动应力和动应矩计算
首发时间:2006-09-06
摘要: 弹性理论由于认定单位面积上的力矩(应矩)的极限为零[2],因此,构件做变速运动时,只有动应力而无动扭应矩和动弯应矩的概念。新概念弹性理论证明应矩的极限不为零[6],证明了纯扭转无剪应力[6]、纯应矩无正应力[6]。因此,对动载荷作用下的弯曲和扭转,必须引进动弯应矩和动扭应矩的概念。本文指出构件做匀加速直线运动时,应力应矩两种理论下的结论相同。推导出圆轴做加速转动时动扭应矩公式,通过实例计算得出:应力理论下得出的安全系数高于应矩理论得出的安全系数。说明应力理论是不安全的。推导出杆件受横向冲击载荷的动应矩;通过两种理论下的实例计算的对比,得出应力理论是不安全的。推导出用应矩表示的受迫振动公式:两种理论下的固有频率完全不同,确定准确的固有频率值对防止共振造成破坏具有非常重大的意义。可见用应矩理论修正动载荷作用下的内力是非常必要的。
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Dynamic Stress and Dynamic MPUA
Abstract:Theory of elasticity regards that the limit of moment per unit area (MPUA) is zero, so when the component shift it movement, there is only dynamic stress but no dynamic MPUA. However, in the new theory of elasticity, it is proved that the MPUA is a necessary quantity to analyze the stress state of a body. So, the dynamic MPUA is also an essential factor be considered to analyze the state of a shift-moving component. In this paper, it is pointed out that these two theories got the same conclusion when the component moves as even-acceleration. The rules of shaft, when it is accelerated rotating, are developed. It is shown that the safe coefficient in now-used theory of elasticity is bigger than new theory. Dynamic MPUA of the pole subjecting impact load is calculated. It is also proved the stress theory is not safe for design the component. The natural frequency of two theories is different when the component is subjected a forced vibration.
Keywords: dynamic stress dynamic MPUA dynamic load coefficient forced vibration natural frequency
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No.8218769181157516****
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