The effect of crack tunneling on crack growth: experiments and CTOA analyses

Abstract This paper compares experimental crack-front shapes recorded at various stages of crack growth with area-average crack growth values during fracture tests conducted on 2024-T351 aluminum alloy plate. Crack-front shapes were determined by fracturing the specimen to a predetermined amount of crack growth and fatigue cycling the specimen for about 4000 cycles at a high stress ratio (Pmin/Pmax) to mark the crack-front location. For each shape, the area-average crack length was determined. The evolution of tunneling was used to create a calibration curve that could be used to adjust surface measured crack-length values, for a more representative comparison with analyses that use a straight crack-front approximation. The analysis compares much more favorably with the average crack growth than with the surface measured values near maximum load. However, the area-average technique tends to over correct crack growth near the crack initiation load. Crack tunneling results show that the area-average technique produces more representative crack-length measurements compared to optical based surface measurements.

[1]  J. Newman,et al.  Measurement and analysis of critical CTOA for an aluminum alloy sheet , 1995 .

[2]  D. Dawicke,et al.  CTOA and crack-tunneling measurements in thin sheet 2024-T3 aluminum alloy , 1994 .

[3]  James H. Starnes,et al.  Analytical Methodology for Predicting Widespread Fatigue Damage Onset in Fuselage Structure , 1998 .

[4]  James C. Newman,et al.  Variations of a global constraint factor in cracked bodies under tension and bending loads , 1995 .

[5]  S. Mahmoud,et al.  The effect of specimen thickness on the experimental characterization of critical crack-tip-opening angle in 2024-T351 aluminum alloy , 2003 .

[6]  M. Ortiz,et al.  FINITE-DEFORMATION IRREVERSIBLE COHESIVE ELEMENTS FOR THREE-DIMENSIONAL CRACK-PROPAGATION ANALYSIS , 1999 .

[7]  James H. Starnes,et al.  Analytical Methodology for Predicting the Onset of Widespread Fatigue Damage in Fuselage Structure , 1996 .

[8]  James C. Newman,et al.  An elastic-plastic finite-element analysis of the J-resistance curve using a CTOD criterion , 1988 .

[9]  C. Shih,et al.  Studies on Crack Initiation and Stable Crack Growth , 1979 .

[10]  J. C. Newman,et al.  Analyses of Buckling and Stable Tearing in Thin-Sheet Materials , 1998 .

[11]  M. F. Kanninen,et al.  Elastic-plastic fracture mechanics for two-dimensional stable crack growth and instability problems , 1979 .

[12]  David J. Smith,et al.  Constraint Effects in Fracture : Theory and Applications ASTM STP 1244 , 1995 .

[13]  D. Parks,et al.  Three-dimensional crack front fields in a thin ductile plate , 1990 .