The effect of cracktip interactions on the curvefitting of mixedmode isopachics
Issac, G., Spencer, A., Worden, K. and DulieuBarton, J.M. (2007) The effect of cracktip interactions on the curvefitting of mixedmode isopachics. At 13th International Conference on Experimental Mechanics (ICEM 13), Alexandroupolis, Greece, 01  06 Jul 2007. Netherlands, Springer2pp, 865858.
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Description/Abstract
Thermoelastic Stress Analysis (TSA) is a fullfield technique for experimental stress analysis that has proved to be extremely effective for studying stress fields in the vicinity of cracktips. An understanding of such fields is vital to the development of effective diagnosis and prognosis algorithms for NonDestructive Testing (NDT) and Structural Health Monitoring (SHM). The key to cracktip studies using TSA is the observation that the stresssum contours (isopachics) in the vicinity of the tip take the form of a simple curve – the cardioid. This was exploited in [1] in order to estimate the Stress Intensity Factors (SIFs) for cracktips in mode 1 and mixedmode opening. The analysis [1] made use of the cardioid nature of the isopachics by deriving expressions for the SIFs in terms of the cardioid area and the positions of certain tangents to the curve.
Recent work by the authors has allowed the estimation of cracktip Stress Intensity Factors (SIFs) by curvefitting a cardioid form to measured isopachics from Thermoelastic Stress Analysis (TSA). Both Genetic Algorithms (GAs) [2] and Differential Evolution (DE) [3] proved successful for the actual parameter estimation, but some of the curvefits indicated that the cardioid form was inappropriate for the base model.
A possible explanation for the poor curvefit is that the cardioid form is only theoretically suitable for an isolated cracktip stress field, as derived from the Westergaard equations. The effect of the other cracktip in a central crack hac been neglected from previous analyses. Further work has [4] considered a mode 1 central crack, placed in a plate, which therefore had two interacting cracktips. Figure 1 shows the analytically derived stress sum field around both an isolated mode 1 crack and a twin cracktip. The curves for an isolated cracktip are shown as solid lines – these curves are true cardioids. The curves for the twin cracktip case are shown as dashed lines. It is clear that these curves are not cardioids, although the level of distortion is quite small for the inner curves.
The object of the current paper is to determine numerically, the stress field for a mixedmode crack system and to quantify the effect of any interactions on the curvefitting procedure and compare with experimental data for a 30o crack.
Item Type:  Conference or Workshop Item (Speech)  

Related URLs:  
Subjects:  T Technology > TJ Mechanical engineering and machinery  
Divisions:  University Structure  Pre August 2011 > School of Engineering Sciences > FluidStructure Interactions 

ePrint ID:  49034  
Date : 


Date Deposited:  22 Oct 2007  
Last Modified:  31 Mar 2016 12:25  
URI:  http://eprints.soton.ac.uk/id/eprint/49034 
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