金属的断裂优秀课件

6.1 Basic types of fracture 断裂的基本类型
According to whether the metal has obvious plastic deformation before fracture, it can be sorted as following : 根据断裂前金属是否有明显的塑性变形可分为
d 2m E dx a
(1-4)
在正弦曲线初期 cos(2m ) 1
宏观断裂
微观断裂
正断与剪断的宏观与微观形式
According to crack trend in microscopic view
从微观上按照裂纹的走向可分为
transgranular fracture 穿晶断裂/晶间~
intergranular fracture 沿晶~
grain晶粒
穿晶断裂
沿晶断裂
Fracture along grain-boundary in polycrystal material
多晶材料沿晶界发生的断裂
- 沿晶脆性断裂 intergranular precipitated brittle continuous film －沿晶析出脆性连续膜
- 沿晶韧性断裂－晶界弱化,出现韧窝 dimple
Under the pulling force, the force which can help two adjacent atomic planes overcome interatomic bonding force, and separate the two atomic planes.
两相邻原子面在拉力σ作用下，克服原子间键合 力作用 ，使原子面分开的应力。
裂纹穿过晶粒内部crack cross the interior of grain
① 穿晶脆性断裂 low speed , high temperature and stress concentration. along some crystal plane--cleavage plane解理面
② 穿晶韧性断裂 micropore coalescence 微孔聚合
6Βιβλιοθήκη Baidu2 脆性断裂 brittle fracture
材料塑性变形能力很低，裂纹尖端的应 力集中不能因塑性变形而松弛。
6.2.1理论断裂强度 theoretical fracture strength
完整晶体在正应力作用下沿某一晶面拉断的强 度。
(1)破坏； (2)成形性。
In this chapter ,we will analyze the
physical essence and laws of fracture. 断裂的物理本质/规律
➢ Definition of fracture
When metallic material deformation forereach its plastic limit , it will divide completely. Then the interatomic force is damaged. 断裂－金属材料在变形超过其塑性极限—完全分
开.原子间结合力遭受破坏。
related subjects
断裂力学 fracture mechanics - macroscopic Stress field 应力场 Strain field 应变场 Fracture criterion 断裂判据
断裂物理 fracture physics - microscopic •Fracture mechanism 断裂机制 •Microstructure 组织
m --- 将原子拉开所需的最大应力，即断裂理 论强度
0 /2m S(i2 nx/)d xm /(1-2)
断裂后出现两个新的断裂面，表面能为2
外力抵抗原子间结合力做的功 = 产生断裂新面的
表面能
m/2r
(1-3)
m2r/
由虎克定律 E E x
a
d E dx
将替换
将(1-1)对x求导
完整晶体拉断示意图 mn为断裂面的迹线；a表示原子面间距
原子间作用模型：原子间作用力与位移间 的关系满足正弦 规律
mSi(2n x/) (1-1)
m --- 将原子拉开所需的最大应力，
即断裂理论强度。
晶体中的内聚力与原子间距的关系
原子间作用模型：原子间作用力与位移间 的关系满足正弦规律
mSi(2n x/) (1-1)
It will largely reduce the rate of finished products and production rate成品率/生产率↓.
挤压制品的周期裂纹
We concern about fracture for two reasons. One is crack’s destructive effect, the other one is that fracture is related to material’s formability .
金属的断裂优秀课件
问题的提出：构件失效、灾难性的后果
cargo ship货船
Plastic deformation 塑性成形 surface/ internal cracks in working materials →integral failure.
加工材料出现表面/内部裂纹→整 体破断
This happens in rolling轧制 ,extrusion挤压, drawing拉拔 ,forging锻造and so on.
brittle fracture 脆性断裂ψ<5% ductile fracture 韧性断裂 ψ>5%
According to the orientation relationship between fracture and acting force 按断裂面相对作用力的取向关系可分为
normal failure 正断 against to σ1 shearing failure 剪断 along the direction of maximum shear