An algorithm for obtaining real stress field of hyperelastic materials based on digital image correlation system

2017 ◽  
Vol 06 (04) ◽  
pp. 1850003 ◽  
Author(s):  
Ziqian Li ◽  
Zishun Liu
Keyword(s):  
Digital Image Correlation ◽  
Stress Field ◽  
Digital Image ◽  
Strain Field ◽  
Soft Matter ◽  
Tensile Tests ◽  
Image Correlation ◽  
Inhomogeneous Materials ◽  
Engineering Strain ◽  
Hyperelastic Materials

Soft matter with hyperelastic behavior may be harnessed for novel applications. However, it is not achievable if the mechanical behaviors of soft matter are not well understood. At present, various traditional extensometers have been used to measure the engineering strain of materials to determine the mechanical properties. The basic assumption of extensometers is that the strain is assumed to be uniform over the gage length. However, this assumption does not hold good in case of experimental specimens having significant nonuniform strain distribution, for example, tensile tests on notched specimens or materials that undergo localized deformations. Hence, it is imperative to adopt a new method which enables us to capture the actual strain field on the surface of a material. Digital image correlation (DIC) technique is an adequate approach that has been widely used in many fields of science and engineering. In this paper, we have presented a mapping algorithm for hyperelastic materials, translating the strain field provided by DIC to the stress field based on continuum mechanics. It overcomes the limitation of extensometers and captures the real stress field for such materials. This method will not only improve the measuring accuracy of stress and strain fields in current experiments, but also greatly promote the study of the localized characteristic for nonlinear and inhomogeneous materials.

Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

2010 ◽  
Vol 1 (4) ◽  
pp. 344-357 ◽  
Author(s):  
V. Richter‐Trummer ◽  
P.M.G.P. Moreira ◽  
S.D. Pastrama ◽  
M.A.P. Vaz ◽  
P.M.S.T. de Castro
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Strain Field ◽  
Image Correlation ◽  
Content Type ◽  
Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

scholarly journals A new methodology to identify minimum strain anatomical lines based on 3-D digital image correlation

2017 ◽  
Vol 8 (2) ◽  
pp. 337-347 ◽  
Author(s):  
Jorge Barrios-Muriel ◽  
Francisco Javier Alonso Sánchez ◽  
David Rodríguez Salgado ◽  
Francisco Romero-Sánchez
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Strain Field ◽  
Three Dimensional ◽  
Wearable Devices ◽  
Plane Motion ◽  
Human Motion ◽  
The Body ◽  
Image Correlation ◽  
Minimum Deformation

Abstract. Today there is continuous development of wearable devices in various fields such as sportswear, orthotics and personal gadgets, among others. The design of these devices involves the human body as a support environment. Based on this premise, the development of wearable devices requires an improved understanding of the skin strain field of the body segment during human motion. This paper presents a methodology based on a three dimensional digital image correlation (3D-DIC) system to measure the skin strain field and to estimate anatomical lines with minimum deformation as design criteria for the aforementioned wearable devices. The errors of displacement and strain measurement related to 3-D reconstruction and out-of-plane motion are investigated and the results are acceptable in the case of large deformation. This approach can be an effective tool to improve the design of wearable devices in the clinical orthopaedics and ergonomics fields, where comfort plays a key role in supporting the rehabilitation process.

scholarly journals Robust Filtering Options for Higher-Order Strain Fields Generated by Digital Image Correlation

2020 ◽  
Vol 1 (4) ◽  
pp. 174-192
Author(s):  
Nedaa Amraish ◽  
Andreas Reisinger ◽  
Dieter H. Pahr
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Tensile Tests ◽  
Image Correlation ◽  
Field Strain ◽  
Strain Fields ◽  
Full Field ◽  
Low Pass ◽  
Discrete Measurement ◽  
Mean Filtering

Digital image correlation (DIC) systems have been used in many engineering fields to obtain surface full-field strain distribution. However, noise affects the accuracy and precision of the measurements due to many factors. The aim of this study was to find out how different filtering options; namely, simple mean filtering, Gaussian mean filtering and Gaussian low-pass filtering (LPF), reduce noise while maintaining the full-field information based on constant, linear and quadratic strain fields. Investigations are done in two steps. First, linear and quadratic strain fields with and without noise are simulated and projected to discrete measurement points which build up strain window sizes consisting of 6×5, 12×11, and 26×17 points. Optimal filter sizes are computed for each filter strategy, strain field type, and strain windows size, with minimal impairment of the signal information. Second, these filter sizes are used to filter full-field strain distributions of steel samples under tensile tests by using an ARAMIS DIC system to show their practical applicability. Results for the first part show that for a typical 12×11 strain window, simple mean filtering achieves an error reduction of 66–69%, Gaussian mean filtering of 72–75%, and Gaussian LPF of 66–69%. If optimized filters are used for DIC measurements on steel samples, the total strain error can be reduced from initial 240−300 μstrain to 100–150 μstrain. In conclusion, the noise-floor of DIC signals is considerable and the preferable filters were a simple mean with s*¯ = 2, a Gaussian mean with σ*¯ = 1.7, and a Gaussian LPF with D0*¯ = 2.5 in the examined cases.

Development of a Railway Track Displacement Monitoring by Using Digital Image Correlation Technique

2014 ◽  
Vol 548-549 ◽  
pp. 683-687 ◽  
Author(s):  
Lenny Iryani ◽  
Hery Setiawan ◽  
Tatacipta Dirgantara ◽  
Ichsan Setya Putra
Keyword(s):  
Digital Image Correlation ◽  
Stress Field ◽  
Digital Image ◽  
Displacement Field ◽  
Image Correlation ◽  
Railway Track ◽  
Remaining Life ◽  
Full Field ◽  
Field Displacement ◽  
Dic Technique

To avoid an unnecessary catastrophic accident due to a failure of a railway track, it is important to have a reliable condition monitoring system for the railway track. The integrity of the railway track can be assessed by monitoring the displacement field of the track, which can then be used to determine the strain and stress field. By knowing the stress history of the track and the S–N curves of the track material, the remaining life of the railway track can be predicted. In the present work, a simple system to monitor and record the displacement field of the railway track has been developed by using Digital Image Correlation (DIC) technique. The set–up to monitor the displacement field of the railway track was developed using a high speed video camera of Nikon J1 to capture the image of the railway track when the train passing through. The DIC technique was then employed off line to measure the displacement field of the 2D image captured. The results showed that the full field displacement measured by using DIC technique gives a good agreement compared to the finite element results. The full field displacement can be used to calculate the strain-stress field, and later on the remaining life assessment can be conducted based on the results.

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