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Investigating the combination effect of warm extrusion and multi-directional forging on microstructure and mechanical properties of Al–Mg2Si composites

Sharifzadeh M., Shaeri M. H., Taghiabadi R., Mozaffari F., Ebrahimi M.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 2

37--47

EN

The combined effect of extrusion and multi-directional forging (MDF) was investigated on microstructure and mechanical properties of aluminum-based composite with 10, 15, and 20 wt% Mg2Si. In the casted Al–Mg2Si composites, the primary and eutectic Mg2Si particles are generally coarse which lead to decreasing their mechanical properties and formability. Extrusion process was utilized to overcome this shortcoming by breakage of the eutectic structure, reduction of Mg2Si size, and the decrease of casting defects. Then, MDF process was applied up to failure on the extruded composites at room temperature. It led to the morphological modification of primary and eutectic Mg2Si phases and the reduction of their size. It was found that the MDF process resulted in a considerable improvement in hardness and shear strength of materials. This may be related to the reduction in the average size of Mg2Si particles with their uniform distribution. In addition, ultimate shear strength is, respectively, increased from 94, 99, and 81 MPa to 119, 116, and 117 MPa for the 10, 15, and 20 wt% Mg2Si aluminum composites after the final pass of MDF. Meanwhile, the normal displacement of composites is reduced at initial passes and increased by the addition of more pass numbers.

2

A bonded particle model for analysis of the flaw orientation effect on crack propagation mechanism in brittle materials under compression

Manouchehrian A., Sharifzadeh M., Marji M. F., Gholamnejad J.

Archives of Civil and Mechanical Engineering

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2014

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Vol. 14, no. 1

40--52

EN

In this paper, implementation of a bonded particle model (BPM) using PFC2D was proposed to study the effect of the flaw orientation on the crack propagation mechanism in brittle materials such as rocks under various compressive loads. For this purpose, several pre-cracked rock specimens with different orientation of flaw under uniaxial and biaxial loads were modeled in PFC2D (bonded particle model) and crack propagation processes were monitored. According to the results, by varying the flaw inclination angle (β), two types of the secondary crack propagation mechanism were detected. Also, it was concluded that the confinement stress affected the crack initiation and propagation mechanism and the increase of it made the crack initiation angle steeper.

3

Quantifying the uncertainty of pillar safety factor by Monte Carlo simulation - a case study

Ghasemi E., Shahriar K., Sharifzadeh M., Hashemolhosseini H.

Archives of Mining Sciences

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2010

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Vol. 55, no 3

623-635

EN

The pillar failure hazards are the major problems in underground coal mines, which are generally unpredictable due to associated uncertainties arising out of the complexity of geological conditions and variability in mining parameters. The pillar safety factor, always considered in pillar design and planning of underground coal mines, may be an important predictor for pillar failures. In this paper, contributing parameters on pillar safety factor for the main panel of Tabas Central Coal Mine, located in the mid-eastern part of Iran which is going to be extracted by room and pillar method, are collected. The mean value of probabilistic pillar safety factor for the case study mine was found to be 1.47. However, the probability of the estimated pillar safety factor of less than or equal to one, was found to be 22.5%. The effects of the random variables on pillar safety factor and probability of pillar failure were determined using Monte Carlo simulation method. Based on results of simulation runs for each variable, the probability of pillar failure was determined. In addition, a multi-variable regression analysis was performed to determine the correlation between the random variables and the pillar safety factor. Uniaxial compressive strength of coal, with the coefficient of correlation of +0.61, was found to be the most important parameter to control the pillar safety factor.

PL

Zagrożenie związane z pękaniem filarów ochronnych stanowi jeden z poważniejszych problemów w podziemnych kopalniach węgla; pękania te są z reguły nieprzewidywalne z uwagi na element niepewności związany ze złożonymi warunkami geologicznymi i z różnorodnością parametrów górniczych. Współczynnik bezpieczeństwa dla filarów, zawsze uwzględniany w procesie projektowania filarów i planowania kopalni podziemnych, może być cennym wskaźnikiem przy prognozowaniu pękania filarów. W artykule tym parametry przyjęte do obliczania współczynnika bezpieczeństwa pochodzą z głównego pola wydobywczego w kopani węgla kamiennego Cabas, położonej w środkowo-wschodnich regionach Iranu. Wybieranie odbywało się metodą filarowo-komorową. Wartość średnia probabilistycznego współczynnika bezpieczeństwa dla filara otrzymana dla kopalni uwzględnionej w studium przypadku wyniosła 1.47. Jednakże prawdopodobieństwo szacowania współczynnika bezpieczeństwa w wysokości 1 lub poniżej wyniosło 22.5%. Wpływ zmiennych losowych na wielkość współczynnika bezpieczeństwa i prawdopodobieństwo pęknięcia filara określone zostały w oparciu o symulacje metodą Monte Carlo. W oparciu o wyniki symulacji prowadzonych dla każdej zmiennej obliczono prawdopodobieństwo pęknięcia filara. Ponadto, przeprowadzono badania metodą regresji wielu zmiennych w celu ustalenia korelacji pomiędzy zmiennymi losowymi a współczynnikiem bezpieczeństwa dla filara. Stwierdzono, że jednoosiowe naprężenia ściskające węgla jest najważniejszym parametrem determinującym współczynniki bezpieczeństwa dla filara, przy współczynniku korelacji wynoszącym +0.61.