Experimental determination of correction factors from Charpy impact testing of API X65 steel with varying specimen thickness

Document Type : Research Note

Authors

1 Marin industrial organization

2 Faculty of Mechanical Engineering University of Birjand, Birjand, Iran

3 Faculty of Mechanical EngineeringŁˆ Payame Noor University, Kerman, IRAN

Abstract

The purpose of this research, in addition to determining the characteristic forces including the yield force and maximum force, is to determine the correction factors to predict the onset of failure in the energy transmission pipelines with high toughness under dynamic (impact) loading. To achieve this goal, an instrumented Charpy impact machine, which plot the force-displacement diagram during the impact test, was used. Then, by dividing the area under the force-displacement diagram into two part, the initiation energy and crack growth energy in API X65 steel were calculated. The results showed that the total energy provided by the machine dial had good agreement with the total energy calculated from the area under the force-displacement curve. Characteristic forces, also, was determined from force-displacement curve as is described in the BS 14556 standard. After that, Power law expressions with high accuracy for describing the behavior of the tested steel against variation of the Charpy sample thickness for crack initiation energy, crack propagation energy and characteristic forces were extracted. Additionally, the average correction factor, which is use in prediction models of energy transmission steel pipelines, was found to be 1.26, which is in good agreement with the available results for the current steel. It was shown that by increasing the thickness, due to transition from plain stress to plain strain condition, the correction factor change from 1.26 to 1.3 once the thickness reaches to 10 mm, while it had not been changed so much from 4 to 9 mm thicknesses. By examining the characteristic forces and drawing the ratio of the yield force to the maximum force versus thickness variation, it was also found that increase in thickness led to a decrease in the work hardening of the steel. Finally, by comparing the results of 450 and 750 Joule Charpy impact testing machines, it was concluded that the use of Charpy impact testing machine with the capacity of less than 750 Joules for steels with a fracture energy of less than 250 Joules gave the same result.

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Sharif Journal of Mechanical Engineering

Articles in Press, Accepted Manuscript
Available Online from 20 June 2024

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