Reliability-based design of sealing bolts
Reliability-based seal bolt design Zhong Xiandong Maoming College Mechanical and Electrical Engineering College, Guangdong Maoming 525000 relying on the calculation formula, and finally gave an example to calculate the geometric dimensions of the sealing bolt. As a result, the reliability design has practical value for the hydraulic unit.
In the design of hydraulic components, the design of the strength of the components is calculated using the conventional design method. This design method is to position both the stress of the ankle 1 and the strength of the material. Let the work stress small Shanghai strength be used as a rule to design the part ruler to make zero. The reliability and the large safety factor are as follows. (1) The strength and stress calculated in the conventional design method are usually only the mean value and the change of the strength and stress. In fact, both strength 3 and stress 8 are random variables, and the six conventional design methods that vary within a certain range according to their respective statistical laws fail to make full use of the material. A large safety factor does not necessarily ensure the safety of hydraulic components. In fact, due to the dispersion of material properties and the randomness of load stress, for the same safety factor, the failure probability can be changed from a low value to an unusable conventional design method failing to give the reliability of the hydraulic component. In view of the above deficiencies of the conventional design method, this paper first discusses the reliability design method, and gives the reliability calculation formula of the hydraulic component, and then applies the formula to the design of the diameter of the sealing bolt. Through comparison and analysis with conventional design methods, it is not difficult to find that reliability design is more reasonable, more advanced and more practical than conventional design, which is the main development direction of today's advanced design methods.
The probability principle of the basic principle of probability design is to determine the probability water quality of the degree and stress distribution. It is a random nature that takes into account design variables and parameters and factors that determine component stress and strength. This method takes the component reliability as a function of the stress and intensity distribution and its parameters, ie, if all design variables and parameters are determined, the stress and intensity distribution are determined and the reliability of the component can be easily calculated; Knowing the distribution of strength and stress, we can find the design variables and parameters under the required reliability. When the stress and the strength are both normally distributed, the reliability equation can be obtained by the joint equation, and then the reliability can be obtained by using the standard normal distribution. The coupling equation is the basic formula of reliability design. 2 Probabilistic design of sealing bolts. Design criteria are determined. A large number of tests show that the stress and strength of bolts are normally distributed.
Yes, tightness requires bolted connections. The failure mode is the yielding of the snail. Therefore, the 讣 criterion is that the probability of the bolt material of the bolt material must be greater than or equal to the reliability of the design requirement, that is, the bolt material is selected, and the strength distribution is determined by the analog method. And the mechanical performance level specified by the national standard of the fastener, the average degree of tension of the normal distribution is 5, the yield limit of the bolt material; the coefficient of variation of the Vc bolt tension; = 0.050.07.
Determine the stress distribution of the bolt. Because the bolt stress is normally distributed, the average working load of the bolt group is the rated working pressure of the power cylinder; the average inner diameter of the power cylinder.
The maximum deviation of each screw is 0. The average value of the stress caused by each bolt mountain. The standard deviation of the stress distribution caused by the working load per bolt. In addition to the working load, the 5 bolt preload It will also cause the pre-stressing stress. Therefore, the mean value of the total tensile stress distribution of the bolt is 5, and the standard deviation is 4. The general form of the coupling equation is written as the coupling equation of the probability of sealing the snail by the formula of 奋1邑1. The solution method is determined by the reliability given by the design, and the normal reliability distribution is used to find the corresponding reliability coefficient. Substituting into the connection equation 12 to solve the required design bolt diameter, 3 example calculation of the known power cylinder inner diameter = 160 Book, working pressure 019.9 from 2, the number of bolts 2 3.1 theoretical calculation bolt material selected as 45 is steel, according to fastener standard 7,85, the selection of bolt parts can be 8.8, which is known by formula 2, and according to formula 47 In order to divide, from the standard state distribution 3 apricots 4 = 0.99999, = 4.26, the above values ​​are substituted into the formula 12 and simplified to obtain 168.7+1250.702 = 0 solution = 12.86, according to the series 5, sealed Bolt parameters are determined to be nominal diameter = 16 boat small diameter heart = 14.3 76 is 7, the pitch is corpse=1.
3.2 Discussion 1 For the sealing bolts of the above examples, if the conventional design method is used, the small diameter core is compared with the probability design method = 12.86, and the thread diameter of the probabilistic design is much smaller than the conventional design. Therefore, the conventional design method often leads to an overly conservative design for insurance, and the mechanism size is large; although the probabilistic design method takes more time than the conventional design method, the size of the mechanism is reduced, and a large economic benefit is brought about.
2 The conventional design method has no accurate measure of the reliability of the bolt connection, and the probabilistic design method can quantify and predict the safety and reliability.
Probability setting juice regards strength and stress as random rolling, does not link reliability, bolt strength and strength, and reveals the inherent relationship between reliability and safety factor, and obtains the mean value of safety factor under fixed reliability. As in the example of this example, the hole = 0.99999 350.819 hinder the body. The safety factor has a mean value of 5, which is in line with the recommendation (4) of the milk, which is the standard test of the probabilistic design method. Zhu Min electric household machine 拽 ;; poor and maintainability 1. Beijing Tsinghua people 7 out, funeral society 200153.
Liu Weixin. Mechanical reliability design. Beijing Tsinghua University Press, 193543551353, 357.35 inflammation. The thread is first set with ten and juice. Beixin Higher Education Press 199571 Xu Wei. The new mechanical design manual is called. Beijing Mechanical Industry Press, 199534 Peng Wensheng. Huang Hualiang. Wang Junrong and so on. Mechanical Design Wuhan Huazhong University of Science and Technology Press. 199689.
4 Conclusion, the probabilistic design method requires that 9 people use the method of counting to determine the ten-container cup, thus. The design is called reliability, but it should also be noted that the outstanding difficulty of this method is that, in addition to requiring the designer to have a good probability theory and mathematical statistics foundation, it is also necessary to use the statistics of the big cockroach. The modern design method has entered the practical stage of engineering. This paper has been successfully applied in the design of hydraulic power cylinder sealing bolts. It is recommended to be promoted in the design of other hydraulic components.
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