Finite element analysis of high-pressure pipeline fixed valve O-ring

Abstract: Using ANSYS to establish a nominal diameter 1500mm, fixed nominal pressure 15MPa high-pressure pipeline ball valve shell and flange joint of rubber O rings to seal the two-dimensional axisymmetric model, the five constant strain energy density function rubber materials Mooney-Revlin constant, the analysis obtained after installation of the contact pressure can not guarantee seal, the contact pressure than the working pressure in the working load is applied, and less than the material allowable pressure, can guarantee the seal. And analyze the contact pressure of the same trench, different cross-section, different compression ratio, section size the greater the compression ratio the greater the width of the contact pressure and the notch fillet radius on the shear stress, the results show that the maximum The contact pressure is greater. Width of contact pressure did not affect the influence of shear stress in the notch fillet radius smaller.

Key words: finite element analysis of the O-shaped rubber ring contact pressure

0 Introduction

Rubber O rings for its low cost, simple structure, as well as to install and easy to use, it is widely used in automotive, power machinery and fluid hydraulic machinery and other fields [1]. In the course is to rely on the rubber itself the flexibility to pre-compression, given to the sealing surface contacts, the formation of the contact pressure on the contact surface to reach the seal. In general, the amount of compression of the O-ring and groove reasonable choice is crucial. At present, however, domestic rubber O-ring design is basically rely on empirical data and qualitative principles. Contact deformation of the O-ring groove and contact stress distribution on the sealing interface is an important parameter affecting its sealing performance. Rubber seal design involves a wide range of theoretical knowledge of solid mechanics, tribology, the science of polymer materials, liquid erosion, and mechanical manufacturing processes, and thus on the contact deformation of the rubber seal in the installation and use of the seal interface accurate calculation of stress, in theory, there is a big difficulty. But with the computer performance, exposure to problem solving methods to produce large finite element analysis software development, simulation analysis for the use of rubber seals, researchers have some success in this regard. The authors use the ANSYS software, combined with the nominal diameter 1500mm, the nominal pressure 15MPa high-pressure pipelines fixed ball shell and the large diameter of the flange O-ring static seal instance, stress and exposure to the rubber O rings in the high-pressure conditions stress finite element analysis is a significant work in a fixed ball of the high-pressure pipeline design and use of rubber O rings to provide a scientific basis.

Establishment of a rubber O-ring finite element model

1.1 Geometric model for finite element analysis of the seals, in view of the complexity of its boundary conditions, so the seals and seal structure of the shell, flange grooves as a whole for analysis. According to the characteristics of the geometry of the sealing structure, materials, boundary conditions, and ANSYS model of the O-shaped rubber seals can be simplified for the plane axisymmetric model [2]. Plane axisymmetric model to simulate three-dimensional structure, the use of expanded command in the ANSYS can observe the changes of the three-dimensional model, so not only does not affect the calculation results, and can improve the calculation speed and thus save a lot of computing time. The establishment of the shell and the flange connection sealed with rubber O rings plane axisymmetric model and the structural parameters shown in Figure 1. Diameter of 100mm, the length of the groove dimensions of 120.28mm, height 80mm.

1.2 Material model rubber sealing material stress-strain relationship is extremely complex, nonlinear characteristics, some scholars have raised is dedicated to describing the function of the rubber material, such as the Mooney-Revlin, Klosenr-Segal model and Bi-derman model. To cope with the finite element program, the Newton-Raphson algorithm for solving nonlinear problems of selection of the Mooney-Revlin [3-4] model to establish the elastoplastic constitutive model of rubber seals.

(1)

Where I1, I2 and I3 for the deformation tensor invariants, λ1 and λ2 and λ3 are the main elongation ratio, γi main strain. For incompressible materials, J = 1.

The more constant the number, the statistics of the curve is more close to true value (ie, better fit), and in this article, we use the finite element analysis of the five constant strain energy density function expansion to rubber contact, in the definition of rubber materials need to enter the six constants, a10, a01, a20, a11, a02, d.

Five constant strain energy density function expansion:

1.3 meshing nitrile rubber Shore hardness (Ha) for 90, the elastic modulus E = 20.925Mpa, Poisson's ratio μ = 0.499, sealing pressure of 15MPa, the analysis model, rubber unit hyperelastic unit HYPER182 shell body and the flange groove unit with linear solid elements PLANE82 model also contains the contact element in ANSYS to establish contact TARGE169, and CONTA172 [5]. Set the shell and the elastic modulus of the flange groove 2E5MPa, Poisson's ratio to 0.3, the Mooney-Rivlin constant

a10 = -4.405658641516, a01 = 6.6154021287924,

a20 = 13.799220070701, a11 = -33.941890263197,

a02 = 23.224803908225, d = .0044194869745528 The

Due to the material of the shell and the flange groove is much higher than the modulus of elasticity of the O-ring material, the shell and the flange groove as a rigid body, using the rigid body type of modeling. The rubber O-ring is a typical incompressible materials. In order to reduce the scale of the model to reduce the computational time to refine the grid in the area of ​​contact may occur, and improve the accuracy of the results. In order to prevent the grid mesh distortion does not occur by the load, so that the calculation results are more accurate, the use of adaptive mesh rezoning techniques, divided into small grid contact surface, the coarse grid for the target surface. Mesh after the O-ring model shown in Figure 2.

1.4 contact conditions of the model using the direct constraint method for solving contact problems in the model. ANSYS, using the contact algorithm based on Newton-Raphson method to examine the interaction of all the contact state, the beginning of each incremental step in order to determine the opening and closure of the slave nodes. By the O-ring, axisymmetric finite element model diagram shows that the model contains three contacts: First, the shell and the O-ring contact; of O-ring and flange groove side contact; O-ring and the underside of the flange groove contact [6]. Shell and the O-ring contact surface as the primary contact surface, the contact area of ​​the O-ring as three contact from the contact surface. The friction model is Coulomb friction, the friction coefficient is 0.35. All of the contacts need to define the stiffness of the two depends on the amount of penetration between the surface contact stiffness. Here we define the contact stiffness of 1000, the scale factor of 0.1 [8].

1.5 boundary conditions and loading mode first constrain all degrees of freedom of the flange groove, using the forced displacement of the rigid body displacement control through the housing wall to simulate the installation process of the rubber O rings, O-ring is in a certain degree of compression state. And then gradually imposed pressure in the lower side of the O-ring to reach the final state. The constraints imposed by shell X direction by applying a displacement, as the amount of compression, the displacement of the shell Y direction 0, the outer boundary of the flange groove X, Y direction displacement is defined as 0. Convergence difficulties when the contact problem taking into account the complexity, the first step to define a only a small displacement of the load analysis step, the contact on the smooth establishment of contact relationships, and the second step and then put the real displacement to reduce the model set to save computing time. On the basis of the calculation results for the first two load steps, and the third is the right of the hydraulic pressure [7]. According to the actual situation shows that the real pressure of the rubber O rings suffered only did not occur with the rigid body contact side of the unit. However, due to the deformation of the rubber O rings and the oppression of the rigid body, can not predict the exact location of the bearing surface, to define the boundary conditions, select the pressure boundary for a possible imposition of pressure boundary vertical to simulate unilateral working pressure role.

1.6 O-ring seal to determine the O-ring contact pressure distribution on the deformation of the seal tank and seal interface is an important parameter affecting the ring performance. Known by the force balance principle to ensure sealing necessary and sufficient condition is that the seals in direct contact on a continuous interface, the contact pressure the stress σ is equal to the pressure, that is, of σ ≥ p.

2 Results and Analysis

2.1 Installation and put pressure on the results from Figure 5 can be seen in the installation is complete, the sealing surface of the maximum contact pressure 9.019MPa, less than the working pressure of 15MPa, alone to install the contact pressure can not guarantee seal. Can be seen from Figure 6 after the installation is complete, the installation is complete, the maximum displacement of the X-direction of the O-shaped rubber seals for 20.006mm maximum displacement of the Y-direction 10.197mm seemingly "dumbbell" shape. Can be seen from Figure 7, after the imposition of the work load 15MPa, the largest 17.457MPa of the O-ring and three contact surfaces of the contact pressure, the peak is always greater than the oil pressure is less than the nitrile rubber maximum compressive stress of 50MPa This ensures that the function of the O-ring seal.