Abstract
In order to study the influence of scratch direction on the deformation characteristics and material removal mechanism of optical glass BK7, nanoscratching experiments were conducted on a Nano indenter using Vickers indenter. Results indicate that the face-forward scratch is more likely to induce the initiation and propagation of lateral cracks, which is found to be more beneficial to material removal processes; in contrast, small chips and debris are released from the machined grooves without introducing lateral cracks in the edge-forward condition, leading to poor material removal efficiency. In addition, the choice of scratch direction can make differences to the elastic recovery rate of optical glass BK7. The results revealed that both the elastic recovery rate and the residual stresses of the material under the face-forward scratching are greater than those of the edge-forward scratching. A theoretical model for coefficient of friction (COF) under different scratch directions was established. It is found that the COF between indenter and workpiece in the edge-forward scratching is larger than the face-forward scratching under otherwise identical conditions, this finding is consistent with experimental results. A stress field analysis using finite element method (FEM) was conducted to understand the different crack initiation and propagation behaviors from different scratch directions. The current study discusses the significance of scratch direction on material removal behavior of optical glass BK7, and the results would encourage further research on investigating the connections between tool geometry and material removal mechanism.
Highlights
Optical glass BK7 has been a promising material widely applied in aeronautics, laser technology, photoelectric communicational, and medical fields because of its stable mechanochemical properties and excellent optical uniformity [1,2,3,4]
In the current study, nanoscratching experiments were conducted on optical glass BK7, using a
In the current study, nanoscratching experiments were conducted on optical glass BK7, using a quadrangular pyramid probe-based indenter to investigate the influence of the indenter direction quadrangular pyramid probe-basedonindenter to investigate the influence indenter direction the material removal mechanism andof thethe material deformation on the material removal mechanism and the material deformation characteristics including the elastic recovery rate and the coefficient of friction (COF)
Summary
Optical glass BK7 has been a promising material widely applied in aeronautics, laser technology, photoelectric communicational, and medical fields because of its stable mechanochemical properties and excellent optical uniformity [1,2,3,4]. For precision and high value-added applications, the material is required to provide accuracy and surface roughness at micro/nano scale. Optical glass BK7 is a typical hard-brittle material which is difficult to machine for precision because of its high hardness and low fracture toughness [5]. Extensive studies investigating the material removal mechanism of hard-brittle materials have been conducted through scratching experiments at micro/nano scale, which provided in-depth understanding of the processing mechanism between abrasive grains and workpiece such as grinding and polishing. Researches have revealed that nanoscratching of hard-brittle materials is a complex process with multiple influencing factors, including scratch speed [6,7,8], shape and geometric parameters of tool [9,10], environment [11], and so on. Many scholars have conducted studies to explore the effect of scratch directions in the processing of materials [12,13,14,15,16]
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