CN109470577B - Method for representing internal stress of TATB-based PBX under force-heat action - Google Patents

Method for representing internal stress of TATB-based PBX under force-heat action Download PDF

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CN109470577B
CN109470577B CN201811319457.3A CN201811319457A CN109470577B CN 109470577 B CN109470577 B CN 109470577B CN 201811319457 A CN201811319457 A CN 201811319457A CN 109470577 B CN109470577 B CN 109470577B
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pbx
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徐尧
刘晨
肖盼
戴斌
杨占锋
李丽
李海宁
何荣芳
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Abstract

The invention discloses a method for representing the internal stress of a TATB-based PBX under the action of force and heat, which comprises the following steps: carrying out in-situ mechanical stress/thermal stress loading on the PBX, obtaining lattice parameters of the TATB crystal by utilizing a neutron diffraction technology, and obtaining the relation between mechanical stress and temperature and the lattice parameters of the TATB crystal; meanwhile, the mesoscopic structure of the PBX is obtained by utilizing an internal microstructure representation technology; and finally obtaining the response behavior rule of the TATB crystal inside the PBX under the action of thermal-force coupling by obtaining the performance inflection point of the PBX through the relationship between the mechanical stress, the temperature and the TATB lattice parameter and the microscopic structure. According to the invention, a neutron diffraction technology is introduced into the research field of energetic materials for the first time, and lattice parameters such as displacement, broadening, asymmetry and the like of a TATB crystal diffraction peak in a PBX under mechanical stress/thermal stress are observed noninvasively without damage, so that basic parameters are provided for macroscopic performance evaluation of the energetic materials.

Description

Method for representing internal stress of TATB-based PBX under force-heat action
Technical Field
The invention relates to a method for characterizing the internal stress of an explosive, in particular to a method for characterizing the internal stress of a TATB-based high polymer bonded explosive under the action of force and heat.
Background
TATB (1,3, 5-triamino-2, 4, 6-trinitrobenzene) is the only insensitive explosive which is currently approved by the U.S. department of energy, and has good safety and stability due to low mechanical sensitivity and thermal sensitivity. Polymer bonded explosives (PBX) based on TATB powder crystals are widely used in the domestic and foreign weapons industries, and research on structural safety, mechanical properties, and detonation properties has been a hot spot at home and abroad.
TATB-based PBX is formed by granulating TATB explosive crystals and an adhesive by a water suspension method into TATB particles (TATB granules) with certain particle size distribution and then pressing the TATB particles. In the forming process, elastic-plastic deformation with different degrees occurs due to the action of external pressure, and certain elastic strain energy can be accumulated after the pressure is removed to generate internal stress. The TATB explosive crystal and the adhesive have great difference in performance, so that the PBX has special mechanical properties different from the traditional particle-filled composite material, and the PBX is a brittle material containing initial damage as can be seen from a large number of microscopic observation and mechanical experiment results. The PBX is subjected to various mechanical and temperature loads during cold and hot processing, machining, transportation, use and storage, and internal stresses may be generated inside the PBX. The initial damage is further evolved by the internal stress, the mechanical property of the explosive is deteriorated in the forms of particle fracture, interface debonding, adhesive matrix cracking, deformation twin crystal, shear band and the like, and the strength and rigidity of the structure are reduced. Under continuous loading, various forms of damage can further grow, polymerize, form macrocracks, and ultimately lead to material failure.
The TATB-based PBX is a polycrystalline, multi-interface, heterogeneous, low-strength complex system formed by bonding and aggregating a plurality of TATB powder crystals, and the strength of the system is low (the compressive strength is less than 45MPa, and the tensile strength is less than 10 MPa). The internal stress will affect the mechanical behavior of each component inside the PBX, and the change of the mechanical behavior of each component inside the PBX is a major factor of the macroscopic change thereof. The research on the mechanical behavior of the PBX system needs to be started from a mesoscopic structure, so that a more accurate mechanical model can be built:
(1) TATB has a planar molecular structure, the crystal of the TATB belongs to a triclinic system and has a layered structure similar to graphite, stronger hydrogen bond action exists between TATB molecules on the same layer, the combination is tight, the action between different layers is very weak, and the response mechanism of a polycrystalline system is complicated due to the anisotropy. The TATB crystal belongs to a brittle material, and a high polymer used as a bonding agent has very good toughness, can bear large deformation, and can play a role in bonding explosive particles and transferring stress. The TATB crystal structure is asymmetric, under the condition of temperature rise, anisotropic expansion occurs, and the anisotropic expansion of the crystal is an important factor causing thermal deformation, internal microcrack and the like of the PBX. The mechanical behavior of each component in the PBX jointly determines the macroscopic performance of the PBX system.
(2) The physical and mechanical properties of PBX (PBX containing TATB group) are generally established on the basis of a stress-strain constitutive relation, microscopic factors such as explosive crystals, adhesives, desensitizers and plasticizers are not considered in detail, and different mechanical response characteristics exist in all components in the PBX under the action of force and heat, so that the research on the TATB strain response rule in the PBX under the action of external thermal stress and mechanical stress is of great significance, the understanding on the structure and performance change of the composite system is deepened, and basic parameters are provided for macroscopic performance evaluation of energetic materials and microstructure simulation of the materials.
In summary, the TATB-based PBX belongs to a typical polycrystalline multi-interface heterogeneous material, the strength of the material is low (the compressive strength is less than 45MPa, and the tensile strength is less than 10MPa), the thermal response of each component in a detailed PBX system is diverse and obvious in difference, the macroscopic mechanical properties are comprehensively influenced, and the research on the material has very important scientific and engineering significance.
Disclosure of Invention
The invention aims to provide a method for obtaining a response behavior rule of a TATB crystal inside a PBX under the action of force-thermal coupling by developing experimental research on neutron diffraction lattice parameters of the PBX and establishing a relation between mechanical stress, thermal stress and the neutron diffraction lattice parameters of the TATB crystal.
The invention is realized by the following steps:
a method for characterizing the internal stress of a TATB-based PBX under the action of force-heat, comprising the following steps:
carrying out in-situ mechanical stress/thermal stress loading on the PBX, obtaining lattice parameters of the TATB crystal by utilizing a neutron diffraction technology, and obtaining the relation between mechanical stress and temperature and the lattice parameters of the TATB crystal;
meanwhile, the mesoscopic structure of the PBX is obtained by utilizing an internal microstructure representation technology;
and finally obtaining the response behavior rule of the TATB crystal inside the PBX under the action of thermal-force coupling by obtaining the performance inflection point of the PBX through the relationship between the mechanical stress, the temperature and the TATB lattice parameter and the microscopic structure.
The further scheme is as follows:
the neutron diffraction technology specifically comprises the following steps:
and (3) controlling the external environment of the PBX by adopting a neutron stress diffraction spectrometer: the temperature is between 55 ℃ below zero and 200 ℃, and the mechanical stress is between 0MPa and 40MPa, so that TATB lattice parameters inside the PBX under the complex force and thermal environment are obtained.
The further scheme is as follows:
the relation between the mechanical stress and the temperature and the lattice parameter of TATB lattice is obtained by the following method:
changes in stress and temperature result in changes in lattice spacing, neutron diffraction measures the lattice spacing between crystallographic planes to derive elastic strain, and then the stress and coefficient of thermal expansion are calculated from the strain. When a crystalline material is irradiated with radiation of a wavelength close to its interplanar spacing, the radiation will be diffracted to form a specific bragg peak, the angle produced by the diffracted radiation being given by the bragg diffraction law:
2dhkl sinθhkl＝λ (1)
in the formula: λ is the wavelength of the radiation; dhkl(hkl) interplanar spacing to produce a bragg peak; thetahklIs the bragg angle.
The observed position of the diffraction peak being related to the incident beam2θhklThe angle, the strain measurement, is in the direction of the scattering vector, which bisects the angle between the incident and diffracted beams. The magnitude of the strain ε can be calculated from the change in interplanar spacing d measured from the sample:
Figure BDA0001857153970000031
in the formula (d)0The values of the interplanar spacing of the unstressed standard sample are shown.
For neutrons generated by a steady-state reactor, a monochromator is used for selecting a neutron beam with a certain fixed wavelength, and the change (delta d) of the interplanar spacing of a sample can cause the corresponding diffraction peak position shift (delta theta). In this way, the diffraction peak of a certain crystal face of the sample is measured, and the peak position of the diffraction peak is determined using a Gaussian/Lorentzian fitting program. The elastic strain therefore becomes:
Figure BDA0001857153970000032
in the formula, theta0The peak position of the Bragg diffraction peak of the unstressed standard sample is shown.
When the principal direction is known, 3-direction measurements are sufficient to determine a complete stress tensor.
Figure BDA0001857153970000033
Figure BDA0001857153970000034
Figure BDA0001857153970000035
Wherein E is the elastic modulus, v is the Poisson's ratio, εxx、εyyAnd εzzThe elastic strain in 3 directions in space was measured from the sample, respectively.
The linear relation between the mechanical stress/temperature of the TATB explosive crystal in a loose state and the neutron diffraction lattice parameter of the TATB crystal is obtained.
The further scheme is as follows:
the internal microstructure characterization technique includes: scanning Electron Microscope (SEM) techniques, microfocus X-ray tomography (μ CT) techniques, neutron small angle scattering (SANS) techniques, etc.
The Scanning Electron Microscope (SEM) technology is a common observation means, is usually used for microscopic characterization of materials with the thickness of 10 nm-1 mm, and can realize high-precision observation of PBX profiles.
The micro-focus X-ray tomography (mu CT) technology is a technology which can obtain three-dimensional structural information of (sub) micron scale in a material without damage. The finite element method and the image digital correlation method combined with the CT image can realize accurate modeling of defects such as cracks and pores in the PBX and accurate measurement of a displacement field.
The neutron small angle scattering (SANS) technique is a powerful tool for quantitative characterization of material porosity, and it allows for resolution of open and closed porosity, resulting in more accurate measurements of total porosity and surface area. And developing a neutron small-angle diffraction characterization technical study, and realizing the quantitative analysis of the PBX microholes.
The above techniques are all the mature prior art, and the present invention can select one or more of them to obtain the mesoscopic structure of the PBX. The application of the above technology is a conventional scheme in the field, and is not described in detail here.
The further scheme is as follows:
the performance inflection point is the inflection point of PBX mesoscopic structure change obtained by an internal microstructure characterization technology.
The characteristic and innovation of the invention are that the neutron diffraction technology is introduced into the research field of energetic materials for the first time, lattice parameters such as displacement, broadening, asymmetry and the like of a TATB crystal diffraction peak in a PBX under mechanical stress/thermal stress are observed noninvasively and nondestructively, the role played by the TATB crystal and a binder in different mechanical stress loading and temperature loading stages in a PBX system is researched from a microscopic scale, response behaviors such as lattice strain and thermal expansion of the TATB crystal and the thermodynamic evolution rule of interaction behaviors of the TATB crystal and the binder are deeply analyzed, and basic parameters are provided for macroscopic performance evaluation of the energetic materials, so that the invention is an innovation of a mechanical microscopic scale research mode of the high-filling composite material with the characteristics of multi-scale and disordered microstructure.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a schematic diagram of a neutron diffraction-in-situ force-thermal effect synchronous scan according to an embodiment of the present invention.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments.
As shown in fig. 1, the present invention provides a method for characterizing the stress in a TATB-based PBX under the action of force-heat, comprising the steps of:
carrying out in-situ mechanical stress/thermal stress loading on the PBX, obtaining lattice parameters of the TATB crystal by utilizing a neutron diffraction technology, and obtaining the relation between mechanical stress and temperature and the lattice parameters of the TATB crystal;
meanwhile, the mesoscopic structure of the PBX is obtained by utilizing an internal microstructure representation technology;
and finally obtaining the response behavior rule of the TATB crystal inside the PBX under the action of thermal-force coupling by obtaining the performance inflection point of the PBX through the relationship between the mechanical stress, the temperature and the TATB lattice parameter and the microscopic structure.
Each of the specific steps of the present invention will be described in detail below.
(1) PBX in-situ neutron diffraction under force and heat conditions
The PBX belongs to a low-strength material, and has a compressive strength of less than 45MPa and a tensile strength of less than 10 MPa; the PBX performance evaluation temperature range is-55-200 ℃; the PBX has explosion risk in a high-temperature state, and is suitable for carrying out small sample tests; in addition to the requirement of neutron diffraction method for steady state reaction neutron reactor. The invention is based on a neutron stress diffraction spectrometer of the nuclear physics and chemical research institute of China institute of engineering and physics, and realizes the nondestructive representation of TATB lattice parameters inside a PBX in a complex force and thermal environment (the temperature is-55-200 ℃, and the mechanical stress is 0-40 MPa).
The neutron stress diffraction spectrometer is a neutron stress diffraction spectrometer of nuclear physics and chemical research institute of China institute of engineering and physics, the resolution delta d/d of the spectrometer is 0.2%, the strain resolution is 50 mu epsilon, and the neutron beam intensity at the position of a sample is as follows: 5.7X 106 n.cm-2 s-1 (20 MW stack power), Adjustable neutron wavelength Range: 0.12nm to 0.28nm, normalized (sampled) volume range: 0.5mm multiplied by 0.5mm to 5mm multiplied by 20mm, the maximum bearing of the sample stage: 500kg, with 5 degrees of freedom (X-Y horizontal movement. + -.300 mm, Z elevation 500mm, rotation 0-360 DEG, inclination. + -.30 DEG), available diffraction angle range: 0 to 140 degrees. Neutron diffraction internal stress measurement is carried out on a sample according to GB/T26140-2010/ISO/TS 21432:2005 neutron diffraction method for nondestructive testing residual stress, lattice spacing between crystallographic planes is measured through neutron diffraction, elastic strain is derived from change of the lattice spacing, and then stress is calculated according to the strain.
The operating principle of neutron stress diffraction spectrometers is described in detail in the above-mentioned national standards.
In the invention, a conventional experimental device capable of realizing the thermal loading effect can be adopted, as long as the PBX can be ensured to carry out in-situ neutron diffraction within the temperature and mechanical stress range meeting the requirements.
In order to realize the lossless representation of TATB lattice parameters inside a PBX in a mechanical loading environment (mechanical stress is 0-40 MPa), a mechanical loading unit is required to have four load loading capacities of tension, compression (uniaxial compression/disc compression), three-point bending and four-point bending within a sample size range of 2mm-30mm and provide a replaceable clamp; the mechanical loading capacity (tension/compression) is not less than 5KN, the reading precision is 1 percent, and the minimum resolution of the loading force is not more than 1N; the stroke of the chuck is not less than 20mm, and the displacement speed range is 0.1mm/min to 2 mm/min.
In order to realize the nondestructive representation of TATB lattice parameters inside a PBX in a high-low temperature loading environment (the temperature is minus 55 ℃ to 200 ℃), the high-low temperature loading range of a high-low temperature loading unit is required to be minus 55 ℃ to plus 200 ℃, the reading precision is not greater than 1 ℃, the temperature fluctuation is not greater than 1 ℃, and the temperature retention time is not less than 20 hours, thereby providing a solution for automatic temperature control.
Based on the above requirements for mechanical loading (force loading) and high and low temperature loading (thermal loading), those skilled in the art can design the relevant thermal loading experimental apparatus according to the above requirements, as long as the requirements of the PBX for thermal and force loading can be satisfied.
(3) Experimental study on relation between mechanical stress/temperature and TATB crystal neutron diffraction lattice parameter
Changes in stress and temperature result in changes in lattice spacing, neutron diffraction measures the lattice spacing between crystallographic planes to derive elastic strain, and then the stress and coefficient of thermal expansion are calculated from the strain. When a crystalline material is irradiated with radiation of a wavelength close to its interplanar spacing, the radiation will be diffracted to form a specific bragg peak, the angle produced by the diffracted radiation being given by the bragg diffraction law:
2dhkl sinθhkl＝λ (1)
in the formula: λ is the wavelength of the radiation; dhkl(hkl) interplanar spacing to produce a bragg peak; thetahklIs the bragg angle.
The observed position of the diffraction peak is 2 theta to the incident beamhklThe angle, the strain measurement, is in the direction of the scattering vector, which bisects the angle between the incident and diffracted beams. The magnitude of the strain ε can be calculated from the change in interplanar spacing d measured from the sample:
Figure BDA0001857153970000061
in the formula (d)0The values of the interplanar spacing of the unstressed standard sample are shown.
For neutrons generated by a steady-state reactor, a monochromator is used for selecting a neutron beam with a certain fixed wavelength, and the change (delta d) of the interplanar spacing of a sample can cause the corresponding diffraction peak position shift (delta theta). In this way, the diffraction peak of a certain crystal face of the sample is measured, and the peak position of the diffraction peak is determined using a Gaussian/Lorentzian fitting program. The elastic strain therefore becomes:
Figure BDA0001857153970000062
in the formula, theta0The peak position of the Bragg diffraction peak of the unstressed standard sample is shown.
When the principal direction is known, 3-direction measurements are sufficient to determine a complete stress tensor.
Figure BDA0001857153970000063
Figure BDA0001857153970000064
Figure BDA0001857153970000065
Wherein E is the elastic modulus, v is the Poisson's ratio, εxx、εyyAnd εzzThe elastic strain in 3 directions in space was measured from the sample, respectively.
The mechanical stress/temperature of the TATB explosive crystal in a loose state and the neutron diffraction lattice parameter of the TATB crystal are in a linear relation; the force-thermal response of TATB explosive crystals in the state of a polycrystalline pressing PBX system is more complicated.
(4) Precise characterization method of PBX (private branch exchange) mesoscopic structure
The project combines a microscopic scale precise characterization method to master the inflection point of the variation of the microscopic structure, realize the precise analysis of different thermal response behaviors of the TATB crystal inside the PBX, and provide experimental support for the research of the mechanical behavior rule of the TATB crystal. Wherein:
the Scanning Electron Microscope (SEM) technology is a common observation means, is usually used for microscopic characterization of materials with the thickness of 10 nm-1 mm, and can realize high-precision observation of PBX profiles.
The micro-focus X-ray tomography (mu CT) technology is a technology which can obtain three-dimensional structural information of (sub) micron scale in a material without damage. The finite element method and the image digital correlation method combined with the CT image can realize accurate modeling of defects such as cracks and pores in the PBX and accurate measurement of a displacement field.
The neutron small angle scattering (SANS) technique is a powerful tool for quantitative characterization of material porosity, and it allows for resolution of open and closed porosity, resulting in more accurate measurements of total porosity and surface area. And developing a neutron small-angle diffraction characterization technical study, and realizing the quantitative analysis of the PBX microholes.
(5) Research on response behavior rule of TATB crystal in PBX under force-thermal coupling effect
Due to the fact that the PBX system plays different roles in TATB crystals and binding agents under the action of mechanical stress and temperature, particularly highly-filled TATB crystals, due to the characteristics of the PBX system and the complex system environment, TATB crystal lattice parameters and microscopic structure changes under the action of thermal coupling can be combined to further study the response behavior rules of the TATB crystals, and basic parameters are provided for macroscopic performance evaluation.
Based on the research of mechanical stress/temperature response of loose TATB crystals, on the basis of carrying out a lot of PBX in-situ mechanical stress loading neutron diffraction experiments and mastering the mechanical response rule of the TATB crystals inside the PBX, the research is gradually deepened to the TATB crystals inside the PBX under the condition of in-situ temperature change, the force-heat composite in-situ loading and experimental data analysis technology for the PBX is developed by combining a precise characterization method of a PBX microscopic structure, the variation rule of neutron diffraction lattice parameters of the TATB crystals is mastered, the internal stress response rule of the PBX under the variation of environmental conditions such as force, heat and the like is deepened, and experimental data input is provided for the PBX macroscopic performance evaluation criterion.
Although the present invention has been described herein with reference to the illustrated embodiments thereof, which are intended to be preferred embodiments of the present invention, it is to be understood that the invention is not limited thereto, and that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.

Claims (2)

1. A method of characterizing the stress in a TATB-based PBX under the action of force-heat, comprising the steps of:
carrying out in-situ mechanical stress/thermal stress loading on the PBX, obtaining lattice parameters of the TATB crystal by utilizing a neutron diffraction technology, and obtaining the relation between mechanical stress and temperature and the lattice parameters of the TATB crystal;
meanwhile, the mesoscopic structure of the PBX is obtained by utilizing an internal microstructure representation technology;
obtaining a performance inflection point of the PBX through the relationship between mechanical stress, temperature and TATB lattice parameters and a microscopic structure, and finally obtaining a response behavior rule of a TATB crystal inside the PBX under the action of thermal-force coupling; the performance inflection point is an inflection point of PBX mesoscopic structure change obtained by an internal microstructure representation technology;
the neutron diffraction technology specifically comprises the following steps:
and (3) controlling the external environment of the PBX by adopting a neutron stress diffraction spectrometer: the temperature is between 55 ℃ below zero and 200 ℃, and the mechanical stress is between 0MPa and 40MPa, so that TATB lattice parameters inside the PBX under the complex force and thermal environment are obtained;
the relation between the mechanical stress and the temperature and the lattice parameter of TATB lattice is obtained by the following method:
changes in stress and temperature can result in changes in lattice spacing, neutron diffraction measures the lattice spacing between crystallographic planes to derive elastic strain, and then the stress and coefficient of thermal expansion are calculated from the strain; when a crystalline material is irradiated with radiation of a wavelength close to its interplanar spacing, the radiation will be diffracted to form a specific bragg peak, the angle produced by the diffracted radiation being given by the bragg diffraction law:
Figure DEST_PATH_IMAGE002
（1）
in the formula: λ is the wavelength of the radiation; dhklHkl interplanar spacing to produce bragg peaks; thetahklIs a Bragg angle;
the observed position of the diffraction peak is 2 theta to the incident beamhklAngular, strain measurements are in the direction of the scattering vector, which bisects the incident beam and the diffractionThe included angle of the beam; the magnitude of the strain ε can be calculated from the change in interplanar spacing d measured from the sample:
Figure DEST_PATH_IMAGE004
（2）
in the formula (d)0The value of the interplanar spacing of the stress-free standard sample is shown;
for neutrons generated by a steady-state reactor, selecting a neutron beam with a certain fixed wavelength by using a monochromator, wherein the change delta d of the crystal face spacing of a sample can cause the corresponding diffraction peak position to shift delta theta; measuring the diffraction peak of a certain crystal face of the sample by using the method, and determining the peak position of the diffraction peak by using a Gaussian/Lorentzian fitting program; the elastic strain therefore becomes:
Figure DEST_PATH_IMAGE006
（3）
in the formula, theta0The peak position of a Bragg diffraction peak of the unstressed standard sample is shown;
when the principal direction is known, 3-direction measurements are sufficient to determine a complete stress tensor;
Figure DEST_PATH_IMAGE008
（4）
Figure DEST_PATH_IMAGE010
（5）
Figure DEST_PATH_IMAGE012
（6）
wherein E is the elastic modulus, v is the Poisson's ratio, εxx、εyyAnd εzzRespectively measuring elastic strain in 3 directions in space from a sample;
the linear relation between the mechanical stress/temperature of the TATB explosive crystal in a loose state and the neutron diffraction lattice parameter of the TATB crystal is obtained.
2. The method of characterizing TATB-based PBX intrinsic stress under force-heat according to claim 1, wherein:
the internal microstructure characterization technique includes: scanning electron microscopy, microfocus tomography or neutron small-angle scattering.
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