Review of fracture toughness (G, K, J, CTOD, CTOA) testing and standardization

Abstract

Stress intensity factor Energy release rate CTOD CTOA J-integral J-R curve K-R curve ASTM standard a b s t r a c tThe present paper gives a technical review of fracture toughness testing, evaluation and standardization for metallic materials in terms of the linear elastic fracture mechanics as well as the elastic-plastic fracture mechanics. This includes the early investigations and recent advances of fracture toughness test methods and practices developed by American Society for Testing and Materials (ASTM). The review describes the most important fracture mechanics parameters: the elastic energy release rate G, the stress intensity factor K, the Jintegral, the crack-tip opening displacement (CTOD) and the crack-tip opening angle (CTOA) from the basic concept, definition, to experimental estimation, test methods and ASTM standardizing practices. Attention is paid to guidelines on how to choose an appropriate fracture parameter to characterize fracture toughness for the material of interest, and how to measure the fracture toughness value defined either at a critical point or in a resistance curve format using laboratory specimens. The relevant ASTM fracture toughness test standards considered in this paper are E399 for K Ic testing, E561 for K-R curve testing, E813 for J Ic testing, E1152 for J-R curve testing, E1737 for J Ic and J-R curve testing, E1290 for CTOD (d) testing, a combined common test standard E1820 for measuring the three parameters of K, J and d, E1921 for the transition reference temperature T 0 testing and the master curve of cleavage toughness K Jc testing, and E2472 for CTOA testing. The effects of loading rate, temperature and crack-tip constraint on fracture toughness as well as fracture instability analysis are also reviewed.

Measurement and Modeling of Hydrogen Environment-Assisted Cracking in Monel K-500

“…[13,49] The HEAC properties in Figure 14, from elastoplastic K J analysis of a small specimen, are quantitatively relevant to a structure under elastic loading, following the J-integral approach. [58,60,66,67,[76][77][78] To verify this assertion, it is necessary to demonstrate K and J dominance of crack tip mechanics. [52] K dominance is established by comparing the uncracked SENT ligament (W-a) and plane strain plastic zone diameter (estimated using the Ramberg-Osgood flow properties for Monel K-500) for the deepest crack and high-elastic K of 50 MPaÖm.…”

J-Integral Calculation by Finite Element Processing of Measured Full-Field Surface Displacements

“…The strain energy release rate can be measured directly from the work done to propagate a sub-critical crack [9], and it has long been the practice to calculate the SIF from the applied loads using analytical solutions or finite element methods with knowledge of the specimen geometry and applied load or displacement boundary conditions [10,11]. Elastic-plastic fracture mechanics also enables the extraction of the SIF or strain energy release rate via measurements of the crack opening displacements [12][13][14]. However, in some cases these standard solutions can be inadequate or inaccurate.…”

Maintenance Actions to Address Fatigue Cracking in Steel Bridge Structures: Proposed Guidelines and Commentary

“…The overall effect is a lower ductile fracture resistance that pushes the mode of failure toward brittle fracture. Low constraint, on the other hand, has the opposite effect resulting in lower crack tip stresses with more crack tip yielding and tends to reduce the possibility of brittle fracture (Zhu & Joyce, 2012). Thicker members are more constrained, behaving in a plain strain mode where deformation or yielding (Poisson effect) is limited, or even prevented.…”

“…(Zhu & Joyce, 2012) and results in large dissipation of energy per unit crack extension. The fracture is characterized by a very jagged surface and extensive plastic deformation, particularly at the edges of the plate where ''necking'' usually can be observed.…”

“…Instances of brittle fracture have elastic deformation that dominates the crack tip and initiation toughness is governed by the material fracture resistance. The stress intensity factor, K, was proposed by Irwin in 1957 to describe the intensity of the stress state immediately ahead of a sharp crack tip as part of LEFM (Zhu & Joyce, 2012). K has the unusual units of stress x length 1/2 (e.g., MpaN!m 5 0.9102 ksiN!in).…”