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第八章 强度理论
§8–1 强度理论的概念 §8–2 四个强度理论及其相当应力 §8–3 莫尔强度理论及其相当应力 §8-4 强度理论的应用
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§8–１ CONCEPTS OF STRENGTH THEORIES
1、Opening words：
1)、Investigation of the tensile, compressive and torsional tests of cast iron and low-carbon steel
§8–2 四个强度理论及其相当应力 一、最大拉应力（第一强度）理论：
认为构件的断裂是由最大拉应力引起的。当最大拉应力达到 单向拉伸的强度极限时，构件就断了。
1、破坏判据： 1b ;(10)
2、强度准则：1 ;(1 0)
3、实用范围：实用于破坏形式为脆断的构件。
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2、Theory of the maximum tensile strain（the second strength）：
1、铸铁与低碳钢的拉、压、扭试验现象是怎样产生的？
P 铸铁拉伸
铸铁压缩
M
P
低碳钢
铸铁
P
2、组合变形杆将怎样破坏？
P
M
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2、Theories of strength：Some assumptions about the cause of the strength failure of materials . 3、Types of failure of materials：⑴ yield； ⑵ rupture 1)、Galileo planted the seed of the first strength theory； 2)、Mariotto’s statement about the rupture of material due to
P Tension of
cast iron
M
Compression of cast iron
P
Lowcarbon steel
Cast iron
P
2)、How will the member rupture in Combined deformations？
P
M
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§8–１ 强度理论的概念 一、引子：
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二、强度理论：是关于“构件发生强度失效（failure by lost strength）起因”的假说。
三、材料的破坏形式：⑴ 屈服； ⑵ 断裂 。 1、伽利略播下了第一强度理论的种子； 2、马里奥特关于变形过大引起破坏的论述，是第二强度理论的 萌芽； 3、杜奎特（C.Duguet)提出了最大剪应力理论；
This theory considers the main cause of rupture to be the maximum tensile stress. The member will rupture as the maximum tensile stress reaches the strength limit in axial tension.
excessive deformation is the flush of the second strength theory； 3)、C.Duguet proposed the theory of the maximum shearing stress；
4)、Maxwell brought forward the theory of the maximum distortional energy theory early, which was known after his letters were published.
1)、Criterion of rupture： 1b ;(10)
2)、strength condition：
1 ;(1 0)
3)、Application range：May be applied to the members with the failure form of brittle rupture.
tension
1b ;(10)
1E 1123 E b
1)、Criterion of failure：ition： 1 2 3
3)、Application range：May be applied to the members with the failure form of brittle rupture .
4、麦克斯威尔最早提出了最大畸变能理论（maximum distortion energy theory）；这是后来人们在他的书信出版后才知道的。
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§8–2 FOUR STRENGTH THEORIES AND
THEIR EQUIVALENT STRESSES
1、Theory of the maximum tensile stress（the first strength）：
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二、最大伸长线应变（第二强度）理论：
认为构件的断裂是由最大伸长线应变引起的。当最大伸长线
应变达到单向拉伸试验下的极限应变时，构件就断了。
1b ;(10)
Mechanics of Materials
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CHAPTER 8 STHENGTH THEORIES
§8–1 Concepts of strength theories §8–2 Four strength theories and their equivalent stresses §8–3 Mohr’s strength theory and its equivalent stress §8-4 Applications of strength theories
This theory considers the main cause of rupture to be the maximum tensile strain. The member will rupture as the maximum tensile strain reaches the limit strain in axial