Mechanics of Materials
CHAPTER16
FURTHER RESEARCH ON MECHANICAL
PROPERTIES OF MATERIALS
§ 16–1 SUMMARY
§ 16–2 EFFECTS OF THE STRAIN RATE AND STRESS RATE ON
MECHANICAL PROPERTIES OF MATERIALS
§ 16–3 EFFECTS OF TEMPERATURE ON MECHANICAL
PROPERTIES OF MATERIALS
§ 16–4 EFFECTS OF TEMPERATURE AND TIME ON MECHANICAL
PROPERTIES OF MATERIALS ·CREEP AND RELAXATION
§ 16–5 MECHANICAL PROPERTIES OF MATERIALS UNDER IMPACT
LOADS · IMPACT TOUGHNESS · TRANSITON TEMPERATURE
第十六章 材料力学性能的进一步研究
§ 16–1 概述
§ 16–2 应变速率及应力速率对材料力学性能的影响
§ 16–3 温度对材料力学性能的影响
§ 16–4 温度与时间对材料力学性能的影响 · 蠕变与松弛
§ 16–5 冲击荷载下材料的力学性能 ·冲击韧度 ·转变温度
§ 16–1 SUMMARY
The mechanical properties of materials at high temperature,in static loading(by quasi-
static test),tension and compression are introduced in the above chapter 1,Real structures or
members usually work under complex conditions,For example,the working temperature of
some petroleum chemical equipments is very slow,and the working temperature of some
internal-combustion engines or gas turbines is very high; the blades of the steam turbines are
always subjected to large centrifugal forces; the prestressed steel bars or wires in the
prestressed steel-bar reinforced concrete always work under high pre-tensile stresses at
normal temperatures for periods of long time; the bridge beams,crane beams and most
motive machines are often subjected to the loads varying alternately with time; the wind-
driven machinery pneumatic hammers and conventional weapons are often subjected to
impact loads repeatly and etc,So the effects of these factors on mechanical properties of
materials are needed to be considered in the strength calculation,
§ 16–1 概述
前面第一章中介绍了材料在高温、静载（用准静态试验）拉
伸、压缩时的力学性能。 实际的结构物或构件往往是在比较复
杂的条件下工作的，例如，石油化工设备中有些机器的工作温度
很低，而内燃机或燃气轮机的工作温度很高；汽轮机的叶片在高
温下长期受很大的离心力作用；预应力钢筋混凝土中的预应力钢
筋或钢丝束则在常温下长期在很高的预拉应力下工作；桥梁、吊
车梁以及绝大多数的动力机械所受荷载多是随时间交替变化的；
风动机械、气锤、常规武器则经常受到冲击载荷的反复作用，等
等。因此在强度计算时常需考虑这些因素对材料力学性能的影响。
Experimental results prove that mechanical properties of
materials are affected obviously by the strain rate
§ 16–2 EFFECTS OF THE STRAIN RATE AND STRESS RATE
ON MECHNICAL PROPERTIES OF MATERIALS
1,Effects of the strain rate on mechanical properties of materials
m m / m m / s3dd ?? t???
??
m m /m m /s3
when it exceeds, The load that makes the strain rate
exceed is customly called dynamic load,
m m /m m /s3
§ 16–2 应变速率及应力速率对材料力学性能的影响
试验结果指出，在应变速率超过 以后，
材料的力学性能就显著地受到应变速率的影响。使构件的应
变速率 超过 的荷载，习惯上称为动荷载。
m m / m m / s3dd ?? t???
?? m m /m m /s3
一、应变速率对材料力学性能的影响
Relationship between the stress rate and
the yield limit
0 20 40 60 80 100
320
300
280
260
240
220
200
s s (MPa)
s (MPa/s) · O
s
e
1
static load
2
2,Effects of the stress rate on mechanical properties of materials
When we test the yield limit of a material in the lab,the loading rate is also
the stress rate in the sample,
Low-carbon steel
Dynamic load
应力速率与屈服极限的关系
0 20 40 60 80 100
320
300
280
260
240
220
200
s s (MPa)
s (MPa/s) · 低碳钢 O
s
e
1
静荷载
2 动荷载
二、应力速率对材料力学性能的影响
在实验室内测定材料的屈服极限时，加载速率也就是试
样中的应力速率。
Effects of temperature on mechanical
properties of materials
§ 16–3 EFFECTS OF TEMPERATURE ON MECHANICAL
PROPERTIES OF MATERIALS
Total trend,
)( C?
)MPa(?
)GPa(E
0 100 200 300 400 500
216
177
137
700
600
500
400
300
200
100
100
90
80
70
60
50
40
30
20
10
(%),??
E
S?
d
b?
?
Temperature increases,E,?S, ?b
decrease ?,? Increase,
But increased with rising of temperature ?b
instead 260 ° ; befores ?,? was reduced at
the same time,But not all the steel materials
have the characteristics shown in the low-carbon
steel at temperatures lower than 260° C,
温度对材料力学性能的影响
§ 16–3 温度对材料力学性能的影响
但在 260° 以前随温度的升高,
?b反而增大，同时 ?,?却减小。但
象低碳钢这种在 260° 以前的特征，
并非所有的钢材都具有。
总趋势,
温度升高,E,?S, ?b下降；
?,? 增大。
)( C?
)MPa(?
)GPa(E
0 100 200 300 400 500
216
177
137
700
600
500
400
300
200
100
100
90
80
70
60
50
40
30
20
10
(%),??
E
S?
d
b?
?
Effects of temperature on mechanical properties of the
chromium-Manganese alloy,
2000
1750
1500
1250
1000
750
500
250
0
-200 -100 0 100 200 300 400 500 600 700 800
)MPa(?
)( C?
d
b?
2.0?
80
70
60
50
40
30
20
10
0
(%)?
温度对铬锰合金力学性能的影响
2000
1750
1500
1250
1000
750
500
250
0
-200 -100 0 100 200 300 400 500 600 700 800
)MPa(?
)( C?
d
b?
2.0?
80
70
60
50
40
30
20
10
0
(%)?
P(KN)
-
-
-
- - -
0 5 10 15
30
20
10
0
C?20?
C?196?
C?253?
Dl(mm) - - -
0 5 10 15
30
20
10
0
C?20?
C?196?
C?253?
P(KN)
Dl(mm)
Temperature decreases,plasticity decreases,the strength limit
increases,
P(kN)
-
-
-
- - -
0 5 10 15
30
20
10
0
C?20?
C?196?
C?253?
Dl(mm) - - -
0 5 10 15
30
20
10
0
C?20?
C?196?
C?253?
P(kN)
Dl(mm)
温度降低，塑性降低，强度极限提高
1,Creep, Under certain high temperature,even if the stress of the member is constant,the plastic
deformation of the member will increase slowly with time until member ruptures,This phenomenon is
called creep,
Note:The stress does not increase,but the bar is elongating by itself,
§ 16–4 EFFECTS OF TEMPERATURE AND TIME ON MECHANICAL
PROPERTIES OF MATERIALS · CREEP AND RELAXATION
P
After longer
time
P
Apply static load
一、蠕变,
在一定的高温下，即使构件上的应力不变，塑性变形却随时间
而缓慢增加，直至破坏。这种现象称为蠕变。
注意：应力没增加，杆自己在长长 ！
§ 16–4 温度与时间对材料力学性能的影响 · 蠕变与松弛
P
经过较长
时间后
P
加静载
The working range of the member can not exceed the stable stage!
e
t
O
A B
C
D
E
Unstable
stage
Stable
stage
Accelerative
stage
Rupture
stage
e 0
Creep curve of the material
构件的工作段不能超过稳定阶段 ！
e
t
O
A B
C
D
E
不稳定
阶段
稳定阶段
加速阶段
破坏
阶段
e 0
材料的蠕变曲线
The stress is
not changed,4321 TTTT ???
The higher the temperature is,
the faster the creep is,
T1
T2
T3
T4
s1
s2
s3
s4
Temperature is
not changed,1234 ???? ???
The higher the stress is,
the faster the creep is,
应力不变
4321 TTTT ???
温度越高蠕变越快
T1
T2
T3
T4
s1
s2
s3
s4
温度不变
1234 ???? ???
应力越高蠕变越快
2,Stress relaxation,
Under certain high temperature,when the total deformation of the member is kept
constant,the elastic deformation will transform into the plastic deformation with time,which
decreases the stress of the member,This phenomenon is called stress relaxation,
The bar elongates by itself!
Unload after longer time
Apply static
load
二、应力松弛,
在一定的高温下，构件上的总变形不变时，弹性变形会随时间
而转变为塑性变形，从而使构件内的应力变小。这种现象称为应
力松弛。
杆也是自己长了一段 ！
经过较长时间后
卸载
加静载
Temperature is
not changed,
123 ??? ??
e2 e
1
e3
The larger the initial stress is,the
larger the initial relaxation rate is,
The initial elastic strain is not
changed,
321 TTT ??
T1
T3
T2
The higher the temperature is,
the larger initial relaxation rate
is,
温度不变
123 ??? ??
e2 e
1
e3
初应力越大，松弛的初速率越大
初始弹性应变不变
321 TTT ??
T1
T3
T2
温度越高，松弛的初速率越大
§ 16–5 MECHANICAL PROPERTIES OF MATERIALS UNDER
IMPACT LOADS · IMPACT TOUGHNESS · TRANSITON TEMPERATURE
As temperature is reduced,increases,while the structure shows
the brittle rupture at low temperatures,Why?
b?
As temperature is reduced,increases,but the impact toughness
of the material is decreased,and the ability to resist rupture is
basically not changed,Therefore,the structure easily ruptures in
brittleness at low temperatures,
b?
§ 16–5 冲击荷载下材料的力学性能 ·冲击韧度 ·转变温度
温度降低,增大，结构反而还发生低温脆断，原因何在？
b?
温度降低,增大，但材料的冲击韧性下降，且抗断裂能
力基本不变，所以，结构易发生低温脆断。
b?
1,Specimen in the impact test
40
55
40
55
10
10
10
10
?45 2
R 0.5
2 R1
Specimen with V cut
Specimen with U cut
specimen
1.冲击试验试件
40
55
40
55
10
10
10
10
?45 2
R 0.5
2 R1
V型切口试样
U型切口试样
试件
2,Impact test
Specimen
2.冲击试验
试件
① Impact toughness of the specimen with,U” cut,
② Impact toughness of the specimen with,V” cut,
?k?
③ Cold short, phenomenon that the impact toughness decreases
with the decreasing of temperatures,
When the temperature is reduced to a value,the material is destroyed
because of breaking before plasticitying occurs,This is the cold short of the
material,The above-mentioned temperature is called the fragility transition
temperature or abbreviated as the transition temperature 。
?k?
work of the impact force
area of the cut AW?
Work of the impact force
W?
①,U”型口试件的冲击韧性,
A
W
k ?? 断口面积
冲击力功?
②,V”型口试件的冲击韧性,
Wk ?? 冲击力功?
③ 冷脆：温度降低，冲击韧性下降的现象称为冷脆。
当温度降低到某一温度下时，材料在发生塑性变形之
前就因拉断而破坏，这就是材料的的冷脆。而上述温度则
称为脆性转变温度或简称转变温度。
The oil carrier is totally destroyed under low
temperatures,