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.

Surface Discontinuity Detection via Direct Strain Imaging

2013 ◽  
Author(s):  
Athanasios Iliopoulos ◽  
John G. Michopoulos
Keyword(s):  
Biaxial Loading ◽  
Strain Tensor ◽  
Strain Imaging ◽  
Engineering Strain ◽  
New Approach ◽  
Full Field ◽  
Full Field Measurement ◽  
Slant Crack ◽  
Novel Method ◽  
Surface Discontinuity

Direct strain imaging is a recently developed full-field strain measurement method that accomplishes full field measurement of the strain tensor on the surface of a deforming body, by using arbitrarily oriented engineering strain measurements. This new approach doesn’t make any assumption on the compatibility of the strain field and thus it allows for consistent representation of media that may be or may not be discontinuous. In this paper, we present a novel method for detecting whether a discontinuity exists on a deformed body by evaluating the validity of the compatibility conditions over the imaging field. This approach can also be used for quantifying the shape and length of the discontinuity or crack. Synthetic numerical experiments based on the exact solution of a slant crack under biaxial loading were conducted to establish the detectability performance and the associated uncertainty of detection. Very encouraging results were derived indicating that for realistic levels of noise the method was found to be able to detect discontinuities as small as 0.3 mm long with very high confidence.

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.

Towards Crack Trajectory Identification via the Direct Strain Imaging Method

2015 ◽  
Author(s):  
Athanasios Iliopoulos ◽  
John G. Michopoulos
Keyword(s):  
Mechanical Load ◽  
Deformable Body ◽  
Accurate Determination ◽  
Strain Tensor ◽  
Strain Imaging ◽  
Imaging Method ◽  
Extended Finite Element ◽  
Strain Compatibility ◽  
Crack Trajectory

In this paper we present an investigation on the feasibility of exploiting the Direct Strain Imaging (DSI) method for the purpose of tracking propagating discontinuities on the surface of a deformable body under mechanical load. The proposed approach is based on a strain compatibility functional that does not require any assumptions about the continuity conditions of the underlying medium. The proposed approach is based on the recently introduced Direct Strain Imaging method that is used to identify with high accuracy the full fields of strain tensor components that are required to define the strain compatibility functional. We performed synthetic numerical experiments based on the exercising the eXtended Finite Element Method solution for simulating a propagating crack of a particular problem in order to assess the feasibility and potential of the proposed approach. We demonstrated that indeed our DSI-based approach can achieve a very accurate determination of the crack trajectory even under noisy conditions.

Full-field X-ray diffraction microscopy using polymeric compound refractive lenses

2014 ◽  
Vol 47 (6) ◽  
pp. 1882-1888 ◽  
Author(s):  
J. Hilhorst ◽  
F. Marschall ◽  
T. N. Tran Thi ◽  
A. Last ◽  
T. U. Schülli
Keyword(s):  
Imaging Techniques ◽  
Light And Electron Microscopy ◽  
Added Value ◽  
Acquisition Time ◽  
Imaging Method ◽  
X Ray Diffraction ◽  
Polymeric Compound ◽  
Full Field ◽  
X Ray ◽  
Diffraction Imaging

Diffraction imaging is the science of imaging samples under diffraction conditions. Diffraction imaging techniques are well established in visible light and electron microscopy, and have also been widely employed in X-ray science in the form of X-ray topography. Over the past two decades, interest in X-ray diffraction imaging has taken flight and resulted in a wide variety of methods. This article discusses a new full-field imaging method, which uses polymer compound refractive lenses as a microscope objective to capture a diffracted X-ray beam coming from a large illuminated area on a sample. This produces an image of the diffracting parts of the sample on a camera. It is shown that this technique has added value in the field, owing to its high imaging speed, while being competitive in resolution and level of detail of obtained information. Using a model sample, it is shown that lattice tilts and strain in single crystals can be resolved simultaneously down to 10−3° and Δa/a= 10−5, respectively, with submicrometre resolution over an area of 100 × 100 µm and a total image acquisition time of less than 60 s.

scholarly journals Raman and Infrared Thermometry for Microsystems

2013 ◽  
Vol 5 (3) ◽  
Author(s):  
Leslie M. Phinney ◽  
Wei-Yang Lu ◽  
Justin R. Serrano
Keyword(s):  
Data Collection ◽  
Spatial Resolution ◽  
Infrared Imaging ◽  
Silicon On Insulator ◽  
Pixel Size ◽  
Full Field ◽  
Infrared Thermometry ◽  
Full Field Measurement ◽  
Typical Data ◽  
Field Temperature

This paper reports and compares Raman and infrared thermometry measurements along the legs and on the shuttle of a SOI (silicon on insulator) bent-beam thermal microactuator. Raman thermometry offers micron spatial resolution and measurement uncertainties of ±10 K. Typical data collection times are a minute per location leading to measurement times on the order of hours for a complete temperature profile. Infrared thermometry obtains a full-field measurement so the data collection time is on the order of a minute. The spatial resolution is determined by the pixel size, 25 μm by 25 μm for the system used, and infrared thermometry also has uncertainties of ±10 K after calibration with a nonpackaged sample. The Raman and infrared measured temperatures agreed both qualitatively and quantitatively. For example, when the thermal microactuator was operated at 7 V, the peak temperature on an interior leg is 437 K ± 10 K and 433 K ± 10 K from Raman and infrared thermometry, respectively. The two techniques are complementary for microsystems characterization when infrared imaging obtains a full-field temperature measurement and Raman thermometry interrogates regions for which higher spatial resolution is required.

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