Application of digital-image-correlation techniques in analysing cracked cylindrical pipes

Abstract

Cracks induced by external excitation on a material that has defects may generate the stress concentration phenomenon. The stress concentration behaviour causes local budding, which will induce the damage of the members made of this material. Thus, developing techniques to monitor the strain variation of a cracked member is an important study. The traditional technique (such as strain gauge) can only measure the average strain of a region. The strain variation within this region cannot be determined. Therefore, it cannot sufficiently reflect the mechanical behaviour surrounding the crack. The Digital image correlation technique recently developed is an image identification technique to be applied for measuring the object deformation. This technique is capable of correlating the digital images of an object before and after deformation and further determining the displacement and strain field of an object based on the corresponding position on the image. In this work, this technique is applied to analyse the mechanics of a cylindrical pipe experiencing crack destruction. The fixing device is used to avoid shaking the specimen during the pressurizing process. The image capture instruments are fixed on the stable frame to measure the deformation of specimen accurately. Through the cylindrical pipe cracking test, the capacity of the digital image correlation technique for surveying the strain variation in a tiny region is validated. Then, the experimental results obtained using the digital image correlation analysis is used to demonstrate the crack development tendency in defect materials and the stress concentration zone

Comparison of Digital Image Correlation (DIC) Technique with Nanomaterial-Based Sensor for the Analysis of Strain Measurements

“…The specimen surface to be studied must have a random dot pattern [16], and the number of pixels / per line in an image defines the spatial resolution. A random dot pattern enables the software to identify and calculate the displacements with accuracy.…”

Extended Digital Image Correlation Method for Mapping Multiscale Damage in Concrete

“…Sutton et al 2009 andLecompte et al 2006 [8,10], to match or track the same subsets located in the reference image and deformed image for retrieving the full-field displacements. The DIC calculates the average gray scale intensity over the subset in deformed and undeformed images, and to perform the correlation of both images by searching the point that has highest grey scale correlating with the initial position of displacement vector in calculating the observable changes in the sequence of images for deriving a deformation field [9]. Using the data from the deformation field the further quantities such as state of strain at any point on the surface can be obtained.…”

“…The previous researches [4][5][6][7][8][9][10] used the standard digital image correlation (DIC) method to carry out strain field measurements of a wide range of engineering materials. For instance, Dai et al [4] used the DIC to investigate deformation behaviour in metals.…”

“…In relation to a damage or crack investigation, Tung and Sui [9] used the DIC for analysing damage in a cylinder pipes. The DIC was used to monitor a strain surrounding the cracks and identifying stress concentration zone in the damaged pipe.…”

Full-Field Temperature Measurement of Stainless Steel Specimens Subjected to Uniaxial Tensile Loading at Various Strain Rates

“…The non-contact optical methods for the measurement of temperature displacement include video extensometers [21], laser speckle correlation [22], interferometry methods [23][24][25] and temperature-calibrated CCD cameras [26]. In addition to IR thermography, the other technique that allows temperature changes to be coupled with strains is digital image correlation (DIC), in which digital images of an object before and after deformation are captured using a non-contact optic and material-independent measuring instrument, and then they are subject to correlation analysis [23,24,27]. High-speed DIC allows deformation and damage mechanisms to be analysed in a quantitative manner [28].…”