Determination of fracture properties of cast steels : final report JCU9S

Abstract

Technology currently exists to estimate the structural durability of cracked sugar mill gears and mill roller shafts. Both SRDC projects JCU2S (Crack detection and durability assessment of low speed gears) and JCU6S (finite element and durability modelling of roller shells and shafts) involve the application of linear elastic fracture mechanics to assess cracked components in• Australian sugar factories. The benefits from these projects could not be fully realised due to the lack of fracture property data for Australian manufactured gear and shaft steels.

This project has utilised testing procedures according to ASTM standards to investigate fracture properties such as the Paris Law coefficient and exponent and the fracture toughness for candidate gear and mill roller steels. Four specimens from each material source were tested to provide preliminary fracture property data. These properties can now be used tentatively to assess the structural durability of cracked milling components manufactured from the same material as the candidate gear and shaft steels. A case study investigating the remaining life of a cracked mill roller using the experimental fracture properties is presented.

The experimental results reported have gone someway in completing our knowledge of the material characteristics of cast steels used in Australian sugar factories. Hence, a better understanding of how components will tolerate different operating conditions is now possible. Conceivable amendments to optimise condition monitoring are now possible using fracture mechanics theory and the appropriate material properties. However, it is recommended that further fracture based testing be undertaken to discover what effects operating conditions and manufacturing techniques have on the fracture properties of cast steels used in the extreme conditions imposed on milling equipment.