| Computer digital analog has become an important means for solving actual problem, dooptimizing design for the test by virtue of digital analog can replace the expensive,time-consuming, even dangerous test. Meanwhile, digital analog calculation has become aneasy, fast and cost saving optimized means. By virtue of computer digital analog, it can alsofulfill visualization to many invisible test processes, facilitate ocular understand testphenomenon, more accurate test result analyzing. Digital analog by means of computer playsa valuable role in providing theretical criteria, helping strengthening the understanding andthe explanation to test result, even in finding out new phenomenon, etc. As some test data aredifficult to measure during the process of supersonic impacting surface nano-crystallization,and the test process is difficult to observe, digital analog is of great important to simulate thetest process.This article adopts with large scale finite element simulation software ANSYS/LS-DYNA and simulates the process of residual stress generated by the treatment ofultrasonic impacting on16MnR specimen sample surface and plastic strain. The ultrasonicimpacting process is that the impact needle strikes16MnR specimen sample surface with acertain speed, enables severe plastic deformation to generate on the specimen surface. Thisarticle adopts with Cowper-Symonds model to proceed digital analog to supersonic impactprocess, analyses the process of residual stress generation, and the residual stress, straindistribution under the function of different ultrasonic impacting parameters. This simulation ischiefly fulfilled on the basis of momentum equation, mass equation, energy equation,boundary condition and material constitutive equation. By the analog, obtain the relationshipamong impacting needle speed, impact needle diameter and specimen residual stress, plasticdeformation. It is shown from the analog result that the larger the impact needle diameter, thelarger the residual stress on specimen surface, the more obvious the plastic deformation it is.In the simulation process, this article analyses the influence of impact time to the distributionof16MnR surface. It can be derived from the analog that, with the increment of ultrasonicimpacting speed and time, the depth of surface residual stress and maximum residual stressincrease.This article also adopts with finite element analytic software to proceed digital analog tothe process of ultrasonic impacting16MnR specimen surface and refining crystal grain. Whenultrasonic impact needle collides16MnR surface with a certain speed, it enables its surface toproduce severe plastic deformation, hence the crystal size of16MnR surface changes. This article successfully embeds Yada crystal grain model to software DEFORM-3D and makesdigital analog by virtue of DEFORM-3D secondary development, the simulation resultsshows that when the plastic deformation excess critical strain, crystal grain size will change,the more severe the surface plastic deformation it is, the more obviously the crystal sizechanges. The degree of grain refining on16MnR surface varies the different ultrasonic impactstrain rates, when the strain rate reaches1000s-1, the average size of grains on the materialsurface is about85.3nm. Under the condition of same ultrasonic impact duration, the averagesize of grains obtained from the test is50nm, the test and numerical simulation results can beregarded as conformity at an order of magnitude. Finally, this article compares digital analogresult to test result, and deduces the process of16MnR surface nanometer-crystallizationprocess.The results show that the process parameters of ultrasonic impacting treatment playimportant roles on the surface nanocrystallizaton. The research results may provide certaintheoretical reference value and significance for further wide application and research ofultrasonic impacting treatment technology. |
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