《材料力学》课程PPT教学课件（双语版）第八章 强度理论

Mechanics of materials CHAPTERS STRENGTHTHEORIES

Mechanics of Materials 1

第八四论

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chaPtER& STHIENGTHTHEORIES □]§8-1 Concepts of strength theories D88-2 Four strength theories and their equivalent stresses □§8-3Mohr’ s strength theory and its equivalent stress D88-4 Applications of strength theories

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 3

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

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 4

STRENGTH THEORIES 88-1 CONCEPTS OF STRENGTH THEORIES 1、 Opening words: 1) Investigation of the tensile, compressive and torsional tests of cast iron and low-carbon steel Compression of 0 Tension of cast iron cast iron Low carbon steel Cast iro P 2) How will the member rupture in Combined deformations? M

1、Opening words： §8–１ CONCEPTS OF STRENGTH THEORIES 1)、Investigation of the tensile, compressive and torsional tests of cast iron and low-carbon steel M Low￾carbon steel Cast iron P P Tension of cast iron P Compression of cast iron 2)、How will the member rupture in Combined deformations？ M P 5

强成论 §8-1强度理论的概念 引子 1、铸铁与低碳钢的拉、压、扭试验现象是怎样产生的? 铸铁拉伸 铸铁压缩 M P 低碳钢 铸铁 P P 2、组合变形杆将怎样破坏? M 6

一、引子： §8–１ 强度理论的概念 1、铸铁与低碳钢的拉、压、扭试验现象是怎样产生的？ M 低碳钢 铸铁 P P 铸铁拉伸 P 铸铁压缩 2、组合变形杆将怎样破坏？ M P 6

STRENGTH THEORIES 2> Theories of strength: Some assumptions about the cause of the strength failure of materials 3 Types of failure of materials: (1)yield; ( 2)rupture 1) Galileo planted the seed of the first strength theory 2) Mariotto's statement about the rupture of material due to 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

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 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. 7

强成论 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:()屈服;(2)断裂 1、伽利略播下了第一强度理论的种子; 2、马里奧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; 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

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。 1、伽利略播下了第一强度理论的种子； 三、材料的破坏形式：⑴ 屈服； ⑵ 断裂 。 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； 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。 8

STRENGTH THEORIES 88-2 FOUR STRENGTH THEORIESAND THEIR EQUIVALENT STRESSES 1> Theory of the maximum tensile stress ( the first strength) 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 1) Criterion of rupture a1=a;(1>0) 2)、 strength condition:σ1≤[o]; (G1>0) 3)Application range: May be applied to the members with the failure form of brittle rupture

§8–2 FOUR STRENGTH THEORIES AND THEIR EQUIVALENT STRESSES 1、Theory of the maximum tensile stress（the first strength）： 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. 1)、Criterion of rupture： ;( 0)  1 =  b  1  2)、strength condition：   ; ( 0)  1    1  3)、Application range：May be applied to the members with the failure form of brittle rupture. 9

次论 §82四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:σ1=an;(σ,>0) 2、强度准则:G1s];(o1>0) 3、实用范围:实用于破坏形式为脆断的构件

§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： ;( 0)  1 =  b  1  2、强度准则：   ; ( 0)  1    1  3、实用范围：实用于破坏形式为脆断的构件。 10