New direct observations of crack closure processes in Al–Li 2090 T8E41

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences physical, and engineering sciences, 1999-10, Vol.357 (1761), p.2755-2775
• Main Authors: Guvenilir, A., Breunig, T. M., Kinney, J. H., Stock, S. R.
• Format: Article
• Language: English
• Subjects: Alloys; Computerized axial tomography; Crack Closure; Crack propagation; Crackface Geometry; Fatigue; Geometry; Imaging; Materials science; Tensile stress; Tomography; X ray computed tomography
• ISSN: 1364-503X; 1471-2962
• DOI: 10.1098/rsta.1999.0464

Earlier, crack opening as a function of position within an optically-opaque notched tensile sample (NT-3) of Al-Li 2090 was reported for four loads by Guvenilir and co-workers; these measurements were made with high resolution X-ray computed tomography. This paper reports the same type of results for a second notched tensile sample (NT-4): the authors believe this to be the second sample whose crack closure was quantified as a function of position. The crack within NT-4 was found to be more planar than and to close differently than that in NT-3. In NT-4, the crack 'zippe' shut from the tip; this is in contrast to the earlier results on the asperity- dominated crack in NT-3 where contact occured primarily behind the open crack tip. During unloading of NT-4, the crack faces came into contact above the closure load defined by the intersection of tangent lines to the upper and lower portions of the load-deflection curve; this is similar to previous observations in sample NT-3. Estimates of da/dN as a function of ΔK for samples NT-3 and NT-4 agree with other' measurements, which suggests that the closure observations of this paper also apply to compact tension samples of Al-Li 2090.