chapter6材料变形课件.ppt

6 材料的变形 Deformation of Materials;*;*;*;*;变形和断裂;*;*;*;*;*;*;*;*;*;*;*;*;*;*;*;*;*;*;*;; The main difference between slip and twinning is that the former does not cause any change in orientation in the sense that any crystallographic direction remain the same with respect to the laboratory coordinate systems. While the latter results in change in orientation. After twinning the two parts of the crystal, twinned and untwinned, are symmetrical to some plane or orientation. Or say, one is the twin of the other.;滑移是指晶体的一部分沿一定的晶面和晶向相对于另一部分发生滑动位移的现象。;滑移线与滑移带(slip lines and slip bands);*;*;*;2. 多滑移(multiple slip);*;Slip occurs when the resolved shear stress acting on slip plane along slip direction reaches a critical value, called the Critical Stress, Critical Resolved Shear Stress (CRSS) and is characteristic of the crystal in question. When , slip starts as when slip starts. depends on material and temperature. For FCC: For BCC: and other structure: ;Solution To solve this problem we must find both and in Equation 6-4. This can be done using the vector dot product:;*;*;Application of Schmid’s law;Example: Given: FCC crystal having {111}110 slip system Determine active slip system in response to tensile loading along .; locate inside the orientation triangle ( ), single slip. locate at the edge of the orientation triangle ( ), double (duplex) slip. locate at the corner of the orientation triangle, multiple slip.;*;*;5. 滑移时晶面的转动与旋转(rotation);转动可能进一步产生多滑移;转动与旋转的原因： 晶体滑移后使正应力分量和切应力分量组成了力偶 ;*;孪晶系 twinning system;FCC晶体的孪生变形;*;密排六方晶格金属滑移系少，常以孪生方式变形。体心立方晶格金属只有在低温或冲击作用下才发生孪生变形。面心立方晶格金属，一般不发生孪生变形，但常发现有孪晶存在，这是由于相变过程中原子重新排列时发生错排而产生的，称退火孪晶。;扭折是不均匀塑性变 形的一种形式，它是 在滑移和孪生难以实 现，或者在变形受到 某种约束时才出现的。 扭折是晶体弯曲变形或 滑移在某些部位受阻， 位错在那里堆积而形成 的。;唉磊充炯烁吊非科遵懒寇础幕的柏电瓢腿武堤榆铝际豪栋结侠门制踌掐憨chapter6材料变形课件chapter6材料变形课件;单晶体的应力-应变曲线;6.3 多晶体的塑性变形 （Plastic deformation of polycrystalline）;(2) 晶界对形变过程的阻碍作用;Cu-4.5Al合金 晶界的位错塞积;*;*;*