无耳托板螺母组件紧固性能研究

Tightening Performance of the Rivetless Nut Plate System

随着航空航天工业的发展,对紧固件的防松性能要求越来越高.打滑失效是新型无耳托板螺母组件一种典型失效形式,当螺母所受扭矩过大时,螺母托板和安装板之间发生打滑,从而失去紧固功能.针对无耳托板螺母组件的打滑失效问题,本文开展了拧脱试验,获得了不同板厚和孔径条件下的极限拧脱力矩.基于Abaqus有限元软件,开展了无耳托板螺母组件的冷挤压和切削工艺仿真,获得了无耳托板螺母组件的残余应力与塑性应变.由于螺母托板与安装板间的摩擦系数难以直接测定,采用试验结合仿真的反推法,建立了摩擦系数的近似线性模型,进而开展了无耳托板螺母组件拧脱的有限元仿真分析,讨论了无耳托板螺母组件中安装板的厚度、孔径以及切削铰孔厚度对拧脱力矩的影响.最后补充了拧脱试验,验证了仿真模型的准确性.结果表明:安装板的板厚、孔径会对冷挤压安装效果有较大影响,较小孔径的安装板在冷挤压安装时会产生更大的塑性变形,因此和螺母托板间有更大的接触应力,安装更为紧密;较大板厚的安装板与螺母托板间的接触应力分布面积更大且更加均匀,两者干涉贴合的效果更好.切削厚度会影响孔边残余应力与塑性应变,进而对拧脱力矩产生影响.利用试验和仿真反推的摩擦系数的近似线性模型所进行仿真预测的安装板尺寸边界,与后续补充试验吻合良好.

As the aerospace industry continues to evolve,the requirements for enhanced antiloosening performance of fasteners have become increasingly stringent.Slippage is a typical failure mode within the rivetless nut plate system.It occurs when the applied torque exceeds the system capacity,leading to a compromise in fastening integrity between the nut plate and installation plate.This study addressed the issue of slippage in the nut plate through a series of torque-out tests.Utilizing the Abaqus finite element analysis software,we simulated the cold expansion and cutting processes specific to the rivetless nut plate system.This approach enabled us to ascertain the residual stress and plastic strain affecting the system efficacy.Given the challenge of directly measuring the friction coefficient between the nut plate and the installation plate,a novel methodology that blended experimental data with simulations was employed to infer the friction coefficient.Through this process,an approximate linear model for the friction coefficient was established,which then informed the finite element analysis conducted during the torque-out tests.This investigation further delved into how the thickness and aperture size of the installation plate,alongside the cutting thickness,influence the torque.Subsequently,complementary tests were conducted to verify the accuracy of the simulation.The results indicate that both the thickness and aperture size of the installation plate have a significant effect on the performance of the cold expansion installation.Specifically,installation plates with smaller apertures induce greater plastic deformation during the cold expansion process,resulting in increased contact stress.Conversely,installation plates with larger thicknesses facilitate a more extensive and evenly distributed contact stress area,yielding better interference fit effects.Moreover,the cutting thickness was found to significantly affect the residual stress and plastic strain around the hole,which,in turn,affects the torque.To validate the accuracy of our simulations,complementary experiments were conducted.These test confirmed that the approximate linear model of the friction coefficient,derived from both experimental and simulation data,accurately predicts the size boundary of the installation plate.The predictions closely aligned with the outcomes of subsequent supplementary tests.