The strength criterion of mechanical parts design is briefly introduced
3. heat resistance criteria, due to friction and other reasons, when the machine is running, the temperature of the machine parts and lubricants will generally rise. Excessive work temperature will lead to a decrease in lubrication effect, and will cause thermal deformation, hardness and strength degradation of the parts, even damage. In the high temperature, metal mechanical parts may be glued and stuck; plastic and other non-metallic mechanical parts may soften, or even melt, and in some cases will cause thermal stress. Heat resistance is generally not the temperature control criterion of mechanical parts exceeds the allowable value, in order to ensure the normal work of the parts, the expression is (3 - 18) in order to improve the temperature control performance, heat dissipation, when necessary, can use water or air cooling measures. 4. vibration stability criteria, when the frequency of excitation is equal to the natural frequency of the object, the amplitude of the object is the largest, the frequency of excitation is different from the natural frequency, and the amplitude of the object is smaller. When the frequency of excitation is close to the natural frequency of the object, the amplitude of the forced vibration is very large. This phenomenon is called resonance. Vibration stability refers to the quality of mechanical components avoiding resonance when the machine is running. In order to prolong the life of the machine, in order to avoid the damage of the shaft and the machine, the vibration stability of the axle is calculated, especially the axis of the high-speed machine.
1, the strength criterion requires that the working stress of the mechanical parts should not exceed allowable stress [Sigma]. The formula is typical: (3-16) lim - ultimate stress of brittle materials by static stress on the ultimate strength, the static stress of plastic materials, the yield limit of zero stress the fatigue limit. S - Safety factor. 2. stiffness criteria mechanical components are subject to elastic deformation when subjected to load. Stiffness is the ability to resist deformation of materials, mechanical parts, or structures subjected to external forces. The stiffness of the material is measured by the external force required to produce the unit deformation. The stiffness of a mechanical part depends on its modulus of elasticity, E or shear modulus, G, geometry and size, and the form of external forces. It is an important work in mechanical design to analyze the rigidity of mechanical parts. For some parts that need to be strictly deformed (such as wings, machine tools, spindles, etc.), stiffness analysis is necessary to control the deformation. We also need to control the stiffness of the parts to prevent vibration or instability. In addition, a spring, such as a spring, must be used to control its stiffness to a reasonable value to ensure its specific function. The stiffness criterion is that the elastic deformation of a component subjected to load is not greater than the allowable elastic deformation. The expression of the stiffness criterion is (3 - 17) y is an elastic deformation quantity, such as deflection, longitudinal elongation (shortening): [y] is the corresponding allowable elastic deformation. The elastic deformation of a part can be obtained by theoretical calculation or by experiment. The allowable deformation depends on the use of the part, and is determined by theoretical analysis or experience.
