Development of an automatic Vickers hardness testing system using image processing technology

TLDR

Hardness, a key material property for machine design, is measured by the Vickers method, which relates indentation size to material hardness, but existing automatic systems only work on polished specimens. The study introduces a fully automatic Vickers hardness system that replicates visual testing accuracy and auto‑adjusts image‑processing thresholds. The system uses image processing to detect indentations, automatically calibrates thresholds, and completes a full test cycle in about 20 s. It achieves JIS‑specified accuracy on rough‑polished samples and processes each indentation in roughly 20 s.

Abstract

The mechanical characteristics of machines or machine parts depend on the properties of the materials from which they are made. Hardness is an especially important index for machine design. The Vickers hardness number of a test material is defined by the surface area of the indentation made in the surface of a test specimen by a diamond pyramid indenter. Diagonal lines that indicate the indentation size are usually several micrometers to several hundred micrometers long, depending on the hardness of the material. Conventional automatic Vickers hardness testing systems have been applied only to specular-polished specimens. A new fully automatic Vickers hardness testing system has been developed that emulates visual Vickers hardness testing in terms of accuracy and that automatically sets the threshold level of the image processor to suit indentation image data. It can be applied not only to the testing of rough-polished specimens while meeting the measurement accuracy specified in Japanese Industrial Standard (JIS) B 7725, but can also process one indentation within 20 s, including the indenting, focusing and image processing time.