Analysis of notch effect in the apparent fracture toughness and the fracture micromechanisms of ferritic–pearlitic steels operating within their lower shelf

Abstract

The fracture resistance of materials is generally higher in notched conditions that in cracked conditions. In other words, when the notch radius increases there is also an increase in the apparent fracture toughness, which is that exhibited in notched conditions. This paper presents an analysis of the notch effect on two ferritic-pearlitic steels operating within their corresponding lower shelf, and develops an experimental The research is completed with the analysis of the evolution of fracture micromechanisms when the notch radius increases, revealing a direct relation between this evolution and the apparent fracture toughness observations.

On the assessment of U-shaped notches using Failure Assessment Diagrams and the Line Method: Experimental overview and validation

“…L r may also be expressed following equation (3), which is totally equivalent to equation (2) [22]: L r evaluates the structural component situation against plastic collapse, and K r evaluates the component against fracture, the assessed component being represented by a point of coordinates (K r , L r ). Once the component assessment point is defined through these coordinates, it is necessary to define the component limiting conditions (i.e., those leading to final failure).…”

“…The authors have published a number of papers analysing the notch effect in different materials (e.g., [3][4][5]11,12]), and have also provided a model for the structural integrity assessment of notches by using the FAD methodology and the Line Method (LM) correction for the consideration of notch effects [13,14]. This model has been validated individually for different materials (e.g., PMMA and Al7075-T651 [13], and structural steels S275JR and S355J2 [14]), but the results are not directly comparable, given that the Failure Assessment Line (FAL) defining the critical situation in the corresponding FAD depends on the material tensile properties, so that the FAL used in the above mentioned research varies with the material being analysed.…”

On the Line Method apparent fracture toughness evaluations: Experimental overview, validation and some consequences on fracture assessments

“…On some occasions, the apparent fracture toughness remains approximately constant above a certain notch radius [6,9,39], and the experimental results differ from the LM or PM predictions (which predict a monotonically increasing fracture resistance when increasing the notch radius), whereas in other cases the experimental results continuously increase with the notch radius [9,38,40]. Some results of the apparent fracture toughness are conservative [2,9], whereas the predictions for other cases perfectly fit the experimental results or are non-conservative [3,6,9]. All this makes it necessary to undertake a sound analysis of the K N mat evaluations provided by the PM and the LM, providing a homogeneous treatment of the experimental data in order to find an answer to the above mentioned issues.…”

“…In the last few years, the present authors have published a number of papers showing the application of the LM to a wide range of materials: polymer PMMA [3], aluminium alloy Al7075-T651 with two different orientations (LT and TL) [6], two common rocks (granite and oolitic limestone) [30], and four structural steels (S275JR, S355J2, S460M and S690Q) [2,31,32]. Moreover, such steels have been tested at 3 different temperatures of their corresponding Ductile-to-Brittle Transition Zone (DBTZ) and, in case of steels S275JR and S355J2, at temperatures equal to their Lower Shelf.…”

“…In fact, as has been widely shown in the literature (e.g., [1][2][3][4][5][6][7][8][9]), components with non-sharp defects or notches exhibit an apparent fracture toughness that is greater than that obtained for cracked components. This generally has direct consequences on the load-bearing capacity of the structural components and also on their structural integrity assessments [4].…”