Reliable prognoses

Calculating the service life of heavy-duty machinery

Terex® Fuchs, which is located in Bad Schönborn in Baden-Württemberg, produces highly dynamic heavy-duty machinery such as cranes and excavators. Inertial forces play a major role in such machinery, since relatively large masses have to be accelerated and decelerated. If the weight of the moving parts can be reduced, less energy is required to move them. The resulting potential faster acceleration increases work speed and thus improves productivity. However, at the same time, it is important not to reduce the service life of components. Where possible, weight reduction should lead to an extended service life. To support this process, the Ulm-based Steinbeis Transfer Center for New Technologies in Traffic Engineering has carried out fatigue life calculations.

To start, the experts in Ulm defined the load scenarios and their cycle times. In doing so, they specified the position of the loading arm as a function of the time and the corresponding load. On this basis, they were then able to calculate finite element (FE) load scenarios, which in turn served as a basis for determining the stress tensor function over time for each joint in the structure. With this, the project team used an S-N curve to carry out fatigue calculations and determine the results on the surface for each of the joints. The welding seams were cross-linked based on structure stress principles and using hexahedron elements.

As the Steinbeis engineers and their project partners at Terex® Fuchs initially suspected, the welding seams are the most critical points on the structure. Their wear and critical positions were clearly identifiable. By varying the geometry, and redesigning and repositioning the welding seams, the Steinbeis experts were able to radically increase the service life compared to the initial design. They were also able to quantify the significance of individual steps taken so that, in addition to these improvements, they could keep an eye on the cost of implementing the measures.

The project team did not stop there. Various usage scenarios were analyzed and wear values were calculated. In doing so, they were able to determine, for example, that “sweeping” – a motion in which the loading arm is pressed to the ground without a load – causes similar wear to an actual loading process.

With comparably little effort, Terex® Fuchs was able to glean very useful information and implement their findings in production by optimizing the structures. The company will use the methods developed as a standard in all subsequent production.

The software used for the project, winLIFE, developed by the Steinbeis Transfer Centers New Technologies in Traffic Engineering, and Traffic Engineering. Simulation.Software has been updated continuously over the past 20 years and nearly 200 licences have been sold worldwide. It is used in areas such as vehicle manufacturing, mechanical engineering, shipbuilding and in the aerospace industry. Recently there has also been growing demand from the wind energy sector.

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