「例2]起重机钢丝绳长60m,名义直径28cm,有效横截面面积 A=2.9cm2,单位长度重量q25.5N/m,[]=30MPa,以a=2m/s2的 加速度提起重50kN的物体,试校核钢丝绳的强度。 解:①受力分析如图: N N=(G+qD)(1+) g ②动应力 L(ltalg) N 4=(G+g+) A 4 g 9)904(50+255601+ 9.8 G(1+a/g) 214MPao-300MPa
( )(1 ) g a Nd = G+qL + ) 9.8 2 (50 10 25.5 60)(1 2.9 10 1 3 4 + + = − =214MPa=300MPa [例2 ] 起重机钢丝绳长60m，名义直径28cm，有效横截面面积 A=2. 9cm2 , 单位长度重量q=25. 5N/m , [] =300MPa , 以a=2m/s2的 加速度提起重50kN 的物体，试校核钢丝绳的强度。 G(1+a/g) Nd L q(1+a/g) ( )(1 ) 1 g a G qL A A Nd d = = + + 解：①受力分析如图: ②动应力
DYNAMIC LOAD 2\ Dynamic stress of the rotating member 诚时d Example 3 A ball of weight G is install on one end of the rotating arm with length L. They are rotating about point O at an equal angular speed in the smooth plane. Knowing permissible stress is [o]. Determine the cross-section areaof the rotating arm (neglecting the weight of the rotating arm) 7 Solution (The free body diagram is shown in the figure The inertia force is GG=man=aRm=@-LG/g ②2 Strength condition 0=Ga/A< G。2GL
GG man Rm LG/ g 2 2 = = = =G A G / ( ) 2 g G GL A G = ②Strength condition Solution：①The free body diagram is shown in the figure: GG L O 2、Dynamic stress of the rotating member: The inertia force is Example 3 A ball of weight G is install on one end of the rotating arm with length L. They are rotating about point O at an equal angular speed in the smooth plane. Knowing permissible stress is []. Determine the cross-section areaof the rotating arm（neglecting the weight of the rotating arm）
二、转动构件的动应力:小心:飞轮炸裂 [例3]重为G的球装在长L的转臂端部,以等角速度在光滑水 平面上绕O点旋转,已知许用应力G,求转臂的截面面积 (不计转臂自重)a 解:①受力分析如图: 惯性力: GG=man=@ Rm=o'LGIg ②强度条件 σ=GG/A] G。2GL 4(g
G ma Rm LG g G n / 2 2 = = = 惯性力： =G A G / ( ) 2 g G GL A G = [例3 ] 重为G的球装在长L的转臂端部，以等角速度在光滑水 平面上绕O点旋转， 已知许用应力[] ，求转臂的截面面积 （不计转臂自重）。 ②强度条件 解：①受力分析如图: GG L O 二、转动构件的动应力: