DEVELOPMENT OF FATIGUE TESTING METHOD OF FORWARDER BUNK

The fatigue phenomena is one of the most common causes of failures in structural mechanics and is due to repeatedly applied loads. Komatsu Forest AB, one of the largest manufacturers of forest machines on planet Earth was in need of a fatigue life test of a forwarder bunk which exposes the bunk in a realistic way. Such a test extends the knowledge of the strength, but also, makes it easier to improve the evolution of the design. To develop this, knowledge about the movements, i.e. the accelerations of the forwarder and its load out in the field were of greatest importance. Therefore, measurements of angles, accelerations and strains were carried out, followed by analysis of correlations in order to know the cause of fatigue. The results showed that lateral acceleration as well as the tilting of the forwarder are responsible of the repetitive strains occurred during runtime. To simulate this in a test, a method which uses two actuators to apply forces supposed to lead to comparable strains of the bunk is developed. The method of equivalent fatigue load is used in order to simplify the more complex real life situation. Despite the complicated movement and forces on the bunks in the field, it seems possible to get an accurate fatigue test with only two actuators. The fatigue testing method showed both good and bad results of the strains at different positions. Some more refinements of the applied force components as well as the positions might be needed before such a test is executed