| With the development of flexible electronic products,single-crystal silicon sheet materials with malleable nanoscale thickness will be widely used.However,such flexible single-crystal silicon sheet materials will inevitably be subjected to external force and strain to cause nanoscale damage in processing and application.At present,the damage mechanism of single-crystal silicon sheet with nanoscale thickness is not clear.In view of the difficulty of experimental research,this paper simulates three processes of monocrystalline silicon substrate impacted by abrasive water jet with silica cluster,pure water jet and single silica cluster by molecular dynamics method,and studies the damage formation mechanism of single crystal silicon sheet under impact.There are two stages in the impact process of abrasive water jet,namely,"impact loading stage" and " substrate rebound recovery stage".In the impact loading stage,with the increase of impact velocity,the silicon substrate will gradually transition from microdamage to a single macroscopic crack along the 45 ° cleavage plane direction,and a double macroscopic crack along the 45° and 135° cleavage plane directions,until the appearance of a double macroscopic crack accompanied by a "hole".The formation of macroscopic cracks will cause the local temperature and tensile stress in the collision zone to propagate along the cleavage plane accordingly.During the recovery stage of substrate,tensile stress continues to propagate and release along the cleavage plane direction,resulting in substrate cracks that will first further expand until they reach a maximum and then gradually close.For the pure water jet process without silica clusters,the damage formation process of silicon substrate is basically consistent with the abrasive water jet process.The combination of local temperature and tensile stress in the collision zone makes the damage pattern of silicon substrate appear as macroscopic cracks along the cleavage plane and "holes" due to material removal.However,due to the "solidification" of the confined water film at the collision zone of the silicon substrate,there is a coupling effect between the clusters and the water molecules,which results in that the critical velocity of macroscopic cracks in the pure water jet is significantly lower than that in the abrasive water jet.However,different from the abrasive water jet and pure water jet impact processes,in the dry impact process of single silica cluster impacting single crystal silicon sheet,because the local temperature in the collision zone plays a dominant role in the substrate damage,the damage form of the substrate will not show macroscopic cracks in the direction of 45 ° and 135 ° cleavage planes,whether it is reflected as "pitting" damage without material removal or "hole-like" damage with material removal.Finally,the second impact process of silicon sheet after the first abrasive water jet impact recovery is simulated at the same speed.The results show that when the impact velocity approaches the critical loss velocity,the maximum tensile stress will lag slightly.At this time,due to the increase of the local temperature and pressure in the impact zone during the impact loading stage,the water flow immersed in the crack will form a certain stress between the cracks,so that the cluster will begin to appear through the substrate and the cracks will further expand during the second.when the impact velocity exceeds the critical velocity,the peak stress hysteresis is significant until it appears at the stage of substrate rebound,which also leads to the crack length of the substrate in the second impact being longer than the first.When the impact velocity is lower or much higher than the critical velocity,and there is little difference in the damage of the substrate before and after.The above results further verify the damage formation mechanism of monocrystalline silicon film under water jet impact of abrasive particles and the repeatability of its formation process under continuous impact. |
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