轴力图的特点:突变值三集中载荷 轴力(图)的简便求法:自左向右 遇到向左的P<,轴力N增量为正; 遇到向右的P→,轴力N增量为负。 8kN 5kN 3kN 5kN 8KN 3kN 26
26 轴力(图)的简便求法： 自左向右: 轴力图的特点：突变值 = 集中载荷 遇到向左的P， 轴力N 增量为正； 遇到向右的P→ ， 轴力N 增量为负。 5kN 8kN 3kN + – 3kN 5kN 8kN
AXIAL TENSIONAND COMPRESSION Example 2 Length of the rod shown in the figure is L. Distributed force q=kx is acted on it direction of the force is shown in the figure try to plot the diagram of axial force ofthe the rod q(x) Solution The free end of the rod is the origin of the coordinate and coordinate x to the right is positive. Take the segment of length x q x on the left of point x, its internal force is rMmm KL Ax N(r) N N(x)=o-khxd ky A2(x)m=-1 27
Solution：The free end of the rod is the origin of the coordinate and coordinate x to the right is positive. Take the segment of length x on the left of point x, its internal force is q KL x O 2 0 2 1 N(x) k xdx k x x = − = − 2 max 2 1 N(x) = − k L Example 2 Length of the rod shown in the figure is L. Distributed force q = kx is acted on it, direction of the force is shown in the figure. Try to plot the diagram of axial force of the the rod. L q(x) N(x) x q(x) N x O – 2 2 kL 27
「例2图示杆长为L,受分布力q=kx作用,方向如图,试画出 杆的轴力图。 解:x坐标向右为正,坐标原点在 q(x) 自由端。 取左侧x段为对象,内力N(x)为: q rMmm N(x) gL N N(x)=5-kxdx=-=,?2 N(xmax ==I kL kL 2 28
28 解：x 坐标向右为正，坐标原点在 自由端。 取左侧x 段为对象，内力N(x)为： q qL x O 2 0 2 1 N(x) k xdx k x x = − = − 2 max 2 1 N(x) = − k L [例2] 图示杆长为L，受分布力 q = kx 作用，方向如图，试画出 杆的轴力图。 L q(x) N x O – 2 2 kL N(x) x q(x)
AXAL TENSIONAND COMPRESSION 81-3 STRESSES ON THE SECTION AND STRENGTH CONDITIONS Bring forward P P the problem P P 1). The magnitude of the internal force can not scale the strength of the structure member 2). Strength: (D Intensity of the distributed internal forces in the section stress; @The load-bearing capacity of the material 1、 Concept of stress 1). Definition: Intensity of the internal force due to the external forces 29
1、Concept of stress §1–3 STRESSES ON THE SECTION AND STRENGTH CONDITIONS Bring forward the problem： 1). The magnitude of the internal force can not scale the strength of the structure member. 2). Strength：①Intensity of the distributed internal forces in the section⎯stress； ②The load-bearing capacity of the material. 1). Definition：Intensity of the internal force due to the external forces. 29 P P P P
§I 1-3截面上的应力及强度条件 问题提出: P P PP 1.内力大小不能衡量构件强度的大小。 2.强度:①内力在截面的分布集度一应力; ②材料承受荷载的能力。 、应力的概念 1.定义:由外力引起的内力集度
30 一、应力的概念 §1–3 截面上的应力及强度条件 问题提出： 1. 内力大小不能衡量构件强度的大小。 2. 强度：①内力在截面的分布集度⎯应力； ②材料承受荷载的能力。 1. 定义：由外力引起的内力集度。 P P P P