直径d=100mm两段机轴用法兰和螺栓联接成传动轴如图所示,轴受扭时的最大剪应力为70MPa,螺栓的直径d<sub>1</sub>=20mm,并布置在<img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041116370218005.jpg?sign=6f2fd2a7e859ce150596f8c51e2bfe4f&t=62d6ea25" />=200mm的圆周上。设螺栓的许用剪应力<img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041116363753328.jpg?sign=c33681d5c886df29cdf14b5105b6e8aa&t=62d6ea25" />=60MPa,则所需螺栓的个数为()个。<br /> <img src="https://nimg.ppkao.com/2019-04/xiaotian/2019041116364978822.jpg?sign=a59fa5b80333f2106cbc500a675ecea4&t=62d6ea25" />
A、6
B、7
C、8
D、9