Rod piece falling impact response test system and impact response full-field spatio-temporal evolution law evaluation method

Abstract

The invention provides a rod piece falling impact response test system, and aims to solve the problems of incomplete test response evaluation, inaccurate initial conditions and difficult impact attitude control of an existing rod-shaped element. The rod piece falling impact response test system comprises a suspension unit, a test unit, a to-be-tested rod-shaped element and a falling table, the suspension unit suspends the to-be-tested rod-shaped element above the falling table in a magnetic attraction mode, and the falling impact speed is controlled through the suspension height. The test unit comprises an impact end image acquisition and processing unit and a plurality of strain sensors; the impact end image acquisition and processing unit is used for capturing a surface image of the to-be-detected rod-shaped element in the impact process so as to obtain a deformation field of an impact end area of the to-be-detected rod-shaped element; and the plurality of strain sensors are adhered to set measuring point positions on the outer surface of the rod-shaped element to be measured at intervals along the axial direction and are used for acquiring deformation of the measuring point positions. In addition, the invention further provides a method for evaluating the full-field spatio-temporal evolution law of the rod piece falling impact response.

Description

TECHNICAL FIELD

[0001] The present application relates to an impact response test system and an impact response space-time evolution law evaluation method, in particular to a rod falling impact response test system and an impact response space-time evolution law evaluation method, and belongs to the technical field of impact test. BACKGROUND

[0002] Rod-shaped components (referred to as "rods" for short) are widely used in heavy industries such as nuclear industrial engineering, such as fuel rods in fast reactor cores in nuclear power technology. Such rods have the risk of accidental falling during installation, transportation and refueling, and falling may cause mechanical damage and thus cause radioactive contamination of the environment, or even change the neutron multiplication factor and cause uncontrolled chain reactions. Therefore, it is particularly important to measure the mechanical response of rod-shaped components such as fuel rods to impact targets at different speeds.

[0003] The mechanical response of rod-shaped components during impact with a target produces a large spatial gradient and time sequence difference, and the deformation can be divided into local large deformation near the impact end and overall vibration deformation. Currently, tests on rod-shaped components generally use Hopkinson bar devices or light gas gun launch devices, which are driven by bullets or gas. However, such loading methods cannot accurately control the impact speed, and a preloading wave is formed in the component due to the large initial overload, which cannot reproduce the initial conditions of the falling scenario. Traditional drop machines rely on clamps to hold objects, and the large length-diameter ratio structure is prone to shaking when clamped, and the falling posture is highly dependent on the simultaneity of the clamp release on both sides, so it is often difficult to obtain the ideal impact posture.

[0004] In the aspect of rod-shaped component impact testing, the local large deformation near the impact end can only be observed after the test is completed, and the space-time evolution of the deformation response during the impact process cannot be obtained, and the near-impact end is usually the weak point of damage. The local large deformation near the impact end is closely related to the local physical properties and contact properties near the impact end, and it is difficult to test the local large deformation without affecting the response of the near-impact end structure using contact testing methods.

[0005] In addition, test testing cannot provide the full-field space-time evolution law of the impact response of rod-shaped component structures ("full-field" refers to the entire rod of the rod-shaped component). As the main control response of the rod-shaped component, test testing can be used as primary data, and if it can be combined with related impact theories to verify each other, the full-field space-time evolution law of the mechanical response of the rod-shaped component can be comprehensively evaluated.

[0006] In view of the above problems, an impact response test system that can accurately control the falling speed and ensure the falling posture, and a rod-shaped component falling impact response full-field space-time evolution law evaluation theory and method are necessary for structural safety evaluation. SUMMARY

[0007] Therefore, the present application provides a rod falling impact response test system, aiming at solving the problems of incomplete evaluation of existing rod element test response, inaccurate initial conditions and difficult control of impact posture.

[0008] The technical scheme of the present application is as follows: a rod falling impact response test system, comprising: a suspension unit, a test unit, a rod-shaped element to be tested and a falling platform;

[0009] The suspension unit suspends the rod-shaped element to be tested above the falling platform by magnetic attraction, and controls the falling impact speed by the suspension height;

[0010] The test unit comprises an impact end image acquisition and processing unit and a plurality of strain sensors;

[0011] The impact end image acquisition and processing unit is used to capture the surface image of the rod-shaped element to be tested during the impact process, and then obtain the deformation field of the near-impact end region of the rod-shaped element to be tested; a plurality of strain sensors are pasted on the outer surface of the rod-shaped element to be tested at the specified measurement point positions along the axial direction, and are used to collect the deformation of the measurement point positions.

[0012] As a preferred mode of the present application, the suspension unit comprises a power supply, a control switch, a power unit, a magnetic base and a magnetic hook;

[0013] The power supply is used to power the power unit and the magnetic base, and the magnetic base is fixed on the packaging box; the packaging box internally packages the circuit for connecting the magnetic base;

[0014] The control switch is used to control the on-off of the circuit for connecting the magnetic base, when the magnetic base is in the power-on state, the magnetic hook is suspended on the magnetic base by magnetic attraction, and the magnetic hook is used to connect the rod-shaped element to be tested;

[0015] The packaging box is provided with vertical slide rails on the transverse two sides, and the packaging box can slide along the slide rails under the drive of the power unit to adjust the height.

[0016] As a preferred mode of the present application, the power unit comprises a rotary motor, a rotary control switch, a chain wheel and a transmission chain;

[0017] The rotary motor has self-locking performance;

[0018] The transmission chain and the chain wheel form a chain transmission; one end of the transmission chain is connected with the packaging box, and the other end is provided with a counterweight; the rotary motor is used to drive the chain wheel to rotate, drive the transmission chain to move, and then drive the packaging box and the magnetic base and the magnetic hook to lift;

[0019] The rotation control switch is provided with two buttons for controlling the rotation motor to rotate forward and reverse respectively.

[0020] As a preferred mode of the present application, the test unit further comprises an acceleration sensor;

[0021] One end of the acceleration sensor is connected to the magnetic hook of the suspension unit, and the other end is connected to the free end of the rod-shaped element to be tested.

[0022] As a preferred mode of the present application, the impact end image acquisition and processing unit comprises a high-speed camera, a data processing unit and a light source;

[0023] The high-speed camera is at least two, which is used to record the whole process of the rod-shaped element to be tested falling off the impact drop platform, capture the surface image of the rod-shaped element to be tested in the impact process, and then send it to the data processing unit;

[0024] The data processing unit identifies the surface image change of the rod-shaped element to be tested by digital image correlation technology, performs three-dimensional reconstruction on the surface image, and obtains the deformation field of the near-impact end region of the rod-shaped element to be tested;

[0025] The light source is used for light supplement when the high-speed camera shoots.

[0026] In addition, based on the above rod falling impact response test system, the present application further provides a rod falling impact response full-field spatiotemporal evolution law evaluation method, which takes the test results of the test system as a hand data, and combines with the related impact theory to mutually verify and comprehensively evaluate the full-field spatiotemporal evolution law of the mechanical response of the rod-shaped element. The specific steps of the evaluation method are:

[0027] S1. Taking the free end of the rod-shaped element to be tested as the origin and the falling direction as the positive direction, a one-dimensional coordinate system is established;

[0028] The above rod falling impact response test system is used to carry out the falling test of the rod-shaped element to be tested, and the elastic modulus E1 and the mechanical response of the rod-shaped element to be tested are obtained. The mechanical response is the strain change law of the measuring point measured by the strain sensor with time, and the curve is the test value curve.

[0029] The elastic modulus E1 is: Wherein, γ is the material density of the rod-shaped element to be tested, Δx is the axial distance of the two measuring points, and Δt is the time difference of the signals reaching the two measuring points.

[0030] S2. According to the elastic modulus E1 of the rod-shaped element to be tested obtained in S1, combined with the plasticity parameters of the material of the rod-shaped element to be tested, the numerical simulation of the rod head quasi-static compression is carried out, the compression force-displacement curve is obtained, and then the impact end linear contact model is established.

[0031] S3. According to the impact end linear contact model established in S2, combined with the motion control equation, boundary conditions and initial conditions of the rod-shaped element to be measured, the control equation group is derived to obtain the infinite series theoretical expression u(x, t) of the axial displacement response of the rod-shaped element to be measured; wherein t is the time variable, x is the one-dimensional space variable, and u(x, t) is the axial displacement response of the rod-shaped element to be measured;

[0032] S4. According to the infinite series theoretical expression u(x, t) of the axial displacement response of the rod-shaped element to be measured obtained in S3, according to the required mechanical response requirements, the required motion response infinite series theoretical expression Φ(x, t) and characteristic equation are obtained by taking different order partial derivatives of the axial displacement with respect to time or space;

[0033] When the first order partial derivative with respect to time t is taken, the infinite series theoretical expression v(x, t) of the axial velocity is obtained;

[0034] When the first order partial derivative with respect to space x is taken, the infinite series theoretical expression ε(x, t) of the axial strain is obtained;

[0035] S5. According to the required motion response infinite series theoretical expression obtained in S4, the first n order is represented as Φ n , and n is initialized to 1;

[0036] S6. Numerically solve the characteristic equation in S3 to obtain the first 2n order numerical solution, and substitute it into the motion response infinite series theoretical expression of the corresponding order;

[0037] S7. According to the corresponding order motion response infinite series theoretical expression obtained in S6, the first n order and the first 2n order theoretical expressions are summed up to obtain the corresponding order theoretical solutions Φ n and Φ 2n ;

[0038] S8. According to the solutions Φ n and Φ 2n solved in S7, draw the curves of Φ n and Φ 2n , and carry out convergence analysis:

[0039] If it is judged as not convergent, the value of n is assigned as 2n, and the step S6 is returned to continue in the order of steps;

[0040] If it is judged as convergent, the convergent order n is determined;

[0041] S9. According to the convergent order obtained in S8, the first n order series approximation solution Φ n of the corresponding motion response Φ of the rod-shaped element to be measured is obtained;

[0042] S10. Comparing the first n order series approximation solution of the axial strain of the rod-like element obtained according to the above steps with the test value obtained in step S1.

[0043] If the error of the two curves is within the set range, it is indicated that the series approximation solution is reliable and can be used for analysis of the unmeasurable physical quantity of the rod-like element or for theoretical analysis of the impact response of the rod-like element of the same material under the same impact speed.

[0044] If the fitting error exceeds the set range, return to step S2 to modify the linear contact model at the impact end, and then execute the steps of S3-S10.

[0045] As a preferred mode of the present application, in S2, the linear contact model can be expressed as F S (δ) = kδ + F0,

[0046] Wherein: F S is the compression force, δ is the compression displacement, k is the equivalent contact stiffness, and F0 is the equivalent contact initial force.

[0047] As a preferred mode of the present application, in S10, the way to modify the linear contact model at the impact end is to increase a correction factor to the equivalent contact stiffness k and / or the equivalent contact initial force F0 in the linear contact model.

[0048] As a preferred mode of the present application, in S3, the motion control equation for the rod-like element to be tested is:

[0049]

[0050] Wherein: μ1 is the Poisson's ratio of the rod-like element to be tested, d is the cross-sectional diameter of the rod-like element, and c is the sound speed of the material of the rod-like element.

[0051] The boundary condition is:

[0052] The cross-sectional force at the free end is 0, i.e.

[0053] The cross-sectional force at the impact end, i.e. the impact contact force, is F d (t), which is opposite to the falling direction,

[0054] Wherein: A is the cross-sectional area of the rod-like element to be tested, and l is the length of the rod body of the rod-like element to be tested.

[0055] Taking the initial time when the rod-like element to be tested starts to contact the drop platform as the initial time, the initial condition is:

[0056] The initial velocity of the rod-like element to be tested is v0, i.e. The initial displacement is 0, i.e. u(x, 0) = 0.

[0057] Substitute δ = u(l,t) into the linear contact model to obtain F S (u(l,t)) = ku(l,t) + F0, let F d (t) = F S (u(l,t)), combined with the above motion control equation of the rod-shaped element to be tested, the boundary conditions and the initial conditions, the control equation group is obtained, and the infinite series theoretical expression u(x,t) of the axial displacement response of the rod-shaped element to be tested is derived:

[0058]

[0059] Wherein, ω n And β n are intermediate variables in the theoretical derivation process, and the relationship between the two is: N represents the order;

[0060] β n is the nth order root of the equation about the parameter β, and the size is arranged in order with the size of n, and the equation about the parameter β is the characteristic equation:

[0061]

[0062] As a preferred mode of the present application, the material sound speed c of the rod-shaped element is obtained by using the rod falling impact response test system of any one of the above claims 1-5 to carry out the falling test of the rod-shaped element to be tested.

[0063] Beneficial effects:

[0064] (1) The test system of the present application adopts magnetic suspension, which can control the falling impact speed by the suspension height, can effectively avoid the prestress distribution and unstable loading speed caused by the traditional axial impact loading of the rod-shaped element, and avoid the unstable falling posture caused by the suspension or grabbing release;

[0065] (2) The suspension unit provided by the present application realizes the effective connection of the rod-shaped element to be tested-magnetic hook-magnetic seat, effectively solves the suspension problem of non-magnetic rods; in addition, an acceleration sensor can be added between the rod-shaped element to be tested and the magnetic hook, and the acceleration data of the free end of the rod-shaped element to be tested can be obtained.

[0066] (3) The test system of the present application provides comprehensive test means, which can non-contact measure the large deformation field near the impact end of the rod-shaped element (obtained by image processing), avoid the influence of the test means itself on the structure or contact property; combined with the contact measurement data at the far end (obtained by arranging strain sensors), together constitute the basic data of the comprehensive description of the space-time evolution law of the rod-shaped element falling impact response.

[0067] (4) The test system of the invention can obtain the elastic modulus of the rod-shaped element under test more accurately by obtaining the time difference of the strain signal, avoiding the inaccuracy of the measurement results caused by factors such as measurement accuracy and fixing method in quasi-static tension.

[0068] (5) The evaluation method provided by the present invention has been verified by the test values ​​of the test system and is a relatively accurate theoretical method; it can quickly predict the spatiotemporal evolution characteristics of the mechanical response of the rod-shaped element under drop impact loading, and can obtain the overall vibration deformation of the rod-shaped element, providing effective expectations for the test and facilitating experimental preparation work such as adjusting the parameters of the test equipment. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the overall structure of the rod drop impact response testing system of the present invention;

[0070] Figure 2 This is a side view of the suspension unit in this invention;

[0071] Figure 3 The flowchart is a method for evaluating the spatiotemporal evolution of the drop impact response of a rod according to the present invention.

[0072] Figure 4 This is a schematic diagram of a one-dimensional coordinate system established with the free end of the rod-shaped element under test as the origin and the direction of fall as the positive direction.

[0073] Figure 5 This is a comparison chart of axial strain data for rod-shaped elements under five different conditions.

[0074] Among them, 1-power supply, 2-control switch, 3-rotary motor, 4-sprocket, 5-transmission chain, 6-magnetic base, 7-magnetic hook, 8-rod-shaped element under test, 8-1-rod body, 8-2-rod head, 9-drop platform, 10-high-speed camera, 11-strain sensor, 12-accelerometer, 13-data processing unit, 14-light source, 15-packaging box, 16-slide rail, 17-rotary control switch. Detailed Implementation

[0075] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0076] Example 1:

[0077] This embodiment provides a rod drop impact response testing system that can accurately control the drop speed, ensure the drop posture, and test the local large deformation and vibration deformation of rod-shaped components during the drop impact process.

[0078] like Figure 1 As shown, the testing system includes: a suspension unit, a testing unit, a rod-shaped element under test 8, and a drop platform 9.

[0079] The hanging unit adopts magnetic suspension to hang the rod-shaped element 8 to be tested, so as to control the initial speed of drop impact by the hanging height, and the magnetic suspension can ensure the stability of the drop posture. Figure 2 As shown in the figure, the hanging unit comprises a power supply 1, a control switch 2, a rotating motor 3, a chain wheel 4, a transmission chain 5, a magnetic base 6 and a magnetic hook 7. The power supply 1 is used to supply power for the rotating motor 3 and the magnetic base 6, and the magnetic base 6 is fixed on the packaging box 15. The packaging box 15 internally packages the circuit connected to the magnetic base 6, and vertical slide rails 16 are arranged on the two lateral sides of the packaging box 15 (the lower ends of the slide rails 16 are supported on the test bench), and the packaging box 15 can slide along the slide rails 16 to adjust the height; meanwhile, the slide rails 16 arranged on the two lateral sides of the packaging box 15 can prevent the magnetic base 6 from shaking in the horizontal plane. The control switch 2 is used to control the power-on and power-off of the magnetic base 6 (i.e. to control the on-off between the power supply 1 and the circuit connected to the magnetic base 6), when the magnetic base 6 is in the power-on state, the magnetic hook 7 is suspended on the magnetic base 6 by magnetic attraction, and the magnetic hook 7 is used to connect the rod-shaped element 8 to be tested.

[0080] The transmission chain 5 and the chain wheel 4 form a chain transmission, one end of the transmission chain 5 is connected to the packaging box 15, and the other end is provided with a counterweight; the rotating motor 3 is used to drive the chain wheel 4 to rotate, drive the transmission chain 5 to move, and then drive the packaging box 15 and the magnetic base 6 and the magnetic hook 7 to ascend and descend. The rotating motor 3 is a motor with self-locking performance.

[0081] As an example, two chain wheels 4 are arranged to form chain transmission with the transmission chain 5, one of the chain wheels 4 is connected to the driving motor 3 as a driving wheel, and the other chain wheel is a driven wheel.

[0082] As an example, the top of the two slide rails 16 is provided with a mounting seat, and the rotating motor 3 and the chain wheel 4 are supported on the mounting seat.

[0083] As an example, a rotating control switch 17 electrically connected to the rotating motor 3 is arranged to facilitate the control of the rotating motor 3. The rotating control switch 17 is provided with two buttons to control the rotation direction of the rotating motor 3, i.e. to control the forward rotation and reverse rotation of the rotating motor 3 through the two buttons respectively; when one of the buttons is pressed for a long time, the chain wheel 4 connected to the rotating motor 3 rotates in a predetermined direction under the drive of the rotating motor 3, drives the transmission chain 5 to move, and then controls the ascending and descending of the magnetic hook 7; when the button is released, the rotating motor 3 immediately stops and locks, and the chain wheel 4 cannot rotate, so that the magnetic hook 7 is kept at the current height. After the magnetic hook 7 is controlled to the set height position, the power supply of the magnetic base 6 is turned off through the control switch 2, and the magnetic hook 7 and the rod-shaped element 8 to be tested drop.

[0084] A drop table 9 is arranged below the packaging box 15 (the drop table 9 is placed on a test table), and the drop table 9 is in direct correspondence with the suspended rod-shaped element 8 to be tested. The suspension height H of the rod-shaped element 8 to be tested from the surface of the drop table 9 can be controlled by controlling the lifting of the magnetic hook 7, so as to control the initial velocity v0 of the drop impact of the rod-shaped element 8 to be tested. The calculation formula of the initial velocity of the drop impact is wherein g is the local gravity acceleration, generally taken as 9.81 m / s 2 In the embodiment, H is controlled to be 815.5 mm, and the initial velocity v0 of the drop impact is 4 m / s.

[0085] The drop table 9 is a cylinder, and the cross-sectional diameter of the cylinder is at least 5 times the cross-sectional diameter of the rod-shaped element 8 to be tested, and the height is at least 2.5 times the diameter of the cylinder. When the rod-shaped element 8 to be tested has no rod head or the rod head is shaped and dissipates less than 15% of the total energy in the impact process, the elastic modulus E2 of the drop table 9 satisfies When E1 is the elastic modulus of the rod-shaped element 8 to be tested, the drop table 9 can be equivalent to a rigid plane; when the rod-shaped element to be tested has a rod head and the plastic dissipation is not less than 15% of the total energy, the drop table 9 can be equivalent to a rigid plane when the elastic modulus E2 of the drop table is E1. As an example, the cross-sectional diameter of the drop table 9 is 92 mm, and the height is 250 mm. When the rod-shaped element 8 to be tested has a hemispherical rod head 8-2, the drop table 9 adopts 45# steel with heat treatment HRC50, and the elastic modulus E2 is 210 GPa, which can be equivalent to a rigid plane.

[0086] The test unit is used to test the deformation field of the rod-shaped element 8 to be tested in the impact process. The test unit includes an impact end image acquisition and processing unit and a plurality of strain sensors 11. The impact end image acquisition and processing unit is used to record the whole process of the rod-shaped element 8 to be tested dropping and impacting the drop table 9, capture the surface image of the rod-shaped element 8 to be tested in the impact process, and then obtain the deformation field of the near-impact end region of the rod-shaped element 8 to be tested. The impact end image acquisition and processing unit includes a high-speed camera 10, a data processing unit 13 and a light source 14.

[0087] The light source 14 includes at least two direction light supplement lamps, which are used for light supplement when the high-speed camera 10 is shooting. The high-speed camera 10 is at least two, which is used to record the whole process of the rod-shaped element 8 to be tested dropping and impacting the drop table 9, capture the surface image of the rod-shaped element 8 to be tested in the impact process, and then send to the data processing unit 13; the data processing unit 13 identifies the surface image change of the rod-shaped element to be tested through the digital image correlation (DIC) technology, obtains the corresponding coordinate change through the measurement window division and the fast Fourier transform cross-correlation algorithm, and carries out three-dimensional reconstruction through the surface image recording in two directions, so as to obtain the deformation field of the near-impact end region of the rod-shaped element 8 to be tested. The test system adopts the image processing mode to obtain the deformation field of the near-impact end region, that is, the local large deformation of the near-impact end.

[0088] A plurality of strain sensors 11 are adhered to the surface of the straight portion of the rod-shaped element 8 to be tested along the axial direction, and the strain sensors 11 are connected to the data acquisition instrument through signal lines to transmit the surface strain of the rod-shaped element 8 to be tested to the data acquisition instrument. The adhesion position of the strain sensor 11 is not recommended to be too close to the free end of the rod-shaped element 8 to be tested, because the strain near the free end is theoretically 0. Therefore, the strain sensor 11 is used to measure the deformation of the rod-shaped element 8 to be tested away from the impact end (but also limited to the vibration deformation of the adhesion position of the strain sensor 11).

[0089] As an example, the adhesion position of the strain sensor 11 is the axial quarter and midpoint position of the rod body of the rod-shaped element 8 to be tested (i.e. the rod body of the rod-shaped element 8 to be tested is divided into four sections along the axial direction, and one strain sensor 11 is adhered at each section point, so that a total of three strain sensors 11 are adhered), and the sampling frequency is at least where l is the length of the rod body of the rod-shaped element 8 to be tested, and c is the sound speed of the material of the rod-shaped element 8 to be tested.

[0090] As an example, there are a plurality of measurement points along the axial direction of the rod body of the rod-shaped element 8 to be tested, and a plurality of strain sensors 11 are spaced apart along the circumferential direction at each measurement point; for example, at the axial quarter and midpoint position of the rod body of the rod-shaped element 8 to be tested, a plurality of strain sensors 11 are spaced apart along the circumferential direction.

[0091] As an example, the test unit further comprises an acceleration sensor 12, the acceleration sensor 12 has external threads at both ends, one end is threadedly connected to the magnetic hook 7 of the suspension unit, and the other end is threadedly connected to the free end of the rod-shaped element 8 to be tested (the lower end of the rod-shaped element 8 to be tested is the impact end, and the upper end is the free end), that is, the rod-shaped element 8 to be tested is connected to the magnetic hook 7 through the acceleration sensor 12, and the acceleration sensor 12 is electrically connected to the data acquisition instrument.

[0092] As an example, the rod-shaped element 8 to be tested comprises a rod body 8-1 (i.e. a straight portion) and a rod head 8-2; the rod body 8-1 (i.e. a straight portion) has a cross-sectional diameter of d = 16 mm and a length of l = 1000 mm; the rod head 8-2 is a rotary body, for example a hemisphere, with a height of h = d / 2 = 8 mm, which is the test impact end. In particular, the rod-shaped element to be tested without a rod head is a cylindrical straight rod. The rod-shaped element 8 to be tested is made of 316 stainless steel, for example, with a density γ = 7800 kg / m 3, the elastic modulus is E1, and the Poisson's ratio is μ1. The outer surface of the club head 8-2 and the surface near the impact end of the shaft 8-1 are made into surface speckles as identification marks for the DIC technique by using a spraying technique before the test. The shaft 8-1 is sprayed in an axial range of 5d = 90 mm (i.e., the spraying range is 90 mm from the connection between the shaft 8-1 and the club head 8-2), so that the part of the rod-shaped element 8 in the picture of the high-speed camera 10 has clear spraying speckles when the rod-shaped element 8 falls on the drop impact platform 9.

[0093] In addition to obtaining the impact mechanical response of the rod-shaped element (i.e., the local large deformation near the impact end and the vibration deformation of the position where the strain sensor 11 is attached), the test system can also accurately calculate the elastic modulus E1 of the rod-shaped element 8.

[0094] The plastic constitutive parameters and the elastic modulus E1 of the rod-shaped element are generally obtained by a quasi-static tensile test, but the measured elastic modulus data obtained by multiple repeated quasi-static tensile tests have obvious differences. For example, for the rod-shaped element 8 made of 316 stainless steel in the embodiment, the elastic modulus obtained by quasi-static tensile test for three times is 181.72 GPa, 177.81 GPa and 159.35 GPa, and the arithmetic mean is 172.96 GPa. The error of the arithmetic mean and the elastic modulus 193 GPa of 316 stainless steel specified in section 3.3 of “Technical Specification for Stainless Steel Structures” (CECS 410-2015) is also large.

[0095] By using the test system in the embodiment, the strain signals of different measuring points are obtained by using the strain sensor 11, and the time difference Δt of two signals (i.e., the signals measured by the strain sensors 11 at two different height positions of the rod-shaped element 8) can be obtained, so that the elastic modulus E1 of the rod-shaped element 8 can be more accurately obtained. wherein γ is the material density of the rod-shaped element 8, and Δx is the axial distance between the two measuring points.

[0096] As an example, the frequency of the strain sensor is 100k, the strain signals of a quartile point and a midpoint are obtained, the time difference Δt of two signals is 0.05ms, and the material sound velocity c of the rod-shaped element 8 can be obtained. Elastic modulus E1 = γc 2 = 195 GPa; and the error of the elastic modulus 193 GPa of 316 stainless steel specified in section 3.3 of “Technical Specification for Stainless Steel Structures” (CECS 410-2015) is only 1.01%. Therefore, the elastic modulus E1 of the rod-shaped element 8 can be accurately obtained by using the test system.

[0097] Embodiment 2:

[0098] On the basis of the above embodiment 1, the present embodiment proposes a method for evaluating the full-field spatio-temporal evolution law of the rod-shaped element drop impact response. The evaluation method is a theoretical evaluation method, which is verified by the elastic modulus and mechanical response of the rod-shaped element obtained by the test system in the above embodiment 1, and obtains the spatio-temporal evolution law of the mechanical response of the rod-shaped element in the impact loading process.

[0099] As shown in Figure 3 , the evaluation method comprises the following steps:

[0100] S1. Determine the material of the rod-shaped element 8 to be tested and the test impact end shape, and establish a one-dimensional coordinate system with the free end of the rod-shaped element 8 to be tested as the origin and the drop direction as the positive direction, as shown in Figure 4 .

[0101] Use the rod drop impact response test system in the above embodiment 1 to carry out drop test of the rod-shaped element 8 to be tested, and obtain the elastic modulus E1 and the mechanical response of the rod-shaped element 8 to be tested. The mechanical response here is the change law of strain with time measured by the strain sensor 11 (i.e. the test value curve).

[0102] S2. According to the elastic modulus E1 of the rod-shaped element 8 to be tested obtained in S1, and combined with the plastic parameters of the material of the rod-shaped element 8 to be tested, carry out numerical simulation of quasi-static compression of the rod head, obtain the compression force-displacement curve, and further establish the impact end linear contact model.

[0103] As an example, the linear contact model can be expressed as F S (δ)=kδ+F0, where: F S is the compression force (quasi-static contact force), δ is the compression displacement, k is the equivalent contact stiffness, and F0 is the equivalent contact initial force.

[0104] In particular, if the rod-shaped element 8 to be tested is without a rod head, for an equivalent rigid drop platform, the equivalent contact stiffness k in the linear contact model tends to 0, and in numerical calculation, a very small value such as 10 -6 can be taken; the equivalent contact initial force F0=γcv0A; where γ is the density of the rod-shaped element 8 to be tested, A is the cross-sectional area of the rod-shaped element 8 to be tested, c is the material sound speed of the rod-shaped element (here the material sound speed is obtained by the test system in the above embodiment 1), and v0 is the initial velocity of drop impact.

[0105] If the impact end of the rod-shaped element 8 to be tested has a ball head, the equivalent contact stiffness k is obtained by quasi-static compression numerical simulation, and the equivalent contact initial force F0=0; for example, for the 316 stainless steel hemispherical rod head in this example, the equivalent contact stiffness k=5.261×10 7 N / m is obtained by quasi-static compression numerical simulation, and the equivalent contact initial force F0=0.

[0106] S3. According to the impact end linear contact model established in S2, the control equation group composed of the motion control equation, boundary condition and initial condition of the rod-shaped element 8 to be tested is combined to derive the infinite series theoretical expression u(x, t) of the axial displacement response of the rod-shaped element 8 to be tested.

[0107] As an example, for a circular cross-section rod-shaped element 8 with a diameter d and a material sound speed c, the motion control equation can be expressed as:

[0108]

[0109] Where t is the time variable, x is the one-dimensional space variable, u(x, t) is the axial displacement response of the rod-shaped element 8, μ1 is the Poisson's ratio of the rod-shaped element 8, d is the cross-sectional diameter of the rod-shaped element 8.

[0110] The boundary condition is:

[0111] The free end cross-sectional force is 0, that is,

[0112] The impact end cross-sectional force, that is, the impact contact force, is F d (t), the direction is opposite to the falling direction,

[0113] Where A is the cross-sectional area of the rod-shaped element 8, the elastic modulus E1 is calculated after the test system in embodiment 1 is tested, and l is the length of the rod-shaped element 8 to be tested.

[0114] Taking the initial time when the rod-shaped element 8 to be tested starts to contact the base plane (the surface of the falling platform 9) as the initial time, the initial condition is:

[0115] The initial speed of the rod-shaped element 8 to be tested is v0, that is, The initial displacement is 0, that is, u(x, 0) = 0.

[0116] Substituting δ = u(l, t) into the linear contact model, F S (u(l, t)) = ku(l, t) + F0, F d (t) = F S (u(l, t)), and combining the control equation group composed of the motion control equation, boundary condition and initial condition of the rod-shaped element 8 to be tested, the infinite series theoretical expression u(x, t) of the axial displacement response of the rod-shaped element 8 to be tested is derived:

[0117]

[0118] Where ω n and β n are intermediate variables in the theoretical derivation process, and the relationship between the two is: t is time variable, x is one-dimensional space variable, l is the length of the rod of the rod-like element 8 to be tested, n represents the order, v0 is the initial speed of the drop impact, c is the sound speed of the material of the rod-like element (the sound speed of the material here is obtained by testing the test system of Embodiment 1 described above), μ1 is the Poisson's ratio of the rod-like element 8 to be tested, d is the diameter of the rod section of the rod-like element 8 to be tested, k is the equivalent contact stiffness, and F0 is the equivalent contact initial force.

[0119] β n is the nth order root of the equation with respect to the parameter β, which is arranged in order of magnitude with n, and the equation can be solved iteratively by using a commonly used numerical method such as Newton's method. The equation (characteristic equation) of the parameter β is as follows:

[0120]

[0121] S4. According to the required mechanical response requirements, the infinite series theoretical expression u(x, t) of the axial displacement response of the rod-like element 8 obtained in S3 is obtained, and the required motion response infinite series theoretical expression Φ(x, t) is obtained by taking different order partial derivatives of the axial displacement with respect to time or space.

[0122] For example, when the first order partial derivative with respect to time t is taken, the axial velocity infinite series theoretical expression v(x, t) is obtained;

[0123] When the first order partial derivative with respect to space x is taken, the axial strain infinite series theoretical expression ε(x, t) is obtained;

[0124] For the position x, the applicable time range is 0≤t≤(3l-x) / c.

[0125] S5. According to the required motion response infinite series theoretical expression obtained in S4, the first n orders are represented as Φ n , such as displacement u n , velocity v n , axial strain ε n , and initialize n=1;

[0126] S6. Numerically solve the characteristic equation (i.e. the equation of the parameter β) in S3 to obtain the first 2n order numerical solution, and substitute it into the motion response infinite series theoretical expression of the corresponding order;

[0127] S7. According to the corresponding order motion response infinite series theoretical expression obtained in S6, the first n order and the first 2n order theoretical expressions are summed up to obtain the corresponding order theoretical solutions Φ n and Φ 2n ;

[0128] S8. According to the solutions Φ n and Φ 2n solved in S7, draw Φ n and Φ2n Convergence analysis is carried out (i.e. whether the shape of the two curves is still obviously changed, or the difference between the two curves is observed or calculated):

[0129] If it is judged that it is not convergent (i.e. the shape of the two curves is obviously changed), the value of n is assigned as 2n, and step S6 is returned to continue in the order of steps;

[0130] If it is judged that it is convergent (i.e. the shape of the two curves is not obviously changed), the convergence order n is determined.

[0131] S9. According to the convergence order obtained in S8, the first n-order series approximation solution of the corresponding motion response Φ (such as displacement, velocity, axial strain) of the measuring rod-shaped element 8 is obtained. n .

[0132] S10. The first n-order series approximation solution of the axial strain of the measuring rod-shaped element 8 obtained according to the above steps and the test value obtained in step S1 are plotted and compared:

[0133] If the two curves are well matched (the error is within the set range), it indicates that the series approximation solution of the theoretical method is reliable, and the n-order approximation solution can be used to analyze the energy and other unmeasurable physical quantities of the rod-shaped element or the theoretical method can be used for theoretical analysis of the impact response of the rod-shaped element of the same material under the same impact speed (the size of the rod-shaped element can be changed);

[0134] If the matching degree is poor (the error exceeds the set range), return to step S2 to modify the linear contact model at the impact end, and then execute the steps of S3-S10 above.

[0135] The reason why the linear contact model at the impact end needs to be modified is mainly the strain rate effect of the material under impact; the specific modification method is to increase the modification factor for the equivalent contact stiffness k and / or the equivalent contact initial force F0 in the linear contact model, i.e. multiplying the equivalent contact stiffness k and / or the equivalent contact initial force F0 by a modification coefficient (the modification coefficient is an empirical value, which can be obtained by numerical simulation of the impact force, and then the modification factor is given by comparing k and F0); for this embodiment, when the linear contact model at the impact end needs to be modified, the equivalent contact stiffness k is multiplied by the modification coefficient 1.24.

[0136] Through the above step S10, the test value of the test system can be used to verify the theoretical method, and a relatively accurate theoretical method can be obtained; based on the theoretical method, the mechanical response of the rod-shaped element in the impact loading process can be theoretically solved, i.e. the overall vibration deformation of the rod-shaped element can be obtained.

[0137] In order to further verify the rationality of the above test system and theoretical evaluation method, for example,Figure 5 The midpoint (x=l / 2) axial strain data obtained by using the test system of embodiment 1, the first 64 order theoretical evaluation data before correction of the impact end linear contact model, the first 64 order theoretical evaluation data after correction of the impact end linear contact model, the data of numerical simulation (hereinafter referred to as simulation 1) by using the elastic modulus of 316 stainless steel obtained by using the test system in embodiment 1, and the data of numerical simulation (hereinafter referred to as simulation 2) by using the arithmetic mean of the elastic modulus of 316 stainless steel obtained by using the quasi-static tensile test are compared. The test data, the theoretical evaluation data and the simulation 1 data have high consistency, which verifies the effectiveness of the theoretical evaluation tool provided in the embodiment; compared with the test data, the maximum strain in simulation 2 is obviously higher than that in simulation 1, and the maximum value appears obviously later, the elastic modulus will affect the stress wave velocity, thereby affecting the pulse width of the strain signal, the appearance time of the maximum value represents the pulse width to some extent, and the elastic modulus can also represent the deformation resistance, the higher the maximum strain is, the greater the deformation is, and the weaker the structure deformation resistance is, which indicates that the elastic modulus in simulation 2 is small, and further verifies the effectiveness of the method for calculating the elastic modulus by using the test system provided in the above embodiment 1.

[0138] The above is a further detailed description of the present application in combination with specific embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the present application.

Claims

1. A drop impact response testing system for rods, characterized in that, include: Suspension unit, test unit, rod-shaped element under test (8) and drop platform (9); The suspension unit uses a magnetic suction method to suspend the rod-shaped element (8) to be tested above the drop platform (9), and controls the drop impact speed by the suspension height; The test unit includes an impact end image acquisition and processing unit and several strain sensors (11); The impact end image acquisition and processing unit is used to capture the surface image of the rod-shaped element (8) to be tested during the impact process, and then obtain the deformation field of the rod-shaped element (8) near the impact end; a number of strain sensors (11) are attached to the outer surface of the rod-shaped element (8) to be tested at intervals along the axial direction to set the measurement point positions, and are used to collect the deformation at the measurement point positions.

2. The drop impact response testing system for rods as described in claim 1, characterized in that, The suspension unit includes a power supply (1), a control switch (2), a power unit, a magnetic base (6), and a magnetic hook (7); The power supply (1) is used to supply power to the power unit and the magnetic base (6), which is fixed on the encapsulation box (15); the encapsulation box (15) encapsulates the circuit for connecting the magnetic base (6); The control switch (2) is used to control the opening and closing of the circuit connecting the magnetic base (6). When the magnetic base (6) is energized, the magnetic hook (7) is suspended on the magnetic base (6) by magnetic attraction. The magnetic hook (7) is used to connect the rod-shaped element (8) to be tested. The packaging box (15) has vertical slide rails (16) on both sides of the horizontal direction. The packaging box (15) can slide along the slide rails (16) under the drive of the power unit to adjust its height.

3. The drop impact response testing system for rods as described in claim 2, characterized in that, The power unit includes: a rotary motor (3), a rotary control switch (17), a sprocket (4), and a transmission chain (5); The rotary motor (3) has a self-locking function; The transmission chain (5) and the sprocket (4) form a chain drive; one end of the transmission chain (5) is connected to the packaging box (15), and the other end is equipped with a counterweight; the rotary motor (3) is used to drive the sprocket (4) to rotate, drive the transmission chain (5) to move, and then drive the packaging box (15), magnetic base (6) and magnetic hook (7) to rise and fall; The rotary control switch (17) has two buttons that control the rotary motor (3) to rotate forward and reverse respectively.

4. The drop impact response testing system for rods as described in claim 2 or 3, characterized in that, The test unit also includes an acceleration sensor (12); One end of the acceleration sensor (12) is connected to the magnetic hook (7) of the suspension unit, and the other end is connected to the free end of the rod-shaped element (8) to be tested.

5. The drop impact response testing system for rods as described in any one of claims 1-3, characterized in that, The impact end image acquisition and processing unit includes: a high-speed camera (10), a data processing unit (13), and a light source (14); At least two high-speed cameras (10) are used to record the entire process of the rod-shaped element (8) being tested falling and impacting the drop platform (9), capture the surface image of the rod-shaped element (8) being tested during the impact, and then send it to the data processing unit (13). The data processing unit (13) identifies the changes in the surface image of the rod-shaped element under test through digital image correlation technology, performs three-dimensional reconstruction of the surface image, and obtains the deformation field of the impact end region of the rod-shaped element (8) under test. The light source (14) is used for supplemental lighting when the high-speed camera (10) takes pictures.

6. A method for evaluating the spatiotemporal evolution of the drop impact response of rod-shaped components, characterized in that, S1. Establish a one-dimensional coordinate system for the body with the free end of the rod-shaped element (8) to be tested as the origin and the falling direction as the positive direction; Using the drop impact response test system of any one of claims 1-5, a drop test is carried out on the rod-shaped element (8) to be tested, and the elastic modulus E1 and mechanical response of the rod-shaped element (8) to be tested are obtained; the mechanical response is the law of change of strain at the measuring point measured by the strain sensor (11) over time, let be the test value curve; The elastic modulus E1 is: Where γ is the material density of the rod-shaped element (8) to be tested, Δx is the axial distance between the two measuring points, and Δt is the time difference between the arrival of the signals at the two measuring points; S2. Based on the elastic modulus E1 of the rod-shaped element (8) to be tested obtained in S1, and combined with the plastic parameters of the material of the rod-shaped element (8) to be tested, carry out quasi-static compression numerical simulation of the rod head to obtain the compression force-compression displacement curve, and then establish the linear contact model of the impact end. S3. Based on the linear contact model of the impact end established in S2, and combined with the control equation set consisting of the motion control equation, boundary conditions and initial conditions of the rod-shaped element (8) to be tested, the infinite series theoretical expression u(x,t) of the axial displacement response of the rod-shaped element (8) to be tested is derived; where t is the time variable, x is the one-dimensional space variable, and u(x,t) is the axial displacement response of the rod-shaped element (8); S4. Based on the infinite series theoretical expression u(x,t) of the axial displacement response of the rod-shaped element (8) obtained in S3, according to the required mechanical response requirements, the infinite series theoretical expression Φ(x,t) and characteristic equation of the required motion response are obtained by taking the partial derivatives of the axial displacement with respect to time or space of different orders. When the first-order partial derivative is taken with respect to time t, the theoretical expression for the infinite series of axial velocity v(x,t) is obtained. When the first-order partial derivative is taken with respect to space x, the theoretical expression for the infinite series of axial strain ε(x,t) is obtained. S5. Based on the theoretical expression of the required infinite series motion response obtained in S4, the first n orders are represented as Φ. n Initialize n = 1; S6. Numerically solve the characteristic equation in S3 to obtain the first 2n-order numerical solutions, and substitute them into the theoretical expression of the infinite series of motion response of the corresponding order. S7. Based on the theoretical expression of the infinite series motion response of the corresponding order obtained in S6, sum the theoretical expressions for the first n orders and the first 2n orders respectively to obtain the theoretical solution Φ for the corresponding order. n and Φ 2n ; S8. Φ calculated based on S7 n and Φ 2n Draw Φ n and Φ 2n Curve, conduct convergence analysis: If the convergence is determined to be non-convergent, assign n to 2n, return to step S6, and continue in the order of steps; If convergence is determined, then the convergence order n is determined. S9. Based on the convergence order obtained in S8, obtain the first n order approximation solution Φ of the corresponding motion response Φ of the rod-shaped element. n ; S10. Compare the nth-order approximation solution of the axial strain of the rod-shaped element obtained from the above steps with the experimental test value obtained in step S1 by plotting a curve: If the errors of the two curves are within the set range, it indicates that the series approximation solution is reliable and can be used to carry out the analysis of unmeasurable physical quantities of rod-shaped elements or to conduct theoretical analysis of the impact response of rod-shaped elements of the same material under the same impact velocity. If the matching error exceeds the set range, return to step S2, correct the linear contact model at the impact end, and then execute steps S3-S10 as described above.

7. The method for evaluating the spatiotemporal evolution of the drop impact response of a rod-shaped element as described in claim 6, characterized in that, In S2, the linear contact model can be expressed as F S (δ)=kδ+F0; Wherein: F S δ is the compressive force, k is the compressive displacement, k is the equivalent contact stiffness, and F0 is the equivalent initial contact force.

8. The method for evaluating the spatiotemporal evolution of the drop impact response of a rod-shaped element as described in claim 7, characterized in that, In S10, the method of correcting the linear contact model at the impact end is to add a correction factor to the equivalent contact stiffness k and / or the equivalent initial contact force F0 in the linear contact model.

9. The method for evaluating the spatiotemporal evolution of the drop impact response of a rod-shaped element as described in claim 7 or 8, characterized in that, In S3, the motion control equation for the rod-shaped element under test is as follows: Where: μ1 is the Poisson's ratio of the measuring rod element, d is the diameter of the rod body section of the measuring rod element; c is the sound velocity of the rod element material; The boundary conditions are: The force at the free end section is 0, that is... The impact force at the cross-section, i.e., the impact contact force, is F. d (t), the direction is opposite to the direction of the fall. Where: A is the cross-sectional area of ​​the measuring rod-shaped element, and l is the length of the rod-shaped element to be measured. Taking the moment when the rod-shaped element under test begins to contact the drop platform as the initial time, the initial conditions are: The initial velocity of the rod-shaped element under test is v0, that is... The initial displacement is 0, i.e., u(x,0)=0; Substituting δ=u(l,t) into the linear contact model, we can obtain F S (u(l,t))=ku(l,t)+F0, let F d (t)=F S (u(l,t)), combined with the control equations consisting of the motion control equations, boundary conditions, and initial conditions of the rod-shaped element to be measured, the infinite series theoretical expression u(x,t) of the axial displacement response of the rod-shaped element to be measured is derived: Where, ω n and β n As intermediate variables in the theoretical derivation process, the relationship between the two is as follows: n represents the order; β n Let be the nth root of the equation with respect to the parameter β, whose magnitudes are ordered with the magnitude of n. The equation with respect to the parameter β is the characteristic equation.

10. The method for evaluating the spatiotemporal evolution of the drop impact response of a rod-shaped element as described in claim 9, characterized in that, The sound velocity c of the rod-shaped element material is obtained by conducting a drop test on the rod-shaped element (8) under test using the rod drop impact response test system of any one of claims 1-5.

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