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1

Deformation failure analysis and identification method of zoning type of actual tunnel surrounding rock

Jing Wei, Gao Yunlong, Jin Rencai, Jing Laiwang

Archives of Civil Engineering

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2023

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Vol. 69, nr 4

549--571

EN

The research on deformation zoning mechanism of tunnel surrounding rock is of great significance for ensuring safe production and disaster prevention in coal mines. However, the traditional deformation zoning theory of tunnel surrounding rock uses the ideal strain softening model as the criterion for judging the zoning type of all tunnel surrounding rock, ignoring the difference between the deformation zoning type of a specific actual tunnel and the basic zoning type of surrounding rock. In order to study the method for determining the actual deformation zoning type of tunnel surrounding rock, the formation mechanism of the actual deformation zoning of tunnel surrounding rock has been revealed. Combined with engineering examples, a method for determining the actual deformation zoning type and boundary stress of specific tunnel surrounding rock has been proposed. The results show that the boundary stress and position of the actual deformation zone are determined by the peak strength fitting line, residual strength fitting line, support strength line, and the position of the circumferential and radial stress relationship lines of each deformation zone. The actual boundary stress of each zone of tunnel surrounding rock is ultimately only related to the basic mechanical properties of the tunnel surrounding rock and the in-situ stress field. The research results can provide reference for disaster management of underground engineering, stability evaluation of surrounding rock, and support scheme design.

2

A review on the deformation mechanism and formability enhancement strategies in incremental sheet forming

Ullah Sattar, Li Yanle, Li Xiaoqiang, Xu Peng, Li Dongsheng

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e55, 2023

EN

The process formability of incremental sheet forming (ISF) is better than the conventional forming processes. Stretching, through-thickness-shear, bending-under-tension (BUT), and compressive forces are the proposed deformation mechanisms for improved formability; however, researchers have not corroborated (on consensus) the relative significance of any one among these. Similarly, researchers observed abrupt fractures (brittle fracture) and fractures preceded by necking (ductile fracture) for different case studies, which initiated a new debate and is still unanswered. Besides, researchers have extended the ISF to energy-assisted ISF to improve the process formability further for materials having a high strength-to-weight ratio. Three prominent energy-assisted ISF are (a) Electric-assisted ISF (E-ISF) works on the principle of lowering the yield stress by raising the temperature and has shown promise for Magnesium and Titanium alloy. (b) The ultrasonic vibration-assisted (UV-ISF) process works on the principle of acoustoplastic softening effect and thus far improved the room temperature material formability while reducing the forming forces. (c) Electromagnetic-assisted ISF (EM-ISF) is a non-contact, high-speed process that utilizes the pulsed magnetic field to apply inertial force, which improves formability by dislocation slips. The EM-ISF and UV-ISF have shown promise to counter the challenges during aluminum alloy forming; however, the work in this regard is still in the initial phase and has not explored its full potential. This study updates the potential research on the current status of the energy-assisted ISF. Different customized testing equipment is discussed that help understand the process mechanism. Microstructural changes in the material occur at normal ISF and with energy-assisted ISF are discussed in detail. Discussion and future work are presented based on the insight from various articles at the end.

3

Investigating the capability of the Lemaitre damage model to establish the incremental sheet forming process

Kumar Pavan, Tandon Puneet

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 2

art. no. e66, 1--18

EN

This paper presents the numerical and experimental investigation of the incremental sheet forming (ISF) process with the Lemaitre damage model to incrementally form parts of conical shapes. The Lemaitre damage model was prepared as a material subroutine (VUMAT) and linked to Abaqus/Explicit. The elastic–plastic parameters for the simulation were identified through tensile testing of the ASTM E8 specimen. The digital image correlation (DIC) was performed during the tensile testing to identify the damage parameters of the Lemaitre damage model. Scanning electron microscopy (SEM)-based area method was used to identify the area fraction vis-a-vis the variation of the strain. Thereafter, the identified area fractions with respect to strains have been calibrated to obtain the damage parameters through an inverse analysis approach. The identified parameters were used to form conical objects of Al1050 H14 sheets of 2 mm thickness through finite element (FE) simulation. The results obtained through FE simulation were compared with the experimental outcomes to investigate the efficiency of the Lemaitre damage model to simulate the ISF process. The responses obtained through FE simulation and experiments have been discussed in terms of limiting wall angle and forming depth, damage evolution, deformation mechanism, forming limit diagram, geometrical accuracy, forming forces, thickness distribution, and surface roughness.

4

Deformation of semicrystalline polymers – the contribution of crystalline and amorphous phases

Bartczak Z.

Polimery

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2017

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T. 62, nr 11-12

787--799

EN

The plastic deformation process of semicrystalline polymers and the micromechanisms involved are discussed. The particular attention is paid to the dependence of deformation on structure and mutual influence of deformation of crystalline and amorphous components. Deformation of a semicrystalline polymer appears a complex series of continuous processes, involving mostly crystallographic deformation mechanisms operating in the crystalline phase. However, a very important role in that sequence is played by the deformation of amorphous interlamellar layers, partially reversible on unloading, which produces not only the high orientation of amorphous component but also influences deeply and supports the deformation of crystalline phase since crystalline lamellae and amorphous interlamellar layers, intimately connected through covalent bonds of chains crossing the interface, can deform only simultaneously and consistently. In particular, an influence of the topology of the amorphous phase, including the density of the molecular network of entangled chains and number of chains connecting adjacent crystalline and amorphous layers, on deformation instabilities of crystalline component in polyethylene are discussed. The induced instabilities of crystallographic slip lead to formation of lamellar kinks and frequently to an extensive fragmentation of lamellae. These transformations of crystalline structure together with restructurization of amorphous phase at high strains influence deeply the formation of the final highly oriented structure of the deformed semicrystalline polymer.

PL

Rozważano przebieg procesu odkształcenia plastycznego polimerów semikrystalicznych i zaangażowane w nim mikromechanizmy, zwracając szczególną uwagę na zależność deformacji od struktury materiału oraz na wzajemny wpływ odkształcenia fazy amorficznej i krystalicznej. Deformacja polimeru semikrystalicznego obejmuje szereg ciągłych procesów, w których zaangażowane są głównie krystalograficzne mechanizmy deformacji, aktywne w fazie krystalicznej. Bardzo ważną rolę w procesie odgrywa też częściowo odwracalne odkształcenie amorficznych warstw międzylamelarnych, które nie tylko prowadzi do wysokiego stopnia orientacji molekularnej w fazie amorficznej, ale wpływa również na deformację fazy krystalicznej. Lamele krystaliczne i amorficzne warstwy międzylamelarne, ściśle połączone wzajemnie wiązaniami kowalencyjnymi w łańcuchach przekraczających granice międzyfazowe, mogą deformować się tylko jednocześnie i spójnie. Omówiono także wpływ topologii fazy amorficznej, w tym gęstości sieci molekularnej splątanych łańcuchów i liczby łańcuchów łączących sąsiednie warstwy krystaliczne i amorficzne, na niestabilności deformacji fazy krystalicznej w polietylenie. Pojawiające się niestabilności poślizgów krystalograficznych prowadzą do powstawania załamań lamel, a często nawet do ich rozległej i silnej fragmentacji. Takie transformacje struktury fazy krystalicznej wraz z restrukturyzacją fazy amorficznej przy dużych odkształceniach wpływają istotnie na końcową, silnie zorientowaną, strukturę zdeformowanego polimeru semikrystalicznego.

5

Współczesne technologie w zwiększaniu bezpieczeństwa w motoryzacji

Świłło S., Czyżewski P., Lisok J.

Logistyka

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2015

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nr 4

6166--6173, CD 2

PL

W artykule zaprezentowano przegląd współczesnych technik stosowanych w przemyśle motoryzacyjnym. W celu zwiększenia stopnia bezpieczeństwa w transporcie drogowym i zmniejszenia skutków wypadków samochodowych prowadzone są liczne badania pozwalające na przewidywanie końcowego efektu zderzeń przy niewielkich prędkościach przemieszczania. Badania te prowadzone są z wykorzystaniem dwóch technik: numerycznej i doświadczalnej, co pozwala znacznie zwiększyć wytrzymałość na zniszczenie takich elementów konstrukcyjnych samochodu jak belka zderzaka lub łącznik kompensacyjny. Autorzy przedstawiają liczne prace i metody oraz stosowane materiały w celu optymalizacji kształtu, co pozwala na maksymalizację pochłanianej podczas zderzenia energii. W związku z tym, że łącznik kompensacyjny elementu zderzaka jest jednym z najważniejszych elementów pozwalających na kontrolowane pochłaniane energii nagromadzonej podczas zderzenia, przedstawiono na zakończenie pełen proces technologiczny wykonania tej części. W wyniku przeprowadzonej symulacji MES zoptymalizowano kształt ze względu na wytrzymałość zniszczeniową co pozwala na spełnienie wymogów kontrolowanej kolizji przy niewielkich prędkościach.

EN

The paper presents a quick survey of current technologies in automotive industry. To reach a high level of safety requirement and minimize the occurrence and consequences of automobile accidents number of studies have been investigated on the prediction the crash event. These investigations are performed by both techniques: numerical and experimental and they can significantly improved crashworthiness of selected auto-parts such a bumper-beam or crash-box under impact loadings. The authors describe several different methods and materials to optimized the shape of these parts for maximum energy absorption. Since the crash-box is one of the most important automotive parts for crash energy absorption a fully dialed process technology of those part was simulated using FEM and presented in this study. As a result, the optimum shape of crash-box was designed where the maximum crashworthiness can satisfy safety requirements for low velocity impact.

6

Mechanism of deformation of a liquid conductor with current

Jakubiuk K.

Journal of Technical Physics

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1998

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Vol. 39, no 3-4

473-482

EN

This paper specifies the kinds of disintegrations of a conductor subjected to current impulses of high density. It was proved that in practical applications the conductors undergo most often so-called striation desintegrations. A 3-stage mechanism of the striations is suggested. Very important is the deformation stage of the conductor. A physical and mathematical model of the phenomena occurning at this stage are presented including the results of numerical calculations. A good agreement of the calculations with the experimental results was obtained.