PSI - Issue 81

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ScienceDirect

Procedia Structural Integrity 81 (2026) 1–2

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords: preface, damage, fracture, modelling, prediction, diagnostics; non-destructive evaluation, environmental effects. 1. Introduction During operation, materials of structural elements are subjected to damage whose nature depends on the mode of loading and operating conditions (high and low temperatures, cyclic loading, corrosive environments, irradiation, etc.). The diagnostics of material damage and its description are highly important for developing methods to improve reliability, predict the residual life of structural elements, and optimise the physical and mechanical properties of materials. Investigations of damage accumulation in metals involve both the development of fundamental descriptions of this phenomenon and methods for assessing the strength and service life of structural elements, accounting for the full set of design and operational factors. VIII International Conference “In - service Damage of Materials: Diagnostics and Prediction”, organised under the auspices of the European Structural Integrity Society (ESIS), has a long history. Previous conferences were held in Ternopil in 2009, 2011, 2013, 2015, 2017, 2019, 2023. The main organisers of these conferences were Ternopil Ivan Puluj National Technical University, Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, the Ukrainian Society on Fracture Mechanics (USFM), and the G.S. Pisarenko Institute for Problems of Strength of the National Academy of Sciences of Ukraine. The USFM presents Ukraine in the ESIS via the Ukrainian National Group. The DMDP 2025 was held online between 15-17 October 2025. This conference brought together leading scientists, researchers, and research scholars to share their experience, research results, and scientific ideas in key areas of fracture and damage mechanics, structural integrity assessment, and maintenance. It has become an interactive platform for discussing recent advances, trends, and practical challenges in fracture mechanics and structural integrity. The Conference hosted 112 presentations from Spain, Belgium, the United Kingdom, Germany, Poland, France, the Slovak Republic, Israel, Latvia,Brazil, Indonesia, Vietnam, South Korea, VIII International Conference “In -service Damage of Materials: Diagnostics and Prediction ” (DMDP 2025) Preface – In-service Damage of Materials: Diagnostics and Prediction Oleg Yasniy a, *, Olha Zvirko b , Volodymyr Iasnii a , Yuri Lapusta c a Ternopil Ivan Puluj National Technical University, 56 Ruska St., Ternopil 46011, Ukraine b Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova St., Lviv 79060, Ukraine c Université Clermont Auvergne, CNRS, Clermont Auvergne INP, Institut Pascal, F-63000 Clermont-Ferrand, France

Japan, and Ukraine that covered the following topics: • Localised and Nonlocalised Damage of Materials; • Damage Prediction; • Non-destructive Testing and Damage Detection; • Degradation Assessment and Failure Prevention;

* Corresponding author. Tel.: +380-352-52-41-81. E-mail address: oleh.yasniy@gmail.com

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.001

Oleg Yasniy et al. / Procedia Structural Integrity 81 (2026) 1–2

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• Crack Initiation and Propagation; • Fractography and Advanced Metallography; • Damage Tolerance; • Environmental Effects; • Durability; • Structural Integrity; • Reliability and Life Extension of Components; • Failure Analysis and Case Studies.

This special issue contains the full-text papers accepted for publication after peer review. We hope that it will be of interest to scientists and engineers working in fracture mechanics, materials science, and structural integrity, as well as to university lecturers and postgraduate students in related disciplines. We also expect it to be useful for practitioners in industrial sectors such as power generation, machinery, transport, the chemical industry, and civil engineering. As Guest Editors of these Conference Proceedings, we thank all authors, reviewers, and members of the organising and programme committees for their contributions and support. Acknowledgements The Guest Editors of this Special Issue wish to express their profound gratitude to Prof. Francesco Iacoviello, Editor-in-Chief of the Procedia Structural Integrity journal, and the dedicated Elsevier staff for their invaluable support throughout the preparation of this issue.

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Procedia Structural Integrity 81 (2026) 321–326

VIII International Conference “In -service Damage of Materials: Diagnostics and Prediction ” (DMDP 2025) Adhesion of Class A500C Steel Reinforcement to Concrete of Various Strengths

Oleksandr Chapiuk a, *, Sergiy Filipchuk b , Oleksandr Suvorov a , Orest Pakholiuk a , Dmytro Kusliuk a ,Iryna Zadorozhnikova a , Olga Uzhegova a , Anastasiia Shevchuk a

a Lutsk National Technical University, Lvivska 75, 43018 Lutsk, Ukraine b National University of Water and Environmental Engineering, Soborna 11, 33000 Rivne, Ukraine

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords: bond between concrete and reinforcement, bond stress, strength, sickle-shaped profile, stress, reinforcement deformations. 1. Introduction A wide range of materials is used in the construction of buildings and structures for various purposes (Dvorkin et al., (2021); Kos et al., (2022). These materials are very often applied in the assembly of load-bearing structures (Babych et al., (2019); Gomon et al., (2019); Kovalchuk et al., (2022); Bosak et al., (2021)), including concrete and reinforced concrete elements (Korniychuk et al., (2024); Filipchuk et al., (2024); Babych and Andriichuk, (2017); Drobyshynets et al., (2024); Parneta et al., (2024); Dovbenko et al., (2024)). The improvement of reinforced concrete structures depends on the development of a theory that adequately reflects the actual structural behaviour during service conditions (Konkol et al., (2019); Rybak et al., (2025); Sobczak-Piastka et al., (2020)). One of the key issues in this context is the determination of the bond between reinforcement and concrete, which plays a crucial role in ensuring the strength, stiffness, and crack resistance of reinforced concrete elements (Chapiuk et al., (2025); Babich et al., (2019); Filipchuk et al., (2023); Chapiuk et al., (2023)). Considerable progress has been made in studying the interaction between concrete and steel reinforcement, which is essential for both reinforced concrete theory and engineering practice. Abstract New experimental data on the bond forces (bond stresses) between sickle-shaped ribbed steel reinforcement of class A500C and normal-weight concrete of various strength classes have been obtained. Pull-out tests of 16 mm diameter steel bars embedded in concrete prisms 5d (80 mm) high were conducted using a hydraulic tensile testing machine. An improved calculation methodology is proposed to ensure a reliable bond between A500C steel reinforcement and normal-weight concrete of varying strength levels. It was established that an increase in concrete strength leads to a proportional increase in the bond capacity of sickle-shaped reinforcement. A linear relationship between the maximum tangential bond stresses and concrete strength was identified, demonstrating good agreement with the experimental results. The proposed linear dependence can be applied in the design of reinforced concrete structures for calculating the ultimate bond strength between sickle-shaped steel reinforcement and normal-weight concrete of various strength classes.

* Corresponding author. Tel.: +38-099-227-19-87; fax: +0-000-000-0000 . E-mail address: ochapiuk1983@gmail.com

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.056

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However, a sufficiently substantiated and comprehensive theory of concrete-reinforcement bond has not yet been fully developed, especially considering the diversity of reinforcement types. Bond deterioration caused by external loading and other factors leads to changes in the structural behaviour of reinforced concrete elements. With increasing load levels and progressive bond degradation, continuous qualitative changes occur in the stress-strain state of the element. Sickle-shaped ribbed reinforcement has been manufactured and used for more than two decades; however, existing studies on the bond behaviour of A500C reinforcement (DSTU 3760:2019; Eurocode 2:2004) with concretes of different strength classes remain insufficient for the accurate and efficient calculation of its anchorage length. This type of reinforcement is recommended for use in both non-prestressed and prestressed concrete structures. Bond strength increases with an increase in the specified concrete strength class, a decrease in the water-cement ratio, and an increase in concrete age. In cases of insufficient anchorage at the ends of reinforcing bars, welded transverse bars or anchor plates are applied. When a reinforcing bar is pushed into concrete, the bond strength is higher than in pull-out tests, which is explained by the resistance of the surrounding concrete to the transverse expansion of the compressed bar. The objective of this study is to analyze experimental data on the influence of concrete strength on the bond behaviour of A500C reinforcement and to establish the corresponding relationship under single short-term and repeated loading conditions.

Nomenclature f cube

cubic strength of concrete prismatic strength of concrete temporary tensile strength of rods

f prism

 u E s A s δ u

initial modulus of elasticity of reinforcement

area of rods

slip (displacement) of the free end of the rod relative to the end of the prisms

stress in the rod at δ u =0.2 mm 0.2% proof stress of reinforcement stress in the rod (beginning of slippage)

σ s 0 m σ 0,2

σ s

tangential stresses

τ um

2. Methods of experimental research The research task was addressed using concrete prisms with a square cross-section, having a side length of 150 mm and a height of 5d, where d = 16 mm is the bar diameter (i.e., 80 mm). The reinforcing bars were positioned in the concrete prisms so that their longitudinal axes coincided, while the protruding parts of the bars allowed fixing one end in the grips of the hydraulic tensile testing machine and measuring, at the other (free) end, the displacement relative to the end face of the concrete prism (Fig. 1a). The mechanical properties of 16 mm diameter A500C steel reinforcing bars were determined by uniaxial tensile tests performed on a hydraulic testing machine in accordance with the standard procedure (Table 1). The load was applied to the bar in increments of 1.0 kN. During loading, the displacement of the free end of the bar relative to the prism face was measured using a dial gauge indicator with a resolution of 0.001 mm, while the bar deformation relative to the concrete prism was measured using a Huggenberger mechanical extensometer with a 20 mm gauge length and a resolution of 0.001 mm (Fig. 1b).

а

b

Fig. 1. General view of specimen testing in the hydraulic tensile machine (a) and measurement of reinforcement displacement using a dial gauge and bar deformation using a Huggenberger extensometer (b).

According to BS 4449:1997, the bond limit state between reinforcement and concrete is defined as the condition at which the slip of the free end of the reinforcing bar relative to the prism face reaches δ u = 0.2 mm. Therefore, this value of δ u corresponds to the reinforcement stress σ s0 .

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Table 1. Mechanical properties of 16 mm diameter A500C steel reinforcing bars Diameter, mm Cross-sectional area, mm² 0.2% proof stress σ 0,2 , MPa Modulus of elasticity E s , MPa

Ultimate tensile strength σ u , М P а

16

201.5

498

200000

675

The mechanical properties of concretes of different strength classes were determined by testing 150 mm concrete cubes and 150 × 150 × 600 mm prisms , which were cast simultaneously with the main specimens (Table 2). The concrete properties are reported at the age corresponding to the start of testing of the main specimens (55 – 72 days).

Table 2. Mechanical properties of concrete Concrete class Cubic compressive strength f cube , MPa

Prismatic compressive strength f prism , MPa

Initial modulus of elasticity, E b , М P а

C12/15 17.8 C16/20 23.5 C20/25 31.1 C25/30 39.5

12.6 16.5 21.7 27.5

210000 220000 230000 260000

3. Results and discussion For each concrete strength class (C12/15, C16/20, C20/25, and C25/30), seven twin specimens were tested (Fig. 2). Three specimens from each group were subjected to single monotonic loading up to failure in order to determine the ultimate bond capacity between reinforcement and concrete. In addition, the bond behaviour of Ø16 mm sickle -shaped A500C reinforcement embedded in concretes of different strength classes was investigated under repeated loading. For this purpose, four specimens of each concrete class were subjected to 10 cycles of repeated loading up to 0.6 of the ultimate load, corresponding to service load conditions. During the 11th cycle, the specimens were intentionally loaded to failure. The experimental results indicated sufficient uniformity in concrete properties within each twin-specimen group.

Fig. 2. General view of the specimens.

Figure 3 presents the slip diagrams δ for specimens P-12/15k-1,2,3. In the specimen notation, the first numbers indicate the design concrete strength class, while the subsequent number denotes the specimen number. The letter “k” indicates specimens subjected to monotonic loading up to failure, whereas the letter “p” denotes specimens tested under repeated loading conditions. For specimens P-12/15k-1,2,3, the slip value δ u = 0.2 mm was reached at reinforcement stresses of σ s0 = 74.5, 72.3, and 69.5 MPa, respectively, with an average value of σ s0m = 72.1 MPa. The standard deviation of stresses relative to the mean value was 2.5 MPa, corresponding to a coefficie nt of variation υ = 0.0346 . These statistical indicators confirm the high homogeneity of this group of specimens. For the remaining specimen groups, the coefficient of variation ranged within υ = 0.0295 -0.0843; therefore, further analysis was performed using average values for each group. In all specimens, slip initiated at approximately the same stress level in the reinforcement; at σ s = 9.95 MPa, the slip was δ = 0.001 mm . Subsequently, the magnitude of bar slip was significantly influenced by concrete strength. Thus, at σ s = 69.5 MPa, the slip values in specimens P-12/15k, P-16/20k, P-20/25k, and P-25/30k were δ = 0.126, 0.034, 0.016, and 0.011 mm , respectively. The bond limit state, corresponding to δ = δ u = 0.2 mm, occurred at reinforcement stresses of σ s = σ s0 = 72.1, 87.2, 132.6, and 160.1 MPa for specimens P-12/15k, P-16/20k, P-20/25k, and P-25/30k, respectively. It should be noted that specimens P-25/30k did not fail immediately after reaching δ u = 0.2 mm, but continued to resist reinforcement pull-out up to δ = 0.28 mm , after which longitudinal splitting of the prisms along the reinforcing bars occurred. In this case, the reinforcement stress was σ s = 74.6 MPa.

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With increasing concrete strength, the difference between δ u = 0.2 mm and the slip value immediately proceeding complete prism failure decreases, and for specimens P-25/30k, this difference was practically negligible (Fig. 4).

Fig. 3. Variation of bar slip δ during loading of specimens P -12/15k- 1,2,3 (σ s – reinforcement stress)

Fig. 4. Relationship between bar slip δ and reinforcement stress σ s : 1 – specimens P-12/15k; 2 – P-16/20k; 3 – P-20/25k; 4 – P-25/30k.

During the first loading cycle of specimens P-12/15p, the average displacement of the reinforcement relative to concrete at the maximum repeated load level ( σ s = 39.8 MPa) was 0.011 mm, while the residual slip after unloading amounted to 0.003 mm. During the second loading and unloading cycle, the maximum slip was 0.012 mm. Residual deformations increased to 0.004 mm after unloading of the seventh cycle. After the eighth cycle, deformations stabilized at 0.014 mm (total) and 0.004 mm (residual). During the 11th cycle, a slip of 0.2 mm was reached at σ s0m = 73.6 MPa, and specimen failure occurred at σ s = 74.6 MPa (Fig. 5). For specimens P-16/20p, the average displacement of the free end of the reinforcement relative to the prism face at the maximum repeated load level ( σ s = 52.2 MPa) during the first cycle was 0.015 mm, while the residual slip amounted to 0.003 mm. From the second to the seventh cycle, both total and residual slips increased by approximately 0.001 mm per cycle, reaching 0.023 mm and 0.008 mm, respectively, at the seventh cycle (Fig. 5). From this cycle onward, slip stabilization occurred. A slip of 0.2 mm was reached during the 11th cycle at σ s0m = 89.5 MPa, while specimen failure occurred at σ s = 91.2 MPa.

Fig. 5. Variation of bar slip δ versus reinforcement stress σ s in specimen P-12/15p: 1 – firstcycle; 2 – eleventh cycle (cycles 2-8 omitted).

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Specimens P-20/25p were subjected to ten loading cycles up to a maximum stress of σ s = 79.6 MPa. After the first cycle, the total displacement of reinforcement relative to concrete was 0.018 mm, with a residual slip of 0.006 mm (Fig. 6). During the second cycle, the maximum slip reached 0.020 mm, and the residual slip was 0.007 mm. Deformations increased slightly with each subsequent cycle, without full stabilization. After the tenth cycle, the total and residual slips were 0.031 mm and 0.013 mm, respectively. During the 11th cycle, a slip of 0.2 mm occurred at σ s0m = 132.8 MPa, at which load the specimen failed.

Fig. 6. Variation of bar slip δ versus reinforcement stress σ s in specimen P-20/25p: 1 – first cycle; 2 – eleventh cycle (cycles 2 – 7 omitted)

For specimens P-25/30p, during the first cycle, the displacement of reinforcement relative to concrete at the maximum repeated stress level ( σ s = 94.5 MPa) was 0.011 mm, with a residual slip of 0.002 mm. During the second cycle, the maximum and residual slips were 0.012 mm and 0.003 mm, respectively. Stabilization of total and residual deformations occurred during the third cycle, reaching 0.013 mm and 0.003 mm, respectively. During the 11th cycle, a slip of 0.2 mm was reached at σ s0m = 146.7 MPa. After repeated loading up to 0.6 of the ultimate load, deformation stabilization occurred between the fourth and sixth cycles, while total slips did not exceed 0.03 mm, corresponding to approximately 15% of the ultimate slip value of 0.2 mm. The maximum stresses recorded during the 11th cycle were consistent with those obtained under single short-term loading. Based on the experimental results, the average maximum tangential bond stresses τ um were calculated for each group of specimens, assuming a uniform distribution along the embedded length of the bar, according to Eq. (1). = 0 . /( ) . (1) Statistical analysis of the obtained results indicates that, for 16 mm diameter reinforcing bars, a linear relationship may be adopted between the maximum tangential bond stresses τ um and the prismatic compressive strength of concrete f prism (Fig. 7a), expressed by Eq. (2). = 0.3 ∙ . (2) The coefficient of determination for this approximation is R² = 0.952 , indicating good agreement with the experimental data. A linear relationship was also observed between the reinforcement stresses σ s0 and the prismatic compressive strength of concrete f prism (Fig. 7b), with a coefficient of determination R² = 0.975 .

Fig. 7. Dependence of the average ultimate tangential bond stresses τ um (a) and reinforcement stresses σ s0 (b) on concrete strength f prism .

4. Conclusions As a result of pull-out tests of 16 mm diameter steel reinforcing bars from concrete prisms using a hydraulic tensile testing machine, new experimental data on the bond behaviour of sickle-shaped A500C reinforcement depending on the strength of

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normal-weight concrete were obtained. It was established that an increase in concrete strength is accompanied by a proportional increase in the bond capacity between sickle-shaped reinforcement and concrete. A linear relationship between the maximum tangential bond stresses and concrete strength was identified, demonstrating good agreement with the experimental results. The proposed linear relationship may be applied in the design of reinforced concrete structures to calculate the ultimate bond strength of sickle-shaped steel reinforcement embedded in normal-weight concretes of various strength classes. References Babich Y, Filipchuk, S, Karavan V., Sobczak-Piastka J., 2019. Research of basic mechanical and deformative properties of high-strength fast-hardening concretes. AIP Conference Proceedings 2077, 020003. Babych, E.M., Andriichuk, O.V., 2017. Strength of Elements with Annular Cross Sections Made of Steel-fiber-Reinforced Concrete Under One-Time Loads. Mater Sci 52, 509 – 513. Babych, Y.M., Savitskiy, V.V., Andriichuk, O.V., Ninichuk, M.V., Kysliuk, D.Y., 2019. Results of experimental research of deformability and crack-resistance of two span continuous reinforced concrete beams with combined reinforcement. IOP Conference Series: Materials Science and Engineering 708(1), 012043. Bosak, A., Matushkin, D., Dubovyk, V., Homon, S., Kulakovskyi, L., 2021. Determination of the concepts of building a solar power forecasting model. Scientific Horizons 24(10), 9-16. BRITISH STANDARD BS 4449: 1997. Specification for Carbon steel bars for the reinforcement of concrete. Chapiuk, O., Kratiuk, O., Zadorozhnikova, I., Boiarska, I., Rud, V., Boiarskyi, M., Mudryy, I., Pelekh, A., 2025. Method for determining the minimum anchorage length of reinforcement in concrete: an experimental study. Procedia Structural Integrity 72, 308-314. Chapiuk, O., Oreshkin, D., Hryshkova, A., Pakholiuk, O., Avramenko, Y., 2023. Adhesion of the Metal and Composite Fiberglass Rebar with the Heavyweight Concrete. Lecture Notes in Civil Engineering 299, 47-60. Dovbenko, V., Kukhniuk, O., Homon, S., Ivaniuk, A., Aleksiievets, V., Savytska, O., Kulakovskyi, L., 2024. Study of the strength properties of concrete impregnated with a polymer composition. Procedia Structural Integrity 59, 702-709. Drobyshynets, S., Babych, Y., Sunak, P., Zadorozhnikova, I., Parfentyeva, I., Pakharenko, V., Homon, S., 2024. Experimental and theoretical studies of fatigue of steel fibre reinforced concrete under low-cycle compression. Procedia Structural Integrity 59, 601-608. DSTU 3760:2019, 2019. Prokat armaturnyy dlya zalizobetonnykh konstruktsiy. Zahalʹn i tekhnichni umovy [Reinforcing bars for reinforced concrete structures. General technical conditions]. Ministry of Regional Development of Ukraine, Kyiv, pp. 18. Dvorkin, L., Bordiuzhenko, O., Zhitkovsky, V., Gomon, S., Homon, S. (2021). Mechanical properties and design of concrete with hybrid steel basalt fiber. E3S Web of Conferences 264, article number 02030. Eurocode 2, 2004: Design of Concrete Structures - Part 1-1: General rules and rules for buildings. CEN, Brussels, pp. 225. Filipchuk, S., Karavan, V., Makarenko, R., Nalepa, O., Chapiuk, O., 2023. Study of reinforcement adhesion to concrete under static and dynamic loads. A IP Conference Proceedings 2949, 020007. Filipchuk, S., Karavan, V., Nalepa, O., Chapiuk, O., Pakholiuk, O., 2024. Stability of slabs made of high-strength concrete subjected to dynamic influence. Procedia Structural Integrity 59, 588-594. Gomon, S., Gomon, P., Pavluk, A., Podhorecki, A., 2019. Complete deflections of glued beams in the conditions of oblique bend for the effects of low cycle loads. AIP Conference Proceedings 2077, 020021. Korniychuck, O., Masiuk, G., Homon, S., Aleksiievets, I., Chapiuk, O., Kaynts, D., Rizak, V., 2024. Deformability of reinforced concrete beams under the action of repeated alternating loads. Procedia Structural Integrity 59, 575-582. Kos, Z., Klymenko, Y., Karpiuk, I., Grynyova, I., 2022. Bearing capacity near support areas of continuous reinforced concrete beams and high grillages. Applied Sciences (Switzerland) 12(2), 685. Kovalchuk, V., Rybak, R., Parneta, B., Onyshchenko, A., Kvasnytsya, R., 2022. Determining patterns of the deformed state of the transport concrete pipe reinforced with a metal clamp under the action of static load. Eastern-European Journal of Enterprise Technologies 5 (7-119), 54 – 60. Matviiuk, O., Homon, S., Petrenko, O., Vikhot, S., 2025. Operation of silor-modified wood in acidic environments: an experimental study. Lecture Notes in Civil Engineering 781, 237-244. Parneta, B., Kovalchuk, V., Rybak, R., 2024. Methodology for Evaluating the Stress-Strain State of Strengthened Concrete Pipe Using the Finite Element Method with FEMAP with NX Nastran. Lecture Notes in Civil Engineering 604, 415-425. Rybak, R., Kovalchuk, V., Parneta, B., 2025. Establishment of Regularities in the Stress-Strain State of Strengthened Reinforced Concrete Pipes Under Force Loads and Thermal Effects. Lecture Notes in Civil Engineering 781, 354 – 362. Sobczak-Piastka J., Babich Y, Filipchuk, S, Karavan V., Nalepa, O., 2020. Research of deformative properties of concrete taking into account the descending branch of deformation. IOP Conference Series: Materials Science and Engineering 960(3), 032057.

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Procedia Structural Integrity 81 (2026) 135–139

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords : pearlitic steel; steelmaking; manufacturing; cold drawing; anisotropic fracture behaviour; fracture micromechanisms. 1. Introduction High-strength prestressing steel wires for civil engineering use in prestressed concrete structures are manufactured by cold drawing a previously hot rolled pearlitic steel bar in several passes to increase the yield strength. The steelmaking process in the form of progressive cold drawing produces important plastic deformations in the material and activates a strain hardening mechanism which is responsible for the extremely high yield strength useful for structural engineering. This heavy drawing also produces microstructural effects in the steel with potential consequences in the matter of fatigue and fracture behaviour. Therefore, although the classical mechanical properties (yield strength, ultimate tensile stress) of high-strength cold drawn pearlitic steels are improved during the steelmaking procedure, further research is needed to provide more insight into the effects of this manufacture method on fracture. In this paper the fracture performance of steels with intermediate levels of cold drawing is studied under triaxial stress states produced by crack-like defects. Thus the drawing intensity (or straining level, or degree of strain hardening, given by the number of cold drawing steps undergone by the steels) is treated as the fundamental variable to elucidate the effects of the manufacturing route on the posterior fracture performance of the material. Abstract The paper studies the anisotropy of crack-induced fracture behaviour in heavily cold drawn pearlitic steels supplied as prestressing steel wires for prestressed concrete. Results demonstrated that progressive cold drawing affects clearly the fracture performance of the steel wires, so that the most heavily drawn steels exhibit anisotropic fracture behaviour with crack deflection , i.e., a change in crack propagation direction that deviates from the original mode I propagation and approaches the wire axis or cold drawing direction (mixed mode propagation). VIII International Conference “In -service Damage of Materi als: Diagnostics and Prediction” (DMDP 2025) Anisotropy of crack-induced fracture behaviour in cold drawn pearlitic steels in the form of prestressing wires: A Tribute to Andrea Mantegna Jesús Toribio* Fracture & Structural Integrity Research Group (FSIRG), University of Salamanca (USAL) E.P.S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain

* Corresponding author. Tel.: +34-677566723; fax: +34-980545002. E-mail address: toribio@usal.es

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.024

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2. Materials and effect of cold drawing Progressive cold drawing of pearlitic steel affects the microstructural arrangement in the form of slenderizing of the colonies, decrease of interlamellar spacing and orientation in the direction of cold drawing (wire axis) of both colonies and lamellae (Toribio and Ovejero, 1997, 1998a, 1998b, 1998c), i.e., inducing microstructural anisotropy. 3. Experimental results & discussion With regard to the fracture behaviour of the progressively cold drawn steel wires in the presence of cracks , pre-cracked rods were subjected to tensile loading up to fracture. Fig. 1 shows the propagation profile for a hot rolled bar (not cold drawn at all) and for a heavily cold drawn pearlitic steel (commercial prestressing steel wire).

II F

f

f I

F

(a)

(b)

Fig. 1. Crack paths (propagation profiles) produced by axial fracture in steels with 0 (a) and 6 (b) cold drawing steps; f: fatigue crack growth; I: mode I propagation; II: mixed mode propagation (propagation step in heavily drawn steels); F: final fracture.

The initial hot rolled material and the slightly drawn steels behave isotropically, i.e., cracking develops in mode I following the initial plane of fatigue crack propagation (Fig. 1a). The most heavily drawn steels exhibit a clearly anisotropic fracture behaviour in the form of crack deflection after the fatigue crack (and some mode I propagation in certain cases) with a deviation angle of almost 90º from the initial crack plane and further propagation in a direction close to the initial one (Fig. 1b). The fractographic analysis of the deflected crack path (region II in Fig. 1b) linked with anisotropic fracture behaviour shows a sort of elongated and oriented cleavage (see Fig. 2), the elongation and orientation being in the direction of the 90º-propagation step, i.e., quasi-parallel to the wire axis or cold drawing direction.

Fig. 2. Scanning electron micrograph of the 90º-propagation step in steel 6 (propagation from left to right).

Fig. 3 shows the macro-fracture surfaces of the progressively drawn steels. A general evolution may be observed from a typically brittle behaviour with a flat fracture surface in steel 0 (and slightly drawn steels) to a more ductile behaviour with a more or less irregular and stepped fracture surface in steel 6 (and heavily drawn steels). Accordingly, the fracture behaviour evolves from isotropic to anisotropic as the degree of cold drawing increases. The stepped appearance of the fracture surfaces in heavily drawn steels is consistent with their strength anisotropy because there are a lot of step embryos (or meso-steps) and finally one of them becomes the final 90º-step that produces the macroscopic crack deflection. Thus the meso-roughness increases with the degree of cold drawing.

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STEEL 0

STEEL 1

STEEL 2

STEEL 3

STEEL 4

STEEL 5

STEEL 6

Fig. 3. Fracture surfaces in all the steels used in the experimental programme.

To analyze the microscopic modes of fracture, a fractographic analysis by scanning electron microscopy (SEM) was performed on the fracture surfaces of all the broken samples, and results are given in Fig. 4 that shows the micro-fracture surfaces. In the first stages of cold drawing (steel 0 which is not cold drawn at all and steel 1) the microscopic fracture mode is cleavage-like. In steels 2 and 3 the fracture process initially develops by micro-void coalescence (MVC) and continues by cleavage. Thus a first MVC region is found before the cleavage-like (brittle) area, the depth of this MVC region being an increasing function of the degree of cold drawing. The most heavily drawn steels (4 to 6) exhibit anisotropic fracture behaviour with a 90º-step, as described above, although certain mode I crack growth appears before the step over a distance in which the MVC micro-fracture mode is predominant although the meso-roughness is higher, as explained above.

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STEEL 0

STEEL 1

STEEL 2

STEEL 3

STEEL 4

STEEL 5

STEEL 6

Fig. 4. Microscopic fracture modes in all the steels used in the experimental programme. The micrographs correspond to the whole surface in steels 0 and 1, the main fracture surface after the initial MVC band in steels 2 and 3, and the main fracture surface after the propagation step in steels 4 to 6. Fracture propagates from the bottom to the top 4. Conclusions The results of this study show that progressive cold drawing affects clearly the fracture performance of pearlitic steels for use in prestressed concrete. While the fracture behaviour of slightly drawn steels is isotropic, the most heavily drawn steels exhibit strength anisotropy and crack deflection. At the microscopic level, clear changes are observed in the micrographs with appearances from cleavage-like (brittle) in the slightly drawn steels to predominant micro-void coalescence (ductile) in the heavily drawn steel. 5. Epilogue: A Tribute to Andrea Mantegna Heavily cold-drawn pearlitic steel wires exhibit in their crack path evidence of strongly anisotropic behavior with a marked deflection/deviation angle of 90º. This resembles Mantegna’s Dead Christ Perspective (MDCP) painting with its relevant and

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innovative change of point of view in the description of the Dead Christ (90º rotated from the traditional perspectives) and the body axis perpendicular to the canvas ( foreshortening perspective ), see Fig. 5.

Fig. 5. Andrea Mantegna: Dead Christ .

References Toribio, J., Ovejero, E., 1997. Microstructure Evolution in a Pearlitic Steel Subjected to Progressive Plastic Deformation. Materials Science and Engineering A234 236, 579 - 582. Toribio, J., Ovejero, E., 1998a. Microstructure Orientation in a Pearlitic Steel Subjected to Progressive Plastic Deformation. Journal of Materials Science Letters 17, 1037 - 1040. Toribio, J., Ovejero, E., 1998b. Effect of Cumulative Cold Drawing on the Pearlite Interlamellar Spacing in Eutectoid Steel. Scripta Materialia 39, 323 - 328. Toribio, J., Ovejero, E., 1998c. Effect of Cold Drawing on Microstructure and Corrosion Performance of High - Strength Steel. Mechanics of Time - Dependent Materials 1, 307 - 319. Toribio, J., Ovejero, E., Toledano, M., 1997. Microstructural Bases of Anisotropic Fracture Behaviour of Heavily Drawn Steel. International Journal of Fracture 87, L83 - L88.

Available online at www.sciencedirect.com

ScienceDirect

Procedia Structural Integrity 81 (2026) 95–97

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords: eutectoid steel; prestressing steel; pearlitic steel; cold drawing; pearlitic microstructure; drawing-induced microstructural evolution; microstructural orientation; pearlite interlamellar spacing decrease; environmentally assisted cracking (EAC); hydrogen embrittlement (HE); hydrogen assisted cracking (HAC); HAC paths; anisotropic behaviour. 1. Introduction High-strength prestressing steel wires are manufactured by progressive cold drawing to increase both the yield strength  Y and the ultimate tensile strength (UTS)  R of the steel and allow it to be used as the main constituent of prestressed concrete structural elements. The manufacture technique consisting of progressive (cumulative) cold drawing of pearlitic wires through a series of dies with diameters progressively thinner produces important microstructural changes in the material that could influence its posterior performance. Evidence exists in the scientific literature showing the anisotropic fracture behaviour of prestressing steel in air (Toribio et al., 1997) as well as in aggressive environments promoting stress corrosion cracking (SCC) in the material (Cherry and Price, 1980; Sarafianos, 1989). This paper analyzes the anisotropy of hydrogen embrittlement (HE) in heavily cold drawn pearlitic steels supplied as prestressing steel wires for prestressed concrete in the presence of crack-like defects. Abstract This paper analyzes the anisotropy of hydrogen embrittlement (HE) in heavily cold drawn pearlitic steels supplied as prestressing steel wires for prestressed concrete in the presence of crack-like defects. In these materials, the manufacturing process by progressive (multi-step) cold drawing produces a preferential orientation of the pearlitic microstructure in the matter of colonies (first microstructural level) and ferrite/cementite lamellae (second microstructural level), thereby inducing strength anisotropy in the steel, and thus the resistance to HE is a directional property depending on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis or cold drawing direction, thus producing mixed mode propagation, the deflection angle being an increasing function of the drawing degree. VIII International Conference “In -service Damage of Materi als: Diagnostics and Prediction” (DMDP 2025) Anisotropy of hydrogen embrittlement induced by cracks in cold drawn pearlitic steels supplied in the form of prestressing wires: A Tribute to Andrea Mantegna Jesús Toribio* Fracture & Structural Integrity Research Group (FSIRG), University of Salamanca (USAL) E.P.S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain

* Corresponding author. Tel.: +34-677566723; fax: +34-980545002. E-mail address: toribio@usal.es

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.017

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2. Materials and microstructural evolution with cold drawing Progressive cold drawing of pearlitic steel affects the microstructural arrangement in the form of slenderizing of the colonies, decrease of interlamellar spacing and orientation in the direction of cold drawing (wire axis) of both colonies and lamellae (Toribio and Ovejero, 1997, 1998a, 1998b, 1998c), i.e., inducing microstructural anisotropy. 3. Experimental programme Slow strain rate tests were performed on transversely precracked steel wires in a corrosion cell containing aqueous solution of 1g/l Ca(OH) 2 plus 0.1g/l NaCl (pH=12.5). The experimental device consisted of a potentiostat and a three-electrode assembly: metallic sample (working electrode), platinum counter-electrode and saturated calomel electrode (SCE: reference). Tests were performed at constant electrochemical potential with the values of – 1200 mV vs. SCE, linked with the cathodic regime of cracking for which the environmental mechanism is hydrogen assisted cracking (HAC) or hydrogen embrittlement (HE). 4. Anisotropy of HAC/HE behaviour The experiments showed a progressive anisotropy of HAC/HE behaviour (Fig. 1), so that the HAC/HE resistance is a directional property depending on the angle in relation to the drawing direction ( strength anisotropy with regard to HAC/HE behaviour). This anisotropic HAC/HE behaviour of the drawn steels can be evaluated by means of the crack path or fracture profile after the tests. Fig. 1 shows the evolution of crack paths with cold drawing under HAC/HE conditions. Fig. 1a offers a 3D-view of these fracture surfaces. For the slightly drawn steels (0, 1 and 2), the crack paths are macroscopically plane and oriented perpendicularly to the loading axis (mode I propagation). Steel 3 exhibits a certain deflection angle evolving to mixed mode cracking. In the most heavily drawn steels (4, 5 and 6) the deflection angle is even higher. Fig. 1b shows the geometric parameters describing the crack path. Fig. 1c offers the evolution of the fracture profile towards the weakest crack path.

F

II F

f

I

F

f

II

f

(a)

II x

x I

F

(b)

h



f

F

f

(c)

0

1

2

3

4

5

6

Fig. 1. Evolution of HAC/HE behaviour with the cold drawing degree: (a) general appearance of the fracture surfaces; (b) geometric parameters describing the crack path; (c) evolution of fracture profiles; f: fatigue crack growth; I: mode I cracking; II: mixed mode cracking; F: final fracture. 5. Discussion In the matter of HAC/HE, the proposed mechanism is hydrogen-enhanced delamination (HEDE), cf. Fig. 2. The lamellar structure of the steel (markedly oriented) which produces anisotropy regarding fracture and hydrogen diffusion, so that hydrogen diffuses mainly in the direction of the plates and can weaken the bonds or interfaces between the ferrite and the cementite lamellae (which are the weakest links even before the hydrogen presence) thus contributing to the hydrogen-induced fracture by delamination or debonding between two similar microstructural units, i.e, at the ferrite/cementite interface or at the pearlitic colony boundaries.

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D



HEDE

D

^

D



Fig. 2. Micromechanism of HAC/HE: hydrogen diffusion in longitudinal and transverse directions and fracture by hydrogen enhanced delamination (HEDE).

6. Conclusion Heavily cold drawn pearlitic steels exhibit anisotropy of hydrogen assisted cracking/hydrogen embrittlement (HAC/HE) behaviour , and there is a strong correlation between the microstructural orientation angles (at the two levels of the pearlitic colonies and lamellae) and the macroscopic crack deflection angles (representing the macroscopic crack paths), clearly demonstrating the influence of the oriented microstructure (and thus of the manufacture process by increasing cold drawing) on the macroscopic HAC/HE behaviour of the steels, towards the weakest crack path . 7. Epilogue: A Tribute to Andrea Mantegna Heavily cold-drawn pearlitic steel wires exhibit in their crack path evidence of strongly anisotropic behavior with a marked deflection/deviation angle of 90º. This resembles Mantegna’s Dead Christ Perspective (MDCP) painting with its relevant and innovative change of point of view in the description of the Dead Christ (90º rotated from the traditional perspectives) and the body axis perpendicular to the canvas ( foreshortening perspective ), see Fig. 3.

Fig. 3. Andrea Mantegna: Dead Christ .

References Cherry, B.W., Price, S.M., 1980. Pitting, Crevice and Stress Corrosion Cracking Studies of Cold Drawn Eutectoid Steels, Corrosion Science 20, 1163 - 1184. Sarafianos, N., 1989. Environmentally Assisted Stress - Corrosion Cracking of High - Strength Carbon Steel Patented Wire, Journal of Materials Science Letters 8, 1486 - 1488. Toribio, J., Ovejero, E., 1997. Microstructure Evolution in a Pearlitic Steel Subjected to Progressive Plastic Deformation. Materials Science and Engineering A234 - 236, 579 - 582. Toribio, J., Ovejero, E., 1998a. Effect of Cumulative Cold Drawing on the Pearlite Interlamellar Spacing in Eutectoid Steel. Scripta Materialia 39, 323 - 328. Toribio, J., Ovejero, E., 1998b. Microstructure Orientation in a Pearlitic Steel Subjected to Progressive Plastic Deformation. Journal of Materials Science Letters 17, 1037 - 1040. Toribio, J., Ovejero, E., 1998c. Effect of Cold Drawing on Microstructure and Corrosion Performance of High - Strength Steel. Mechanics of Time - Dependent Materials 1, 307 - 319. Toribio, J., Ovejero, E., Toledano, M., 1997. Microstructural Bases of Anisotropic Fracture Behaviour of Heavily Drawn Steel. International Journal of Fracture 87, L83-L88.

Available online at www.sciencedirect.com

ScienceDirect

Procedia Structural Integrity 81 (2026) 18–22

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords: pearlitic steel; cold drawing; multiscale microstructural evolution; prior austenite grain; pearlitic colonies; pearlite lamellae. 1. Introduction High-strength eutectoid pearlitic steels are used as (i) constituent materials of rails ( pearlitic rail steels ) in mass after hot rolling, as analyzed by Masoumi et al. (2019) and Ferreira et al. (2022); (ii) constituent materials of prestressed concrete structures, bridge cables and wire ropes in wire form as key elements in civil engineering ( cold drawn pearlitic steel wires ) after hot rolling and heavy cold drawing, as studied in depth in the past by Toribio (1992, 2006) and Borchers and Kirchheim (2016); (iii) reinforcement materials in vehicle tires in the form of tiny wires after heavy cold drawing ( cold drawn pearlitic steel wires ), as analyzed by Yan et al. (2019) and Mihaliková et al. (2017). Abstract This paper analyzes the anisotropy of microstructure in heavily cold drawn pearlitic steels supplied in the form of prestressing steel wires for prestressed concrete. It is shown that these materials exhibit after manufacturing a sort of anisotropic microstructure that is markedly oriented in a direction quasi-parallel to the wire axis or cold drawing direction. The article formulates a philosophical approach based on the concept of palimpsestus , studying in particular the evolution during the manufacturing stages by progressive cold drawing of the following material levels: (i) the prior austenitic grain ( zero, or virtual, or palimpsestus microstructural level ); (ii) the pearlitic colony ( first microstructural level ); (iii) the pearlite lamellae ( second microstructural level ). Results demonstrate that the slender pearlitic colony (after cold drawing) – more than the prior austenitic grain (that is also virtually cold drawn in the palimpsestus approach) – is the microstructural unit governing the cleavage facet size in the case of brittle fracture. As an epilogue, and based on the philosophical idea of palimpsestus , the paper pays a heartfelt tribute to the Japanese cities of Hiroshima and Nagasaki. VIII International Conference “In -service Damage of Materi als: Diagnostics and Prediction” (DMDP 2025) Anisotropy of microstructure in cold drawn pearlitic steel wires: A philosophical approach based on the concept of palimpsestus & A tribute to the Japanese cities of Hiroshima and Nagasaki Jesús Toribio* Fracture & Structural Integrity Research Group (FSIRG), University of Salamanca (USAL) E.P.S., Campus Viriato, Avda. Requejo 33, 49022 Zamora, Spain

* Corresponding author. Tel.: +34-677566723; fax: +34-980545002. E-mail address: toribio@usal.es

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.004

Jesús Toribio et al. / Procedia Structural Integrity 81 (2026) 18–22

19

Previous research by Toribio and Ovejero (1997, 1998a, 1998b, 1998c) showed that progressive cold drawing of pearlitic steel affects the microstructural arrangement in the form of slenderizing of the colonies, decrease of interlamellar spacing and orientation in the direction of cold drawing (wire axis) of both colonies and lamellae. This paper offers a philosophical approach to the multiscale microstructural evolution in progressively cold drawn pearlitic steel based on the idea of palimpsestus , analyzing in particular: (i) the prior austenitic grain ( zero, or “virtual”, or “palimpsestus” microstructural level ); (ii) the pearlitic colony ( first microstructural level ); (iii) the pearlite lamellae ( second microstructural level ). The final aim of the article is the clarification of the critical fracture unit governing cleavage fracture in cold drawn pearlitic steels supplied in the form of prestressing steel wires for prestressed concrete. 2. Critical fracture unit in cold drawn pearlitic steels: a “palimpsestus” approach The prior austenitic grain of the steel ( zero, or “virtual”, or “palimpsestus” microstructural level ) disappears during the eutectoid transformation. Nevertheless, its boundary as a set of material points represents a geometrical domain that can be analyzed (the “ previous writing ” in the material in this kind of palimpsestus approach ) and such a set of points (domain) evolves during cold drawing and becomes more slender and elongated in the cold drawing direction (wire axis), in a sort of “ rewriting ” in the material over the previous text, although the latter still remains in the steel as a heritage. This is a palimpsestus approach, from the conceptual point of view, or an updated lagrangian formulation , from the continuum mechanics viewpoint. Fig. 1 sketches the palimpsestus approach by showing the evolution of the boundary of the prior austenitic grain during cold drawing from the hot rolled pearlitic steel (Fig. 1a) to the heavily cold drawn pearlitic steel (Fig. 1b). The pearlitic colonies also evolve with cold drawing from regular shape in the hot rolled material (Fig. 1a) to elongated and slenderised in the heavily cold drawn steel (Fig. 1b), as described by Toribio and Ovejero (1997, 1998a).

(a)

(b)

Fig. 1. Scheme showing the crystallographic orientation of ferrite, the pearlite (ferrite/cementite) lamellae, the pearlitic colonies and the “virtual” boundary of the prior austenitic grain in a: (a) a hot rolled pearlitic steel; (b) heavily cold drawn pearlitic steel.

In the matter of the pearlite (Fe/Fe 3 C) lamellae ( second microstructural level ), they are randomly oriented in any direction of alignment in the hot rolled material (Fig. 1a), becoming markedly oriented along the cold drawing direction (wire axis) in the heavily cold drawn steel (Fig. 1b). In addition, there is an increase of packing closeness associated with a decrease of pearlite interlamellar spacing (compare Figs. 1a and 1b), as analyzed and reported by Toribio and Ovejero (1998b, 1998c). In order to evaluate the critical fracture unit , it is interesting to analyze the crystallographic orientation of ferrite. In the hot rolled material (Fig. 1a) that has a randomly oriented pearlitic microstructure in the matter of colonies and lamellae (first and second microstructural levels), all pearlite colonies belonging to the same prior austenite grain share a common crystallographic orientation of ferrite. This is the reason why, in the case of conventional cleavage taking place in an isotropic pearlitic steel the conventional cleavage facet size is a function of the prior austenite grain size (Park and Bernstein, 1979). On the other hand, in the case of the heavily cold drawn material (Fig. 1b) that has a markedly oriented pearlitic microstructure in the matter of colonies and since both levels have evolved (in particular, rotated ) during cold drawing, that rotation being the cause of the microstructural orientation, in the same manner as the prior austenite grain is also, in certain sense, cold drawn (even though it does not exist any more after the eutectoid transformation), but one can imagine a “virtual” cold drawing of it, during which the evolution of its boundary (material points defining it) can be analyzed in an updated lagrangian formulation or a “palimpsestus” approach (metaphorically as rewriting over a previous text in an old table). Thus, the prior austenitic grain (“virtual” or “palimpsestus” grain), in spite of the fact that it does not exist , is virtually cold drawn and takes a new, elongated and oriented shape, as suggested in Fig. 1b, thereby modifying the previous crystal orientation of ferrite inside it, that becomes now governed by the parallel lamellae inside a slender pearlitic colony. Then the pearlite colony more than the prior austenite grain could be taken as critical fracture unit in the drawn material, because different pearlite colonies in the same grain follow distinct orientations paths along the manufacturing route. Therefore the slender pearlitic colony