四、许用应力齿轮传动的尺寸和重量,主要决定于许用应力的大小;因此在设计时,正确地选用许用应力是一个很重要的条件。齿轮在工作时,轮齿是受着循环变化的应力。由材料性质可知,应力与应力变化循环的次数有关。应力变化循环次数N_Ц的值愈大,则可能产生破坏的载荷(或破坏的应力)就愈小,直至达到疲劳极限(这时的循环次数以N_(ЦB)表示,并称为应力循环基数)如[图四]所示。所以在确定许用应力时,应该考虑应力变化循坏的次数,且必须使许用应力在相应的 Fourth, the allowable stress The size and weight of the gear drive, mainly determined by the size of the allowable stress; so in the design, the correct choice of allowable stress is a very important condition. When the gear is working, the gear teeth are subject to cyclic changes in stress. It can be seen from the material properties that the stress and stress change cycle times. The greater the value of the stress change cycle N_Ц, the smaller the load that can cause damage (or the stress of failure) until the fatigue limit is reached (the number of cycles in this case is expressed as N_ (ЦB) and is called the stress cycle basis) As shown in [Figure 4]. Therefore, in determining the allowable stress, should consider the number of changes in the stress changes, and must allow the stress in the corresponding