽  
pp. 361-375 ◽  
Author(s):  
J E Nuñez ◽  
G Glinka
Keyword(s):  
Finite Element ◽  
Plane Stress ◽  
External Load ◽  
Cyclic Load ◽  
Time Dependent ◽  
Cyclic Loads ◽  
Creep Response ◽  
Stress Components ◽  
Estimation Of Time ◽  
Good Agreement

A method for the estimation of time-dependent strains and stresses in notches subjected to a cyclic load is discussed in the paper. The proposed solution is an extension of the methodology proposed previously for notches under a steady external load. A new algorithm is proposed to predict the creep response near notches in plane stress components subjected to cyclic loads. Predictions were compared with finite element data, and good agreement was obtained for various geometrical and material configurations.

Analysis of Creep Induced Strains and Stresses in Notches Subjected to Cyclic Load

2005 ◽  
Author(s):  
Enrique Nunez ◽  
Gregorz Glinka
Keyword(s):  
Finite Element ◽  
Plane Stress ◽  
External Load ◽  
Cyclic Load ◽  
Time Dependent ◽  
Cyclic Loads ◽  
Creep Response ◽  
Stress Components ◽  
Estimation Of Time ◽  
Good Agreement

A method for the estimation of time-dependent strains and stresses in notches subjected to cyclic load is discussed in the paper. The proposed solution is an extension of the methodology proposed previously for notches under steady external load. A new algorithm is proposed to predict creep response near notches in plane stress components subjected to cyclic loads. Predictions were compared against finite element data and good agreement was obtained for various geometrical and material configurations.

Aerodynamic Simulation of Vertical-Axis Wind Turbines

2013 ◽  
Vol 81 (2) ◽  
Author(s):  
A. Korobenko ◽  
M.-C. Hsu ◽  
I. Akkerman ◽  
Y. Bazilevs
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Vertical Axis ◽  
Time Dependent ◽  
Computational Results ◽  
Vertical Axis Wind Turbine ◽  
Vertical Axis Wind Turbines ◽  
Moving Domain ◽  
Aerodynamic Simulation ◽  
Good Agreement

Full-scale, 3D, time-dependent aerodynamics modeling and simulation of a Darrieus-type vertical-axis wind turbine (VAWT) is presented. The simulations are performed using a moving-domain finite-element-based ALE-VMS technique augmented with a sliding-interface formulation to handle the rotor-stator interactions present. We simulate a single VAWT using a sequence of meshes with increased resolution to assess the computational requirements for this class of problems. The computational results are in good agreement with experimental data. We also perform a computation of two side-by-side counterrotating VAWTs to illustrate how the ALE-VMS technique may be used for the simulation of multiple turbines placed in arrays.

A Numerical Approach for Simulation of Rock Fracturing in Engineering Blasting

2010 ◽  
Vol 1 (2) ◽  
pp. 38-58
Author(s):  
Mani Ram Saharan ◽  
Hani S. Mitri
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Numerical Modelling ◽  
Plane Stress ◽  
Numerical Approach ◽  
The Other ◽  
Rock Fracturing ◽  
Experimental Tool ◽  
Element Elimination ◽  
Good Agreement

An approach for simulation of rock fracturing as a result of engineering blasting is presented in this paper. The approach uses element elimination technique within the framework of finite element method to capture the physics of engineering blasting. The approach does not require pre-placement of fracture paths which is the severe drawback of the other existing methodologies and approaches. Results of plane stress modelling for isotropic brittle rock behaviour are presented in this paper and these results are in good agreement with the existing knowledge base. The authors also review the existing approaches of numerical modelling to compare the efficacy of the element elimination technique. It is anticipated that the further developments with this approach can prove to be good experimental tool to improve engineering blasting operations.

Large deformation finite element analysis of non-linear viscoelastic membranes with reference to thermoforming

1993 ◽  
Vol 28 (1) ◽  
pp. 31-51 ◽  
Author(s):  
S Shrivastava ◽  
J Tang
Keyword(s):  
Finite Element ◽  
Relaxation Function ◽  
Time Dependent ◽  
Large Strains ◽  
Element Analysis ◽  
Contact Conditions ◽  
Non Linear ◽  
Linear Viscoelastic ◽  
Finite Element Formulations ◽  
Good Agreement

This paper reports on the development of finite element formulations and computer programs for modelling free and constrained inflation of thin polymeric sheets in the context of thermoforming of plastic articles. In recognition of the generally time-dependent viscoelastic behaviour of polymers, and the large strains encountered in thermoforming applications, the material is modelled as non-linear visoelastic. For this purpose the constitutive relation proposed by Christensen (1)† is adopted, assuming the relaxation function to be exponential. Most of the published work on non-linear viscoelastic membranes deals with simple axisymmetric geometries, while the finite element formulations presented in this work are for both axisymmetric and non-axisymmetric membrane inflations, including contact against constraining surfaces. Both frictionless and slipless idealizations of contact conditions are studied. The finite element solutions of free and constrained inflations of circular membranes serve as illustrative examples for the axisymmetric case, while those for elliptical membranes demonstrate the non-axisymmetric cases. Comparison of the finite element results with the analytical solutions obtained (Appendix 1) for some simple free and constrained inflation problems shows good agreement.

Shakedown Analysis of Axisymmetric Nozzles Under Primary and Secondary Cyclic Loads

2009 ◽  
Author(s):  
Dan Vlaicu
Keyword(s):  
Finite Element ◽  
Lower Bound ◽  
Stress Field ◽  
Material Properties ◽  
Cyclic Load ◽  
Elastic Stress ◽  
Nonlinear Material ◽  
Cyclic Loads ◽  
Shakedown Analysis ◽  
Elastic Plastic

In this paper, the finite element method is used to develop the lower bound limit for the elastic shakedown analysis of axisymmetric nozzles under periodic loading conditions. The Nonlinear Superposition Method is employed to calculate the lower bound shakedown loads by quoting Melan’s theorem in a nonlinear finite element analysis. The calculation is divided into two separate iterations which are blended with a technique that matches the elastic-plastic part of the analysis with the linear part. In the first part of the calculation, the cyclic load is applied as a static load to generate an elastic stress field in the structure. The same cyclic load is subsequently combined with the constant fraction of the load in the second part of the calculation, and the total load is applied in an elastic-plastic analysis that exceeds the yield limit. For each solution increment, the residual stress is generated from the superposition of the elastic stress field scaled through the applied cyclic load and the shakedown stress field calculated from the nonlinear analysis. The results obtained from the lower bound method are compared with the full cyclic loading analyses based on nonlinear material properties, and this paper discusses the choice of the global shakedown in terms of the radial strain, and the local through thickness shakedown defined by the hoop strain. Furthermore, this paper presents the development of a generic model that emulates the behavior of the finite element model under cyclic loads in a simplified form, with the statistical representation based on a sampling of base-model data for a variety of test cases. The probabilistic method takes variations of the geometrical dimensions, nonlinear material properties, and pressure load as the input parameters, whereas the response variable is defined in terms of the lower bound of the shakedown loads.

Modeling of Crack Growth With Dwell Time for Aero-Engine Spectra Loadings in a Ni-Based Superalloy

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Erik Storgärds ◽  
Kjell Simonsson ◽  
Sören Sjöström ◽  
David Gustafsson ◽  
Tomas Månsson
Keyword(s):  
Cyclic Load ◽  
Sustained Load ◽  
Cyclic Loads ◽  
Surface Cracks ◽  
Multiple Tests ◽  
Linear Elastic ◽  
Modeling Concept ◽  
Aero Engine ◽  
Elastic Fracture ◽  
Good Agreement

Testing and simulation of aero-engine spectra with dwell times are reported in this paper. The modeling concept used is built on linear elastic fracture mechanics (LEFM) and provides a history-dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra: (1) cyclic loads, (2) combined sustained load and cyclic loads, and (3) slow load ramps and cyclic loads, all for surface cracks at 550 °C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.

Modelling of Crack Growth With Dwell Time for Aero Engine Spectra Loadings in a Ni-Based Superalloy

2015 ◽  
Author(s):  
Erik Storgärds ◽  
Kjell Simonsson ◽  
Sören Sjöström ◽  
David Gustafsson ◽  
Tomas Månsson
Keyword(s):  
Crack Growth ◽  
Inconel 718 ◽  
Dwell Time ◽  
Cyclic Load ◽  
Sustained Load ◽  
Cyclic Loads ◽  
Surface Cracks ◽  
Multiple Tests ◽  
Aero Engine ◽  
Good Agreement

Testing and simulation of aero engine spectra with dwell times are reported in this paper. The modelling concept used is built on LEFM and provides a history dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra, 1) cyclic loads, 2) combined sustained load and cyclic loads and 3) slow load ramps and cyclic loads, all for surface cracks at 550°C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.

Shear Difference Method and Application in Orthotropic Photoelasticity

1976 ◽  
Vol 98 (4) ◽  
pp. 369-374 ◽  
Author(s):  
C. E. Knight ◽  
H. Pih
Keyword(s):  
Plane Stress ◽  
Difference Method ◽  
Two Dimensional ◽  
The Third ◽  
Material Orientation ◽  
Stress Components ◽  
Tensile Strip ◽  
Principal Directions ◽  
Stress Optic Law ◽  
Good Agreement

The shear difference method is developed here for application to orthotropic photoelasticity problems. The two-dimensional stress-optic law which was presented in another paper is used. The stress-optic law provides two equations for the three plane stress components and the shear difference method may be used to obtain the third relation. This paper presents the development of the general orthotropic shear difference method for any material orientation. For orientations aligned with the material principal directions, the relations are identical to the isotropic shear difference method. The solution of an orthotropic tensile strip with a central hole demonstrates application of the orthotropic shear difference method and further confirms the orthotropic stress-optic law. Good agreement was found between the photoelastic and theoretical solutions.

Failure Mechanisms of MEMS Thermal Actuators

2006 ◽  
Author(s):  
Nasim Paryab ◽  
Hamid Jahed ◽  
Amir Khajepour
Keyword(s):  
Finite Element ◽  
Failure Modes ◽  
Failure Mechanisms ◽  
Time Dependent ◽  
Cyclic Loads ◽  
Creep Failure ◽  
Thermal Actuators ◽  
Mems Actuators ◽  
Cause Of Failure ◽  
Dependent Failure

Predicting and eliminating failure modes of MEMS polysilicon thermal actuators as one of the elementary bricks of a more complicated device can save months of time as well as money to repair, reproduce, or even redesign the device. There are validated reports of time-dependent failure in flexural polysilicon MEMS actuators. MEMS thermal actuators are under high temperature and cyclic loads. Therefore, fatigue and creep are suitable candidates in determining failure mechanisms. Here, both fatigue and creep failure mechanisms are studied theoretically and experimentally. A comprehensive finite element modeling is employed to find temperature and stress distribution in the actuators. It is shown, that polysilicon MEMS thermal actuator are less prone to fatigue failure and creep is the main cause of failure in MEMS thermal actuators.

A Finite Element Analysis of Stress Fields in Vickers Indentation on Brittle Materials

2007 ◽  
Vol 329 ◽  
pp. 403-408 ◽  
Author(s):  
Bing Zhang ◽  
Masato Yoshioka
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Brittle Materials ◽  
Element Model ◽  
Time Dependent ◽  
Stress Fields ◽  
Element Analysis ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Good Agreement

A three dimensional finite element model for Vickers indentations on brittle materials is presented in order to analyze the stress distribution. The objective of this paper is to study when and where cracks are most likely to initiate and propagate in the indentation cycle based on the analyzed stresses. Therefore the time-dependent stresses around and below the surface of the contact area during the indentation cycle, especially at the end of loading and at the beginning of unloading phase are investigated in detail. The analytical results are shown to be in good agreement and verified with the experimental results.

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