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1
Content available Influence of material thickness on the ductile fracture of steel plates for shipbuilding
Jakub Kowalski, Janusz Kozak
Polish Maritime Research
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2022
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nr 3
160--166
EN
In the shipbuilding industry, the risk of brittle fractures is relatively high because some units operate in arctic or subarctic zones and use high thickness (up to 100 mm) steel plates in their structures. This risk is limited by employing certified materials with a specific impact strength, determined using the Charpy method (for a given design temperature) and by exercising control over the welding processes (technology qualification, production supervision, and non-destructive tests). However, for offshore constructions, such requirements may prove insufficient. For this reason, regulations employed in constructing offshore structures require conducting crack tip opening displacement (CTOD) tests for steel and welded joints with thicknesses exceeding 40 mm for high tensile strength steel and 50 mm for other steel types. Since classification codes do not accept the results of CTOD tests conducted on specimens of sub-sized dimensions, the problem of theoretically modelling the steel construction destruction process is of key importance, as laboratory tests for notched elements of considerable thickness (100 mm and higher) are costly and problems stemming from high loads and a wide range of recorded parameters are not uncommon. The aim of this research is to find a relationship between material thickness and CTOD value, by establishing and verifying a numerical model that allows recalculating a result obtained on a sub-size specimen to a full- size specimen for a ductile fracture mode. This work presents results and conclusions from numerical modelling and compares them with laboratory test results of the elastic-plastic properties of high thickness steel, typically used in offshore applications.
2
Content available Experimental and numerical investigation on specimen geometry effect on the ctod value for VL-E36 shipbuilding steel
Kowalski Jakub
Polish Maritime Research
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2021
|
nr 3
110--116
EN
There are special cases in the marine industry, where additional material tests, such as the fracture toughness test, must be performed. Additional fracture toughness tests, such as CTOD (Crack Tip Opening Displacement), are typically performed on three-point bend specimens. The dimension that defines all the specimen dimensions is the thickness of the material to be tested. It is recommended by classification societies (e.g. DNVGL) to test specimens that are twice as high as the material thickness. The width determines the length and, therefore, the weight of the specimen which, for a 100 mm plate is over 140 kg. Current ASTM E1820, BS7448-1 and ISO 12135 testing standards also allow for proportions other than those recommended. This results in a much smaller test piece. Reducing the specimen size allows the testing machine to achieve lower forces than a specimen with a width to thickness ratio of two. This paper presents the effect of changing the specimen geometry on CTOD test results. Research was performed for specimens with a height to thickness ratio of one and two. Abaqus software was used for numerical calculations. The numerical results were, at selected points, verified experimentally.
3
Content available remote Krytyczne podejście inżynierskie w budowie rurociągów magistralnych
Sędek Piotr
Inżynier Budownictwa
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2021
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nr 1
81--83
PL
W artykule opisano przykład zastosowania krytycznego podejścia inżynierskiego (ECA) w ocenie kryteriów jakościowych dla przykładowego rurociągu przesyłowego na gaz ziemny. Porównano wymiary niezgodności krytycznych wyliczonych wg procedur ECA z wymaganiami wg normy PN-ISO 5817. Łagodniejsze wymagania wynikające z ECA umożliwiają znaczne zmniejszenie zakresu prac naprawczych w budowie rurociągów, co wiąże się z obniżeniem kosztów.
EN
The article describes an example use case of the engineering critical assessment (ECA) in assessing the quality criteria for a natural gas transmission pipeline. The critical defect dimensions calculated according to the ECA procedures have been compared to the requirements of PN-ISO 5817. More flexible requirements as described in the ECA make it possible to significantly minimize the scope of repair works in the pipeline construction, therefore reducing costs.
4
Content available remote Wyznaczanie wielkości krytycznych odporności na pękanie stali i złączy spawanych
Werner K., Rozumek D., Wojsyk K., Zajączkowski J.
Przegląd Spawalnictwa
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2018
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R. 90, nr 8
56--61
PL
W pracy przedstawiono wyniki badań różnych gatunków stali i ich złączy spawanych oraz wzory (równania), które zastosowano do wyznaczenia wielkości krytycznych dla kryteriów odporności na pękanie. Dotyczą one zarówno zakresu liniowo-sprężystej, jak i sprężysto-plastycznej mechaniki pękania. Ponadto porównano eksperymentalnie wyznaczone rozwarcie czoła pęknięcia (CTOD) z wartościami obliczonymi według proponowanej w literaturze zależności, określającej jego korelację z wynikami badań udarności stali i złączy spawanych. Oceniono zgodność odporności na pękanie z użyciem dostępnych i znanych równań.
EN
The paper presents the results of tests on various steel grades and their welded joints as well as the formulas used to determine the critical values for toughness on crack criteria. They concern both the linear-elastic and the elastic-plastic range fracture mechanics. In addition, experimental and calculated crack tip opening displacement (CTOD) was compared based on their correlation with the results of standard impact tests of steel and welded joints. The compatibility of toughness on crack using different patterns was also evaluated.
5
Content available The effect of notch depth on CTOD values in fracture tests of structural steel elements
Kowalski J., Kozak J.
Polish Maritime Research
|
2018
|
nr 2
85--91
EN
In elements of steel structures working at low temperatures, there is a risk of appearance of brittle fracture. This risk is reduced through the use of certified materials having guaranteed strength at a given temperature. A method which is most frequently used to determine brittle fracture toughness is the Charpy impact test, preformed for a given temperature. For offshore structures intended to work in the arctic climate, the certifying institutions more and more often require Crack Tip Opening Displacement (CTOD) tests instead of conventional impact tests, especially for steel and welded joints of more than 40 mm in thickness in the case of high-strength steel, and more than 50 mm for the remaining steels. The geometry of specimens and the test procedure are standardised; however, these standards provide some margin for specimen notch depth. The paper analyses the effect of notch depth difference, within the range permitted by the standards, on the recorded CTOD values of a given material. The analysis was performed via numerical modelling of destruction of specimens with different notch geometries and further verification of the obtained numerical results in laboratory tests. The calculations were carried out at the Academic Computer Centre in Gdansk.
6
Content available remote Zastosowanie systemu cyfrowej korelacji obrazu do badań krytycznego rozwarcia wierzchołka szczeliny w betonie zawierającym popiół lotny
Golewski G. L.
Materiały Budowlane
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2018
|
nr 12
82--85
PL
W artykule przedstawiono wyniki badań odporności na pękanie betonów z dodatkiem popiołów lotnych (Fly ash – FA), których celem było określenie wpływu dodatku FA na wartość nieliniowego parametru mechaniki pękania, tj. krytycznego rozwarcia wierzchołka szczeliny (CTODc). Badania przeprowadzono z wykorzystaniem dwóch urządzeń pomiarowych, tzn. prasy MTS 810 i systemu cyfrowej korelacji obrazu (DIC) z oprogramowaniem ARAMIS. Wartości parametrów mechaniki pękania obliczone na podstawie danych z systemu ARAMIS określają zachowanie się materiału konstrukcyjnego bezpośrednio w momencie inicjacji rysy pierwotnej. Przedstawione wyniki badań wskazują na przydatność metody DIC w tego typu eksperymentach, natomiast artykuł potwierdził duży potencjał techniki DIC w oznaczaniu odporności na kruche pękanie w betonie z dodatkiem FA.
EN
This paper presents results of fracture toughness tests of concrete modified with the addition of fly ash (FA). A nonlinear fracture mechanics parameter were analyzed in this studies, i.e. the critical crack tip opening displacement (CTODc). This factor were determined based on the results obtained from the MTS 810 press and the Digital Image Correlation system (DIC) with ARAMIS software. Based on the studies it was found that, the values of CTODc calculated on the basis of data from the ARAMIS system show the behaviour of the structural material directly at the moment of initiation of the initial crack. The presented research results show the usefulness of the DIC method in this type of experiments, whereas the article confirmed the high potential of DIC technique in determinations fracture toughness in concrete with FA additives.
7
Content available Experimental and numerical analysis of fracture in 41Cr4 steel – issues of the stationary cracks
Graba M.
International Journal of Applied Mechanics and Engineering
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2018
|
Vol. 23, no. 1
37--63
EN
This paper analyzes the process of fracture in 41Cr4 steel on the basis of experimental and numerical data obtained for non-propagating cracks. The author’s previous and latest experimental results were used to determine the apparent crack initiation moment and fracture toughness for the material under plane strain conditions. Numerical simulations were carried out to assess changes in the J-integral, the crack tip opening displacement, the size of the plastic region and the distribution of stresses around the crack tip. A complex numerical analysis based on the true stress-strain curve was performed to determine the behavior of 41Cr4 steel under increasing external loads.
8
Content available A numerical analysis of selected elastic-plastic fracture parameters for DEN(T) plates under plane strain conditions
Graba M.
International Journal of Applied Mechanics and Engineering
|
2017
|
Vol. 22, no. 1
49--80
EN
This paper provides a numerical analysis of selected parameters of fracture mechanics for double-edge notched specimens in tension, DEN(T), under plane strain conditions. The analysis was performed using the elastic-plastic material model. The study involved determining the stress distribution near the crack tip for both small and large deformations. The limit load solution was verified. The J-integral, the crack tip opening displacement, and the load line displacement were determined using the numerical method to propose the new hybrid solutions for calculating these parameters. The investigations also aimed to identify the influence of the plate geometry and the material characteristics on the parameters under consideration. This paper is a continuation of the author’s previous studies and simulations in the field of elastic-plastic fracture mechanics.
9
Content available Numerical analysis of the influence of in-plane constraints on the crack tip opening displacement for SEN(B) specimens under predominantly plane strain conditions
Graba M.
International Journal of Applied Mechanics and Engineering
|
2016
|
Vol. 21, no. 4
849--866
EN
This paper presents a numerical analysis of the relationship between in-plane constraints and the crack tip opening displacement (CTOD) for single-edge notched bend (SEN(B)) specimens under predominantly plane strain conditions. It provides details of the numerical model and discusses the influence of external load and in-plane constraints on the CTOD. The work also reviews methods for determining the CTOD. The new formula proposed in this paper can be used to estimate the value of the coefficient dn as a function of the relative crack length, the strain hardening exponent and the yield strength - dn(n, σ0/E, a/W), with these parameters affecting the level of in-plane constraints. Some of the numerical results were approximated using simple mathematical formulae.
10
Content available Influence of the crack tip model on results of the finite elements method
Graba M., Gałkiewicz J.
Journal of Theoretical and Applied Mechanics
|
2007
|
Vol. 45 nr 2
225-237
EN
The paper contains recommendations of finite element models of the crack tip neighborhood to obtain results independent of the finite element mesh. The recommendations are valid for elastic-plastic problems and finite strains. As an example, analysis of single edge notched specimens under bending is presented.
PL
W pracy przeprowadzono analizę wpływu modelu MES na wartość naprężeń przed frontem pęknięcia w materiałach sprężysto-plastycznych, wyznaczaną w sposób numeryczny wartość całki J oraz rozwarcie wierzchołka pęknięcia (RWP). Obliczenia prowadzono dla płaskiego stanu odkształcenia przy założeniu dużych odkształceń.
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