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为了研究薄板拉伸性能的尺寸效应及其产生的微观机制,对晶粒尺寸相似但厚度不同的H80薄板试样进行了拉伸试验和显微硬度试验.通过建立晶界区域强化模型和晶粒间的弱弱组合变形机制,研究了薄板的厚度尺寸、晶粒尺寸及显微硬度分布对拉伸力学性能的影响.结果显示:强度指标值和塑性指标值均随厚度尺寸的减小而降低,呈现越小越弱的尺寸效应现象,但强度指标和塑性指标的变异因子值却呈现越小越强的相反规律.薄板的横向硬度均值随厚度尺寸的增大而增大,而横向硬度值的变异因子却随厚度尺寸的增大而减小.随厚度尺寸的减少,晶界区域所占百分比的减少和单个晶粒所占百分比的增加是产生拉伸性能尺寸效应现象的根本原因.此外,显微硬度分析表明:易变形区域形成的概率随厚度尺寸的减小而增大,易变形区域的集中变形是引起薄板试样过早断裂的原因.

In order to investigate size effects on the tensile properties of thin sheets and deformation mechanism,tensile tests and micro-hardness tests of H80 thin sheet specimens with similar grain sizes but different thickness were performed.In order to study the effects of thickness,grain size and the micro-hardness distribution on the tensile properties of thin sheets,grain boundary strengthening model and weak grain deformation mechanism were built.According to the experimental data,strength and plasticity both decreases with thickness decreasing,which presents a size effect of thinner sheets,weaker strength.However,the variation coefficient of strength and plasticity presents an opposite law.The transverse mean hardness of thin sheets increases with the increase of thickness,while the variation coefficient is contrary for transverse hardness.The reason why the size effect of tensile properties occurs is that the percentage of grain boundary decreases and the percentage of single grain increases with thickness decreasing.In addition,the micro-hardness results indicate that the formation probability of easy forming areas increases with thickness decreasing and intensively deforming of easy forming areas is the main reason for premature fracture of the thin sheets.