钛合金柔性联轴节设计优化与疲劳验证
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摘要
在直升机传动系统中,联轴器是关键动部件之一,在工作过程中不仅要传递扭矩,而且要具有良好的轴向与角向补偿能力。目前国内联轴器大多采用钢制叠片型式,其主要缺点是重量较重,构件的抗疲劳能力较低,很难满足直升机快速发展的要求。随着钛合金在直升机产业的广泛发展,一种新型钛合金柔性联轴节应运而生,它相对钢制膜片大大提高了功重比。由于钛合金联轴节采用整体膜盘结构,其可靠性要求很高,本文以钛合金联轴节为研究对象,旨在探索其结构优化设计与疲劳寿命分析方法。
本文在探索钛合金柔性联轴节的结构特点与设计方法的基础上,应用有限元方法对联轴节进行强度分析,发现联轴节的最大应力位于型面的转接圆角区域。针对该疲劳危险点,提出了基于有限元分析的结构优化设计方法,建立了以联轴节的最大当量应力为目标函数的优化模型,应用NASTRAN分析软件对圆型凸台联轴节进行了优化分析,优化后的联轴节的最大当量应力下降约5.5%。优化结果表明,该联轴节由于结构的局限性,优化仍不能满意地消除转接圆角处应力集中的现象,所以在结构上对联轴节的凸台形状进行了改进设计,将圆型凸台改为扇型凸台,改进后的联轴节应力水平下降明显,比原结构的最大当量应力下降12.5%。
本文还建立了联轴节的疲劳寿命估算方法,即根据有限元方法分析所获得的最大当量应力,采用雨流法对载荷进行循环计数,根据有限元分析结果将载荷循环转换为关键部位的应力循环,利用迟滞回线将应力谱转换为应变谱,利用应变-寿命曲线计算损伤,并按Miner线性累积损伤原理计算了联轴节的疲劳寿命。计算结果表明,联轴节的优化设计明显提高了其疲劳寿命。
最后,对钛合金柔性联轴节改进前后的两种构型分别进行疲劳试验考核。试验后,疲劳裂纹均发生在型面的转接圆角处,试验循环数与计算寿命的最大误差为18%。试验结果表明:本文的优化方法是有效的,经优化联轴节寿命延长了约6倍;所采取疲劳寿命估算方法是较准确的,预估到了裂纹出现的部位和时间。
Coupling is a critical rotation part in the transmission system of helicopter, which not only transfers torque, but also possesses excellent axial and angular compensation capability during operation. Most domestic couplings at present are steel laminated type with main disadvantages of heavy weight and low fatigue characteristics which won’t meet the fast development of helicopter. With the wide use of titanium alloy in helicopter industry, a new type of titanium alloy flexible coupling which has a great progress in power-weight ratio emerges as the times require, featuring in a high reliability as it is an integrated diaphragm structure. This thesis makes research on titanium alloy flexible coupling to explore its structure-design optimization and method of fatigue life analysis.
Finite element method are applied in this thesis to analyze the strength of titanium alloy coupling on the basis exploring its structure characteristics and designing method, which finds that maximum stress is located in the fillet area of the profile. And designing method with structure optimization is put forward for this fatigue danger, in which, optimization model considering maximum equivalent stress of the coupling as objective function is set up and the maximum equivalent stress of the coupling decreases about 5.5% after optimization when NASTRAN analyzing software is applied for optimization analysis on round boss coupling. The optimization results shows that due to structure limits of the coupling, optimization can’t eliminate stress concentration at fillet satisfactorily. And an improvement is made on boss shape of the coupling, which becomes a sector boss. The stress of the coupling after improvement greatly decreases and the maximum equivalent stress decreases about 12.5%.
This thesis also establishes the method of calculating the fatigue life of the flexible coupling. According to the maximum equivalent stress obtained by finite element method, rain flow method is applied to cycle calculation of load. Load cycle is converted to stress cycle of critical position based on results of finite element analysis. Stress spetrum is converted to strain spectrum chart utilizing hysteresis loop. Damage is calculated by strain-life curve and fatigue life of the coupling is calculated per Miner linear cumulative damage hypothesis. The calculation shows that fatigue life of the coupling is greatly improved by optimization design.
Finally, fatigue test assessment is made separately on the two configurations before and after improvement of titanium alloy flexible coupling. After test, fatigue cracks are all occurred at transition fillet of the profile, the maximum error between number of test cycle and life-time calculated is 18%. Test result shows that optimization method is effective by increasing the fatigue life about six times and fatigue life analysis is accurate by making an accurate evaluation on position and time that the cracks occurs.
本文在探索钛合金柔性联轴节的结构特点与设计方法的基础上,应用有限元方法对联轴节进行强度分析,发现联轴节的最大应力位于型面的转接圆角区域。针对该疲劳危险点,提出了基于有限元分析的结构优化设计方法,建立了以联轴节的最大当量应力为目标函数的优化模型,应用NASTRAN分析软件对圆型凸台联轴节进行了优化分析,优化后的联轴节的最大当量应力下降约5.5%。优化结果表明,该联轴节由于结构的局限性,优化仍不能满意地消除转接圆角处应力集中的现象,所以在结构上对联轴节的凸台形状进行了改进设计,将圆型凸台改为扇型凸台,改进后的联轴节应力水平下降明显,比原结构的最大当量应力下降12.5%。
本文还建立了联轴节的疲劳寿命估算方法,即根据有限元方法分析所获得的最大当量应力,采用雨流法对载荷进行循环计数,根据有限元分析结果将载荷循环转换为关键部位的应力循环,利用迟滞回线将应力谱转换为应变谱,利用应变-寿命曲线计算损伤,并按Miner线性累积损伤原理计算了联轴节的疲劳寿命。计算结果表明,联轴节的优化设计明显提高了其疲劳寿命。
最后,对钛合金柔性联轴节改进前后的两种构型分别进行疲劳试验考核。试验后,疲劳裂纹均发生在型面的转接圆角处,试验循环数与计算寿命的最大误差为18%。试验结果表明:本文的优化方法是有效的,经优化联轴节寿命延长了约6倍;所采取疲劳寿命估算方法是较准确的,预估到了裂纹出现的部位和时间。
Coupling is a critical rotation part in the transmission system of helicopter, which not only transfers torque, but also possesses excellent axial and angular compensation capability during operation. Most domestic couplings at present are steel laminated type with main disadvantages of heavy weight and low fatigue characteristics which won’t meet the fast development of helicopter. With the wide use of titanium alloy in helicopter industry, a new type of titanium alloy flexible coupling which has a great progress in power-weight ratio emerges as the times require, featuring in a high reliability as it is an integrated diaphragm structure. This thesis makes research on titanium alloy flexible coupling to explore its structure-design optimization and method of fatigue life analysis.
Finite element method are applied in this thesis to analyze the strength of titanium alloy coupling on the basis exploring its structure characteristics and designing method, which finds that maximum stress is located in the fillet area of the profile. And designing method with structure optimization is put forward for this fatigue danger, in which, optimization model considering maximum equivalent stress of the coupling as objective function is set up and the maximum equivalent stress of the coupling decreases about 5.5% after optimization when NASTRAN analyzing software is applied for optimization analysis on round boss coupling. The optimization results shows that due to structure limits of the coupling, optimization can’t eliminate stress concentration at fillet satisfactorily. And an improvement is made on boss shape of the coupling, which becomes a sector boss. The stress of the coupling after improvement greatly decreases and the maximum equivalent stress decreases about 12.5%.
This thesis also establishes the method of calculating the fatigue life of the flexible coupling. According to the maximum equivalent stress obtained by finite element method, rain flow method is applied to cycle calculation of load. Load cycle is converted to stress cycle of critical position based on results of finite element analysis. Stress spetrum is converted to strain spectrum chart utilizing hysteresis loop. Damage is calculated by strain-life curve and fatigue life of the coupling is calculated per Miner linear cumulative damage hypothesis. The calculation shows that fatigue life of the coupling is greatly improved by optimization design.
Finally, fatigue test assessment is made separately on the two configurations before and after improvement of titanium alloy flexible coupling. After test, fatigue cracks are all occurred at transition fillet of the profile, the maximum error between number of test cycle and life-time calculated is 18%. Test result shows that optimization method is effective by increasing the fatigue life about six times and fatigue life analysis is accurate by making an accurate evaluation on position and time that the cracks occurs.
引文
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[2]刘夏石,中国新一代直升机的发展方向[J],第14届全国直升机年会论文集,2003:23-26
[3]丁文强,国外先进的直升机传动系统研究[J],中国国防科学技术报告,2002:18-20
[4] Peacock D.K.,Latest Titanium Alloys Address Specialized Engineering Needs[J],The Metable Society,1987,54(2):72-73
[5] KA THYWANG,The use of Titanium for Medical Applications in USA[J]. Material Science and Engineering A,1996,23(3): 134
[6]王哲,飞机结构应用钛合金应注意的问题[J],钛工业发展,2000(3):27-28
[7]陈石卿,钛在先进飞机上的应用[J],钛合金信息,1997(3):22
[8]许映国、李雅峰等,直升机译文集[M],内部资料,2002:28-48
[9]王心丰,汤亮均,联轴器,航空发动机设计手册第12册[M],航空工业出版社.2002.
[10]陆中兴,周慧仙,膜片式联轴器的结构特性和设计方法[J],天津机械,1982(2)
[11]丁雪兴,金属膜片联轴器的膜片疲劳寿命计算及分析,[学位论文],兰州理工大学,2004
[12]李加锋,衡井武,金属叠片挠性联轴器的选型[J],江苏船舶,2002,17(2):26-28
[13]徐伟,冯桂军,周开勤,膜片联轴器的强度与刚度分析[J],机械设计,1992(5)
[14]曹逸苍,膜片联轴器及膜片材料[J],传动技术,1998(1):20-27
[15]申清潭,膜片式联轴器失效机理探讨[J],武汉科技大学学报(自然科学版),1999(4).
[16]许峰,薛克敏,国内外钛合金等温锻造进展[J],皖西学院学报,2007,23(5):48-50
[17]张行健,吕宏军,王琪,陈永来,周晓建,钛合金模锻工艺的研究进展[J],材料导报, 2007(11):105-108
[18]曲银化,孙建科,孟祥军,钛合金等温锻造技术研究进展[J],钛工业进展,2006(1):12-15
[19]刘道新,何家文,经不同表面改性处理的钛合金的微动疲劳和微动磨损行为对比研究[J],摩擦学报,2005,25(1):13-16
[20]宁向荣,新型膜盘式柔性联轴节的抗疲劳设计[J],南华动力,2007(4):63-66
[21]徐启清,钢片挠性联轴器的特性和设计[J],传动技术,1999(3)
[22]曹春晓,我国航空用钛合金面临的21世纪挑战[J],钛工业发展,1995(5):1-5
[23]李明怡,航空用钛合金材料[J],世界有色金属,2000(6):17-20
[24]张高会等,钛合金及其表面处理的现状与展望[J],世界科技研究与发展,2003(8): 62-67
[25] Froes F.H.,Alloy Design and Property Interrrelations of Metal Beta Titanium Alloys in Forging and Properites of Aerospace Materials[J],The Metable Society,1977,16(4):143-163
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