非晶合金中锯齿流变动力学的研究

摘要

非晶合金在外力场的作用下会出现间接性的锯齿流,锯齿具有空间和时间的无序分布性,能够反映塑性变形过程中剪切带的演化过程.借助于混沌理论、自组织临界理论、统计分析、分形和平均场理论等数学方法进行了锯齿动力学研究.发现非晶合金的塑性流变行为与材料的本征结构、试样尺寸、加载试验机的刚度、温度和应变速率等密切相关,揭示了非晶合金的塑性变形过程中剪切带滑移不稳定性的演化特点.试样尺寸小、低温或高应变速率下加载的韧性非晶试样的塑性流变动力学呈现类自组织临界状态,锯齿的幅值分布具有无标度性特点,剪切带之间的交互作用强,剪切带过程相对稳定.低温下大的分形维数说明剪切带分叉速率快,触发了剪切带之间的交互作用.简单的平均场理论证实了非晶合金的塑性可受应变速率调控.这些结论为进一步探索非晶合金的塑性提供了新的思路.%Intermittent serrated flows reflecting the evolution of shear bands,which is characterized by spatiotemporal disordered distribution,can be seen during compressive plastic deformation in amorphous alloys.Chaotic,self-organized criticality(SOC),classical statistical analysis,fractal,and mean-filed theory model are used to investigate the dynamics of plastic flows in response to variant conditions.It is found that the serration dynamics significantly depends on intrinsic structural properties,sample size,stiffness of loading machine,temperature and strain rate,revealing the evolution of shear-band instability.SOC-like state can be obtained in ductile materials with small sample size under low temperatures or high strain rates.It hints about shear bands move in a scale-free intermittent fashion and the great interaction of shear bands.The largest shear-branching rate is indicated by the largest fractal dimension at low temperature,which shows an enhanced fractal behavior.Simple mean-filed theory model (MFT) verifies that plasticity can be tuned by imposed strain rates.These are of great implication for the exploration of plasticity in amorphous alloys.