Displacement pattern matching and boundary-element methods for elastic-plastic stress analysis

Sirkis, James S.; Taylor, C. E.

doi:10.1007/bf02322698

Cited by 11 publications

(5 citation statements)

References 17 publications

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“…The spacing of the grid spots (or pitch), which essentially equates to gauge length, must also be chosen such that individual grid spots can be easily distinguished. In order to obtain reliable results, Sirkis and Taylor [28] recommend a grid spot diameter of at least 10 pixels and a lower limit on the grid spacing of between 2-3 times the spot diameter. In this investigation these recommendations were achieved by using a grid of 2.5mm diameter spots at 5mm centres (Fig.…”

Section: 1mentioning

confidence: 99%

Flexural strain and crack width measurement of steel-fibre-reinforced concrete by optical grid and electrical gauge methods

Robins

Austin

Chandler

et al. 2001

Cement and Concrete Research

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This item was submitted to Loughborough's Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/ FLEXURAL STRAIN AND CRACK WIDTH MEASUREMENT OF STEEL FIBRE REINFORCED CONCRETE BY OPTICAL GRID AND ELECTRICAL GAUGE METHODSPeter Robins, Simon Austin and Peter Jones, Department of Civil and Building Engineering Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK Keywords: crack detection (B), fibre reinforcement (E), fracture toughness (C), image analysis (B), modelling (E) Abstract: A research programme is discussed that has investigated the fracture of steel fibre reinforced sprayed concrete under flexural loading, with the aim of developing a stress-block model to predict flexural behaviour in the form of a load-deflection response. This paper reports the work associated with establishing the strain and crack-width profiles in relation to mid-span beam deflection. A strain analysis technique is described, which combines the use of electrical strain gauges with a semi-automated grid method (using digital image processing) for measuring and monitoring the strain and crack-width profile over the depth of a fibre reinforced beam during a flexural test.This novel strain analysis technique has established strain/crack-width data which forms a key part of a stress-block approach for predicting residual flexural strength, an essential requirement of a much needed design rationale for steel fibre reinforced concrete. Introduction Research ObjectivesThe work reported here formed part of a larger research project investigating the reinforcing mechanisms and fracture processes associated with steel fibre reinforced sprayed concrete under flexural load. A major aim of this project was to develop a model -based on conventional principles of mechanics -to predict flexural behaviour in the form of a load-deflection response, and thereby predict flexural toughness performance.The principal objective of this study was to test the following hypothesis: given the matrix compressive strength, fibre volume, fibre type, cross-section dimensions and loading geometry of a steel fibre reinforced sprayed concrete beam, the flexural loaddeflection curve can be predicted using a stress-block diagram approach, if the following principal parameter relationships are known: the uniaxial compressive stress-strain relationship; the uniaxial tensile stress-strain relationship; the single fibre pull-out load versus crack-width relationship; the number, distribution, embedment lengths and orientation of the fibres bridging the cracked section of the beam; and the strain profile and the crack-width profile in relation to mid-span beam deflection. This paper presents work carried out on the last principal parameter listed above, that is the strain and crack-width profiles, whilst that on fibre pullout and distribution are reported elsewhere [1, 2]. ...

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Section: 1mentioning

confidence: 99%

Flexural strain and crack width measurement of steel-fibre-reinforced concrete by optical grid and electrical gauge methods

Robins

Austin

Chandler

et al. 2001

Cement and Concrete Research

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“…Substituting the displacement gradients into constitutive relationships, we obtain the stress rate components on the boundary &id( ( ) = ci~kli~k,l( ( ) --(rOd((), (11) where c~y is the elastic constitutive tensor, which in the case of an isotropic medium, is given by…”

Section: Y~°k(x)di~j(x -Y)dv~mentioning

confidence: 99%

“…Moslehy and Ranson [8], Umeagukwu et al [9] and Balas et al [10] introduced BEM experimental hybrid techniques, but all these are restricted to the elastic regime. Later Sirkis and Taylor [11] have developed a two-dimensional hybrid experimental-numerical technique for elastoplastic stress analysis. That technique results from merging the BEM and image processing.…”

Section: Introductionmentioning

confidence: 99%

Elastoplastic crack analysis by boundary integral method and surface spectrum measurement

Sládek

Držík

1995

Int J Fract

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The paper describes a hybrid experimental-numerical technique for elastoplastic crack analysis. It consists of the experimental surface spectrum measurement of plastic strains ahead the crack tip and the boundary element method (BEM). The light scattering method is used to measure the power density spectrum from which the values of plastic strains are obtained by comparison with a calibration experiment on the same material. Plastic strains obtained experimentally are conveniently used for the calculation of unknown boundary displacement or traction vectors by the boundary element method. Instead of an iterative solution of the boundary integral equations in pure numerical solution, the boundary unknowns are computed once for a required loading level. Also asymptotic d~stribution of strains or stresses is not needed in the evaluation of the domain integral for the BEM formulation in the vicinity of the crack tip. Significant CPU time saving is achieved in comparison with the pure BEM solution. The method presented is illustrated by the example for a three point bending specimen with an edge crack.

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“…By comparing the grid of the deformed specimen to that of the undeformed reference state, the displacements and strains which are developed in the specimen during the loading can be quantified. There is a variety of approaches used to perform the image analysis, such as spot centroid tracking [5,6], cross-grid tracking [9], the spectral method [10,11] and Fourier transformation of the grid patterns [12]. The grid method has been successfully applied to obtain the displacement and strain mapping in various materials and structures, such as perforated aluminum strips [13], cracks in lamellar TiAl [14], three dimensional surface deformations of metals [15], necking zone of a tensile specimen [16] and small animal bones [17].…”

Section: Introductionmentioning

confidence: 99%

“…The grid method is one of the oldest methods for obtaining full-field deformation measurements [1][2][3][4][5][6][7][8][9]. A grid usually consists of lines, circles, dots or other shapes assembled in regular patterns.…”

Section: Introductionmentioning

confidence: 99%

Grid Method for Microscale Discontinuous Deformation Measurement

et al. 2011

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The objective of this paper is to explore both grid method and Digital Image Correlation (DIC) technique for microscale and discontinuous displacement measurements, such as those associated with crack tips. First, the principle of the grid method is revisited. The grid method and DIC technique are then applied to computer generated images to calculate the displacement field around crack tips. Finally, the grid method is applied to actual experimental images of fracture tests which are conducted inside a Scanning Electron Microscope (SEM) chamber. A new technique is developed to generate microscale pattern that is suitable for both grid method and DIC technique. The displacement fields calculated from grid method are compared with those from DIC technique to identify the strengths and weaknesses of each technique for the microscale and discontinuous displacement measurements. It has been determined that grid method can obtain data closer to the discontinuity than DIC; however, DIC produces smoother displacement fields at the far field. Using this new pattern generation technique, both grid method and DIC technique can be applied to the fracture test at the microscale to complement with each other to achieve the best experiment results.

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Displacement pattern matching and boundary-element methods for elastic-plastic stress analysis

Cited by 11 publications

References 17 publications

Flexural strain and crack width measurement of steel-fibre-reinforced concrete by optical grid and electrical gauge methods

Flexural strain and crack width measurement of steel-fibre-reinforced concrete by optical grid and electrical gauge methods

Elastoplastic crack analysis by boundary integral method and surface spectrum measurement

Grid Method for Microscale Discontinuous Deformation Measurement

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