Crack growth behavior of aluminum alloy 6061 T651 under uniaxial and biaxial planar testing condition

2015 ◽  
Author(s):  
S. Henkel ◽  
E. Liebelt ◽  
H. Biermann ◽  
S. Ackermann
Keyword(s):  
Crack Growth ◽  
Tensile Load ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Proportional Loading ◽  
Center Crack ◽  
T Stress ◽  
Crack Tips ◽  
Alloy 6061

The crack growth behavior of the aluminum alloy 6061 T651 was investigated using cruciform specimens with a measurement area of 120 x 120 x 2 mm3 with two center crack configurations of the starting notch parallel to one of the loading axes and under an angle of 45°, respectively. For the case with crack direction in one of the loading axes the load ratio R = ?min / ?max as well as the force parallel to the crack direction (resulting in different T-stresses) were changed. Crack growth rate was studied under varying T-stress. Also the retardation after single overloads was determined for R = 0.1, R = 0.5 and R = 0.8. As a result a change in T-stress does not significantly affect crack growth rate on high R ratios (R = 0.5) for constant ?F loading. In case of lower R-ratios (R = 0.1) crack growth retardation was observed at presence of a static tensile load parallel to the crack growth direction due to higher influence of crack closure. Furthermore, such tensile load results in longer retardation periods after applying an overload at R = 0.1. Less pronounced overload retardation can be assumed with tensile force FX for R = 0.8 and 1.3 times overloads. Non proportional loading with a phase shift in time between the two axes of 45° and 90° results in a mixed mode situation (mode I / mode II) at the crack tip of a crack which is orientated under 45° to the loading axes. Mode I and mode II fractions change during every cycle. A phase change of 45° did not change crack growth significantly compared with proportional load. Crack branching occurred when changing from proportional loading to non-proportional 90° phase shifted loading. The two crack tips of the center crack under 45° divided in 4 crack tips under approximately 90° to the loading axes which were simultaneous propagating for more than 10 mm. Finally, two crack tips propagated faster than the remaining two. The stress intensity factors KI and KII as well as the T-stress where calculated by FEA (ABAQUS). For the 45° crack orientation and the non-proportional load case with 90° phase shift linear elastic FEA calculations show that there are time dependent rotating principal stress axes on the crack tip during one cycle. In the unnotched (uncracked) specimen there are fixed principal stress axes also in the phase shifted loading case. The configuration with 4 cracks has a significant higher ?KI than the configuration with two crack tips while ?KII is significantly lower. In addition uniaxial crack growth measurements were performed on SENB specimen in the size of 10 x 20 x 100 mm3 covering the threshold and Paris-region for loading ratios R = 0.1, 0.3, 0.5, 0.8.

Mode I Ductile Crack Growth of 1TCT Specimen Under Large Cyclic Loading: Part III

2019 ◽  
Author(s):  
Kiminobu Hojo
Keyword(s):  
Cyclic Loading ◽  
Crack Growth ◽  
Large Scale ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Piping System ◽  
Ductile Crack ◽  
Reference Stress ◽  
Ductile Crack Growth

Abstract Fitness for service rules and a calculation method for ductile crack growth under large scale plastic cyclic loading have not been established even for Mode I. In a paper presented at the PVP2018 conference the authors presented methods to establish how to determine the parameters of the combined hardening plasticity rule and applied it to simulate the ductile crack growth behavior of 1TCT specimens of the different load levels. Also, ΔJ calculations using the reference stress method, and a ΔJ-basis fatigue crack growth rate derived from that on ΔK-basis according to JSME rules for FFS were applied to estimate the crack growth under cyclic loading in excess of yield. Since in the 2018 paper identified some gaps were found between experiments and the predicted crack growth behavior, several equations of the reference stress method are evaluated in the present paper. Additionally, the prediction procedure using the ΔJ calculation by the reference stress method and the da/dN−ΔJ curve based on the JSME rules for FFS are applied to pipe fracture tests under cyclic loading. Their applicability is discussed for the case of an example piping system.

scholarly journals Fatigue Crack Growth Behavior of PWA 1484 Single Crystal Superalloy at Elevated Temperatures

1995 ◽  
Author(s):  
Jack Telesman ◽  
Louis J. Ghosn
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Driving Force ◽  
Narrow Band ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Fatigue Crack Growth Behavior ◽  
Crack Driving Force

A study was done to determine the fatigue crack growth behavior of a PWA 1484 single crystal nickel base superalloy in a temperature range of 427°C to 871°C. Two distinctive failure modes were observed which were a function of both temperature and frequency. At lower temperatures and higher frequencies crack growth occured on the {111} octahedral slip planes at an oblique angle to the loading direction. Higher temperatures and decrease in frequencies favored a Mode I type failure process. The failure mode transitions were explained by invoking arguments based on environmental damage mechanisms. The fatigue crack growth rate data were analyzed using three different crack driving force parameters. The parameters investigated consisted of the Mode I stress intensity parameter corrected for the inclined crack trajectory, and two different octahedral Mode II parameters which are based on the calculation of resolved shear stresses on the {111} slip systems. The Mode I ΔK parameter did a fair job in correlating the data but did not collapse it into a single narrow band. The two octahedral crack driving force parameters, ΔKRSS and a newly proposed ΔKOCT, collapsed all the data into a single narrow band. In addition to correlating the fatigue crack growth rates, the two octahedral parameters also predicted the {111} planes on which the crack growth took place.

Mode I Ductile Crack Growth of 1TCT Specimen Under Large Cyclic Loading: Part II

2018 ◽  
Author(s):  
Kiminobu Hojo ◽  
Shinichi Kawabata ◽  
Naoki Ogawa
Keyword(s):  
Cyclic Loading ◽  
Crack Growth ◽  
Load Cycle ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Ductile Crack ◽  
Cycle Number ◽  
Ductile Crack Growth ◽  
Hardening Rules

The ductile crack growth calculation method under excessive cyclic loading has not been established in the rules for fitness for service, even for Mode I. On the paper for the PVP2017 conference, the authors simulated ductile crack growth behavior of CT specimens under cyclic loading within a committee of the Japan Welding Society, and showed that the Chaboche model and bilinear kinetic hardening rules underestimated the load in compression. The discrepancy between the prediction results and the experimental results were also shown to become larger with increasing load cycle number. In this paper, the authors tried to establish how to determine the parameters of the combined hardening rule and then applied it to simulate the ductile crack growth behavior of the 1TCT specimens for loading levels different from that of last year. Also, the simplified ΔJ calculation, for example the reference stress method, and the crack growth rate from the JSME rules for FFS were applied to estimate the ductile crack growth. Based on this approach, the crack growth analysis method was investigated in order to incorporate into the JSME rules for large cyclic loading.

Mode I Ductile Crack Growth of CT Specimen Under Large Cyclic Loading

2017 ◽  
Author(s):  
Kiminobu Hojo ◽  
Shinichi Kawabata
Keyword(s):  
Growth Rate ◽  
Cyclic Loading ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Ductile Crack ◽  
Hardening Rule ◽  
Ductile Crack Growth

Ductile crack growth calculation method under excessive cyclic loading in a fitness for service rule has not been established even in Mode I. The authors simulated ductile crack growth behavior of CT specimens under cyclic loading executed in a committee of the Japan Welding Society. Sensitivity of the used stress-strain curves by monotonic or cyclic loading and the effect of the hardening rule were investigated. For evaluation of the crack growth rate under excessive cyclic loading, the parameter ΔJ was applied and compared with the rate of the JSME rules for FFS.

Paris law relations for an epoxy-based adhesive

2019 ◽  
Vol 234 (2) ◽  
pp. 291-299 ◽  
Author(s):  
AVM Rocha ◽  
A Akhavan-Safar ◽  
R Carbas ◽  
EAS Marques ◽  
R Goyal ◽  
...  
Keyword(s):  
Crack Growth ◽  
Damage Parameter ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mode I ◽  
Mode I Crack ◽  
Loading Conditions ◽  
Fatigue Crack Growth Behavior ◽  
Paris Law ◽  
R Ratio

Depending on the expression used in Paris law relation, crack growth rate can be a function of loading conditions. However, for design purposes, it is costly and time consuming to obtain a complete map for fatigue crack growth behavior of adhesives. Accordingly, using a damage parameter where the Paris law constants are similar for different loading conditions is very helpful. In this paper, mode I crack growth (FCG) tests were performed at different loading conditions. Results show that performing one experiment would be enough to obtain Paris law constants if the effect of R ratio is considered in the relations.

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