Reliability evaluation method for 3D printing nylon wing

Abstract

According to the reliability evaluation method for the 3D printing nylon wing, the technical problems that experimental research is difficult and the result of a material model is inaccurate in the 3D printing nylon wing are solved, a research method combining tests and finite elements is used, the constructed material model is more accurate, the finite elements are verified, and the reliability of the 3D printing nylon wing is improved. By using the finite element, reliability evaluation is more convenient and lower in cost, meanwhile, the evaluation method disclosed by the invention is adopted to perform reliability analysis on the wing structure subjected to 3D printing, and the probability that the wing structure can complete a predetermined function is judged.

Description

Technical Field

[0001] The invention belongs to the field of 3D printing material structure reliability analysis, and specifically relates to a 3D printing nylon wing reliability assessment method. Background Art

[0002] With the continuous development of 3D printing technology, its application is becoming more and more extensive, especially in drones. Since the product is built layer by layer, this will lead to anisotropic behavior of the material, thus affecting the product quality. Therefore, it is necessary to study the mechanical properties and reliability analysis of 3D printing materials. Summary of the invention

[0003] The purpose of the present invention is to propose a reliability assessment method for 3D printed nylon wings based on the fact that the layer-by-layer construction of 3D printed wings leads to the anisotropic behavior of materials, thus resulting in unqualified product quality. The finite element method is used to study the material properties of 3D printing, and the reliability analysis of the 3D printed wing structure is performed to evaluate whether it can complete the predetermined function.

[0004] To achieve the above object, the present invention provides the following technical solution: a reliability assessment method for 3D printed nylon wings, comprising the following steps:

[0005] S1, specimens for tensile and shear tests were printed by 3D printing technology;

[0006] S2, performing tensile and shear tests on the sample, obtaining corresponding material parameters, and analyzing its failure mode;

[0007] S3, establishing a material model according to the material parameters and failure modes described in S2;

[0008] S4, using the material model described in S3 to perform finite element simulation on the sample of the tensile test, comparing the result of the finite element simulation with the result of the tensile test in S1, and judging the deviation between the two. If the deviation is greater than 10%, continue to adjust the finite element; if the deviation is less than 10%, proceed to the next step;

[0009] S5, using the same 3D printing technology and materials as the S1 to print the wings;

[0010] S6, analyzing and calculating the load on the wing, applying the load on the wing, and attaching a strain gauge on the wing to collect the strain, and repeating the test multiple times to avoid accidental data;

[0011] S7, establishing a finite element model of the wing, applying the material model described in S3 as a material input for simulation, performing finite element simulation on the wing, comparing the simulation result of the wing with the strain result collected by the wing test, and determining the deviation between the two. If the deviation is greater than 10%, continue to adjust the finite element simulation model of the wing; if the deviation is less than 10%, proceed to the next step;

[0012] S8, descriptive statistics and test distribution of material parameters obtained from tensile and shear tests;

[0013] S9, Latin hypercube sampling method is used to sample from the probability distribution of each probability variable;

[0014] S10, inputting each group of sampling data into the finite element model of the wing to calculate the stress on the wing and check the distribution;

[0015] S11, use the stress-strength interference model to solve the reliability of the wing structure, calculate the reliability index of the wing structure, and perform reliability analysis.

[0016] Preferably, in S1, the 3D printing technology is selective laser sintering technology, and the printing material used is nylon 12.

[0017] Preferably, in S2, the tensile and shear tests are carried out according to ISO 527 and GB / T28889-2012 standards, respectively.

[0018] Preferably, in S3, the established material model, namely the material constitutive model, includes an elastic-plastic relationship and a damage model.

[0019] Preferably, in S4, the deviation between the finite element simulation result and the tensile test result is the stress deviation corresponding to the same strain of the two.

[0020] Preferably, in S6, the lift force of the wing in actual flight is calculated using the lift formula, and a sandbag is used as a load to be applied to the printed wing, and the gravity of the sandbag is equal to the calculated lift force. A number of strain gauges are attached, and the strain gauges are connected to a static strain tester, and the instrument is connected to a computer, and a dynamic signal acquisition and analysis system matched with the tester is used to read and collect strain.

[0021] Preferably, in S7, the deviation between the simulation result of the wing and the strain result collected through the wing test is the deviation between the average value of each collection point of the wing test under several tests and the simulation result corresponding to the position of each collection point, and each collection point has a corresponding deviation.

[0022] Preferably, in S8, descriptive statistics and test distribution are performed on the elastic modulus and shear modulus of the two printed samples in two directions under tensile and shear tests.

[0023] Preferably, in S11 , the strength of the horizontally printed tensile specimen is used as the strength R, and the stress in S10 is used as the stress S.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. A reliability assessment method for 3D printed nylon wings disclosed in the present invention solves the technical problems of experimental research difficulties and inaccurate material model results of 3D printed nylon wings. The present invention uses a research method combining experiments and finite elements to make the constructed material model more accurate and verify the finite elements. The use of finite elements makes reliability assessment more convenient and less costly.

[0026] 2. The present invention discloses a reliability assessment method for a 3D printed nylon wing, which performs a reliability analysis on the 3D printed wing structure and determines the probability that the wing structure can complete the predetermined function. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is an overall flow chart of the reliability assessment method of 3D printed nylon wings of the present invention.

[0028] Figure 2 It is the placement direction and coordinate system of the sample in the method of the present invention.

[0029] Figure 3 It is the stress deviation corresponding to the strain in the finite element simulation and tensile test results in the method of the present invention.

[0030] Figure 4 Schematic diagram of wing load distribution of the present invention.

[0031] Figure 5 This is a diagram of the overall device for testing the wing of the present invention.

[0032] Figure 6 These are the finite element boundary conditions and loads of the wing of the present invention.

[0033] Figure 7 It is a schematic diagram of the stress and strength interference of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the solution method of the present invention, the present invention is further described in detail below with reference to specific embodiments in conjunction with the accompanying drawings. However, this method is not limited to a specific example and can be applied to similar situations.

[0035] Please refer to the relevant drawings. The reliability assessment method for 3D printed nylon wings provided by the present invention is used to evaluate the structural reliability of a certain type of single-sided UAV wing printed using nylon material using the SLS process, including the following steps:

[0036] Step 1: According to ISO 20753 and GB / T 28889-2012 standards, the geometric dimensions of the dog-bone tensile specimen and the V-shear specimen were determined respectively. 12 tensile nylon 12 specimens were printed by SLS process, of which 6 were placed horizontally and printed vertically, i.e. horizontal tensile specimens; the other 6 were placed vertically and printed vertically, i.e. vertical tensile specimens. The printing method and quantity of shear specimens are the same as those of tensile specimens. The placement direction and printing direction (Z axis) are as follows: Figure 2 As shown, the subscript L is used to represent the material parameters in the z direction, and the subscript T is used to represent the material parameters in the xy plane.

[0037] Step 2: Perform tensile and shear tests according to ISO 527 and GB / T 28889 standards to obtain test data. Elastic modulus E T , E L , tensile strength σ t,T , σ t,L , Poisson's ratio ν TT , ν LT As shown in the following table:

[0038] Number <![CDATA[E T (MPa)]]> <![CDATA[σ t，T (MPa)]]> <![CDATA[v TT ]]> <![CDATA[E L (MPa)]]> <![CDATA[σ t，L (MPa)]]> <![CDATA[v LT ]]> 1 1478.95 42.49 0.42 919.73 15.31 0.38 2 1400.04 40.60 0.38 853.23 6.51 0.36 3 1501.53 40.61 0.37 1036.46 11.52 0.41 4 1460.67 42.84 0.41 1208.54 16.54 0.41 5 1456.08 44.66 0.38 1125.71 13.51 0.38 6 1404.31 44.21 0.38 1134.14 11.98 0.49 Average 1450.26 42.57 0.39 1046.30 12.56 0.41

[0040] Shear modulus G TT , G LT , the maximum force F during shearing T , F L As shown in the following table:

[0041] Number <![CDATA[F T (N)]]> <![CDATA[G TT (MPa)]]> FL(N) <![CDATA[G LT (MPa)]]> 1 3195.30 756.90 3236.60 411.74 2 2957.78 785.11 2762.61 387.09 3 3172.58 540.75 1993.28 435.19 4 3076.54 389.42 2610.81 422.51 5 3127.14 427.23 - - 6 3049.18 430.52 - - Average 3096.42 554.99 2650.83 414.13

[0042] And analyze the failure mode of the specimens.

[0043] Step 3: Construct a material model based on test data and failure modes.

[0044] Step 4: Use finite element software to perform tensile simulation, input the material model into the simulation, and verify the accuracy of the material model. If the deviation between the simulation and the test is greater than 10%, continue to adjust the simulation model until the deviation is less than 10%. The stress deviation between the test and simulation results is as follows: Figure 3 shown.

[0045] Step 5: Use the same material and printing process as the sample to print a certain type of single-sided UAV wing for testing. Paste several strain gauges on the upper surface of the wing. The strain gauges are connected to a multi-channel static strain tester. The instrument is connected to a computer and a dynamic signal acquisition and analysis system that matches the tester is used to read and collect strain.

[0046] Step 6: Calculate the lift during takeoff. The lift formula is as follows:

[0047] Q=1 / 2C y ρV2A Formula 1

[0048] In formula 1, Y is lift, C is y is the lift coefficient, ρ is the air density, V is the flight speed, and A is the wing area.

[0049] Place the wing upside down, with the upper wing surface at the bottom and the lower wing surface at the top. Fix the wing root and use a lifting platform to support the wing tip to keep the entire wing balanced. Place sandbags on the lower wing surface so that the gravity and lift of the sandbags are equal. The sandbags are placed on the entire lower wing surface. The gravity of the sandbags near the leading edge is larger, and gradually decreases along the chord length. The force at the trailing edge is the smallest. The load distribution diagram is shown as follows: Figure 4 After turning on the data collector, manually adjust the lifting platform to make it slowly and evenly descend until the lifting platform is completely out of contact with the wing. Wait until the wing is stable before stopping the collection and saving the collected data. Repeat the operation several times to avoid accidental data. The entire device is as follows: Figure 5 shown.

[0050] Step 7: Establish the finite element model of the wing, with the same boundary conditions and loads as the test, such as Figure 6 As shown, the established material model is input into the finite element for simulation, and the average value of the strain result of the wing test is compared with the simulated strain result at the corresponding acquisition point. If the deviation is greater than 10%, the wing finite element model is adjusted until the deviation is less than 10%. Since the upper wing surface is compressed, the strain is negative, and the sign does not indicate the size. The results of the wing test and the wing finite element simulation are shown in the table:

[0051]

[0052] Step 8: Convert the elastic modulus E of the tensile and shear tests T , E L and shear modulus G TT , G LT As uncertainty parameters, descriptive statistical analysis was performed on the uncertainty parameters. The elastic modulus E T , E L The descriptive statistics results are shown in the table:

[0053]

[0054] Shear modulus G TT , G LT The descriptive statistics results are shown in the table:

[0055]

[0056] And test the distribution, elastic modulus E T ,E L and shear modulus G TT ,G LT The normality test results are shown in the table:

[0057]

[0058] *Lilliefors significance correction. **This is a lower bound for true significance.

[0059] The results show that all parameters obey normal distribution.

[0060] Step 9: After determining the variable type of each parameter, Latin hypercube sampling method is used to sample the probability distribution of each probability variable. 50 samplings are performed to obtain 50 sets of elastic modulus E in two directions under tensile tests. T and E L And the shear modulus G in two directions under shear test TT and G LT The sampling data of .

[0061] Step 10: Input each set of sampling data into the finite element for calculation to obtain the maximum stress S of the wing corresponding to each set of sampling data. F , Latin hypercube sampling data and finite element simulation results are shown in the table:

[0062]

[0063] Wing stress S F Test distribution, S F The KS and SW normality test results are shown in the table:

[0064]

[0065] *Lilliefors significance modified.

[0066] Step 11: Use the stress-strength interference model to solve the reliability of the wing structure. Reliability is the probability that the structure can complete the intended function within a specified time and under specified conditions. It is often expressed as the failure probability P fTo express the reliability of the structure, in order to facilitate calculation, a reliability index β corresponding to the failure probability is introduced, such as Figure 7 Schematic diagram of stress and strength interference.

[0067] Stress-Strength Interference Model:

[0068] Z=g(R,S)=RS Formula 2

[0069] In Formula 2, Z is the difference between strength and stress, which is also a random variable, indicating the margin to ensure the safe and reliable strength of the structure, R is the strength, and S is the stress.

[0070] The uncertainty parameters of the wing structure are shown in the table:

[0071] Uncertain variables Average value (MPa) Standard deviation (MPa) Variable Types R 42.57 1.72 Normal variable S 1.41 0.04 Normal variable

[0072] Standardize Z to the standard Y space, where Y is a standard normal distribution variable Y~N(0,1), and its probability density function and cumulative distribution function are shown in equations (3) and (4).

[0073]

[0074] The failure probability of the structure is:

[0075]

[0076] where f Z( z) is the probability density function of Z, σ Z is the standard deviation of Z, μ Z is the mean of Z.

[0077] The probability of failure can be expressed using a reliability index:

[0078]

[0079] The calculated value of β=23.92 indicates that the probability of structural failure is very low, thus judging that the wing structure can complete the intended function.

[0080] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present invention shall also fall within the protection scope of the present invention. The present invention does not elaborate on some of the known technologies of those skilled in the art.

Claims

1. A reliability assessment method for 3D printed nylon wings, characterized in that: The following steps are involved: S1, specimens for tensile and shear tests were printed by 3D printing technology; S2, performing tensile and shear tests on the sample, obtaining corresponding material parameters, and analyzing its failure mode; S3, establishing a material model according to the material parameters and failure modes described in S2; S4, using the material model described in S3 to perform finite element simulation on the sample of the tensile test, comparing the result of the finite element simulation with the result of the tensile test in S1, and judging the deviation between the two. If the deviation is greater than 10%, continue to adjust the finite element; if the deviation is less than 10%, proceed to the next step; S5, using the same 3D printing technology and materials as the S1 to print the wings; S6, analyzing and calculating the load on the wing, applying the load on the wing, and attaching a strain gauge on the wing to collect the strain, and repeating the test multiple times to avoid accidental data; S7, establishing a finite element model of the wing, applying the material model described in S3 as a material input for simulation, performing finite element simulation on the wing, comparing the simulation result of the wing with the strain result collected by the wing test, and determining the deviation between the two. If the deviation is greater than 10%, continue to adjust the finite element simulation model of the wing; if the deviation is less than 10%, proceed to the next step; S8, descriptive statistics and test distribution of material parameters obtained from tensile and shear tests; S9, Latin hypercube sampling method is used to sample from the probability distribution of each probability variable; S10, inputting each group of sampling data into the finite element model of the wing to calculate the stress on the wing and check the distribution; S11, use the stress-strength interference model to solve the reliability of the wing structure, calculate the reliability index of the wing structure, and perform reliability analysis.

2. A reliability assessment method for 3D printed nylon wings according to claim 1, characterized in that: In S1, the 3D printing technology is selective laser sintering technology, and the printing material used is nylon 12.

3. A reliability assessment method for 3D printed nylon wings according to claim 1, characterized in that: In S6, the load is calculated by the lift formula, and a sandbag is used as the load, and the gravity of the sandbag is equal to the lift.

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