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1

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.

2

Badania fraktograficzne spajanych stopów Al-Mg

Czechowski M.

Przegląd Spawalnictwa

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2006

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R. 78, nr 5-6

32-34

PL

Przedstawiono charakterystyczne dla spajanych stopów AI-Mg powierzchnie pęknięcia próbek z badań odporności na korozję naprężeniową przy małej prędkości odkształcania oraz z badań niskocyklowego zmęczenia. Badano stopy AI-Mg spajane metodami MIG oraz zgrzewane tarciowo z przemieszaniem materiału (FSW). Główny nacisk położono na określenie czynników wpływających na rozwój pęknięć w aspekcie mikrostrukturalnym. Ocena mikrostruktur oraz powierzchni dróg pękania wykonana została za pomocą mikroskopu skaningowego elektronowego o dużej rozdzielczości Philips XL30 i przystawki EDAX do mikroanalizy składu chemicznego za pomocą dyfraktometru rentgenowskiego EDS. Zaobserwowano, że zarodkowanie pęknięć powstaje na granicach międzyfazowych osnowy z wydzieleniami, a rozwój pęknięcia głównego zachodzi poprzez łączenie mikropustek.

EN

One introduced characteristic for welded AI-Mg alloys surfaces of the crack of samples from research of the stress corrosion cracking at the slow strain rate tests and from Iow-cycle fatigue tests. The AI-Mg alloy welded by MIG and by friction stir welding (FSW) were investigated. The main pressure was put on the qualification of influent factors on the development of cracks in the microstructure aspect. The metallographic tests was carried out by the scanning electron microscope (SEM) with the chemical composition analysis (energy dispersive spectroscopy, EDS). One observed that the initiated of cracks came into being on interphasic borders of the matrix with particles. The development of the main crack happens through the joining microvoids.

3

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.

4

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.