Wyniki wyszukiwania - Biblioteka Nauki

1

Development of a fatigue testing machine to study crack initiation and propagation in high carbon high strength steel during rolling contact

100%

Rozwadowska J. , Kida K. , Santos E. C. , Honda T. , Kanemasu K. , Hashimoto K.

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2011

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tom z. 99

46-48

EN

An innovative type of one-point rolling contact fatigue (RCF) machine was developed to investigate crack initiation and propagation in metals. The microstructural changes and propagation of subsurface cracks during rolling contact in specimens tested by using the new device were studied by laser confocal microscope and X-ray diffraction. It was shown that this new method presents several important advantages compared to the conventional thrust type RCF machines.

2

Dislocation-based and continuum models of crack tip shielding in fatigue

100%

Pokluda J.

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2011

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tom z. 99

44-45

EN

Along with external forces and the macro-geometry of cracked bodies, the local stress intensity factors k at fronts of brittle and fatigue cracks are also determined by internal residual stress fields and the crack front mi- crogeometry (extrinsic shielding). Consequently, the values of k that represent a real crack driving force can be significantly different from those of the remote. This means that, even in the frame of two-parameter linear-elastic fracture mechanics, a characterization of the crack-tip stress field only by K and T is not sufficient at all.

3

The key problems of local approach to cleavage fracture

100%

Kotrechnko S.

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2011

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tom z. 99

30-32

EN

The local approach (LA) to fracture has been considerably developed over the past two decades, not only to provide a better understanding of the frac- ture behavior of materials, in particular the failure micromechanisms, but also to deal with loading conditions which cannot easily be handled with the conventional global fracture mechanics. However, recent findings have demonstrated limitation of both the predictive capabilities and fundamental assumptions of conventional versions of LA to fracture. The main reason of the problems lies in empirical nature of existing versions of LA to cleavage fracture because all of them are based on empirical Weibull distribution which was obtained for very brittle materials, such as ceramics, so, it can’t account for specific features of cleavage fracture of metal. This appears, specifically, in the fact that Weibull distribution parameters, aren’t material’s constants but depend on the temperature, notch radius and plastic strain value.

4

Numerical calculation of the aircraft skin with multi-site damage

80%

Leski A.

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2009

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tom nr 25

37-47

EN

The presence of the multi-site damage (MSD) in an aircraft structure can result in catastro-phic damage when the residual strength is not sufficient to sustain operational loads. In this paper the influence of the MSD crack size on the residual strength was examined. As a crack criterion the crack tip opening angle (CTOA) was applied in the numerical simulation of the stable tearing. The CTOA criterion was implemented in the commercial software, the MSC.Marc, by means of additional user subroutines. The verification of this implementation was carried out and the obtained results are consistent with those presented in literature. The influence of the MSD crack size was determined for two crack scenarios: with a lead-ing crack and without one.

5

Analiza wytrzymałości prostoliniowych i spawanych elementów rurociągów ze stali 10CrMoG10 stosowanych w kotłach średniej mocy SEFAKO

80%

Dzioba I.

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2008

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tom Z. 7

65-70

PL

W artykule przedstawiono ocenę wytrzymałości prostoliniowych i spawanych elementów rurociągów z kotłów średniej mocy produkowanych przez fabrykę SEFAKO. Analizę wykonano w oparciu o procedury FITNET. Uzyskane wyniki wskazują, że analizowane elementy wykonano z wysokim współczynnikiem zapasu wytrzymałości.

EN

The strength analysis of the straight and welded pipeline components of the SEFAKO boiler plant has been performed according to the FITNET procedures. The results obtained confirm that tested components have been the height value of reserve factor.

6

Interaction between 3D stress corrosion cracks

80%

Touzet M. , Lamazouade M. , Puiggali M.

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2007

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tom Vol. 7, nr 1(11)

55-60

EN

To predict the time to failure of a structure due to stress corrosion crack network, overall crack growth behavior must be studied. When many cracks are initiated in an enclosed area, neighboring cracks may affect the stress field ahead the crack tips and then affect their crack growth rates. The interactions between cracks depend on their relative positions and on their sizes. The present work presents the experimental behavior of crack networks by in-situ observations and proposed a finite element analysis of interacting 3D cracks.

7

Relation Structure - Fracture Resistance in Process of Estimate the Weldability of Low Alloy Steels: Part I

80%

Ratanowski E.

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tom Vol. 10, nr 4(26)

32-40

EN

The relationship between microstructure and mechanical properties of structural materials is still relevant problem in the theory of materials science and mechanical engineering. The question is how the macro-mechanical parameters can be derived from the microscale mechanisms taking into account local structural heterogeneities. Another question is how to make quantitative descriptions of the strength and toughness properties of welded joints made of non-matching weld metal. These problems are the objects of welding and mechanical investigation and they are related to estimation of weldability. The results of this study concern the evaluation stress state at interface of the under- and overmatched weld joints. After formulating a simplified model of under- and overmatched weld joints an analysis was made of stress at interface for the cases of perpendicular and non - perpendicular orientation of the zones (soft - layer and hard - layer) relative to the load action direction under tension.

8

Pękanie kompozytów warstwowych z materiałów o charakterystyce nieliniowej

80%

Jaroniek M. , Niezgodziński T.

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2011

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tom z. 99

98-100

EN

Fabrication of the functionally graded materials (FGM) can be obtained by layered mixing of two materials of different thermo-mechanical properties with different volume ratios gradually changed from layer to layer such that first layer has only a few particles of the other phase and last has maximum volume ratio of this other phase. The material (FGM) is functionally graded thermal and stress barrier. Fracture problems in the layer can be studied using J integral in finite element method, because it is not path independent Consider a laminate composite in plane stress conditions, multi-layered beam bonded to planes. The fracture mechanics problem will be analysed using the photoelastic visualisation of the fracture events in a model structure.

9

Problems of hydrogen interaction with metals and methods of structures lifetime estimation.

70%

Kurzydłowski K. , Nykyforchyn H.

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2007

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tom Vol. 65, nr 11

55-69

EN

The hydrogen induced degradation of the properties and microstructure of the low carbon low-alloyed steels due to exploitation and exposition to the hydrogenated environment at ambient and elevated temperatures have been considered. The essential decrease of mechanical (impact strength, creep), corrosion (corrosion rate) and corrosion-mechanical (stress corrosion cracking) properties of exploited metal to compare with that in the virgin state is demonstrated. Especially high sensitivity of an effective range of stress intensity factor of fatigue crack growth to in-service degradation is shown. Weld metal is more sensitive to hydrogen degradation and even tensile mechanical properties of strength and plasticity are sensitive enough to "in-bulk" material degradation. An approach to the residual life time evaluation of the power plant steam pipe lines is developed, which allows to take into account the negative hydrogen effect. Some electrochemical parameters are especially sensitive to in-service degradation of steels at high and low temperatures as well. A good correlation between changes of electrochemical and mechanical properties in the steel degradation process gives prospects for the development of NDT methods for evaluation of the current state of exploited steels. The results discussed show that inspection of the surfaces of installations to find corrosion or mechanical damage alone may not be sufficient for proper evaluating risk of failure.

10

The displacement discontinuity technique in fracture mechanics: the subsurface crack problem

70%

Kourkoulis S. K. , Exadaktylos G. E.

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2001

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tom Vol. 53, nr 4-5

421-437

EN

The displacement discontinuity technique is employed for the determination of the critical conditions causing propagation of a preexisting finite fracture that lies close to the free boundary of a semi-infinite medium. The technique is applied by using a suitably adapted commercial indirect boundary element code, permitting the determination of the displacement, strain and stress fields in multiply-connectedelastic bodies. The critical conditions are then determined by employing a suitable failure criterion. The results of the numerical analysis are compared with the respective ones obtained from a series of experiments with pre-cracked specimens simulating the semi-infinite medium. The agreement is proved to be satisfactory.

11

The influence of material properties on the Q-stress value near the crack tip for elastic-plastic materials

70%

Graba M.

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2008

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tom Vol. 46 nr 2

269-190

EN

In the paper, the values of the Q-stress determined for various elastic-plastic materials for single edge notched specimens in bending (SEN(B)) are presented. The influence of the yield strength, the work-hardening exponent and the crack length on the Q-parameter is tested. The numerical results are approximated by closed form formulas.

PL

W pracy przedstawione zostaną wartości naprężeń Q wyznaczone dla szeregu materiałów sprężysto-plastycznych dla próbek trójpunktowo zginanych (SEN(B)), które powszechnie wykorzystuje się do wyznaczania odporności na pękanie w warunkach laboratoryjnych. Omówiony zostanie wpływ granicy plastyczności i wykładnika umocnienia na wartość naprężeń Q, a także wpływ długości pęknięcia. Wyniki obliczeń numerycznych aproksymowano formułami analitycznymi. Rezultaty pracy stanowią podręczny katalog krzywych J-Q, możliwy do wykorzystania w praktyce inżynierskiej.

12

Kryterium energetyczne wzrostu krzywoliniowej trajektorii szczeliny

70%

Mróz K. , Doliński K.

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2011

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tom z. 99

117-119

EN

In the presentation the analysis of crack curving or instability under mode I loading conditions will be discussed. The simplified approach is used, namely the MK-criterion [7,8,9] based on the linear elastic fracture mechanics (LEFM). In the criterion it is assumed that crack growth follows the direction of minimum distortion energy density at a distance corresponding to specified value of dilatation energy.

13

Fracture of reinforced concrete slab in early exploitation stage

70%

Ziliukus A. , Ziogas G.

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2011

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tom z. 99

71-73

EN

The application of reinforced concrete in modern construction ranges from foundations, columns to various aperture beams, ceilings, roofings, dams and reservoirs. Depending on the type of impact, a reinforced concrete construction has to meet certain strength and quality requirements. The durability of a reinforced concrete construction is influenced to a great degree by the technological solutions selected, physical and chemical processes involved, as well as the ambient environment during the early hardening stage of concrete, any of the above mentioned can cause damage in concrete. Physical and chemical processes in concrete tend to occur at different stages of hardening, therefore, their effects on concrete differ. Quite often, follow- ing the removal of the formwork, cracks can be observed on the surface of a reinforced concrete construction which could have been caused by the above mentioned factors. Early damage in reinforced concrete constructions is detrimental in terms of their further exploitatin [1,2].

14

Relacja struktura - odporność na pękanie w procesie oceny spawalności stali niskostopowych

60%

Ranatowski E.

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2007

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tom Z. 4

101-103

PL

Spawanie traktowane jest aktualnie jako proces specjalny, którego rezultaty nie mogą być w pełni ocenione, zbadane i sklasyfikowane, co ostatecznie stwarza pewien stopień ryzyka i niepewności pracy konstrukcji spawanych. Proces spawania związany jest bezpośrednio z lokalną zmianą energii wewnętrznej łączonych materiałów a jego realizacja w sposób naturalny prowadzi do lokalnej zmiany stanu materiału wyrażającego się w przemianach struktury i właściwości mechanicznych, z czym związany jest stopień uwrażliwienia materiału spawanego i ocena spawalności. Jest to relacja bardzo złożona, o sprzężeniu zwrotnym, co w sensie fizycznym prowadzi do ustalenia związku pomiędzy modułami: polem termicznym – ewolucją mikrostruktury – polem mechanicznym, o wzajemnym oddziaływaniu o charakterze synergicznym. Ocena stopnia uwrażliwienia różnych gatunków stali powinna więc polegać na analizie wymiarowej określonych wyżej modułów, przy ścisłym zapisie fizykalnym zachodzących w nich procesów. Istota problemu oceny spawalności polega więc na ocenie skutków powtórnej ingerencji metalurgicznej w stali w obszarze spoiny, ponownej krystalizacji oraz przemianach strukturalnych, najczęściej o charakterze zupełnie odmiennym, którą posiadała stal przed procesem spawania. Podobne uwagi można odnieść do obszaru bezpośrednio przylegającego do spoiny (SP) – strefy wpływu ciepła (SWC), gdzie zachodzą przemiany struktury w stanie stałym. Lokalne oddziaływanie termiczne w procesie spawania w wyniku oddziaływania więzów mechanicznych jest również źródłem naprężeń własnych i deformacji, tworząc nowy stan mechaniczny powstającego złącza spawanego.

EN

Currently the welding as a technological process is concerned with special processes, the results of which cannot be checked in a complete degree by subsequent control, test of production what finally causes uncertainty of work of welded constructions. The process of welding is related to the local change of the internal energy of welded system and that leads to the local change of state of material expressing by change of microstructure and mechanical properties. This phenomena decide on the assessment of susceptibility of materials under defined welding condition and estimate of the weldability. It is compound relation and the mechanical behaviour of welded joints is sensitive to the close coupling between modules: heat transfer, microstructure evolution an mechanical fields. Welding process in physical meaning it is jointed with three laws govern mass and heat flow the laws of conservation of: mass, momentum and energy. The knowledge of the run of thermo-dynamical process under welding indicates on the possibility of active modelling and control of welding process with use intensive and extensive parameters. As the weld metal cools in the temperature range 2300 to 1800°K, the dissolved oxygen and deoxidising elements in liquid steel react to form complex oxide inclusions of 0,1 to 1 μm size range. In the temperature range 1800 to 1600°K, solidification of liquid to δ ferrite starts und envelops these oxide inclusions. After δ ferrite transforms to austenite in the temperature range 1100 to 500°K, the austenite transforms to different ferrite morphologies such as ferrite: allotriomorphic, Widmanstättena, and acicular. The macro-mechanical heterogeneity of welded structures is one of their primary features. The heterogeneous nature of the weld joints is characterised by macroscopic dissimilarity in mechanical properties. Numerical weldability analysis is a new powerful research and development tool which is useful for metallurgistics technologist and design engineers. Saying strictly the numerical analysis of weldability comprises thermodynamic, thermomechanical and microstructural modelling of the welding process. The result of this analysis is material susceptibility (SU). The fracture resistance of welded joints is mainly characterised by normalised parameters: SU1 = KIth / KIC for cold cracking or in the exploitation condition by SU2 =δ / δ c or J / Jc, SU1 ≠ SU2 . From above-mentioned equations result that does not exist one global parameter which defines the step of susceptibility SU of base materials has been also executed with use of SINTAP program.

15

Assessment of degrading processes progress in the old brigde steel in terms of fracture mechanics - part one - the investigation of possibilities

60%

Szata M. , Lesiuk G. , Pękalski G.

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2009

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tom nr 6

EN

Long-time operating parts from old bridges (particularly erected at the turn of 19th and 20th century) show inclination to the brittle fracture. This type of fracture is initiated as a result of the degrading processes intensity. Structural degrading processes participate into the basic mechanical properties - it is particularly visible in the puddled steel. These processes consist in progressive decomposition of the bainite and pearlite area into carbides and nitrides. The separation of nitrides and carbides inside ferrite grain (and of course onto boundary) is also taken into account. In this paper, the investigation results related to registration fatigue crack growth rate have been presented. For the examination, a part of Piaskowy Brigde in Wroclaw (erected in 1861) was used. The differences in kinetics of fatigue crack growth are also presented. A new energy model has been reminded in the last part of the paper. The main advantages in description of fatigue crack growth have been determined due to a new critical quantity - the energy parameter deltaH [J/m2

PL

Długotrwale eksploatowane stale mostowe, szczególnie pochodzące z konstrukcji wzniesionych na przełomie XIX/XX wieku, wykazują skłonność do kruchego pękania. Kruche pękanie inicjowane jest na skutek intensyfikacji procesów degradacyjnych - degradacji strukturalnej oraz degradacji wytrzymałościowej podstawowych własności mechanicznych (zwłaszcza stale zgrzewne). Procesy degradacyjne polegają w ogólności na postępującym rozpadzie perlitu, wydzieleniach węglików i azotków, zarówno na granicach jak i wewnątrz ziarn. W pracy przedstawiono wyniki badań takich stali mostowych (pochodzących głównie z mostu Piaskowego we Wrocławiu rok bud. 1861) z punktu widzenia metod mechaniki pękania. W wyniku badań otrzymano wykresy kinetyki pękania zmęczeniowego, zgodnie z założeniami norm. Dzięki zastosowaniu kryterium energetycznego wyznaczono również nowy typ wykresu kinetyki pękania zmęczeniowego, bazujący na energii dyssypowanej w każdym cyklu widma obciążenia cyklicznego.

16

Teoretyczne podstawy wymiarowania materiałów i konstrukcji z wykorzystaniem mechaniki pękania

60%

Ranatowski E.

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2002

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tom Z. 52(240)

75-89

PL

W artykule scharakteryzowano ogólne zasady wymiarowania i podobieństwa materiałów i konstrukcji z formalnego punktu widzenia, wykorzystując podobieństwo modelu i układu rzeczywistego w fizycznej przestrzeni wymiarowej. Praktyczną analizę wymiarową rozszerzono o parametry i kryteria mechaniki pękania. Dalsza część poświęcona została syntetycznej charakterystyce głównych zasad mechaniki pękania, stosownych parametrów i wynikających z tego kryteriów.

EN

The article presents general materials and constructions dimensioning and mechanical similarity rules drawing on the similarities of the model and the real systems in the physical dimensioning space. The practical dimensioning analysis has been extended by fracture parameters and criterions. Further on in the paper one is offered a brief characteristics of the basic fracture mechanics parameters and criterions.

17

Praktyczne aspekty wymiarowania materiałów i konstrukcji z wykorzystaniem mechaniki pękania

60%

Ranatowski E.

|

2002

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tom Z. 52(240)

91-99

PL

W pracy przedstawiono praktyczne aspekty wykorzystania zasad wymiarowania i podobieństwa oraz mechaniki pękania do wymiarowania materiałów i konstrukcji (wraz z przykładami obliczeniowymi). Wykonano modyfikację klasycznego modelu E-T-M opartego o normalizowaną wartość [wzór] a także normalizowaną wartość [wzór].

EN

The paper presents practical aspects of dimensioning rules, mechanical similarity and fracture mechanics parameters and criterions and some analytical examples. The modified fracture parameters; ratio of driving forces [...] parameters of Engineering Treatment Model (E-T-M.) and normalised value of [...] are given.

18

Wytężenie i trwałość rurociągów parowych

60%

Okrajni J. , Mutwil K. , Cieśla M. , Miśnicki M.

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2006

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tom R. 48, nr 7-8

74-78

PL

W artykule skoncentrowano się na problematyce stanu technicznego i trwałości energetycznych rurociągów pary, łączących komory zaworów z turbiną. Szczególną uwagę zwrócono na znaczenie metod z zakresu mechaniki pękania. Podstawy metodyczne opierające się na teoretycznym ujęciu wytężenia elementów ze szczelinami zilustrowano przykładami badań rurociągów po wieloletniej eksploatacji.

EN

The problem of technical state assessment and durability of power steam pipelines that connect the headers with turbines has been described in the paper. The particular attention has been paid on the fracture mechanics methods. The methodological backgrounds based on the theoretical approach of cracked component effort have been illustrated by the examples of the pipelines after the long operating period.

19

Effect of temperature on tensile fracture mechanisms of a Ni-base superalloy

60%

Sajjadi S. A. , Zebarjad S. M.

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2007

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tom Vol. 28, nr 1

34-40

EN

Purpose: The Ni-base superalloy GTD-111 is used in manufacturing of the first stage blades of powerful gas turbines (over 125MW). The alloy posses appropriate microstructure and high temperature properties through precipitation hardening heat treatment. Among the properties, tensile properties of the alloy have strong influence on stability and life of the blades. Design/methodology/approach: Tensile tests over a wide range of temperatures from 25 to 950°C with a constant strain rate of 10 -4s -1 were performed to study the tensile fracture mechanisms of the cast and heat treated superalloy. Scanning electron microscopy was used to provide structural and fractography evidence of the superalloy GTD-111at different temperatures. Findings: The fractography results of the tensile tested specimens were in good agreement with the variation in alloy ductility. Many fractography features such as: transgranular and intergranular fracture with fine dimples, cleavage facets and a combination of them were observed in the specimens tested at different temperatures. Research limitations/implications: Because fatigue is an important fracture mechanism at the service condition of the alloy it is suggested for future research to work on the simultaneous effects of tension and fatigue on the fracture mechanisms although, tensile properties alone are important for the alloy. Originality/value: It was found that different fracture mechanisms operated in different temperature ranges for example, while transgranular dimple fracture was dominant at 650°C, the dominant fracture mechanism at room temperature was intergranular.

20

Damage mechanism in AlSi1MgMn alloy

60%

Mrówka-Nowotnik G.

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2008

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tom Vol. 29, nr 2

93-96

EN

Purpose: The main task of this work was to study the fracture mechanism in 6082 aluminium alloy. Design/methodology/approach: Microstructure and fractografic examination has been carried out on the samples in the peak aged condition after static tensile tests, crack resistance test and tensile test in the presence of sharp notch using an optical microscope - Nikon 300, scanning electron microscope HITACHI S-3400 (SEM) in a conventional back-scattered electron mode and JEOL - JEM 2100 ARP TEM/STEM electron microscope on polished sections etched in Keller solution. Findings: It has been found that, at room temperature, general cavitation (nucleaction of voids) occurs after appreciable strain. The nucleation of voids results from debonding along certain particle/matrix interfaces. Observations of microstructure revealed second fracture mechanism initiated by cracking of brittle intermetallic phases. Practical implications: All this knowledge . identification of the microstructural parameters for the different modes of void nucleation and cracking of intermetallic phases leading to fracture of the alloy . can be used to predict maximum ductility before fracture of tensile specimens. Originality/value: For deformation at room temperature different void populations have been defined: void nucleated by intermetallic particle fracture, by s particle/matrix decohesion and by �ż particle/matrix decohesion.