WO2016173567A2 - 镍基高温紧固件的防断裂设计方法 - Google Patents

镍基高温紧固件的防断裂设计方法 Download PDF

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WO2016173567A2
WO2016173567A2 PCT/CN2016/084248 CN2016084248W WO2016173567A2 WO 2016173567 A2 WO2016173567 A2 WO 2016173567A2 CN 2016084248 W CN2016084248 W CN 2016084248W WO 2016173567 A2 WO2016173567 A2 WO 2016173567A2
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stress
high temperature
fastener
design
crack
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WO2016173567A3 (zh
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轩福贞
谈建平
宫建国
刘霞
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Shanghai Turbine Co Ltd
East China University of Science and Technology
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Shanghai Turbine Co Ltd
East China University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/18—Performing tests at high or low temperatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/20—Metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21H—MAKING PARTICULAR METAL OBJECTS BY ROLLING, e.g. SCREWS, WHEELS, RINGS, BARRELS, BALLS
    • B21H1/00—Making articles shaped as bodies of revolution
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B1/00—Devices for securing together, or preventing relative movement between, constructional elements or machine parts
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M99/00—Subject matter not provided for in other groups of this subclass
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8803—Visual inspection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
    • G01N27/83—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws by investigating stray magnetic fields
    • G01N27/84—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws by investigating stray magnetic fields by applying magnetic powder or magnetic ink
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B5/00—Joining sheets or plates, e.g. panels, to one another or to strips or bars parallel to them
    • F16B5/02—Joining sheets or plates, e.g. panels, to one another or to strips or bars parallel to them by means of fastening members using screw-thread
    • F16B5/0275—Joining sheets or plates, e.g. panels, to one another or to strips or bars parallel to them by means of fastening members using screw-thread the screw-threaded element having at least two axially separated threaded portions

Definitions

  • the invention belongs to the field of nickel-based high-temperature fasteners, relates to a crack-proof design method of a nickel-based high-temperature fastener, and more particularly to a fastener design using a high-strength, low-toughness nickel-based superalloy as a material.
  • Design methods such as nickel-based high-temperature bolts, studs, nuts, etc.
  • the power of a single unit of supercritical power station has reached more than 1000MW, the working parameter is 600-650°C/32-35MPa, and the design life is up to 30 years; the inlet temperature of the advanced aero-engine turbine is as high as 1980-2080°C, and the thrust-to-weight ratio is above 15-20.
  • the longest life on the aircraft exceeds 40,000 hours; the current 700 °C thermal power and 4th generation nuclear power technology are also based on high temperature and high pressure parameters and long design life.
  • Nickel-based high-temperature fasteners are general term for a class of mechanical parts used in the case of fastening nickel-based alloys and fastening two or more parts into a whole in a high-temperature environment, including: bolts and screws. Columns, nuts, etc., are widely used in electric power, refining, metallurgy and aviation.
  • the current nickel-based high-temperature fastener design method is based on strength theory.
  • the general process is: obtaining working condition parameters, selecting materials, determining pre-tightening force, designing fastener arrangement and size, fastener force analysis, and Strength check under various conditions (considering the effects of relaxation).
  • the conventional fastener design method in the prior art is not suitable for the nickel-based high-temperature fastener with high temperature strength but excellent toughness. It is urgent to develop a nickel-based material in a high temperature environment. A new method for the design of fasteners against breakage.
  • the present invention proposes a new method for preventing fractures of nickel-based fasteners in a high temperature environment, and provides a new fastener strength design process, thereby solving the present There are problems in the technology.
  • the invention provides a method for preventing breakage of a nickel-based high-temperature fastener, the method comprising the following steps:
  • design condition parameters comprising: a design temperature T, the ambient medium, the design cycle, material grades are fastened and structure size to achieve the desired function of the fastening force of P;
  • the data includes: a linear expansion coefficient ⁇ b and ⁇ v of the fastener material and the fastened material, an elastic modulus E of the fastener material, tensile properties, stress relaxation properties, High temperature crack propagation threshold value K th ;
  • step S 8 assuming that the maximum allowable crack size determined in step S 7 is perpendicular to the fastener force method, combined with the high temperature crack propagation threshold value K th , the maximum allowable service stress ⁇ th is calculated, wherein Where F I is obtained by stress intensity factor manual query or finite element method calculation, a is the crack length;
  • step S 9 comparing whether the service stress ⁇ s in step S 5 is smaller than the maximum allowable service stress ⁇ th in step S 8 ; if yes, performing step S 10 ; otherwise returning to step S 4 and decreasing the pre-tightening stress ⁇ p ;
  • the step S in the material property data 3 is obtained by the material properties of a database query, if the query than is required to obtain the corresponding experimental test.
  • the linear expansion coefficient is obtained by a thermal dilatometer test; the elastic modulus E is obtained by a dynamic thermomechanical analyzer test; and the tensile properties are obtained by a high temperature round bar tensile test;
  • the stress relaxation property is obtained by a high temperature relaxation test test;
  • the high temperature crack propagation threshold value K th is obtained by using a compact tensile specimen for a high temperature crack growth test to obtain an initial stress intensity factor and a crack initiation time curve, and extrapolating the curve or interpolated temperature threshold K th crack at the design cycle.
  • the high temperature crack propagation threshold value K th under the design cycle is subjected to a short-time high temperature crack growth test, and the test data is based on Calculated regularly, where K is the stress intensity factor, t i is the crack initiation time, B and The material parameters are obtained by fitting the experimental data; the design period is substituted into the fitted equation, and the stress intensity factor K under the design cycle is calculated as the crack extension threshold K th .
  • the maximum allowable step S 7 the minimum size of the crack can be detected NDT inspection and defect size and manufacturing costs into consideration is determined.
  • the non-destructive testing technique includes visual inspection, magnetic particle detection, and radiation detection.
  • the invention aims at the conventional fastener design method in the prior art and cannot guarantee the integrity of the high-strength and low-toughness nickel-based high-temperature fastener, and develops a new anti-fracture design of the nickel-based material fastener under high temperature environment.
  • the method provides a new fastener strength design process.
  • FIG. 1 is a block flow diagram of a preferred embodiment of the present invention.
  • FIG. 2 is a graph of stress relaxation curves at different initial loads obtained from a relaxed specimen test in accordance with a preferred embodiment of the present invention.
  • FIG. 3 is a graph of initial stress intensity factor and crack initiation time as measured by a compact tensile specimen in accordance with a preferred embodiment of the present invention.
  • FIG. 4 is a schematic view showing the shape of a bolt and its internal and external surface crack defects in the embodiment of the present application.
  • the invention provides a method for preventing breakage of a nickel-based high-temperature fastener, the method comprising the following steps:
  • design working condition parameters such as design temperature T, environmental medium, design cycle, material grade and structural size of the member to be fastened, force required to achieve the fastening function (sealing force) P;
  • step S 2 selecting a fastener material according to the design temperature and the environmental medium in step S 1 ;
  • material performance data such as linear expansion coefficients ⁇ b and ⁇ v of fastener materials and fastened materials, elastic modulus E of fastener materials, tensile properties, stress relaxation properties, high temperature crack growth threshold Value K th ;
  • step S 8 assuming that the maximum allowable crack size determined in step S 7 is perpendicular to the fastener force method, combined with the high temperature crack propagation threshold value K th , the maximum allowable service stress ⁇ th is calculated by the following formula
  • F I can be obtained by the stress intensity factor manual query or the finite element method, and a is the crack length;
  • step S 9 comparing whether the service stress ⁇ s in step S 5 is smaller than the maximum allowable service stress ⁇ th in step S 8 ; if yes, performing step S 10 ; otherwise returning to step S 4 and decreasing the pre-tightening stress ⁇ p ;
  • the step S 3 the above-described material properties data obtained by material properties can query the database, if need not query the corresponding test.
  • the linear expansion coefficient can be obtained by a thermal expansion test;
  • the elastic modulus can be obtained by a dynamic thermomechanical analyzer;
  • the tensile properties can be obtained by a high temperature round bar tensile test;
  • the relaxation performance can be obtained by performing a high temperature relaxation test;
  • the high temperature crack propagation threshold value can be obtained by using a short tensile specimen for short-time high temperature crack growth test to obtain the initial stress intensity factor and crack initiation time curve.
  • the curve extrapolation or interpolation can obtain the crack propagation threshold value under the design period.
  • the initial stress intensity factor and the crack initiation time curve can be drawn using origin software, excel software or hand-drawn, and the equation is adopted.
  • the equation is fitted, where K is the stress intensity factor, t i is the crack initiation time, B and The material parameters were obtained by fitting the experimental data. Substituting the design period into the fitted equation, the stress intensity factor K obtained under the design cycle is calculated as the crack extension threshold K th .
  • ⁇ r can be obtained by material properties database query, if the query can not obtain high-temperature relaxation test test relaxation curve, the curve can be relaxed origin software, excel software or hand-drawn draw, out- Push or interpolation; ⁇ s is the smaller of ⁇ p + ⁇ t and ⁇ p and ⁇ r is smaller.
  • step S 7 the maximum allowable flaw size according to the respective minimum NDT as visual inspection, magnetic particle testing, radiation detected can be detected and the detected defect size, the manufacturing cost into consideration is determined.
  • the fracture prevention design method of the nickel-based high temperature fastener of the present invention comprises the following steps:
  • determining the stable service stress ⁇ s determining the design temperature and the residual stress ⁇ r in the design cycle; ⁇ r can be obtained through the material property database query, if the query can not be performed, the relaxation curve can be obtained by the high temperature relaxation test, and the relaxation curve can be obtained.
  • Use origin software excel software or hand-drawn to draw, extrapolate or interpolate;
  • determining the maximum allowable crack size determining the maximum allowable crack size according to the non-destructive testing provisions of the fastener
  • step S 108 determining a maximum allowable service stress ⁇ th : assuming that the maximum allowable crack size determined in step S 107 is perpendicular to the fastener force method, combined with the high temperature crack extension threshold K th , the maximum allowable service stress ⁇ th is calculated;
  • the service stress ⁇ th can be calculated by the following formula
  • F I can be obtained by the stress intensity factor manual query or the finite element method, and a is the crack length;
  • step S 109 comparing whether the service stress ⁇ s in step S 105 is smaller than the maximum allowable service stress ⁇ th in step S 108 ; if yes, performing step S 110 ; otherwise lowering the pre-stress ⁇ p , performing steps S 105 to S 110 until ⁇ s ⁇ th ;
  • FIG. 4 is a schematic view showing the shape of a bolt and its internal and external surface crack defects in the embodiment of the present application.
  • D o is the outer diameter of the bolt
  • D i is the inner diameter of the bolt
  • a is the crack length
  • ⁇ s is the service stress of the bolt
  • the outer surface crack indicates the crack on the outer surface of the bolt
  • the inner surface crack indicates the inner surface of the bolt. There is a crack.
  • a steam turbine high temperature steam valve requires a valve bolt design.
  • the bolt design temperature is 560 ° C
  • the atmospheric environment the design cycle is 100,000 hours
  • the sealing force required for the valve is 8500000 N
  • the valve material is GX12CrMoWVNbN10-1-1
  • the valve sealing surface outer diameter is 1695 mm
  • the inner diameter is 1085 mm.
  • the bolt design temperature T is 560 ° C
  • the valve material is GX12CrMoWVNbN10-1-1
  • the valve sealing surface outer diameter is 1695mm
  • the inner diameter is 1085mm
  • the sealing force P required for the valve is 8500000N.
  • the bolt material is Inconel 783 alloy.
  • Inconel 783 alloy chemical composition (mass fraction, %)
  • the linear expansion coefficient ⁇ b of Inconel 783 alloy at 560°C was 1.22E-5 1/°C
  • the linear expansion coefficient ⁇ v of GX12CrMoWVNbN10-1-1 steel at 560°C was 1.24.
  • the static modulus E at 560 ° C was 144 GPa using a static test.
  • a round bar tensile test at 560 ° C was carried out, and the test obtained 0.2% plastic elongation R p0.2 of 630 MPa.
  • the stress relaxation sample at 560 ° C was tested to obtain the stress relaxation performance under different loads.
  • the residual stress ⁇ and time t curve were plotted using the original software, as shown in Fig. 2.
  • the residual stress ⁇ r after extrapolation to obtain 100000 hours is 300 MPa.
  • the number of bolts is determined to be 24, and the effective sectional area of the bolt is 1180 mm 2 .
  • the design bolt outer diameter D o is 46mm, and the inner diameter D i is 25mm. As shown in Figure 4.
  • the maximum allowable crack size is 1 mm deep.
  • F I can be obtained by the stress intensity factor manual, and the F I values of the inner and outer surface cracks are all 1.19.
  • the maximum allowable service stress ⁇ th is 156 MPa.
  • the number of bolts is determined to be 24, the effective sectional area of the bolt is 2280 mm 2 , the outer diameter D o of the bolt is 60 mm, and the inner diameter D i is 25 mm;
  • the maximum allowable crack size is 1 mm deep
  • F I can be obtained by the stress intensity factor manual, and the F I values of the inner and outer surface cracks are all 1.16.
  • the maximum allowable service stress ⁇ th is 160 MPa.
  • the service stress ⁇ s under steady conditions is less than the maximum allowable service stress ⁇ th .

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Abstract

本发明涉及镍基高温紧固件的防断裂设计方法，该方法包括以下步骤：S1、获取设计工况参数；S2、选择紧固件材料；S3、获取材料性能数据；S4、确定单个紧固件的预紧应力；S5、确定稳定工况下的服役应力σs；S6、设计紧固件的个数n、有效截面积A及其分布；S7、确定允许的最大裂纹尺寸；S8、结合高温裂纹扩展门槛值Kth，确定最大允许服役应力σth；S9、比较服役应力σs是否小于最大允许服役应力σth；若是则设计周期内该紧固件安全；否则返回S4步并降低预紧应力σp。

Description

镍基高温紧固件的防断裂设计方法 技术领域
本发明属于镍基高温紧固件领域，涉及一种镍基高温紧固件的防断裂设计方法，更具体地说，涉及以高强度、低韧性的镍基高温合金为材料的紧固件设计，如镍基高温螺栓、螺柱、螺母等的设计方法。
背景技术
为符合节能降耗、高效环保的原则，电力、炼化、冶金以及航空等领域的设备呈现出更高温度、更大压力、更长服役时间的发展趋势。如超临界电站单机组的功率已达1000MW以上，工作参数600-650℃/32-35MPa，设计寿命达30年；先进航空发动机涡轮前进口温度高达1980-2080℃，推重比达到15-20以上，最长机上寿命超过4万小时；目前致力发展的700℃火电、第4代核电技术也均是基于高温高压参数以及长设计寿命。随着设备运行参数不断提升，现广泛使用的铁素体、马氏体以及奥氏体等耐热钢材料将不能满足部件对材料使用性能的要求，这些工艺设备的实现必须大量使用强度更高、蠕变特性更好的镍基高温合金。
镍基高温紧固件是指以镍基合金为材料，高温环境下紧固两个或两个以上零件紧固连接成为一个整体时所采用的一类机械零件的总称，主要包括：螺栓、螺柱、螺母等，广泛应用于电力、炼化、冶金以及航空等领域。
现行的镍基高温紧固件的设计方法以强度理论为基础，一般流程为：获取工况参数、选材、确定预紧力、设计紧固件排布及尺寸、紧固件受力分析、各种工况下强度校核(考虑松弛影响)。
然而，镍基高温紧固件断裂事件屡见不鲜，如靖远第二发电有限公司汽轮机GH4145合金螺栓断裂(2011年)、国产百万千瓦超临界电站发生大批Inconel 783合金螺栓断裂(2012年)等，严重时造成停车、停产，导致巨大经济损失。究其原因是，镍基高温合金，虽然具有较高的高温强度及抗松弛性能，但其高温韧性具有显著的时间相关性，长时服役后的韧性较低。保障高温镍基紧固件在服役周期内不发生断裂成为了设计关键。对于这一类性能特性的材料，使用常规的基于强度理论的紧固件设计方法，虽然表象上表现出较高的安全系数，但并未考虑材料断裂性能这一关键的决定性因素，故而无法保障设备的安全运行。
因此，针对现有技术中常规紧固件设计方法并不适用于高温强度高但韧性并不优异的镍基高温紧固件这一问题，本领域迫切需要开发出一种高温环境下镍基材料紧固件的防断裂设计新方法。
发明内容
针对镍基高温合金强度高、韧性低的特点，本发明提出了高温环境下镍基材料紧固件的防断裂设计新方法，提供了一种新的紧固件强度设计工艺，从而解决了现有技术中存在的问题。
本发明提供了一种镍基高温紧固件的防断裂设计方法，该方法包括以下步骤：
S1、获取设计工况参数，所述参数包括：设计温度T、环境介质、设计周期、被紧固材料牌号及结构尺寸、实现紧固功能所需的力P；
S2、根据步骤S1中的设计温度T及环境介质选择紧固件材料；
S3、获取材料性能数据，所述数据包括：紧固件材料和被紧固材料的线性膨胀系数αb及αv，紧固件材料的弹性模量E、拉伸性能、应力松弛性能、高温裂纹扩展门槛值Kth；
S4、根据步骤S2中选择的材料，确定单个紧固件的预紧应力σp，其中，σp＝0.5Rp0.2，式中Rp0.2表示紧固件的0.2％塑性延伸强度；
S5、确定步骤S1中的设计温度T及设计周期下的应力松弛后的剩余应力σr，其中，σr通过材料性能数据库查询获得，或者通过进行高温松弛试验测试获得松弛曲线，采用origin软件、excel软件或手绘绘制松弛曲线，并对曲线进行外推或内插得到；计算稳定工况下的温度应力σt＝E(αv-αb)T；确定稳定工况下的服役应力σs，其中，σs为σp+σt和σp中较大者与σr比较取较小者；
S6、设计紧固件的个数n、有效截面积A及其分布；
S7、根据紧固件的无损检测规定，确定允许的最大裂纹尺寸；
S8、假定步骤S7中确定的允许的最大裂纹尺寸垂直于紧固件受力方法，结合高温裂纹扩展门槛值Kth，计算得到最大允许服役应力σth，其中，
Figure PCTCN2016084248-appb-000001
式中FI是通过应力强度因子手册查询或有限元法计算获得的，a是裂纹长度；
S9、比较步骤S5中的服役应力σs是否小于步骤S8中的最大允许服役应力σth；若是则执行步骤S10；否则返回步骤S4，并降低预紧应力σp；
S10、设计周期该紧固件不会发生裂纹扩展，构件安全；给出紧固件材料、个 数n、有效截面积A及其分布。
在一个优选的实施方式中，步骤S3中所述的材料性能数据是通过材料性能数据库查询获得的，若查询不到则需进行相应的试验测试获得。
在另一个优选的实施方式中，所述线性膨胀系数采用热膨胀仪测试获得；所述弹性模量E采用动态热机械分析仪测试获得；所述拉伸性能采用高温圆棒拉伸测试获得；所述应力松弛性能进行高温松弛试验测试获得；所述高温裂纹扩展门槛值Kth采用紧凑拉伸试样进行高温裂纹扩展试验测试获得初始应力强度因子与裂纹起裂时间曲线，并将曲线外推或内插得到设计周期下的高温裂纹扩展门槛值Kth。
在另一个优选的实施方式中，所述设计周期下的高温裂纹扩展门槛值Kth通过进行短时高温裂纹扩展试验，对测试数据依据
Figure PCTCN2016084248-appb-000002
规律计算得到，式中，K为应力强度因子，ti表示裂纹起裂时间，B与
Figure PCTCN2016084248-appb-000003
为材料参数，由试验数据拟合得到；将设计周期代入拟合后的方程，计算获得该设计周期下的应力强度因子K即为裂纹扩展门槛值Kth。
在另一个优选的实施方式中，在步骤S6中，根据步骤S5中得到的服役应力σs，综合考虑密封面尺寸和力P，根据P＝nAσs，设计紧固件的个数n、有效截面积A及其分布。
在另一个优选的实施方式中，步骤S7中允许的最大裂纹尺寸根据无损检测技术的最小可检出缺陷尺寸及检测和制造成本综合考量确定。
在另一个优选的实施方式中，所述无损检测技术包括目视检测、磁粉检测和射线检测。
有益效果：
本发明针对现有技术中常规紧固件设计方法并不能保障高强度、低韧性的镍基高温紧固件的完整性，开发出一种高温环境下镍基材料紧固件的防断裂设计新方法，提供了一种新的紧固件强度设计工艺。
附图说明
附图是用以提供对本发明的进一步理解的，它只是构成本说明书的一部分以进一步解释本发明，并不构成对本发明的限制。
图1是根据本发明的较佳实施方式的流程框图。
图2是根据本发明的较佳实施方式的由松弛试样测试获得的不同初始载荷下的应力松弛曲线图。
图3是根据本发明的较佳实施方式的由紧凑拉伸试样测得的初始应力强度因子与起裂时间的曲线图。
图4是本申请实施例中螺栓形貌及其内外表面裂纹缺陷示意图。
具体实施方式
本发明提供了一种镍基高温紧固件的防断裂设计方法，该方法包括以下步骤：
S1、获取设计工况参数，如设计温度T、环境介质、设计周期、被紧固构件的材料牌号及结构尺寸、实现紧固功能所需的力(密封力)P；
S2、根据步骤S1中的设计温度及环境介质选择紧固件材料；
S3、获取材料性能数据，如紧固件材料和被紧固材料的线性膨胀系数αb及αv、紧固件材料的弹性模量E、拉伸性能、应力松弛性能、高温裂纹扩展门槛值Kth；
S4、根据步骤S2中选择的材料，确定单个紧固件的预紧应力，一般取σp＝0.5Rp0.2，式中Rp0.2表示紧固件的0.2％塑性延伸强度；
S5、确定步骤S1中设计温度和设计周期下的应力松弛后的剩余应力σr；计算稳定工况下的温度应力σt＝E(αv-αb)T；确定稳定工况下的服役应力σs；
S6、设计紧固件的个数n、有效截面积A及其分布；
S7、根据紧固件的无损检测规定，确定允许的最大裂纹尺寸；
S8、假定步骤S7中确定的允许的最大裂纹尺寸垂直于紧固件受力方法，结合高温裂纹扩展门槛值Kth，由下式计算得到最大允许服役应力σth
Figure PCTCN2016084248-appb-000004
其中FI可通过应力强度因子手册查询或有限元法计算获得，a是裂纹长度；
S9、比较步骤S5中的服役应力σs是否小于步骤S8中的最大允许服役应力σth；若是则执行步骤S10；否则返回步骤S4，并降低预紧应力σp；
S10、设计周期该紧固件不会发生裂纹扩展，构件安全；给出紧固件材料、个数n、有效截面积A及其分布。
在本发明中，在步骤S3中，上述材料性能数据可通过材料性能数据库查询获得，若查询不到则需进行相应的试验测试。
较佳地，线性膨胀系数可采用热膨胀仪测试获得；弹性模量可采用动态热机械分析仪测试获得；拉伸性能可采用高温圆棒拉伸测试获得；松弛性能可进行高温松弛试验测试获得；高温裂纹扩展门槛值可采用紧凑拉伸试样进行短时高温裂纹扩展试验测试获得初始应力强度因子与裂纹起裂时间曲线，曲线外推或内插得到设计周期下的裂纹扩展门槛值。
较佳地，初始应力强度因子与裂纹起裂时间曲线可采用origin软件、excel软件或手绘进行绘制，并采用方程
Figure PCTCN2016084248-appb-000005
方程进行拟合，式中K为应力强度因子，ti为裂纹起裂时间，B与
Figure PCTCN2016084248-appb-000006
为材料参数，由试验数据拟合得到。将设计周期代入拟合后的方程，计算获得该设计周期下的应力强度因子K即为裂纹扩展门槛值Kth。
较佳地，在步骤S5中，σr可通过材料性能数据库查询获得，若查询不到可进行高温松弛试验测试获得松弛曲线，松弛曲线可采用origin软件、excel软件或手绘进行绘制，进行外推或内插得到；σs为σp+σt和σp中较大者与σr比较取较小者。
较佳地，根据步骤S5中工作状态下的服役应力σs，综合考虑密封面尺寸、密封力P等因素，根据P＝nAσs，设计紧固件的个数n、有效截面积A及其分布。
较佳地，在步骤S7中，允许的最大裂纹尺寸可根据相应无损检测技术如目视检测、磁粉检测、射线检测的最小可检出缺陷尺寸及检测、制造成本综合考量确定。
以下参看附图。
图1是根据本发明的较佳实施方式的流程框图。如图1所示，本发明的镍基高温紧固件的防断裂设计方法包括以下步骤：
S101、获取工况参数：根据设计条件，如设计温度、环境介质、设计周期、被紧固构件的材料牌号及结构尺寸、实现紧固功能所需的力(密封力)P，获取设计工况参数；
S102、选材：根据步骤S101中的设计温度及环境介质，选择紧固件材料；
S103、获取材料性能数据：获取紧固件材料和被紧固材料的线性膨胀系数α、紧固件材料的高温弹性模量E、高温拉伸性能如0.2％塑性延伸强度Rp0.2、紧固件材料的应力松弛性能、紧固件材料的高温裂纹扩展门槛值Kth；
S104、确定预紧应力σp：根据步骤S102中选择的材料，确定单个紧固件的预紧应力，一般取σp＝0.5Rp0.2；
S105、确定稳定服役应力σs：确定设计温度和设计周期内的剩余应力σr；σr可通过材料性能数据库查询获得，若查询不到可进行高温松弛试验测试获得松弛曲线，松弛曲线可采用origin软件、excel软件或手绘进行绘制，进行外推或内插得到；
计算稳定工况下的温度应力σt＝E(αv-αb)T，其中E为弹性模量，αv为被紧固材料的线性膨胀系数，αb为紧固件材料的线性膨胀系数，T为设计温度；
确定稳定工况下的服役应力σs为σp+σt和σp中较大者与σr比较取较小者；
S106、确定紧固件个数及尺寸：根据步骤S105中工作状态下的服役应力σs，综合考虑密封面尺寸、密封力P等因素，根据P＝nAσs，设计紧固件的个数n、有效截面积A及其分布；
S107、确定允许最大裂纹尺寸：根据紧固件的无损检测规定，确定允许的最大裂纹尺寸；
S108、确定最大允许服役应力σth：假定步骤S107确定的允许最大裂纹尺寸垂直于紧固件受力方法，结合高温裂纹扩展门槛值Kth，计算得到最大允许服役应力σth；最大允许服役应力σth可由下式计算得到
Figure PCTCN2016084248-appb-000007
其中FI可通过应力强度因子手册查询或有限元法计算获得，a是裂纹长度；
S109、比较步骤S105中的服役应力σs是否小于步骤S108中的最大允许服役应力σth；若是则执行步骤S110；否则降低预紧应力σp，进行步骤S105至S110直至σs<σth；
S110、构件安全，给出设计结果：设计周期该紧固件不会发生裂纹扩展，构件安全；步骤S102及S106中确定的紧固件材料、紧固件的个数n、有效截面积A及其分布为本次设计结果。
图4是本申请实施例中螺栓形貌及其内外表面裂纹缺陷示意图。如图4所示，Do为螺栓外径，Di为螺栓内径，a为裂纹长度，σs为螺栓服役应力，外表面裂纹表示螺栓外表面存在裂纹的情况，内表面裂纹表示螺栓内表面存在裂纹的情况。
实施例
下面结合具体的实施例进一步阐述本发明。但是，应该明白，这些实施例仅用于说明本发明而不构成对本发明范围的限制。下列实施例中未注明具体条件的试验方法，通常按照常规条件，或按照制造厂商所建议的条件。除非另有说明，所有的百分 比和份数按重量计。
实施例1：
某汽轮机高温蒸汽阀门需要进行阀门螺栓设计。螺栓设计温度为560℃，大气环境，设计周期100000小时，阀门所需的密封力为8500000N，阀门材料为GX12CrMoWVNbN10-1-1，阀门密封面外径为1695mm，内径为1085mm。
工艺流程如下：
一、获取设计工况参数。螺栓设计温度T为560℃，阀门材料为GX12CrMoWVNbN10-1-1，阀门密封面外径为1695mm、内径为1085mm，阀门所需的密封力P为8500000N。
GX12CrMoWVNbN10-1-1钢化学成分(质量分数，％)
C Si Mn P S Cr Mo Ni W V N Nb Fe
0.14 0.28 0.93 0.008 0.006 9.51 0.99 0.73 0.99 0.19 0.048 0.086 剩余
二、根据560℃设计温度选择螺栓材料为Inconel 783合金。
Inconel 783合金化学成分(质量分数，％)
C Mn S P Si Cr Ni Fe Al Nb Ti B Cu Co
0.01 0.025 0.002 0.004 0.038 2.99 28.24 26.04 5.24 2.99 0.20 0.0049 0.009 剩余
三、采用热膨胀仪(德国耐驰)测试获得Inconel 783合金560℃下的线性膨胀系数αb为1.22E-5 1/℃，GX12CrMoWVNbN10-1-1钢560℃下的线性膨胀系数αv为1.24E-5 1/℃。采用静态法测试获得560℃下的弹性模量E为144GPa。进行560℃下圆棒拉伸试验，测试获得0.2％塑性延伸强度Rp0.2为630MPa。进行560℃下应力松弛试样，测试获得不同载荷下的应力松弛性能，采用origin软件绘制剩余应力σ与时间t曲线，见图2。采用紧凑拉伸试样，进行560℃空气环境下的高温裂纹扩展试验，获得初始应力强度因子K与裂纹起裂时间ti曲线，采用origin软件绘制并拟合曲线
Figure PCTCN2016084248-appb-000008
曲线外推得到100000小时时的裂纹扩展门槛值为10.4MPa√m(m表示米)，见图3。
四、确定单个螺栓的预紧应力，σp＝0.5Rp0.2＝0.5×630MPa＝315MPa。
五、根据Inconel 783合金560℃不同载荷下的应力松弛曲线，外推获得100000小时后的剩余应力σr为300MPa。计算稳定工况下的温度应力σt＝E(αv-αb)T＝144000×(1.24E-5－1.22E-5)×560＝16MPa。确定稳定工况下的服役应力σs＝[[σp+σt,σp]max,σr]min＝[[315+16,315]max,300]min＝300MPa。
六、综合考虑密封面尺寸、密封力P等因素，根据P＝nAσs，确定螺栓个数为24个，螺栓有效截面积为1180mm2。考虑到施工等要求，设计螺栓外径Do为46mm，内径Di为25mm。如图4所示。
七、根据无损检测规定，允许的最大裂纹尺寸为1mm深的线缺陷。
八、当允许的最大裂纹垂直于紧固件受力方法为最危险工况，如图4所示，结合高温裂纹扩展门槛值Kth＝10.4MPa√m，计算最大允许服役应力σth
Figure PCTCN2016084248-appb-000009
其中FI可通过应力强度因子手册查询获得，内、外表面裂纹的FI值均为1.19。最大允许服役应力σth为156MPa。
九、明显，稳定工况下的服役应力σs大于最大允许服役应力σth。降低预紧应力σp为140MPa。进行五至九步分析，详细如下：
9-5、计算得到稳定工况下的服役应力σs＝[[σp+σt,σp]max,σr]min＝[[140+16,140]max,300]min＝156MPa；
9-6、确定螺栓个数为24个，螺栓有效截面积为2280mm2，螺栓外径Do为60mm，内径Di为25mm；
9-7、根据无损检测规定，允许的最大裂纹尺寸为1mm深的线缺陷；
9-8、当允许最大裂纹垂直于紧固件受力方法为最危险工况，结合高温裂纹扩展门槛值Kth，计算最大允许服役应力σth
Figure PCTCN2016084248-appb-000010
其中FI可通过应力强度因子手册查询获得，内、外表面裂纹的FI值均为1.16。最大允许服役应力σth为160MPa。
9-9、稳定工况下的服役应力σs小于最大允许服役应力σth。
十、560℃，100000小时设计周期内螺栓不会发生裂纹扩展，构件安全。该高温蒸汽阀门需要螺栓24个，螺栓直径Do＝60mm，内径Di＝25mm，材料为Inconel783合金。
上述所列的实施例仅仅是本发明的较佳实施例，并非用来限定本发明的实施范围。即凡依据本发明申请专利范围的内容所作的等效变化和修饰，都应为本发明的技术范畴。
在本发明提及的所有文献都在本申请中引用作为参考，就如同每一篇文献被单独引用作为参考那样。此外应理解，在阅读了本发明的上述讲授内容之后，本领域技术人员可以对本发明作各种改动或修改，这些等价形式同样落于本申请所附权利要求书所限定的范围。

Claims (7)

  1. 一种镍基高温紧固件的防断裂设计方法，该方法包括以下步骤：
    S1、获取设计工况参数，所述参数包括：设计温度T、环境介质、设计周期、被紧固材料牌号及结构尺寸、实现紧固功能所需的力P；
    S2、根据步骤S1中的设计温度T及环境介质选择紧固件材料；
    S3、获取材料性能数据，所述数据包括：紧固件材料和被紧固材料的线性膨胀系数αb及αv，紧固件材料的弹性模量E、拉伸性能、应力松弛性能、高温裂纹扩展门槛值Kth；
    S4、根据步骤S2中选择的材料，确定单个紧固件的预紧应力σp，其中，σp＝0.5Rp0.2，式中Rp0.2表示紧固件的0.2％塑性延伸强度；
    S5、确定步骤S1中的设计温度T及设计周期下的应力松弛后的剩余应力σr，其中，σr通过材料性能数据库查询获得，或者进行高温松弛试验测试获得松弛曲线，采用origin软件、excel软件或手绘绘制松弛曲线，并对曲线进行外推或内插得到；计算稳定工况下的温度应力σt＝E(αv-αb)T；确定稳定工况下的服役应力σs，其中，σs为σp+σt和σp中较大者与σr比较取较小者；
    S6、设计紧固件的个数n、有效截面积A及其分布；
    S7、根据紧固件的无损检测规定，确定允许的最大裂纹尺寸；
    S8、假定步骤S7中确定的允许的最大裂纹尺寸垂直于紧固件受力方法，结合高温裂纹扩展门槛值Kth，计算得到最大允许服役应力σth，其中，
    Figure PCTCN2016084248-appb-100001
    式中FI是通过应力强度因子手册查询或有限元法计算获得的，a是裂纹长度；
    S9、比较步骤S5中的服役应力σs是否小于步骤S8中的最大允许服役应力σth；若是则执行步骤S10；否则返回步骤S4，并降低预紧应力σp；
    S10、设计周期该紧固件不会发生裂纹扩展，构件安全；给出紧固件材料、个数n、有效截面积A及其分布。
  2. 如权利要求1所述的方法，其特征在于，步骤S3中所述的材料性能数据是通过材料性能数据库查询获得的，若查询不到则需进行相应的试验测试获得。
  3. 如权利要求1所述的方法，其特征在于，所述线性膨胀系数采用热膨胀仪测试获得；所述弹性模量E采用动态热机械分析仪测试获得；所述拉伸性能采用高温圆棒拉伸测试获得；所述应力松弛性能进行高温松弛试验测试获得；所述高 温裂纹扩展门槛值Kth采用紧凑拉伸试样进行高温裂纹扩展试验测试获得初始应力强度因子与裂纹起裂时间曲线，并将曲线外推或内插得到设计周期下的高温裂纹扩展门槛值Kth。
  4. 如权利要求3所述的方法，其特征在于，所述设计周期下的高温裂纹扩展门槛值Kth通过进行短时高温裂纹扩展试验，对测试数据依据
    Figure PCTCN2016084248-appb-100002
    规律计算得到，式中，K为应力强度因子，ti表示裂纹起裂时间，B与
    Figure PCTCN2016084248-appb-100003
    为材料参数，由试验数据拟合得到；将设计周期代入拟合后的方程，计算获得该设计周期下的应力强度因子K即为裂纹扩展门槛值Kth。
  5. 如权利要求1所述的方法，其特征在于，在步骤S6中，根据步骤S5中得到的服役应力σs，综合考虑密封面尺寸和力P，根据P＝nAσs，设计紧固件的个数n、有效截面积A及其分布。
  6. 如权利要求1所述的方法，其特征在于，步骤S7中允许的最大裂纹尺寸根据无损检测技术的最小可检出缺陷尺寸及检测和制造成本综合考量确定。
  7. 如权利要求6所述的方法，其特征在于，所述无损检测技术包括目视检测、磁粉检测和射线检测。
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