Industry: Mining, Railroad, Heavy Equipment
End Users: Arcelor Mittal, CSX, ADEX
Solution: Improved existing industrial product by increasing linear fatigue level and overall safety factors.
"Fatigue" has been found as the root of failure of many mechanical components such as turbines and other rotating equipment operating under intense, repeated cyclical loads.
Designers normally consider the most important safety consideration to be the overall strength of the component, assembly, or product. To design for this, engineers want to create a design that will stand up to the probable ultimate load, and add a safety factor to that, for insurance. In operation, however, the design is very unlikely to experience static loads. Much more frequently, it will experience cyclical variation, and undergo multiple applications of such load variation, which may lead to failure over time.
The definition of fatigue, in fact, is: "failure under a repeated or otherwise varying load, which never reaches a level sufficient to cause failure in a single application." The symptoms of fatigue are cracks that result from deformation in localized areas. Such deformation usually results from stress concentration sites on the surface of a component, or a pre-existing, virtually undetectable, defect on or just below the surface. While it may be difficult or even impossible to model such defects in finite element analysis (FEA), variability in materials is a constant, and small defects are very likely to exist. FEA can predict stress concentration areas, and can help our engineers to design the product to minimize the onset of fatigue.
A manufacturing company was experiencing "fatigue" with a lug component used in industrial digging products. Like the links on a chainsaw, there are more than 1,200 of these lugs, connected and rotating at high speeds to perform its task. A slight break or weakening of the lug could have dramatic impact, and potentially life-threatening results. Vallmar Engineering was brought in to 1) diagnose the root cause of the fatigue and 2) to increase the productivity and safety factors of the lug by 40 percent.
The first step was to diagnose the root cause of the fatigue. The general analysis methodology was to use a half-symmetry model for the Lug block as-is from current geometry. A linear-static analysis was performed using the finite element cod with Solid Works / Cosmos and procedures as follows;
1. Original part configurations with material specs per SW, AISI.
2. Original and updated part geometry evaluations.
3. Thickness and surface analysis.
4. Curvature tangency and blend surface analysis.
5. Von Mises Stress Analysis.
Through these various testing functions, the Vallmar Engineering team was able to identify the weaknesses of the current design.
In order to address these areas, Vallmar Engineering revisited the above five-step process, focusing on the areas where the design had failed. The product was then remodeled and recreated to reach the desired 40 percent improvement in productivity and safety.
The product has now been in use for several years.
- Achieved a 40% increase in productivity
- Improved overall safety of the end product