STRESSES Mechanics of Materials 1 第五章弯曲应力 材料力学 2 §5–1 FORWORD §5–2 NORMAL STRESS ON THE CROSS SECTION OF THE BEAM IN PLANAR BENDING §5–3 SHEARING STRESS ON THE CROSS SECTION OF THE BEAM IN PLANAR BENDING §5–4 STRENGTH CONDITIONS OF THE NORMAL STRESS AND SHEARING STRESS OF THE BEAM REASONABLE SECTION OF THE BEAM §5–5 PLANAR BENDING OF UNSIMMETRIC BEAMBENDING CENTER OF THE OPENED THIN-WALLED SECTION §5–6 LIMIT BENDING MOMENT OF A MATERIAL WITH PLASTICITY CONSIDERED CHAPTER 5 STRESSES IN BENDING 3 §5–1 引言 §5–2 平面弯曲时梁横截面上的正应力 §5–3 梁横截面上的剪应力 §5–4 梁的正应力和剪应力强度条件梁的合理截面 §5–5 非对称截面梁的平面弯曲开口薄壁截面的弯曲中心 §5–6 考虑材料塑性时的极限弯矩 第五章弯曲应力 4 §5-1 FORWARD 1、(Internal forces) stresses on the cross section of the bending member Internal forces Shearing force Q Shearing stress t Bending moment M Normal stress s STRESSES IN BENDING 5 §5-1 引言 弯曲应力 1、弯曲构件横截面上的(内力)应力 内力 剪力Q 剪应力t 弯矩M 正应力s 6 There are only normal stresses in the section under plane bending beam of pure bending (There is only M and no Q in the cross section). There are shearing stresses in the section under plane bending beam of transverse bending. (There are Q and M in the cross section). 2、Study method Longitudinal plane of symmetry P1 P2 Such as: STRESSES IN BENDING 7 平面弯曲时横截面s 纯弯曲梁(横截面上只有M而无Q的情况) 平面弯曲时横截面t 剪切弯曲(横截面上既有Q又有M的情况) 弯曲应力 2、研究方法 纵向对称面 P1 P2 例如: 8 Deformation of some portion of the beam in which there are only bending moment and no shearing stress is called pure bending. Such as portion AB. P P a a A B Q M x x Pure Bending: STRESSES IN BENDING P P Pa 9 某段梁的内力只有弯矩没有剪力时,该段梁的变形称为纯弯曲。如AB段。 弯曲应力 P P a a A B Q M x x 纯弯曲(Pure Bending): P P Pa 10