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硬度是衡量金属材料软硬程度的一个重要指标。对于“硬度”这个概念虽早已被人们所熟悉,但目前尚无确切的定义。这是因为硬度不仅取决于材料本身的性质(原子间的结合力,晶体形式,临界抗切应力),同时也取决于试验方法和试验条件。它是材料的弹性、塑性,形变强化率、强度,韧度等一系列不同物理量的综合性能指标,一般认为,硬度是指金属表面局部体积内抵抗变形或破裂的能力。它常常与材料在静负荷下的强度相对应。通过长朝积累,人们建立了强度与硬度的经验关系。例如布氏硬度HB与抗拉强度σ_8之间有如下关系:
Hardness is a measure of the hardness of metal materials, an important indicator. Although the concept of “hardness” has long been familiar, there is no definitive definition yet. This is because hardness depends not only on the nature of the material itself (inter-atomic bonding, crystal form, critical shear stress), but also on the test method and test conditions. It is the material’s elasticity, plasticity, deformation enhancement rate, strength, toughness and a series of different physical quantities of the overall performance indicators, the general view is that the hardness of the metal surface of the local volume resistance to deformation or rupture ability. It often corresponds to the strength of the material under static load. Through long-term accumulation, people establish the empirical relationship between strength and hardness. For example, the relationship between Brinell hardness HB and tensile strength σ_8 is as follows: