CN105260574A - Critical plane method fatigue failure criterion-based high-cycle multi-axial fatigue life prediction method - Google Patents

Abstract

The invention provides a critical plane method fatigue failure criterion-based high-cycle multi-axial fatigue life prediction method, relating to the field of fatigue strength. The method comprises the steps of (1) constructing a high-cycle multi-axial fatigue criterion; (2) by substituting two conditions of uniaxial loading and pulsation cycle loading, deducing parameters in a formula; (3) reading high-cycle multi-axial constant-amplitude loading test data, and determining the position of a critical plane; (4) by calculated shearing strength amplitude, normal stress amplitude and mean normal stress on the critical plane, calculating equivalent stress amplitude by using an equation; (5) calculating high-cycle fatigue life under multi-axial constant-amplitude load by using a stress-life curve. After the method is used for estimating the high-cycle fatigue life under multi-axial constant-amplitude load, a better prediction effect is achieved.

Description

A kind of all Multiaxial Fatigue Life Prediction methods of height based on critical surface method Fatigue criteria

Technical field

The present invention relates to metal non-proportional loading strength fields, refer in particular to the high-cycle fatigue life method under multiaxis constant amplitude loading.

Background technology

The Fatigue Failures of machinery is the one of the main reasons causing in commission mechanical component and component failure.Such as in fields such as aircraft, boats and ships, engineering machinery, mechanical component and component often bear the effect of complicated alternate load for a long time, finally because fatigue failure causes accident to account for more than 80 percent of total failare factor.Have fairly perfect theory in single shaft fatigue field at present and have accumulated mass data and experience, but actual in commission each major mechanical parts bear complicated Multiaxial Proportional and the effect of nonproportional cycle loading usually.Due to the variation of multi-axis stress state, direction of crack propagation, the complicacy of load history, so traditional single shaft fatigue strength theory has been not suitable with present designing requirement, instead non-proportional loading strength theory, especially high all Multiaxial Fatigue Life Prediction methods become the important method solving component of machine Problem of Failure in actual military service.Traditional height week Multiaxial Fatigue Life Prediction often ignores the impact of mean stress, therefore considers that the height week Multiaxial Fatigue Life Prediction method of mean stress impact is worth research.

Summary of the invention

The object of the invention is the requirement for non-proportional loading Intensity Design, proposes a kind of height based on critical surface method Fatigue criteria week Multiaxial Fatigue Life Prediction method.

The all Multiaxial Fatigue Life Prediction methods of a kind of height based on critical surface method Fatigue criteria provided by the present invention, the steps include:

Step 1): thin walled tube test specimen is drawn-is turned round disproportional Sine-wave loading, with face, maximum shear place for critical surface, utilizes the fatigue damage parameter on this face: shear stress width C _a, normal stress width N _a, mean normal stress N _mconstructing a nonlinear combination form is height week non-proportional loading criterion.

Step 2): solve the α in formula, β, λ.By substituting into two kinds of uniaxial loading situations, be respectively uniaxial tension fatigue limit f _-1load and purely turn round fatigue limit t _-1load, release λ=t _-1.Load situation by pulsating cyclic again, utilize the correction of Goodman equation to obtain σ in formula _ufor uniaxial tension strength degree.To sum up release a kind of based on the high all non-proportional loading failure criteria of critical surface method:

$\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}\≤t_{-1}$

Step 3): read high all multiaxis Identical loading test figures.Often organize in test figure to comprise and load normal stress width σ _a, shear stress width τ _a, mean normal stress σ _m, average shearing stress τ _m, phase differential δ.

Step 4): determine critical surface position.In order to consider load average shearing stress on the impact of fatigue damage, think that crackle is at maximum shear place plane initiation and propogation, namely with face, maximum shear place for critical surface.

Step 5): by the shear stress width C on the critical surface that calculates _a, normal stress width N _awith mean normal stress N _m, utilize formulae discovery to go out equivalent stress width:

${\mathrm{\τ}}_{eq}=\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}$

Step 6): utilize equivalent stress width τ _eqbe the S-N curve of-1 with stress ratio, calculate the high-Cycle Fatigue Life Prediction under multiaxis constant amplitude loading.

Described step 1) and step 2) construct containing three Damage Parameters (shear stress width C _a, normal stress width N _a, mean normal stress N _m) nonlinear combination form be height week non-proportional loading criterion, the method, by this Damage Parameter of common maximum （normal） stress is decomposed into normal stress width and mean normal stress, considers the Different Effects to fatigue damage generation respectively.

Compared with prior art, the present invention has following beneficial effect:

The present invention proposes a kind of height based on critical surface method Fatigue criteria week Multiaxial Fatigue Life Prediction method.The method is by being decomposed into normal stress width and mean normal stress by this Damage Parameter of common maximum （normal） stress, consider the Different Effects that they produce for fatigue damage respectively, construct the Fatigue criteria of a tri-consult volume, and the determination of critical surface considers the impact of average shearing stress.Applied widely, and based on critical surface law theory, explicit physical meaning, the material constant related to is less, is convenient to engineer applied.By verification experimental verification, the high-Cycle Fatigue Life Prediction estimation that employing the method is carried out under multiaxis constant amplitude loading obtains good prediction effect.

Accompanying drawing explanation

The process flow diagram of all Multiaxial Fatigue Life Prediction methods of the height based on critical surface method Fatigue criteria that Fig. 1 provides for the inventive method.

Embodiment

With verification experimental verification, the specific embodiment of the present invention is described by reference to the accompanying drawings.

High-cycle fatigue life under the multiaxis constant amplitude loading that the present invention will carry out, make use of a kind of Fatigue criteria based on critical surface method and forecast model, and by its fiduciary level of verification experimental verification and accuracy.

Step 1): thin walled tube test specimen is drawn-is turned round disproportional Sine-wave loading, under utilizing the oblique section formula in the mechanics of materials can calculate given loading environment, determine on critical surface each stress value, as shear stress width C _a, normal stress width N _a, mean normal stress N _m.

Step 2): with face, maximum shear place for critical surface, utilize the fatigue damage parameter on this face: shear stress width C _a, normal stress width N _a, mean normal stress N _mconstructing a nonlinear combination form is $\sqrt{C_a^2+{\mathrm{\αN}}_a^2+{\mathrm{\βN}}_m^2}\≤\mathrm{\λ}$ Height week non-proportional loading criterion.

Step 3): solve the α in formula, β, λ.By substituting into two kinds of uniaxial loading situations, be respectively uniaxial tension fatigue limit f _-1load and purely turn round fatigue limit t _-1load, release λ=t _-1.Load situation by pulsating cyclic again, utilize the correction of Goodman equation to obtain σ in formula _ufor uniaxial tension strength degree.To sum up release a kind of height based on critical surface method week non-proportional loading failure criteria:

$\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}\≤t_{-1}$

Step 4): the fatigue data reading three groups of materials: 7075-T651 aluminium alloy, 30CrMnSiA steel, LY12CZ aluminium alloy.Utilize Papadopoulos formula, determine maximum shear C _maxplace plane, i.e. critical surface position, and calculate the shear stress width C on this critical surface _a, normal stress width N _awith mean normal stress N _m.

Step 5): by the shear stress width C on the critical surface that calculates _a, normal stress width N _awith mean normal stress N _m, utilize formulae discovery to go out equivalent stress width:

${\mathrm{\τ}}_{eq}=\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}$

Step 6): utilize equivalent stress width τ _eqbe the S-N curve of-1 with stress ratio, calculate the high-Cycle Fatigue Life Prediction under multiaxis constant amplitude loading.The expression formula of the S-N curve of such as 7075-T651 aluminium alloy is τ _a=719.08 (N _f) ^-0.1194, N in formula _ffor fatigue lifetime.Multi-axis stress state is converted into uniaxial stress state, τ _eq=719.08 (N _f) ^-0.1194, can fatigue lifetime be calculated.

In order to verify that the present invention proposes a kind of week of the height based on critical surface method Fatigue criteria Multiaxial Fatigue Life Prediction method effect, predicting the outcome of this method gained is compared with the test life of multiaxial experiment gained, result shows, based on the critical surface method Fatigue criteria proposed, the Multiaxial Proportional drawn by computing method of the present invention, disproportional fatigue life prediction value are compared with test actual life, and its error factor is most within 3 times.The method, based on critical surface method, considers normal stress width and mean normal stress respectively to the Different Effects of all Multiaxial Fatigue Damages of height.The high-Cycle Fatigue Life Prediction estimation that the method proposed is carried out under multiaxis constant amplitude loading obtains good prediction effect.

Claims (2)

1., based on a height week Multiaxial Fatigue Life Prediction method for critical surface method Fatigue criteria, it is characterized in that: step is as follows,

Step 1): thin walled tube test specimen is drawn-is turned round disproportional Sine-wave loading, with face, maximum shear place for critical surface, utilizes the fatigue damage parameter on this face: shear stress width C _a, normal stress width N _a, mean normal stress N _mconstructing a nonlinear combination form is $\sqrt{C_a^2+{\mathrm{\αN}}_a^2+{\mathrm{\βN}}_m^2}\≤\mathrm{\λ}$ Height week non-proportional loading criterion;

Step 2): solve the α in formula, β, λ; By substituting into two kinds of uniaxial loading situations, be respectively uniaxial tension fatigue limit f _-1load and purely turn round fatigue limit t _-1load, release load situation by pulsating cyclic again, utilize the correction of Goodman equation to obtain σ in formula _ufor uniaxial tension strength degree; To sum up release a kind of based on the high all non-proportional loading failure criteria of critical surface method:

$\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}\≤t_{-1}$

Step 3): read high all multiaxis Identical loading test figures; Often organize in test figure to comprise and load normal stress width σ _a, shear stress width τ _a, mean normal stress σ _m, average shearing stress τ _m, phase differential δ;

Step 4): determine critical surface position; Quote Wang Cong method, think that crackle is at maximum shear place plane initiation and propogation, namely with face, maximum shear place for critical surface, consider the impact of average shearing stress on fatigue damage;

Step 5): by the shear stress width C on the critical surface that calculates _a, normal stress width N _awith mean normal stress N _m, utilize formulae discovery to go out equivalent stress width:

${\mathrm{\τ}}_{eq}=\sqrt{C_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+\[4{\left(\frac{t_{-1}}{f_{-1}}\right)}^2-1\]N_a^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)+4t_{-1}^2(\frac{1}{{\mathrm{\σ}}_u^2}+\frac{2}{f_{-1}{\mathrm{\σ}}_u})N_m^2({\mathrm{\θ}}_c,{\mathrm{\φ}}_c)}$

Step 6): utilize equivalent stress width τ _eqbe the S-N curve of-1 with stress ratio,

Calculate the high-Cycle Fatigue Life Prediction under multiaxis constant amplitude loading.

2. all Multiaxial Fatigue Life Prediction methods of a kind of height based on critical surface method Fatigue criteria according to claim 1, is characterized in that: described step 1) and step 2) construct containing three Damage Parameters (shear stress width C _a, normal stress width N _a, mean normal stress N _m) nonlinear combination form be height week non-proportional loading criterion, the method, by this Damage Parameter of common maximum （normal） stress is decomposed into normal stress width and mean normal stress, considers the Different Effects to fatigue damage generation respectively.