为探究应变速率对双相合金层裂强度的影响，本研究采用分子动力学方法模拟了Ti-6Al-4V双相合金在不同冲击速度下的层裂过程，发现随着应变速率增大，其层裂强度先增大后减小。首次提出并验证了层裂机制由经典层裂变为微层裂时存在临界应变速率(ε ?_c)。ε ?≤ε ?_c时发生经典层裂；ε ?>ε ?_c时发生微层裂。揭示了层裂机制由经典层裂变为微层裂时的内在机理与位错密度和熔化程度密切相关。发生经典层裂时，孔洞在两相向而行的稀疏波相遇产生的拉伸应力下形核，位错密度增加导致层裂强度增大。发生微层裂时，孔洞在拉伸应力和高温熔化的力热耦合影响下形核、长大和贯通，熔化程度增大导致层裂强度减小。

To investigate the effect of strain rate on spall strength of Ti-6Al-4V dual-phase alloy, the spall processes of Ti-6Al-4V dual-phase alloy under different impact velocities were simulated by molecular dynamics method. It was found that the spall strength increased first and then decreased with increasing strain rate. The critical strain rate (ε ?_c) for the transformation of spall mechanism from classic spall to micro-spall was proposed and verified for the first time. The classic spall occurred when ε ?≤ε ?_c, while the micro-spall occurred when ε ?>ε ?_c. The internal mechanism for the transformation of spall mechanism from classic spall to micro-spall was closely related to dislocation density and melt ratio was revealed. The voids nucleated under the tensile stress produced by the meeting of two opposite rarefaction waves when the classic spall occurred. The increase of dislocation density led to the increase of spall strength. The voids nucleated under the stress-thermal synergistic effect of tensile stress and high temperature melt when the micro-spall occurred. The increase of melt ratio led to the decrease of spall strength.