Abstract
Taking M12.5 × 1.25 × 65-10.9 bolt as an example, this paper studies the extreme distribution of the minimum value of bolt tensile strength in order to evaluate the reliability and stability of bolt product quality and to verify the production process. Through data collection, parameter estimation, distribution test and extreme prediction, it is concluded that: 1) the distribution of the minimum value of bolt tensile strength conforms to Gumbel extreme distribution; 2) when the return period is 10000, the predicted minimum tensile strength is 1071.7 MPa ± 3.2 MPa, k = 2. It is higher than the minimum value of 1040 MPa required by ISO 898-1 standard.
Highlights
Fasteners are the most widely used standard parts in the mechanical industry
From the skewness coefficient and kurtosis coefficient of the sample, we can see that: 1) the distribution of the minimum tensile strength at the low value range tends to deviate from the center more than that at the high value range; 2) it may have a few small extreme values; 3) the minimum value is not concentrated near the average value; 4) it has a long left tail [11,12]
It can be seen that Dn=0.1166
Summary
According to ISO 898-1:2013 standard [1], the tensile strength of fasteners cannot be lower than the specified value. The general requirements for nondestructive testing and metallographic structure defects of metal materials shall be less than or equal to the specified value, i.e. the maximum value shall not be exceeded, which belongs to the application research of maximum value distribution. The mechanical properties of metal materials, such as strength, plasticity, hardness, impact absorbed energy, fatigue and so on, are generally required to be greater than or equal to the specified value, i.e. not less than the minimum value, which belongs to the application research of minimum value distribution. Predict the minimum tensile strength that may occur for the production department to evaluate the reliability and stability of bolt product quality and to verify the specific production process
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