Miniature specimens are widely being used to determine tensile properties of various size-limited new materials, especially quickly evaluate or monitor changes in mechanical properties of in-service reactor components to ensure their continuous operation with large safe margins. Although tensile properties of the miniature specimens are investigated extensively, the basic mechanism on such size effects, especially tensile plasticity, is not understood well. Here, tensile properties of A588 low alloy steel specimens with different gauge lengths and thicknesses are systematically investigated in situ using the digital image correlation technique. The findings reveal that the increase in the post-necking elongation with decreasing the specimen gauge length and the decrease with decreasing the specimen thickness are due to the scale-dependent strain-rate sensitivity, whereas the constant uniform elongation is attributed to the stable strain hardening exponent. An empirical formula on the relationship between the total elongation and the strain-rate sensitivity is proposed to describe the basic mechanism behind the specimen size-dependent elongation.

中文翻译：

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用数字图像相关技术研究低合金钢微型试样的拉伸塑性

微型试样被广泛用于确定各种尺寸受限的新材料的拉伸性能，特别是快速评估或监测在役反应堆组件的机械性能变化，以确保其连续运行并具有较大的安全裕度。尽管对微型试样的拉伸性能进行了广泛的研究，但对这种尺寸效应，尤其是拉伸塑性的基本机制尚不清楚。在这里，使用数字图像相关技术在原位系统地研究了具有不同标距长度和厚度的 A588 低合金钢试样的拉伸性能。研究结果表明，随着试样标距长度的减小，颈缩后伸长率的增加和试样厚度的减小是由于尺度相关的应变率敏感性，而恒定的均匀伸长率归因于稳定的应变硬化指数。提出了一个关于总伸长率和应变率敏感性之间关系的经验公式来描述试样尺寸相关伸长率背后的基本机制。