涂层强化材料低应力多碰塑性累积研究与建模
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摘要
在工程领域中,很多零部件由于频繁重复进行碰撞接触—分离的运动而失效,通常这些零部件承受的应力很低(约为材料屈服极限的1/5～1/2)。研究发现,零件承受多碰载荷而失效的多种起因都可以归结为材料发生宏观塑性变形。针对此现象,本文进行了低应力多碰动态响应试验,研究了1Cr18Ni9Ti试件和经激光涂层强化后的1Cr18Ni9Ti试件在同样工况条件下的动态响应行为,建立了其宏观塑性累积应变数学模型。
对实验室自制的第一代多碰试验机进行了改进。(1)在液压油路控制部分,利用两个插装阀和一个电磁换向阀代替原有的旋转换向阀;(2)在电气控制部分,增加了限位装置和计数系统;(3)在测试系统部分,选择了合适的压电式传感器,设计了与此配套的夹具和工作台;设计并加工了两组大小规格不同的弹簧,对两组弹簧做了标定。
选用化工泵、阀类多碰零件常用的不锈钢1Cr18Ni9Ti和高强度Ni-2合金作为低应力多碰试验材料。对试件进行坐标网格化,提出了分层塑性响应方法,在相同的多碰条件下(碰撞应力? =100MPa,碰撞行程h=20mm,碰撞频率p=4Hz),对1Cr18Ni9Ti试件和经激光涂层强化后的1Cr18Ni9Ti涂层试件进行了多碰试验。研究了材料随时空变化的疲劳应变及累积规律,提出了“趋表效应”的概念,得出以下结论:(1)在最初的几千次碰撞中,试件的变形最明显,随着碰撞次数的增加,试件变形越来越小,大约在25万次后趋于稳定;(2)试件表层的变形量、应变率、硬度变化最大,随着层深的增加,呈梯度性迅速衰减;(3)经激光涂层强化后的试件,不论是涂层还是基体都比未经激光涂层强化的试件有更好的抗多碰形变能力。
建立了一定应力下,多碰塑性累积应变与碰撞次数、单元层坐标之间的关系。对1Cr18Ni9Ti试件和经激光涂层强化后的涂层试件分别建立了累积应变数学模型。根据该数学模型,代入碰撞次数N和单元层坐标y,可以比较精确的求出在一定应力?之下,距表面距离为y处的累积应变?。
试验结果表明:碰撞应力很小,仅为材料屈服极限的1/5～1/2时,仍然会出现可测的累积宏观塑性变形现象,说明低应力多碰试验中具有较低门槛值。低应力多碰塑性变形有别于一次冲击变形、一般的疲劳失效、棘轮效应和蠕变,是一种不能用普通的冲击功来描述的具有特殊机理的形变现象,激光涂层可以有效的抵抗多碰塑性变形。
In the engineering field, many of the parts fail due to repeated impacting with the conduct of the collision-separating movements and the stress on these parts are usually very low (about 1/5～1/2 of materials’yield strength). It is found that the failures of parts which work under repeated impact load can be attributed to macroscopic cumulate deformation. According to these phenomena, this thesis did the repeated impact test about the parts of 1Cr18Ni9Ti with laser coating and the parts without laser coating under the same low stress condition and then built the math model of macroscopic cumulate deformation.
This thesis improved the first generation of the repeated impact testing machine. (1) In the part of hydraulic circuit, designed a new reversal valve used one electromagnetic directional valve and two cartridge valves; (2) in the part of electric control, designed a new inhibiting device and a counting system; (3) in the part of test system, chose a piezoelectric transducer and designed a new jig and operating floor. Also designed two kinds of spring and calibrated them.
1Cr18Ni9Ti and nickel-base alloy Ni-2 always used in the chemical pumps and valves are selected as test materials. Meshed the parts and put forward the new way of layered plastic distortion response. Repeated impact test are conducted both of the parts with laser coating and the parts without laser coating under the same condition (impact stress ? =100MPa, impact stroke h=20mm, impact frequency p=4Hz). The thesis researched on the fatigue strain of materials with time changing and cumulative laws. Put forward the concept of skin effect and get the conclusions: (1) during the initial thousands of times the deformation is obvious and the deformation becomes decrease with impact times increasing. At last it will be steady after twenty-five thousand times;(2) the deformation, the strain ratio and the hardness change of the surface are maximum, with the layer depth increasing the deformation, the strain ratio and the hardness change become smaller and smaller;(3) both coating and base of coating strengthening parts have better capacity of resist repeated impact deformation.
The relationship among cumulate strain, impact times and coordinate has been built. The models about cumulate strain of 1Cr18Ni9Ti parts and coating strengthening parts have been made. According to the models, the cumulate strain? will be solve if substitution of its impact times N and coordinate y under the stress? .
The experimental results show: there will also be macroscopic cumulate deformation when the impact stress is very low which is 1/5～1/2 of materials’yield strength. All above note that there is a lower threshold value ?K th in the repeated impact test. The low stress repeated-impact plastic deformation, different from the once impact deformation, the general fatigue failure, the ratchet effect and creep can not be measured by AK. The laser coating has a better capacity of resist repeated impact deformation.
对实验室自制的第一代多碰试验机进行了改进。(1)在液压油路控制部分,利用两个插装阀和一个电磁换向阀代替原有的旋转换向阀;(2)在电气控制部分,增加了限位装置和计数系统;(3)在测试系统部分,选择了合适的压电式传感器,设计了与此配套的夹具和工作台;设计并加工了两组大小规格不同的弹簧,对两组弹簧做了标定。
选用化工泵、阀类多碰零件常用的不锈钢1Cr18Ni9Ti和高强度Ni-2合金作为低应力多碰试验材料。对试件进行坐标网格化,提出了分层塑性响应方法,在相同的多碰条件下(碰撞应力? =100MPa,碰撞行程h=20mm,碰撞频率p=4Hz),对1Cr18Ni9Ti试件和经激光涂层强化后的1Cr18Ni9Ti涂层试件进行了多碰试验。研究了材料随时空变化的疲劳应变及累积规律,提出了“趋表效应”的概念,得出以下结论:(1)在最初的几千次碰撞中,试件的变形最明显,随着碰撞次数的增加,试件变形越来越小,大约在25万次后趋于稳定;(2)试件表层的变形量、应变率、硬度变化最大,随着层深的增加,呈梯度性迅速衰减;(3)经激光涂层强化后的试件,不论是涂层还是基体都比未经激光涂层强化的试件有更好的抗多碰形变能力。
建立了一定应力下,多碰塑性累积应变与碰撞次数、单元层坐标之间的关系。对1Cr18Ni9Ti试件和经激光涂层强化后的涂层试件分别建立了累积应变数学模型。根据该数学模型,代入碰撞次数N和单元层坐标y,可以比较精确的求出在一定应力?之下,距表面距离为y处的累积应变?。
试验结果表明:碰撞应力很小,仅为材料屈服极限的1/5～1/2时,仍然会出现可测的累积宏观塑性变形现象,说明低应力多碰试验中具有较低门槛值。低应力多碰塑性变形有别于一次冲击变形、一般的疲劳失效、棘轮效应和蠕变,是一种不能用普通的冲击功来描述的具有特殊机理的形变现象,激光涂层可以有效的抵抗多碰塑性变形。
In the engineering field, many of the parts fail due to repeated impacting with the conduct of the collision-separating movements and the stress on these parts are usually very low (about 1/5～1/2 of materials’yield strength). It is found that the failures of parts which work under repeated impact load can be attributed to macroscopic cumulate deformation. According to these phenomena, this thesis did the repeated impact test about the parts of 1Cr18Ni9Ti with laser coating and the parts without laser coating under the same low stress condition and then built the math model of macroscopic cumulate deformation.
This thesis improved the first generation of the repeated impact testing machine. (1) In the part of hydraulic circuit, designed a new reversal valve used one electromagnetic directional valve and two cartridge valves; (2) in the part of electric control, designed a new inhibiting device and a counting system; (3) in the part of test system, chose a piezoelectric transducer and designed a new jig and operating floor. Also designed two kinds of spring and calibrated them.
1Cr18Ni9Ti and nickel-base alloy Ni-2 always used in the chemical pumps and valves are selected as test materials. Meshed the parts and put forward the new way of layered plastic distortion response. Repeated impact test are conducted both of the parts with laser coating and the parts without laser coating under the same condition (impact stress ? =100MPa, impact stroke h=20mm, impact frequency p=4Hz). The thesis researched on the fatigue strain of materials with time changing and cumulative laws. Put forward the concept of skin effect and get the conclusions: (1) during the initial thousands of times the deformation is obvious and the deformation becomes decrease with impact times increasing. At last it will be steady after twenty-five thousand times;(2) the deformation, the strain ratio and the hardness change of the surface are maximum, with the layer depth increasing the deformation, the strain ratio and the hardness change become smaller and smaller;(3) both coating and base of coating strengthening parts have better capacity of resist repeated impact deformation.
The relationship among cumulate strain, impact times and coordinate has been built. The models about cumulate strain of 1Cr18Ni9Ti parts and coating strengthening parts have been made. According to the models, the cumulate strain? will be solve if substitution of its impact times N and coordinate y under the stress? .
The experimental results show: there will also be macroscopic cumulate deformation when the impact stress is very low which is 1/5～1/2 of materials’yield strength. All above note that there is a lower threshold value ?K th in the repeated impact test. The low stress repeated-impact plastic deformation, different from the once impact deformation, the general fatigue failure, the ratchet effect and creep can not be measured by AK. The laser coating has a better capacity of resist repeated impact deformation.
引文
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2.傅戈雁,石世宏等.覆层零件多碰碰撞试验与失效特征[J].材料科学与工程学报.2004,22,(2):216-219
3.陈训浩.应制定多次冲击试验国家标准[J].冶金标准化与质量.1998,36,(9):29-30
4.王力民.材料力学实验指导书[M].长沙:中南工业大学出版社.1991
5.邱克.材料力学[M].北京:国防工业出版社.2009
6.哈富宽.金属力学性质的微观理论[M].北京:科学出版社.1983
7.余宗森,田中卓.金属物理[M].北京:冶金工业出版社.1982,319-338
8.周惠久,黄明志.金属材料强度学[M].北京:科学出版社.1989,332-369
9.石世宏,傅戈雁,孙承峰.多冲载荷对镍基激光涂层及基体的影响[J].机械工程材料2005,29,(11):28-30
10.Collins J A. Failure of materials in Mechanical Design [M]. JohnWiley & Sons, Inc ., 1981,725-745
11.王步瀛.机械零件强度计算的理论和方法[M].北京:高等教育出版社,1986,10
12.K.Wellinger and H.Breckel.Kenngr?ssen und Verschleiss beim Stoss metallischer Werkstoffe [J]. Wear. 1969, 13(4):257-281
13.P.A.Engel. Impact wear of materials [M].Amsterdam:Elsvier Scientific,1976
14.R.G.Bayer, P.A.Engel and J.L.Sirico.Impact wear testing machine [J]. Wear.1972 19,(3):343-354
15.西安交通大学强度研究所.多次冲击载荷下的体积效应和缺口效应[J].西安交通大学学报,1977,18,(4):1-8
16.Ramanan Pitchumani, Nishant Gupta,Gabriel M.H.Meesters,Brian Scarlett. Analysis of Single Particle Attrition during Impact Experiments[J].Particle & Particle Systems Characterization 2003,20,(5):323-326
17.周惠久,黄明志.在多次重复冲击载荷下钢的断裂抗力等研究[J].西安交通大学学报,1962,3,(1):1-20
18.邵天敏等.等离子喷涂涂层的碰撞响应频谱分析[J].清华大学学报(自然科学版),1998,84,(4):52
19.Zhu, Xiaodong, Dou, Hailin,Ban, Zhigang, Liu, Yixiong,He, Jiawen. Repeated impact test for characterization of hard coatings Surface and Coatings Technology 2007 ,201(2):5493-5497
20.王爱华,谢长生,李树栋.铝合金表面激光熔覆Fe-Al青铜过渡区的组织结构及其在小能量多冲作用下的行为[J].稀有金属材料与工程, 1999,30,(5):289
21.李学敏.冲击载荷下热喷涂涂层的塑性变形行为分析[J].甘肃工业大学学报, 1997,23,(2):25
22.石世宏,傅戈雁等.多冲接触载荷下不锈钢零件激光表面熔覆层组织及其失效行为[J].金属热处理,2002,27,(3):16-19
23.石世宏,傅戈雁,欧阳八生,彭如恕.多冲接触载荷下涂层零件低应力宏观塑性行为[J].机械工程学报.2005,41,(4):137-142
24.傅戈雁,石世宏,欧阳八生,彭如恕.覆层零件多冲碰撞试验与失效特征[J].材料科学与工程学报2004,22,(4):216-219
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