Papers by Keyword: Cohesive Zone

Abstract: In this paper, a viscoelastic-damage cohesive zone model is formulated and discussed. The interface element constitutive law has two elastic and damage regimes. Viscoelastic behaviour has been assumed for the shear stress in the elastic regime. Three element Voigt model has been used for the formulation of relaxation modulus of the material. Shear Stress has been evaluated in the elastic regime of the interface with integration over the history of the applied strain at the interface. Damage evolution proceeds according to the bilinear cohesive constitutive law up to the complete decohesion. Numerical examples for one element model has been presented to see the effect of parameters on cohesive constitutive law.

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.

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.

Abstract: A hot model is established to study the cohesive zone of COREX melter gasifier in this paper., in this experiment, the paraffin and corn are used to simulate DRI, coke and lump coal respectively, the influences of ore/coke volume ratio, raceway gas temperature and raceway gas volume on the cohesive zone are analyzed using image processing method.

Abstract: This work presents numerical methods used for predicting crack paths in technicalstructures based on the theory of linear elastic fracture mechanics. The FE-method is usedin combination with an efficient remeshing algorithm to simulate crack growth. A post pro-cessor providing loading parameters such as the J-integral and stress intensity factors (SIF) ispresented. Path-independent contour integrals are used to avoid special requirements concern-ing crack tip meshing and to enable efficient calculations for domains including interfaces andinternal boundaries. In particular, the interaction of cracks and internal boundaries and inter-faces is investigated. The simulation combines crack propagation within elastic bodies and atbi-material interfaces. The latter is based on a cohesive zone model. The presented numericalresults of crack paths are verified by experiments.

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.

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.

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.

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.

Abstract: Adhesives are widely used in our life and industrial world. However, it is difficult to characterize their mechanical properties because those strongly depend on environmental and mechanical conditions such as temperature, humidity or strain rate. In this paper, we focus on the strain rate dependence of the interfacial strength and investigate the interfacial strength by peel tests under several peel rates. The results show that, in lower rate region (under 1.0 mm/s), the interfacial strength is constant and, in transition region (1.0 to 10 mm/s) the interface strength increased with the peel rate. In middle rate region (10 to 103 mm/s), the interfacial strength is constant again. Over 103 mm/s region, the interfacial strength drops and became lower than those in middle rate cases. From the observation of peeling front by a high speed video camera, the deformation behavior of adhesives changes with the peel rate.􀀁Finite element analysis by using cohesive zone model is also conducted, and influence of the rate dependency of adhesive and base material is discussed.