Experimental Validation of the 2D Meshless Random Grid Method

2011 ◽  
Author(s):  
Athanasios Iliopoulos ◽  
John G. Michopoulos ◽  
Adrian C. Orifici ◽  
Rodney S. Thomson
Keyword(s):  
Experimental Validation ◽  
Grid Method ◽  
Element Analysis ◽  
Full Field ◽  
Full Field Measurement ◽  
Preliminary Validation ◽  
Systematic Effort ◽  
Random Grid ◽  
Open Hole ◽  
Accuracy Performance

This paper presents the first systematic effort for the experimental validation of the 2D Meshless Random Grid Method (MRGM) for the full field measurement of displacement and strain fields. Although the MRGM has been demonstrating very promising characteristics of accuracy, performance and ease of application based on previously conducted sensitivity analysis supported by virtual data, extensive experimental validation was not available until now. This work comes to fill this gap and presents preliminary validation results against strain gauge data collected from open hole tension experiments of composite specimens. In addition, strain and displacement field verification is performed by comparison studies with finite element analysis results.

Performance Analysis and Experimental Validation of the Direct Strain Imaging Method

2013 ◽  
Author(s):  
Athanasios Iliopoulos ◽  
John G. Michopoulos ◽  
John C. Hermanson
Keyword(s):  
Experimental Validation ◽  
Strain Tensor ◽  
Operating Parameter ◽  
Strain Imaging ◽  
Imaging Method ◽  
Engineering Strain ◽  
Full Field ◽  
Strain Measurements ◽  
Full Field Measurement ◽  
Preliminary Validation

Direct Strain Imaging accomplishes full field measurement of the strain tensor on the surface of a deforming body, by utilizing arbitrarily oriented engineering strain measurements originating from digital imaging. In this paper an evaluation of the method’s performance with respect to its operating parameter space is presented along with a preliminary validation based on actual experiments on composite material specimens under tension. It has been shown that the method exhibits excellent accuracy characteristics and outperforms methods based on displacement differentiation.

Effects of Anisotropy on the Performance Sensitivity of the Mesh-Free Random Grid Method for Whole Field Strain Measurement

2009 ◽  
Author(s):  
A. P. Iliopoulos ◽  
J. G. Michopoulos
Keyword(s):  
Sensitivity Analysis ◽  
Anisotropic Medium ◽  
Orientation Angle ◽  
Grid Method ◽  
Strain Fields ◽  
Mesh Free ◽  
Random Grid ◽  
Open Hole ◽  
Realistic Choice ◽  
Accuracy Performance

The recently developed mesh-free random grid method (MFRGM) has been exhibiting very promising characteristics of accuracy, adaptability, implementation flexibility and efficiency. These are essential features enabling material characterization methodologies that depend on the experimental measurement of displacement and strain fields. The aim of the present paper is to present a sensitivity analysis that aids into determining the effects of the material or loading orientation of an anisotropic medium with an open hole and critical computational parameters characterizing the MFRGM in terms of its accuracy performance. First a brief outline of the MFRGM is provided. A sensitivity analysis based on the effect of the orientation angle of an anisotropic medium with an open hole is presented for a realistic choice of experimental (optical) characteristics. Finally, the effects of the mean dot size and dot distance (that are essential experimental parameters of the method) on the strain fields, are presented.

Shear Test on CFRP Full-Field Measurement and Finite Element Analysis

2010 ◽  
Vol 112 ◽  
pp. 49-62 ◽  
Author(s):  
Sébastien Mistou ◽  
Marina Fazzini ◽  
Moussa Karama
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Shear Modulus ◽  
Shear Test ◽  
Image Correlation ◽  
Optical Methods ◽  
Strain Gauges ◽  
Element Analysis ◽  
Full Field ◽  
Full Field Measurement

The purpose of this work is to study the Iosipescu shear test and more precisely its ability to characterize the shear modulus of a carbone/epoxy composite material. The parameters influencing this identification are the fibre orientation, the geometry of the notch and the boundary conditions. Initially these parameters were studied through the finite element analysis of the shear test. Then, the measurement of the shear strains was carried out by traditional methods of measurement (strain gauges) but also by optical methods. These optical methods: the digital image correlation and the electronic speckle pattern interferometry (ESPI); allow for various levels of loading, to reach a full-field measurement of the shear strain. This enabled us to study the strain distribution on the section between the two notches. The finite element model enabled us to study the parameters influencing the calculation of the shear modulus in comparison with strain gauges, image correlation and ESPI. This work makes it possible to conclude on optimal parameters for the Iosipescu test.

Accuracy of Inverse Composite Laminate Characterization via the Mesh Free Random Grid Method

2009 ◽  
Author(s):  
J. G. Michopoulos ◽  
A. P. Iliopoulos ◽  
T. Furukawa
Keyword(s):  
Grid Method ◽  
Constitutive Law ◽  
Forward Solution ◽  
Strain Fields ◽  
Flat Surfaces ◽  
Mesh Free ◽  
Random Grid ◽  
Open Hole ◽  
Constitutive Parameters

The present paper reports on the progress towards the evaluation of the Mesh Free Random Grid Method (MFRGM) for the inverse constitutive characterization of composite materials. The method provides the capability for the remote (non contact) measurement of displacement and strain fields of structures bounded by flat surfaces that deform under various mechanical and generalized loading conditions. The known forward solution of an anisotropic plate with an open hole, loaded at infinity, is used to generate synthetic images MFRG. The inverse problem for determining the constitutive parameters formulated directly on the generalized constitutive law. Performance of the technique is evaluated by the usage of just one frame corresponding to one set of strain state for various amounts of noise. The evaluation is repeated by utilizing frames corresponding to different rotations of the laminate relative to the loading direction. Finally the exceedingly accurate behavior of the methodology is discussed.

Optical full-field measurement of strain at a microscopic scale with the grid method

2006 ◽  
Author(s):  
Raphaël Moulart ◽  
René Rotinat ◽  
Fabrice Pierron ◽  
Gilles Lerondel ◽  
Pascal Royer
Keyword(s):  
Field Measurement ◽  
Grid Method ◽  
Full Field ◽  
Microscopic Scale ◽  
Full Field Measurement

Performance Analysis of the Mesh-Free Random Grid Method for Full-Field Synthetic Strain Measurements

Strain ◽  
2010 ◽  
Vol 48 (1) ◽  
pp. 1-15 ◽  
Author(s):  
A. P. Iliopoulos ◽  
J. G. Michopoulos ◽  
N. P. Andrianopoulos
Keyword(s):  
Performance Analysis ◽  
Grid Method ◽  
Full Field ◽  
Strain Measurements ◽  
Mesh Free ◽  
Random Grid

An Investigation of the Ring Hoop Tension Test for Anisotropic Tubes

2014 ◽  
Author(s):  
Christopher P. Dick ◽  
Yannis P. Korkolis
Keyword(s):  
Contact Pressure ◽  
Tension Test ◽  
Negligible Effect ◽  
Image Correlation ◽  
Element Analysis ◽  
Material Response ◽  
Full Field ◽  
Al 6061 ◽  
Full Field Measurement ◽  
Nominal Thickness

The ring hoop tension test (RHTT) is investigated experimentally and numerically to determine its validity and limitations in predicting the hoop response of materials in tubular form. Our experiments involved RHT-Testing of Al-6061-T4 tubes. Digital image correlation (DIC) was used to capture the strain evolution in the gage section of the specimens, giving a full-field measurement of the strains. The local hoop stress-strain response of the material was assessed in this way. Finite element analysis was used to further investigate the effects of friction, eccentricity and contact pressure on the recorded response. Friction was found to have a negligible effect on the recorded response for friction coefficient values of 0.01 and lower. However, it was found that larger values of friction may render the test meaningless. Tube eccentricity of the magnitude present in the tubes tested here (±4% of the nominal thickness) was determined to have no effect on the material response. It was also determined that tubes should not be turned to a uniform thickness as this may induce machining damage and release the existing residual stresses, thus causing error in determining the tube response in the hoop direction. The contact pressure was found to not significantly affect the state of uniaxial tension in the specimen and thus to have a negligible effect on the material response. By comparing the hoop with the axial response, the material anisotropy of the Al-6061-T4 tubes was established.

A Computational Workbench for Remote Full Field 2D Displacement and Strain Measurements

2009 ◽  
Author(s):  
J. G. Michopoulos ◽  
A. P. Iliopoulos
Keyword(s):  
Grid Method ◽  
Experimental Results ◽  
Loading Conditions ◽  
Strain Fields ◽  
Full Field ◽  
Strain Measurements ◽  
Flat Surfaces ◽  
Mesh Free ◽  
Random Grid ◽  
Computational Implementation

The present paper reports on the progress towards the development of a computational workbench infrastructure that implements the Mesh Free Random Grid Method (MFRGM) for the remote (non contact) measurement of displacement and strain fields. The method is applicable to structures bounded by flat surfaces that deform under various mechanical and generalized loading conditions. A brief description of MFRGM is followed by the description of the current prototype of a software workbench developed for the computational implementation of the algorithms involved with the analysis display and export of the experimental results associated with any specific applications of the method. Displacement validation as well as two examples of its usage are also presented.

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