How do you model and simulate low cycle and high cycle fatigue behavior using finite element analysis?

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Fatigue is a common cause of failure in engineering components and structures, especially in cyclic loading conditions. It involves the initiation and propagation of cracks due to repeated stress or strain fluctuations. Depending on the number of cycles and the magnitude of the load, fatigue can be classified into low cycle and high cycle regimes. How do you model and simulate these different types of fatigue behavior using finite element analysis (FEA)? In this article, you will learn the basics of fatigue analysis, the differences between low cycle and high cycle fatigue, and the methods and tools for FEA simulation.

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Hamilton Feijó

Certified Economist | 100X ?? Linkedin Top Voice | Innovation and Strategy Specialist | Business Manager | Corporate…
Shahab Zangeneh, PhD

Fitness for Service (FFS) assessment
Apoorva Tyagi

Sensor Development at Danfoss | RWTH Aachen

1 Fatigue analysis basics

Fatigue analysis is the process of evaluating the durability and reliability of a material or a component under cyclic loading. It involves three main steps: loading definition, material characterization, and life prediction. Loading definition refers to the specification of the load history, frequency, amplitude, and spectrum that the component is subjected to. Material characterization refers to the determination of the material properties and parameters that affect the fatigue behavior, such as stress-strain curves, fatigue curves, fracture toughness, and damage models. Life prediction refers to the estimation of the number of cycles or the time until failure, based on the stress or strain response of the component and the material fatigue criteria.

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2 Low cycle and high cycle fatigue

Low cycle fatigue (LCF) occurs when the component experiences a relatively small number of cycles (usually less than 10^4) with high stress or strain amplitudes (usually above the elastic limit). LCF is characterized by plastic deformation, cyclic hardening or softening, and crack initiation at stress concentrations or defects. High cycle fatigue (HCF) occurs when the component experiences a large number of cycles (usually above 10^6) with low stress or strain amplitudes (usually within the elastic range). HCF is characterized by elastic deformation, negligible hardening or softening, and crack initiation at microstructural features or surface irregularities.

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Hamilton Feijó

Certified Economist | 100X ?? Linkedin Top Voice | Innovation and Strategy Specialist | Business Manager | Corporate Social Responsibility |
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a) In my experience, understanding the differences between low cycle and high cycle fatigue is crucial to accurately modelling and simulating fatigue behaviour. b) For example, in the case of low cycle fatigue, the focus is on plasticity and localised plastic deformation, while in high cycle fatigue, the emphasis is on elastic deformation and cumulative damage over time.

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3 FEA methods for fatigue analysis

FEA is a numerical technique that can simulate the stress or strain response of a component under various loading conditions, using a discretized model of the geometry and the material properties. FEA can be used for both LCF and HCF analysis, but the methods and assumptions may differ. For LCF analysis, FEA usually involves a nonlinear static or dynamic analysis, where the material behavior is modeled using plasticity or viscoplasticity models, and the load history is applied as a series of steps or increments. The stress or strain history at each element or node is then used to calculate the fatigue life using strain-based criteria, such as the Coffin-Manson or the Chaboche models. For HCF analysis, FEA usually involves a linear static or dynamic analysis, where the material behavior is modeled using elasticity models, and the load history is applied as a sinusoidal or random function. The stress or strain amplitude or range at each element or node is then used to calculate the fatigue life using stress-based criteria, such as the S-N or the Basquin models.

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Shahab Zangeneh, PhD

Fitness for Service (FFS) assessment
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Fatigue analysis in pressure vessels, can be carried out by ASME Section VIII, Division 2, this section involves the use of Finite Element Analysis (FEA) methods to assess the structural integrity of the vessel under cyclic loading conditions.

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4 FEA tools for fatigue analysis

There are various software tools that can perform FEA for fatigue analysis, either as standalone applications or as add-ons or modules for general-purpose FEA software, such as ANSYS Fatigue, ABAQUS Fatigue, MSC Fatigue, nCode DesignLife, and FE-SAFE. These tools can offer a range of features and capabilities, from importing or creating FEA models and load histories to selecting material properties and fatigue models, performing stress or strain analysis and post-processing, calculating fatigue life or damage and displaying results, performing sensitivity or optimization studies, to generating reports or documentation.

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Apoorva Tyagi

Sensor Development at Danfoss | RWTH Aachen
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FEMFAT is a great tool which is based on FKM guidelines for fatigue life calculation. It allows the user to import stress states from popularly used FEA softwares (Abaqus, Ansys etc.).

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Anbazhagan Ramasamy

Simulation Engineer at Nemak Europe GmbH
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FEMFAT is also widely used in automotive field in Germany. It has advanced capabilities to consider local material properties of cast components

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Bilal Zahid

Senior Mechanical Design Engineer | Static Equipment | QMS Auditor | ASME | API | UL | TEMA | ASTM | SAES (ARAMCO Std.) | ISO | ANSYS FEM
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Inbuilt Ansys fatigue tool is a direct fatigue analysis tool. On other hand, Ansys static structural can also be used along with ASME Section VIII Div 2 fatigue analysis procedure.

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5 Tips and best practices for FEA simulation

Performing FEA simulation for fatigue analysis can be a complex and demanding task, requiring close attention to detail and accuracy. To achieve better results, it’s important to select an appropriate FEA method and tool for your fatigue problem, taking into account the type of loading, material, geometry, and failure mode. Additionally, validate your FEA model and assumptions against experimental data or analytical solutions. Use a suitable mesh size and refinement, avoiding any distortion or stress concentration. Make sure to apply realistic boundary conditions and load cases that reflect the actual service environment and variability. Additionally, use consistent units and coordinate systems to avoid errors or confusion. Check your FEA results for convergence, stability, and plausibility, identifying any anomalies or errors. Finally, interpret your fatigue life predictions with caution, considering the uncertainties and limitations of the FEA and the fatigue models.

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Bilal Zahid

Senior Mechanical Design Engineer | Static Equipment | QMS Auditor | ASME | API | UL | TEMA | ASTM | SAES (ARAMCO Std.) | ISO | ANSYS FEM
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FEA simulation is not a straightforward procedure with set formulae. It can have endless simulation possibilities, but we need to find an optimum solution (economically in terms of computing power) with best possible accuracy. Following parts would require a keen aye: 1) Simplification of model (but not over simplification) 2) Boundary conditions 3) Detecting the unrealistic stresses arising due to model defects

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Gulshan Singh, PhD

DOER || Top Voice || IIT Kanpur || x-GE || Exp.-Germany & India || Data Science, Analytics & Viz. || Maintenance Cost Reduction
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Large variations in fatigue life for the same material and loading condition are a fact of life. Therefore it is critical to consider uncertainties in the material properties and assumptions in the computational analyses. Incorporating these uncertainties provides fatigue life approximation and variance/confidence bounds in the estimate.

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How do you model and simulate low cycle and high cycle fatigue behavior using finite element analysis?

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1 Fatigue analysis basics

2 Low cycle and high cycle fatigue

3 FEA methods for fatigue analysis

4 FEA tools for fatigue analysis

5 Tips and best practices for FEA simulation

6 Here’s what else to consider

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