切向加载、卸载和振荡强耦合下机床螺栓结合部之摩擦能量耗散机制

Frictional energy loss mechanism of bolt joint interface in machine tools considering transverse loading-unloading-oscillating strong interaction

在保持微凸体受法向力恒定的状态下,侧重导出切向力和变形量的切向加载、切向卸载和切向振荡接触方程。当2个球形微凸体接触时,构建每循环中切向接触摩擦能量耗散力学模型。按照赫兹静力弹性法向接触理论,得到微凸体顶端曲率半径。根据微凸体分担法向力的光滑性与连续性法则,校正临界弹性变形微接触面积与临界变形量的数学表达式。面向有条件等式,在弹性和纯塑性变形基础上,建立整个结合部法向力与切向接触摩擦能量耗散的理论模型。以北京机电院高技术股份有限公司直线电机驱动Linear MC6000普莱诺五面体加工中心上的龙门横梁-导轨螺栓结合部为研究对象,分析法向预紧力、表面粗糙轮廓分形维数、切向力、分形粗糙度、相关因子、单轴向屈服应变及静摩擦因数等7个相对独立参数对切向接触摩擦能量耗散的影响规律。可视化的数值分析结果表明:切向接触摩擦能量耗散随着法向预紧力的增大先增大后减小;表面粗糙轮廓分形维数在较小范围内,切向接触摩擦能量耗散随着表面粗糙轮廓分形维数或分形粗糙度的增大而增大;表面粗糙轮廓分形维数在较大范围内,切向接触摩擦能量耗散随着表面粗糙轮廓分形维数或分形粗糙度的增加而减小;切向接触摩擦能量耗散随着切向力、相关因子、单轴向屈服应变的增加而加大;切向接触摩擦能量耗散随着静摩擦因数的增加而降低与经典结论完全相反,这是因为当静摩擦因数较大时,根据近代分形几何理论可知法向预紧力越大,微滑趋势将更小,导致较小切向接触摩擦能量耗散。

When a normal force acting on an asperity kept constant,the tangential loading,tangential unloading and tangential oscillating contact equations between tangential force and deformation were deduced in detail. The mechanical model for shear contact frictional energy dissipation per cycle was built when two spherical asperities contacted.Based on Hertz static elastic normal contact theory,the curvature radius of the asperity＆#39;s top was derived. Owing to the smooth and continuous properties of normal force of microcontact,the mathematical expressions about critical elastic deformation micro-contact area and critical deformation were modified.Facing the equations with conditions and based on elastic and purely plastic deformation,the theoretical models for bolt joint interface normal force and transverse contact frictional energy dissipation were established.A gantry beam-rail bolt joint interface was taken as a study object in the Linear MC6000 Plano pentahedral machining center driven by a linear motor of Beijing Machine and Electricity Institute High-Tech Company Limited.The influence laws of normal preload,fractal dimension of a surface harsh profile, tangential force,fractal roughness,related factor,uniaxial yield strain and static friction coefficient on the transverse contact frictional energy dissipation were analyzed.Furthermore,the visual numerical analysis results showed that the transverse contact frictional energy dissipation firstly increases and then diminishes with increase in normal preload;the transverse contact frictional energy dissipation increases with increase in the fractal dimension or fractal roughness of a＆amp;nbsp;surface rough profile in the smaller range of the fractal dimension of the surface rough profile;the transverse contact frictional energy dissipation decreases with increase in the fractal dimension or fractal roughness of a surface rough profile in the larger range of fractal dimension of the surface rough profile;the transverse contact frictional energy dissipation increases with increase in tangential force,related factor and uniaxial yield strain;that the transverse contact frictional energy dissipation decreases with increase in static friction coefficient is completely opposite to the classical conclusion, this is because that when the static friction coefficient becomes larger,the normal preload becomes higher based on the neoteric fractal geometric theory,and the tendency of microslip becomes much smaller,so the transverse contact frictional energy dissipation becomes smaller.