A tri-bevel diamond anvil cell and a design method thereof

Abstract

This invention relates to the field of ultra-high pressure physics experimental apparatus, and particularly to a three-faced diamond anvil cell and its design method. The anvil includes a central anvil face and sequentially connected first, second, and third inclined faces. Each inclined face has a radially increasing first to third diameter and a first to third inclined face angle, forming a gradient load-bearing transition zone. The design method includes: establishing a diamond-tungsten gasket coupled constitutive model; parametrically modeling the three-faced structure; performing finite element optimization with the goal of maximizing the pressure at the center of the sample chamber and constraints such as the maximum principal strain of the diamond as the basis; and determining the optimal geometric parameters. This invention breaks through the pressure bottleneck of approximately 400 GPa of traditional diamond anvil cells, achieving a static high pressure of 600 GPa, and reducing the risk of stress concentration and failure at the anvil face.

Description

Technical Field

[0001] This invention relates to the field of ultra-high pressure physics experimental apparatus technology, and in particular to a three-slanted diamond anvil cell and its design method. Background Technology

[0002] In existing technologies, to increase the maximum achievable pressure of a diamond anvil cell, methods such as reducing the diameter of the central anvil, using a beveled anvil, increasing the loading force, optimizing the gasket material, or employing a dual-stage anvil are commonly used. Among these, the single-beveled diamond anvil is a commonly used high-pressure anvil structure. It increases pressure by setting a bevel at a certain angle on the outer side of the central anvil, allowing the load to be more concentratedly transferred to the sample cavity region. However, in practical applications, traditional single-beveled anvils often face significant bottlenecks in the pressure range above approximately 400 GPa. Further increasing the loading force leads to significant elastic deformation, edge stress concentration, and the risk of local instability in the diamond anvil tip region, easily causing anvil cell damage or sample cavity depressurization, making it difficult to stably obtain higher pressures.

[0003] To further overcome the pressure limit of traditional single-sloping anvils, existing technologies have proposed annular anvils, bi-stage micro-anvils, and other complex microstructure anvil designs. These solutions can improve the stress state at the anvil tip to some extent and raise the static pressure to a higher range. However, such structures typically place extremely high demands on micro / nano fabrication precision, secondary anvil assembly, sample loading, and experimental alignment, resulting in problems such as high fabrication difficulty, complex operation, insufficient repeatability, and limited experimental windows. Especially in conventional diamond anvil cell experimental systems, complex anvil structures often struggle to balance high pressure output, convenient sample loading, and experimental repeatability. Furthermore, existing diamond anvil cell design methods still rely heavily on empirical parameters and simplified mechanical models. In existing simulation analyses, diamond materials are often simplified as linear elastic, isotropic, or small-deformation materials, making it difficult to accurately describe the large elastic deformation, anisotropic crystal response, and potential microscopic deformation mechanisms such as dislocations and twins that occur in diamond under pressures of hundreds of GPa. Meanwhile, the metal gasket undergoes significant large-deformation elastoplastic flow under extreme compression, and its flow behavior directly affects the sample cavity pressure, anvil stress concentration, and diamond failure risk. However, existing technologies often fail to perform unified coupling analysis of the complex constitutive response of diamond anvils and the large deformation elastoplastic behavior of tungsten gaskets, resulting in a lack of sufficiently reliable mechanical basis for anvil surface structure optimization. Summary of the Invention

[0004] The object of the present invention is to provide a three-inclined-plane diamond anvil cell (DAC) and its design method. By establishing a coupled constitutive model of diamond and tungsten gasket under extreme loads, the number of inclined planes, inclined plane diameter, inclined plane angle and anvil surface size of the diamond anvil are predicted and optimized, so that the DAC can break through the traditional pressure bottleneck of about 400 GPa without using a complex two-stage micro-anvil structure and achieve a pressure output of 600 GPa.

[0005] To achieve the above object, the present invention provides a three-inclined-plane diamond anvil cell, including a central anvil surface, a first inclined plane, a second inclined plane and a third inclined plane at the loading end of the diamond anvil; The central anvil surface is used to directly act on the tungsten gasket and the sample chamber; the first inclined plane connects the central anvil surface and the second inclined plane, the second inclined plane connects the first inclined plane and the third inclined plane, and the third inclined plane connects the second inclined plane and the external support area of the diamond anvil; the central anvil surface has a central anvil surface diameter d0, the first inclined plane has a first diameter D1 and a first inclined plane angle α1, the second inclined plane has a second diameter D2 and a second inclined plane angle α2, and the third inclined plane has a third diameter D3 and a third inclined plane angle α3; the first inclined plane, the second inclined plane and the third inclined plane form a gradient-bearing transition zone in the radial direction.

[0006] Preferably, the central anvil surface diameter d0 is 10 - 50 μm, the first diameter D1 is 150 - 350 μm, the first inclined plane angle α1 is 5° - 12°, the second diameter D2 is 350 - 550 μm, the second inclined plane angle α2 is 10° - 20°, the third diameter D3 is 500 - 700 μm, and the third inclined plane angle α3 is 15° - 25°.

[0007] Preferably, the central anvil surface diameter d0 is 20 μm, the first diameter D1 is 250 μm, the first inclined plane angle α1 is 8.5°, the second diameter D2 is 450 μm, the second inclined plane angle α2 is 15°, the third diameter D3 is 580 μm, and the third inclined plane angle α3 is 19° or 21°.

[0008] Preferably, the first diameter D1, the second diameter D2 and the third diameter D3 increase layer by layer radially outward, and the first inclined plane angle α1, the second inclined plane angle α2 and the third inclined plane angle α3 increase layer by layer radially outward, and satisfy D1 < D2 < D3 and α1 << α2 << α3, forming a gradient-bearing transition zone.

[0009] Preferably, a design method of a three-inclined-plane diamond anvil cell includes the following steps: S1. Establish a diamond-tungsten gasket coupled constitutive model, including a diamond large deformation constitutive sub-model and a tungsten gasket large deformation elastic-plastic constitutive sub-model; S2. Perform parametric modeling on the three-faced diamond anvil, and determine that the design variables include at least the central anvil diameter d0, the first diameter D1, the first facet angle α1, the second diameter D2, the second facet angle α2, the third diameter D3, and the third facet angle α3. S3. Finite element calculations were performed based on the coupled constitutive model and the parameterized model to obtain the sample cavity center pressure, maximum principal strain of diamond, equivalent stress, cumulative crystal plasticity, and external flow rate of tungsten gaskets under different combinations of geometric parameters. S4. Taking the maximization of the pressure at the center of the sample cavity as the optimization objective, and using the maximum principal strain of diamond, equivalent stress, cumulative crystal plasticity, and external flow rate of the tungsten gasket as constraints, the optimal combination of geometric parameters is determined to obtain a three-sided diamond anvil cell.

[0010] Preferably, in S1, the diamond large deformation constitutive model uses a fourth-order strain energy function to describe the anisotropic, nonlinear and large elastic deformation of diamond during the diamond anvil loading process. It also introduces close-packed dislocation slip, non-close-packed dislocation slip and twinning deformation mechanisms, and sets a failure limit of no more than 100 GPa for the maximum shear force, in order to characterize the local plastic activity and failure risk of diamond under extreme loads.

[0011] Preferably, in S1, the large deformation elastoplastic constitutive model of the tungsten gasket models the tungsten gasket as a large deformation isotropic elastoplastic material, considering the nonlinear effect of its elastic constant changing with pressure, in order to describe the elastoplastic yielding and non-associated plastic flow behavior of the gasket during the diamond anvil compression process.

[0012] Preferably, in S4, the constraints include: the maximum principal strain of diamond does not exceed the first preset threshold, the equivalent stress does not exceed the second preset threshold, the cumulative amount of crystal plasticity does not exceed the third preset threshold, and the external flow rate of the tungsten gasket does not exceed the fourth preset threshold; the optimal combination of geometric parameters makes the center pressure of the sample cavity of the three-sided diamond anvil cell reach about 600 GPa.

[0013] The advantages and beneficial effects of this invention compared to the prior art are: 1. This invention breaks through the pressure bottleneck of approximately 400 GPa of traditional diamond anvil cells by using a gradient geometry design of a three-sloping diamond anvil cell, achieving a static high-pressure output of 600 GPa, and significantly expanding the experimental pressure range for scientific research under extreme conditions.

[0014] 2. This invention is based on the diamond-tungsten gasket coupled constitutive finite element optimization method for anvil structure design. It integrates the large elastic deformation and crystal plasticity mechanism of diamond with the large deformation elastoplastic behavior of tungsten gasket for unified coupling analysis. It can accurately predict the stress and strain distribution and potential failure area of ​​diamond anvil under multi-megabar loading, so that the structural optimization has a reliable mechanical basis.

[0015] 3. This invention does not rely on a complex two-stage micro-anvil structure. It can achieve ultra-high pressure loading simply by optimizing the multi-sloping geometry of a single-crystal diamond anvil. This avoids the difficulties of assembling, sliding, positioning and loading samples in the two-stage micro-anvil, and reduces the complexity of the device and the cost of use.

[0016] 4. This invention, through a finite element optimization strategy that aims to maximize the pressure at the center of the sample cavity and constrains the maximum principal strain of diamond, equivalent stress, cumulative crystal plasticity, and external flow rate of the tungsten gasket, can systematically determine the optimal combination of diameter and angle for each level of inclined plane, effectively reducing the reliance of diamond anvil design on traditional trial and error.

[0017] 5. This invention has strong engineering applicability. It can guide the initial design of novel three-bevel diamond anvil cells, as well as be used for secondary optimization of existing single-bevel or double-bevel anvil structures. It can also be extended to high-pressure loading scenarios for other gasket materials or sample systems.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a three-sided diamond anvil cell in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the process of establishing an anisotropic elastoplastic constitutive model of diamond under large deformation in this embodiment of the invention. Figure 3 This is a flowchart illustrating the establishment of a large deformation isotropic elastoplastic constitutive model of a tungsten gasket in an embodiment of the present invention. Figure 4 This is a flowchart of a three-sided diamond anvil cell design method according to an embodiment of the present invention. Detailed Implementation

[0020] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] like Figure 1 As shown, the present invention provides a three-bevel diamond anvil cell, comprising a central anvil cell facet, a first bevel, a second bevel, and a third bevel at the diamond anvil loading end; The central anvil is used to directly act on the tungsten pad and the sample cavity; the first inclined surface connects the central anvil with the second inclined surface, the second inclined surface connects the first inclined surface with the third inclined surface, and the third inclined surface connects the second inclined surface with the external support area of ​​the diamond anvil; the central anvil has a central anvil diameter d0, the first inclined surface has a first diameter D1 and a first inclined surface angle α1, the second inclined surface has a second diameter D2 and a second inclined surface angle α2, and the third inclined surface has a third diameter D3 and a third inclined surface angle α3; the first inclined surface, the second inclined surface, and the third inclined surface form a gradient load-bearing transition zone in the radial direction.

[0023] In one embodiment, the loading end of the diamond anvil is provided with a central anvil face, a first inclined face, a second inclined face, and a third inclined face in sequence from top to bottom (or from center to outside). The central anvil face is a flat micro-tablet located at the top of the anvil, used to directly contact the tungsten pad and sample cavity and transmit axial load. The first inclined face surrounds the outer side of the central anvil face, with its inner edge connecting to the outer edge of the central anvil face and its outer edge connecting to the inner edge of the second inclined face. The outer edge of the second inclined face then connects to the inner edge of the third inclined face. The outer edge of the third inclined face finally transitions to the external support area of ​​the diamond anvil face (i.e., the cylindrical or truncated conical part of the anvil body). The central anvil face has a central anvil face diameter d0, the first inclined face has a first diameter D1 and a first inclined face angle α1, the second inclined face has a second diameter D2 and a second inclined face angle α2, and the third inclined face has a third diameter D3 and a third inclined face angle α3. Here, "slope angle" is defined as the angle between the slope and the anvil axis or horizontal reference plane, used to characterize the degree of slope inclination; "diameter" is defined as the maximum outer diameter of the corresponding slope on the horizontal projection plane. Since the diameters and angles of the three slopes are all distributed radially outward in a gradient pattern, the first, second, and third slopes together constitute a gradient load-bearing transition zone that extends outward from the central anvil. The function of this transition zone is to disperse the originally highly concentrated stress at the edge of the central anvil to a larger load-bearing area in the radial direction, causing the stress and strain fields inside the diamond to continuously decrease from the center outward, avoiding stress abrupt changes and local instability common in single-slope structures, thus providing a structural basis for overcoming the traditional pressure bottleneck of approximately 400 GPa.

[0024] Preferably, the diameter d0 of the central anvil is 10-50 μm, the first diameter D1 is 150-350 μm, the first bevel angle α1 is 5°-12°, the second diameter D2 is 350-550 μm, the second bevel angle α2 is 10°-20°, the third diameter D3 is 500-700 μm, and the third bevel angle α3 is 15°-25°.

[0025] In one embodiment, the diameter d0 of the central anvil is preferably 10 μm to 50 μm. This range balances high pressure generation efficiency with the mechanical strength of the anvil: a smaller diameter, while beneficial for increasing pressure, significantly increases processing difficulty and the risk of brittle fracture; a larger diameter makes it difficult to increase the pressure in the sample chamber. The first diameter D1 is preferably 150 μm to 350 μm, and the first bevel angle α1 is preferably 5° to 12°. This combination allows the load to transition smoothly from the central anvil to the first bevel, avoiding excessive shear stress at the first transition edge. The second diameter D2 is preferably 350 μm to 550 μm, and the second bevel angle α2 is preferably 10° to 20°. This bevel bears the main stress dispersion function, and its size range matches the bottom end support size of a conventional diamond anvil. The third diameter D3 is preferably 500 μm to 700 μm, and the third bevel angle α3 is preferably 15° to 25°. This bevel is close to the external support area. A larger diameter and angle are beneficial for uniformly introducing residual stress into the anvil body and preventing circumferential cracks from forming at the anvil waist. The above parameter range was determined through extensive finite element parameter scanning and high-pressure experiments. It can bring the sample cavity center pressure close to the target of about 600 GPa while ensuring the integrity of the diamond structure and the effectiveness of the tungsten pad support, and at the same time taking into account the feasibility of micromachining precision.

[0026] Preferably, the diameter d0 of the central anvil is 20 μm, the first diameter D1 is 250 μm, the first bevel angle α1 is 8.5°, the second diameter D2 is 450 μm, the second bevel angle α2 is 15°, the third diameter D3 is 580 μm, and the third bevel angle α3 is 19° or 21°.

[0027] In one embodiment, the central anvil diameter d0 is 20 μm, a size easily achievable with existing micromachining techniques and providing sufficient initial pressure amplification. The first diameter D1 is 250 μm, and the first bevel angle α1 is 8.5°. This combination significantly reduces the stress concentration factor at the edge of the central anvil while maintaining high-pressure sealing in the central region. The second diameter D2 is 450 μm, and the second bevel angle α2 is 15°. This bevel constitutes the main load transition zone. Finite element analysis has verified that the maximum shear force inside the diamond at this size can be controlled within a safe level. The third diameter D3 is 580 μm, and the third bevel angle α3 is either 19° or 21°. The 19° option is suitable for experimental scenarios requiring higher pressure limits, while the 21° option achieves a more conservative balance between pressure output and structural redundancy. Under the specific parameter combination mentioned above, finite element simulation calculations show that the pressure at the center of the sample chamber can reach approximately 600 GPa, and the maximum shear force of diamond does not exceed 100 GPa. This indicates that the three-sloped structure effectively suppresses local plastic activity and failure risk of diamond while achieving ultra-high pressure output.

[0028] Preferably, the first diameter D1, the second diameter D2, and the third diameter D3 increase layer by layer in the radially outward direction, and the first inclined plane angle α1, the second inclined plane angle α2, and the third inclined plane angle α3 increase layer by layer in the radially outward direction, and satisfy D1 < D2 < D3 and α1 << α2 << α3, forming a gradient-bearing transition zone.

[0029] In one embodiment, the monotonically increasing constraint relationship between the diameters of each inclined plane and the inclined plane angles in the three-inclined-plane diamond anvil is emphasized. Specifically, the first diameter D1, the second diameter D2, and the third diameter D3 increase layer by layer in the radially outward direction and satisfy D1 < D2 < D3; at the same time, the first inclined plane angle α1, the second inclined plane angle α2, and the third inclined plane angle α3 increase layer by layer in the radially outward direction and satisfy α1 << α2 << α3. Here, "radially outward" refers to the direction in which the radius increases from the center of the anvil axis toward the outer edge; "increasing layer by layer" means that the diameter and angle of the subsequent inclined plane are strictly greater than those of the previous one. This monotonically increasing geometric constraint ensures that there are no sudden changes in diameter or angle between adjacent inclined planes, thus forming a smooth curvature transition or tangent continuity at the intersection lines between the first inclined plane and the second inclined plane, and between the second inclined plane and the third inclined plane, avoiding stress singularities caused by geometric discontinuities. The multi-stage continuous bearing transition zone thus formed enables the stress contour lines inside the diamond anvil to spread uniformly in concentric circles from the center outward when the anvil bears an axial load, rather than having stress line concentration and local shear band concentration at the edge of a single inclined plane, significantly improving the structural stability of the anvil under a target pressure of about 600 GPa.

[0030] Preferably, as Figures 2-4 shown, a design method for a three-inclined-plane diamond anvil includes the following steps: S1. Establish a diamond-tungsten gasket coupling constitutive model, including a diamond large deformation constitutive sub-model and a tungsten gasket large deformation elastic-plastic constitutive sub-model; S2. Perform parametric modeling on the three-inclined-plane diamond anvil, and determine that the design variables at least include the center anvil surface diameter d0, the first diameter D1, the first inclined plane angle α1, the second diameter D2, the second inclined plane angle α2, the third diameter D3, and the third inclined plane angle α3; S3. Perform finite element calculations based on the coupling constitutive model and the parametric model to obtain the central pressure of the sample cavity, the maximum principal strain of the diamond, the equivalent stress, the crystal plasticity cumulative amount, and the outer flow rate of the tungsten gasket under different combinations of geometric parameters; S4. Take the maximization of the central pressure of the sample cavity as the optimization goal, and take the maximum principal strain of the diamond, the equivalent stress, the crystal plasticity cumulative amount, and the outer flow rate of the tungsten gasket as the constraint conditions to determine the optimal combination of geometric parameters and obtain the three-inclined-plane diamond anvil.

[0031] This embodiment discloses a design method for a three-faceted diamond anvil, including the following steps: S1, establishing a diamond-tungsten gasket coupled constitutive model. This model is composed of two sub-models connected by contact interface conditions. The diamond large deformation constitutive sub-model is responsible for describing the anisotropic hyperelastic response and crystal plastic evolution of the anvil, while the tungsten gasket large deformation elastoplastic constitutive sub-model is responsible for describing the yielding and flow behavior of the gasket. The two are coupled through displacement coordination and force balance at the anvil-gasket contact surface. S2, parametrically modeling the three-faceted diamond anvil. In computer-aided design (CAD) or finite element preprocessing software, the central anvil diameter d0, the first diameter D1, the first slope angle α1, the second diameter D2, the second slope angle α2, the third diameter D3, and the third slope angle α3 are defined as independently driveable design variables. A parametric geometric template is constructed to generate calculation models with different size combinations in batches. S3. Finite element analysis is performed based on a coupled constitutive model and a parametric model. An implicit nonlinear solver is used to simulate the DAC loading process. Key response quantities such as the sample cavity center pressure, maximum principal strain of diamond, equivalent stress, cumulative crystal plasticity, and external flow rate of the tungsten gasket are extracted under each combination of geometric parameters. S4. A multi-objective optimization problem is established, with maximizing the sample cavity center pressure as the single optimization objective. The constraints are that the four response quantities do not exceed their respective preset thresholds. Gradient optimization algorithms or surrogate model optimization algorithms are used to find the optimal solution in the parameter space. The final output is the optimal combination of geometric parameters that satisfies all constraints and maximizes the center pressure, thus obtaining the final design scheme of the three-sided diamond anvil cell. This method transforms the traditional experience-based trial-and-error design process into a quantitative inversion design based on mechanical simulation, significantly shortening the R&D cycle and improving design reliability.

[0032] Preferably, in S1, the diamond large deformation constitutive model uses a fourth-order strain energy function to describe the anisotropic, nonlinear and large elastic deformation of diamond during the diamond anvil loading process. It also introduces close-packed dislocation slip, non-close-packed dislocation slip and twinning deformation mechanisms, and sets a failure limit of no more than 100 GPa for the maximum shear force, in order to characterize the local plastic activity and failure risk of diamond under extreme loads.

[0033] In one embodiment, the sub-model employs a fourth-order strain energy function to describe the anisotropic, nonlinear, and large elastic deformation behavior of diamond during diamond anvil cell loading. The fourth-order strain energy function refers to the hyperelastic constitutive relation that retains the fourth-order term in the power series expansion of the strain invariants, capable of capturing the nonlinear changes in lattice parameters and stiffness differences between different crystal orientations of diamond under pressures of hundreds of GPa. Based on this, close-packed plane dislocation slip, non-close-packed plane dislocation slip, and twinning deformation mechanisms are introduced. "Close-packed planes" refer to the family of crystal planes with the highest atomic packing density in diamond crystals, where the critical shear stress required for dislocation slip along these planes is relatively low. "Twinning deformation" refers to a portion of the crystal undergoing symmetrical shearing along a specific crystal plane, forming a uniform shear with twin orientation. Meanwhile, the model is coupled with a failure limit of no more than 100 GPa for the maximum shear force. This limit serves as an upper limit criterion for the accumulation of crystal plasticity. When the maximum shear force at any integration point in the finite element calculation reaches or exceeds 100 GPa, the region is determined to enter a high-risk failure state. Through the above constitutive framework, the initiation location, evolution path, and potential failure risk of local plastic activity inside the diamond anvil under extreme loads can be accurately characterized, overcoming the limitation that traditional linear elastic or isotropic simplified models cannot predict microscopic damage on the anvil surface.

[0034] Preferably, in S1, the large deformation elastoplastic constitutive model of the tungsten gasket models the tungsten gasket as a large deformation isotropic elastoplastic material, considering the nonlinear effect of its elastic constant changing with pressure, in order to describe the elastoplastic yielding and non-associated plastic flow behavior of the gasket during the diamond anvil compression process.

[0035] In one embodiment, the sub-model models the tungsten gasket as a large-deformation isotropic elastoplastic material. "Large deformation" refers to the strain amplitude of the gasket during DAC compression, which can reach tens of percentage points, necessitating consideration of geometric nonlinear (finite strain) effects. "Isotropic elastoplastic" assumes that the macroscopic mechanical response of polycrystalline tungsten is the same in all directions, and its deformation can be decomposed into a recoverable elastic component and an unrecoverable plastic component. The model further considers the nonlinear effect of elastic constants (including elastic modulus and Poisson's ratio) changing with pressure; that is, as the sample chamber pressure increases, the elastic modulus of tungsten exhibits a pressure hardening trend. This effect is achieved by introducing a pressure-dependent elastic constant update function. The plastic flow behavior is described using the non-associated plastic flow rule. "Non-associated" means that the plastic potential function is different from the yield function, which can more accurately reflect the volumetric invariance or slight shear dilatation characteristics of tungsten under high-pressure shear. Through this constitutive model, finite element calculations can reproduce the elastoplastic yielding, radial outflow, and thickness reduction behavior of tungsten gaskets during diamond anvil compression, providing reliable mechanical input for predicting the uniformity of sample cavity pressure, the supporting reaction force of the gasket on the diamond anvil, and whether the outflow of the gasket exceeds the safety threshold.

[0036] Preferably, in S4, the constraints include: the maximum principal strain of diamond does not exceed the first preset threshold, the equivalent stress does not exceed the second preset threshold, the cumulative amount of crystal plasticity does not exceed the third preset threshold, and the external flow rate of the tungsten gasket does not exceed the fourth preset threshold; the optimal combination of geometric parameters makes the center pressure of the sample cavity of the three-sided diamond anvil cell reach about 600 GPa.

[0037] In one embodiment, the first preset threshold corresponds to the upper limit of the maximum principal strain of diamond. By applying a target pressure load to the tri-slope structure in the coupled constitutive model, the distribution extreme value of the maximum principal strain in the diamond region is monitored. The critical strain value at which this extreme value has not yet caused lattice instability or a significant drop in the stress-strain curve is taken as the threshold to ensure that the diamond is in the elastic-dominant stage. The second preset threshold corresponds to the upper limit of the equivalent stress. Based on the multiaxial strength limit of diamond under the corresponding confining pressure, combined with the failure risk index of a maximum shear force of 100 GPa, the safe envelope boundary of the equivalent stress peak value of the high stress zone of the anvil and subsurface in the finite element calculation is taken as the threshold. The third preset threshold corresponds to the upper limit of the cumulative amount of crystal plasticity. Based on the definition of the cumulative amount of equivalent plastic shear strain in the crystal plastic framework, the cumulative response curve of the shear strain of each slip system is tracked when the maximum shear force is close to 100 GPa. The inflection point value before the dislocation pile-up and twin intersection have formed a through crack channel is taken as the threshold to control the local plastic activity to be in a dispersed and reversible stage. The fourth preset threshold corresponds to the upper limit of the allowable flow rate outside the tungsten gasket. The radial displacement or mass flow rate of the gasket's outer edge under different geometric parameters is calculated using a finite element model. The critical flow rate value at which the gasket does not experience excessive radial leakage and the central region of the sample cavity still maintains effective support thickness is taken as the threshold. These four thresholds together constitute a multi-objective optimization safety constraint envelope. Under the optimal combination of geometric parameters, the pressure at the center of the sample cavity of the three-sided diamond anvil cell reaches approximately 600 GPa, simultaneously satisfying all threshold constraints and achieving a synergistic optimization of high-pressure output and structural safety.

[0038] In this embodiment, the diamond-tungsten pad coupled constitutive model includes two parts: a diamond crystal constitutive model and a tungsten pad constitutive model. For the diamond crystal, its elastic response is described using a nonlinear anisotropic elastic energy function, and its strain energy density function can be expressed as: ; in, , and These represent the second, third, and fourth order elastic constants, respectively. Represents the components of the Lagrange strain tensor. Based on the elastic deformation gradient. Constructing the Lagrange strain tensor : ; in, Let be the unit tensor. Further, by differentiating the strain energy function with respect to stress, we obtain the Cauchy stress in the diamond crystal: ; Where J is the deformation gradient The determinant. For crystal slip or twinning deformation, analytical shear stress is used as the driving force. : ; in, It is a second-order Piola-Kirchhoff stress. Let be the Schmid tensor of the α-th slip system or twin system. The activation condition of the slip system can be expressed as: ; in, The critical shear force inherent in the slip system. The resistance generated by slippage. When the above conditions are met, the slippage rate is described using the Orowan relation: ; in, The density of movable dislocations. For the size of the Burgers vector, The dislocation velocity is used, and the evolution of the defect density inside a diamond crystal is described by combining the equations for dislocation nucleation, annihilation, and multiplication: .

[0039] The activation criterion for twins is as follows: in, The critical shear stress at which the inherent twinning begins. The twin volume evolution is determined using: ; in, It is the shear strain constant. It is the twin volume evolution rate in the α-slip system.

[0040] For tungsten gaskets, a nonlinear isotropic elastoplastic constitutive model is adopted. Its elastic energy function is expressed as: ; in, G, L, m, n are elastic constants, I1, I2, I3 are strain invariants, and the Euler strain tensor is used. Describe the elastic deformation of the tungsten gasket: ; The relationship between the elastic constant and the pressure p is as follows: ; The corresponding Cauchy stress tensor is: ; The yield condition for tungsten gaskets is determined using a pressure-dependent method: Where s is the deviatoric stress tensor, and the yield strength varies with pressure as follows: ; When the yield function reaches zero, the plastic deformation is updated using the non-associated plastic flow rule: ; And the plastic multipliers are solved by Newton-Raphson iteration: ; When the following conditions are met: ; The stress update is considered to converge. Finally, a uniform tangent stiffness matrix Cd for the diamond crystal model and a uniform tangent stiffness matrix Cg for the tungsten gasket model are constructed respectively, which accelerates the convergence speed of the model.

[0041] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A tri-bevel diamond anvil cell characterized by, It includes the central anvil surface, the first inclined surface, the second inclined surface, and the third inclined surface at the loading end of the diamond anvil; The central anvil surface is used to directly act on the tungsten gasket and the sample chamber; the first inclined surface connects the central anvil surface and the second inclined surface, the second inclined surface connects the first inclined surface and the third inclined surface, and the third inclined surface connects the second inclined surface and the external support area of the diamond anvil; the central anvil surface has a central anvil surface diameter d0, the first inclined surface has a first diameter D1 and a first inclined surface angle α1, the second inclined surface has a second diameter D2 and a second inclined surface angle α2, and the third inclined surface has a third diameter D3 and a third inclined surface angle α3; the first inclined surface, the second inclined surface, and the third inclined surface form a gradient-bearing transition zone in the radial direction.

2. A tri-bevel diamond anvil cell according to claim 1, wherein, The central anvil surface diameter d0 is 10 - 50 μm, the first diameter D1 is 150 - 350 μm, the first inclined surface angle α1 is 5° - 12°, the second diameter D2 is 350 - 550 μm, the second inclined surface angle α2 is 10° - 20°, the third diameter D3 is 500 - 700 μm, and the third inclined surface angle α3 is 15° - 25°.

3. A tri-surfaced diamond anvil cell according to claim 2, wherein, The central anvil surface diameter d0 is 20 μm, the first diameter D1 is 250 μm, the first inclined surface angle α1 is 8.5°, the second diameter D2 is 450 μm, the second inclined surface angle α2 is 15°, the third diameter D3 is 580 μm, and the third inclined surface angle α3 is 19° or 21°.

4. A tri-bevel diamond anvil cell according to claim 1, wherein, The first diameter D1, the second diameter D2, and the third diameter D3 increase layer by layer radially outward, and the first inclined surface angle α1, the second inclined surface angle α2, and the third inclined surface angle α3 increase layer by layer radially outward, and satisfy D1 < D2 < D3 and α1 << α2 << α3, forming a gradient-bearing transition zone.

5. A method of designing a tri-bevel diamond anvil cell, characterized by, It includes the following steps: S1. Establish a diamond-tungsten gasket coupling constitutive model, including a diamond large deformation constitutive sub-model and a tungsten gasket large deformation elastic-plastic constitutive sub-model; S2. Perform parametric modeling on the three-inclined-surface diamond anvil, and determine that the design variables at least include the central anvil surface diameter d0, the first diameter D1, the first inclined surface angle α1, the second diameter D2, the second inclined surface angle α2, the third diameter D3, and the third inclined surface angle α3; S3. Perform finite element calculations based on the coupling constitutive model and the parametric model to obtain the central pressure of the sample chamber, the maximum principal strain of the diamond, the equivalent stress, the crystal plasticity accumulation, and the external flow of the tungsten gasket under different combinations of geometric parameters; S4. Take the maximization of the central pressure of the sample chamber as the optimization goal, and take the maximum principal strain of the diamond, the equivalent stress, the crystal plasticity accumulation, and the external flow of the tungsten gasket as the constraint conditions to determine the optimal combination of geometric parameters and obtain the three-inclined-surface diamond anvil.

6. The method of designing a tri-bevel diamond anvil cell according to claim 5, wherein, In the above S1, the diamond large deformation constitutive sub-model uses a fourth-order strain energy function to describe the anisotropy, nonlinearity, and large elastic deformation of the diamond during the loading process of the diamond anvil, and introduces the dislocation slip on the close-packed plane, the dislocation slip on the non-close-packed plane, and the twinning deformation mechanism, and sets a failure limit that the maximum shear force does not exceed 100 GPa to characterize the local plastic activity and failure risk of the diamond under extreme loads.

7. The method of designing a tri-bevel diamond anvil cell according to claim 5, wherein, In S1, the large deformation elastoplastic constitutive model of the tungsten gasket models the metallic tungsten gasket as a large deformation isotropic elastoplastic material, considering the nonlinear effect of its elastic constant changing with pressure, in order to describe the elastoplastic yielding and non-associated plastic flow behavior of the gasket during the diamond anvil compression process.

8. The method of designing a tri-bevel diamond anvil cell according to claim 5, wherein, In S4, the constraints include: the maximum principal strain of diamond does not exceed the first preset threshold, the equivalent stress does not exceed the second preset threshold, the cumulative amount of crystal plasticity does not exceed the third preset threshold, and the external flow rate of the tungsten gasket does not exceed the fourth preset threshold. Under the optimal combination of geometric parameters, the sample cavity center pressure of the three-sided diamond anvil cell is 600 GPa.

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