固体材料的结构层次及其动力变形与破坏

Structural hierarchy and dynamic deformation and fracture of solids

材料(岩体、金属等)具有复杂的结构层次,材料结构层次影响着材料的力学特性及其变形与破坏过程。从材料的结构层次的观点研究了材料动力变形与破坏。由研究可以看出,材料变形破坏的时间与空间尺度之间存在着紧密的关系,慢速过程发生于大尺度水平上,而快速过程发生于微细观水平上。材料变形破坏的塑性或者脆性特性取决于裂纹尖端处空穴盘能否在裂纹扩展前长大到临界尺寸,并转化为位错环。如果来得及长大到临界尺寸,那么就会有塑性破坏,否则就会有脆性破坏。正是由于这种原因在强度对于应变率的依赖关系中出现了塑性—脆性及脆性—塑性转变。材料在强烈受激状态下势能起伏及群体受激谱都要发生调整,在微细观水平上材料粒子发生了相关联的运动。正是这种相干运动使得材料在外部作用逐渐增强的情况下出现不同尺度的涡旋运动,进而使得材料的黏性随着应变率的增加而减小。

Materials （rock, metals and etc. ） have complex structural hierarchy which influences the mechanical properties of materials and their deformation and fracture processes. The dynamic deformation and fracture of materials were researched from the angle of the structural hierarchy. The research shows that there exists close relationship between spatial and temporal scales of deformation and fracture of materials. Generally slow processes take place at macroscopic structural levels and quick processes are related to meso-or micro-structural levels. The plastic or brittle property of deformation and fracture of materials depend on whether the vacancy disc at the tip of main crack develops to the critical size and transforms into dislocation ring before the growth of the main crack. If the vacancy disc has time to grow to the critical size before the growth of the main crack, then the deformation and fracture of materials demonstrate plastic property, and other wise, the deformation and fracture of materials will be brittle. It is for this reason that the ductile-to-brittle and brittle-to-ductile transitions under dynamic loading with the increase of strain rate arise. Under highly excited state the rearrangement of potential pattern and spectrum of collective excitation of material particles take place, and correlated motion of particles arises. It is the correlated motion that causes the appearance of eddies of different sizes in material and the decrease of viscosity with the increase of intensity of external loading.