《材料力学》课程PPT教学课件（双语版）第十四章 交变应力

Mechanics of materials CHAPTERIA ALTERNATNGSTRESS

Mechanics of Materials

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CHAPTER 14 ALTERNATING STRESS §14-1 SUMMARY 8 14-2 SOME NOMENCLATURE IN THE ALTERNATING STRESS $14-3 ENDURANCE LIMIT OF A MATERIALS AND ITS TEST D 8144 ENDURANCE LIMIT OF A MEMBER AND ITS CALCULATION D314-5 CALCULATION OF THE FATIGUE STRENGTH OF THE MEMBER UNDER SYMMETRIC CYCLES D814-6 SIMPLE INTRODUCTION OF MECHANICAL PROPERTIES OF MATERIALS AT NON-CONSTANT TEMPERATURES AND STATIC LOADS

CHAPTER 14 ALTERNATING STRESS §14–1 SUMMARY §14–2 SOME NOMENCLATURE IN THE ALTERNATING STRESS §14–3 ENDURANCE LIMIT OF A MATERIALS AND ITS TEST §14–4 ENDURANCE LIMIT OF A MEMBER AND ITS CALCULATION §14–5 CALCULATION OF THE FATIGUE STRENGTH OF THE MEMBER UNDER SYMMETRIC CYCLES §14–6 SIMPLE INTRODUCTION OF MECHANICAL PROPERTIES OF MATERIALS AT NON-CONSTANT TEMPERATURES AND STATIC LOADS

第十四章交变应力 □§14-1概述 □§142交变应力的几个名词术语 §143材料持久限及其测定 §144构件持久限及其计算 §145对称循环下构件的疲劳强度计算 §146非常温静载下材料力学性能简介

第十四章 交变应力 §14–1 概述 §14–2 交变应力的几个名词术语 §14–3 材料持久限及其测定 §14–4 构件持久限及其计算 §14–5 对称循环下构件的疲劳强度计算 §14–6 非常温静载下材料力学性能简介

ALTERNATING STRESS 814-1 SUMMARY I Alternating stress: Stress at a point inside a member is changing periodically with time. This kind of stress is called the alternating stress 1gh-pressure LoW-pressure oil oil Fold iron thread

§14–１ SUMMARY 1、Alternating stress：Stress at a point inside a member is changing periodically with time. This kind of stress is called the alternating stress. Fold iron thread PP PP high-pressure oil Low-pressure oil

交实应 §141概述 、交变应力:构件内一点处的应力随时间作周期性变化,这 种应力称为交变应力。 高藤油 低瓜油 折铁丝

§14–１ 概 述 一、交变应力：构件内一点处的应力随时间作周期性变化，这 种应力称为交变应力。 折铁丝 PP PP

ALTERNATING STRESS 2, Developing process of the fatigue failure Failure of materials under the action of an alternating stress, in custom, is called the fatigue failure 1). Sub-structures and microscopic structures produce changes and the core of the permanent damage is formed 2). Microcosmic cracks are produced 3). Microcosmic cracks expand merge and form the leading crack 4). The macroscopic leading crack expand steadily 5). The structure losts its stability or ruptures completel

2、Developing process of the fatigue failure: 1).Sub-structures and microscopic structures produce changes and the core of the permanent damage is formed. 2).Microcosmic cracks are produced. 3).Microcosmic cracks expand 、 merge and form the“leading” crack. 4).The macroscopic “leading” crack expand steadily. 5).The structure losts its stability or ruptures completely. Failure of materials under the action of an alternating stress, in custom, is called the fatigue failure

交实应 二、疲劳破坏的发展过程: 材料在交变应力下的破坏,习惯上称为疲劳破坏。 1.亚结构和显微结构发生变化,从而永久损伤形核。 2.产生微观裂纹。 3.微观裂纹长大并合并, 形成“主导”裂纹。 4.宏观主导裂纹稳定扩展。 5.结构失稳或完全断裂

二、疲劳破坏的发展过程: 1.亚结构和显微结构发生变化，从而永久损伤形核。 2.产生微观裂纹。 3.微观裂纹长大并合并， 形成“主导”裂纹。 4.宏观主导裂纹稳定扩展。 5.结构失稳或完全断裂。 材料在交变应力下的破坏，习惯上称为疲劳破坏

ALTERNATING STRESS 3 Characteristics of the fatigue failure: 1) work s< 2). The happening of rupture needs some numbers of cycling 3).The failure is of the brittle rupture 4) The rupture area shows obviously different zones (Smooth zone and coarse zone)

3、Characteristics of the fatigue failure: 1). .  work  jx 2).The happening of rupture needs some numbers of cycling. 3).The failure is of the brittle rupture. 4).The rupture area shows obviously different zones. （Smooth zone and coarse zone）

交实应 三、疲劳破坏的特点: 工作<<Ox 2.断裂发生要经过一定的循环次数。 3.破坏均呈脆断 4.“断口”分区明显。 (光滑区和粗糙区)

三、疲劳破坏的特点: 2.断裂发生要经过一定的循环次数。 3.破坏均呈脆断。 4.“断口”分区明显。 （光滑区和粗糙区）  工作  jx 1.