Getting started with Fatigue Analysis using Ansys nCode DesignLife

Overview

Mechanical failures regularly cause injuries, substantial financial losses, and deaths. Thus, minimizing failure is a critical design objective.

Failure due to repetitive loadings is the most common cause of structural failure. Structural fatigue is the initiation and growth of cracks under repetitive loading. Fatigue failure occurs when a crack propagates to a critical length and compromises the structural integrity of the structure. Fatigue is the dominant mechanism in almost all structural failures.

Fatigue damage is cumulative and often undetectable. It develops from repeated loadings at levels insufficient to cause failure in a single application. Fatigue failures are particularly devasting because they occur rapidly under seemingly normal operating conditions to seemingly healthy structures.

Structures are tested to determine their susceptibility to fatigue failure, but the usefulness of fatigue tests is limited. It is often unrealistic to fatigue test an entire structure, so the tests do not exactly represent the real-world structure. Fatigue tests are slow and expensive to conduct, and they produce wide data scatter so multiple tests are needed to obtain a statistically relevant data set. It is also impossible to conduct fatigue tests early in the design process because the design is not finalized; and unrealistic to conduct fatigue tests late in the design process to evaluate design variations.

Using CAE to assess fatigue damage has many advantages over physical testing. It can be used to define more efficient physical tests, efficiently assess more design options, and consider more loading conditions. It also can be utilized early in the design process to compare design variations and late in the design process to assess the effect of design modifications.

Ansys nCode DesignLife can be used to simulate the fatigue reliability of structures under actual usage conditions. The closer the simulated and testing are to the real product and usage, the greater confidence in the engineering results. Thus, Ansys nCode DesignLife is a valuable tool for developing reliable, safe designs.

There are several methodologies used in CAE fatigue simulations. The proper usage depends on the stress level, material data, loading mechanism, and structural features.

Learning Outcomes

Following completion of this premium learning material, you will be able to: 

• Describe the underlying physical nature of fatigue failure.
• Recount the two most common approaches to predicting fatigue life: the stress-life method and the strain-life method.
• Recognize the most important component concepts of computational fatigue analysis, including the handling of mean stresses, techniques for cycle counting and damage accumulation, and the effect of surface conditions.
• Describe the end-to-end solution procedure for stress-life analysis with Ansys nCode DesignLife in Ansys Mechanical.
• Recognize the importance of several nCode DesignLife solution setup options, including mean stress correction, multiaxial assessment, and load mapping.

Prerequisites

• Experience performing structural analyses in Ansys Mechanical.

Estimated Time: 2 Hours 30 minutes