An experimental methodology for quantitative characterization of multi-site fatigue crack nucleation in high-strength Al alloys

2016 ◽  
Vol 39 (6) ◽  
pp. 696-711 ◽  
Author(s):  
Y. Jin ◽  
P. Cai ◽  
Q. B. Tian ◽  
C. Y. Liang ◽  
D. J. Ke ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Nucleation ◽  
High Strength ◽  
Al Alloys ◽  
Experimental Methodology ◽  
Quantitative Characterization ◽  
Fatigue Crack Nucleation

scholarly journals Characterization of Surface Fatigue Crack Nucleation and Microstructurally Small Crack Growth in High Strength Aluminum Alloys

2021 ◽  
Vol 7 ◽  
Author(s):  
Robert Fleishel ◽  
Cole Cauthen ◽  
Steven Daniewicz ◽  
Andrew Baker ◽  
J. Brian Jordon ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Aluminum Alloys ◽  
Crack Growth ◽  
Surface Crack ◽  
Crack Nucleation ◽  
High Strength ◽  
Small Crack ◽  
Fatigue Crack Nucleation ◽  
Small Crack Growth ◽  
High Strength Aluminum Alloys

It is well established that fatigue crack nucleation and small crack growth in high strength aluminum alloys are highly influenced by the surrounding microstructure including grain boundaries, texture, inclusion barriers, among other factors. As such, specific and targeted experimental and computational methods are necessary to accurately capture and predict the discrete behavior of microstructurally small fatigue cracks. In this study, surface fatigue crack nucleation and microstructurally small crack growth in high strength aluminum alloys, commonly used in aerospace applications, are evaluated through a holistic approach encompassing fatigue testing, crack measurement, and computational prediction of crack growth rates. During fatigue testing, crack shapes and growth are quantified using a novel surface replication technique that is applied to investigate crack nucleation, as well as to collect validation data that includes an accurate description of crack shape during crack propagation, a challenging and essential component in predicting crack growth. Computational simulation of fatigue crack growth in non-straight, complex surface crack arrays typically requires high fidelity analysis using computationally expensive methods to account for the mathematical and geometrical complexities inherent in the solution. A dislocation distribution based technique has been previously demonstrated to rapidly and accurately predict the stress intensity factors for through cracks of complex shape. This method was expanded and investigated as an approach for rapidly predicting the crack growth rate of kinked and tortuous surface crack arrays, using the crack configuration and bulk material properties as inputs. To investigate the accuracy and effectiveness of this characterization approach, surface crack growth in AA7075-T7351 was experimentally analyzed and modeled under high cycle and low cycle fatigue conditions. This comprehensive approach was determined to be an expedient and applicable method for characterizing and evaluating the nucleation and crack growth rate of non-planar microstructurally small and short crack configurations.

A Micromechanical Approach to Model Residual Stress Relaxation and Fatigue Crack Nucleation in High Strength Gear Steels

2007 ◽  
Author(s):  
Rajesh Prasanna ◽  
David L. McDowell
Keyword(s):  
Fatigue Crack ◽  
Residual Stresses ◽  
Shot Peening ◽  
Thermal Loading ◽  
Crack Nucleation ◽  
Fatigue Behavior ◽  
High Strength ◽  
Operating Conditions ◽  
Fatigue Crack Nucleation ◽  
Shock Peening

It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Of particular interest here are the residual stresses induced through shot peening process. Compressive residual stresses of high magnitudes are induced at and near the surface during shot peening process by virtue of constrained plastic deformation. These stresses enhance the service life of component by resisting fatigue crack nucleation and growth on surface of the specimen. Unfortunately, these residual stresses can relax significantly due to subsequent mechanical and/or thermal loading even under normal operating conditions.

scholarly journals Micromechanical Modeling of Fatigue Crack Nucleation around Non-Metallic Inclusions in Martensitic High-Strength Steels

Metals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1258 ◽  
Author(s):  
Benjamin Schäfer ◽  
Petra Sonnweber-Ribic ◽  
Hamad ul Hassan ◽  
Alexander Hartmaier
Keyword(s):  
Fatigue Crack ◽  
Crack Nucleation ◽  
Micromechanical Model ◽  
High Strength Steels ◽  
High Strength ◽  
Fatigue Crack Nucleation ◽  
Metallic Inclusions ◽  
Microstructural Defects ◽  
Loading Axis ◽  
Inclusion Matrix

Martensitic high-strength steels are prone to exhibit premature fatigue failure due to fatigue crack nucleation at non-metallic inclusions and other microstructural defects. This study investigates the fatigue crack nucleation behavior of the martensitic steel SAE 4150 at different microstructural defects by means of micromechanical simulations. Inclusion statistics based on experimental data serve as a reference for the identification of failure-relevant inclusions and defects for the material of interest. A comprehensive numerical design of experiment was performed to systematically assess the influencing parameters of the microstructural defects with respect to their fatigue crack nucleation potential. In particular, the effects of defect type, inclusion–matrix interface configuration, defect size, defect shape and defect alignment to loading axis on fatigue damage behavior were studied and discussed in detail. To account for the evolution of residual stresses around inclusions due to previous heat treatments of the material, an elasto-plastic extension of the micromechanical model is proposed. The non-local Fatemi–Socie parameter was used in this study to quantify the fatigue crack nucleation potential. The numerical results of the study exhibit a loading level-dependent damage potential of the different inclusion–matrix configurations and a fundamental influence of the alignment of specific defect types to the loading axis. These results illustrate that the micromechanical model can quantitatively evaluate the different defects, which can make a valuable contribution to the comparison of different material grades in the future.

Low-Cycle fatigue crack nucleation and early growth in Ti-17

1978 ◽  
Vol 9 (8) ◽  
pp. 1159-1167 ◽  
Author(s):  
A. W. Funkenbusch ◽  
L. F. Coffin
Keyword(s):  
Fatigue Crack ◽  
Crack Nucleation ◽  
Low Cycle Fatigue ◽  
Early Growth ◽  
Cycle Fatigue ◽  
Fatigue Crack Nucleation
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