scholarly journals Fatigue Tests on Buried or Repaired Dented Steel Pipeline Specimens

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2031
Author(s):  
Vitor Paiva ◽  
Giancarlo Gonzáles ◽  
Ronaldo Vieira ◽  
Alexandre Ribeiro ◽  
José Maneschy ◽  
...  
Keyword(s):  
Hot Spot ◽  
Fatigue Cracks ◽  
Cyclic Strain ◽  
Field Measurements ◽  
Fatigue Tests ◽  
Image Correlation ◽  
Test Results ◽  
Steel Pipeline ◽  
Full Field ◽  
Fatigue Equation

This paper presents the results of fatigue tests performed on dented steel pipeline specimens that were tested under different environmental conditions and subjected to cyclic internal pressure. Thirty-three pipe specimens were divided into three groups and tested under three different conditions. A first set of nine dented specimens was tested in air without any restrictions. A second set of eight specimens was tested while buried in the soil. A third set of sixteen specimens was tested in air, after the dents had been repaired by composite material sleeves. Hot-spot cyclic strain amplitudes were measured using two experimental techniques: Digital Image Correlation (DIC) and Fiber Optic Bragg Strain Gauges (FBSG). At first, all thirty-three specimens were tested in air along five full cycles in order to carry out full-field measurements using DIC to identify and quantify strain concentration at sites that were potential locations for fatigue cracks to initiate. Close to these point-locations, measurements of strains using FBSG were also made, and the results were then compared with the DIC results. FBSG were also used during the cyclic pressure loading process while the specimens were being tested, in such a way as to monitor the influence of the environment in the dented areas. The test results demonstrated that a simple uniaxial Manson-Coffin fatigue equation that uses the universal exponents proposed by Manson, together with the circumferential strain amplitude measured at the hot spots can be used to predict the fatigue life of the dented specimens. Moreover, it was determined that the measured strains at the hot-spot locations were not influenced by the soil coverage, although showing a considerable and beneficial decrease in their amplitudes caused by the composite repair reinforcements.

scholarly journals Evaluation of a low-cost approach to 2-D digital image correlation vs. a commercial stereo-DIC system in Brazilian testing of soil specimens

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
M. Arza-García ◽  
C. Núñez-Temes ◽  
J. A. Lorenzana ◽  
J. Ortiz-Sanz ◽  
A. Castro ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Accuracy Assessment ◽  
Low Cost ◽  
Field Measurements ◽  
Image Correlation ◽  
Strain Gauges ◽  
Source Image ◽  
Full Field ◽  
Cost Approach

AbstractDue to their cost, high-end commercial 3D-DIC (digital image correlation) systems are still inaccessible for many laboratories or small factories interested in lab testing materials. These professional systems can provide reliable and rapid full-field measurements that are essential in some laboratory tests with high-strain rate events or high dynamic loading. However, in many stress-controlled experiments, such as the Brazilian tensile strength (BTS) test of compacted soils, samples are usually large and fail within a timeframe of several minutes. In those cases, alternative low-cost methods could be successfully used instead of commercial systems. This paper proposes a methodology to apply 2D-DIC techniques using consumer-grade cameras and the open-source image processing software DICe (Sandia National Lab) for monitoring the standardized BTS test. Unlike most previous studies that theoretically estimate systematic errors or use local measures from strain gauges for accuracy assessment, we propose a contrast methodology with independent full-field measures. The displacement fields obtained with the low-cost system are benchmarked with the professional stereo-DIC system Aramis-3D (GOM GmbH) in four BTS experiments using compacted soil specimens. Both approaches proved to be valid tools for obtaining full-field measurements and showing the sequence of crack initiation, propagation and termination in the BTS, constituting reliable alternatives to traditional strain gauges. Mean deviations obtained between the low-cost 2D-DIC approach and Aramis-3D in measuring in-plane components were 0.08 mm in the perpendicular direction of loading (ΔX) and 0.06 mm in the loading direction (ΔY). The proposed low-cost approach implies considerable savings compared to commercial systems.

Full Field Measurements of the Dynamic Response of AA6061-T6 Aluminum Alloy Under High Strain Rate Compression and Torsion Loads

2012 ◽  
Author(s):  
Gbadebo Owolabi ◽  
Daniel Odoh ◽  
Akindele Odeshi ◽  
Horace Whitworth
Keyword(s):  
Aluminum Alloy ◽  
High Speed ◽  
High Strain ◽  
Shear Bands ◽  
Field Measurements ◽  
Image Correlation ◽  
Deformation Analysis ◽  
Deformation And Failure ◽  
Full Field ◽  
Structural Applications

Aluminum alloys exhibit an attractive combination of mechanical and physical properties such as high stiffness and low density, which favors their utilization in many structural applications. Thus, increasing the structural applications of aluminum alloy is the driving force for the need to adequately understand its deformation and failure mechanisms under various types of dynamic loading conditions. In this study, full field plastic deformation of AA6061-T6 aluminum alloy at high strain-rates under compressive and torsion loads are measured using split Hopkinson compression and torsion bars and a high speed digital image correlation system. The stress-strain curves obtained using the high speed digital cameras are compared with results obtained from the elastic waves in the compression and torsion bars. A post deformation analysis of the specimen also shows strain localization along narrow adiabatic shear bands in the AA6061-T6 alloy.

scholarly journals A Method for Calibrating a Digital Image Correlation System for Full-Field Strain Measurements during Large Deformations

2019 ◽  
Vol 9 (14) ◽  
pp. 2828 ◽  
Author(s):  
Robert Blenkinsopp ◽  
Jon Roberts ◽  
Andy Harland ◽  
Paul Sherratt ◽  
Paul Smith ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Large Deformations ◽  
Speckle Pattern ◽  
Field Measurements ◽  
Image Correlation ◽  
Field Strain ◽  
Full Field ◽  
Error Distributions ◽  
Multiple Deformation

Numerous variables can introduce errors into the measurement chain of a digital image correlation (DIC) system. These can be grouped into two categories: measurement quality and the correlation principle. Although previous studies have attempted to investigate each error source in isolation, there are still no comprehensive, standardized procedures for calibrating DIC systems for full-field strain measurement. The aim of this study, therefore, was to develop an applied experimental method that would enable a DIC practitioner to perform a traceable full-field measurement calibration to evaluate the accuracy of a particular system setup in a real-world environment related to their specific application. A sequence of Speckle Pattern Boards (SPB) that included artificial deformations of the speckle pattern were created, allowing for the calibration of in-plane deformations. Multiple deformation stages (from 10% to 50%) were created and measured using the GOM ARAMIS system; the results were analysed and statistical techniques were used to determine the accuracy. The measured strain was found to be slightly over-estimated (nominally by 0.02%), with a typical measurement error range of 0.34% strain at a 95% confidence interval. Location within the measurement volume did not have a significant effect on error distributions. It was concluded that the methods developed could be used to calibrate a DIC system in-situ for full-field measurements of large deformations. The approach could also be used to benchmark different DIC systems against each other or allow operators to better understand the influence of particular measurement variables on the measurement accuracy.

scholarly journals Validation of a multi-scale Ti-6Al-4V drilling model by means of thermomechanical field measurements

2021 ◽  
Author(s):  
Camille Bonnet ◽  
Thomas Pottier ◽  
Yann Landon ◽  
Abdallah Bouzid
Keyword(s):  
High Speed ◽  
Infrared Camera ◽  
Field Measurements ◽  
Image Correlation ◽  
3D Fem ◽  
Full Field ◽  
Multi Scale ◽  
Thermal Fields ◽  
Significant Magnitude ◽  
Drilling Operations

Drilling operations lead to temperatures and forces that may locally reach significant magnitude and thus impair the surface and material integrity. Optimizing the cutting conditions could limit these degradations, which are more significant in the case of low thermal conductivity materials such as titanium alloys. Robust numerical modelling is a relevant alternative to such issues but must rely on strong in-process experimental measurements. Unfortunately, the confined nature of the cutting area during drilling prevent from any straight forward field-measurement. The proposed multi-scale strategy consists in validating the developed 3D FEM models both at micrometric and millimetric scales, using coupled full-field measurements. The limited access to the cutting area is overcome by means i) of oblique cutting tests at microscale and ii) tube drilling tests. Thermal fields are evaluated using an infrared camera while kinematic fields are determined by image correlation (DIC) using a high-speed camera. The experimental and numerical fields are then compared, and numerical results are extended over several revolutions by means of purely thermal 2D analytical model.

scholarly journals Identification of a macroscopic anisotropic damage model using digital image correlation and the equilibrium gap method

2010 ◽  
pp. 229-240
Author(s):  
Laurent Crouzeix ◽  
Jean-Noël Périé ◽  
Francis Collombet ◽  
Bernard Douchin
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Damage Model ◽  
Field Measurements ◽  
Image Correlation ◽  
Anisotropic Damage ◽  
Biaxial Test ◽  
Displacement Fields ◽  
Full Field ◽  
Constitutive Parameters

The aim of the work is to demonstrate how an anisotropic damage model may be identified from full field measurements retrieved during a heterogeneous test. The example of a biaxial test performed on a 3D C / C composite is used. In a first step, the displacement fields measured by classical Digital Image Correlation are used as input data of a finite difference version of the Equilibrium Gap Method. A benefit from unloadings (assumed to be elastic) is shown to retrieve a damage law. In a second step, inelastic strains can be assessed from the total measured strain and the elastic estimated strains. The constitutive parameters relative to the inelastic part of the model are then identified.

Fatigue Crack Monitoring Using Image Correlation

2008 ◽  
Vol 385-387 ◽  
pp. 341-344
Author(s):  
Pablo Lopez-Crespo ◽  
A. Shterenlikht ◽  
Eann A Patterson ◽  
J.R. Yates ◽  
Philip J. Withers
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Industrial Applications ◽  
Image Correlation ◽  
Small Scale ◽  
Full Field ◽  
Complex Formulation

A novel methodology based on a combination of experimental and analytical methods is used for monitoring the stress intensity factor in fatigue cracks subjected to constant amplitude loads. Full-field displacement information is fitted, following a multi-point over-deterministic approach, to an analytical model. This is developed from Muskhelishvili’s complex formulation. The methodology allowed accurate monitoring of the stress intensity factor during three fatigue cycles when small-scale yielding conditions were achieved. Moreover for larger loads where important plastic deformation occurs around the crack tip, Dugdale’s correction accounted for the differences between theoretical and calculated stress intensity factors. Accordingly the tool provides an indirect approach for measuring crack tip plasticity. Due to the fact that image correlation is relatively simple to use and is a non-contacting technique, the approach pioneered in this work seems ideal for monitoring fatigue cracks in industrial applications.

scholarly journals Research on three dimensional detection system of fatigue cracks of steel box girder

2018 ◽  
Vol 175 ◽  
pp. 03007
Author(s):  
Su Lin ◽  
Zhang Jian ◽  
Cheng Xi
Keyword(s):  
Detection System ◽  
Fatigue Cracks ◽  
Three Dimensional ◽  
Fatigue Tests ◽  
Steel Bridge ◽  
Test Results ◽  
Box Girder ◽  
Detection Scheme ◽  
Steel Box Girder ◽  
Homogeneous Test

The fatigue cracks are inevitably existed in steel bridges after they are working for a fairly short time because of the environmental pollution, overloading vehicles and larger numbers of automobiles. How to efficiently detect the fatigue cracks, especially the initial fatigue cracks, become one of the most important question to be solved for the steel box girder. The static and fatigue tests of the orthotropic steel bridge deck models were carried out in this research paper, which presented the fatigue damage developing laws, compared the test results with homogeneous test results in existing documents. Three dimensional micro detection scheme of fatigue cracks in steel box girder with three dimensional detection system is studied. Through the data from the testing design, the important characteristic width and length of the fatigue crack can be achieved, which can be used for the grasping of the mechanism of the steel box girder.

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