英汉双语材料力学14PPT课件

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
§14–１ SUMMARY 1、Alternating stress：Stress at a point inside a member is changing
三、疲劳破坏的特点:
1. 工作jx 。
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）
§14–2 SOME NOMENCLATURE IN THE ALTERNATING STRESS
1、Cycle characteristics：
max
m
min
o
5、Stable alternating stress：cycle characteristics and the cycle period are not changed.
a 0
m max
min
max
m
a
t
mino
mmax min
o
t
五、稳定交变应力：循环特征及周期不变。
2.脉动循环： r min 0 max
amax
t
m0
T
四、几种特殊的交变应力：
max
mo min
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a
T
1.对称循环：
r min 1 max
amax
t
m0
max
m a
mino mmax min
o
2).Fluctuating cycle： r min 0 max
a m
t
max
2
3).Static cycle：
t
r min 1 max
a
T
m in
r
m m
a a
x x
min
;( min max ) ;( max min )
2、Mean stress：
t
mmax2min
3、Amplitude of stress：
amax2min
max
m min
o
§14–2 交变应力的几个名词术语
a
T
一、循环特征：
m in
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
r
m m
a a
x x
min
;( min max ) ;( max min )
二、平均应力：
t
mmax2min
三、应力幅：
amax2min
4、Several special alternating stresses：
1).Symmetric cycle：
max
mo a
min
r min 1 max
ruptures completely.
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。
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）
periodically with time. This kind of stress is called the alternating stress.
high-pressure oil
Low-pressure
oil
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Fold iron thread
§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
Mechanics of Materials
1
2
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
a m max
2
3.静循环：
r min 1 max
a 0
mmax min
Example 1 A bolt connected the connecting with rod in a generator is
种应力称为交变应力。
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折铁丝
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.