Abstract
A high-magnification moiré interferometer, particularly suitable for near-tip field analysis in cracked materials, is described. It has a submillimeter field of view, a high-resolution image sensor (1.4 million pixels), X-Y-Z translation stage and an optical fiber light delivery system. These features enable the microscope head to observe the crack tip while the specimen is loaded in a standard tensile test machine. Automated fringe pattern analysis, using temporal phase shifting and spatial phase unwrapping, enables thex ory displacement component to be measured and the corresponding in-plane strain component computed. The displacement placement accuracy is better than 40 nm, and the effective strain gage dimension is ∼ 25 μm. Furthermore, the interferometer has a built-in white light microscope that allows the observation of the specimen granular microstructure in exact registration with the displacement field. The interferometer has hence been employed to investigate the near-tip fields of a precracked stainless steel specimen under load. The influence of the grain boundaries on the measured displacement fields was relatively minor. The near-tip strain field shows a significant asymmetrical behavior despite pure mode lloading conditions.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Paris, P. andErdogan, F., “A Critical Analysis of Crack Propagation Laws,”Trans. ASME J. Basic Eng. Ser. D,85,528–534 (1963).
Richter, R. andBurmeister, H.-J., “Effects of Grain Boundary Properties on Intergranular Cracking in Fatigued FCC Metals,”Acta Mat.,45,715–725 (1997).
Huang, Y., Zhang, L., Guo, T.F., andHwang, K.-C., “Mixed Mode Near-tip Fields for Cracks in Materials with Strain-gradient Effects,”J. Mech. Phys. Solids,45,439–465 (1997).
Fleck, N.A. andHutchinson, J.W., “A Phenomenological Theory for Strain Gradient Effects in Plasticity,”J. Mech. Phys. Solids,41,1825–1857 (1993).
Post, D., “Moir'e Interferometry for Deformation and Strain Studies,”Opt. Eng.,24,663–667 (1985).
Walker, C.A., “A Historical Review of Moiré Interferometry,” EXPERIMETAL MECHANICS,34,281–299 (1994).
Han, B. andPost, D., “Immersion Interferometer for Microscopic Moiré Interferometry,” EXPERIMENTAL MECHANICS,32,38–43 (1992).
Melin, L.G., Goldrein, H.T., Huntley, J.M., Nilsson, S., andPalmer, S.J.P., “A Study of Mode-I Delamination Cracks by High Magnification Moiré Interferometry,”Composite Sci. Tech.,58,515–525 (1998).
Goldrein, H.T., “Applications of Optical Strain-measurement Techniques to Composite Materials,” Ph.D. thesis, University of Cambridge (1996).
Huntley, J.M., Palmer, S.J.P., Goldrein, H.T., andMelin, L.G., “Microstructural Strain Analysis by High Magnification Moiré Interferometry,”Proc. SPIE,3545,86–95 (1995).
Post, D., Han, B., andIfju, P., “High Sensitivity Moiré,”Experimental Analysis for Mechanics and Materials, Springer-Verlag, New York (1994).
British Standard BS6835: 1988, “Method for Determination of the Rate of Fatigue Crack Growth in Metallic Materials” (1988).
Schwider, J., Burow, R., Elssner, K.-E., Grzanna, J., Spolaczyk, R., andMerkel, K., “Digital Wave-front Measuring Interferometry: Some Systematic Error Sources,”Appl. Opt.,22,3421–3432 (1983).
Buckland, J.R., Huntley, J.M., andTurner, S.R.E., “Unwrapping Noisy Phase Maps b Use of a Minimum-cost-matching Algorithm,”Appl. Opt.,34,5100–5108 (1995).
Vrooman, H.A. andMaas, A.A.M., “New Image Processing Algorithms for the Analysis of Speckle Interference Patterns,”Proc. SPIE,1163,51–61 (1989).
Rice, J.R. andRosengren, G.F., “Plane Strain Deformation Near a Crack Tip in a Power Law Hardening Material,”J. Mech. Phys. Solids,16,1–12 (1968).
Hutchinson, J.W., “Singular Behavior at the End of a Tensile Crack in Hardening Material,”J. Mech. Phys. Solids,16,13–27 (1968).
Han, G., Sutton, M.A., andChao, Y.J., “A Study of Stationary Cracktip Deformation Fields in Thin Sheets by Computer Vision,” EXPERIMENTAL MECHANICS,34,125–140 (1994).
Wissuchek, D.J., Mackin, T.J., DeGraef, M., Lucas, G.E., andEvans, A.G., “A Simple Method for Measuring Surface Strains around Cracks,” EXPERIMENTAL MECHANICS,36,173–179 (1996).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
La Porta, F.A., Huntley, J.M., Chung, T.E. et al. High-magnification moiré interferometer for crack tip analysis of steels. Experimental Mechanics 40, 90–95 (2000). https://doi.org/10.1007/BF02327553
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF02327553