EXPERIMENTAL AND NUMERICAL ANALYSIS OF PRELOAD IN BOLTED COMPOSITE JOINTS WITH TEMPERATURE LOADS

Pretensioned bolted joints of polymer matrix composite structural components show a loss of preload due to viscoelastic properties of the matrix and a load direction perpendicular to fiber orientation. In this work, an experimental investigation and a numerical prediction of the bolt preload is performed for three different T700 Epoxy laminate plates at room temperature and at 70 degrees C. Bolt preload is measured by using an embedded strain gauge inside M 8 bolts as well as by force washers for a period of up to 48 days without external loadings. The simulation is carried out in two ways: viscoelastic exact solution and quasi-elastic approach using a three-dimensional finite element model of test setup, differences between both methods are negligible. The numerical analysis show a high influence of fiber volume fraction and laminate thickness on preload behaviour. Compared to the test results, simulation gives lower preload losses. Furthermore, the test results show a lower influence of laminate layup on bolt preload behaviour at room temperature than at 70 degrees C. The comparison of test results between quasi-isotropic laminate and steel specimen show an almost identical preload loss at room temperature, whereas the preload loss of quasi-isotropic laminate is approximately twice of steel specimen at 70 degrees C.