CN106896133A - A kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue - Google Patents

Abstract

A kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue, is related to Machine Design fatigue strength field.Steps of the method are:(1) plane where finding maximum shear strain amplitude, i.e. critical surface；Calculate equivalent temperature；The isothermal fatigue solved under being circulated at one is damaged；Axial stress time history and corresponding temperature-time course under one stable circulation load is obtained by stress-strain Constitutive Relationship or lag loop and appropriate number is divided into, calculate per portion creep impairment, the cumulative creep impairment obtained under a stable circulation load；After determining phase angular dimensions, calculate isothermal fatigue and damage and the Mutual damage between creep impairment；The cumulative thermal mechanical fatigue obtained under a cyclic loading is damaged.Result illustrates that the method can preferably predict multiaxis banner Thermomechanical Fatigue Life.

Description

A kind of multiaxis Life Prediction of Thermomechanical Fatigue based on isothermal fatigue and creep fatigue Method

Technical field

The present invention relates to fatigue strength field, the multiaxis Thermomechanical Fatigue Life based on isothermal fatigue and creep fatigue is refered in particular to Forecasting Methodology.

Background technology

Many engineering components generally run under mechanical load and the simultaneous adverse circumstances of thermal cycling loads, such as aircraft Engine, gas turbine, steam turbine and boiler etc., the especially startup at them and dwell period, by these structures of serious curtailment The life-span of part and causing trouble.In order that it works with security and stability, the Life Prediction Model of these key members is ground Study carefully.Although having been achieved for some progress, these researchs are only limitted to single shaft thermal mechanical fatigue, add the complexity of experiment with The costliness of expense, over the past several decades in only a few studies person multiaxis thermal mechanical fatigue is studied.

The life prediction of current multiaxis thermal mechanical fatigue is mainly the isothermal fatigue it being converted under hot conditions, and this But ignore damage of the creep impairment to component in the case of kind, thus it is this it is traditional predicted with fatigue at high temperature it is thermomechanical tired The reliability of labour's method exists uncertain.Accordingly, it is considered to influence of the creep impairment to thermal mechanical fatigue, research it is a kind of based on etc. Warm fatigue and the multiaxis Life Prediction of Thermomechanical Fatigue method of creep fatigue are significant

The content of the invention

Present invention aim at the demand for development for multiaxis thermal mechanical fatigue, it is proposed that a kind of based on isothermal fatigue and compacted Become the multiaxis Life Prediction of Thermomechanical Fatigue method of fatigue.

A kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue provided by the present invention, Its step is：

Step 1)：Plane, i.e. critical surface where maximum shear strain amplitude are determined by strain-time history.

Step 2)：Calculate critical surface on damage parameters, including maximum shear strain amplitude, adjacent cutouts strain turning point it Between normal strain width and corresponding temperature, according to propose equivalent temperature model determine equivalent temperature；

Step 3)：Calculated according to the damage parameters on critical surface, equivalent temperature and stretching unified model non-proportional loading model Isothermal fatigue is damaged；

Step 4)：The axial direction under a stable circulation load is obtained by constitutive relationship of stress-strain or lag loop Stress-time history and temperature-time histories；

Step 5)：Axial stress-time history and temperature-time histories are divided into appropriate number, with every a The average value of point stress value and terminal stress value is processed as creep stress, temperature with same method, obtains creep temperature.

Step 6)：Relation (the creep rupture equation of material) according to stress, temperature and creep fracture time calculates each The creep impairment of part, the creep impairment of all numbers that then add up, the total creep as under a stable circulation load is damaged；

Step 7)：Determine the phase angle between axial strain and temperature, determine that exhaustion creep is handed over by uniaxial test data Interaction factor, the Mutual damage between fatigue and creep is calculated according to the Mutual damage model for proposing；

Step 8)：Isothermal fatigue under the cyclic loading that adds up is damaged, creep impairment and Mutual damage obtain one and follow Multiaxis under ring load is thermomechanically always damaged, you can obtain bimetry.

Compared with prior art, the present invention has the advantages that：

The present invention proposes a kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue.The party Method multiaxis thermal mechanical fatigue is damaged be converted into solution isothermal fatigue damage, creep impairment and exhaustion creep Mutual damage three it With.The method need not carry out the thermal mechanical fatigue experiment of complexity, it is only necessary to determine relevant parameter, computational methods are simple.Pass through Checking, carries out the estimation of multiaxis Thermomechanical Fatigue Life and obtains preferable prediction effect using the method.

Brief description of the drawings

Fig. 1 is to illustrate the process for determining the normal strain scope on critical surface between adjacent cutouts strain.

Fig. 2 is to illustrate the process that equivalent temperature is determined when range of temperature is dullness.

Fig. 3 is to illustrate the process that equivalent temperature is determined when range of temperature is non-monotonic.

Fig. 4 is to illustrate segmentation one axial stress of stable circulation (stretched portion)-time history and temperature history.

Fig. 5 is for phase difference is 0 °, phase between axial strain and temperature between axial strain and shear strain in actual tests Potential difference is 0 ° of load condition, referred to as MIPTIP.

Fig. 6 is for phase difference is 0 °, phase between axial strain and temperature between axial strain and shear strain in actual tests Potential difference is 180 ° of load condition, referred to as MIPTOP.

Fig. 7 is for phase difference is 90 °, phase between axial strain and temperature between axial strain and shear strain in actual tests Potential difference is 0 ° of load condition, referred to as MOPTIP.

Fig. 8 is for phase difference is 90 °, phase between axial strain and temperature between axial strain and shear strain in actual tests Potential difference is 180 ° of load condition, referred to as MOPTOP.

Fig. 9 is to go through axial stress (the stretched portion)-time obtained (corresponding to the load condition of Fig. 5) from actual tests Journey and temperature-time histories.

Figure 10 is axial stress (the stretched portion)-time obtained (corresponding to the load condition of Fig. 6) from actual tests Course and temperature-time histories.

Figure 11 is axial stress (the stretched portion)-time obtained (corresponding to the load condition of Fig. 7) from actual tests Course and temperature-time histories.

Figure 12 is axial stress (the stretched portion)-time obtained (corresponding to the load condition of Fig. 8) from actual tests Course and temperature-time histories.

Figure 13 is the histogram of the bimetry under four kinds of load conditions and true lifetime.

Figure 14 is that the bimetry under four kinds of load conditions is distributed with true lifetime under bi-coordinate system, and two oblique lines are two Times factor band.

Figure 15 is method schematic diagram.

Specific embodiment

Specific embodiment of the invention is described with reference to the drawings, but the present invention is not limited to following examples.

A kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue, specific embodiment is such as Under：

Step 1)：Determine that maximum shear strains place plane, i.e. critical surface by the strain history for loading.

Step 2)：Calculate critical surface on damage parameters, including maximum shear strain amplitude, adjacent cutouts strain turning point it Between normal strain width and corresponding temperature, and according to propose equivalent temperature model determine equivalent temperature, T₁、T₂Respectively correspond to In the temperature of adjacent cutouts strain, when range of temperature is for dullness, using the two average value, when the non-list of range of temperature Timing, turns to select point T using increasing₃To synthesize equivalent temperature T_eq。

Step 3)：Isothermal fatigue is calculated according to damage parameters, equivalent temperature and stretching unified type model to damage, using following Two formulas can calculate isothermal fatigue and damage.

WhereinThe material constant of equivalent temperature is all corresponded to,It is springform Amount,It is isothermal fatigue period, Δ γ/2 are the shear strain width on critical surface,It is to correspond to adjacent shear on critical surface Normal strain course between shear strain.

Step 4)：When obtaining the axial stress under a stable circulation according to stress-strain Constitutive Relationship or lag loop Between course and temperature-time course；

Step 5)：Axial stress time history and temperature-time course are divided into appropriate number, with every a starting point Stress value and terminal stress value obtain average value as creep rupture stress, and temperature is processed with same method.

Wherein σ_a(i)、σ_a(i+1) i-th part of stress value of beginning and end, σ are respectively_cI () is creep rupture stress, T I () and T (i+1) are respectively i-th part of temperature value of beginning and end, T_cI () is creep temperature.

Step 6)：Relation according to stress, temperature and creep fracture time is calculated per a creep impairment, is then added up The total creep that the creep impairment of all numbers is under the stable circulation is damaged；

f(T_c(i),σ_c(i),t_c(i))=0

Δt_i=t_i+1-t_i

Wherein t_cI () is i-th part of creep fracture time, f is creep rupture stress, creep temperature, creep fracture time The functional relation of three.t_i、t_i+1Respectively i-th part of initial time and end time, Δ t_iIt is the difference between the two, D_cFor creep is damaged Wound.

Step 7)：Determine the phase angle between axial strain temperature, calculated between fatigue and creep according to the model for proposing Mutual damage；

D_fc=α (D_f·D_c)^β

Wherein D_fcIt is Mutual damage, β is interaction factor (being fitted according to single shaft thermal mechanical performance test data), and α should for axial direction Become and the phase difference influence coefficient between temperature, expression formula is as follows

θ is the phase difference between axial strain and temperature.

Step 8)：Cumulative isothermal fatigue damage, creep impairment and Mutual damage obtain the thermomechanical total damage under a circulation Wound, you can obtain bimetry.

D_tmf=D_f+D_fc+D_c

Wherein D_tmfFor thermal mechanical fatigue is damaged, D_fIt is fatigue damage, N_tmfIt is thermal mechanical fatigue period.

The present invention is tested by related multiaxis thermal mechanical fatigue and the present invention is further illustrated, the loading ripple of experiment Shape is triangular waveform, and test material is the high temperature alloys of Haynes 188, according to the phase difference between strain and temperature experiment point Into four types, concrete condition refer to the attached drawing 5-14.Step 3) high temperature alloys of material Haynes 188 that are used, related data Come from the Materials Handbook of bibliography and correlation.Step 5) in functional relation model select the Miller of Larsen one (L-M) side Journey, my this 4 kinds of (G-D) equation, a graceful gloomy Suo Kepu (M-S) equations and Man Sen mono- Ha Fute (M-H) equation of the Tang of Pueraria lobota one are lasting Equation, and select the equation wherein by time yield data fitting best (i.e. standard deviation minimum, coefficient correlation are maximum) to make It is final creep rupture equation.

In order to verify the present invention propose multiaxis Life Prediction of Thermomechanical Fatigue method effect, by this method obtained by it is pre- The life-span that survey lifetime results are obtained with thermal mechanical fatigue experiment is compared, and as a result shows, the mistake of bimetry and result of the test Difference is dispersed within 2 times of factors.It is therefore proposed that the multiaxis Thermomechanical Fatigue Life based on isothermal fatigue and creep impairment side Method can preferably predict the Thermomechanical Fatigue Life under the conditions of multiaxial loading.

Claims (2)

1. a kind of multiaxis Life Prediction of Thermomechanical Fatigue method based on isothermal fatigue and creep fatigue, it is characterised in that：Step It is as follows,

Step 1)：Plane, i.e. critical surface where maximum shear strain are determined by strain-time history；

Step 2)：Calculate right between the damage parameters on critical surface, including maximum shear strain amplitude, adjacent cutouts strain turning point The normal strain width answered and corresponding temperature, equivalent temperature, T are determined according to the equivalent temperature model for proposing₁、T₂Respectively critical surface Upper adjacent cutouts strain turns to select a little corresponding temperature；When temperature changing process is in monotonicity, using T₁、T₂The average value of the two； When temperature changing process is in nonmonotonicity, turn to select point T using increasing₃To synthesize equivalent temperature T_eq；

$T_{eq}=\frac{T_1+T_2}{2}$

$T_{eq}=\frac{T_{2+}2T_3+T_1}{4}$

Step 3)：Isothermal fatigue is calculated according to damage parameters, equivalent temperature and stretching unified type model to damage, using following two Formula can calculate isothermal fatigue and damage；

${\[{\mathrm{\ϵ}}_n^{*2}+\frac{1}{3}{\left(\frac{\mathrm{\Δ}\mathrm{\γ}}{2}\right)}^2\]}^{\frac{1}{2}}=\frac{{\mathrm{\σ}}_{f_{T_{eq}}}^{\′}{\left(2N_{Teq}\right)}^{b_{T_{eq}}}}{E_{T_{eq}}}+{\mathrm{\ϵ}}_{f_{T_{eq}}}^{\′}{\left(2N_{T_{eq}}\right)}^{c_{T_{eq}}}$

$D_f=\frac{1}{N_{T_{eq}}}$

WhereinThe material constant of equivalent temperature is all corresponded to,It is elastic modelling quantity,It is isothermal fatigue period, Δ γ/2 are the shear strain width on critical surface,It is to correspond to adjacent cutouts on critical surface Normal strain course between strain, D_fFor isothermal fatigue is damaged；

Step 4)：Axial stress-the time under a stable circulation is obtained according to constitutive relationship of stress-strain or lag loop Course and temperature-time histories；

Step 5)：Axial stress-time history and temperature-time histories are divided into appropriate number, should with every a starting point Force value and terminal stress value obtain average value as creep rupture stress, and temperature is processed with same method；

${\mathrm{\σ}}_c\left(i\right)=\frac{{\mathrm{\σ}}_a\left(i\right)+{\mathrm{\σ}}_a(i+1)}{2}$

$T_c\left(i\right)=\frac{T\left(i\right)+T(i+1)}{2}$

Wherein σ_a(i)、σ_a(i+1) i-th part of stress value of beginning and end, σ are respectively_cI () is creep rupture stress, T (i) and T (i+1) i-th part of temperature value of beginning and end, T are respectively_cI () is creep temperature；

Step 6)：Relation (the creep rupture equation of material) according to stress, temperature and creep fracture time is calculated per portion Creep impairment, the total creep that the creep impairment of all numbers that then add up is under the stable circulation is damaged；

f(T_c(i), σ_c(i), t_c(i))=0

Δt_i=t_i+1-t_i

$D_c=\underset{i=1}{\overset{m}{\Σ}}{D}_{ci}=\underset{i=1}{\overset{m}{\Σ}}\frac{{\mathrm{\Δt}}_i}{t_{ci}}=\frac{{\mathrm{\Δt}}_1}{t_{c1}}+\frac{{\mathrm{\Δt}}_2}{t_{c2}}+\mathrm{...}+\frac{{\mathrm{\Δt}}_m}{t_{cm}}$

Wherein t_cI () is i-th part of creep fracture time, f is creep rupture stress, creep temperature, creep fracture time three Functional relation.t_i、t_i+1Respectively i-th part of initial time and end time, Δ t_iIt is t_i、t_i+1The difference between the two, D_cIt is creep Damage；

Step 7)：Determine the phase angle between axial strain temperature, the friendship between fatigue and creep is calculated according to the model for proposing Mutually damage；

D_fc=α (D_f·D_c)^β

Wherein D_fcIt is Mutual damage, β is interaction factor, and α is the phase difference influence coefficient between axial strain and temperature, table It is as follows up to formula

θ is the phase difference between axial strain and temperature；

Step 8)：Cumulative isothermal fatigue damage, creep impairment and Mutual damage obtain the thermomechanical total damage under a circulation, i.e., Can obtain bimetry.

D_tmf=D_f+D_fc+D_c

$N_{tmf}=\frac{1}{D_{tmf}}$

Wherein D_tmfFor thermal mechanical fatigue is damaged, D_fFor isothermal fatigue is damaged, N_tmfIt is thermal mechanical fatigue period.

2. a kind of multiaxis Life Prediction of Thermomechanical Fatigue side based on isothermal fatigue and creep fatigue according to claim 1 Method, it is characterised in that：The related data of the material for being used comes from the Materials Handbook of bibliography and correlation.