Crack instability in ductile materials analyzed by the method of interpolated ellipses
The subject of this work is the description of the experimental “method of interpolated ellipses” (MIE) and its application in fracture mechanics studies. The MIE is a new technique based on the optical monitoring of deformations during the loading processes of hexagonal grids of dots deposited on the surface of the monitored specimen. Loading the specimen deforms a cricle on the surface into an ellipse. Each ellipse is interpolated by six neighboring dots of the hexagonal grid. Knowledge of the ellipse parameters directly yields the magnitude and the direction of principal strains on the specimen surface. Principal strain evolution yields knowledge of evolution of the plastic strain field by numerical postprocessing. Experimental results obtained from fracture tests of specimens with varying constraint at the crack tip have proven the evolution of plastic strain field to be a discontinuous process. This has been shown to be especially the case at the decisive time interval just before crack instability occurs.
Key WordsGrid method method of interpolated ellipses plastic zones thermodynamic fracture concept
Unable to display preview. Download preview PDF.
- 1.Vavrik D., “Optical Identification of Surface Plastic Zone Shape and Size Near Crack Tip,” PhD Thesis, Czech Technical University, Prague (1999).Google Scholar
- 2.Zemankova, J. et al., “Thermodynamical Concept of Fracture Mechanics,” Final reprot of Grant No 106/95/1433 GACR, ITAM CAS, Prague (1998).Google Scholar
- 4.Sewenhuijsen, P.J., “Current Trends in Obtaining Deformation Data from Grids.Experimental Techniques,17,22–26 (1983).Google Scholar
- 5.Korous, J., Fiala, Z., andBielak, O., “Numerical Computation of Quantities of Two-Parameter Fracture Mechanics for a TDCB Specimen,” Engineering Mechanics,4, (2),87–93 (1997).Google Scholar
- 7.Sih, G.C., Mechanics of Fracture Initiation and Propagation, Kluwer Academic, Dordrecht (1991).Google Scholar
- 8.Thireos, C.G. andGdoutos, E.E., “Crack Curving under Mode I Loading,”Proceedings of the 4th Greek National Congress on Mechanics, Vol, 1, 375–383 (1995).Google Scholar