阅读说明：本技术 一种飞机长桁与蒙皮连接细节疲劳额定值的确定方法 (Method for determining fatigue rating of aircraft stringer and skin connection detail ) 是由 史志俊 王亚芳 纪露明 张联营 于 2020-12-29 设计创作，主要内容包括：本发明属于飞机疲劳计算技术领域,公开了一种飞机长桁与蒙皮连接细节疲劳额定值的确定方法。虑了受剪情况下长桁与蒙皮连接紧固件的排数对疲劳性能的影响,并结合上下蒙皮剪流差计算挤压应力与远端应力比,计算DFR值更准确。(The invention belongs to the technical field of airplane fatigue calculation, and discloses a method for determining a fatigue rating value of connection details of an airplane stringer and a skin. The influence of the row number of the stringer and skin connecting fasteners on the fatigue performance under the shearing condition is considered, the ratio of the extrusion stress to the far-end stress is calculated by combining the shear flow difference of the upper skin and the lower skin, and the DFR value is calculated more accurately.)

1. A method for determining fatigue ratings for details of an aircraft stringer to skin connection, the method comprising:

s1, determining the joint of the stringer and the skin to be calculated, constructing an air-ground circulation, and calculating the combined stress sigma of the joint of the stringer and the skin under different working conditions in the air-ground circulation process₁₂Stringer stress σ, stress σ of the first skin₁Stress σ of the second skin₂Shear stress τ of the first skin₁Shear stress τ of the second skin₂(ii) a The first skin is the skin on the upper part of the stringer, and the second skin is the skin on the lower part of the stringer;

s2, determining the maximum value sigma of the combined stress under different working conditions in the process of the ground-air ground circulation_12maxMaximum value of stringer stress σ_maxMaximum stress σ of the first skin_1maxMaximum stress σ of the second skin_2maxMaximum shear stress τ of the first skin_1maxMaximum shear stress τ of the second skin_2max；

If the maximum shear stress tau of the first skin_1maxOr the maximum shear stress τ of the second skin_2maxMaximum, go to S3;

if maximum value of stringer stress σ_maxMaximum value of combined stress σ_12maxMaximum stress sigma of the first skin_1maxOr maximum stress σ of the second skin_2maxMaximum, go to S4;

s3, if the maximum shearing stress tau of the first skin_1maxIf the stress is large, the stress of the first skin is taken as a reference stress; if the maximum shear stress tau of the second skin_2maxIf the stress is large, the stress of the second skin is taken as a reference stress; calculating a structural detail fatigue rating DFR from the reference stress;

s4, if the maximum value sigma of the combined stress_12maxLarge, with the combined stress as the reference stress; if maximum value of stringer stress σ_maxLarge, with stringer stress as the reference stress; if the maximum stress σ of the first skin_1maxLarge, taking the stress of the first skin as a reference stress; if the maximum stress σ of the second skin_2maxLarge, taking the stress of the second skin as a reference stress; and calculating a structural detail fatigue rating DFR according to the reference stress.

2. The method of claim 1, wherein, in S1,

the combination of the stresses is such that,

stringer stress:

stress σ of the first skin₁Stress σ of the second skin₂：

Shear stress τ of first skin₁Shear stress τ of the second skin₂：

Wherein, F_NRepresenting stringer axial force, F_yi，F_y2Representing load of the skin in the stringer direction, F_xy1，F_xy2Representing skin shear load, Ast representing stringer area, b₁Denotes the width of the first skin, b₂Denotes the width, t, of the second skin₁Denotes the thickness of the first skin, t₂The thickness of the second skin is indicated.

3. The method for determining the fatigue rating of the aircraft stringer-skin connection details as claimed in claim 1, wherein in S3, the fatigue rating of the structural details DFR is calculated from the reference stress, specifically:

obtaining the critical shear stress tau_cr(ii) a Subjecting the skin to maximum shear stress tau_maxAnd critical shear stress τ_crComparing, judging whether the skin enters a buckling state or not, and judging the maximum shearing stress tau of the skin_maxIs the maximum shear stress tau of the first skin_1maxAnd maximum shear stress τ of the second skin_2maxA larger value of;

(1) if tau_max≥τ_crAnd then the skin enters a buckling state, and the structural detail fatigue rated value DFR is calculated according to the following formula:

DFR_S＝DFR_Sbase×K×U×R₀

DFR_Sbase＝100/(0.9+0.23τ_max/τ_cr)

subjecting DFR to_sDFR as a structural detail fatigue rating;

wherein, K represents a material constant,u represents the Boss coefficient, R_cRepresenting a component fatigue rating coefficient;

(2) if tau_max＜τ_crAnd if the skin does not enter the buckling state, calculating the structural detail fatigue rated value DFR according to the following formula:

DFR_S＝DFR_Sbase×A×B×C×D×E×U×R_c

DFR_Sbase＝121×M×ψ

subjecting DFR to_sDFR as a structural detail fatigue rating;

a, B, C, D, E are correction coefficients, M is a material constant, and ψ is a load transfer coefficient.

4. A method of determining fatigue ratings for details of aircraft stringer to skin connections according to claim 3,

for a riveted joint:

for a threaded joint:

wherein, tau_maxThe ground-to-ground maximum stress of the shear stress is expressed, d represents the fastener diameter, and n represents the fastener row number.

5. The method of claim 4 for determining fatigue rating for details of aircraft stringer to skin attachment,

for a single row bolt/rivet connection:

for multiple rows of bolt/rivet connections:

wherein (q)₁-q₂) Denotes τ_maxGround-to-air ground stress, τ, of shear difference corresponding to operating conditions_maxThe ground-to-ground maximum stress of the shear stress is represented, S represents the fastener pitch, d represents the fastener diameter, and n represents the fastener row number.

6. The method for determining the fatigue rating of the aircraft stringer-skin connection details as claimed in claim 1, wherein in S4, the fatigue rating of the structural details DFR is calculated from the reference stress, specifically: DFR ═ DFR_base×A×B×C×D×E×U×R_c。

7. The method of claim 6 for determining fatigue rating for details of aircraft stringer to skin attachment,

if the fastener is a single-row fastener:

for aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

wherein A, B, C, D, E, U are correction coefficients, K_tgRepresenting the structural stress concentration factor.

8. The method of claim 6 for determining fatigue rating for details of aircraft stringer to skin attachment,

if the fastener is a plurality of rows:

for aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

wherein A, B, C, D, E, U are correction coefficients, K_tgRepresenting the structural stress concentration factor.

Technical Field

The invention belongs to the technical field of airplane fatigue calculation, and particularly relates to a method for determining a fatigue rating value of connection details of an airplane stringer and a skin.

Background

At present, when the connection fatigue life of the fuselage stringer and the skin of the transport aircraft is calculated, a DFR method is generally adopted for calculation. In general, the stringers and the skin are considered to be subjected to equal course load, and a structural mode without load transmission fasteners is adopted during structural DFR calculation, and the structural shearing condition is not considered.

However, under some special working conditions, the skin is subjected to large shear stress and may enter a buckling state, the DFR value is calculated according to a structure mode of a non-load-transmission fastener, complete consideration is obviously not taken into consideration, and the calculation result is also in danger.

Meanwhile, when the shearing of the skin is calculated, the influence of the row number of the connecting fasteners on the nail transmission load is not considered, so that a certain deviation exists in the calculation result.

Disclosure of Invention

The invention aims to provide a method for determining a fatigue rating of connection details of a stringer and a skin of an airplane, which systematically considers the loading condition of a structure and considers whether the sheared skin enters the buckling condition or not, and can calculate the DFR value of the structure more accurately.

In order to achieve the purpose, the invention is realized by adopting the following technical scheme.

A method of determining aircraft stringer to skin connection detail fatigue ratings, the method comprising:

s1, determining the joint of the stringer and the skin to be calculated, constructing an air-ground circulation, and calculating the combined stress sigma of the joint of the stringer and the skin under different working conditions in the air-ground circulation process₁₂Stringer stress σ, stress σ of the first skin₁Stress v of the second skin₂Shear stress τ of the first skin₁Shear stress τ of the second skin₂(ii) a The first skin is the skin on the upper part of the stringer, and the second skin is the skin on the lower part of the stringer;

s2, determining the maximum value sigma of the combined stress under different working conditions in the process of the ground-air ground circulation_12maxMaximum value of stringer stress σ_maxMaximum stress σ of the first skin_1maxMaximum stress σ of the second skin_2maxMaximum shear stress τ of the first skin_1maxMaximum shear stress τ of the second skin_2max；

If the maximum shear stress tau of the first skin_1maxOr the maximum shear stress τ of the second skin_2maxMaximum, go to S3;

if maximum value of stringer stress σ_maxMaximum value of combined stress σ_12maxMaximum stress sigma of the first skin_1maxOr maximum stress σ of the second skin_2maxMaximum, go to S4;

s3, if the maximum shearing stress tau of the first skin_1maxIf the stress is large, the stress of the first skin is taken as a reference stress; if the maximum shear stress tau of the second skin_2maxIf the stress is large, the stress of the second skin is taken as a reference stress; calculating a structural detail fatigue rating DFR from the reference stress;

s4, if the maximum value of the combined stress is upsilon_12maxLarge, with the combined stress as the reference stress; if maximum value of stringer stress σ_maxLarge, with stringer stress as the reference stress; if the maximum stress σ of the first skin_1maxLarge, taking the stress of the first skin as a reference stress; if the maximum stress σ of the second skin_2maxLarge, taking the stress of the second skin as a reference stress; and calculating a structural detail fatigue rating DFR according to the reference stress.

The technical scheme of the invention has the characteristics and further improvements that:

1) in the step S1, the first step,

combined stress

Stringer stress:

stress σ of the first skin₁Stress σ of the second skin₂：

Shear stress τ of first skin₁Shear stress τ of the second skin₂：

Wherein, F_NRepresenting stringer axial force, F_yi，F_y2Representing load of the skin in the stringer direction, F_xy1，F_xy2Representing skin shear load, Ast representing stringer area, b₁Denotes the width of the first skin, b₂Is shown asWidth of two skins, t₁Denotes the thickness of the first skin, t₂The thickness of the second skin is indicated.

2) In S3, calculating a structural detail fatigue rating DFR according to the reference stress, specifically:

obtaining the critical shear stress tau_crSetting the maximum shear stress tau of the skin_maxAnd critical shear stress τ_crComparing, judging whether the skin enters a buckling state or not, and judging the maximum shearing stress tau of the skin_maxIs the maximum shear stress tau of the first skin_1maxAnd maximum shear stress τ of the second skin_2maxA larger value of;

(1) if tau_max≥τ_crAnd then the skin enters a buckling state, and the structural detail fatigue rated value DFR is calculated according to the following formula:

DFR_S＝DFR_Sbase×K×U×R₀

DFR_{S base}＝100/(0.9+0.23τ_max/τ_cr)

subjecting DFR to_sDFR as a structural detail fatigue rating;

wherein K represents a material constant, U represents a boss coefficient, and R_cRepresenting a component fatigue rating coefficient;

(2) if tau_max＜τ_crAnd if the skin does not enter the buckling state, calculating the structural detail fatigue rated value DFR according to the following formula:

DFR_S＝DFR_Sbase×A×B×C×D×E×U×R_c

DFR_{S bae}＝121×M×ψ

subjecting DFR to_sDFR as a structural detail fatigue rating;

a, B, C, D, E are correction coefficients, M is a material constant, and ψ is a load transfer coefficient.

3)

For the

For the

Wherein, tau_maxThe ground-to-ground maximum stress of the shear stress is expressed, d represents the fastener diameter, and n represents the fastener row number.

4) For a single row bolt/rivet connection:

for multiple rows of bolt/rivet connections:

wherein (q)₁-q₂) Denotes τ_maxGround-to-air ground stress, τ, of shear difference corresponding to operating conditions_maxThe ground-to-ground maximum stress of the shear stress is represented, S represents the fastener pitch, d represents the fastener diameter, and n represents the fastener row number.

5) In S4, calculating a structural detail fatigue rating DFR according to the reference stress, specifically: DFR ═ DFR_bace×A×B×C×D×E×U×R_q。

6) If the fastener is a single-row fastener:

for aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

wherein A, B, C, D, E, U are correction coefficients, K_tgRepresenting the structural stress concentration factor.

7) If the fastener is a plurality of rows:

for aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

wherein A, B, C, D, E, U are correction coefficients, K_tgRepresenting the structural stress concentration factor.

The method for determining the detail fatigue rating of the connection structure of the stringer and the skin of the class-delivery aircraft systematically considers the loading condition of the structure and the buckling condition of the sheared skin, and can calculate the DFR value of the structure more accurately.

Drawings

FIG. 1 is a schematic flow chart of a method for determining fatigue rating of aircraft stringer-skin connection details according to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of a stringer-skin connection provided in accordance with an embodiment of the present invention;

FIG. 3 is a schematic view of a finite element model of a stringer and skin connection structure according to an embodiment of the present invention.

Detailed Description

The invention provides a method for determining a fatigue rating of connection details of a stringer and a skin of an aircraft, which mainly comprises the following steps:

1. judging the loading form of the skin by adopting the maximum stress of the ground, thereby providing a calculation mode of the fatigue rating of the structural details;

2. whether the sheared skin enters the buckling condition or not is considered in the calculation process, and different calculation methods are given;

3. under the shearing condition, the row number of the stringer and skin connecting fasteners is considered, the ratio of the extrusion stress to the far-end stress is calculated by combining the shear flow difference of the upper skin and the lower skin, and the DFR value is further calculated.

In particular, as shown in figure 1,

step one, determining a stringer and skin connecting part to be calculated, constructing an air-ground circulation, and calculating combined stress sigma under different working conditions in the air-ground circulation process₁₂Stringer stress σ; stress σ of skin 1₁Stress σ of the skin 2₂Shear stress tau of the skin 1₁Shear stress tau of the skin 2₂(ii) a Wherein, skin 1 is the skin on the upper portion of the stringer, and skin 2 is the skin on the lower portion of the stringer.

The combined stress calculation formula is as follows:

combined stress

Stringer stress:

skin 1, 2 stress:

shear stress of skins 1, 2:

in the formula:

F_Ngirder axial force

F_y1，F_y2-load of skin in stringer direction

F_xy1，F_xy2Skin shear load

Ast-stringer area

b₁，b₂Width of skin 1, 2

t₁，t₂Skin 1, 2 thickness

Step two, comparisonMaximum value sigma of combined stress under the same working condition_12maxMaximum value of stringer stress σ_maxMaximum stress σ of the skin 1_1maxMaximum stress σ of the skin 2_2maxMaximum shear stress tau of the skin 1_1maxMaximum shear stress tau of the skin 2_2max。

If tau_1maxOr τ_2maxMaximum, calculate according to step three;

if σ_max、σ_12max、σ_1maxOr σ_2maxAnd if the maximum value is obtained, calculating according to the step four.

Step three, if tau_1maxIf the stress is large, the stress of the skin 1 is taken as a reference stress; if tau_2maxAnd if the stress is large, the stress of the skin 2 is taken as a reference stress.

Obtaining the critical shear stress tau_crSetting the maximum shear stress tau of the skin_maxAnd critical shear stress τ_crAnd comparing to judge whether the skin enters a buckling state.

(1) If tau_max≥τ_crThe skin then enters buckling, at which time the structural detail fatigue rating, DFR, may be calculated as follows:

DPR_S＝DFR_{S base}×K×U×R_c

DFR_{S base}＝100/(0.9+0.23τ_max/τ_cr)

subjecting DFR to_SAs a structural detail fatigue rating DFR, where:

k-material constant

Coefficient of U-convex

Rc-component fatigue rating coefficient

(2) If tau_max＜τ_crAnd the skin does not enter buckling, and then the structural detail fatigue rating DFR is calculated according to the single shear of the web and the edge strip:

DFR_S＝DFR_{S base}×A×B×C×D×E×U×R_c

DFR_{S base}＝121×M×ψ

subjecting DFR to_SAs a structural detail fatigue rating DFR, where: a, B, C, D, E-correction systemNumber of

M-material constant

Psi-load transfer coefficient, when psi > 1, taking psi-1

Riveting a joint:

the screw joint:

for a single row bolt/rivet connection:

for multiple rows (2 rows and above) of bolt/rivet connections:

in the formula:

(q₁-q₂)——τ_maxground-to-air ground stress of shear flow difference corresponding to working condition

τ_maxGround-to-air maximum stress of shear stress

S-fastener spacing

d-fastener diameter

n-number of fastener rows

Step four, if sigma_12maXLarge, with the combined stress as the reference stress; if σ_maxLarge, with stringer stress as the reference stress; if σ_1maxLarge, taking the stress of the skin 1 as a reference stress; if σ_2maxLarge, with the skin 2 stress as the reference stress.

At this point, the structural DFR may be calculated according to the non-load fastener structural details:

DFR＝DFR_base×A×B×C×D×E×U×R_c

(1) if it is a single-row fastener

For aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

(2) if it is a multi-row fastener

For aluminum alloy structures:

for the titanium alloy structure:

for medium strength steel structures:

in the formula: a, B, C, D, E, U-correction factor

K_tg-structural stress concentration factor.

The first embodiment is as follows:

step one, selecting a connection part of a stringer and a skin at a certain position of a certain airplane as a calculation object. The skin material is 2024-T3, and the thickness is 1.5 mm; the stringer is made of 7050-T7451 materials, the thickness of the edge strip is 1.5mm, the stringer and the edge strip are connected by a single row of rivets with the diameter of 5, and the connection section is shown in figure 2.

In the finite element model of the whole machine, as shown in fig. 3, the load corresponding to the part is found out, and the combined stress σ is calculated₁₂Stringer stress σ, stress σ of skin 1₁Stress σ of the skin 2₂Shear stress tau of the skin 1₁Shear stress tau of the skin 2₂. The combined stress calculation formula is as follows:

combined stress:

stringer stress:

skin 1, 2 stress:

shear stress of skins 1, 2:

and step two, finding out the maximum value corresponding to each stress. Maximum value of combined stress σ_12maxMaximum stringer stress σ of 56.3MPa_maxMaximum stress σ of skin 1 at 60.8MPa_1maxMaximum stress σ of skin 2 of 51.6MPa_2maxMaximum shear stress τ of skin 1 at 53.7MPa_1mcxMaximum shear stress τ of skin 2 at 70.4MPa_2max71.6 Mpa. The maximum shear stress of the skin 2 is the maximum stress. DFR calculation was performed according to step three.

And step three, taking the stress of the skin 2 as a reference stress. And judging whether the skin enters a buckling state or not. Critical shear stress tau_cr＝80.78MPa，τ_2max＜τ_orAnd when the bending state is not entered, performing DFR calculation according to single shearing of the web plate and the edge strip.

DFR_S＝DFR_Sbase×A×B×C×D×E×U×R_c

DPR_8base＝121×M×ψ

Riveting a joint:

for a single row bolt/rivet connection:

calculating to obtain: psi 0.554

Aluminum alloy: m is 1

The various coefficients are found according to the relevant standards as follows: a is 0.95, B is 1.0, C is 1.0, D is 1.0, E is 1.0, U is 1.0.Rc is 1.0

The DFR value calculated for this structure is: DFR_S＝63,64MPa。

The method for determining the detail fatigue rating of the connection structure of the stringer and the skin of the class-delivery aircraft systematically considers the loading condition of the structure and also considers whether the sheared skin enters the buckling condition, so that the DFR value of the structure can be calculated more accurately; the method for calculating the detail fatigue rating of the stringer and skin connecting structure of the class-delivery aircraft considers the influence of the row number of connecting fasteners of the stringer and the skin under the shearing condition on the fatigue performance, calculates the ratio of the extrusion stress to the far-end stress by combining the shear flow difference of the upper skin and the lower skin, and calculates the DFR value more accurately. The method for calculating the detail fatigue rating of the connection structure of the stringer and the skin of the class-delivery aircraft has clear theoretical basis and simple and convenient steps, and is convenient for computer programming to realize automatic calculation.