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首页> 外文期刊>Journal of Materials Research >Finite Element Analysis And Experimental Investigation Of The Hertzian Assumption On The Characterization Of Initial Plastic Yield
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Finite Element Analysis And Experimental Investigation Of The Hertzian Assumption On The Characterization Of Initial Plastic Yield

机译：初始塑性屈服特性的赫兹假设的有限元分析和实验研究

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Sudden displacement excursions during load-controlled nanoindentation of relatively dislocation-free surfaces of metals are frequently associated with dislocation nucleation, multiplication, and propagation. Insight into the nanomechanical origins of plasticity in metallic crystals may be gained through estimation of the stresses that nucleate dislocations. An assessment of the potential errors in the experimental measurement of nucleation stresses, especially in materials that exhibit the elastic-plastic transition at small indentation depths, is critical. In this work, the near-apex shape of a Berkovich probe was measured by scanning probe microscopy. This shape was then used as a "virtual" indentation probe in a 3-dimensional finite element analysis (FEA) of indentation on <100>-oriented single-crystal tungsten. Simultaneously, experiments were carried out with the real indenter, also on <100>-oriented single-crystal tungsten. There is good agreement between the FEA and experimental load-displacement curves. The Hertzian estimate of the radius of curvature was significantly larger than that directly measured from the scanning probe experiments. This effect was replicated in FEA simulation of indentation by a sphere. These results suggest that Hertzian estimates of the maximum shear stresses in the target material at the point of dislocation nucleation are a conservative lower bound. Stress estimates obtained from the experimental data using the Hertzian approximation were over 30% smaller than those determined from FEA.
机译：在相对无位错的金属表面进行负荷控制的纳米压痕过程中，突然的位移偏移通常与位错成核，繁殖和扩散有关。可以通过估计使位错成核的应力来获得对金属晶体可塑性的纳米力学起源的洞察力。对成核应力的实验测量中潜在误差的评估至关重要，尤其是对于在小压痕深度下表现出弹塑性转变的材料而言。在这项工作中，通过扫描探针显微镜法测量了贝尔科维奇探针的近端形状。然后将此形状用作<100>取向单晶钨的压痕的三维有限元分析（FEA）的“虚拟”压痕探针。同时，用真实的压头对<100>取向的单晶钨进行了实验。 FEA和实验载荷-位移曲线之间有很好的一致性。曲率半径的赫兹估计显着大于扫描探针实验直接测量的曲率半径。这种效果在球的压痕的FEA模拟中得以复制。这些结果表明，位错成核点时目标材料中最大剪切应力的赫兹估计是一个保守的下界。使用赫兹近似从实验数据获得的应力估算值比从FEA确定的应力估算值小30％以上。

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