Shear strength diagnostics of machine parts

Abstract

This study presents an effective non-destructive method for determining the ultimate shear strength of parts made of structural carbon and alloy steels. The shear strength was determined using the method of controlled part indentation. In addition, a new material characteristic – a shear hardening modulus – is proposed. The experimental study was carried out using an IR 5143-200 software and hardware complex for metal testing and a double-shear testing device. Steel samples of the following grades were examined: steel 10, 20, 35, 45, 20Kh, 40Kh, 25KhGT and 30KhGSA. The value of plastic hardness was used as a strength characteristic due to its advantages over other hardness values. The conducted experiments found a significant discrepancy (up to 20%) between the reference and experimental values of shear strength. Dependencies for determining the shear strength of structural carbon and alloy steel samples were obtained. The accuracy of these dependencies was determined to be sufficient for engineering calculations both according to the obtained experimental results and literature sources. The error associated with shear strength determination does not exceed ±5%. In addition, the paper provides some types of safety parts that can be destroyed by shear loads. The underestimated reference values of the ultimate strength can lead to increased unrealizable safety margins and, as a result, an increase in the specific metal amount of joints. The proposed non-destructive method for shear strength determination exhibits the accuracy sufficient for engineering practice and can be used when manufacturing, operating and repairing various machine parts and units.