Fatigue and damage analysis of elastomeric silent block in light aircrafts

Silent block are frequently replaced in light aircrafts due to deterioration of the elastomeric isolators. Failure of these elastomeric silent blocks is caused by the radial load and axial displacement leading to fatigue and wear. The damage here is influenced by geometry and rigidity of the elastomer. Based on these criteria we have developed a tribological model and a test equipment to evaluate the reliability which can suggest an appropriate material for these applications. Tests were performed for different elastomers such as polyurethane subtype 1 (PUM 60A), polyurethane subtype 2 (PUM 70A) and polyurethane subtype 3 (PUA 90A) with geometrical modifications by having overhangs ranging from 1 mm to 4 mm. The load was induced based on the progressive loading principle where different load levels from 80% to 150% of the compressive strength were used. Test results show that for specimens with relatively less overhang, the induced stresses are higher. Moreover, the material properties play a significant role where the debris and collar formation are rather less for rigid elastomers. Based on these two-parameters, we define the reliable and critical zones which give the operation reliability coefficient. The reliability coefficient for PUM 60A, PUM 70A and PUA 90A are 0.4, 3.2 and 6 respectively. Thus evaluation for service life can be brought in practice based on the reliability coefficient using the current tribological model.