Fatigue-Crack-Propagation Rates Under Random Excitation

1967 ◽  
Vol 89 (1) ◽  
pp. 55-68 ◽  
Author(s):  
R. Plunkett ◽  
N. Viswanathan
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Random Excitation ◽  
Cantilever Beams ◽  
Constant Amplitude ◽  
Stress Cycles ◽  
Level Constant

Fatigue-crack-propagation rates have been measured for 2024-T3 aluminum cantilever beams in reversed bending under constant amplitude, two-level constant amplitude, and random excitations. For the two-level tests there is a large interaction between the crack-propagation rates caused by stress cycles of different amplitudes. The high-low sequence gives a delay and the low-high sequence a higher rate than a simple no interaction assumption would predict. This is confirmed in the random-excitation tests where the crack-propagation rate for low damping is much higher than that for high damping for exactly the same distribution and level of stress peaks.

The Study on Fatigue Crack Propagation in Metal Using Finite Element Analysis

2011 ◽  
Vol 462-463 ◽  
pp. 657-662
Author(s):  
K.A. Zakaria ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Cast Alloy ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Repeated Loading ◽  
Constant Amplitude ◽  
Element Analysis ◽  
Standard Size

Fatigue in materials is caused by repeated loading and unloading cycles below the ultimate strength of a material. Fatigue tests are expensive since they required a lot of time consuming. Simulation of fatigue crack propagation using commercial software can reduce the costs related to time. The purpose of this study is to compare the fatigue crack propagation in metal under variable and constant amplitude loading. A standard size of aluminum cast alloy specimen according to ASTM E647 document was modelled using a pre-processor and it was later being analysed. In another aspect, strain gauges were attached to an engine mounting bracket and connected to the data acquisition set in order to capture the actual strain signals when an automobile was driven on to different road conditions. For the simulation purpose, a constant amplitude loading was then derived from a variable amplitude loading obtained from the data capturing process. The related parameters on between different road conditions, variable and constant amplitude loadings and crack propagation rate were presented. The relationship between those parameters were finally correlated and discussed.

Effect of Periodic Overloads on Fatigue Crack Propagation in Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1065-1070
Author(s):  
J. Heidemann ◽  
J. Albrecht ◽  
G. Lütjering
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Tests ◽  
Propagation Mechanism ◽  
Constant Amplitude ◽  
R Ratio

The influence of variable amplitude loading on fatigue crack propagation was investigated for two high purity versions of the alloy Al 2024 in sheet form, one with fine equiaxed grains, and the other with coarse elongated grains. Fatigue tests on center cracked specimens were conducted in vacuum at constant amplitude (R-ratio of 0.1) and with periodically applied single tensile overloads with an overload ratio of 1.5. The number of intermittent baseline cycles between consecutive overloads was varied (n=100 and n=10.000). Detailed fractographic investigations were carried out for the identification of changes in the fracture surfaces due to the overloads. Crack closure measurements were performed in all cases. The results revealed a strong influence of the overloads on the crack propagation rate. Whether overloads are retarding or accelerating the fatigue crack propagation depends on the crack propagation mechanism at constant amplitude loading and the number of intermittent baseline cycles. For n=100 retardation occurred for the fine grained alloy exhibiting homogeneous slip at constant amplitude while acceleration was observed for the alloy with coarse elongated grains showing pronounced slip band fracture at constant amplitude. For n=10.000, the formation of steps parallel to the direction of crack propagation by overloads is assumed to be the reason for the observed increase in fatigue crack propagation resistance resulting in retardation for both alloys compared to constant amplitude and n=100. The influence of crack closure on the overload effects was minor. This was verified by additional tests at R=0.5.

On Three-Dimensional Fatigue Crack Propagation under Constant Amplitude Loading

2010 ◽  
Vol 97-101 ◽  
pp. 852-855
Author(s):  
Yu Ting He ◽  
Wen Jun Shu ◽  
Ren Yu Liu ◽  
Rong Hong Cui
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Axial Stress ◽  
Three Dimensional ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Crack Propagation Rate ◽  
Constant Amplitude ◽  
Alloy Plate

The equation of fatigue crack propagation rate is indispensable to precisely predict the fatigue life of structure containing three-dimensional crack under constant amplitude loading. Considering the crack closure effects and thickness effects in real structures, the equation of fatigue crack propagation rate under tri-axial stress state is presented. And the fatigue propagation lives of LY12-BCZYU aluminium alloy plate specimens with central through crack are predicted by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Test Stand for Analysis of Fatigue Crack Propagation under Bending with Torsion

2008 ◽  
Vol 144 ◽  
pp. 90-93 ◽  
Author(s):  
Grzegorz Gasiak ◽  
Grzegorz Robak
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Digital Camera ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Test Stand ◽  
Crack Development ◽  
Fatigue Crack Propagation Rate ◽  
Fatigue Crack Development

The paper presents a test stand for measurements of fatigue crack propagation. The stand includes a fatigue machine MZGS–100 and a device for registration of the crack length. The test stand is equipped with a stereoscopic microscope with fluent magnification of 7× – 67.5×. The microscope can be applied for observation of fatigue crack development. The microscope is also equipped with a digital camera, which enables continuous observation of fatigue crack development on the computer monitor and it is not necessary to stop the machine. The test results obtained at this stand can be used for determination of fatigue life and fatigue crack propagation rate.

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