Papers by Keyword: Cohesive Zone

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Authors: S.Z. Li, Jian Cheng, W.Q. Ma
Abstract: The paper describes a method to forecast the cohesive zone of blast furnace whose shape is very important for the quality of iron and the efficiency of iron-making industry. This method builds a model that can be observed during the operation of iron making. The model considers that during the chemical reaction the ore, the coke and the gas abide by two equations: the equation of conservation of mass and the equation of heat conservation. Based on this presumption, by dividing the blast furnace into a series of homocentric circles in the height direction and resolving the equations in every homocentric circle with its own parameters, we can get the relationship between temperature and height of the inner blast furnace. And then, according to the fusibility character of the ore, we can forecast the shape and position of the cohesive zone. Finally, the paper visualizes the cohesive zone of blast furnace and discusses some results achieved through the application of such method to a real blast furnace.
Authors: Xiao Hui Huang, Wen Guang Liu, Guo Qun Zhao, Xin Hai Zhao
Abstract: In this investigation, we propose a new concept to embed cohesive zone into the continuum structure of bone cement, an example of brittle material, in investigating the mechanical behavior and fracture mechanism and to predict the fracture which elastic fracture mechanics (EFM) is unable to. Four finite element (FE) models with embedded cohesive zones for the simulations of tensile, compression, double shear and 3-point bending tests have been implemented. Cohesive zones (CZ) are embedded at high risks of fracture with orientations determined by fracture mode. A bilinear cohesive traction-separation law (TSL) is applied. The fracture parameters in traction-separation curve are validated and justified in the simulations to agree well with the force-displacement curves in the four practical tests. Apart from the maximum load, the perpetual safe working load (SWL) in theory also can be predicted by tracing the history of the stiffness degradation of fractured cohesive zone by means of simulation. A distinct advantage of our numerical model is that it is able to extend to investigate the mechanical behavior and fracture mechanism of other brittle materials. The proposed method with embedded cohesive zones in FE models can be introduced to predict the fracture and to forecast the maximum load and safe working load (SWL) of the continuum structure in more complicated loading conditions.
Authors: Rashid K. Abu Al-Rub, Ammar Alsheghri
Abstract: A cohesive zone damage-healing model (CZDHM) derived based on the laws of thermodynamics for self-healing materials is presented. The well-known nominal, healing, and effective configurations of classical continuum damage mechanics are extended to self-healing materials. A new physically-based internal crack healing state variable is proposed for describing the healing evolution within the crack cohesive zone. The effects of temperature, crack-closure, and resting time on the healing behavior are discussed. Numerical examples are conducted to show the various novel features of the formulated CZDHM.
Authors: Li Hao Han, Zhi Guo Luo, Xiao Lei Zhou, Zhan Xia Di, Jun Jie Sun, Zong Shu Zou, Yu Zhu Zhang
Abstract: The cohesive zone plays very important role in the operation of COREX melter gasifier, up to now, definition of the cohesive boundary has always been a challenging task. In this paper, a two-dimensional hot model of melter gasifier, in which paraffin and corn are used to simulate DRI, coke and lump coal respectively, has been established to study the cohesive boundary in this paper. While the whole experimental process is recorded by the high-speed camera, the image processing method is put forward to define the cohesive boundary quantificationally.
Authors: Ying Guang Liu, Xiao Dong Mi, Song Feng Tian
Abstract: To research the effect of grain size on the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials by considering a typical case where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, the cohesive zone size is assumed to be equal to the grain size d of the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It was found that the critical stress intensity factor increases with the increasing of grain size d of the NC matrix as well as the coarse grain size D. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size rather than that of NC matrix.
Authors: Sunil Bhat, Vijay G. Ukadgaonker
Abstract: Strength mismatch effect across weld interfaces, generated by welding weak and strong steels, influences fatigue and fracture properties of a welded bimetallic composite. Advancing fatigue crack tip in weak parent steel is shielded from the remote load when it reaches near the interface of ultra strong weld steel. Entry of crack tip plasticity into weld steel induces load transfer towards weld which dips crack growth rates thereby enhancing the fatigue life of the composite. A computational model for fatigue life prediction of strength mismatched welded composite under K dominant conditions is validated by experimental work in this paper. Notched bimetallic compact tension specimens, prepared by electron beam welding of weak alloy and strong maraging steels, are subjected to fatigue testing in high cycle regime.
Authors: Vijay G. Ukadgaonker, Sunil Bhat
Abstract: When a Mode I crack in soft steel body grows and reaches near the perpendicular interface of ultra strong steel body, its cohesive zone penetrates into the interface body which influences the crack tip parameter. The paper presents finite element analysis of the cohesive zone across the interface of such elastically matched but strength mismatched bodies in linear elastic regime. Parent alloy steel (ASTM 4340) body and interface maraging steel (MDN 250) body are considered for analysis. The cohesive zone is modeled in accordance with the Dugdale criterion. J integral is evaluated over the path around the interface to examine the effect of cohesive stresses on the crack tip. The results are compared vis-à-vis those obtained from the theoretical model. The two are in very good agreement with each other.
Authors: M.G.D. Geers, R.L.J.M. Ubachs, M. Erinc, M.A. Matin
Abstract: The past years have triggered considerable scientific efforts towards the predictive analysis of the reliability of solder connections in micro-electronics. Undoubtedly, the replacement of the classical Sn-Pb solder alloy by a lead-free alternative constitutes the main motivation for this. This paper concentrates on the theoretical, computational and experimental multi-scale analysis of the microstructure evolution and degradation of the conventional solder material Sn-Pb and its most promising lead-free alternative, a Sn-Ag-Cu (SAC) alloy. Special attention is given to the thermal anisotropy of bulk SAC and the interfacial fatigue failure of SAC interconnects.
Authors: Gang Pan, Xun Liang Liu, Zhi Wen
Abstract: The Corex process, which consists of the upper reduction shaft and the melter-gasifier is an alternative ironmaking process to the blast furnace. The Corex melter-gasifier is a countercurrent reactor to produce liquid iron. Directly reduced iron(DRI), noncoking coal, and other additives are charged to the melter-gasifier at their respective temperature, and O2 is blown through the tuyeres. Moving bed of melter-gasifier is an important zone for reduction of iron oxide and melting of DRI, in which lump coal is a function as skeleton of moving bed replacing coke. A two-dimensional mathematical model was developed for describing gas flowing in the moving bed of Corex melter-gasifier. The gas velocity and pressure distribution were obtained. Further more, the effects of deadman porosity and cohesive zone, burden profile and height of moving bed above tuyere on the gas velocity and pressure distribution were studied.
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