Equivalent axial stiffness of various components in bolted joints subjected to axial loading

Managing the axial stiffness of various components in a bolted joint is a major industrial concern for modelling different tightening processes and for accurate fatigue dimensioning. This paper presents a new approach for calculating the axial stiffness of the several elements of a bolt (the head and the engaged part), the nut and the fastened plates. Finite element modelling based on deformation energy improves the existing models and take in to account the type of materials and coefficients of friction of various elements in contact. From these corrections, approaches for axial stiffness calculation based on empirical formulas are proposed for easier application and for future FE modelling bolted joints using beam elements. Finally, the theoretical study is validated by an original experimental approach.