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首页> 外文期刊>International Journal of Solids and Structures >Reassessing spherical indentation: Contact regimes and mechanical property extractions
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Reassessing spherical indentation: Contact regimes and mechanical property extractions

机译：重新评估球形压痕：接触方式和机械性能提取

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This work concerns systematic finite element simulations of spherical indentation experiments in solids with a vast combination of mechanical properties. The simulations are performed with large and small-strain implementations of the J_2-flow and J_2-deformation theories of plasticity for frictionless and frictional spherical and parabolic contacts. An in-depth comprehension is gained on the mechanics of the transition from the elasto-plastic to the fully-plastic indentation regimes, which allows us to (i) propose general correlations between hardness p?, yield strength σ_(ys), power-law strain hardening coefficient n, and Young's modulus E, enabling mechanical property extractions in polycrystalline metals from hardness measurements performed at different normalized penetrations a/D, (ii) revisit prior conceptions about the contact regimes governing spherical indentation experiments, (iii) examine the validity of self-similarity analyses to fully-plastic indentation experiments, and (iv) find equivalencies between sharp and spherical hardness measurements. Strict analogies are first established between the transition from the elasto-plastic to the fully-plastic contact regimes in sharp and spherical indentations. This is accomplished by considering a constancy in the relationship between normalized hardness p?/σ0.1 and E/σ_(0.1) at different a/D and n values, where σ_(0.1) in the characteristic (representative) indentation strain in the spirit of Tabor's analyses. A detailed discussion is then given on the mechanistic origin to the contact deformation regimes, addressing the role of large deformations and the validity of self-similarity assumptions upon the spherical indentation behavior. The analysis shows that the elasto-plastic regime has different mechanistic origins depending on the ranges of a/D and n. Similarly, full-plasticity leads to three distinct indentation behaviors depending on the proximity of the strain hardening response to the perfectly-plastic model with n = 0, the assumed plasticity theory, and whether material pileup or sinking-in develop. The overall results are framed in the context of contact deformation maps, describing the evolution from the elasto-plastic to the fully-plastic regimes. The extraction of mechanical properties from the above general hardness relations is then confronted against numerous experiments performed in model polycrystalline metals, where guidelines are given to reduce the impact of frictional effects and to improve assessment of the actual σ_(ys) in the material. Finally, a comprehensive discussion on the accuracy of flow vs. deformation plasticity theories in the modeling of indentation experiments is provided. It is suggested that while the flow theory reproduces the contact response in recrystallized polycrystals, deformation plasticity may be more relevant in predicting hardness values in work-hardened metals.
机译：这项工作涉及在固体力学范围广泛结合的固体中进行球形压痕实验的系统有限元模拟。使用无摩擦和摩擦球形和抛物线形接触的塑性的J_2流动和J_2变形理论的大应变和小应变实现方式进行了仿真。对从弹塑性压痕过渡到全塑性压痕机制的机理有了深入的了解，这使我们能够（i）提出硬度p′，屈服强度σ_（ys），功率-之间的一般关系。规律的应变硬化系数n和杨氏模量E，可以从在不同归一化熔深a / D下进行的硬度测量中提取多晶金属的机械性能，（ii）重温关于控制球形压痕实验的接触方式的先前概念，（iii）检查自相似性分析在全塑料压痕实验中的有效性，并且（iv）在锋利硬度和球形硬度测量之间找到等效关系。首先在尖锐的球形凹痕从弹塑性接触方式过渡到完全塑性接触方式之间建立严格的类比。这是通过在不同的a / D和n值下考虑归一化硬度p？/σ0.1和E /σ_（0.1）之间的关系的恒定性来实现的，其中σ_（0.1）在特征（代表）压痕应变中塔博尔分析的精神。然后详细讨论了接触变形机制的机理起源，讨论了大变形的作用以及自相似假设对球形压痕行为的有效性。分析表明，根据a / D和n的范围，弹塑性区具有不同的机理起源。类似地，全塑性会导致三种不同的压痕行为，这取决于应变硬化响应与n = 0的完全塑性模型的接近程度，假定的塑性理论以及材料堆积或下沉的发展。总体结果以接触变形图为背景，描述了从弹塑性到全塑性状态的演变。然后，从上述一般硬度关系中提取机械性能会遇到在模型多晶金属中进行的大量实验，在该实验中给出了减少摩擦效应的影响并改善对材料中实际σ_（ys）的评估的准则。最后，对压痕实验建模中流动与变形可塑性理论的准确性进行了全面的讨论。有人提出，虽然流动理论再现了再结晶多晶中的接触响应，但变形塑性在预测加工硬化金属的硬度值时可能更相关。

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