A strength test method for large-size high-strength parachute

Abstract

The application discloses a kind of methods for strength test of large size high-strength parachute, including: the size of full-size parachute is reduced to the size of equal mechanical strength, and parachute for impact test is designed;Determine the weight M of counterweight and the lifting stroke L, and carry out impact test.The application can complete the strength verification of large size parachute under the condition of size limited test field, and can achieve the effect of accurately evaluating parachute impact load.

Description

Technical Field

[0001] This invention belongs to the field of design technology for aerodynamic deceleration parachutes for aircraft, and can be used for strength verification of the force transmission path of large-size high-strength parachutes. Background Technology

[0002] A parachute is a flexible, deployable aerodynamic deceleration device. It is lightweight, compact, and deploys quickly to generate a large drag surface, producing significant deceleration force. Typically, the aerodynamic force of a parachute is greatest at the moment of deployment. Therefore, parachute strength must be considered during design and verified through ground testing. Common methods for verifying parachute strength include wind tunnel testing, airdrop testing, and ground impact testing. Wind tunnel and airdrop testing require extensive coordination, have long testing cycles, and are costly. Ground impact testing is the most economical method, primarily assessing the strength of the longitudinal force transmission path of the parachute under dynamic load descent, and is the preferred method for professional parachute strength verification.

[0003] Ground impact tests are conducted on a gantry crane. Due to technical and site limitations, the gantry height is limited, making traditional ground impact tests impossible for large-sized parachute products. Impact load is the most crucial technical indicator in ground impact tests. The calculated impact load affects the design of the test plan. In the traditional linear elastic coefficient calculation method, the elastic coefficient is assumed to be constant: elastic coefficient = breaking strength / (rope length * breaking elongation). This value is larger than the actual rope elastic coefficient, leading to greater displacement under nonlinear conditions (actual conditions) than under linear conditions (assumed calculation conditions). Furthermore, the total energy under nonlinear conditions (actual conditions) is greater than under linear conditions (assumed calculation conditions), resulting in a discrepancy between the calculated impact load and the actual situation. Summary of the Invention

[0004] The technical problem solved by this invention is: to address the issue that ground strength verification tests for large-size parachutes cannot be carried out due to limitations in the size of the test site, this invention proposes a low-cost strength verification test method for the force transmission path of large-size high-strength parachutes.

[0005] The technical solution of this invention is:

[0006] A method for strength testing of large-size high-strength parachutes includes:

[0007] 1) Based on the experimental conditions, calculate the longitudinal length L0 of the parachute used in the impact test;

[0008] 2) Based on the longitudinal length L0 obtained in step a), the full-size parachute is scaled down to the same mechanical strength to design a parachute for impact testing.

[0009] 3) Based on the parachute for the impact test obtained in step 2), calculate the weight M of the counterweight required under the verification load conditions and the lifting stroke L;

[0010] 4) Using the weight M of the counterweight required under the verification load conditions obtained in step 3) and the lifting stroke L, conduct a drop test.

[0011] Preferably, the force transmission path strength of the parachute used in the impact test is consistent with that of the full-size parachute.

[0012] Preferably, the number of parachute lines used in the drop test is the same as that of the full-size parachute, the process parameters for connecting the radial belt and the parachute lines are the same, and the parachute line loop interfaces are completely identical.

[0013] Preferably, the longitudinal length L0 of the parachute used in step 1) of the impact test is specifically:

[0014] L0 = H0 - L1 - L2

[0015] Where H0 is the effective height of the top of the test tower sling from the ground, L1 is the overall length of the sling and sensor connection, and L2 is the vertical distance between the parachute and the ground when the parachute is suspended in the drop test state.

[0016] Preferably, during the drop test, the lifting point and the liftable hook are fixedly installed on the gantry 1; the lifting point, the sling, the sensor and the drop test parachute are connected in sequence; the liftable hook is connected to the bottom edge buckle of the parachute canopy through the release mechanism; a counterweight is placed in the canopy of the drop test parachute.

[0017] Preferably, step 3) involves obtaining the required counterweight weight M and lifting stroke L under the verification load conditions, specifically as follows:

[0018] 31) Each component of the parachute used in the crash test is denoted as a series unit, with all parts within the component made of the same material; the breaking strength, elongation at break, number, and length of each of the m units are obtained, forming a series unit parameter matrix A; the series unit parameter matrix A is an m-row, 4-column matrix, with each row containing the breaking strength, elongation at break, number of parts within the component, and total length of the component:

[0019] A(i,1) is the measured fracture strength of the material;

[0020] A(i,2) is the measured elongation at break of the material;

[0021] A(i,3) represents the number of parts within the component;

[0022] A(i,4) is the total length of the component;

[0023] Where i = 1, 2, ..., m;

[0024] 32) Perform raw material-level static tensile tests on the materials used in each series unit individually to obtain the load-displacement curve F. i -X i And obtain the maximum load FMAX at fracture failure. i and the maximum displacement XMAX i ;

[0025] Then there is,

[0026] A(i,1)=FMAX i ,

[0027] A(i,2)=XMAX i / l0,

[0028] Wherein, l0 is the length of the material used for the experiment measured before the experiment;

[0029] 33) Remove abnormal data from the load-displacement curve to ensure that the load-displacement curve is a monotonic curve;

[0030] 34) The load-displacement curve is regularized to obtain the regularized load-displacement curve;

[0031] 35) Using interpolation, construct the load-displacement curve FX of the force transmission path:

[0032] Let the maximum allowable load FMAX be equal to the minimum value among the maximum loads of all series elements;

[0033] Define F as an n-dimensional vector, denoted as F = [0:FMAX / n:FMAX]; where n is the amount of sampled data for the load-displacement curve.

[0034] X is obtained by interpolating the regularized load-displacement curve:

[0035] X=interp(FNORM1*A(1,1)*A(1,3), 1)*A(2,3), i *A(i,1)*A(i,3), XNORM i *A(i,2)*A(i,4)), F);

[0036] 36) Using dynamic methods, calculate the impact load F under the conditions of counterweight weight M and drop stroke h. L ;

[0037]

[0038] x| t＝0 =0

[0039] F L =interp(X,F,x)

[0040] Where v is velocity, t is time, x is distance traveled, and g is the acceleration due to gravity.

[0041] Preferably, the regularized load-displacement curve FNORM i -XNORM i In the middle, FNORM i =F i / FMAX i XNORM i =X i / XMAX i .

[0042] Compared with the prior art, the advantages of the present invention are mainly reflected in:

[0043] This invention addresses the problem that traditional ground impact testing methods are ineffective for large-size parachutes due to technical and site limitations. It proposes a ground impact testing method suitable for large-size parachutes, enabling equal strength verification and offering economic efficiency and feasibility. The load-elongation variation of special textile materials is non-linear. The shape of the load-displacement curve for special textile materials is related to the fabric structure and yarn mechanical characteristics, with the elastic coefficient initially small and then increasing. Traditional linear elastic coefficient calculation methods assume a constant elastic coefficient, which does not reflect the true physical state. The non-linear model more closely approximates the actual state, resulting in more accurate calculations. Attached Figure Description

[0044] Figure 1 Schematic diagram of the test plan.

[0045] Figure 2 Diagram of a conventional impact test lifting scheme.

[0046] Figure 3 Diagram of the lifting scheme for the impact test of this invention.

[0047] Figure 4 Experimental flowchart.

[0048] Figure 5 A graph before data cleaning.

[0049] Figure 6 A graph after data cleaning.

[0050] Figure 7 Regularized load-displacement curve.

[0051] Figure 8 Flowchart of impact load calculation method. Detailed Implementation

[0052] This invention provides a strength testing method for large-size high-strength parachutes, proposing a test scheme for scaled-down parachutes of equal strength and a method for calculating test parameters. This method enables the verification of the strength of large-size parachutes under size-constrained test conditions. Figure 4 As shown, the specific implementation steps are as follows:

[0053] a) Based on the experimental conditions, calculate the longitudinal length L0 of the parachute 5 used in the impact test. For example... Figure 1 As shown, the effective height of the test tower sling above the ground is H0, the overall length of the sling and sensor is L1, and the height above the ground after the entire parachute system is connected is H1. In the suspended state of the drop test parachute 5, the vertical distance between the parachute and the ground is L2. Therefore, the dimensions of the drop test parachute are L0 = H0 - L1 - L2.

[0054] b) Equal-strength scaled-down parachute design: Based on the longitudinal length L0 obtained in step a), the full-size parachute is scaled down to the same strength to obtain the impact test parachute 5, ensuring that the force transmission path strength of the impact test parachute 5 is consistent with that of the full-size parachute. Specifically, the number and specifications of the parachute lines of the equal-strength scaled-down impact test parachute are completely consistent with those of the full-size parachute; the number and specifications of the radial straps are completely consistent; the process parameters (risk, stitch type, stitch density) of the connection between the radial straps and the parachute lines are completely consistent; and the parachute line loop interfaces are completely consistent. The canopy size is a scaled-down size, and the canopy material should be strength-checked. If necessary, the canopy material should be reinforced or a multi-layer canopy should be used. In one embodiment of the present invention, a comparison between the full-size parachute and the equal-strength scaled-down parachute is shown in Table 1.

[0055] Table 1 Comparison of full-size parachutes and equivalent-scale parachutes

[0056]

[0057] c) Calculate test parameters: Calculate the corresponding elastic coefficient based on the scaled-down parachute system length, and calculate the required weight M and lift stroke L of the counterweight 6 under the verification load conditions. Since the only change in the scaled-down parachute system length is the same as the full-size parachute, the quantity and specifications of the force transmission path materials are identical. Therefore, compared to the full-size parachute, the scaled-down parachute system elastic coefficient is increased, allowing for a large load impact with a smaller counterweight 6 and lift stroke. The required weight M and stroke L of the counterweight 6 are obtained through dynamic calculations. The main steps include:

[0058] like Figure 8As shown, the series units of the force transmission path are analyzed. Each component is considered a series unit, with all parts within the component made of the same material. The fracture strength, elongation at break, number of parts, and length of each of the m units are obtained, forming a series unit parameter matrix A. The series unit parameter matrix A is an m x 4 matrix, with each row containing the unit's fracture strength, elongation at break, number of parts within the component, and total component length. That is:

[0059] A(i,1) is the measured fracture strength of the material;

[0060] A(i,2) is the measured elongation at break of the material;

[0061] A(i,3) represents the number of parts within the component;

[0062] A(i,4) is the total length of the component;

[0063] Where i = 1, 2, ..., m.

[0064] For example, in one embodiment of the present invention, the first row of matrix A is radial belt units, the second row is paracord units, and the subsequent rows are suspender straps, connecting straps, and other units in sequence.

[0065] A(1,1) is the measured breaking strength of the radial band, A(1,2) is the breaking elongation of the radial band, A(1,3) is the number of radial bands, and A(1,4) is the length of the radial band.

[0066] A(2,1) is the measured breaking strength of the paracord, A(2,2) is the breaking elongation of the paracord, A(2,3) is the number of paracords, and A(2,4) is the length of the paracord.

[0067] A(i,1) (i∈3,4……m) represents the measured fracture strength of the remaining materials.

[0068] A(i,2) (i∈3,4……m) represents the measured elongation at break for the remaining materials.

[0069] A(i,3) (i∈3,4……m) represents the number of parts in the remaining components.

[0070] A(i,4) (i∈3,4……m) is the total length of the remaining components;

[0071] 1) Perform raw material-level static tensile tests on the materials used in each series unit individually. Before the test, measure the length of the test material and record it as l0, and obtain the load-displacement curve F. i -X i The maximum load FMAX at fracture failure. i Let A(i,1) (i=1,2……m).

[0072] The maximum displacement is XMAX iXMAX i / l0 is A(i,2)(i=1,2...m).

[0073] 2) Perform data cleaning on the load-displacement curve to ensure the curve is monotonic. Before data cleaning, as follows... Figure 5 As shown, in static tensile tests of materials, the curves obtained directly are not monotonic due to equipment errors, inherent material characteristics, and residual tensile force after fracture. Therefore, the curve data needs to be cleaned to remove outliers and ensure that the load-displacement curve is monotonic. The cleaned data is shown below. Figure 6 As shown.

[0074] 3) Regularize the load-displacement curve. The maximum load value is FMAX. i The maximum displacement is XMAX i ;

[0075] Then we have:

[0076] FNORM i =F i / FMAX i ;

[0077] XNORM i =X i / XMAX i ;

[0078] The regularized load-displacement curve is obtained as follows: Figure 7 As shown.

[0079] 4) The load-displacement curve FX of the force transmission path is constructed using the interpolation method.

[0080] The maximum allowable load FMAX is the minimum load of each series element, that is:

[0081] FMAX = min(A(i,1));

[0082] n represents the amount of load-displacement curve data for constructing the force transmission path (i.e., the number of sampling points). F is an n-dimensional vector, denoted as F = [0:FMAX / n:FMAX].

[0083] X through FNORM i XNORM i Curve interpolation yields:

[0084] Define the interpolation function:

[0085] Let vectors P and Q be mappings to each other, treat P as the independent variable and Q as the dependent variable, and define interp(P,Q,F) as the interpolation function of F on Q(P).

[0086] The specific calculation method for the interpolation function is as follows: if vector P contains t elements, denoted as p j j = 1, 2, ..., t, p j Arranged in ascending order, there is p1 <p2<……<p t .

[0087] The corresponding vector Q contains t elements, denoted as q. j j = 1, 2, ..., t;

[0088] For any value F, if there exists p k ≤F <p k+1 And there is q k =Q(p k ), q k+1 =Q(p k+1 If k+1∈[2, t], then

[0089] interp(P,Q,F)=q k +(q k+1 -q k (pp) k ) / (p k+1 -p k );

[0090] Then we have:

[0091] X=interp(FNORM1*A(1,1)*A(1,3), 1)*A(2,3), i *A(i,1)*A(i,3), XNORM i *A(i,2)*A(i,4)), F).

[0092] The equation has already converted the radial elongation of the belt and paracord into the vertical elongation through certain calculations.

[0093] 5) The impact load under certain conditions of weight M and stroke h can be calculated by solving the following differential equation using the dynamic method.

[0094]

[0095] x| t＝0 =0

[0096] F L=interp(X,F,x)d) Test Implementation: Compared with the traditional sand injection test, it should be noted that due to the increased elastic coefficient of the force transmission path of the equal-strength scaled parachute, when connected in series with the sling, the sling itself has elasticity, which will reduce the elastic coefficient of the entire test link. Therefore, the sling of the parachute 5 used for the drop test should be as short as possible. In the traditional drop test, the drop stroke is provided by raising the bottom of the parachute lines and releasing them. The drop stroke is mainly provided by the size of the sling. However, in order to obtain a larger elastic coefficient, the sling size should be as short as possible, which will limit the drop stroke. This invention proposes a scheme to raise the bottom of the canopy. When designing the parachute 5 used for the drop test, the canopy is raised by sewing buckles at the bottom of the canopy, and the length of the parachute lines is also included in the drop stroke, which can improve the drop efficiency.

[0097] Before data cleaning Figure 5 As shown, in static tensile tests of materials, the curves obtained directly are not monotonic due to equipment errors, inherent material characteristics, and residual tensile force after fracture. Therefore, the curve data needs to be cleaned to remove outliers and ensure that the load-displacement curve is monotonic. The cleaned data is shown below. Figure 6 As shown. The load-displacement curve is regularized. The regularized load-displacement curve is shown below. Figure 7 As shown.

[0098] Example

[0099] The effective height of the test tower sling above the ground is H0, the length of the connection between the sling and the sensor is L1, and the height of the entire parachute system above the ground after connection is H1. A schematic diagram of the traditional parachute impact test procedure is shown below. Figure 2 As shown. A schematic diagram of the impact test process proposed in this invention is shown below. Figure 3 As shown. Lifting point 2 is connected to the test parachute via a tension sensor and slings. The parachute canopy and counterweight 6 are directly lifted via a liftable hook 3 connected to the bottom edge buckle of the canopy, ensuring H2-H1=L. A ground-based remote release mechanism 4 allows the test parachute to freely fall under the action of counterweight 6, generating a dynamic load used to verify the parachute's strength. When calculating the impact load, the load-displacement curve is cleaned to ensure it is monotonic.

[0100] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make possible variations and modifications to the technical solutions of the present invention using the disclosed methods and techniques without departing from the spirit and scope of the invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall fall within the protection scope of the present invention. Where there is no conflict, the embodiments of this application and the technical features thereof can be combined with each other.

[0101] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for testing the strength of large-size high-strength parachutes, characterized in that, include: 1) Based on the experimental conditions, the longitudinal length L0 of the parachute (5) used in the impact test was calculated by reverse calculation; 2) Based on the longitudinal length L0 obtained in step 1), the full-size parachute is subjected to dimensional scaling down treatment with equal mechanical strength to design and obtain the parachute for the impact test (5). 3) Based on the parachute (5) obtained in step 2), calculate the weight M and lifting stroke L of the counterweight (6) required under the verification load conditions; 4) Using the weight M of the counterweight (6) required under the verification load conditions obtained in step 3) and the lifting stroke L, conduct a drop test; Step 1) The longitudinal length L0 of the parachute (5) used for the impact test is as follows: L0 = H0 - L1 - L2 Wherein, H0 is the effective height of the top of the test tower sling from the ground, L1 is the overall length of the connection between the sling and the sensor, and L2 is the vertical distance between the parachute (5) and the ground when the parachute (5) is suspended in the drop test state. During the drop test, the lifting point (2) and the liftable hook (3) are fixedly installed on the gantry (1); the lifting point (2), the sling, the sensor and the drop test parachute (5) are connected in sequence; the liftable hook (3) is connected to the bottom edge buckle of the parachute canopy through the release mechanism (4); a counterweight (6) is placed in the canopy of the drop test parachute (5). Step 3) The method for obtaining the weight M of the counterweight (6) required under the verification load conditions and the lifting stroke L is as follows: 31) Each component in the drop test parachute (5) is recorded as a series unit, and the materials of the parts in the component are the same; obtain the breaking strength, breaking elongation, number, and length corresponding to m units respectively to form the series unit parameter matrix A; the series unit parameter matrix A is an m-row 4-column matrix, and each row contains the breaking strength, breaking elongation, number of parts in the component, and total length of the component: A(i,1) is the measured fracture strength of the material; A(i,2) is the measured elongation at break of the material; A(i,3) represents the number of parts within the component; A(i,4) is the total length of the component; Where i = 1, 2, ..., m; 32) Perform raw material-level static tensile tests on the materials used in each series unit individually to obtain the load-displacement curve F. i -X i And obtain the maximum load FMAX at fracture failure. i and the maximum displacement XMAX i ; Then there is, A(i,1)= FMAX i , A(i,2) =XMAX i / l0, Wherein, l0 is the length of the material used for the experiment measured before the experiment; 33) Remove outlier data from the load-displacement curve to ensure that the load-displacement curve is monotonic; 34) Regularize the load-displacement curve to obtain the regularized load-displacement curve; 35) Using interpolation, construct the load-displacement curve FX of the force transmission path: Let the maximum allowable load FMAX be equal to the minimum value among the maximum loads of all series elements; Define F as an n-dimensional vector, denoted as F = [0: FMAX / n: FMAX]; where n is the amount of sampled data for the load-displacement curve. X is obtained by interpolating the regularized load-displacement curve: X=interp(FNORM1 A(1,1) A(1,3),XNORM1 A(1,2) A(1,4) 2 / π,F)+ interp(FNORM2 A(2,1) A(2,3),XNORM2 A(2,2) A(2,4) cos(bow(2 A(1,4) / π / A(2,4))),F)+ interp(FNORM i A(i,1) A(i,3),XNORM i A(i,2) A(i,4),F)? 36) Using dynamic methods, calculate the impact load F under the conditions of the weight M of the counterweight (6) and the fall stroke h. L ; Where v is velocity, t is time, x is distance traveled, and g is the acceleration due to gravity. Regularized load-displacement curve FNORM i - XNORM i In the middle, FNORM i =F i / FMAX i XNORM i =X i / XMAX i .

2. The method for strength testing of large-size high-strength parachutes according to claim 1, characterized in that, The parachute (5) used in the impact test has the same force transmission path strength as the full-size parachute.

3. The method for strength testing of large-size high-strength parachutes according to claim 1, characterized in that, The number of parachute lines for the impact test parachute (5) is the same as that of the full-size parachute, the process parameters for connecting the radial belt and the parachute lines are the same, and the parachute line loop interfaces are completely identical.

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