Predicting Fatigue Failures with Confidence

Learn about MSC Nastran Embedded Fatigue

The article below is by Wayne Tanner, CEO of Leading Edge Engineering, an MSC Software Business Partner.

Wayne will be presenting a unique hands-on workshop in Coppell, TX on March 21, giving engineers the opportunity to learn this process themselves. Registration is free >> http://pages.mscsoftware.com/load-fatigue2013

Many companies already use FEA to analyze their structures, but typically use a set of static or inertial limit loads, and modal analysis to validate their products. While these loads usually work well as screening loads and have proven successful at eliminating catastrophic failures, they typically don't do an adequate job of simulating and predicting failures. Increasingly, there is a need to do a better job of predicting failures early in the development process, and developing solutions without the expense (in terms of time and dollars) of multiple physical prototype iterations. Predicting failures can significantly reduce long term warranty costs, and be used to optimize the structure.

Load/Fatigue Process Overview

A virtual load/ fatigue analysis process uses an Adams Multi-Body Dynamics (MBD) loads of the system to calculate the response and loads of the system as it operates through a virtual set of events or duty cycle. These loads are then exported to a MSC Nastran FE model to recover the stresses in the component of interest. These stress histories are then used to calculate the fatigue life of the components with the appropriate fatigue algorithms for welds, parent material, etc.

While a virtual load/fatigue process is intended to test a system prior to building a prototype and performing physical testing, it needs to be correlated with test data. The ultimate goal is for the load/fatigue process to augment (not eliminate) the physical testing process. There are some parameters such as damping and tire interactions which need to be determined from physical testing. For this reason, the virtual process needs to be developed in coordination with testing, and correlated back to the physical test. During each successive development cycle, more confidence is developed in the MBD system model, and improved model parameters are developed in the virtual process, but it can be used to simulate events that are difficult to setup and test, information (loads, stresses, strain, etc.) can be gathered from any point on the system, and complete built/ test cycles can be eliminated.

Implementing a virtual loads/fatigue process requires expertise in several advanced disciplines (Multi-body Dynamics, FEA Dynamics, Fatigue Analysis, and Test Correlation). This is a process which may take several simulation/test/correlation and develop models with the appropriate level of sophistication. Successful companies usually have one or more engineers who are tasked with championing this process and build confidence and experience with working through the challenges of correlating their product development process to focus on fatigue and loads vs. single loadcases and hotspot stresses.

Want to learn more?

• Join us on March 21 for a free hands-on workshop in Coppell, TX. Details/ registration can be found here: http://pages.mscsoftware.com/load-fatigue2013
• Read the entire article in our Simulating Reality Magazine
• E-mail the original author for questions at wtanner@leadedge.com

Learn about MSC Nastran Embedded Fatigue