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.

Cyclic Cohesive Zone Model for Simulation of Fatigue Failure Process in Adhesive Joints

2014 ◽  
Vol 606 ◽  
pp. 217-221 ◽  
Author(s):  
Mahzan Johar ◽  
Mohamad Shahrul Effendy Kosnan ◽  
Mohd Nasir Tamin
Keyword(s):  
Fatigue Failure ◽  
Adhesive Joint ◽  
Cohesive Zone ◽  
Damage Evolution ◽  
Cohesive Zone Model ◽  
Failure Process ◽  
Interface Strength ◽  
Zone Model ◽  
Strength And Stiffness ◽  
Cyclic Damage

Progressive failure process of adhesive joint under cyclic loading is of particular interest in this study. Such fatigue failure is described using damage mechanics with the assumed cohesive behaviour of the adhesive joint. Available cohesive zone model for monotonic loading is re-examined for extension to capture cyclic damage process of adhesive joints. Damage evolution in the adhesive joint is expressed in terms of cyclic degradation of interface strength and stiffness. Mixed-mode fatigue fracture of the joint is formulated based on relative displacements and strain energy release rate of the interface. A power-law type variation for each of these cohesive zone model parameters with accumulated load cycles is assumed in the presence of limited experimental data on cyclic interface fracture process. The cyclic cohesive zone model (CCZM) is implemented in commercial finite element analysis code and the model is validated using adhesively bonded 2024-T3 aluminium substrates with epoxy-based adhesive film (FM73M OST). The CCZM model is then examined for cyclic damage evolution characteristics of the adhesive lap joint subjected to cyclic displacement of Δδ = 0.1 mm, R=0 so as to induce shear-dominant fatigue failure. Results show that the cyclic interface damage started to initiate and propagate symmetrically from the both overlap edges and degradation of interface strength and stiffness started to accumulate after 0.5 cycles of displacement elapsed. The predicted results are consistent with the mechanics of relatively brittle interface failure process.

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.

scholarly journals Effect of Mesh Sensitivity and Cohesive Properties on Simulation of Typha Fiber/Epoxy Microbond Test

Computation ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 2
Author(s):  
Ikramullah ◽  
Andri Afrizal ◽  
Syifaul Huzni ◽  
Sulaiman Thalib ◽  
H. P. S. Abdul Khalil ◽  
...  
Keyword(s):  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Natural Fibers ◽  
Large Data ◽  
Zone Model ◽  
Damage Initiation ◽  
Fine Mesh ◽  
Cohesive Properties ◽  
Macro Scale ◽  
Microbond Test

The microbond test for natural fibers is difficult to conduct experimentally due to several challenges including controlling the gap distance of the blade, the meniscus shape, and the large data spread. In this study, a finite element simulation was performed to investigate the effects of the bonding characteristics in the interface between the fiber and matrix on the Typha fiber/epoxy microbond test. Our aim was to obtain the accurate mesh and cohesive properties via simulation of the Typha fiber/epoxy microbond test using the cohesive zone model technique. The axisymmetric model was generated to model the microbond test specimen with a cohesive layer between the fiber and matrix. The cohesive parameter and mesh type were varied to determine the appropriate cohesive properties and mesh type. The fine mesh with 61,016 elements and cohesive properties including stiffness coefficients Knn = 2700 N/mm3, Ktt = 2700 N/mm3, and Kss = 2700 N/mm3; fracture energy of 15.15 N/mm; and damage initiation tnn = 270 N/mm2, ttt = 270 N/mm2, and tss = 270 N/mm2 were the most suitable. The cohesive zone model can describe the debonding process in the simulation of the Typha fiber/epoxy microbond test. Therefore, the results of the Typha fiber/epoxy microbond simulation can be used in the simulation of Typha fiber reinforced composites at the macro-scale.

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.

Microstructural damage characterization of concrete under freeze-thaw action

2017 ◽  
Vol 27 (10) ◽  
pp. 1551-1568 ◽  
Author(s):  
Q Luo ◽  
DX Liu ◽  
Pizhong Qiao ◽  
QG Feng ◽  
LZ Sun
Keyword(s):  
Computed Tomography ◽  
Transition Zone ◽  
Three Dimensional ◽  
Interfacial Transition Zone ◽  
X Ray ◽  
Freeze Thaw ◽  
Microstructural Damage ◽  
Damage Characterization ◽  
X Ray Computed ◽  
Concrete Materials

This paper conducts a quantitative analysis of microstructural damage evolution of concrete materials under freeze-thaw action using three-dimensional X-ray computed tomography. The study employs two resolution-scales to evaluate concrete samples under various cycles of freeze-thaw action. The three-dimensional microstructural damage characterization, pore network (porosity, pore size, and pore distribution) as well as the defects in the aggregates are specifically investigated. The microstructures of concrete under different freeze-thaw action show that the interfacial transition zone is most likely to be damaged first under frost attack. Furthermore, the freeze-thaw action deteriorates not only the interfacial transition zone but also cement matrix and aggregates. The impact of freeze-thaw cycles is notable on the internal micro-pores and micro-cracks of the concrete. More pores and cracks can be nucleated during the freeze-thaw action, and further accumulate and grow in the paste and aggregates, eventually leading to final failure of concrete materials. As demonstrated in this study, three-dimensional X-ray computed tomography is capable of acquiring microstructures of concrete and revealing existence of internal pores and cracks in different phases of concrete, and more effective to characterize accumulated damage of concrete due to freeze-thaw action.

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.

Sign in / Sign up

Export Citation Format

Share Document