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.

Numerical Analysis of Laser Shock Peening as a Process for Generation of Compressive Residual Stresses in Open Hole Specimens

2011 ◽  
Vol 681 ◽  
pp. 267-272 ◽  
Author(s):  
Goran Ivetic ◽  
Ivan Meneghin ◽  
Enrico Troiani
Keyword(s):  
Fatigue Crack ◽  
Numerical Analysis ◽  
Residual Stresses ◽  
Crack Nucleation ◽  
Laser Shock Peening ◽  
Laser Shock ◽  
Fatigue Crack Nucleation ◽  
Open Hole ◽  
Shock Peening ◽  
Compressive Residual Stresses

A numerical analysis of Laser Shock Peening (LSP) process is illustrated, applied to an open hole specimen. This specimen is representative of a section of an aircraft fuselage lap joint, typically prone to fatigue crack nucleation at the rivet holes. The effect of the residual stress field induced by LSP on the fatigue life of open hole specimens is investigated. The results show that significant compressive residual stresses can be introduced in fatigue sensitive areas using LSP, postponing fatigue crack nucleation.

Fatigue Crack Retardation in LSP and Sp Treated Aluminium Specimens

2014 ◽  
Vol 891-892 ◽  
pp. 986-991 ◽  
Author(s):  
Elke Hombergsmeier ◽  
Vitus Holzinger ◽  
Ulrike C. Heckenberger
Keyword(s):  
Fatigue Crack ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Shot Peening ◽  
Laser Shock Peening ◽  
Laser Shock ◽  
Propagation Behavior ◽  
Shock Peening ◽  
Compressive Residual Stresses ◽  
Crack Propagation Behavior

Highly loaded aircraft components have to fulfill strict fatigue and damage tolerance requirements. For some components besides the crack initiation mainly the fatigue crack propagation behavior is the main design criteria. To improve the crack propagation behavior of a component several methods are known or have been described in literature. For thin aircraft panels i.e. the application of crenellations [1] or bonded doublers [2, 3] can be a solution. For thick structures mainly the introduction of compressive residual stresses is beneficial. In this paper the potential of compressive residual stresses obtained by Laser Shock Peening (LSP) and Shot Peening (SP) is investigated. By means of Laser Shock Peening the residual compressive stress field can extend much deeper below the treated surface than that produced by conventional Shot Peening (i.e. with steel or ceramic balls) [4, 5]. The effect of such deep compressive stress profile results in a significantly higher benefit in fatigue behavior after Laser Shock Peening or after the combination of Laser Shock Peening and Shot Peening on top. The measurement of residual stresses as a depth profile has been performed by incremental hole drilling (ICHD) and contour method. Finally crack propagation tests have been carried out to validate the process technology approach.

Computed Dependence of Rubber'S Fatigue Behavior on Strain Crystallization

2009 ◽  
Vol 82 (1) ◽  
pp. 51-61 ◽  
Author(s):  
W. V. Mars
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Operating Conditions ◽  
Fatigue Threshold ◽  
Crack Growth Behavior ◽  
Fatigue Crack Nucleation ◽  
Nucleation Behavior ◽  
Wide Range

Abstract This work explores the consequences of strain crystallization on rubber's fatigue crack nucleation behavior over an extensive space of operating conditions, including tension and compression loading states, and relaxing and non-relaxing cycles. The study considers, via computation, how the nonlinear elastic stress-strain behavior, the fatigue crack growth characteristics, and the damage accumulation law combine to produce the Haigh diagram and the Cadwell diagram. Four hypothetical materials are studied, which differ in their crystallization and associated fatigue crack growth behavior. The calculations demonstrate that a relatively simple idealization can credibly predict the unique shape and sensitivities of observed fatigue behavior over a wide range of conditions. They also clarify how features of the Haigh and Cadwell diagrams are linked to the occurrence of crystallization and to parameters such as the power-law slope and the fatigue threshold.

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.

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.

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