CN103308334B - A kind of component fatigue appraisal procedure of Nonlinear Cumulative - Google Patents

Abstract

The invention discloses a kind of component fatigue appraisal procedure of Nonlinear Cumulative, for carrying out Fatigue Assessment to the component under the effect of luffing stress time-histories, comprising the following steps: pre-service is carried out to the standard stress time-histories of component, obtains peak-to-valley value sequence; Carry out rain-flow counting, extract Cyclic Stress sequence that this component experiences, that comprise effect precedence, estimate the fatigue damage that calibrated bolck causes; Estimate the life-span of component.The present invention can be used for the Fatigue Assessment of bearing luffing stress members, can consider the precedence that Cyclic Stress applies, and also can consider and estimate the impact that overload is accumulative on fatigue, being particularly suitable for the Fatigue Assessment based on Monitoring Data in monitoring structural health conditions.

Description

A kind of component fatigue appraisal procedure of Nonlinear Cumulative

Technical field

The invention belongs to component fatigue evaluation areas, especially the component fatigue appraisal procedure of Nonlinear Cumulative.

Background technology

In current existing Fatigue Assessment method, mainly bear the situation of constant amplitude load for component, main employing S-N curve method; And for slightly complicated luffing load, after utilizing cycle count method extraction stress spectra, general linearly tired Miller (Miner) law added up that adopts assesses degree of fatigue.

But the fatigue accumulation of material is a non-linear process, the loading sequence of Cyclic Stress has appreciable impact to damage is accumulative, and thus the theory of Miller criterion and corresponding assessment result and actual conditions exist comparatively big error; In addition, Miller criterion is a theory being more suitable for high cycle fatigue, can not consider the impact that the overload effect of contingency is accumulative on fatigue.

Summary of the invention

Goal of the invention: the present invention will provide a kind of appraisal procedure, carries out Fatigue Damage Assessment to the component or material bearing luffing stress time-histories.

Technical scheme: a kind of component fatigue appraisal procedure of Nonlinear Cumulative, comprises the steps:

Step 1, standard stress time-histories σ to component ^blockt () carries out pre-service, obtain peak-to-valley value sequence p (i);

Step 2, rain-flow counting is carried out to described peak-to-valley value sequence p (i), extract Cyclic Stress sequence C that this component experiences, that comprise effect precedence;

The fatigue damage recruitment Δ D that step 3, calculating calibrated bolck cause _block;

The life-span of step 4, calculating component.

In described step 2, according to the extracted in order Cyclic Stress sequence C of component institute elapsed-time standards.

Described step 3 comprises the following steps:

I, taking-up stress amplitude sequence Δ σ (i);

Ii, be that index travels through all Cyclic Stress with i, calculate the damage increment dD that this circulation causes _i;

Iii, to damage increment dD _isummation, calculates the fatigue damage recruitment Δ D that calibrated bolck causes _block:

In described step I i, point three kinds of situations calculate damage increment dD _i:

A) Δ σ _i<=h ₁time

dD _i＝0 (1)

B) h ₁< Δ σ _i<=h ₂time,

${\mathrm{dD}}_i=\frac{{\left[(\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i+2{\mathrm{\&sigma;}}_{m,i})\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}---\left(2\right)$

C) Δ σ (i) > h ₂time, first by the b of non-overloaded) situation estimation, be designated as

$A=\frac{{\left[(\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i+2{\mathrm{\&sigma;}}_{m,i})\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}.$

And be modified on this basis

${\mathrm{dD}}_i=(1-D_i)\{1-{[1-A({\mathrm{\&alpha;}}_i+1)]}^{\frac{1}{{\mathrm{\&alpha;}}_i+1}}\}---\left(3\right)$

Wherein i is index, and D is fatigue damage amount, because of but an amount along with time variations, Δ σ, σ _mbe stress amplitude and mean stress respectively, with index i change, need to be write as σ _m,iwith Δ σ _iform, B and β is material constant, and α is with the relevant function f (Δ σ) of stress amplitude Δ σ, is write as α with index i change _i=f (Δ σ _i) form, stress amplitude threshold value h ₁fatigue stress threshold value, Δ σ (i) < h ₁time, any fatigue effect can not be produced, h ₂for the judgement threshold of overload, Δ σ (i) > h ₂time, belong to overload condition.

Described step 4 comprises: make initial fatigue damage be zero (D ₀=0) the impairment value ultimate value D, during given inefficacy simultaneously _f, in units of calibrated bolck, constantly apply this load, repetition carry out step 3 until fatigue damage value reaches the limit values D _f.

In step 2, described rain-flow counting adopts 4 diagnostic methods, specific as follows:

The all values of i, traversal peak-to-valley value data (p (i)), for the particular value (p (i)) at current location i place, gets four adjacent peak valley points and carries out judgement 4 diagnostic methods; Obtain the Cyclic Stress sequence extracted and (be designated as C ₀, C ₀for M ₀the matrix of × 2, wherein M ₀for the circulation peak-to-valley value (p that is total and remaining, that cannot extract temporarily extracted _r0(i)) sequence;

Ii, by p _r0i () sequence disconnects from maximal value, then by end to end, form new sequence, be designated as p _r(i), this sequence can not produce the Cyclic Stress that cannot extract; To p _ri () be implementation step first again), and add the Cyclic Stress newly extracted to C ₀the Cyclic Stress sequence that middle formation is final, is designated as C, and C is the matrix of M × 2, and wherein M is the circulation sum extracted; Obtain Cyclic Stress sequence C, C contains the Cyclic Stress comprising precedence.

In described step 1, traversal standard stress time-histories σ ^blockall data σ in (t) ^block(i), judge the positive negativity of [σ (i)-σ (i-1)] × [σ (i)-σ (i+1)]: if positive number, then stress σ (i) is labeled as peak value or valley, takes out and put into peak-to-valley value data p (i) successively; If negative, then skip.

Beneficial effect: the present invention can consider the precedence (fatigue damage non-linear accumulative) that Cyclic Stress applies, also can consider and estimate the impact that overload effect is accumulative on fatigue, operating feature of the present invention is particularly suitable for the Fatigue Assessment based on Monitoring Data in monitoring structural health conditions.

Accompanying drawing explanation

Fig. 1 is the frame diagram of Fatigue Assessment of the present invention;

Fig. 2 a and Fig. 2 b is rain-flow counting schematic diagram of the present invention;

Fig. 3 is the process schematic that the present invention calculates fatigue damage increment;

Fig. 4 a and Fig. 4 b is the sample result figure that the present invention obtains the parameter alpha=f (Δ σ) of material;

Fig. 5 is the schematic diagram of the parameter B that the present invention obtains material, β;

Fig. 6 a and Fig. 6 b is loop blocks and the assessment result schematic diagram of the present invention's bridge member embodiment.

Embodiment

The present invention, on the basis of damage mechanics, rain flow method scheduling theory and technology, gives a kind of component fatigue appraisal procedure of Nonlinear Cumulative.The assessment that the present invention adds up for the non-linear fatigue damage of bearing luffing stress members, the precedence that Cyclic Stress applies can be considered, also can consider and estimate the impact that overload is accumulative on fatigue, the present invention is particularly suitable for the Fatigue Assessment based on Monitoring Data in monitoring structural health conditions.

As shown in Figure 1, the component fatigue appraisal procedure of a kind of Nonlinear Cumulative of the present invention comprises several step:

1, to the standard stress time-histories σ that component is representative ^blockt () (being called calibrated bolck, block), carries out pre-service and obtains peak-to-valley value sequence p (i);

2, rain-flow counting is carried out to p (i), extract Cyclic Stress sequence C that this component experiences, that comprise effect precedence;

3, estimate that the fatigue damage that calibrated bolck causes increases Δ D _block;

4, the life-span of component is estimated.

In step 1, pre-service refers to extracts stress course σ ^blockt the peak value in () and valley, method is: traversal σ ^blockall data σ in (t) ^block(i), judge the positive negativity of [σ (i)-σ (i-1)] × [σ (i)-σ (i+1)]: if positive number, then σ (i) is labeled as peak value or valley, takes out and put into storage peak-to-valley value data p (i) successively; If negative, then skip.Head and the tail two number of σ (i) is certain peak value or valley.

The peak-to-valley value data of will be discharged successively after preprocessing process terminates, are designated as p (i).

In step 2, described rain-flow counting adopts 4 diagnostic methods, and step is first-second:

The all values of first, traversal peak-to-valley value data p (i), for the value p (i) at current location i place, gets four adjacent peak valley points and judges.Rule of judgment:

A), as depicted in figure 2, if p (i) be trough and p (i+1) >p (i) time, meet p (i+2) >p (i) and the condition of p (i+3) >p (i+1); Extract the stress recycle to extinction that path is p (i+1) → p (i+2) → p (i+1), with the matrix [σ of 1 × 2 _m, Δ σ] this circulation of format record, remove simultaneously p (i+1) point and p (i+2) point; Position i is reduced 2, returns above-mentioned judgement;

B), as shown in accompanying drawing 2b, if p (i) be crest and p (i+1) <p (i) time, meet p (i+2) <p (i) and the condition of p (i+3) <p (i+1); Extract the stress recycle to extinction that path is p (i+1) → p (i+2) → p (i+1), with the matrix [σ of 1 × 2 _m, Δ σ] this circulation of format record, remove simultaneously p (i+1) point and p (i+2) point; Position i is reduced 2, returns above-mentioned judgement;

Wherein, σ _mfor the mean stress of this Cyclic Stress, computing method are σ _m=(p (i+1)+p (i+2))/2; Δ σ is the stress amplitude of this Cyclic Stress, and computing method are Δ σ=Abs (p (i+1)-p (i+2)), and wherein Abs () is for taking absolute value.

C), do not meet above-mentioned a) or b) arbitrary condition, do not process, position i is added 1, return above-mentioned judgement.

After step first terminates, obtain the Cyclic Stress sequence extracted and (be designated as C ₀, C ₀for M ₀the matrix of × 2, wherein M ₀for extract circulation sum) and peak-to-valley value that is remaining, that cannot extract temporarily (be designated as p _r0(i)) sequence.

Second, by p _r0i () sequence disconnects from maximal value, then by end to end, form new sequence, be designated as p _ri (), this sequence can not produce the Cyclic Stress that cannot extract.To p _ri () be implementation step first again), and add the Cyclic Stress newly extracted to C ₀the Cyclic Stress sequence that middle formation is final, is designated as C, and C is the matrix of M × 2, and wherein M is the circulation sum extracted.

Step second) terminate after, obtain Cyclic Stress sequence C, C contains the Cyclic Stress comprising precedence.

As shown in Figure 3, in step 3, the process calculating the fatigue damage increase Δ D that calibrated bolck causes is i)-iii):

I), from Cyclic Stress Matrix C take out secondary series, i.e. stress amplitude sequence Δ σ (i), total length and the Cyclic Stress number of note Δ σ (i) are N _cycles.

Ii) two stress amplitude threshold value h, are determined ₁and h ₂.Wherein h ₁it is fatigue stress threshold value.Δ σ (i) < h ₁time can not produce any fatigue effect.Δ σ (i) > h ₂time, belong to overload condition, at this moment likely can produce plasticity.Travel through all Cyclic Stress (taking i as index), calculate the damage increment dD that this circulation causes _ibe divided into three kinds of situations

A) Δ σ _i<=h ₁time

dD _i＝0 (1)

B) h ₁< Δ σ _i<=h ₂time,

${\mathrm{dD}}_i=\frac{{\left[(\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i+2{\mathrm{\&sigma;}}_{m,i})\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}---\left(2\right)$

C) Δ σ (i) > h ₂time, first by the b of non-overloaded) situation estimation, be designated as

$A=\frac{{\left[(\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i+2{\mathrm{\&sigma;}}_{m,i})\mathrm{\&Delta;}{\mathrm{\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}.$

Be modified on this basis

${\mathrm{dD}}_i=(1-D_i)\{1-{[1-A({\mathrm{\&alpha;}}_i+1)]}^{\frac{1}{{\mathrm{\&alpha;}}_i+1}}\}---\left(3\right)$

Wherein i is index.D is fatigue damage amount, because of but an amount changed along with the time (Cyclic Stress sequence).Identical with definition above, Δ σ, σ _mbe stress amplitude and mean stress respectively, therefore with index i change, need to be write as σ _m,iwith Δ σ _iform.B and β is material constant.α is with the relevant function f (Δ σ) of stress amplitude Δ σ, is thus also write as α with index change _i=f (Δ σ _i) form.

Iii) the fatigue damage increase Δ D that calibrated bolck causes, is calculated _block:

${\mathrm{\&Delta;D}}_{\mathrm{block}}={\mathrm{\&Sigma;}}_{i=1}^{N_{\mathrm{cycles}}}d{D}_i$

Described step 3) neutron step I i) theory origin as follows, according to damage mechanics theory, the fatigue that the Cyclic Stress exceeding fatigue threshold causes accumulative (rate) is,

$\frac{\mathrm{dD}}{\mathrm{dn}}=\frac{{\left[(\mathrm{\&Delta;\&sigma;}+2{\mathrm{\&sigma;}}_m)\mathrm{\&Delta;\&sigma;}\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D)}^{\mathrm{\&alpha;}}}$

Wherein D, Δ σ, σ _m, B, β, α with define above identical

Above-mentioned formula integration can be obtained step I i) in several formulas, situation b) be the D in above formula right-hand member is regarded as circulation in constant obtained, and situation c) be consider that the lower damage of overload may have the change of can not ignore, and thus moves on to left end integration and obtains by D.In theory, the formula of step c) situation also can be used in the situation of non-overloaded.Here making differentiation is to average out between counting yield and accuracy.

In step 3, sub-step material parameter B ii), β, α method of testing must determine by means of the Woehler curve of single shaft cycle facigue and controlled strain torture test.

First the form of α=f (Δ σ) is determined.Carry out the testing fatigue of the equal stress width under different order of magnitude, obtain the curve of fatigue and the fatigue damage accumulation curve of material.

Fig. 4 a gives the figure that certain stainless steel bears the fatigue damage D of different equal stress width effects.On the other hand, the damage evolution equation in theory under single shaft cyclic loading can obtain following form:

$D=1-{\{1-\frac{N}{N_f}[1-{(1-D_f)}^{{\mathrm{\&alpha;}}_i+1}\left]\right\}}^{\frac{1}{{\mathrm{\&alpha;}}_i+1}}$

Fatigue damage summation curve under differently strained width Δ σ is all drawn the α under different stress amplitude with above-mentioned equation model, then with suitable curve α--Δ σ relation, general useable linear relation describes this relation:

α＝kΔσ+α ₀

Provide in Fig. 4 b certain stainless steel Δ σ be 600,500 and 480MPa stress amplitude under α value, by parameter k and α can be obtained to the matching of this figure ₀.

Then B is determined, the value of β.In theory, the period formula lost efficacy under the cyclic loading of single shaft is

$N_f=\frac{B_1(\mathrm{\&beta;}+3)}{\mathrm{\&alpha;}+1}\mathrm{\&Delta;}{\mathrm{\&sigma;}}^{-(\mathrm{\&beta;}+3)}$

In formula, parameter alpha is determined.Parameter beta+3 and B ₁(β+3)/(α+1) can by the Woehler curve N under the loop cycle load of generation equal stress width _f(Δ σ) carrys out matching and determines.

Fig. 5 gives the S-N curve of certain stainless steel test specimen under constant amplitude cyclic load, by obtaining β+3, B to the matching of this curve ₁(β+3)/(α+1).Finally B can be obtained, β.

In step 4, the method in the life-span of estimation component is make initial fatigue damage be D ₀=0, the impairment value ultimate value D simultaneously during given inefficacy _f, in units of calibrated bolck, constantly apply this load, repetition carry out step 3) until fatigue damage value reaches D _f.

Fig. 6 a and Fig. 6 b provides loop blocks and the assessment result of certain bridge member.Fig. 6 a is the Cyclic Stress block of input, and Fig. 6 b is the tired summation curve provided after assessment.In curve, one is the tired accumulated result provided according to Miller criterion, and one is the fatigue evolution result provided according to the present invention, obviously can find out that the present invention can consider tired accumulative nonlinear characteristic in figure.

Claims (5)

1. a component fatigue appraisal procedure for Nonlinear Cumulative, is characterized in that comprising the steps:

Step 1, standard stress time-histories σ to component ^blockt () carries out pre-service, obtain peak-to-valley value data p (i);

Step 2, rain-flow counting is carried out to described peak-to-valley value data p (i), extract Cyclic Stress sequence C that this component experiences, that comprise effect precedence;

The fatigue damage recruitment Δ D that step 3, calculating calibrated bolck cause _block;

The life-span of step 4, calculating component;

Described step 3 comprises the following steps:

I, taking-up stress amplitude sequence Δ σ (i);

Ii, be that index travels through all Cyclic Stress with i, calculate the damage increment dD that this circulation causes _i;

Iii, to damage increment dD _isummation, calculates the fatigue damage recruitment Δ D that calibrated bolck causes _block;

In described step I i, point three kinds of situations calculate damage increment dD _i:

A) Δ σ _i<=h ₁time

dD _i＝0 (1)

B) h ₁< Δ σ _i<=h ₂time,

${\mathrm{dD}}_i=\frac{{\left[({\mathrm{\&Delta;\&sigma;}}_i+{2\mathrm{\&sigma;}}_{m,i}){\mathrm{\&Delta;\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}---\left(2\right)$

C) Δ σ (i) > h ₂time, first by the b of non-overloaded) situation estimation, be designated as

$A=\frac{{\left[({\mathrm{\&Delta;\&sigma;}}_i+{2\mathrm{\&sigma;}}_{m,i}){\mathrm{\&Delta;\&sigma;}}_i\right]}^{\frac{\mathrm{\&beta;}+3}{2}}}{B(\mathrm{\&beta;}+3){(1-D_i)}^{{\mathrm{\&alpha;}}_i}}$

And be modified on this basis

${\mathrm{dD}}_i=(1-D_i)\{1-{[1-A({\mathrm{\&alpha;}}_i+1)]}^{\frac{1}{{\mathrm{\&alpha;}}_i+1}}\}---\left(3\right)$

Wherein i is index, and D is fatigue damage amount, is an amount along with time variations, Δ σ, σ _mbe stress amplitude and mean stress respectively, with index i change, need to be write as Δ σ _iand σ _{m, i}form, B and β is material constant, and α is with the relevant function f (Δ σ) of stress amplitude Δ σ, is write as α with index i change _i=f (Δ σ _i) form, stress amplitude threshold value h ₁fatigue stress threshold value, Δ σ (i) < h ₁time, any fatigue effect can not be produced, h ₂for the judgement threshold of overload, Δ σ (i) > h ₂time, belong to overload condition.

2. the component fatigue appraisal procedure of a kind of Nonlinear Cumulative according to claim 1, is characterized in that: in described step 2, according to the extracted in order Cyclic Stress sequence C of component institute elapsed-time standards.

3. the component fatigue appraisal procedure of a kind of Nonlinear Cumulative according to claim 1, is characterized in that: described step 4 comprises the following steps: make initial fatigue damage be zero D ₀=0, the damage limit value Df simultaneously during given inefficacy _,in units of calibrated bolck, continuous load application, repetition carry out step 3 until fatigue damage value reaches damage limit value D _f.

4. the component fatigue appraisal procedure of a kind of Nonlinear Cumulative according to claim 1, is characterized in that: in step 2, and described rain-flow counting adopts 4 diagnostic methods, specific as follows:

The all values of i, traversal peak-to-valley value data p (i), for particular value p (i) at current location i place, gets four adjacent peak valley points and carries out judgement 4 diagnostic methods; Obtain the Cyclic Stress sequence C extracted ₀, C ₀for M ₀the matrix of × 2, wherein M ₀for the circulation peak-to-valley value p that is total and remaining, that cannot extract temporarily extracted _r0(i) sequence;

Ii, by peak-to-valley value p _r0i () sequence disconnects from maximal value, then by end to end, form new sequence, be designated as p _r(i), this sequence can not produce the Cyclic Stress that cannot extract; To p _ri () be implementation step i again), and add the Cyclic Stress newly extracted to Cyclic Stress sequence C ₀the Cyclic Stress sequence C that middle formation is final, C is the matrix of M × 2, and wherein M is the circulation sum extracted; Obtain Cyclic Stress sequence C, C contains the Cyclic Stress comprising precedence.

5. the component fatigue appraisal procedure of a kind of Nonlinear Cumulative according to claim 1, is characterized in that: in described step 1, traversal standard stress time-histories σ ^blockall data σ in (t) ^block(i), judge the positive negativity of [σ (i)-σ (i-1)] × [σ (i)-σ (i+1)]: if positive number, then stress σ (i) is labeled as peak value or valley, takes out and put into peak-to-valley value data p (i) successively; If negative, then skip.