1. Failure forms of mechanical parts: overall fracture, excessive residual deformation, surface damage of parts (corrosion, wear and contact fatigue), failure caused by damage to normal working conditions
2. Requirements that the designed parts should meet: requirements to avoid failure within the predetermined life cycle (strength, stiffness, life), structural processability requirements, economic requirements, low mass requirements, reliability requirements
3. Design criteria for parts: strength criteria, stiffness criteria, life criteria, vibration stability criteria, reliability criteria
4. Parts design methods: theoretical design, empirical design, model test design
5. Commonly used materials for mechanical parts: metal materials, polymer materials, ceramic materials, composite materials
6. The strength of parts is divided into: static stress strength and variable stress strength
7. Stress ratio r = -1 is symmetrical cyclic stress; r = 0 is pulsating cyclic stress
8. BC stage is strain fatigue (low cycle fatigue); CD is the finite life fatigue stage; the line segment after point D represents the infinite life fatigue stage of the specimen; point D is the endurance fatigue limit
9. Measures to improve the fatigue strength of parts: reduce the influence of stress concentration on parts as much as possible (load reduction grooves, open ring grooves), select materials with high fatigue strength, and specify heat treatment methods and strengthening processes that can improve the fatigue strength of materials.
10. Sliding friction: dry friction, boundary friction, fluid friction and mixed friction
11. The wear process of parts: running-in stage, stable wear stage, severe wear stage; we should strive to shorten the running-in period, extend the stable wear period, and delay the onset of severe wear.
12. Classification of wear: adhesion wear, abrasive wear, fatigue wear, erosion wear, corrosion wear, fretting wear
13. Lubricants are divided into four types: gas, liquid, solid and semi-solid; greases are divided into calcium-based grease, nano-based grease, lithium-based grease and aluminum-based grease.
14. The common connection thread type is an equilateral triangle, which has good self-locking performance; the transmission efficiency of rectangular transmission thread is higher than other threads; trapezoidal transmission thread is the most commonly used transmission thread
15. Commonly used connection threads require self-locking properties, so single-thread threads are mostly used; transmission threads require high transmission efficiency, so double-thread or triple-thread threads are mostly used
16. Ordinary bolt connection (through holes or reamed holes are opened on the connected parts), stud connection, screw connection, set screw connection
17. The purpose of pre-tightening threaded connections is to enhance the reliability and tightness of the connection and to prevent gaps or relative slippage between the connected parts after being loaded. The fundamental problem of loosening threaded connections is to prevent the relative rotation of the screw pair when loaded. (Friction anti-loosening, mechanical anti-loosening, and anti-loosening by destroying the motion relationship of the screw pair)
18. Measures to improve the strength of threaded connections: reduce the stress amplitude that affects the fatigue strength of bolts (reduce the stiffness of bolts or increase the stiffness of connected parts), improve the uneven distribution of load on thread teeth, reduce the influence of stress concentration, and adopt reasonable manufacturing processes.
19.Key connection types: flat key connection (both sides are working surfaces), semicircular key connection, wedge key connection, tangential key connection
