Profile shift is a highly effective technique for optimizing the performance of spur gear transmission systems.However,tooth surface wear is inevitable during gear meshing due to inadequate lubrication and long-term o...Profile shift is a highly effective technique for optimizing the performance of spur gear transmission systems.However,tooth surface wear is inevitable during gear meshing due to inadequate lubrication and long-term operation.Both profile shift and tooth surface wear(TSW)can impact the meshing characteristics by altering the involute tooth profile.In this study,a tooth stiffness model of spur gears that incorporates profile shift,TSW,tooth deformation,tooth contact deformation,fillet-foundation deformation,and gear body structure coupling is established.This model efficiently and accurately determines the time-varying mesh stiffness(TVMS).Additionally,an improved wear depth prediction method for spur gears is developed,which takes into consideration the mutually prime teeth numbers and more accurately reflects actual gear meshing conditions.Results show that consideration of the mutual prime of teeth numbers will have a certain impact on the TSW process.Furthermore,the finite element method(FEM)is employed to accurately verify the values of TVMS and load sharing ratio(LSR)of profile-shifted gears and worn gears.This study quantitatively analyzes the effect of profile shift on the surface wear process,which suggests that gear profile shift can partially alleviate the negative effects of TSW.The contribution of this study provides valuable insights into the design and maintenance of spur gear systems.展开更多
目的探讨氟化钠护齿剂对幼儿园儿童乳牙患龋率和龋面变化的影响。方法选取2017年1月本地区10所公办幼儿园共330名儿童作为研究对象,随机分为三组,每组各110名儿童,A组给予氟化钠护齿剂(含5%氟化钠)0.2 m L/次,1次/年;B组给予入氟化钠护...目的探讨氟化钠护齿剂对幼儿园儿童乳牙患龋率和龋面变化的影响。方法选取2017年1月本地区10所公办幼儿园共330名儿童作为研究对象,随机分为三组,每组各110名儿童,A组给予氟化钠护齿剂(含5%氟化钠)0.2 m L/次,1次/年;B组给予入氟化钠护齿剂0.1 m L/次,1次/年;C组儿童作为空白对照组,记录涂氟后三组儿童2年内乳牙患龋率、龋面均、新增龋面变化、致龋菌检出情况以及涂氟后尿氟浓度变化。结果A组与B组干预后第2年龋齿发生率分别为37.27%、39.09%低于C组51.82%(P<0.05);A组、B组第1年、第2年龋均值低于C组(P<0.05);A组与B组儿童涂氟后第1年与第2年乳牙颊舌面、邻面、牙合面新生龋面均值低于C组(P<0.05);A组与B组儿童干预第2年变形链球菌、远缘链球菌、乳杆菌检出率低于C组(P<0.05);A组、B组儿童涂氟后6 h、12 h尿氟浓度高于C组儿童(P<0.05);三组儿童涂氟后24 h、48 h尿氟浓度比较差异无统计学意义(P>0.05);A组与B组儿童涂氟后龋齿发生率、龋均值、新生龋面、致龋菌检出率比较差异无统计学意义(P>0.05)。结论氟化钠的应用可降低幼儿园儿童龋齿发生率,减少新生龋面,降低致龋菌检出率,无需涂布过多剂量的氟化钠即可达到较好的防龋效果,安全性较高。展开更多
The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads t...The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures.To address this issue,a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method.The tooth profile surface roughness was considered,and its evolution during repeated meshing was simulated using the Archard wear formula.The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion.The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable.Variations in the wear depth and fatigue damage around the pitch point are described,and the effect of surface roughness on the fatigue life is addressed.The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness.Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.展开更多
Due to the excellent self-centering and load-carrying capability,curvic couplings have been widely used in advanced aero-engine rotors.However,curvic tooth surface errors lead to poor assembly precision.Traditional ph...Due to the excellent self-centering and load-carrying capability,curvic couplings have been widely used in advanced aero-engine rotors.However,curvic tooth surface errors lead to poor assembly precision.Traditional physical-master-gauge-based indirect tooth surface error measurement and circumferential assembly angle optimization methods have the disadvantages of high cost and weak generality.The unknown tooth surface fitting mechanism is a big barrier to assembly precision prediction and improvement.Therefore,this work puts forward a data-driven assembly simulation and optimization approach for aero-engine rotors connected by curvic couplings.The origin of curvic tooth surface error is deeply investigated.Using 5-axis sweep scan method,a large amount of high-precision curvic tooth surface data are acquired efficiently.Based on geometric models of parts,the fitting mechanism of curvic couplings is uncovered for assembly precision simulation and prediction.A circumferential assembly angle optimization model is developed to decrease axial and radial assembly runouts.Experimental results show that the assembly precision can be predicted accurately and improved dramatically.By uncovering the essential principle of the assembly precision formation and proposing circumferential assembly angle optimization model,this work is meaningful for assembly quality,efficiency and economy improvement of multistage aero-engine rotors connected by curvic couplings.展开更多
基金Supported by National Natural Science Foundation of China (Grant No.52275061)。
文摘Profile shift is a highly effective technique for optimizing the performance of spur gear transmission systems.However,tooth surface wear is inevitable during gear meshing due to inadequate lubrication and long-term operation.Both profile shift and tooth surface wear(TSW)can impact the meshing characteristics by altering the involute tooth profile.In this study,a tooth stiffness model of spur gears that incorporates profile shift,TSW,tooth deformation,tooth contact deformation,fillet-foundation deformation,and gear body structure coupling is established.This model efficiently and accurately determines the time-varying mesh stiffness(TVMS).Additionally,an improved wear depth prediction method for spur gears is developed,which takes into consideration the mutually prime teeth numbers and more accurately reflects actual gear meshing conditions.Results show that consideration of the mutual prime of teeth numbers will have a certain impact on the TSW process.Furthermore,the finite element method(FEM)is employed to accurately verify the values of TVMS and load sharing ratio(LSR)of profile-shifted gears and worn gears.This study quantitatively analyzes the effect of profile shift on the surface wear process,which suggests that gear profile shift can partially alleviate the negative effects of TSW.The contribution of this study provides valuable insights into the design and maintenance of spur gear systems.
文摘目的探讨氟化钠护齿剂对幼儿园儿童乳牙患龋率和龋面变化的影响。方法选取2017年1月本地区10所公办幼儿园共330名儿童作为研究对象,随机分为三组,每组各110名儿童,A组给予氟化钠护齿剂(含5%氟化钠)0.2 m L/次,1次/年;B组给予入氟化钠护齿剂0.1 m L/次,1次/年;C组儿童作为空白对照组,记录涂氟后三组儿童2年内乳牙患龋率、龋面均、新增龋面变化、致龋菌检出情况以及涂氟后尿氟浓度变化。结果A组与B组干预后第2年龋齿发生率分别为37.27%、39.09%低于C组51.82%(P<0.05);A组、B组第1年、第2年龋均值低于C组(P<0.05);A组与B组儿童涂氟后第1年与第2年乳牙颊舌面、邻面、牙合面新生龋面均值低于C组(P<0.05);A组与B组儿童干预第2年变形链球菌、远缘链球菌、乳杆菌检出率低于C组(P<0.05);A组、B组儿童涂氟后6 h、12 h尿氟浓度高于C组儿童(P<0.05);三组儿童涂氟后24 h、48 h尿氟浓度比较差异无统计学意义(P>0.05);A组与B组儿童涂氟后龋齿发生率、龋均值、新生龋面、致龋菌检出率比较差异无统计学意义(P>0.05)。结论氟化钠的应用可降低幼儿园儿童龋齿发生率,减少新生龋面,降低致龋菌检出率,无需涂布过多剂量的氟化钠即可达到较好的防龋效果,安全性较高。
基金The work was supported by the National Key R&D Program of China(Grant No.2018YFB2001300).
文摘The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears.Meanwhile,the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures.To address this issue,a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method.The tooth profile surface roughness was considered,and its evolution during repeated meshing was simulated using the Archard wear formula.The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion.The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable.Variations in the wear depth and fatigue damage around the pitch point are described,and the effect of surface roughness on the fatigue life is addressed.The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness.Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.
基金co-supported by the National Basic Research Project(Nos.J2022-VII-0001-0043 and 2017-VII-0010-0104)the Fundamental Research Funds for the Central Universities,and the National Natural Science Foundation of China(No.72231008)。
文摘Due to the excellent self-centering and load-carrying capability,curvic couplings have been widely used in advanced aero-engine rotors.However,curvic tooth surface errors lead to poor assembly precision.Traditional physical-master-gauge-based indirect tooth surface error measurement and circumferential assembly angle optimization methods have the disadvantages of high cost and weak generality.The unknown tooth surface fitting mechanism is a big barrier to assembly precision prediction and improvement.Therefore,this work puts forward a data-driven assembly simulation and optimization approach for aero-engine rotors connected by curvic couplings.The origin of curvic tooth surface error is deeply investigated.Using 5-axis sweep scan method,a large amount of high-precision curvic tooth surface data are acquired efficiently.Based on geometric models of parts,the fitting mechanism of curvic couplings is uncovered for assembly precision simulation and prediction.A circumferential assembly angle optimization model is developed to decrease axial and radial assembly runouts.Experimental results show that the assembly precision can be predicted accurately and improved dramatically.By uncovering the essential principle of the assembly precision formation and proposing circumferential assembly angle optimization model,this work is meaningful for assembly quality,efficiency and economy improvement of multistage aero-engine rotors connected by curvic couplings.
