A method for simultaneous characterization of mechanical properties and microstructure of single granular materials

Abstract

The present invention discloses a method for simultaneously characterizing the mechanical properties and microstructure of a single granular body. This method is suitable for simultaneously characterizing the mechanical properties and microstructure of explosive granular bodies and other energetic material crystals or granular materials. The test process includes six steps: sample preparation, sample installation, parameter adjustment of a mechanical-optical microscope combined test system, mechanical-optical real-time monitoring testing, analysis of the granular body's compression performance and optical images, and simultaneous characterization of its mechanical properties and microstructure. A dedicated compression test fixture is designed, and an evaluation basis for the simultaneous characterization of mechanical properties and microstructure is proposed. The present invention monitors the deformation characteristics of a single granular body during compression. The test process is observable, and the test conditions are more scientific and reasonable, improving the accuracy of the characterization. The method is also simple to operate and requires less experimental personnel.

Description

Technical Field

[0001] The present invention belongs to the field of explosive performance and microstructure characterization, and relates to a characterization method for real-time monitoring of the compression performance and microstructure of a single granular body based on a mechanical-optical microscope combined test system, and in particular to a basic step and evaluation criterion for obtaining the stress-strain relationship and real-time microstructure changes of explosive granular bodies under mechanical load. Background Art

[0002] Typical high-energy explosive granules are formed by bonding energetic materials with polymer binders. Their microstructure consists of energetic material crystals, polymer binders, and micro-interfaces between the energetic material and the binder. During the compaction process, the granules undergo displacement, elastic deformation of the particles, and brittle deformation of some particles. Interfaces within the granules, such as between energetic material crystals, between energetic material crystals and polymer binders, and pores, all have varying effects on the granules' microstructure. The state changes of the granules and their components during the compaction of explosives are crucial for setting compaction parameters and controlling the density and quality of the finished parts. The deformation and crushing of granules are the stages where mechanical properties change most significantly. Therefore, analyzing the changes in the deformation and structural characteristics of granules under load is crucial and crucial for both granule forming and explosives quality control.

[0003] The simultaneous characterization of the mechanical properties and microstructure of a single granular body involves performing compression tests on a single granular body under load, simultaneously obtaining the granular body's compression properties and microstructural morphology, and characterizing and evaluating the granular body's deformation characteristics. The granular body pressing process has always been a "black box" process, making it difficult to directly observe the dynamic changes of the granular body and its components. Typically, methods for determining the microstructure and micromechanical properties of explosives primarily measure the internal structure of the crystal (such as cracks, crystals, and the lower limit of the total amount of voids) and micromorphology (such as aspect ratio, sphericity, and particle size). Liquid sinking and floating experiments and light transmission optical microscopy are used to observe internal defects in the crystal; scanning electron microscopy is used to observe the crystal surface structure; mercury porosimetry is used to determine pores ranging from 0.005 to 50 μm; and small-angle X-ray scattering is used to test internal micro- and nano-defects in the crystal. This method establishes the relationship between crystal particle defects and granular body formability, arguing that both internal and surface defects in the crystal affect the safety of the charge. Meanwhile, domestic quantitative characterization of microstructural integrity primarily relies on micromechanical damage and micro-image analysis. Because the compacting process remains a "black box," direct observation of the dynamic changes in the bulk and its components is difficult. Therefore, current methods primarily characterize the state of the compact, bulk, and explosive crystals at a specific pressure point. Current characterization techniques include electron microscopy, refractive index matching microscopy, polarizing microscopy, scanning electron microscopy, apparent density, and computed tomography (CT). With the advancement of control and computer technology, X-ray tomography has been increasingly applied to explosives microstructure characterization and process monitoring. X-ray tomography can non-destructively characterize the internal structural evolution of bulk particles during compression. Particle morphology changes and contact relationships can reveal the interaction patterns between compressed particles, while particle displacements indirectly reflect stress transfer within the explosive. These characterization methods rely solely on micromechanical properties and micro-image analysis of energetic material crystals and are clearly unsuitable for simultaneous characterization of both the micromechanical properties and microstructure of bulk materials. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for synchronously characterizing the mechanical properties and microstructure of a single granular body, so as to solve the problems existing in the synchronous characterization of micromechanics and microstructure of explosive granular bodies, energetic material crystals or other granular materials. The method includes the steps of sample preparation, sample installation, parameter adjustment of the mechanical-optical microscope combined test system, mechanical-optical real-time monitoring test, compression performance and optical image analysis of granular bodies, and synchronous characterization of mechanical properties and microstructure.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for simultaneously characterizing the mechanical properties and microstructure of a single granular body comprises the following steps:

[0007] Step 1: Sample preparation: crush the bulk material into particles that can pass through a 5.0 mm sieve, and remove the fine particles that pass through a 0.2 mm sieve. For bulk materials that can pass through a 5.0 mm sieve without crushing, use the original sample for testing.

[0008] Step 2: Specimen installation: Apply double-sided tape to the particle attachment surface of the compression test fixture dedicated to the mechanical stage. Place the individual particles on the double-sided tape to secure them. Then, secure the compression test fixture to the mechanical stage with nuts. Finally, place the mechanical stage on the stage of the optical microscope.

[0009] Step 3: Adjust the parameters of the mechanical-optical microscope combination system: According to the magnification of the optical microscope objective lens, adjust the working distance and magnification of the optical microscope objective lens, and at the same time adjust the light source direction, contrast, acquisition interval and acquisition time required for image acquisition; set the test rate, sampling interval and compression mode parameters of the mechanical test system;

[0010] Step 4: Mechanical-optical real-time monitoring test: Simultaneously click the mechanical stage drive button and the optical microscope real-time recording button. The mechanical test software records the stress, time, and strain parameters of the granular body under the compressive load. The optical microscope monitors the microstructure of the granular body under different deformation states in real time. When the specimen is observed to be completely deformed under the optical microscope, stop the drive button and the optical microscope recording button.

[0011] Step 5: Compression performance and optical image analysis of the granular body: The force-displacement curve and stress-strain curve of the granular body under compression are obtained through compression mechanics test data, and the image is recorded in real time by an optical microscope;

[0012] The compressive stress and strain formulas obtained from the compression mechanics test data are as follows:

[0013] σ=F / (π·r 2 )

[0014]

[0015] In the above formula, σ is stress, F is the force during the compression process of the granular body, r is the radius of the granular body, ε is the strain, Δl is the current deformation of the granular body, and l is the particle size of the granular body;

[0016] By recording images in real time through an optical microscope, the corresponding optical images of different deformation amounts, i.e., different displacements, can be obtained synchronously;

[0017] Step 6: Synchronous characterization of mechanical properties and microstructure: Synchronous correlation is performed on the compressive mechanical properties and the simultaneously acquired optical images. The relationship between the image numbers corresponding to the current displacement is as follows:

[0018] Δl=(l / P)×(n-1)

[0019] Derived: n = Δl / l × P + 1 = ε × P + 1

[0020] In the above formula, Δl is the current deformation of the granular body, i.e., the current displacement; l is the particle size of the granular body, i.e., the total displacement; P is the total number of images; n is the image sequence number; and ε is the strain;

[0021] Based on the displacement and strain in the force-displacement curve and stress-strain curve of the granular body, the corresponding optical images can be inferred to analyze its microstructure.

[0022] The present invention also includes the following technical features:

[0023] Specifically, the compression test fixture is made of hard aluminum and is an integrated structure, including a mounting end and a clamping end. The thickness of the mounting end and the clamping end are both 5.5 mm, the total width of the mounting end and the clamping end is 17 mm, the left and right length of the mounting end is 36 mm, and the left and right length of the clamping end is 10 mm. Four nut holes are provided on the mounting end, and the inner diameter of the nut hole is 4.2 mm, which is used for fixed installation on the mechanical carrier; the end face of the clamping end is a granular bonding surface with a size of 10 mm × 5.5 mm.

[0024] Specifically, there are two compression test fixtures, which are fixedly mounted on the mechanical platform in a mirror-symmetrical manner and with the compression ends of the two compression test fixtures facing each other. During the compression process, the granular body sticking surfaces of the two compression test fixtures approach each other to apply pressure to the granular body.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] The present invention can evaluate the mechanical properties and microstructure of a single granular body under a compressive load, solving the technical problem of the lack of a simultaneous characterization method for the micromechanics and microstructure of granular bodies.

[0027] The present invention adopts a mechanical-optical microscope test system to monitor the deformation characteristics of a single granular body during the pressing process. The test process is observable, the test conditions are more scientific and reasonable, and the accuracy of the characterization is improved. At the same time, the method is simple to operate and has low requirements for the experimenter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a method process for simultaneously characterizing the mechanical properties and microstructure of individual granular bodies.

[0029] Figure 2 yes Figure 1 Method for special compression fixture piece.

[0030] Figure 3 It is a mechanical-optical microscope combined test system.

[0031] Figure 4 It is the force-displacement (deformation) curve of the granular body.

[0032] Figure 5 It is the stress-strain curve of granular material.

[0033] Figure 6 are optical microscopic images at different displacement points.

[0034] The meaning of each number in the figure is:

[0035] 1. Compression fixture, 11. Mounting end, 12. Pressing end, 13. Nut hole, 2. Mechanical stage, 3. Data acquisition system, 4. Optical microscope, 41. Stage. DETAILED DESCRIPTION

[0036] The present invention is based on a large amount of research work and proposes a method for synchronous characterization of the mechanical properties and microstructure of a single granular body based on a mechanical-optical microscope combined test system. The method is suitable for the synchronous characterization of the mechanical properties and microstructure of explosive granular bodies, other energetic material crystals or granular materials, and includes sample preparation, sample installation, parameter adjustment of the mechanical-optical microscope combined test system, mechanical-optical real-time monitoring test, compression performance and optical image analysis of granular bodies, and synchronous characterization of mechanical properties and microstructure. A set of special compression test fixtures is designed in the method, and an evaluation basis for the synchronous characterization of mechanical properties and microstructure is proposed. The outstanding advantage of the present invention is that it can simultaneously obtain the compression performance of a single granular body and the changes in the deformation structure during the compression process. The test conditions are more scientific and reasonable, which solves the problem that the granular body has been in a "black box" state during the compression process.

[0037] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0038] Example 1:

[0039] like Figures 1 to 6 As shown, this embodiment provides a method for simultaneously characterizing the mechanical properties and microstructure of a single granular body. The granular body in this embodiment is: a certain explosive granular body, whose basic components are octogenol, FE2462, S33 plastic, paraffin, and polytetrafluoroethylene. The sample is in the form of quasi-spherical solid particles and is non-volatile.

[0040] like Figure 1 As shown, the single granular method provided by the present invention includes six steps: sample preparation, sample installation, parameter adjustment of the mechanical-optical microscope combined test system, mechanical-optical real-time monitoring test, compression performance and optical image analysis of the granular body, and simultaneous characterization of mechanical properties and mesostructure. The mechanical properties and mesostructure of a certain explosive granular body are simultaneously characterized according to the process steps of simultaneous characterization of the mechanical properties and mesostructure of the granular body.

[0041] The specific steps include:

[0042] Step 1, sample preparation: crush the bulk or granular materials into particles that can pass through a sieve with a mesh size of 5.0 mm, and remove the fine particles that pass through a sieve with a mesh size of 0.2 mm; for bulk or granular materials that can pass through a sieve with a mesh size of 5.0 mm without crushing, use the original sample for testing; arrange the bulk according to particle sizes such as 0.5 mm, 1 mm, and 1.5 mm to facilitate the exploration of mechanical property laws. In this embodiment, bulk with a particle size of about 1.5 mm is also screened out. When crushing explosive bulk, use non-ignitable tools or remote crushing mechanical equipment to prevent combustion and explosion safety accidents. All processed samples are not artificially dried to ensure that the test state is consistent with the actual state.

[0043] Step 2, sample installation: stick double-sided tape on the inner wall of the special compression test fixture of the mechanical stage, place a single granular body on the double-sided tape to fix it, then fix the test fixture to the mechanical stage through two nuts, and finally place the mechanical stage on the stage of the optical microscope. Specifically, first stick double-sided tape on the side of a compression test fixture with a length of 10mm and a width of 5.5mm, place granular bodies with a particle size of 1.5mm on the double-sided tape, then install the compression test fixture on the mechanical stage, and finally install another compression test fixture on the mechanical stage. After the two compression test fixtures are installed, the distance between the other compression test fixture and the sample is between 0.1mm and 0.2mm.

[0044] like Figure 2As shown in the figure, the compression test fixture is made of hard aluminum. The compression test fixture is an integrated structure, including a mounting end and a clamping end. The thickness of the mounting end and the clamping end are both 5.5 mm, the total width of the mounting end and the clamping end is 17 mm, the left and right length of the mounting end is 36 mm, and the left and right length of the clamping end is 10 mm. There are four nut holes on the mounting end, and the inner diameter of the nut hole is 4.2 mm, which is used for fixed installation on the mechanical carrier; the end face of the clamping end is the granular body bonding surface, with a size of 10 mm × 5.5 mm; there are two compression test fixtures, and the two compression test fixtures are fixedly mounted on the mechanical carrier in a mirror-symmetrical manner and the compression ends of the two compression test fixtures are opposite. During the compression process, the granular body bonding surfaces of the two compression test fixtures approach each other to apply pressure to the granular body; the maximum compression stroke between the two compression test fixtures is 5 mm, and compression tests can be performed on samples with a diameter of no more than 5 mm for granular bodies or granular materials.

[0045] Step three, adjustment of the parameters of the mechanical-optical microscope combination system: Since the present invention is aimed at the problem of synchronization between mechanical properties and microstructures, a mechanical acquisition system and an optical acquisition system are required for simultaneous real-time monitoring. According to the magnification of the optical microscope objective lens, adjust the working distance and magnification of the optical microscope objective lens, and at the same time adjust the direction of the light source, contrast, acquisition interval and acquisition time required for image acquisition; set the test rate, sampling interval time, compression mode and other parameters of the mechanical test system. Specifically, open the mechanical test system software, set the test mode to "compression", the sample sampling interval to 0.5s, and the test rate to 0.5mm / min; open the test software of the optical microscope, and adjust the magnification and working distance through the objective lens according to the state of the sample observed by the microscope until the sample is displayed as the largest and clearest. At the same time, the direction and contrast of the light source can be adjusted to adjust the best state of the observed sample. Finally, set the time interval for collecting images to mix, and the acquisition time to about 5min.

[0046] like Figure 3 As shown, the mechanical-optical microscope combined test system includes a mechanical stage, a data acquisition system and an optical microscope. The mechanical stage is arranged on the stage of the optical microscope and is located directly below the objective lens of the optical microscope. The data acquisition system is connected to the mechanical stage to collect test data.

[0047] Step 4, mechanical-optical real-time monitoring test: click the mechanical stage drive button and the optical microscope real-time recording button at the same time, the mechanical test software records the stress, time, strain and other parameters of the granular body under the compressive load; the optical microscope monitors the microstructure morphology of the granular body under different deformation states in real time, and stops the drive button and the optical microscope recording button when the specimen is completely deformed under the optical microscope. Specifically, press the mechanical stage drive button and the optical microscope real-time recording button at the same time, at this time, the mechanical software records the force, displacement (deformation), test rate and other parameters every 0.5s; the optical microscope saves a real-time image every mix time interval, and stops recording after the test is completed.

[0048] Step 5. Compression performance and optical image analysis of granular bodies: Through compression mechanics test data, the force-displacement curve and stress-strain curve of the granular body under compression force are obtained, and the images recorded in real time by the optical microscope are synchronously analyzed at key moments.

[0049] (1) The mechanical test system obtains the force F, time s and displacement (deformation) Δl during the compression process of the granular body. The force-displacement curve is shown in Figure 4 .

[0050] Through data processing:

[0051] σ=F / (π·r 2 )=F / (π·0.75 2 )

[0052] ε=Δl / l=Δl / 1.5

[0053] In the above formula, σ is stress, F is the force during the compression process of the granular body, r is the radius of the granular body, ε is the strain, Δl is the current deformation of the granular body, and l is the particle size of the granular body;

[0054] The compressive stress-strain curve of a certain explosive granular body is obtained as shown in Figure 5 .

[0055] (2) Real-time monitoring images of optical microscope

[0056] Through the video recording function of the optical microscope, a real-time image of the compression process of a certain explosive was obtained, and a photo was collected at a certain interval or a certain displacement. Figure 4 The force-displacement curves are shown in Figure 2 when the displacements are 0 mm, 0.35 mm, 0.8 mm, and 1.0 mm. Figure 6 (a)~(d).

[0057] Step 6: Synchronous characterization of mechanical properties and microstructure: Synchronous correlation is performed on the compressive mechanical properties and the simultaneously acquired optical images. The relationship between the image numbers corresponding to the current displacement is as follows:

[0058] Δl=(l / P)×(n-1)

[0059] That is: n = Δl / l × P + 1 = ε × P + 1

[0060] In the above formula, Δl is the current deformation of the granular body, that is, the current displacement (i.e., a point on the abscissa of the force-displacement curve), l is the particle size of the granular body, that is, the total displacement, P is the total number of images, n is the image number, and ε is the strain;

[0061] Based on the displacement and strain in the force-displacement curve and stress-strain curve of the granular body, the corresponding optical images can be inferred to analyze its microstructure.

Claims

1. A method for simultaneously characterizing the mechanical properties and microstructure of a single granular body, characterized in that: The following steps are involved: Step 1: Sample preparation: crush the bulk material into particles that can pass through a 5.0 mm sieve, and remove the fine particles that pass through a 0.2 mm sieve. For bulk materials that can pass through a 5.0 mm sieve without crushing, use the original sample for testing. Step 2: Specimen installation: Apply double-sided tape to the particle attachment surface of the compression test fixture dedicated to the mechanical stage. Place the individual particles on the double-sided tape to secure them. Then, secure the compression test fixture to the mechanical stage with nuts. Finally, place the mechanical stage on the stage of the optical microscope. Step 3: Adjust the parameters of the mechanical-optical microscope combination system: According to the magnification of the optical microscope objective lens, adjust the working distance and magnification of the optical microscope objective lens, and at the same time adjust the light source direction, contrast, acquisition interval and acquisition time required for image acquisition; Set the test rate, sampling interval, and compression mode parameters of the mechanical test system; Step 4: Mechanical-optical real-time monitoring test: Simultaneously click the mechanical stage drive button and the optical microscope real-time recording button. The mechanical test software records the stress, time, and strain parameters of the granular body under the compressive load. The optical microscope monitors the microstructure of the granular body under different deformation states in real time. When the specimen is observed to be completely deformed under the optical microscope, stop the drive button and the optical microscope recording button. Step 5: Compression performance and optical image analysis of the granular body: The force-displacement curve and stress-strain curve of the granular body under compression are obtained through compression mechanics test data, and the image is recorded in real time by an optical microscope; The compressive stress and strain formulas obtained from the compression mechanics test data are as follows: σ=F / (π·r 2 ) ε=Δl / l In the above formula, σ is stress, F is the force during the compression process of the granular body, r is the radius of the granular body, ε is the strain, Δl is the current deformation of the granular body, and l is the particle size of the granular body; By recording images in real time through an optical microscope, the corresponding optical images of different deformation amounts, i.e., different displacements, can be obtained synchronously; Step 6: Synchronous characterization of mechanical properties and microstructure: Synchronous correlation is performed on the compressive mechanical properties and the simultaneously acquired optical images. The relationship between the image numbers corresponding to the current displacement is as follows: Δl=(l / P)×(n-1) Derived: n = Δl / l × P + 1 = ε × P + 1 In the above formula, Δl is the current deformation of the granular body, i.e., the current displacement; l is the particle size of the granular body, i.e., the total displacement; P is the total number of images; n is the image sequence number; and ε is the strain; Based on the displacement and strain in the force-displacement curve and stress-strain curve of the granular body, the corresponding optical images can be inferred to analyze its microstructure.

2. The method for simultaneously characterizing the mechanical properties and microstructure of a single granular body according to claim 1, characterized in that: The compression test fixture is made of hard aluminum and is an integrated structure, including a mounting end and a clamping end. The thickness of the mounting end and the clamping end are both 5.5 mm, the total width of the mounting end and the clamping end is 17 mm, the left and right length of the mounting end is 36 mm, and the left and right length of the clamping end is 10 mm. Four nut holes are provided on the mounting end, and the inner diameter of the nut hole is 4.2 mm, which is used for fixed installation on the mechanical carrier; the end face of the clamping end is a granular body bonding surface with a size of 10 mm × 5.5 mm.

3. The method for simultaneously characterizing the mechanical properties and microstructure of a single granular body according to claim 2, characterized in that: There are two compression test fixtures, which are fixedly mounted on the mechanical platform in a mirror-symmetrical manner and with their compression ends facing each other. During the compression process, the granular body sticking surfaces of the two compression test fixtures approach each other to apply pressure to the granular body.

Images