1. The failure mode 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
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2. Requirements that the design parts should meet: requirements to avoid failure within the predetermined life period (strength, stiffness, life), structural process requirements, economic requirements, small quality requirements, and reliability requirements
3. Part design criteria: strength criteria, stiffness criteria, life criteria, vibration stability criteria, reliability criteria
4. Design methods of parts: 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. The 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 enduring fatigue limit
9. Measures to improve the fatigue strength of parts: reduce the influence of stress concentration on the parts as much as possible (load reduction groove, open ring groove), select materials with high fatigue strength and stipulate 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, and severe wear stage; efforts should be made to shorten the run-in period, prolong the stable wear period, and delay the arrival of severe wear
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12. Classification of wear: adhesive 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. Ordinary connecting thread is an equilateral triangle with good self-locking property; the transmission efficiency of rectangular transmission thread is higher than that of other threads; trapezoidal transmission thread is the most commonly used transmission thread
15. Commonly used connecting threads require self-locking properties, so single-thread threads are often used; transmission threads require high transmission efficiency, so double-thread or three-thread threads are mostly used
16. Ordinary bolt connection (with a through hole or hinged hole on the connected part), double-headed stud connection, screw connection, set screw connection
17. The purpose of threaded connection pre-tightening: to enhance the reliability and tightness of the connection, and to prevent gaps or relative slippage between the connected parts after loading. The fundamental problem of threaded connection loosening: preventing relative rotation of the screw pair when loaded. (Friction anti-loosening, mechanical anti-loosening, anti-loosening by destroying the screw pair motion relationship)
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18. Measures to improve the threaded connection strength: reduce the stress amplitude that affects the fatigue strength of the bolt (reduce the bolt stiffness or increase the stiffness of the connected parts), improve the uneven load distribution on the thread teeth, reduce the influence of stress concentration, and use 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 transmission is divided into: friction type and meshing type
21. The instantaneous maximum stress of the belt occurs at the place where the tight side of the belt begins to wind around the small pulley; the belt changes four times for one cycle
22. Tensioning of V-belt transmission: regular tensioning device, automatic tensioning device, tensioning device using tensioning pulley
23. The number of chain links of the roller chain is generally an even number (the number of teeth of the sprocket is an odd number), and the excessive chain link is used when the roller chain is an odd number.
24. The purpose of chain drive tensioning: to avoid poor meshing and chain vibration when the sag of the loose side of the chain is too large, and to increase the meshing wrap angle between the chain and the sprocket
25. Gear failure mode: broken teeth, tooth surface wear (open gear), tooth surface pitting (closed gear), tooth surface gluing, plastic deformation (ridges appear on the driven wheel, grooves appear on the driving wheel)
26. Gears with a hardness greater than 350HBS or 38HRS are called hard-faced gears; otherwise, they are soft-faced gears
27. Improving the manufacturing accuracy and reducing the diameter of the gear to reduce the peripheral speed can reduce the dynamic load; in order to reduce the dynamic load, the gear can be repaired at the top of the tooth; the gear teeth are made into a drum shape to improve the gear 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 has changed and no longer coincides with the pitch circle.
30. The failure mode of worm drive: pitting corrosion, tooth root fracture, tooth surface gluing and excessive wear; failure often occurs on the worm gear
31. Power loss of closed worm drive: meshing wear loss, bearing wear loss, oil splash loss when parts entering the oil pool stir oil
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32. The worm drive must calculate the heat balance according to the condition that the calorific value per unit time is equal to the heat dissipation in the same time. Measures: add heat sinks and increase the heat dissipation area, install fans at the end of the worm shaft to speed up air flow, and install heat sinks in the transmission box Built-in circulating cooling pipeline
33. The conditions for forming hydrodynamic lubrication: the two surfaces that slide relatively must form a convergent wedge-shaped gap; the two surfaces separated by the oil film must have sufficient relative sliding speed, and its movement must make the lubricating oil flow from the large mouth into the small mouth; lubrication The oil must have a certain viscosity, and the oil supply must be sufficient
34. The basic structure of rolling bearings: inner ring, outer ring, hydrodynamic 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 respectively d=10mm, 12mm, 15mm, 17mm 04 means d= 20mm, 12 means d=60mm
36. Basic rating life: 10% of the bearings in a group of bearings have pitting damage, and 90% of the bearings do not have pitting damage, and the number of working hours is the life of the bearing
37. Basic rated dynamic load: 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 each, one point is bidirectionally fixed and the other end fulcrum is swimming, and both ends are floating support
39. Bearings are divided by load: shaft (bending moment and torque), mandrel (bending moment), drive shaft (torque)
