One of the most important issues about the composites behavior in different loading conditions is the initiation and propagation of various damage modes that have significant effects on the application of these materials. Fiber/matrix debonding is one of the first damage modes that appears in different composites and causes the formation of other damage modes like matrix cracking. In the present study, by using the Cohesive Zone model (CZM) as well as an extended finite Element method (XFEM) and by applying a transverse loading on different representative volume Elements (RVE’s) in micromechanical scale, the effects of initiation and propagation of different damage modes like fiber/matrix debonding and matrix cracking will be studied. To this aim, the authors start by studying the behavior of Cohesive Zone model and validating the applied method by simulating the previous researchs. Then, the effects of Cohesive Zone on different volume Elements will be studied and the results will compare with each other. Finally by entering the effects of matrix cracking initiation and propagation using the extended finite Element method, effects of Cohesive Zone damage and matrix cracking will be studied simultaneously based on finite Element method and using Abaqus software.

Stable ductile crack growth in 3 mm thick AISI 304 stainless steel specimens has been investigated experimentally and numerically. Multi-linear Isotropic Hardening method coupled with the Von-Mises yield criterion was adopted for modeling elasto-plastic behavior of the material. Mode-I CT fracture specimens have been tested to generate experimental load-displacement-crack growth data during stable crack growth. The critical fracture energy (JIc) was then determined using the finite Elements results in conjunction with the experimental data. The effect of in-plane constraints on the numerical-experimental JIc calculation was then investigated. The results of finite Element solution were used to tailor an exponential CZM model for simulation of mode-I stable crack growth in CT specimens. It is found that the adopted CZM is generally insensitive to the applied constraints to the crack tip stress state and thus it can effectively be used for simulating crack growth in this material.

Due to high strength and stiffness in comparison with their weights, laminated composite materials are widely used in many structures such as aerospace. Therefore to predict their mechanical response, the understanding of their failure mechanisms is very important. The delamination between composite layers and adhesive joints is one of the main damage modes of these materials. In this research, the Cohesive Zone model is used to predict the damage evaluation of composite wing adhesive joints. The advantage of this method is the modeling of delamination growth without any requirements to the presence of initial crack and remeshing. Moreover to predict the probable damage in composite layers the Ladeveze progressive damage model has been implemented in Abaqus using user defined code (Umat) and also the importance of considering the intralaminar failure on the acceleration in damage initiation and propagation in adhesively bonded joints have been evaluated. The results verify the proper accuracy of implemented method. Furthermore, the results of solid Cohesive Elements showed to be more accurate in predicting damage initiation and evaluation in comparison to shell Elements. Finally effects of adhesive properties such as thickness and quality of bonding in load capability of wing structure have been investigated.

Bone is a biological tissue whose main components are different from the mechanical aspect. Some of the bone diseases are due to mutations in the bone structure at the nano scale, while their clinical symptoms appear at the macro scale. Therefore, the evaluation of bone at micro and nano scales is important. In the current study, the finite Element modeling is performed to evaluate the mechanical properties and behavior of bone at the nano scale and the Cohesive Element is applied. After its verification, the stress distribution and elastic properties are compared with the analytical model. Limited studies are available on strain ratio and it is presented for different Cohesive Elements in the current study. The influence of mineral volume fraction and mechanical properties of collagen is investigated. The comparison between finite Element models and the other ones demonstrate an excellent agreement. The collagen- hydroxyapatite interface with unknown mechanical properties is the most important parameter in the model and the thick water layer with Van der Waals interaction and viscous shear is determined as the most probable Cohesive layer. The parametric studies indicate the significant effect of nonlinear collagen on the model. To decrease the calculation in models, the proposed unit cell with periodic boundary conditions could be employed.

The finite Element Method (FEM), and other numerical methods, in recent years, is widely used in modeling of the fracture problem. Remeshing requirements and mesh sensitivity are the major disadvantages in analyzing crack growth using conventional FEM methods. Recently, advanced FEM methods, such as the Extended Finite Element Method (X-FEM), have been proposed to model discontinuities through the Elements. The advantage of these methods is that remeshing is not required in the crack growth process. The Cohesive crack method is a simplified field model to simulate the complicated behavior of the crack growth in quasi-brittle materials. In this paper, we use the advantages of the X-FEM and crack length control method for modeling of the Cohesive crack growth.

Cone penetration test is one of the methods widely used for measuring the soil mechanical strength. It can also be used as a simple method to calibrate soil parameters in the discrete Element method (DEM) simulations. In this study, a DEM model for the interaction of a cone penetrometer with a clay loam soil was developed and the possibility of finding relationships between the cone index and the parameters of the model for different levels of moisture and soil density was investigated. A hybrid contact model, hysterical spring - linear cohesion was used to simulate the soil. Sensitivity analysis of the model parameters showed cohesion, coefficient of internal friction and particle yield strength are the most important parameters affecting the cone index. Laboratory cone penetration tests using a tension-compression loading frame were performed in remolded soil at two moisture contents of 11 and 16% each at two bulk densities of 1000 and 1150 kg m-3. By fitting the measured and simulated cone index- depth profiles, values ​​for particle yield strength were obtained which showed a strong correlation (R2 = 0.97) with the maximum cone index in the tested soils. The results were validated using plate sinkage test. As a general conclusion, the cone penetration test can be used to calibrate the yield strength of soil particles in the discrete Element simulations.

Due to high strength and stiffness in comparison with their weights, laminated composite materials are widely used in many structures such as aerospace and naval structures. Therefore, the understanding of their failure mechanisms to predict their mechanical response is of high importance. One of the major aforementioned mechanisms is the delamination which commonly occurs in skin/stiffener joints. In the present paper, a comparative study on the delamination in composite skin/stringer structures under 3 point and 4 point bending loads is performed by the finite Element method (FEM) employing the Cohesive Elements. The detailed effects of stacking sequence on the damage of structure are investigated. A user defined interface Element has been implemented in the Ansys software in continuum damage mechanics framework based on the bilinear Cohesive Zone model. The advantage of this method is the modeling of delamination growth without any requirements to the presence of initial crack and remeshing. Comparison of the obtained results from FEM with that of experiment justifies the capability of the employed model to predict the delamination initiation and propagation. The results indicate that in the 3 point bending load, the damage initiates from the adhesive between skin and stringer, while in 4 point bending load it initiates from the interface Elements between skin layers near the adhesive bond. Finally, in order to increase the strength of skin/stringer structures, the results strongly recommend preventing the use of 45 and 90 degrees plies near each other around the adhesive bond.

Initiation and progression of cracks in a saturated porous media is an important topic which has attracted considerable attention from researchers in the recent years. Extended finite Element method (EFEM) is a contemporary technique removing the necessity of consecutive meshing of the problem in the analysis process. In the EFEM by enriching the Elements whose discontinuity there exists, there is no need for re-meshing at each step of the analysis. . In this paper, EFEM is used to evaluate progression of Cohesive crack in a two phase saturated porous media. To analyze the saturated porous media, at the first, the equations of mass conservation, momentum conservation, and energy conservation are established to consider simultaneous effects of displacement, pressure, and temperature on the crack progression. The Cohesive model is used to simulate crack progression. Heavy-side functions are used to enrich finite Elements and the resulting system of equations are solved by Newton Raphson method. Finally, the two numerical models were analyzed by other researchers is considered to evaluate the derived relationships. Numerical result show that maximum variation by other researchers is 5%.

This paper reports the finite Element modeling of axial crack growth in a thin aluminum tube under gaseous detonation loading. The finite Element method was used to handle the moving load and also the nonlinear characteristics of the problem. The simulation results were compared with the experimental results reported in the literature and also with the results obtained from an analytical model. Moreover, the Cohesive Element with traction-separation law was used for the crack growth modeling. The final part of the paper is devoted to comparisons between the numerical crack growth simulations obtained from the current work and the numerical results based on the CTOA criteria that were previously reported in the literature. The very good agreement between the two methods was indicative of the robustness of the implemented procedures.

Fracture of femur is considered as one of the most significant causes of disability and death, especially among the elderly. Therefore, there is a global effort towards noninvasive assessment of the femoral fractures. This study was aimed at investigation of the mechanical behavior of human femur subjected to various loading orientations, under the two categories of high-stiffness (HS) and low-stiffness (LS) loading conditions. The experimental and computational analysis of deformation and fracture patterns were carried out using the QCT images and finite Element analysis. The predictions of the force and fracture pattern of the HS and LS specimens were performed using linear and nonlinear finite Element analyses, respectively. Also, the Cohesive Zone model (CZM) was used to simulate the damage initiation and propagation in the finite Element analysis of latter specimens. Comparison between the results of the numerical analysis and the experimentation showed successful simulation and prediction of fracture force of human femur under various loading orientations.