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机械零件上所受的疲劳载荷一般由静载荷与交变载荷组合而成,此类零件的设计均涉及疲劳问题。例如:起重机上的吊杆,当吊钩不带载时,杆内只有其自重引起的应力。这是杆内的最小应力。而当起重机吊起额定的最大负载时,杆内就出现了由自重加负载引起的最大应力。这样的起吊过程会多次重复,因而应按疲劳问题进行设计。受疲劳载荷的机械零件设计通常是基于“无限寿命”的假定,即应力循环在10~6以上。在许多情况下,用“有限寿命”来计算已完全能满足设计要求了。这样既可减轻重量又能降低成本。就拿前面提到的吊杆来说,如果每小时起吊4次,以每年工作2,000小时,十年中的应力循环也只有80,000次。
Fatigue load on mechanical parts is generally a combination of static load and alternating load. The design of such parts involves fatigue problems. For example: crane boom, when the hook is not loaded, the rod only the weight of its own stress. This is the minimum stress in the rod. When the crane lifts the rated maximum load, the maximum stress caused by self-weight and load appears in the rod. Such lifting process will be repeated many times, so fatigue design should be carried out. Mechanical parts subject to fatigue loading are usually based on the assumption of “infinite life”, ie stress cycling is above 10-6. In many cases, using “finite life” to calculate has fully met the design requirements. This will both reduce weight and reduce costs. Taking the aforementioned boom, if you hoist 4 times an hour to work 2,000 hours a year, the stress cycle in a decade is only 80,000 times.