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Determination of Critical Damage Function Values of CW008A Copper and S355 Steel in Tensile and Torsion Tests

Walczuk-Gągała Patrycja, Pater Zbigniew, Wójcik Łukasz, Lis Konrad

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no 2

173--180

EN

The article describes the problem of material fracture in metal forming processes. It describes and compares the values of damage functions obtained in classical tensile and torsion tests of two materials, i.e. CW008A copper and S355 steel under cold forming conditions. The presented research methodology includes experimental tests and numerical simulation carried out using Simufact.Forming v.15 software. The damage values were analysed according to various criteria, including the growth and coalescence of micro cracks (Rice&Tracey, Oyane, Argon), the initiation and development of ductile cracking in forming processes (Freudenthal, Cockroft-Latham, Brozzo, Oh) and using extended phenomenological models based on the history of stress triaxiality (Ayada) or the mean and equivalent stress (Zhan). The conducted tests showed that the values of the damage function depend on: the calibration test, the material grade and the geometry of the specimen.

2

Determination of the Value of the Damage Function in 1050A Aluminium Alloy

Walczuk-Gągała Patrycja, Pater Zbigniew, Wójcik Łukasz

Advances in Science and Technology. Research Journal

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2020

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Vol. 14, no 2

49--55

EN

The article presents the problem of material cracking in metal forming processes. The authors describe and compare the values of damage obtained in classic tensile and compression tests as well as rotational compression of 1050A aluminium alloy in cold working conditions. The presented research methodology contains experimental tests as well as a numerical simulation conducted in Simufact.Forming v.15. An analysis of the damage values was calculated according to the normalised Cockcroft-Latham criterion. The research conducted showed that the damage value in the rotational compression test is greater than the values obtained by the means of other tests.

3

The Problem of Material Fracture Prediction in Cross Rolling Processes

Pater Zbigniew, Tomczak Janusz, Bulzak Tomasz, Zniszczyński Andrzej

Advances in Science and Technology. Research Journal

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2018

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Vol. 12, no 4

184--189

EN

The paper deals with the problem of material fracture prediction in metal forming processes. It was found that the application of well-established solutions for ductile fracture prediction to the modelling of cross rolling processes leads to serious errors. These errors result from the fact that the limit value of the damage function determined via uniaxial tensile and compression tests is too low. Therefore, it is necessary to devise a new test in which the state of stress is similar to that in a cross wedge rolling process characterized by the occurrence of alternating compressive and tensile stresses.

4

Preliminary analysis of a rotary compression test

Pater Zbigniew, Walczuk Patrycja, Lis Konrad, Wójcik Łukasz

Advances in Science and Technology. Research Journal

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2018

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Vol. 12, no 2

77--82

EN

The paper addresses the problem of material fracture in cross rolling processes. A new test based on rotary compression for determining limit values of the damage function after the Cockroft-Latham criterion is proposed. A FEM analysis is performed to determine the stress and strain states in a workpiece subjected to this test. The numerical results demonstrate that the axial region of the workpiece is characterized by the presence of alternating tensile and compressive stresses conducive to fracture. The distribution of the Cockroft-Latham integral in the axial region of the workpiece is determined.

5

Wpływ stanu naprężenia na odkształcenie i pękanie materiału w procesie wykrawania

Kut S.

Prace Naukowe Politechniki Warszawskiej. Mechanika

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2007

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z. 216

87--92

PL

Na wielkość plastycznego odkształcenia materiału do momentu pękania decydujący wpływ ma stan naprężenia. Analizując proces kształtowania w płaskim stanie naprężenia, stan ten możemy jednoznacznie określić przy pomocy wskaźnika stanu naprężenia k. W procesie wykrawania stan naprężenia panujący w obszarze cięcia nie jest stały, ale zmienia się w trakcie jego przebiegu. Zależy również od wielu czynników, głównie geometrycznych np. kształtu narzędzi, wielkości szczeliny wykrawania, itd. Analizę stanu naprężenia przeprowadzono na poszczególnych etapach zagłębienia stempla w materiał do momentu początku pękania dla trzech różnych wielkości szczelin. Wykazano wpływ stanu naprężenia na wartość granicznego odkształcenia pękania materiału. Ponadto wyznaczono eksperymentalnie kształt profilu powierzchni przecięcia poszczególnych wykrojek w zależności od luzu wykrawania.

EN

The state of stress significantly influences the fracture strain until material failure. Analyzing the blanking process in the plane stress condition, such a state of stress can be determined unequivocally with k stress triaxiality. During the blanking process, the state of stress within the cutting area is not constant and changes during this process. This depends also on several factors, mainly geometrical, e.g. tool shape, dimension of punching slot, etc. The state of stress analysis has been performed on individual phases of punch displacement in the material until crack initiation, for three slot dimensions. The state of stress effect on the dimension of limit material fracture strain has been indicated. Moreover, the cross-cut section profile shape has been experimentally determined.

6

Particle fracture and phase transformations induced by electrical discharge assisted mechanical milling

Calka A., Wexler D.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

465-468

EN

A novel device for milling, incorporating high voltage, low current electrical discharges was constructed and its application for materials processing investigated [1, 2]. This type of milling has been found to result in rapid fracture rates, enhanced mechano-chemical reactions and novel reaction paths. We present recent studies of fracturing, agglomeration and phase formation using this method applied to a vibrational rod mill. The effect of spark discharge milling condition on particle size and surface morphology was investigated for a number of different materials including; alumina, NiZr, Ni plus Si, Mg-Zn alloy of eutectic composition. In these experiments, variations in milling vibrational amplitude resulted in variations in nominal average spark length for samples discharged milled under repeated impact. It was confirmed that during discharge milling, rapid fracturing occurs wervery short milling times and is accompanied by the formation of both fine particles and agglomerates. Large vibrational amplitudes tended to promote increased particle agglomeration in both ceramics and metals, while discharge milling with lower vibrational amplitudes promoted the formation of finer particles and smaller agglomerates. In the case of alumina, particle coarsening and spheroidisation was believed to result from repeated sintering of individual particles. For metals, alloys and metallic glasses, the tendency for coarsening and formation of spherical particles resulted from some combination of partial melting and deformation. Spark milling of Mg-Zn eutectic decomposition product was found to result in formation of the metastable eutectic phase, Mg7Zn3.