Who knows what the design criteria for machine parts are, and how they are designed?
5. life standards, in order to ensure that the machine in a certain life span of normal work, in the design of mechanical parts, it is necessary to request the life of mechanical parts. It should be explained that parts can be replaced during the life of the machine, that is, the life of some mechanical parts is shorter than the life of the machine. The life of mechanical parts is mainly affected by fatigue, wear and corrosion of materials. In order to avoid failure caused by parts fatigue, such as fatigue fracture, fatigue strength should be calculated according to the fatigue limit corresponding to the life of mechanical parts. That is to say, according to the requirements of life and the specific speed of parts, according to formula (3-6), the fatigue limit is calculated when the stress cycle number is N. Then the strength condition is calculated and the fatigue strength is calculated. When the fatigue strength is satisfied, the stress cycle times of the mechanical parts can be guaranteed before the damage. Wear is usually unavoidable. Under certain conditions, corrosion is inevitable, such as structural members of bridges, corrosion of buried steel pipelines, etc.. In the design, mainly to ensure the mechanical parts in life, not excessive wear and corrosion. The mechanism of wear is still fully mastered, and there are many factors affecting wear. Generally, the wear resistance of friction pairs is improved according to the tribological design principle. The main measures are as follows: reasonable selection of friction pairs, reasonable choice of lubricant and additives, and control of the working conditions of friction pairs, such as pressure, sliding speed and temperature rise. So far, there is no practical and effective method for calculating corrosion life
