1. Failure modes 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 design parts should meet: requirements to avoid failure within the predetermined life period (strength, stiffness, life), structural processability requirements, economic requirements, low quality requirements, reliability requirements
3. Design criteria for parts: strength criteria, stiffness criteria, life criteria, vibration stability criteria, reliability criteria
4. Part design methods: theoretical design, experience design, model test design
5. Materials commonly used in mechanical parts: metal materials, polymer materials, ceramic materials, composite materials
6. The strength of the 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 effect of stress concentration on the parts as much as possible (load reduction groove, open-loop groove), select materials with high fatigue strength and specify heat treatment methods and strengthening processes that can improve the fatigue strength of the material
10. Sliding friction: dry friction, boundary friction, fluid friction and mixed friction
11. Parts wear process: running-in stage, stable wear stage, severe wear stage; should try to shorten the running-in period, extend the stable wear stage, and postpone the arrival 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, aluminum-based grease
14. The common connection thread is an equilateral triangle with good self-locking; the transmission efficiency of rectangular transmission threads is higher than other threads; trapezoidal transmission threads are the most commonly used transmission threads
15. The commonly used connection thread requires self-locking, so single-thread is mostly used; the transmission thread requires high transmission efficiency, so double- or three-thread is often used
16. Ordinary bolt connection (through holes or hinged holes are formed in the connected parts), stud connection, screw connection, set screw connection
17. The purpose of thread connection pre-tightening: to enhance the reliability and tightness of the connection, to prevent gaps or relative slippage between connected parts after being loaded. The fundamental problem of loosening the thread connection: to prevent the relative rotation of the screw pair under load. (Anti-loosening of friction anti-loosening, mechanical anti-loosening, and damage to the movement of spiral pair)
18. Measures to improve thread connection strength: reduce the stress amplitude that affects the fatigue strength of the bolt (reduce the stiffness of the bolt or increase the rigidity of the connected part), improve the uneven distribution of load on the thread teeth, reduce the effect of stress concentration, adopt reasonable Manufacturing process
19. Key connection type: flat key connection (both sides are working surfaces), semicircular key connection, wedge key connection, tangential key connection
20. Belt drive is divided into: friction type and mesh type
21. The instantaneous maximum stress of the belt occurs when the tight edge of the belt begins to wrap around the small pulley; the stress changes four times during a belt
22. Tensioning with V-belt drive: periodic tensioning device, automatic tensioning device, tensioning device using tensioning wheels
23. The number of roller chain links is generally even (the odd number of sprocket teeth is taken), when the roller chain is odd, excessive links are used
24. The purpose of the chain drive tension: to avoid poor meshing and chain vibration when the loose side of the chain is too large, and to increase the angle of engagement between the chain and the sprocket
25. Failure modes of gears: broken gear teeth, tooth surface wear (open gears), tooth surface pitting (closed gears), tooth surface glue, plastic deformation (ridges on driven wheels and grooves on driving wheels)
26. The hardness of the gear working surface greater than 350HBS or 38HRS is called hard face gear; on the contrary, it is a soft tooth gear
27. Improve the manufacturing accuracy, reduce the gear diameter to reduce the peripheral speed, and reduce the dynamic load; in order to reduce the dynamic load, the gear tip can be trimmed; the gear teeth of the gear are made into a drum shape to improve the teeth Load distribution
28. Tanr = z1: q (diameter coefficient) The larger the lead angle, the higher the efficiency and the worse the self-locking property
29. Displace the worm gear. After the displacement, the pitch circle of the worm gear and the pitch circle still coincide, but the pitch line of the worm changes and no longer coincides with the pitch circle.
30. Failure modes of worm drive: pitting corrosion, broken roots, gluing of tooth surfaces and excessive wear; failures often occur on worm gears
31. Power loss of closed worm drive: gear wear loss, bearing wear loss, oil splash loss when parts entering the oil sump
32. The worm drive must perform heat balance calculation measures based on the condition that the amount of heat generated per unit time is equal to the amount of heat dissipation in the same time: install heat sinks and increase the heat dissipation area, install a fan at the end of the worm shaft to accelerate the air flow, and transfer the Built-in circulating cooling line
33. Conditions for the formation of hydrodynamic lubrication: the two surfaces that slide relatively must form a converging wedge-shaped gap; the two surfaces separated by the oil film must have sufficient relative sliding speed, and their movement must cause the lubricating oil to flow from the large port into the small port; lubrication The oil must have a certain viscosity and the oil supply must be sufficient
34. Basic structure of rolling bearing: inner ring, outer ring, hydraulic body, cage
35. 3 tapered roller bearings, 5 thrust ball bearings, 6 deep groove ball bearings, 7 angular contact bearings, N cylindrical roller bearings 00, 01, 02, 03 d = 10mm, 12mm, 15mm, 17mm 04 means d = 20mm, 12 means d = 60mm
36. Basic rated life: 10% of the bearings in a group of bearings have pitting damage, and 90% of the speed or working hours without pitting damage are taken as the life of the bearing
37. Basic dynamic load rating: When the basic rated life of the bearing is exactly 106 revolutions, the load that the bearing can bear
38. Bearing configuration method: two fulcrums are fixed in one direction, one fulcrum is fixed in both directions, the other end fulcrum travels, and both ends support
39. Bearings are divided according to load: rotating shaft (bending moment and torque), mandrel (bending moment), transmission shaft (torque)
