CN103308334A - Nonlinear cumulative fatigue evaluation method for member - Google Patents

Abstract

The invention discloses a nonlinear cumulative fatigue evaluation method for a member. The nonlinear cumulative fatigue evaluation method is used for carrying out fatigue evaluation on the member under the action of a variable amplitude stress time history and comprises the following steps of preprocessing a standard stress time history of the member to obtain a peak valley value sequence; counting rain flows, extracting a stress cycle sequence which is experienced by the member and contains an action precedence order and estimating fatigue damage caused by a standard block; estimating the service life of the member. The nonlinear cumulative fatigue evaluation method disclosed by the invention can be used for bearing the variable amplitude stress member of the fatigue evaluation and is especially suitable for fatigue evaluation based on monitoring data in the structure health monitoring. According to the nonlinear cumulative fatigue evaluation method, the precedence order applied by stress cycle can be considered and the influence of overload on fatigue cumulation can also be considered and estimated.

Description

A kind of component fatigue appraisal procedure of non-linear accumulation

Technical field

The invention belongs to the component fatigue evaluation areas, the component fatigue appraisal procedure of especially non-linear accumulation.

Background technology

In the present existing Fatigue Assessment method, the situation at member mainly bears the constant amplitude load mainly adopts the S-N curve method; And at complicated slightly luffing load, after utilizing cycle count method extraction stress spectrum, general Miller (Miner) law of linear fatigue accumulative total that adopts is assessed degree of fatigue.

But the fatigue accumulation of material is a non-linear process, and the loading sequence of Cyclic Stress has appreciable impact to damage accumulative total, thereby the theory of Miller criterion exists than mistake with corresponding assessment result and actual conditions; In addition, the Miller criterion is a theory that more is applicable to high cycle fatigue, can not consider that the overload effect of contingency is to the influence of fatigue accumulative total.

Summary of the invention

Goal of the invention: the present invention will provide a kind of appraisal procedure, and member or the material that bears luffing stress time-histories carried out the fatigue damage assessment.

Technical scheme: a kind of component fatigue appraisal procedure of non-linear accumulation comprises the steps:

Step 1, to the standard stress time-histories σ of member ^Block(t) carry out pre-service, obtain peak-to-valley value sequence p (i);

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

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

Step 4, calculating life of components.

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

Described step 3 may further comprise the 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 _iThe fatigue damage recruitment Δ D that calibrated bolck causes is calculated in summation _Block:

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

A) Δ σ _i＜=h ₁The time

dD _i＝0 (1)

B) h ₁＜Δ σ _i＜=h ₂The time,

${\mathrm{dD}}_i=\frac{{\left[(\mathrm{\Δ}{\mathrm{\σ}}_i+2{\mathrm{\σ}}_{m,i})\mathrm{\Δ}{\mathrm{\σ}}_i\right]}^{\frac{\mathrm{\β}+3}{2}}}{B(\mathrm{\β}+3){(1-D_i)}^{{\mathrm{\α}}_i}}---\left(2\right)$

C) Δ σ (i)＞h ₂The time, press the b of non-overload earlier) the situation estimation, be designated as

$A=\frac{{\left[(\mathrm{\Δ}{\mathrm{\σ}}_i+2{\mathrm{\σ}}_{m,i})\mathrm{\Δ}{\mathrm{\σ}}_i\right]}^{\frac{\mathrm{\β}+3}{2}}}{B(\mathrm{\β}+3){(1-D_i)}^{{\mathrm{\α}}_i}}.$

And be modified on this basis

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

Wherein i is index, and D is the fatigue damage amount, thereby is an amount that changes along with the time, Δ σ, σ _mBe respectively stress amplitude and mean stress, change with index i, need be write as σ _{M, i}With Δ σ _iForm, B and β are material constants, α is with the relevant function f (Δ σ) of stress amplitude Δ σ, changes with index i and is write as α _i=f (Δ σ _i) form, stress amplitude threshold value h ₁Be the fatigue stress threshold value, Δ σ (i)＜h ₁The time, will can not produce any fatigue effect, h ₂Be the judgement threshold of overload, Δ σ (i)＞h ₂The time, belong to overload condition.

Described step 4 comprises: make that initial fatigue damage is zero (D ₀=0), the impairment value ultimate value D during given inefficacy the simultaneously _f, be unit with the calibrated bolck, constantly apply this load, repetition carry out step 3 until the fatigue damage value value of reaching capacity D _f

In step 2, described rain-flow counting adopts 4 diagnostic methods, and is 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, is got four adjacent peak valley points and is judged 4 diagnostic methods; The Cyclic Stress sequence that obtains to extract (is designated as C ₀, C ₀Be M ₀* 2 matrix, wherein M ₀Be the circulation peak-to-valley value (p total and remaining, that can't extract temporarily that extracts _R0(i)) sequence;

Ii, with p _R0(i) sequence disconnects from maximal value, then with end to end, forms new sequence, is designated as p _r(i), this sequence will can not produce the Cyclic Stress that can't extract; To p _r(i) implementation step first again), and with the Cyclic Stress of newly extracting add C to ₀The final Cyclic Stress sequence of middle formation is designated as C, and C is the matrix of M * 2, wherein the circulation sum of M for extracting; Obtain the Cyclic Stress sequence C, C has comprised the Cyclic Stress of precedence.

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

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

Description of drawings

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

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

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

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

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

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

Embodiment

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

As shown in Figure 1, the component fatigue appraisal procedure of a kind of non-linear accumulation of the present invention comprises several steps:

1, to the representative standard stress time-histories σ of member ^Block(t) (be called calibrated bolck, block) carry out pre-service and obtain peak-to-valley value sequence p (i);

2, p (i) is carried out rain-flow counting, extract that this member experiences, comprise the Cyclic Stress sequence C that acts on precedence;

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

4, estimate life of components.

In the step 1, pre-service refers to extract stress course σ ^Block(t) peak value in and valley, method is: traversal σ ^Block(t) all the data σ in ^Block(i), judge the positive negativity of [σ (i)-σ (i-1)] * [σ (i)-σ (i+1)]: if positive number then is labeled as peak value or valley with σ (i), take out and put into successively storage peak-to-valley value data p (i); If negative is then skipped.Head and the tail two numbers of σ (i) are certain peak value or valley.

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

In the 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, is got four adjacent peak valley points and is judged.Rule of judgment:

A), shown in accompanying drawing 2a, if p (i) is that trough is p (i+1)〉during p (i), satisfy p (i+2)〉p (i) and p (i+3)〉condition of p (i+1); Extracting the path is the stress recycle to extinction of p (i+1) → p (i+2) → p (i+1), the matrix [σ with 1 * 2 _m, Δ σ] format record should circulation, remove p (i+1) point and p (i+2) point simultaneously; I reduces 2 with the position, returns above-mentioned judgement;

B), shown in accompanying drawing 2b, if p (i) is crest when being p (i+1)＜p (i), satisfy the condition of p (i+2)＜p (i) and p (i+3)＜p (i+1); Extracting the path is the stress recycle to extinction of p (i+1) → p (i+2) → p (i+1), the matrix [σ with 1 * 2 _m, Δ σ] format record should circulation, remove p (i+1) point and p (i+2) point simultaneously; I reduces 2 with the position, returns above-mentioned judgement;

Wherein, σ _mBe 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 satisfy above-mentioned a) or b) arbitrary condition, do not process, i adds 1 with the position, returns above-mentioned judgement.

After the step first finished, the Cyclic Stress sequence that obtains to extract (was designated as C ₀, C ₀Be M ₀* 2 matrix, wherein M ₀The circulation sum that be to extract) and peak-to-valley value remaining, that can't extract temporarily (be designated as p _R0(i)) sequence.

Second, with p _R0(i) sequence disconnects from maximal value, then with end to end, forms new sequence, is designated as p _r(i), this sequence will can not produce the Cyclic Stress that can't extract.To p _r(i) implementation step first again), and with the Cyclic Stress of newly extracting add C to ₀The final Cyclic Stress sequence of middle formation is designated as C, and C is the matrix of M * 2, wherein the circulation sum of M for extracting.

Step second) after the end, obtain the Cyclic Stress sequence C, C has comprised the Cyclic Stress of precedence.

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

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

Ii), determine two stress amplitude threshold value h ₁And h ₂H wherein ₁It is the fatigue stress threshold value.Δ σ (i)＜h ₁The time will can not produce any fatigue effect.Δ σ (i)＞h ₂The time, belong to overload condition, at this moment might produce plasticity.Travel through all Cyclic Stress (be index with i), calculate the damage increment dD that this circulation causes _iBe divided into three kinds of situations

A) Δ σ _i＜=h ₁The time

dD _i＝0 (1)

B) h ₁＜Δ σ _i＜=h ₂The time,

${\mathrm{dD}}_i=\frac{{\left[(\mathrm{\Δ}{\mathrm{\σ}}_i+2{\mathrm{\σ}}_{m,i})\mathrm{\Δ}{\mathrm{\σ}}_i\right]}^{\frac{\mathrm{\β}+3}{2}}}{B(\mathrm{\β}+3){(1-D_i)}^{{\mathrm{\α}}_i}}---\left(2\right)$

C) Δ σ (i)＞h ₂The time, press the b of non-overload earlier) the situation estimation, be designated as

$A=\frac{{\left[(\mathrm{\Δ}{\mathrm{\σ}}_i+2{\mathrm{\σ}}_{m,i})\mathrm{\Δ}{\mathrm{\σ}}_i\right]}^{\frac{\mathrm{\β}+3}{2}}}{B(\mathrm{\β}+3){(1-D_i)}^{{\mathrm{\α}}_i}}.$

Be modified on this basis

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

Wherein i is index.D is the fatigue damage amount, thereby is an amount that changes along with the time (Cyclic Stress sequence).Identical with definition above, Δ σ, σ _mBe respectively stress amplitude and mean stress, so change with index i, need be write as σ _{M, i}With Δ σ _iForm.B and β are material constants.α is with the relevant function f (Δ σ) of stress amplitude Δ σ, thereby is also write as α with the index variation _i=f (Δ σ _i) form.

Iii), calculate the fatigue damage increase Δ D that calibrated bolck causes _Block:

${\mathrm{\ΔD}}_{\mathrm{block}}={\mathrm{\Σ}}_{i=1}^{N_{\mathrm{cycles}}}d{D}_i$

Described step 3) neutron step I i) theory origin is as follows, and according to damage mechanics theory, surpass the fatigue accumulative total (rate) that the Cyclic Stress of tired threshold causes and be,

$\frac{\mathrm{dD}}{\mathrm{dn}}=\frac{{\left[(\mathrm{\Δ\σ}+2{\mathrm{\σ}}_m)\mathrm{\Δ\σ}\right]}^{\frac{\mathrm{\β}+3}{2}}}{B(\mathrm{\β}+3){(1-D)}^{\mathrm{\α}}}$

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

Above-mentioned formula integration can be obtained step I i) in several formulas, situation b) be to regard as in circulation the D in the following formula right-hand member constant resulting, and situation c) be consider overload down damage the variation of can not ignore may be arranged, thereby D moved on to the left end integration obtain.In theory, the formula of step c) situation also can be used in the situation of non-overload.Here making differentiation is in order to average out between counting yield and accuracy.

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

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

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

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

All use above-mentioned equation model to draw α under the different stress amplitudes fatigue damage summation curve under the differently strained width of cloth Δ σ, use suitable curve match α then--Δ σ relation, general useable linear concerns to describe this relation:

α＝kΔσ+α ₀

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

Determine B, the value of β then.In theory, the period formula that lost efficacy under the cyclic loading of single shaft is

$N_f=\frac{B_1(\mathrm{\β}+3)}{\mathrm{\α}+1}\mathrm{\Δ}{\mathrm{\σ}}^{-(\mathrm{\β}+3)}$

In the formula,

Parameter alpha is definite.Parameter beta+3 and B ₁(β+3)/(α+1) can be by the Woehler curve N under the loop cycle load that produces the equal stress width of cloth _f(Δ σ) comes match to determine.

Fig. 5 has provided the S-N curve of certain stainless steel test specimen under the constant amplitude cyclic load, can obtain β+3, B by the match to this curve ₁(β+3)/(α+1).Finally can obtain B, β.

In step 4, estimate that the method for life of components is, make that initial fatigue damage is D ₀=0, the impairment value ultimate value D during simultaneously given the inefficacy _f, be unit with the calibrated bolck, constantly apply this load, the step 3) of carrying out of repetition reaches D until the fatigue damage value _f

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

Claims (7)

1. the component fatigue appraisal procedure of a non-linear accumulation is characterized in that comprising the steps:

Step 1, to the standard stress time-histories (σ of member ^Block(t)) carry out pre-service, obtain peak-to-valley value sequence (p (i));

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

Fatigue damage recruitment (the Δ D that step 3, calculating calibrated bolck cause _Block);

Step 4, calculating life of components.

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

3. the component fatigue appraisal procedure of a kind of non-linear accumulation according to claim 1, it is characterized in that: described step 3 may further comprise the 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 _i) summation, calculate fatigue damage recruitment (the Δ D that calibrated bolck causes _Block).

4. the component fatigue appraisal procedure of a kind of non-linear accumulation according to claim 3 is characterized in that: in described step I i, divide three kinds of situations to calculate damage increment (dD _i):

A) Δ σ _i＜=h ₁The time

dD _i＝0 (1)

B) h ₁＜Δ σ _i＜=h ₂The time,

C) Δ σ (i)＞h ₂The time, press the b of non-overload earlier) the situation estimation, be designated as

And be modified on this basis

Wherein i is index, and D is the fatigue damage amount, is an amount that changes along with the time, Δ σ, σ _mBe respectively stress amplitude and mean stress, change with index i, need be write as Δ σ _iAnd σ _{M, i}Form, B and β are material constants, α is with the relevant function f (Δ σ) of stress amplitude Δ σ, changes with index i and is write as α _i=f (Δ σ _i) form, stress amplitude threshold value h ₁Be the fatigue stress threshold value, Δ σ (i)＜h ₁The time, will can not produce any fatigue effect, h ₂Be the judgement threshold of overload, Δ σ (i)＞h ₂The time, belong to overload condition.

5. the component fatigue appraisal procedure of a kind of non-linear accumulation according to claim 1, it is characterized in that: described step 4 may further comprise the steps: make that initial fatigue damage is zero (D ₀=0), the damage limit value (D during given inefficacy the simultaneously _f), be unit with the calibrated bolck, constantly apply this load, the step 3 of carrying out of repetition reaches damage limit value (D until the fatigue damage value _f).

6. the component fatigue appraisal procedure of a kind of non-linear accumulation according to claim 1 and 2 is characterized in that: in step 2, described rain-flow counting adopts 4 diagnostic methods, and is 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, is got four adjacent peak valley points and is judged 4 diagnostic methods; Obtain the Cyclic Stress sequence (C of extraction ₀), C ₀Be M ₀* 2 matrix, wherein M ₀Be the circulation peak-to-valley value (p total and remaining, that can't extract temporarily that extracts _R0(i)) sequence;

Ii, with peak-to-valley value (p _R0(i)) sequence disconnects from maximal value, then with end to end, forms new sequence, is designated as p _r(i), this sequence will can not produce the Cyclic Stress that can't extract; To p _r(i) implementation step first again), and with the Cyclic Stress of newly extracting add Cyclic Stress sequence (C to ₀) the final Cyclic Stress sequence (C) of middle formation, C is the matrix of M * 2, wherein the circulation sum of M for extracting; Obtain Cyclic Stress sequence (C), C has comprised the Cyclic Stress of precedence.

7. the component fatigue appraisal procedure of a kind of non-linear accumulation according to claim 1 is characterized in that: in described step 1, travel through standard stress time-histories (σ ^Block(t)) all the data (σ in ^Block(i)), judge the positive negativity of [σ (i)-σ (i-1)] * [σ (i)-σ (i+1)]: if positive number then is labeled as peak value or valley with stress (σ (i)), take out and put into successively peak-to-valley value data (p (i)); If negative is then skipped.

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