Integranular Fracture: The Effect of Grain Boundary Orientation and Crack Growth Directions

1999 ◽  
Vol 586 ◽  
Author(s):  
Jeffrey W. Kysar
Keyword(s):  
Grain Boundary ◽  
Single Crystal ◽  
Intergranular Fracture ◽  
Cohesive Zone ◽  
Fracture Behavior ◽  
Cohesive Zone Model ◽  
Boundary Energy ◽  
Zone Model ◽  
Directional Dependence ◽  
Symmetric Tilt

ABSTRACTIntergranular fracture is a common failure mechanism for which many issues remain to be resolved. In this study we investigate intergranular fracture behavior of specially oriented symmetric tilt bicrystals of aluminum as well as the fracture behavior of a crack along the interface of a copper-sapphire bicrystal. We begin by describing briefly the structure of a symmetric tilt grain boundary which leads to a discussion of the types of issues related to intergranular fracture that can be addressed with symmetric tilt grain boundaries. We then discuss in detail one of these issues, that of the directional dependence of fracture, and present results of finite element simulations of a copper-sapphire bicrystal specimen that exhibits the directional dependence of fracture. The simulations account for the single crystal nature of the constituents and use a cohesive-zone model, for which the grain boundary energy can be varied, to simulate the fracture process along the interface. The directional dependence of fracture emerges from the simulations for a broad range of parameters in the constitutive models of both the single crystal constituents as well as the interfacial cohesive-zone.

scholarly journals Modeling the Ductile Brittle Fracture Transition in Reactor Pressure Vessel Steels Using a Cohesive Zone Model Based Approach

2013 ◽  
Author(s):  
Pritam Chakraborty ◽  
S. Bulent Biner
Keyword(s):  
Crack Growth ◽  
Pressure Vessel ◽  
Cohesive Zone ◽  
Fracture Behavior ◽  
Cohesive Zone Model ◽  
Pressure Vessels ◽  
Reactor Pressure Vessel ◽  
Zone Model ◽  
Fracture Properties ◽  
Reactor Pressure

Fracture properties of Reactor Pressure Vessel (RPV) steels show large variations with changes in temperature and irradiation levels. Brittle behavior is observed at lower temperatures and/or higher irradiation levels whereas ductile mode of failure is predominant at higher temperatures and/or lower irradiation levels. In addition to such temperature and radiation dependent fracture behavior, significant scatter in fracture toughness has also been observed. As a consequence of such variability in fracture behavior, accurate estimates of fracture properties of RPV steels are of utmost importance for safe and reliable operation of reactor pressure vessels. A cohesive zone based approach is being pursued in the present study where an attempt is made to obtain a unified law capturing both stable crack growth (ductile fracture) and unstable failure (cleavage fracture). The parameters of the constitutive model are dependent on both temperature and failure probability. The effect of irradiation has not been considered in the present study. The use of such a cohesive zone based approach would allow the modeling of explicit crack growth at both stable and unstable regimes of fracture. Also it would provide the possibility to incorporate more physical lower length scale models to predict DBT. Such a multi-scale approach would significantly improve the predictive capabilities of the model, which is still largely empirical.

Cohesive Zone Model for Crack Propagation in a Viscoplastic Polycrystal Material at Elevated Temperature

2006 ◽  
Vol 306-308 ◽  
pp. 187-192
Author(s):  
Yan Qing Wu ◽  
Hui Ji Shi
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Matrix Material ◽  
Rate Sensitivity ◽  
Zone Model ◽  
Dissipation Energy ◽  
Plastic Dissipation

This study looks at the crack propagation characteristics based on the cohesive zone model (CZM), which is implemented as a user defined element within FE system ABAQUS. A planar crystal model is applied to the polycrystalline material at elevated temperature in which grain boundary regions are included. From the point of energy, interactions between the cohesive fracture process zones and matrix material are studied. It’s shown that the material parameter such as strain rate sensitivity of grain interior and grain boundary strongly influences the plastic and cohesive energy dissipation mechanisms. The higher the strain rate sensitivity is, the larger amount of the external work will be transformed into plastic dissipation energy than into cohesive energy which could delay the rupturing of cohesive zone. By comparisons, when strain rate sensitivity decreases, plastic dissipation energy is reduced and the cohesive dissipation energy increases. In this case, the cohesive zones fracture more quickly. In addition to the matrix material parameter, influence of cohesive strength and critical displacement in CZM on stress triaxiality at grain interior and grain boundary regions are also investigated. It’s shown that enhancing cohesive zones ductility could improve matrix materials resistance to void damage.

scholarly journals Numerical Simulation of Crack Propagation in Flexible Asphalt Pavements Based on Cohesive Zone Model Developed from Asphalt Mixtures

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1278 ◽  
Author(s):  
Pengfei Liu ◽  
Jian Chen ◽  
Guoyang Lu ◽  
Dawei Wang ◽  
Markus Oeser ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Cohesive Zone ◽  
Fracture Behavior ◽  
Cohesive Zone Model ◽  
Mechanical Design ◽  
Design Methods ◽  
Asphalt Mixtures ◽  
Asphalt Pavements ◽  
Fracture Mechanisms ◽  
Zone Model

To give engineers involved in planning and designing of asphalt pavements a more accurate prediction of crack initiation and propagation, theory-based models need to be developed to connect the loading conditions and fracture mechanisms present in laboratory tests and under traffic loading. The aim of this study is to develop a technical basis for the simulation of fracture behavior of asphalt pavements. The cohesive zone model (CZM) approach was applied in the commercial FE software ABAQUS to analyze crack propagation in asphalt layers. The CZM developed from the asphalt mixtures in this study can be used to simulate the fracture behavior of pavements and further optimize both the structure and the materials. The investigations demonstrated that the remaining service life of asphalt pavements under cyclic load after the initial onset of macro-cracks can be predicted. The developed CZM can, therefore, usefully supplement conventional design methods by improving the accuracy of the predicted stress states and by increasing the quality, efficiency, and safety of mechanical design methods by using this more realistic modeling approach.

scholarly journals Microstructural damage evolution and its effect on fracture behavior of concrete subjected to freeze-thaw cycles

2018 ◽  
Vol 27 (8) ◽  
pp. 1272-1288 ◽  
Author(s):  
Yijia Dong ◽  
Chao Su ◽  
Pizhong Qiao ◽  
LZ Sun
Keyword(s):  
Computed Tomography ◽  
Cohesive Zone ◽  
Damage Evolution ◽  
Fracture Behavior ◽  
Cohesive Zone Model ◽  
Zone Model ◽  
X Ray ◽  
Freeze Thaw ◽  
Microstructural Damage ◽  
Macro Scale

Concrete structures in cold regions are exposed to cyclic freezing and thawing environment, leading to degraded mechanical and fracture properties of concrete due to microstructural damage. While the X-ray micro-/nano-computed tomography technology has been implemented to directly observe concrete microstructure and characterize local damage in recent years, the freeze-thawed damage evolution processes and its effect on overall mechanical performance are not well understood. In this paper, the X-ray nano-computed tomography technology and micro-scale cohesive zone model are combined to quantitatively investigate microstructural damage evolution and its effect on fracture behavior of freeze-thawed concrete samples in three-point bending tests. A two-level micro-to-macro scale finite element model is developed based on computed tomography microstructural images with microcracks due to freeze-thaw cycles. The macroscopic load–deflection curves and fracture energies are simulated and compared favorably with experimental results. Simulation results demonstrate that microcracks caused by freeze-thaw actions are the primary reason for degradation of concrete mechanical properties. Fracture behaviors of frost-damaged concrete with different mortar and interfacial transition zone strength and fracture constants are also simulated and discussed. The combined X-ray nano-computed tomography technology and cohesive zone model proposed is effective in characterizing fracture behavior of concrete and capturing freeze-thaw cycle-induced microstructural damage evolution and its effect on fracture process of concrete.

Influence of the Cohesive Zone Model Shape Parameter on Asphalt Concrete Fracture Behavior

2008 ◽  
Author(s):  
Seong Hyeok Song ◽  
Glaucio H. Paulino ◽  
William G. Buttlar ◽  
Glaucio H. Paulino ◽  
Marek-Jerzy Pindera ◽  
...  
Keyword(s):  
Asphalt Concrete ◽  
Cohesive Zone ◽  
Fracture Behavior ◽  
Shape Parameter ◽  
Cohesive Zone Model ◽  
Zone Model ◽  
Concrete Fracture
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