PSI - Issue 77

P. Santos et al. / Procedia Structural Integrity 77 (2026) 339–347

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P. Santos et al. / Structural Integrity Procedia 00 (2025) 000 – 000

product, with which the steel acquires its definitive characteristics. In particular, the three-point bending specimens (SEB) and the varieties of compact specimens (CTs) contemplated in the ASTM E1820 (2021) and ASTM E1737 (1996) standards to measure the crack growth resistance by means of the J-integral are hardly compatible with high-strength hot or cold-drawn steel products, such as pressure pipes or high-strength bars for structural uses in civil engineering for pre- or post-stressing of concrete, cable-staying or macro-crack sewing of concrete. This work addresses the fracture behaviour of the lath martensite steel with which ultrahigh strength bars, of 23 mm diameter, were manufactured with the aim of improving the low fracture toughness of the more widely used pearlitic-ferritic bars. The geometrical incompatibility of the bending or compact specimen configurations with such a limited diameter is overcome by the BS-8571 (2018) with the single-edge-notch tensile specimen (SENT). In addition to the direct geometrical adaptation and the straightforwardness of tensile loading, the BS-8571 (2018) method has the advantage of not requiring displacement measurements along the load line to determine the strain energy absorbed by the specimen . Instead, the crack mouth opening displacement (CMOD) must be measured on the notched face of the specimen with two coupled extensometers. This measured CMOD plays an analogous role to the load - displacement for determining the experimental J-integral values, according to Cravero et al. (2007) and Teixeira et al. (2018) improves the method accuracy and, as stated by Iordachescu et al. (2018), eases the use of video extensometry measurement systems. This possibility, when considered together with the option explicitly contemplated in the standard of testing in a liquid medium, becomes relevant especially for the assessment of hydrogen assisted cracking resistance of a steel. Given the above, the fracture behaviour of the lath martensite steel is also analysed with the cohesive crack theory. Similar approaches were made by Jemblie et al., (2017), though the results were mainly qualitative. The analysis requires the cohesive model to be particularized for the SENT crack configuration in order to predict the test results specified by the BS-8571 (2018). The Green function proposed by Chell (1976) and the Maxwell reciprocity theorem, as formulated by Rice (1972) for cracked Hookean solids, are used for this purpose. 2. Experimentation 2.1. Material The material employed to carry out the research is an ultrahigh-strength martensitic steel, with the chemical composition given in Table 1. It was supplied by the manufacturer as 23 mm diameter smooth bars, ready for being commercialized as structural tendon-bars or prestressed reinforcements in the construction industry. The mechanical properties describing the steel behaviour were determined by tensile testing cylindrical specimens of 5 mm diameter, machine cut from the bars. Table 2 shows these average values obtained in the four tensile tests performed and the Ramberg-Osgood constants derived from the stress-strain curves. Table 1. Chemical composition of the analyzed bar steel. C Mn Si P S Cu Ni Cr Mo Ti V Fe 0.45 0.65 1.77 0.017 0.004 0.01 0.06 0.15 0.02 0.03 0.003 Bal

Table 2. Mechanical properties the bar analyzed steel.

Elastic modulus, [GPa]

Yield strength , [MPa]

Tensile strength [MPa]

Maximum uniform elongation, [%]

Ramberg-Osgood constants  =  0  1/n n  0 [MPa]