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1

A suitability assessment using an instrumented impact test of the use of selected structural steel grades on the basis of their changes in response to exposure to fire

Zajdel Paulina

Technical Transactions

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2021

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Vol. 118, iss. 1

art. no. e2021007

EN

In this article, changes occurring in structural steel after exposure to fire are described and discussed. The steel structure before and after fire determines its susceptibility to brittle cracking. The individual phases of cracking are described and interpreted on the basis of a load-displacement graph, directly obtained from the Charpy impact test. The relationship between the intensity of individual fracture energies and the type and appearance of the sample fractures are demonstrated. The program of planned Charpy impact tests and expected hazards after the exposure to fire of selected steel grades are presented. Standard simplified load-displacement graphs are assigned to the steel transition curve. The course of various cracking mechanisms occurring in the case of brittle fractures and plastic fractures are discussed. The aim of this article is to evaluate the possibility of the assessment of structural steel after a fire based on results obtained during the Charpy impact test.

PL

W artykule omówiono zmiany zachodzące w stali konstrukcyjnej po chaotycznej obróbce termicznej, jaką jest pożar. Struktura stali przed i po pożarze determinuje jej podatność na kruche pękanie. Poszczególne fazy pękania zostały opisane i zinterpretowane na podstawie wykresu siła–przemieszczenie, uzyskanego bezpośrednio z badania udarności oprzyrządowanym młotem Charpy’ego. Wykazano zależność pomiędzy wielkością poszczególnych energii pęknięcia a rodzajem i wyglądem przełomu próbki. Zaprezentowano program planowanych badań udarności za pomocą oprzyrządowanego młota Charpy’ego oraz spodziewane zagrożenia występujące po pożarowej obróbce termicznej w wybranych gatunkach stali. Typowe, normowe uproszczone wykresy siła – przemieszczenie przyporządkowano do krzywej przejścia stali w stan kruchy. Omówiono przy tym przebieg różnych mechanizmów pękania, zachodzących w przypadku przełomu kruchego i alternatywnie, przełomu plastycznego. Celem artykułu jest potwierdzenie możliwości miarodajnej oceny stali konstrukcyjnej po pożarze na podstawie wyników uzyskanych podczas próby udarności oprzyrządowanym młotem Charpy’ego.

2

Evaluation of four fracture criteria in compressive loading conditions

Bořkovec J., Petruška J.

Postępy w Inżynierii Mechanicznej

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2013

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nr 1(1)

7--16

EN

Suitability of various fracture criteria in the case of compressive loading conditions are performed in this work. Four fracture criteria were investigated: constant fracture strain, EWK, Oh and Xue-Wierzbicki. The first two are already implemented in PamCrash v2005.1, while the latter two had to be programmed as a user material. These models were applied to the technological process of bolt-head trimming. The digital simulation was compared with the experimental results. Constant strain fracture had insufficient results because calibration conditions were not consistent with the simulation. Xue-Wierzbicki is a versatile criterion, but it is not suitable for compressive loading conditions either. Good conformity was observed with EWK and Oh criteria.

PL

W pracy przedstawiono przydatność różnych kryteriów pękania w warunkach obciążeń ściskających. Badano cztery kryteria: stałych odkształceń, EWK, Oh oraz Xue-Wierzbickiego. Pierwsze dwa są zaimplementowane w programie PamCrash v.2005.1, natomiast dwa pozostałe należało zaprogramować. Stwierdzono, że kryterium stałych odkształceń daje niewystarczające rezultaty, a kryterium Xue-Wierzbickiego, chociaż uniwersalne, jest nieprzydatne dla warunków obciążeń ściskających. Dobrą zgodność uzyskano dla kryteriów EWK i Oh.

3

Comparison of various ductile fracture models and their fracture envelopes

Sebek F., Kubik P., Hulka J, Petruska J.

Modelling and Optimization of Physical Systems

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2013

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z. 12

53--58

EN

For the best prediction of ductile fracture when complex loading is applied, it is necessary to calibrate and to use convenient ductile fracture model. Ductile fracture initiation is especially influenced by the shape of fracture envelope. Hence, such model should consider the dependence of the stress triaxiality and deviatoric state parameter to fracture strain. In this paper are presented shapes of fracture envelopes for various fracture models which were calibrated for the austenitic stainless steel. Firstly, the plasticity of given steel was investigated. Then, the calibration constants of selected ductile fracture models were identified using various specimens and experiments. Finally, the description of their suitability is discussed.

CS

Pro co nejlepší predikci tvárného porušování při aplikování komplexního zatěžování je třeba kalibrovat a používat vhodný model tvárného porušování. Iniciace tvárného porušování je zvláště ovlivněna tvarem plochy porušení. Tudíž takový model by měl uvažovat dopad triaxiality napětí a deviátorového parametru na lomové přetvoření. V tomto článku jsou prezentovány tvary ploch porušení pro různé modely porušování, které byly kalibrovány pro austenitickou nerezovou ocel. Nejprve byla studována plasticita dané oceli. Poté byly identifikovány kalibrační konstanty vybraných modelů tvárného porušování pomocí různých vzorků a experimentů. Nakonec je diskutován popis vhodnosti jejich použití.

4

Ductile fracture locus of AC4CH-T6 cast aluminium alloy

Mae H., Teng X., Bai Y., Wierzbicki T.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 2

100-105

EN

Purpose: Cast aluminium alloys have found wide application to manufacture lighted-weight components of complex shape in automotive and aerospace industries. To improve the strength and ductility of cast aluminium alloys, it is necessary to study their fracture properties by conducting a series of tests. This study addresses calibration of ductile fracture property of the cast aluminium alloy (AC4CH-T6) made by the gravity die casting with sand mold. Design/methodology/approach: 6 round bar specimens and 6 butterfly specimens are machined from the actual cast component. The tensile tests on the smooth and notched round bar specimens are performed to calibrate the fracture strain in the range of high positive stress triaxialities. The combined loading tests on the butterfly specimens are carried out using a uniquely designed Universal Biaxial Testing Device (UBTD). These tests cover the fracture properties in the rage of low and negative stress triaxialities. Detailed finite element models of all the tests are developed. The fracture locus in the space of the effective plastic strain to fracture and the stress triaxiality are constructed in a wide rage from -1/3 to 1.0. Findings: It is found that material ductility sharply decreases with the stress triaxiality. The material ductility at the negative stress triaxiality is much higher than that in the positive stress triaxiality. Research limitations/implications: Large spread of data is observed for those tests repeated on the same loading configuration, necessitating the statistical analysis of the fracture processes. Practical implications: It is expected that such a fracture criterion would be able to correctly predict the fracture response of actual cast aluminum components under complex loading in the practical applications. Originality/value: The conventional researches focused on the material ductility at the stress triaxiality larger than +1/3. The present study showed the material ductility at the wide range of stress triaxiality from -1/3 to 1.0.

5

Some remarks on the relation between microstructure and mechanical properties in mismatched weld joints.

Ranatowski E.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

745-748

EN

A brief consideration of the constraint effect in relation microstructure - mechanical properties in micro- and macroscopic scale at heterogeneous weld joints. The strength of heterogeneous weld joints and conditions for producing the brittle and ductile fracture in under- and overmatched weld joints under static tension are presented.

PL

Ustalono zwięzłą charakterystykę wpływu więzów mechanicznych w relacji struktura-własności mechaniczne w skali mikro- i makroskopowej dla niejednorodnych połączeń spawanych. Określono warunki wytrzymałościowe oraz powstania kruchych lub ciągliwych pęknięć w w/w połączeniach spawanych podczas rozciągania.

6

Crack initiation analysis in structural steel by application of micromechanical approach.

Rakin M., Cvijovic Z., Grabulov V., Sedmak A.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

741-744

EN

Crack initiation in a structural steel, following void nucleation, growth and coalescence, has been analysed. The so-called coupled approach of micromechanical analysis of material damage has been applied. Such an approach is based on experimental testing of both precracked and non-precracked specimens, finite element (FE) calculations and metallurgical analysis. Numerical analyses of ductile-fracture initiation in ferritic steel were carried out through participation in the round robin project organised by European Structural Integrity Society (ESIS) [1]. Smooth round specimens and CT specimens were tested. Critical values of micromechanical damage parameters determined for smooth specimen were used to predict the onset of crack initiation in CT specimen and subsequently to model its stable growth. The analysis of the first phase of ductile fracture, void nucleation, was carried out by applying quantitative metallographic analysis of size and number of non-metallic inclusions. Based on this analysis, initial void volume fraction, used as input information in the large strain (updated Lagrangian) FE calculation, was determined. The results obtained suggest that the critical values of micromechanical parameters according to GTN model may be used for approximate prediction of ductile fracture initiation on CT specimen for tested steel.