Sharif Digital Repository

Masonry infills are vastly used as surrounding walls and partitions. Presence of infill in a building causes some change in strength, stiffness, period and generally seismic behavior of the structure.Mainly there are 5 modes of failure including 1- interface cracking 2- sliding along bed joint 3- diagonal cracking 4- corner crushing and 5- ultimate failure. According to these failures, three stages of strength as shear strength, corner strength and ultimate strength can be defined.Diagonal crack can be calculated by slip surface method grown in Sharif university of Technology. Based on this method the strength of infill wall falls down as the cohesive strength of mortar loses and so the slip... 

Prediction of crack growth is one of the greatest achievements of continuum mechanics in 20th century. However, in spite of Griffith’s achievements, nowadays lots of subjects remain unchallenged in the field of Fracture Mechanics. Concrete and asphalt concrete are two of the most popular material in civil engineering and crack growth prediction in these materials are very important. Cohesive crack model is one of the models which is used for prediction of crack growth in quasi-brittle material such as concrete and it has been used widely in recent years because of simplicity and good agreement with experiment.The aim of this thesis is three-dimensional static and dynamic cohesive modeling of... 

In this research, delamination in compound laminated materials under the I mode loading is studied. In this way, a Double Cantilever Beam is investigated, which is the only experiment to study delamination in standard compound laminated materials. At first, a survey and comprehension of the failure of these materials is performed and the major mode of failure, which is named Delamination Mode is understood. Next, a survey on the possible methods of investigating the delamination phenomena is presented. In the next chapter, possible numerical methods are analysed, and the better performance of Cohesive Zone Model and Virtual Crack Closure Technique is studied. In this research, using the... 

Chromium oxide coatings (Cr2O3) have been widely used due to their remarkable properties in corrosion, wear, optical and mechanical applications. So far, several methods have been used to prepare Cr2O3 thin films. In this study, the chromium oxide was produced by the sol-gel method and dip coated on the low carbon steel and glass substrates. In this context, we encountered with the problem of incoherency of the Cr2O3 ceramic coating to the steel substrates. It is highly likely that this problem be due to causes such as: a) thermal stresses due to the difference between the thermal expansion coefficients of the substrate and the coating, b) incoherent substrate/coating interface due to their... 

Nowadays in high-tech industries there is a serious demand for using advanced materials. Functionally graded materials (FGMs) are in the last generations of these group of materials. FGMs have shown good behavior in special conditions. According to sensitive applications of FGMs , there is a large amount of effort to understand it’s behavior in the presence of crack. Finite element method and other numerical methods, in recent years are widely used in modeling fracture problems.Remeshing requirements and mesh sensitivity are among the disadvantages of analyzing crack growth using the conventional FEM. Recent finite element methods such as extended finite element method, are proposed to model... 

In recent years, more attention has been paid to the development of lightweight concrete (LWC). Study of such this material had been marked due to more importance of use of it.It is now well known that in order to model cracks the finite element model is more suitable.The fracture of quasi-brittle material such as concreteincludesthe fracture process zone (FPZ).Cohesive zone model is considered the most common model used for FPZ modeling.Therefore, in this article the propagation of cohesive cracks inLWC is modeled using the extended finite element method (XFEM). In this study, modeling showed fastgrowth and propagation of cracks inLWC. Due to its cavities and pores, LWC shows to be more... 

Crack propagation in materials is an attractive problem in engineering because of the impact on the safety as well as economic issues. Much research studies have been done on the crack initiation, crack propagation criteria and path in the materials with different characteristics and conditions. Crack modeling depending on the material properties in brittle and quasi-brittle materials is done as Linear Elastic Fracture Mechanics (LEFM) and cohesive crack, respectively. The aim of this thesis is the modeling of crack propagation using energy method and comparing it with the cohesive crack. In order to model this problem, it is necessary to solve the governing equilibrium equation of the... 

In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract... 

The present paper proposes a micromechanical damage model for two and three dimensional Representative Volume Element (RVE) with randomly distributed cohesive rough slit-like and penny-shaped micro cracks (Barenblatt-Dugdale type). First, the influence of crack roughness on the crack opening under macro hydrostatic stress state is studied and then the energy release contribution to material damage process is estimated. Considering the fractality of the crack trajectories yields to lower values of the volume crack opening. This will result in lower energy release rate in RVE and higher levels of material resistance. Based on the energy release rate of RVE, the effective material properties... 

Single lap-shear (SLS) specimens of 2.54, 6.35 and 12.7 mm long SAC305 solder joints were prepared with three different adherend thicknesses. The fracture force was measured at a shear strain rate of 0.01 s-1 for different geometries in the lap-shear configuration in which mode ІІ loading is established. Elastic-plastic fracture mechanics (EPFM) theory was considered to find the energy dissipated in each case using a finite element model (FEM). The fracture energy was found by cohesive zone modeling (CZM) using pre-defined parameters. Both 2D and 3D models were used to explain the variations of fracture energy by evaluating the effective factors that demonstrated the level of constraints on...