FATIGUE STRENGTH PREDICTION OF BOLTED JOINT STRUCTURES OF CARBON FIBRE REINFORCED POLYMER COMPOSITE BASED ON THE MICROMECHANICS

In this paper, the theory of micro-mechanics of failure (MMF) is extended to analyze the fatigue progressive failure and predict the strength for the bolted joint structures of carbon fibre reinforced polymer (CFRP) composite. The MMF approach includes the material strength characterization and structure strength design for the CFRP structures. The material strength characterization includes macro-mechanics experiments for the unidirectional laminates, micro-mechanics analysis and MMF critical parameters extraction. The structure strength design includes modelling of a specific structure, macroscopic stress analysis, microscopic stress magnification, constituents' failure judgments, material properties degradation and crack propagation in the structures. The feature of the approach is that the material properties degradation of each element in each calculation step is determined by the constituents' failure judged physically by the MMF parameters of the key points in the micro-mechanics model. The structure strength design is realized by developing the user defined material (UMAT) subroutine with FORTRAN scripts on the ABAQUS platform. The evolution of initial failure and progressive failure of the double-bolt double shear lap joint of the UTS50/E51 laminate under the static loading and the fatigue loading, respectively, is analyzed in detail by using the MMF approach. Based on the MMF approach, the fatigue tensile loading failure mechanism for the UTS50/E51 double-bolt joints structures and its S-N curves is analyzed, and a comparison with the test results is conducted.