Effects of countersunk hole geometry errors on the fatigue performance of CFRP bolted joints

Due to good aerodynamic performance and reliability, countersunk bolt joint is one of the most commonly used connection methods for carbon fiber reinforced polymer (CFRP) components in the aircraft. However, the countersunk hole machining process is inevitably accompanied by geometric errors, which will directly affect the mechanical properties of the joint structure. This paper presents a numerical and experimental investigation on the effect of countersunk hole geometry errors on the fatigue performance of CFRP bolted joints. FE model of CFRP countersunk bolted joints with designed geometry errors are established, and the rationality of the FE analysis was verified by fatigue life and failure forms. The CFRP bolted structure failure mechanism under fatigue load and influence of hole-making geometry error (including countersunk fillets radius, countersunk depth, and countersunk angle) on the fatigue life are investigated. Based on the relationship between fatigue life and the geometry error, the corresponding tolerances for CFRP bolt joint countersunk hole are determined as well. The research results can provide a reference for establishing reasonable geometric accuracy requirements for CFRP joint hole machining.

Modeling of Thermal Contact Resistance of Ball Screws Considering the Load Distribution of Balls

A new analytical method for the modeling of the thermal contact resistance of ball screws considering the load distribution of balls is proposed in this research. The load on balls is analyzed by the force analysis of ball screws, and then, the thermal contact resistance is obtained by the minimum excess principle and Majumdar–Bhushan (MB) fractal theory. The proposed method is validated by experimental results. The comparison with experimental and former results indicates that it is an effective method to evaluate the thermal contact resistance of ball screws. On that basis, effects of axial load, axial pretension, and geometry error of balls are discussed. It is concluded that the thermal contact resistance of ball screws increases along with axial load increase. The load on balls all decreases with axial pretension increase, and the thermal contact resistance of ball screws decreases with the axial pretension increase as well. When the axial load is applied on the nut in an axial-pretension ball screw, the load distribution in Nut A or B becomes less homogenized when the nut moves from nut position parameter ξ = 0 to 1. When the nut moves to ξ = 0.25, the thermal contact resistance will reach a minimum value, and it gets a maximum value at the nut position ξ = 1. The interval range of load and thermal contact resistance are obtained via uncertain analysis. It is concluded that the geometry error has much greater effects on the balls far away from the spacer.

A novel geometry error measurement methodology for coaxiality evaluation

In this paper, we proposed a new device for geometry errors measurement and coaxiality evaluation, and the corresponding methodology for coaxiality evaluation from measurement data is presented, which allows to characterize multiple holes at a time. Unlike traditional measurement system a laser sensor is mounted onto out of the holes so that multi-hole surfaces can be “seen” by the senor when it rotates around a fixed axis. First the intersections (or ellipse profiles) of the sensor’s scanning plane and holes, are computed by fitting. Then, the center coordinates and profile points of the ellipse are computed and transformed to the 3D global coordinate frame. Finally the centerline of the hole is determined from the 3D profile points by using a weighted least-squares fitting algorithm. In addition, to reduce the effect of noises on the measurement result, error analysis and compensation techniques are studied to improve the measurement accuracy. A case study is presented to validate the measurement principle and data processing approach.