In order to optimize the structure of anvils, finite element method is used to simulate two kinds of structures, one of which has a support ring but the other one does not. According to the simulated results, it is found that the maximum value of pressure appears at the center of culet when the bevelled angle is about 20°. Comparing the results of these two kinds of structures, we find that the efficiency of pressure transformation for the structure without support ring is larger than that for the structure with support ring. Considering the effect of von Mises stress, two kinds of tungsten carbide opposite anvils have been manufactured with bevelled angle of 10°. The experimental results for these two anvils are in good agreement with the simulation.
By employing neutron diffraction technique with in situ highpressure loading apparatus, it is accessible to detect on time the phase transition, strength, and texture of materials under extreme high pressure. As a powerful characterization method, this kind of in situ neutron diffraction technique has shed light on microstructure and properties of complex compounds [
The development of this technique benefited from the progress of opposite highpressure apparatus. Introduction of diamond anvil cell has revolutionized the study of materials under extreme high pressure [
Up to now, much attention has been paid to the finite element analysis, for studying the relationship between the structure of anvils and the pressure. The relationship between the stress and strain of diamond anvils has been analysed by the finite element modeling [
The highpressure loading apparatus mentioned in the present paper is designed as the normal MAOBELL type structure, which is schematically shown in Figure
Schematic diagram of in situ highpressure loading apparatus for neutron scattering experiment.
The simulation model contains two parts: a bevelled anvil and a pyrophyllite gasket. In particular, two kinds of anvils are made, one of which has the support ring and the other one does not. The material parameters used in the simulation are shown in Table
The material parameters used in the simulation [
Model  Material  Young’s modulus (GPa)  Poisson ratio  Density (kg m^{−3}) 

Anvil  YG8  600  0.22 

Support ring  45CrNiMoVA  206  0.30 

Gasket  Pyrophyllite  5.42  0.12  — 
Figure
Schematic configuration of tungsten carbide anvils (a) without and (b) with support ring.
As mentioned above, two kinds of structures are considered for the finite element models which are, respectively, with and without the support ring. An elasticplastic analysis is conducted on the anvils. A perfectly cohesive interface is supposed to exist between the anvil and gasket. Solid 95 is chosen as element type; choose target 170 and contact 174 as target surface type and contact surface type in ANSYS software. For the structure with a support ring, a uniform pressure load is applied along the underside of anvil or support ring. The axial crosssection of anvils is circular, and the finite model of 1/2 its semisectional view is shown as in Figure
The finite model of its semisectional view.
For the case of a uniform pressure over a circular area on a semiinfinite slab [
Figure
Relationship between the bevelled angles and the vertical stress.
In addition, we observe that stress increases from the center to the edge of culet under highpressure load. The concentration region of vertical stress isoline is not identical if the bevelled angle changed. Considering the increment range of vertical stress, it is from 20% to 35%. That is similar to the conclusion provided by Forsgren and Drickamer [
It has been proved that the shear stress determines the usage life of anvil [
Based on the simulation result, we find that the maximum value of shear stress appears at the edge of anvil face. Its value decreases from the edge to the center. Anymore, we find that the von Mises stress has intimate relations to the vertical stress that has similar changing trend, which has been referred to by Han et al. [
Considering that the maximum value of von Mises stress increases the risk of causing broken anvils, we set the bevelled angle to 10° and manufacture two kinds of anvils, whose shapes are the same as simulated models mentioned above. Then, we carry out a series of highpressure experiments using pyrophyllite as the gasket. The normal way to test the high pressure is based on Bridgeman’s research that chooses Bi and ZnTe as the materials to identify pressure, because these kinds of materials cause phase transition at special pressure [
The information shown in Table
The relationship between extra load and sample chamber pressure for models A and B.
ZnTe 
Extra load 
Pressure 
Bi 
Extra load 
Pressure 

III  7.8  5.5 ( 
III  5.5  2.55 ( 
IIIII  11.2  9.6 ( 
IIIII  8.0  2.7 ( 
IIIIV  13.8  12.6 ( 
IIIIV  12.0  7.7 ( 
According to the information, we could deduce two conclusions. The first one is that these simulated results are essentially consistent with the experiment data. However, it is obvious that whole simulation results are larger than experiment results. We ascribe this phenomenon to deviations in experiment progress, because we defined that every part in the system was perfectly contacted in simulation model. However, a perfectly cohesive interface is not actual in experiments. It is inevitable to introduce pressure loss. The second one is that model A has larger pressure transmission efficiency than model B. Analyzing the reason that resulted in this phenomenon, we focus on two factors. One is the effect that comes from different hardness of support ring and the other one is the pressure loss at contact surface between anvil and support ring. In order to judge the influence, we design the third anvil C with support ring using WC material and bevelled angle as 10°. A series of simulation experiments under different load were developed. Comparing the chamber pressure in different loading situation, we could find what introduced this effect.
In Figure
Relationship between the extra load and the chamber pressure using three kinds of anvils.
In this paper, a computational method that simulates stress distribution on tungsten carbide anvils used in opposite highpressure loading apparatus has been performed. We obtain that the opposite value of vertical stress is equal to the sample pressure at the center of culet. After completing a series of simulations, we deduce that the sample pressure generated by utilizing the structure of anvil with no support ring is higher than the structure of anvil with support ring. Comparing the simulation results and highpressure experiment results of anvils with bevelled angle as 10°, we find that relationships between them were similar. This conclusion is efficient to provide that this method introduced in this paper is correct. Utilizing this simulated method, people could obtain the optimum structure of anvils used in highpressure opposite apparatus easily. Based on these novel ways, in situ highpressure neutron diffraction technology would be much more powerful method to analyse the microstructure and properties of complex compounds.
The authors declare that there is no conflict of interests regarding the publication of this paper.