Four-hole experiment and joint diagnostic method

Abstract

The present application relates to the technical field of aiming at small space and large mass micro-objects, based on the principle of comparison and complement, a four-hole experiment and joint diagnosis method is designed in a light gas gun loading platform, including: 1, designing a four-hole experiment device; 2, an Asaywindow signal processing method suitable for studying the mass of large mass micro-objects is proposed, compared with the traditional algorithm, the accuracy is greatly improved; 3, a PDV data inversion algorithm suitable for studying the velocity of multiple particles is proposed, compared with the traditional algorithm, the secondary velocity and noise can be filtered out, and the signal-to-noise ratio is improved. In the method, the purpose of pre-depositing metal powder is two, first, artificially controlling the mass of large mass micro-objects, second, the calculation accuracy of Asaywindow can be quantitatively evaluated. The present application diagnoses the velocity and area density of micro-objects in situ, can construct the three-dimensional micro-objects evolution mechanism, and has high scientific and engineering value.

Description

Technical Field

[0001] This invention relates to the field of aiming at large-mass micro-spraying materials in a small space, and more specifically, to a four-hole test and combined diagnostic method. Background Technology

[0002] When a shock wave is unloaded from a metal free surface or metal / gas interface, the surface of a metallic material subjected to impact loads can undergo micro-cracks or even large-area fragmentation, generating high-velocity particles. The response process of such materials is highly complex. The dynamic phenomenon of high-velocity, small-sized particles generated on the surface of a metallic material is often referred to as micro-ejection. Research on micro-ejection primarily focuses on the velocity, size, mass, shape of the micro-ejected particles, and the factors influencing their formation.

[0003] High-impact loading provides metallic materials with a high-temperature, high-pressure environment, which exacerbates damage when defects exist within or on the surface of the material. Furthermore, impact failure often results in micro-jetting, delamination, phase transformation, and complex fragmentation. Impact processes in gaseous environments further raise scientific questions regarding particle transport. High-impact material transport is characterized by high speed and short duration, making precise diagnosis even more challenging, especially when defects exist at material interfaces or within the material. Therefore, a series of sophisticated measurement techniques have been developed. For material damage assessment, direct methods such as X-ray radiography, proton radiography, and analysis of recovered samples are used, while indirect methods such as measuring the velocity history of the material's free surface are employed. In research on material fragmentation and gas mixing, a combination of techniques, including the Asay window, Photonic Doppler Velocimetry (PDV), piezoelectric probes, X-ray radiography, and high-speed shadow radiography, is used for combined diagnostic observation. The combined use of multiple measurement methods has more advantages for gaining a deeper understanding of the material response process under impact, such as the transport and mixing of particles in the gas environment of micro-jet spraying, and the dynamic behavior of the material itself, such as delamination.

[0004] Research on micro-spraying of metal surfaces is extremely important in fields such as shock wave and detonation physics, pyrotechnic encapsulation, weapon science, and shock compression. It is an indispensable part of developing more stable and reliable materials to resist material fragmentation under strong impacts. At the same time, in-depth research into this physical process and its mechanisms is also of great significance for testing material interfaces under extreme conditions and for engineering applications such as inertial confinement fusion.

[0005] The formation of micro-jet particles depends on free-face defects (surface scratches, near-surface pores, and grain boundaries, etc.) and the loading and unloading process of shock waves. It involves multiple research directions such as material microstructure, phase transformation, and shock melting, and belongs to a typical interdisciplinary frontier physics problem. Due to the complexity of the micro-jet formation mechanism and the current limitations of diagnostic capabilities, research on this physics problem is not yet sufficient. Summary of the Invention

[0006] The present invention provides a four-hole experimental and combined diagnostic method that can better study the velocity and areal density of micro-sprayed materials.

[0007] The four-well test and combined diagnostic method according to the present invention includes the following steps:

[0008] I. Design a four-well experimental setup, including a target with four wells. Well 1 is pre-deposited with metal powder and diagnosed using PDV (Polymerization Device) to observe the velocity behavior of the micro-spray and metal powder under impact loading. Well 2 is pre-deposited with metal powder and diagnosed using Asay window technology to assess the quality of the metal powder and micro-spray. Well 3 is left unfilled with powder and its quality is assessed using Asay window technology, serving as a control group for well 2. Well 4 is left unfilled with powder and its velocity is assessed using PDV, serving as a control group for well 1.

[0009] Second, conduct comparative experiments to jointly diagnose the characteristics of micro-sprayed materials.

[0010] Preferably, the four holes are Φ5mm×1mm in size.

[0011] As a preferred method, the Asay window technique is improved to diagnose the mass of micro-jet particles. Combining momentum and mass conservation conditions, the improved Asay window technique yields a higher mass increment (dm) of the micro-jet particle surface. e From (1), we get:

[0012]

[0013] In equation (1), dm e,t v is the surface mass increment at time t. e,t The velocity of the microjet is determined by the distance from the coating window to the free surface of the deposited powder and the time it takes for the powder to reach the window, in meters (m). e,t It is the surface mass at time t, m AL It's the quality of the aluminum foil, u w,t The interfacial velocity of the thin film is measured by a PDV probe, P t It is the stress of the micro-sprayed particles impacting the film-coated window at time t.

[0014] Preferably, the stress P of the micro-sprayed particles impacting the coated window is...t :

[0015] D w,t =c w +λu w,t (2)

[0016]

[0017] In the formula: c w =5.148km / s, λ=1.358, ρ w =2.64g / cm 3 It is the Hugnoiot parameter of the LiF window, D w,t The shock wave velocity is represented by the LiF window.

[0018] Preferably, when PDV is being diagnosed, the Short Time Fourier Transform (STFT) method is used to analyze the PDV signal results, and the smallest resolvable frequency f is determined. min The number of points N and the sampling rate f of the Fourier transform s The relationship between them can be obtained from formula (4):

[0019]

[0020] Sampling rate f s The relationship between the sampling interval ΔT and the sampling interval is:

[0021]

[0022] As shown in equation (4), f min Inversely proportional to the number of sampling points of the PDV interference signal, suppose an object moves at a speed of 1.5 km / s. The PDV technology uses a laser with a wavelength of 1550 nm, and the frequency corresponding to formula (5) is 1.936 GHz. Therefore, the resolvable relative velocity Δv of PDV is:

[0023]

[0024]

[0025] As can be seen from formula (6), for a signal with a given time length, it is necessary to increase the number of its change points to improve the speed resolution.

[0026] Preferably, the Short Time Fourier Transform (STFT) method applies a small analytical window function h(t) that can move along the time axis to the signal, and performs a Fourier transform to extract the frequency components of the signal in this time domain. Since the window function is movable, the Fourier transform of the signal within the required time range can be obtained. Its basic definition is:

[0027] STFTx (τ,f)=∫x(t)h(t-τ)e -j2πft dt (8)

[0028] The short-time Fourier transform adds an analysis window to the time domain. By moving the analysis window along the time axis, the spectrum of each time period can be obtained. The frequency corresponding to the maximum magnitude in each time period is found, which is Δf in that time period, and then the average velocity is obtained.

[0029] As a preferred option, in the comparative experiment, the particle dynamics behavior characteristics diagnosed by particles-PDV will observe the moment when the particle swarm motion disappears, which can provide an auxiliary reference for the cutoff time of the Asaywindow experiment.

[0030] As a preferred option, in the comparative experiment, the velocity initiation time of the interface is given in the Asay window signal, that is, the time when the fastest particle arrives at the coating window. At the same time, the average velocity of particles arriving at the coating window at different times can also be obtained, which can be compared and corrected with the signal obtained by parts-PDV.

[0031] As a preferred method, in the comparative experiment, the cumulative mass change of the powder particles in both the pore and void micro-spraying processes can be obtained simultaneously through the particles / empty-Asay window comparison. The difference between the two can be used to calculate the areal mass m of the deposited powder particles in the experiment. e,t The process of change.

[0032] This invention proposes an Asay window model suitable for large-mass micro-spraying materials, achieved by pre-adhering large-mass metal particles (56.02–96.77 mg / cm³). 2 The experiment verified that the average error was 17.67%, improving the detection capability of the Asaywindow diagnostic technology in the large-mass micro-jetting range. This invention proposes a combined diagnostic technology of four-hole semi-adhesive powder test and PDV+Asay window. The diagnostic results of different holes complement each other, which can be used to study the velocity and areal density evolution of micro-jetting materials in situ, and has important value for the study of micro-jetting.

[0033] This invention proposes an Asay window signal processing method suitable for studying the mass of large-mass micro-jet materials, which significantly improves accuracy compared to traditional algorithms.

[0034] This invention proposes a PDV data inversion algorithm suitable for studying multi-particle velocities. Compared with traditional algorithms, it can filter out secondary velocities and noise, thereby improving the signal-to-noise ratio. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the four-hole half-powder-coating experimental apparatus in the embodiment;

[0036] Figure 2 This is a simplified diagram of the stress wave inside the substrate when subjected to a shock wave in the embodiment.

[0037] Figure 3 This is a schematic diagram of the static noise signal inversion results of the PDV system in the embodiment;

[0038] Figure 4(a) is a schematic diagram of the free surface velocity at the bottom of the hole in the exp03 experiment in the embodiment;

[0039] Figure 4(b) is a schematic diagram of the particle PDV signal in the exp03 experiment in the example;

[0040] Figure 4(c) is a schematic diagram of the interface velocity-time T relationship in the exp03 experiment in the embodiment;

[0041] Figure 4(d) shows the micro-jet mass M per unit area in the exp03 experiment in the example. e - Schematic diagram of the relationship between time T;

[0042] Figure 5(a) is a schematic diagram of the velocity of the free surface at the bottom of the hole in the exp04 experiment in the embodiment;

[0043] Figure 5(b) is a schematic diagram of the particle PDV signal in the exp04 experiment in the example;

[0044] Figure 5(c) is a schematic diagram of the interface velocity-time T relationship in the exp04 experiment in the embodiment;

[0045] Figure 5(d) shows the unit area micro-jet mass M of the exp04 experiment in the example. e - Schematic diagram of the relationship between time T;

[0046] Figure 6(a) is a schematic diagram of the free surface velocity at the bottom of the hole in the exp05 experiment in the embodiment;

[0047] Figure 6(b) is a schematic diagram of the particle PDV signal in the exp05 experiment in the example;

[0048] Figure 6(c) is a schematic diagram of the interface velocity-time T relationship in the exp05 experiment in the embodiment;

[0049] Figure 6(d) shows the unit area micro-jet mass M of the exp05 experiment in the example. e - Schematic diagram of the relationship between time T;

[0050] Figure 7 This is a schematic diagram of the free surface PDV scattering signal in exp03 in the embodiment;

[0051] Figure 8 This is a schematic diagram of typical motion images of powder and micro-spraying in a vacuum, as shown in the examples. Detailed Implementation

[0052] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0053] Example

[0054] Based on the principles of contrast and complementarity, this embodiment designs a four-hole experimental and joint diagnostic method in a light gas gun loading platform, which includes the following steps:

[0055] I. Design a four-hole experimental setup (e.g.) Figure 1 As shown, the target body has four holes with a size of Φ5mm×1mm. Considering the edge rarefaction effect in the substrate after the projectile impacts the target body, the size of the four holes is constrained within a Φ18mm circle to ensure that the particles in the holes are subjected to planar shock wave loading during the experiment, but are not affected by the edge rarefaction effect. Four-well powder deposition design: Well 1 (particles-PDV) is pre-deposited with metal powder and diagnosed by PDV (laser Doppler velocimetry) to observe the velocity behavior characteristics of micro-jet particles and metal powder under impact loading; Well 2 (particles-Asay window) is pre-deposited with metal powder and diagnosed by Asay window technology to diagnose the quality of metal powder and micro-jet particles; Well 3 (empty-Asay window) is left empty, and the quality of micro-jet particles is diagnosed by Asay window technology, serving as a control group for Well 2; Well 4 (empty-PDV) is left empty, and the velocity of micro-jet particles is diagnosed by PDV, serving as a control group for Well 1; The start-up time of the free surface at the bottom of the well is given (as the zero time of the measurement system), and the velocity of micro-jet particles at the bottom of the well may be observed; Since it is difficult to ensure perfect surface flatness at the bottom of the well during machining, two wells with similar flatness at the bottom must be selected as control groups in the design of the comparison wells.

[0056] In powder-coating experiments, when the shock wave reaches the substrate-sample contact surface, the metal powder immediately leaves the substrate (this can be considered an instantaneous event). When the flyer impacts the substrate, it generates three types of rarefaction waves within the substrate, such as... Figure 2 As shown, surface micro-spraying is mainly related to the rarefaction waves reflected from the free surface. There are slight differences between holes with powder deposition and empty holes when shock waves are reflected from the free surface. With powder deposition (which can be considered a loose material), the rarefaction waves reflected from the free surface are weaker than those from empty holes (without powder deposition). Since the powder moves immediately upon arrival of the shock wave, the resulting reflected rarefaction waves are closer to the empty hole control group. Furthermore, the experiment selected two holes with similar flatness at the bottom as a control group, so it can be assumed that the micro-spraying behavior of each hole is consistent under the same impact conditions.

[0057] Second, conduct comparative experiments to jointly diagnose the characteristics of micro-sprayed materials.

[0058] In the comparative experiment,

[0059] (1) The particle dynamic behavior characteristics diagnosed by particles-PDV will observe the disappearance time of particle swarm motion, which can be used as an auxiliary reference for the cutoff time of Asaywindow experiment.

[0060] (2) In the comparative experiment, the velocity start time of the interface is given in the Asay window signal, that is, the time when the fastest particle arrives at the coating window. At the same time, the average velocity of the particles arriving at the coating window at different times can also be obtained, which can be compared and corrected with the signal obtained by parts-PDV.

[0061] (3) In the comparative experiment, the cumulative mass change of the powder pores and the void micro-spraying were obtained simultaneously by comparing the particles / empty-Asay window. The surface mass m of the deposited powder particles in the experiment can be obtained by subtracting the two. e,t The process of change.

[0062] The purpose of pre-depositing metal powder in this method is twofold: firstly, to artificially control the mass of large-mass micro-jet materials; and secondly, to quantitatively assess the computational accuracy of the Asay window. This invention, combined with in-situ diagnosis of the velocity and areal density of micro-jet materials, can construct a three-dimensional mechanism of micro-jet evolution and development, possessing significant scientific and engineering value.

[0063] Improvements to Asay Window Data Processing Methods

[0064] The differences in the Asay window technology used in this embodiment are as follows: the thickness of the selected film was adjusted to a certain extent, and the signal processing method was improved (considering the influence of the aluminum film itself and the cumulative mass of the micro-sprayed material). When calculating the mass distribution of the micro-sprayed material, the following assumptions were used: (1) When the shock wave is reflected on the free surface of the sample, all the deposited powder leaves the substrate in a very short time (approximately instantaneous); (2) The distribution of the micro-sprayed material is uniform in the lateral direction, that is, the micro-sprayed material is in one-dimensional motion; (3) The collision between the micro-sprayed material and the coating window is a completely inelastic collision, with no reverse motion; (4) The shock wave is not reflected on the free surface of the LiF window within the effective time, which will not cause coating fluctuation; (5) The LiF window always remains transparent; (6) The mass of the deposited powder particles in the powder-adhesive experiment studied in this embodiment is relatively large (greater than the surface mass of the adhered aluminum film), and the influence of the mass of the aluminum film itself and the cumulative mass on the film is considered.

[0065] An improved Asay window technique was developed to diagnose the mass of jet-propelled particles. By incorporating momentum and mass conservation conditions, the improved Asay window technique yielded an increased surface mass (dm) of the jet-propelled particles.e From (1), we get:

[0066]

[0067] In equation (1), the first term on the right is the innovation term of the improved method, and the second term is the classic Asay window data processing term.

[0068] In equation (1), dm e,t v is the surface mass increment at time t. e,t The velocity of the microjet is determined by the distance from the coating window to the free surface of the deposited powder and the time it takes for the powder to reach the window, in meters (m). e,t It is the surface mass at time t, m AL It's the quality of the aluminum foil, u w,t It is the interfacial velocity of the thin film measured by a PDV probe (after refractive index correction), P t This is the stress of the micro-sprayed particles impacting the coated window at time t (since the Asay window used in this embodiment is fixed on the test platform and has a relatively large mass compared to the micro-sprayed particles, the stress P impacting the window is assumed to be...). t The duration is only within the dt interval.

[0069] Stress P of micro-sprayed particles impacting the coated window t :

[0070] D w,t =c w +λu w,t (2)

[0071]

[0072] In the formula: c w =5.148km / s, λ=1.358, ρ w =2.64g / cm 3 It is the Hugnoiot parameter of the LiF window, D w,t The shock wave velocity is represented by the LiF window.

[0073] Interpretation of multi-target PDV (Photonic Doppler Velocimetry) signals

[0074] The signal obtained after reflection from multiple moving objects and interference with the original laser is inherently complex, with the degree of complexity depending on the concentration and velocity distribution of the objects. Under impact loading, the particle swarm exhibits characteristics such as high velocity and low density at the front end, and high density and relatively low particle velocity at the rear end. Considering laser scattering within the micro-jet would be very complex. Current experimental studies are based on the premise that the laser is confined to the motion of the outermost layer of particles and does not scatter within the particle swarm. Theoretically, the study of signals from multi-particle micro-jet involves Mie scattering theory, and the results are quite complex.

[0075] Because it is difficult to determine the specific particle velocity and position distribution within the particle swarm during impact loading, and the direction of laser scattering within the particle swarm and the number of particles it passes through are also difficult to determine, the processing of PDV signals involving Mie scattering theory is still difficult to apply experimentally. Currently, the commonly used approach is to assume that the laser beam is confined to the outermost layer of the micro-jet particle swarm and that the laser does not scatter within the particle swarm; or to consider the equivalent particle size and the scattering of the laser within the particle swarm, but the wavelength after reflection is the equivalent effect of multiple particles in this path (i.e., equivalent to the effect of scattering by a single particle). Regardless of the assumption, neither approach addresses the frequency change within a single beam path.

[0076] We assume that the scattering of laser light within the particle swarm in the powder-coating experiment is limited to the outermost part of the particle swarm and does not undergo multiple scatterings. At the same time, we consider the equivalent effect and regard the reflected light of each small beam passing through different particles as the result of the reflection equivalent effect of a "single particle".

[0077] Processing PDV signal data from multiple moving particles is challenging, especially when the velocity differences among the particles are small, and the frequencies of each target are also quite similar, requiring high frequency resolution to separate the different frequency curves. When performing PDV diagnostics, the Short Time Fourier Transform (STFT) method is used to analyze the PDV signal results, with the smallest resolvable frequency f being... min The number of points N and the sampling rate f of the Fourier transform s The relationship between them can be obtained from formula (4):

[0078]

[0079] Sampling rate f s The relationship between the sampling interval ΔT and the sampling interval is:

[0080]

[0081] As shown in equation (4), f minInversely proportional to the number of sampling points of the PDV interference signal, suppose an object moves at a speed of 1.5 km / s. The PDV technology uses a laser with a wavelength of 1550 nm, and the frequency corresponding to formula (5) is 1.936 GHz. Therefore, the resolvable relative velocity Δv of PDV is:

[0082]

[0083]

[0084] As can be seen from formula (6), for a signal with a given time length, it is necessary to increase the number of its change points to improve the speed resolution.

[0085] The Short Time Fourier Transform (STFT) method applies a small, movable analytical window function h(t) to the signal and performs a Fourier transform to extract the signal's frequency components in that time domain. Since the window function is movable, the Fourier transform of the signal within the desired time range can be obtained. Its basic definition is:

[0086] STFT x (τ,f)=∫x(t)h(t-τ)e -j2πft dt (8)

[0087] The short-time Fourier transform adds an analysis window to the time domain. By moving the analysis window along the time axis, the spectrum of each time period can be obtained. The frequency corresponding to the maximum magnitude in each time period is found, which is Δf in that time period, and then the average velocity is obtained.

[0088] Because the Short-Time Fourier Transform (SFT) uses a fixed window width, it cannot achieve optimal resolution for both rapidly changing and stable time periods. Considering the Heisenberg uncertainty principle, a suitable window length must be manually selected for signal analysis. For rapidly changing signals, a smaller window is chosen to obtain higher time-domain resolution. Currently, both domestically and internationally, the SFT is generally used for spectral analysis of complex signals with multi-particle motion, mainly because it offers faster signal processing speed and allows for multiple processing runs with different window sizes.

[0089] Experimental Results and Analysis

[0090] The micro-spraying behavior of free surfaces of metallic materials under impact loading and its transport process in a gaseous environment remain a key focus for researchers. This embodiment utilizes the advantages of PDV and improved Asay window combined diagnostic technology to simulate the surface micro-spraying of metallic materials under impact loading and analyze the kinetic characteristics of the deposited powder under different impact conditions.

[0091] Relevant physical parameters of materials

[0092] To ensure the scientific rigor of the impact loading experiment, numerous experimental parameters, including the mass and dimensions of the target, sample, flyer, and window, must be strictly recorded before the experiment. In this embodiment, all experiments used micron-sized spherical copper powder with a size ranging from 1 to 3 μm. The target and testing platform were both made of aluminum 6061, and the flyer was made of metallic aluminum. The Hugnoiot parameters of the relevant materials used in the experiment are shown in Table 4.

[0093] Table 1. Hugoniot parameters of experimental materials

[0094]

[0095]

[0096] The velocity of the experimental flying piece was accurately measured using a magnetovelocity measuring device. The experimental design details are shown in Table 2. The impact pressure and particle velocity results within the target substrate are shown in Table 3, and the mass of powder deposited within the target is shown in Table 4.

[0097] As shown in Table 3, the experimental pressure range was 10.5–13.5 GPa, and the substrate density after impact compression was 3.04 g / cm³. 2 The experimental results show that the tensile stress and defects at the free surface under impact loading lead to the generation of micro-sprayed particles (as shown in Table 2, there are certain defects on the surface of the holes).

[0098] Table 2 Experimental Design Details

[0099]

[0100] a The experiment was conducted using a "sleeve" type measuring platform.

[0101] b. An experiment was conducted using a "separate" measurement platform.

[0102] Table 3 Impact state of the substrate in the experiment (u H D represents particle velocity. H (This indicates the shock wave velocity, T0 represents the initial ambient temperature, and the subscript H represents the substrate state after shock loading.)

[0103]

[0104]

[0105] Table 4 Powder Deposition Quality

[0106] Experiment number <![CDATA[Powder mass M T / mg]]> <![CDATA[Powder surface density M a / (mg / cm -2 )]]> exp01 22 112.05 exp02 11 56.02 exp03 11 56.02 exp04 19 96.77 exp05 17 86.58

[0107] Noise analysis of static experiments

[0108] Because the PDV system itself contains noise and other signals, which will interfere with the analysis of the actual experimental signals, it is necessary to analyze the noise signals of the system itself. First, a static noise signal analysis of the system is performed. The specific method is as follows: the experimental design and setup are consistent with the actual experiment, the target is stationary while the experimental signals are recorded. Channel C1 of a multi-channel oscilloscope is selected, and its signal is randomly selected for static noise analysis.

[0109] Figure 3 The result of static noise signal inversion for the PDV system. Figure 3 By selecting the three values ​​with the largest signal amplitude in the channel, the noise signal of the experimental instrument itself was found to have the following characteristics: 1. The overall noise signal is discrete, chaotic, and irregular; 2. A noise band appears at the 3875 m / s position, which accounts for a high proportion of the signal amplitude throughout the entire test phase, and its corresponding noise frequency is 5 GHz; 3. The noise signal exists throughout the entire static experiment, and there is no instance of the signal being highly concentrated in a short period of time. Although the noise signal persists throughout the entire experimental study period, its disordered and highly discrete nature means that the noise does not affect the determination of the velocity band signal of the multi-particle motion.

[0110] Results and Analysis of the Four-Hole Double-Asay Window Experiment

[0111] This experiment used the above data processing method to compare and diagnose the quality of moving powder particles and the quality of micro-sprayed particles, verifying the reliability of the method. The experimental design is shown in Table 2 (exp03-exp05), and the results of the three experiments are shown in Figures 4(a), 4(b), 4(c), 4(d), 5(a), 5(b), 5(c), 5(d), 6(a), 6(b), 6(c), and 6(d).

[0112] As shown in Figures 4(a), 5(a), and 6(a), the free surface signals from the three experiments indicate the initiation time of the sample's free surface after impact loading. All three experiments exhibit the same characteristic: the velocity stabilizes for approximately 400 ns before briefly increasing again. This is because when the shock wave reaches the interface between the free surface and the vacuum, it reflects a rarefaction wave within the substrate. Multiple reflections followed by reloading of the substrate's free surface cause a secondary velocity increase.

[0113] Typical PDV signals of a free surface with an open hole are as follows: Figure 7 As shown in the figure, the movement of a large number of micro-sprays was observed within the green box. This segment represents the movement of three equivalent particles corresponding to the three largest amplitudes of the selected signal. However, the signal at 255 μs is not as discrete as the signal within the green box, which further proves that after the sample target has been moving stably for a certain period of time, it eventually breaks into a large number of micro-sprays due to the complex interaction between the sparse wave reflected by the free surface and the substrate.

[0114] Analysis of Figures 4(b), 5(b), and 6(b) reveals that the motion signals of the powder and micro-sprayed material can be observed well in the PDV signals of the powder tank in all three experiments. The best signal was observed in experiment exp04 with a lower loading speed, which showed three-stage particle motion. Because the PDV test probe directly observes high-speed particles, it is prone to premature damage after experiencing numerous particle impacts. This results in the particle velocity duration observed in Figures 4(b), 5(b), and 6(b) being shorter than the particle motion duration observed in Figures 4(c), 5(c), and 6(c). Therefore, the PDV signal cutoff time can only provide a limited reference.

[0115] The velocity changes at the interface of the empty (i.e., hollow hole) in Figures 4(c), 5(c), and 6(c) also confirm that even without powder deposition, micro-sprays with varying velocities appear at the bottom of the hole under strong impact loading. The different arrival times of the two Free Surfaces in Figures 4(c), 5(c), and 6(c) indicate the offset of the target's free surface on the impact test platform. Different holes (copper and empty represent the powder tank and hollow hole, respectively) in the three experiments all had time differences when impacting the test platform. In experiments exp03 and exp05, the hollow hole (the side of the empty experimental tank facing the Asay window test technique) impacted the test platform first; in experiment exp02, the powder hole (the powder experimental tank facing the Asay window test technique) impacted the test platform first. When calculating the mass of micro-sprays from the empty hole in this experiment, the time endpoint should be consistent with the cutoff time of the copper (powder tank); otherwise, more micro-spray mass will be introduced into the hollow hole, affecting the experimental results. In the two experiments, exp03 and exp05, the termination time of empty and copper was selected based on the arrival time of the free surface, with the endpoint of the powder-PDV signal as a secondary reference.

[0116] The target's offset during flight may be due to different deformations of the edge substrate secured by its four screws under impact loading. This will cause differences in the cutoff times of the copper powder groove and the voids in the Asay window signal, which will introduce some error into the diagnosis of particle mass-motion. Table 5 shows the experimental and theoretical values ​​of the Asay window in four experiments, with a relative error of error = |(M a -(M ec -M ee )) / M a |, where M ec M is the experimental value for the copper. ee The experimental values ​​are for empty conditions. The initial projectile tilt angle G during the experiment was also calculated.r The calculation method is as follows Where Δh is the difference in edge height of each flyer, and L is the flyer diameter of 24mm (tolerance is ±0.1). The results are shown in Table 6.

[0117] Table 5 Calculated and theoretical values ​​of four Asay experiments (powder deposition mass M) a And the experimentally measured particle mass M e )

[0118]

[0119] Table 6. Inclination G of projectile fragments r

[0120] Experiment number L / mm △h / mm <![CDATA[G r / °]]> exp03 24.05 0.204 0.486 exp04 23.99 0.212 0.506 exp05 24.02 0.198 0.472

[0121] Table 6 shows that the tilt angle of the projectile fragments in the three experiments was around 0.5°, indicating strong consistency among the fragments in the three experiments. The projectile fragments were close to head-on impacts when accelerating into the target. Due to the lack of an empty control group in experiment exp02, it is impossible to know the mass of micro-spray material generated by the breakage at the bottom of the hole in this experiment. However, Table 5 shows that the powder deposition mass in experiment exp03 was consistent with that in experiment exp02, and the impact loading rates were similar. The cumulative mass of copper particles in the two experiments differed by only 4.28%. It can be roughly inferred that the mass of micro-spray material generated at the bottom of the hole in experiment exp02 was no higher than that in experiment exp03.

[0122] For experiment exp03, as shown in Figure 4(a), a large bulge appears in the empty signal, while the same signal characteristic is not observed in the copper signal. We believe that the signal fluctuation over such a long period may be caused by the impact of large micro-cracked material on the coating window, so this bulge signal was not calculated for the cumulative mass of the voids in this experiment. As a control group, the empty area must also have micro-spraying material generated during this period, which would reduce the cumulative mass of the micro-spraying material in the empty area (voids). Therefore, the experimental error of 6.48% will be less than the true value.

[0123] The experimental result of exp04 showed the largest error among the three experiments. As shown in Figure 5(c), the hole containing the powder impacted the test platform first in this experiment, earlier than the empty hole in the control group. Combined with Table 6, the tilt angle of the projectile in this experiment was higher than in the other two experiments. This may be because the substrate of the target was more severely broken after the projectile impact, resulting in lower consistency of the free surface movement of the four holes. The termination time of this experiment was chosen based on the arrival time of the copper free surface, and a value of 63.81 mg / cm³ was found in the empty segment. 2This is significantly higher than the empty signal results of the other two experiments. However, a comparison revealed that the diagnostic results of the copper segment in this experiment were close to those of the exp05 experiment. Therefore, the reason for the large error in this experiment may be that not all the deposited copper powder and broken micro-spray material in the copper were diagnosed, and the measured micro-spray mass was smaller than the actual value, resulting in a large error in this experiment.

[0124] The improved Asay window calculation method showed an average error of 17.67% in the powder-adhesion experiment for high-quality deposition, demonstrating that the substrate surface breakage of powder pores and voids was relatively consistent, and the assumption that the breakage of each pore was consistent was reasonable. Although this error may be lower than the true value, it is still a significant improvement compared to the 50% error in Asay-type powder-adhesion experiments. However, further experimental data is needed to confirm this.

[0125] Typical images of the mixed motion of powder and microjet printing are as follows: Figure 8 As shown, the three densely packed regions represent the brief acceleration of the powder within the orifice, the powder's independent movement after leaving the orifice, and the high-speed zone where high-speed micro-sprays and powder move together. The high-speed zone is characterized by the high-speed micro-sprays generated by substrate breakage catching up with the powder, resulting in momentum exchange and a renewed increase in powder velocity, moving together with the high-speed micro-sprays that haven't undergone momentum exchange. We observed that the powder begins to move first, followed by the generation of micro-sprays, and also exhibits a high-speed particle band. We have reason to believe that due to the high velocity of the micro-sprays, momentum exchange with the moving powder is inevitable. Figure 8 At 273.2 μs, particles with a velocity of around 4.0 km / s appear, but their number is relatively small. The vast majority of particles after momentum exchange have velocities concentrated in the range of 2.9 km / s, indicating that momentum exchange is random and that there are relatively few particles undergoing high-speed exchange. PDV technology can only observe particles moving at the very front of the particle swarm, while Asay window technology can complementarily observe the motion of particles at the rear.

[0126] This embodiment designs a four-hole experiment and a combined diagnostic method based on the principles of contrast and complementarity. By comparing different free surface states (pre-coated or uncoated with metal particles), combining PDV and an improved Asaywindow testing technique, it studies the velocity and areal density of micro-sprayed material and pre-coated metal particles. The new experimental design allows the diagnostic techniques to complement each other, enabling a more comprehensive quantitative depiction of the evolution of micro-sprayed material and pre-coated metal particles, which is of significant value for the study of micro-spraying.

[0127] This embodiment proposes an Asay window model suitable for large-mass micro-spraying materials, by pre-adhering large-mass metal particles (56.02~96.77mg / cm³). 2The average error was verified to be 17.67% in the experiment. This embodiment designed a combined diagnostic technique of four-hole semi-adhesive powder test and PDV+Asay window. The diagnostic results of different holes complement each other, which can be used to study the velocity and areal density evolution of micro-sprayed material in situ.

[0128] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A four-well test and combined diagnostic method, characterized in that: Includes the following steps:

1. Design a four-hole experimental setup, including a target body with four holes. Hole 1 is pre-deposited with metal powder and diagnosed by PDV. Observe the velocity behavior characteristics of the micro-spray and metal powder under impact loading. Metal powder was pre-deposited in well 2 and the quality of the metal powder and micro-spray was diagnosed using Asay window technology. No powder was placed in well 3, and the quality of the micro-sprayed material was diagnosed using the Asay window technique, serving as a control group for well 2. No powder was placed in well 4, and the micro-spraying velocity was diagnosed by PDV, serving as a control group for well 1. The Asay window technique is improved to diagnose the mass of jets. Combining the conditions of momentum and mass conservation, the mass increment of the jet surface obtained by the improved Asay window technique is obtained from (1): ； In formula (1) It is the surface mass increment at time t. The velocity of the micro-sprayed material is determined by the distance from the coating window to the free surface of the deposited powder and the time it takes for the powder to reach the window. It is the surface mass at time t. It's about the quality of the aluminum foil. The interfacial velocity of the thin film is measured by a PDV probe. It is the stress of the micro-spray material impacting the film-covered window at time t; Stress from micro-spray impacting the coated window : ； In the formula: c w =5.148km / s, =1.358, It is the Hugnoiot parameter of the LiF window. The shock wave velocity is the LiF window. Second, conduct comparative experiments to jointly diagnose the characteristics of micro-sprayed materials.

2. The four-well test and combined diagnostic method according to claim 1, characterized in that: The dimensions of the four holes are: .

3. The four-well test and combined diagnostic method according to claim 2, characterized in that: When diagnosing PDV, the Short Time Fourier Transform (STFT) method is used to analyze the PDV signal results, determining the smallest frequency that can be resolved. The number of points N and the sampling rate in the Fourier transform The relationship between them can be obtained from formula (4): ； Sampling rate With sampling interval The relationship between them is: ； As shown in equation (4), The relative velocity is inversely proportional to the number of sampling points of the PDV interference signal. Assuming an object moving at a speed of 1.5 km / s, and using a laser with a wavelength of 1550 nm in PDV technology, the frequency corresponding to formula (5) is 1.936 GHz. Therefore, the resolvable relative velocity of PDV is... for: ； As can be seen from formula (6), for a signal with a given time length, it is necessary to increase the number of its change points to improve the speed resolution.

4. The four-well test and combined diagnostic method according to claim 3, characterized in that: The Short Time Fourier Transform (STFT) method applies a small analysis window function that can be shifted along the time axis to the signal. To extract the frequency components of the signal in this time domain, a Fourier transform is performed. Since the window function is movable, the Fourier transform of the signal within the required time range can be obtained. Its basic definition is: ； The Short-Time Fourier Transform (SFT) involves applying an analysis window in the time domain. Moving this window along the time axis yields the spectrum for each time interval. The frequency corresponding to the maximum magnitude within each time interval is then identified. Then, the average speed is obtained.

5. The four-well test and combined diagnostic method according to claim 4, characterized in that: In the comparative experiment, the particle dynamics behavior characteristics diagnosed by particles-PDV will observe the moment when the particle swarm motion disappears, which can provide an auxiliary reference for the cutoff time of the Asaywindow experiment.

6. The four-well test and combined diagnostic method according to claim 5, characterized in that: In the comparative experiment, the velocity initiation time of the interface is given in the Asay window signal, which is the time when the fastest particle arrives at the coating window. At the same time, the average velocity of particles arriving at the coating window at different times can also be obtained, which can be compared and corrected with the signal obtained by parts-PDV.

7. The four-well test and combined diagnostic method according to claim 6, characterized in that: In the comparative experiment, by comparing the particles / empty-Asay window, the cumulative mass change of the powder particles with both pore and void micro-sprays can be obtained simultaneously. Subtracting the two yields the areal mass of the deposited powder particles in the experiment. The process of change.

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