Study on ASTM E399 and ASTM E1921 standards

Abstract

A B S T R A C T Costs of ASTM E399 and ASTM E1921 tests, which were developed to determine the fracture toughness (K Ic ) and the ductile-brittle transition temperature of ferritic steels, respectively, are considered high and the procedures are also very complicated. In this study, a method, which is more cost-effective and easier to carry out, is proposed.Keywords fracture toughness; the ductile-brittle transition temperature. N O M E N C L A T U R EB = thickness of test specimen B * * = thickness of test specimen at T * * temperature B 0 = gross thickness of test specimen (side grooves ignored) B x = thickness of the specimen to obtain the ductile-brittle transition temperature C = constant H 0 = constant with thermal activation energy unit for a certain material k = Boltzmann constant K Ic = fracture toughness K 0 IC = value of K IC at T = 0 K K * * Ic = value of K Ic at T * * temperature K Id = dynamic fracture toughness K jc (0) = K jc for a specimen of size B 0 , K jc(med) = the median value of fracture toughness obtained by J-Integral.K min = 20 MPa (m) 1/2 . m = temperature sensitivity of fracture toughness n = strain hardening coefficient T = test temperature, K T k = constant temperature, K T 0 = reference temperature, K σ y (0) − σ 0 = effective value of yield stress when T = 0 Ḱ ε = plastic deformation raté ε 0 = constant with plastic deformation rate unit, depending on internal structure of material (pre-exponential factor) α = temperature sensitivity of yield strength σ c = the critical stress effective ρ c = distance from the crack tip σ y = yield strength at T temperature σ 0 = athermal part of yield strength σ * * y = yield strength at T

A study on the ASTM E1921 standard in determining the fracture toughness of ferritic steels

“…The reason behind this is that the yield strength of BCC latticed metals and alloys changes with temperature and strain rate. Similarly, fracture toughness changes with temperature and strain rate …”

“…A hypothesis was accepted for ferritic steels regarding the exponential dependence of plastic deformation at the crack tip of fracture toughness on thermo‐activation energy …”

A new method for determining the fracture toughness of main pipeline steels

“…A hypothesis was developed on ferritic steels by taking account of the exponential dependence to plastic deformation at the crack tip of the fracture toughness on thermo‐activation energy analysis . The mathematical expression of this hypothesis is given in formula ().…”

“…Considering that K μ and σ c parameters are not in relation to temperature and strain rate, the following equations for K IC are accepted according to test results …”

“…The method used in the present study that reveals the relationship between the fracture toughness and the basic mechanical properties aims to eliminate the need for cracked specimens in the determination of the fracture toughness. The basis of the used method on the thermo‐activation energy analysis of the plastic deformation of metals is composed of the relationship between the fracture toughness and strain rate, temperature, grain size and mechanical properties …”