Research On Mechanical Properties Of KDP Crystal In Ultra-Precision Machined Surface

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...