1. Failure forms of mechanical parts: overall fracture, excessive residual deformation, surface damage of parts (corrosion, wear and contact fatigue), failure caused by destruction of normal working conditions 2. Requirements that designed parts should meet: requirements to avoid failure within the predetermined life period (strength, stiffness, life), structural processability requirements, economic requirements, small mass requirements, reliability requirements 3. Design criteria for parts: strength criteria, stiffness criteria, life criteria, vibration stability criteria, reliability criteria 4. Design methods for 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. 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 relief grooves, open-loop grooves), 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. Wear process of parts: running-in stage, stable wear stage, severe wear stage; efforts should be made 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, micro-motion 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 tooth profile of ordinary connecting threads is an equilateral triangle with good self-locking performance; the transmission efficiency of rectangular transmission threads is higher than that of other threads; trapezoidal transmission threads are the most commonly used transmission threads. 15. Commonly used connecting threads require self-locking performance, so single-line threads are mostly used; transmission threads require high transmission efficiency, so double-line or triple-line 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 of threaded connections: 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 relaxation: to prevent the spiral pair from rotating relative to each other when loaded. (Friction anti-loosening, mechanical anti-loosening, destroying the motion relationship of the spiral pair to prevent loosening) 18. Measures to improve the strength of threaded connections: reduce the stress amplitude that affects the fatigue strength of the bolt (reduce the stiffness of the bolt or increase the stiffness of the connected parts), improve the phenomenon of uneven load distribution on the thread teeth, reduce the influence of stress concentration, and adopt a reasonable manufacturing process 19. Key connection types: flat key connection (both sides are working surfaces), semicircular key connection, wedge key connection, tangential key connection 20. Belt drives are divided into: friction type and meshing type 21. The instantaneous maximum stress of the belt occurs at the beginning of the tight edge of the belt around the small pulley; the stress changes four times in one circle of the belt 22. Tensioning of V-belt drives: regular tensioning device, automatic tensioning device, tensioning device using a tensioning wheel 23. The number of links in a roller chain is generally an even number (the number of teeth on the sprocket is an odd number), and the roller When the chain is an odd number, use an over-link. 24. The purpose of chain drive tensioning is to avoid poor meshing and chain vibration when the loose side of the chain sags too much, and to increase the meshing angle between the chain and the sprocket. 25. Gear failure forms: tooth breakage, tooth surface wear (open gears), tooth surface pitting (closed gears), tooth surface bonding, plastic deformation (ridges appear on the driven wheel and grooves appear on the driving wheel). 26. Gear working surface hardness greater than 350HBS or 38HRS is called hard-faced gear; otherwise it is a soft-faced gear. 27. Improving manufacturing accuracy and reducing gear diameter to reduce circumferential speed can reduce dynamic loads. In order to reduce dynamic loads, the gear can be edged on the tooth top. The purpose of making the gear teeth into a drum shape is to improve the tooth 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. After the worm gear is displaced, the pitch circle and pitch circle of the worm gear still coincide, but the pitch line of the worm gear has changed and no longer coincides with its pitch circle. 30. Failure forms of worm gear transmission: pitting, tooth root fracture, tooth surface bonding and excessive wear; failure often occurs on the worm gear. 31. Power loss of closed worm gear transmission: meshing wear loss, bearing wear loss, oil splash loss when the parts entering the oil pool stir the oil. 32. The worm gear transmission must be calculated for thermal balance based on the condition that the heat generated per unit time is equal to the heat dissipated in the same time. Measures: add heat sinks and increase the heat dissipation area, install fans at the end of the worm shaft to accelerate air flow, and install circulating cooling pipes in the transmission box. 33. Conditions for the formation of hydrodynamic lubrication: the two surfaces sliding relative to each other must form a converging wedge-shaped gap; the two surfaces separated by the oil film must have a sufficient relative sliding speed, and their movement must make the lubricating oil flow from the large mouth into the small mouth and out; the lubricating oil must have a certain viscosity, and the oil supply must be sufficient. 34. The basic structure of rolling bearings: 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 are d=10mm, 12mm, 15mm, 17mm respectively. 04 means d=20mm, 12 means d=60mm36. Basic rated life: The speed or working hours at which 10% of the bearings in a group of bearings suffer pitting damage, while 90% do not suffer pitting damage is regarded as the life of the bearing37. Basic rated dynamic load: The load that the bearing can withstand when the basic rated life of the bearing is exactly 106 revolutions38. Bearing configuration method: Double fulcrums are fixed in each direction, one fulcrum is fixed in both directions and the other end of the fulcrum is floating, and both ends are floatingly supported39. Bearings are divided into: rotating shaft (bending moment and torque), spindle (bending moment), transmission shaft (torque)
