【作者】 马恩财；

【导师】 王洪祥；

【作者基本信息】 哈尔滨工业大学 ， 机械设计及理论， 2006， 硕士

【摘要】 压痕实验和刻划实验是测量脆性材料弹性、塑性和断裂性能的简单方法。KDP(Potassinm Dihydengen Phosphate,简写KH2PO4)晶体作为一种优质的非线性光学材料目前广泛应用于激光频率转换器的电光开关中。KDP晶体具有易潮解、易碎等不利于光学加工的特点,目前国内外广泛采用单点金刚石切削技术。然而,到目前为止,在研究KDP晶体超精密加工机理时,人们很少关注KDP晶体表面力学性能方面的有关问题,很难找到有价值的相关数据。本文首先通过纳米压痕实验获得了KDP晶体近表层的力学性能,包括:弹性性能(弹性模量E)和塑性性能(纳米硬度H)。实验结果表明:KDP晶体同一晶面不同晶向上的硬度和弹性模量呈现出强烈的各向异性并且都存在着压痕的尺寸效应现象,即随着载荷的增加硬度和弹性模量值减小。然后分别利用Meyer定律、弹性恢复模型、PSR模型和修正的PSR模型对KDP晶体的纳米压痕尺寸效应进行了系统的分析。其次,为了更好地理解近表层力学性能的变化规律,确定KDP晶体最佳的切削方向,本文利用不同的公式对KDP晶体不同晶向的断裂韧性值KIC进行了计算,确定了KDP晶体容易发生脆性断裂的晶体方向,分析了不同晶向断裂韧性呈现出差异的主要原因。同时对KDP晶体超精密加工表面的残余应力σr进行了计算,分析了残余应力的产生原因。最后,利用压痕实验得到的材料性能参数,基于圣维南定理建立了KDP晶体的压痕仿真模型。通过ABAQUS有限元分析软件进行了压痕过程的有限元仿真,得到了KDP晶体的载荷-位移曲线和加/卸载过程中的等效应力变化状况,并且通过对比仿真得出的载荷-位移曲线得到了KDP晶体的应力-应变曲线,最终确定了KDP晶体材料的屈服应力。有限元仿真结果可以为表面力学性能参数的评价提供参考数据。更多还原

【Abstract】 Indentation tests and single-point scratch tests are probably the simplest methods of measuring the elastic, plastic and fracture behavior of brittle materials. KDP(Potassium Dihydrogen Phosphate, it is shorting KH2PO4) crystal is a non-linear optical material used for laser frequency conversion and electrooptic modulators. KDP has several weak points such as soft, brittle and deliquescent from the machining point of view, it is typically diamond machined. However, up to now, mechanical properties have received little attention in the research on the mechanism of ultra-precision mechined of KDP crystal, it is hard to find useful data on its near-surface mechanical properties.Firstly, in this paper, the indentation experiments of KDP crystal are carried out by instrumented indentation testing, the near-surface mechanical properties have been investigated include the elastic property, Young’s modulus E; the plastic property, hardness H. The results show hardness and elastic modulus have strongly anisotropy in the different crystallographic orientation of the same crystal plane and the nanoindentation size effect, according to which the hardness and elastic modulus increases as the indentation load is diminished. The indentation size effect is analyzed by the law of Meyer elastic recovery, PSR model and modified PSR model.Secondly, in order to in-depth understand the laws of near-surface mechanical properties and definite the best cutting direction of KDP crystal, the fracture toughness KIC and residual stressσr in the different crystallographic orientation are calculated by different formulations, the effect of some factors on fracture toughness KIC and residual stressσr are analyzed.Finally, a finite element simulation model of indentation process is developed based on the law of Sheng-Weinan and the material properties which are obtained by various experiments, the indentation process is simulated by ABAQUS finite element analysis software. The load-displacement curve of nanoindentation and the changing laws of equivalent stress on the load/unload process are obtained. The curve of stress-strain can be acquired by load-displacement curve, and the yield stress is achieved in the end. The simulated更多还原