Probabilistic

What does it mean to have a safety factor of 3? It is better than a safety factor of 2, but how does it relate to the risk and reliability of your design? And at what cost? Some people simply use lower bound material properties to account for variability. This simple minded approach ignores variability and uncertainties associated with loading, analysis and geometric variables. Probabilistic fatigue analysis is a much better tool to obtain estimates of the failure probability and to quantify the relative influence of variability and uncertainty in all of the input parameters so that the life drivers can be identified.

eFatigue determines failure probabilities by replacing deterministic values with statistical distributions for any of the input variables in the Constant Amplitude Calculators. The Probabilistic Calculators can be used in conjunction with more complex Fatigue Analyzers by defining an equivalent constant amplitude load.

Outputs from the analysis include probability of failure plots as well as tables of probabilistic sensitivity factors. These factors quantify the relative variability or uncertainty of each input variable. This allows you to concentrate your resources on the ones that are the most important and have the most influence on the reliabiliy of your products.

Finders are provided to obtain the necessary input information for material properties and stress concentration or stress intensity factors. Guidance is provided to help you select appropriate statistical distributions and variability.

Fatigue Calculators

• Stress-Life
  Use this method for long life situations where the strength of the material and the nominal stress control the fatigue life.
• Strain-Life
  This method is used for finite fatigue lives where plasticity around stress concentrations is important.
• Crack Growth
  Use this method to determine how long it will take a crack to grow to a critical size.

Finders

• Stress Concentration Factors
  Compute the stress concentration factor for holes, grooves, notches, shoulders, and keyways.
• Stress Intensity Factors
  Compute the stress intensity factor for plates with various shaped cracks.
• Material Properties
  Find material properties for fatigue analysis.

Technical Background

• Statistical Distributions
• Normal
• Log-Normal
• Uniform
• Gumbel
• Weibull
• Statistical Simulations
• Generating Random Variables
• Correlated Variables
• Monte Carlo Simulation
• Probabilistic Sensitivity Factors
• Stress-Life
• Loading Variability
• Materials
• Modifying Factors
• Stress Concentration
• The Simulation
• Output Results
• Strain-Life
• Loading Variability
• Materials
• Stress Concentration
• The Simulation
• Output Results
• Crack Growth
• Loading Variability
• Materials
• Stress Intensity Factor
• The Simulation
• Output Results