1. Failure modes of mechanical parts: overall cracking, excessive residual deformation, damage to the surface of the part (corrosion, wear, and tactile fatigue), and failure caused by damage to normal operating conditions.
2. Requirements that the planned components should meet: requirements to prevent failure within the predetermined service life (strength, stiffness, lifespan), structural manufacturability requirements, economic requirements, minimum mass requirements, and reliability requirements.
3. Design principles for components: strength principle, stiffness principle, lifespan principle, vibration stability principle, and reliability principle.
4. Part planning methods: theoretical planning, empirical planning, and model test planning.
5. Commonly used materials for mechanical parts: metallic materials, polymer materials, ceramic materials, and composite materials.
6. The strength of a component is divided into: static stress strength and alternating stress strength.
7. A stress ratio r = -1 indicates symmetrical cyclic stress; r = 0 indicates pulsating cyclic stress.
8. Stage BC represents strain fatigue (low-cycle fatigue); stage CD represents the finite-life fatigue stage; the line segment after point D represents the infinite-life fatigue stage of the specimen; point D is the durability fatigue limit.
9. Methods to improve the fatigue strength of parts: Minimize the impact of stress concentration on parts (unloading grooves, open-loop 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, chasm friction, fluid friction, and mixed friction
11. Wear process of parts: break-in stage, stable wear stage, and severe wear stage; efforts should be made to shorten the break-in period, extend the stable wear period, and postpone the onset of severe wear.
12. Classification of wear: Adhesive wear, abrasive wear, fatigue wear, erosive wear, corrosive wear, fretting wear
13. Lubricants are classified into four types: gaseous, liquid, solid, and semi-solid; greases are classified into four types: calcium-based grease, sodium-based grease, lithium-based grease, and aluminum-based grease.
14. Generally, the thread profile of connecting threads is an equilateral triangle, which has good self-locking properties; rectangular transmission threads have higher transmission efficiency than other threads; trapezoidal transmission threads are the most commonly used transmission threads.
15. Commonly used connecting threads require self-locking properties, so single-start threads are often used; transmission threads require high transmission efficiency, so double-start or triple-start threads are often used.
16. General bolt connections (with through holes or reamed holes in the connected parts), stud connections, screw connections, and set screw connections.
17. The purpose of pre-tightening threaded connections: to enhance the reliability and tightness of the connection, preventing gaps or relative slippage between the connected parts under load. The fundamental issue in loosening threaded connections: preventing relative rolling of the helical pair under load. (Friction-based anti-loosening, mechanical anti-loosening, and anti-loosening due to damage to the helical pair's movement connection)
18. Methods to improve the strength of threaded connections: reduce the stress amplitude affecting bolt fatigue strength (reduce bolt stiffness or increase the stiffness of the connected parts), improve the uneven load distribution on the thread teeth, reduce the impact of stress concentration, and select appropriate manufacturing processes.
19. Key connection types: flat key connection (both sides are working surfaces), semi-circular key connection, wedge key connection, tangential key connection.
20. Belt drives are divided into: friction type and meshing type.
21. The instantaneous maximum stress on the belt occurs at the point where the belt begins to wrap around the small pulley on the tight side; the stress changes four times per revolution of the belt.
22. V-belt drive tensioning: timed tensioning devices, active tensioning devices, tensioning devices using tensioning pulleys.
23. The number of links in a roller chain is generally even (the number of teeth on the sprocket is odd). When the number of links in a roller chain is odd, transition links are used.
24. The purpose of chain drive tensioning: to prevent poor meshing and chain vibration when the slack side of the chain is too large, and also to increase the wrap angle between the chain and the sprocket.
25. Gear failure modes: tooth breakage, tooth surface wear (open gears), tooth surface pitting (closed gears), tooth surface scuffing, and plastic deformation (driven gears exhibit ridges, driving gears exhibit grooves).
26. Gears with a working surface hardness greater than 350 HBS or 38 HRS are called hardened gears; otherwise, they are soft-surface gears.
27. Improving manufacturing precision and reducing gear diameter to decrease circumferential speed can both reduce dynamic load; to further reduce dynamic load, the gear teeth can be edged; making the gear teeth into a drum shape is to improve the distribution of load along the tooth direction.
28. Tanr = z1:q (diameter coefficient). The larger the lead angle, the higher the efficiency, but the worse the self-locking performance.
29. After repositioning the worm gear, the pitch circle and pitch radius of the worm gear still coincide, but the pitch line of the worm is altered and no longer coincides with its pitch circle.
30. Failure modes of worm gear drives: pitting, tooth root breakage, tooth surface scuffing, and excessive wear; failure often occurs on the worm wheel.
31. Power losses in closed worm gear drives: meshing wear loss, bearing wear loss, and oil splashing loss when parts enter the oil sump for stirring.
32. Worm gear drives require thermal balance calculations based on the condition that the heat generated per unit time equals the heat dissipation within a given time. Methods include: adding heat sinks and increasing the heat dissipation area; adding a fan to the worm shaft end to accelerate airflow; and installing circulating cooling pipes inside the transmission housing.
33. Conditions for hydrodynamic lubrication: The two relatively sliding surfaces 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 allow lubricating oil to flow in from the larger opening and out from the smaller opening; the lubricating oil must have a certain viscosity, and the oil supply must be sufficient.
34. The basic structure of a rolling bearing: inner ring, outer ring, hydraulic elements, and 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, and 03 respectively indicate d=10mm, 12mm, 15mm, and 17mm; 04 indicates d=20mm; and 12 indicates d=60mm.
36. Basic Additional Life: The life of a bearing is defined as the number of speeds or operating hours at which 10% of the bearings in a group experience pitting failure, while 90% do not.
37. Fundamental Additional Dynamic Load: The load that the bearing can withstand when its fundamental additional life is exactly 106 revolutions.
38. Bearing assembly methods: Double-supported bearings, each fixed in one direction; one-supported bearing, fixed in both directions with the other end movable; bearings with movable ends.
39. Bearings are classified by load: rotating shafts (bending moment and torque), spindles (bending moment), and drive shafts (torque).
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