The establishment of the 3D solid model is based on the 3D design software such as AutoCAD to build the solid model and transform it into. The SAT file is imported into the finite element general-purpose calculation software for calculation. In order to reduce the size of the problem and increase the calculation speed, some rounding and chamfering can be removed, and the load and boundary conditions can be simplified as necessary. For example, between the connecting rod body and the bolt, the large and small head bearing and the connecting rod body Complex contact problems are treated as node coupling.
According to the structural characteristics of the connecting rod, the three-dimensional model and the meshing map of the connecting rod are selected according to the symmetry plane to select the 1/4 of the connecting rod for stress analysis, and the symmetric displacement constraint is applied on the symmetry plane. Considering that enough bolt preload is taken, the connecting rod and the big head cover are always close together, they are considered to be connected together in the finite element model, and the tetrahedral unit is used for meshing <1>, as shown.
Working condition and load calculation link in the work type: 120 or 180. The maximum compression load of the big head of the connecting rod and the maximum tensile load of the small head of the connecting rod are cosine distribution in the range of 120, and the maximum tensile load and the connecting head of the connecting rod The maximum compression load of the small head of the rod is cosine distributed in the range of 180, and the inertial force acts on all nodes <2>.
According to the design calculation diagram of the compressor, the maximum connecting rod force is 70kN, the connecting rod, the big head cover and the connecting rod bolt material are all alloy steel, the elastic modulus E=206GPa, the Poisson's ratio=0.3, and the ultimate tensile strength is 735MPa. <3>.
There are two types of stress states for analysis: a. The tension state is stressed. Because the cylinder arrangement of the ZW30/11.27 labyrinth seal compressor is vertical, the maximum tension condition of the connecting rod occurs when the compressor piston moves to near the bottom dead center, near the end of the exhaust.
b. Forced under pressure. The maximum compression condition of the connecting rod occurs when the compressor piston moves to near top dead center, near the end of the exhaust.
Stress analysis of the finite element stress analysis of the connecting rod The stress in this paper is obtained by the following formula: DBeB=LN(1) The strain matrix B is the matrix obtained by interpolating the coordinates of the interpolation function N, and the number of times the interpolation polynomial is obtained is Lower once. Therefore, the strain and stress accuracy obtained by the derivative operation are lower than the displacement u, that is, the solution obtained by the above two equations may have a large error, and the error of the stress solution is manifested in the following three aspects: a. Balance equation; b. The stress at the interface between the unit and the unit is generally discontinuous; c. The boundary condition of the force is generally not satisfied at the boundary S of the force.
Because the equilibrium equation, the boundary condition of the force, and the continuous condition of the internal force at the interface of the element are the Euler equations of the functional p, the Euler equation can be accurately satisfied only if the displacement variation is completely arbitrary. In the finite element method, only when the cell size tends to zero, the equilibrium equation, the boundary condition of the force, and the continuous condition of the force at the interface of the element can be accurately satisfied; when the cell size is finite, these equations can only be approximated. Satisfied. Unless the order of the actual stress changes is equal to or lower than the stress order of the unit used, only an approximate solution is obtained.
Smoothing of element stress based on least squares method It has been pointed out that the stress field solved by displacement element is discontinuous in the whole domain. In order to reduce the workload of improving the stress result, in the case of unit subdivision, the unit stress can be used locally. The method of smoothing and averaging gives a continuous stress field in the whole domain. When the cell size continues to shrink, the weighted least squares of the cell and the unweighted least squares of the cell are equivalent. Due to the positive definiteness of the function, the weighted least squares of the universe is the sum of the least squares of each cell. Therefore, when the unit is small enough, the smoothing can be performed in each unit.
When the connecting rod is pulled, the maximum pulling force value is 70kN, which is respectively loaded into the outer semicircle 120 range of the small end of the connecting rod (converted to the pressure according to the cosine distributed on the force surface) and the outer semicircle 180 of the connecting rod big head (converted to the pressure according to the cosine) Distributed on the force surface). The inertial force acts evenly on all nodes.
When the connecting rod is pressed, the maximum pressure value is 59kN, which is respectively loaded into the semicircle 180 range of the small end of the connecting rod (converted to the pressure according to the cosine distributed on the force surface) and the inner semicircle 120 range of the connecting rod head (converted to the pressure according to the cosine) Distributed on the force surface). The inertial force acts evenly on all nodes.
The stress calculation result of the connecting rod under the tension state is the stress contour map of the model x direction under the tension state. It can be seen that when the connecting rod is subjected to the tensile force, the maximum stress in the x direction (17014 MPa) appears on the outer side of the symmetry plane of the small head of the connecting rod, and the distribution is uneven; the stress value of the whole connecting rod is not large and evenly distributed. .
The design of the connecting rod design of the labyrinth compressor can be seen from the stress distribution diagram of the connecting rod of the labyrinth compressor. The maximum stress of the connecting rod in the tension state is concentrated at the small end of the connecting rod, and the top of the small end of the connecting rod should be Machining a boss to strengthen the strength here; the maximum stress of the connecting rod under pressure is concentrated on the connecting rod shaft near the big end of the connecting rod and the small end of the connecting rod. The design here should pay attention to the transition of the arc. To reduce the concentration of stress.
After the analysis and calculation, it can be affirmed that the connecting rod of ZW30/11.27 labyrinth seal compressor working under design pressure meets the strength requirement. Using ANSYS 8.0 software analysis, it is convenient to obtain the strength value of the labyrinth piston compressor connecting rod working under the design pressure, which provides a convenient and quick method and tool for the strength of the compressor parts, and also a maze. The design and manufacture of the compressor provides a theoretical basis.
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