Experimental Technique for Elevated Temperature Mode I Fatigue Crack Growth Testing of Ni-Base Metal Foils

2006 ◽  
Vol 129 (4) ◽  
pp. 594-602 ◽  
Author(s):  
L. Liu ◽  
J. W. Holmes
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Constant Amplitude ◽  
Stress Intensity Range ◽  
Metallic Foils

Details are provided for an experimental approach to study the tensile fatigue crack growth behavior of very thin metallic foils. The technique utilizes a center-notched specimen and a hemispherical bearing alignment system to minimize bending strains. To illustrate the technique, the constant amplitude fatigue crack growth behavior of a Ni-base superalloy foil was studied at temperatures from 20°C to 760°C. The constant amplitude fatigue tests were performed at a frequency of 2Hz and stress ratio of 0.2. The crack growth rate versus stress intensity range data followed a Paris relation with a stress intensity range exponent m between 5 and 6; this exponent is significantly higher than what is commonly observed for thicker materials and indicates very rapid fatigue crack propagation rates can occur in thin metallic foils.

Fatigue Crack Growth of β-21S Titanium Alloy Under Constant Amplitude and miniTWIST Flight Spectra at 25°C and 175°C

1997 ◽  
Vol 119 (4) ◽  
pp. 387-392
Author(s):  
R. R. Stephens ◽  
R. I. Stephens ◽  
A. L. Veit ◽  
T. P. Albertson
Keyword(s):  
Titanium Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Curves ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Constant Amplitude ◽  
Near Threshold

β-21S titanium alloy sheet fatigue crack growth behavior was investigated at 25°C and 175°C under constant amplitude (R = 0.1 and 0.5) and miniTWIST flight spectra. Based upon nominal ΔK values, constant amplitude fatigue crack growth behavior at 175°C was either similar to (R = 0.1), or slightly better than (R = 0.5) 25°C. With crack closure taken into account, the fatigue crack growth curves at 175°C, plotted as a function of Keff, were shifted to the left of the fatigue crack growth curves at 25°C at near threshold values. Under flight spectra conditions, fatigue crack growth life at 175°C was 40 to 90 percent longer than at 25°C. Flight spectra life calculations using NASA/FLAGRO based upon constant amplitude fatigue crack growth data, were primarily conservative but in good agreement with experimental data. Fatigue crack growth was transgranular with crystalline facets and striations that were evident at higher constant amplitude fatigue crack growth rates and with the miniTWIST spectra. Striations were observed to a limited extent at threshold and near threshold conditions at 25°C, but not at 175°C. Based upon desirable constant and variable amplitude fatigue crack growth and fatigue/fracture crack morphology, this β-21S sheet alloy appears to be an acceptable material for damage tolerant aerospace situations between 25°C and 175°C.

A Parametric Study of Fatigue Crack Growth Behavior in Adhesively Bonded Metallic Structures

1978 ◽  
Vol 100 (1) ◽  
pp. 46-51 ◽  
Author(s):  
M. M. Ratwani
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Intensity Factors ◽  
Adhesively Bonded

Problems of adherend cracks inadhesively bonded structures are considered in this paper. Two different methods of analysis, namely the finite element method and the integral equation approach, are used to obtain the stress intensity factors, which are compared with those obtained experimentally. The results of fatigue crack growth tests on two-ply, adhesively bonded panels with a width of 300 mm and 150 mm, a crack at a hole, and a cracked plate with a bonded stiffener are discussed. Fatigue crack growth behavior predictions based on the analytical stress intensity factors are correlated with those obtained from experiments for a variety of test geometries. The influence of adhesive type, adhesive thickness, and stiffener thickness on crack growth behavior are discussed for the case of a cracked plate with a bonded stiffener.

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