Reliability analysis of O-ring considering temperature

Aiming at the stress of the O-ring and the relaxation of the stress in time, and the results show that: high temperature has a great influence on the stress distribution and offset rate of the O-ring; the reliability of shear failure and leakage failure of the O-ring It shows a downward trend over time, with a sharp decline in the early stage and a change in the later decline rate; the multiple failure reliability of the O-ring changes sharply in the early stage and then basically stabilizes, indicating that the O-ring does not fail in the early stage of use, and it fails in the later stage The probability error.

The hydraulic sealing system is an important part of the mechanical device, and it is widely decomposed in the nuclear, aviation and automotive industries. As a typical seal in the hydraulic system, the failure of the O-ring will cause the hydraulic system seal to fail and may cause a major accident. For example, in 1983, an O-ring on the continuous thruster on the right side of the US space shuttle “Challenger” failed, causing the explosion of the space shuttle.

Usually, O-rings are composed of polymer material rubber. Its design and analysis involve solid mechanics, tribology, polymer materials science, thermodynamics and mechanical manufacturing technology and other theoretical knowledge. Usually, finite element software can be used to analyze O-rings. Perform analysis. The O-ring undergoes a large deformation by being compressed, thereby generating stress to achieve the sealing of the hydraulic system. To meet the sealing performance of the O-ring, the maximum contact stress of the O-ring must be at least greater than the pressure of the sealing medium under the reduced shear strength of the O-ring. There are many factors that affect the stress of O-rings, including sealing structure parameters such as compressibility, structure size parameters, friction factor of the contact surface, and environmental factors such as sealing medium pressure and temperature. By establishing a finite element model, the influence of influencing factors on the performance of O-rings can be analyzed. For example, Chen Guoding and others found the pressure placement of the medium, contact stress and Mises stress; Zhou Hongzhi and others converted the maximum contact stress between the O-ring and the shaft to compress the compression ratio, and the oil pressure increased, but under the condition of constant oil pressure Mises stress does not always increase precipitation with the increase of compression rate; Ren Quanbin et al.’s research shows that the gap between the upper and lower flanges, the initial compression rate of the sealing ring affects the maximum contact stress cracks, and the seal grooves and grooves The chamfered groove at the bottom has an obvious influence on the shear stress; Wu Guangping analyzed the influence of the friction factor on the shear stress and found that the temperature of the sealing medium in the sealing system is often higher in practical engineering applications. The increase of O-ring will cause the change of O-ring stress and accelerate the relaxation of O-ring. Therefore, temperature has a great influence on the reliability of O-ring.

At present, experiments are generally used to study the effect of temperature on the performance of O-rings. For example, Bernstein and Gillen used the characteristics of high-temperature accelerator O-ring mutations to perform accelerated life tests of O-rings. Hyung-Kyu et al. compared high temperature through experiments. Compared with the test, the reliability analysis of the O-ring under the influence of temperature using finite element software is not affected by human factors, and it also has the advantages of saving cost. However, the O-ring will be accompanied by large deformation and large strain during the load bearing process. If the influence of temperature on the stress is considered at the same time, and the high temperature also accelerates the aging of the O-ring rubber, the finite element modeling will be very complicated. . Therefore, the use of finite element software is used to conduct reliability simulation analysis of O-rings under the influence of temperature.

The author of this paper considers studying the influence of temperature on O-rings, establishes a finite element model model for proper simplification, analyzes the influence of temperature on O-ring stress, maximum contact stress and its relaxation, and takes temperature field, compressibility and medium pressure as The main influencing factors and the use of response surface method to calculate the reliability of O-rings in the relaxation process have certain reference value for the theoretical analysis and practical engineering applications of O-rings used in high-temperature media.

1. Thermal-solid phase analysis of O-ring

As the temperature will cause the thermal expansion of the O-ring structure and cause the stress change, the stress analysis of the O-ring includes thermal analysis and structural analysis. The thermal analysis includes the replacement heat exchange of the cylinder block and the O-ring caused by the temperature difference, hydraulic oil and The convective heat transfer between the O-ring and the cylinder and the heat radiation of the O-ring to the outside; the structural analysis includes the Mises stress analysis of all forms of the O-ring and the contact stress analysis of the contact surface. Analyze, combine conversion heat transfer, convection heat transfer, thermal radiation and finite element structure analysis, and perform thermo-solid phase analysis on O-rings.

4. Theory

(1) Temperature relaxes the O-ring stress.

(2) Picking up temperature, medium pressure and compression rate as the main influencing factors, using the response surface method to calculate the reliability of the O-ring at each moment when it is discrete, it is found that the reliability of the O-ring first changes in the initial stage of sealing, and then it is reliable The degree gradually decreases. For the O-ring studied by the author of this article, if the O-ring does not fail in about 100 s, the probability of failure of the O-ring in the later period is wasted, which has certain significance for other O-rings used in engineering.

(3) The study of the influence of the displacement of the O-ring due to friction on the stress and continuity of the O-ring will be a direction for subsequent research.

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