this Dissertation arises due to the need for validation of the Extended Finite Element Method, si... more this Dissertation arises due to the need for validation of the Extended Finite Element Method, since in the area of mechanical engineering there are still some hightech companies using classical methods to evaluate some of its components, which translates into efficiency loss with increased production time and higher costs of materials and personnel. The objective of this Dissertation consists in validating the Extended Finite Element Method by comparing the results obtained by classic model for a given material with an exterior geometry and loading predetermined. The Dissertation is within the scope of Linear Elastic Fracture Mechanics and consists of shaping a crack located in a hollow shaft using the Abaqus software. After validating the use of the Extended Finite Element Method, the same procedure is used to propagate a crack in a shaft of an aircraft engine crankshaft in order to determine the useful life of the engine by the spread of crack fatigue through the Paris law.
American Journal of Engineering and Applied Sciences, 2021
In this study, a Finite Element Method (FEM) analysis is presented for the loss of stability in e... more In this study, a Finite Element Method (FEM) analysis is presented for the loss of stability in elastic states of very slender pinned without friction box-section thin-walled column axially compressed. From the FEM buckling linear stress analyses are determined the compressing critical forces for 36 cases, presented in tables and as the surface functions in dependence on the slenderness ratio and cross-section. Also are presented graphs obtained from the FEM post-buckling linear stress analysis for the elastic central line, slope, deflection and states of the stresses and strains of the box-section column 202812500 mm made of steel, by the assumption that a maximal deflection equals the half of a side dimension. The obtained from the FEM computing function and surface graphs are compared and then discussed with graphs corresponding to Euler's and Technical Stability Theory (TSTh) results. Finally are compared graphs of the stresses and strains of box-section thin-walled column 202812500 obtained from FEM and TSTh, but under compressing critical force determined according to TSTh.
Pre-freezing is an important stage in freeze-drying processes. For the lyophilization of a cell, ... more Pre-freezing is an important stage in freeze-drying processes. For the lyophilization of a cell, freezing not only plays a role for primary dehydration, but it also determines the amount of residual (intracellular or extracellular) water, which in turn can influence the solution properties and the choice of operation parameters. The freezing of human platelets in lyoprotectant solution is theoretically investigated here. A two-parameter model and an Arrhenius expression are used to describe cell membrane permeability and its temperature dependency. It is assumed that the intracellular solution is composed of four components: sodium chloride, trehalose, serum protein and water, while the extracellular solution consists of three components. Non-ideal solution behaviors are predicted using measured data. The concentration of maximally freeze-concentrated solution is estimated on the basis of an assumption of solute hydration. The impacts of lyoprotectant composition and extracellular sub-cooling on intracellular super-cooling and residual water content in the cell are analyzed. The values of activation energy of hydraulic permeability at low temperatures are tested to study their impact on the critical cooling rate. As the mass fraction extracellular lyoprotectant (trehalose+bovineserum albumin) increases from 5 wt% to 20 wt%, the intracel-lular water content at the end of freezing does not change, but the intracellular solution undergoes much higher super-cooling degree. Increasing the mass ratio of trehalose to bovine serum albumin does not change the intracellular water content , but can mitigate intracellular super-cooling. While 0.05 mol/kg trehalose is loaded into platelet, the total quantity of residual water at the end of freezing may raise by 4.93%. The inclusion of dimethyl sulfoxide (Me 2 SO) in protectant may bring negative impacts to the drying stage by increasing the residual water content and lowering the drying temperature.
Coconut fibre reinforced polymer composites are gaining popularity in the field of engineering du... more Coconut fibre reinforced polymer composites are gaining popularity in the field of engineering due to the many benefits that come with them such as low cost of production, easy fabrication, enhanced strength compared to other polymer composites. Of late, there has been an increase in the use of composites that are naturally based because they have many benefits. In line with this, the current research is focused on the mechanical properties of coconut fiber reinforced epoxy composites. The effect of the fibre content on the flexural and compressive characteristics of the epoxy composites was investigated. Chemical treatment of the coconut fibres was performed using 50% bleaching concertation. The composites were fabricated in random orientations withe fibre length of 10 mm as recommended by the literature. Scanning Electron Microscopy (SEM) was used to examine the fractured surfaces. The main findings are that the increase in the volume fraction of the coconut fibre in the epoxy composites increases the flexural and compressive strengths. SEM showed that the main failure mechanisms were brittle nature in the epoxy regions and pullout and breakage of fibres in the coconut region.
Journal of Aircraft and Spacecraft Technology , 2020
A plane quadrangular element with geometric anisotropy has been developed to perform 2D Finite El... more A plane quadrangular element with geometric anisotropy has been developed to perform 2D Finite Elements Analyses in cases where high stress concentrations, varying with very different laws along two orthogonal directions, are present. The element has been implemented into a finite element code. To validate the element behavior, analyses in the adhesive of a single lap joint and in a bimaterial interface have been performed, comparing the stress fields obtained with those get from different methodologies (analytical, experimental and numerical with very fine meshes). It has been found that, using the same number of nodes, the analyses with the developed element returned better results with respect to the ones obtained with standard geometric isotropic elements
CMES-Computer Modeling in Engineering and Sciences, 2020
Ceramics are extensively used in protective structures which are often subjected to projectile im... more Ceramics are extensively used in protective structures which are often subjected to projectile impacts. During an impact process of a ceramic target by a projectile, fragmentation occurs in both the target and the projectile. It is challenging to simulate such events and predict residual mass and velocity of the projectile. In this work, we attempt to use smoothed particle hydrodynamics (SPH) in LS-DYNA to reproduce fragmentation of the target and the projectile and predict residual mass and velocity of the projectile during a projectile impact of a ceramic target. SPH models for an alumina ceramic tile impacted by a blunt tungsten heavy alloy projectile are established. SPH simulation results of residual mass and velocity of the projectile as well as ejecta and bulge movements of the ceramic tile are obtained and compared with experimental data and simulation results of other numerical approaches. It is found that SPH simulation can properly reproduce the impact fragmentation of the target and the projectile, and shows advantages over existing numerical approaches in the prediction accuracy of residual mass and velocity. Moreover, effects of some numerical aspects of SPH, including particle spacing, contact treatment and parameters in artificial viscosity and smoothing length, on simulation results are identified. A simple approach using identical smoothing length and balanced artificial viscosity is proposed to reduce particle spacing sensitivity. The observed parametric effects and the proposed approach will provide guidance to set appropriate parameters values for SPH simulation of impact fragmentation.
CMES - Computer Modeling in Engineering and Sciences, 2020
Supercritical carbon dioxide (Sc-CO2) jet rock breaking is a nonlinear impact dynamics problem in... more Supercritical carbon dioxide (Sc-CO2) jet rock breaking is a nonlinear impact dynamics problem involving many factors. Considering the complexity of the physical properties of the Sc-CO2 jet and the mesh distortion problem in dealing with large deformation problems using the finite element method, the smoothed particle hydrodynamics (SPH) method is used to simulate and analyze the rock breaking process by Sc-CO2 jet based on the derivation of the jet velocity-density evolution mathematical model. The results indicate that there exisits an optimal rock breaking temperature by Sc-CO2. The volume and length of the rock fracture increase with the rising of the jet temperature but falls when the jet temperature exceeds 340 K. With more complicated perforation shapes and larger fracture volumes, the Sc-CO2 jet can yield a rock breaking more effectively than water jet, The stress analysis shows that the Sc-CO2 rock fracturing process could be reasonably divided into three stages, namely the fracture accumulation stage, the rapid failure stage, and the breaking stabilization stage. The high diffusivity of Sc-CO2 is identified as the primary cause of the stress fluctuation and W-shaped fracture morphology. The simulated and calculated results are generally in conformity with the published experimental data. This study provides theoretical guidance for further study on Sc-CO2 fracturing mechanism and rock breaking efficiency.
The knowledged of the mechanical behavior of structures subjected to cyclic loading is a very imp... more The knowledged of the mechanical behavior of structures subjected to cyclic loading is a very important issue. It allows engineers to do a proper design, therefore the relevant mechanical properties and behavior must be well known and understood; This includes mixed-mode fracture mechanics problems. The present research consists of a study about the path of fatigue crack propagation under mixed mode loading situations. Known geometries were modied to promote mode II crack propagation; the study involved numerical simulations which were compared with experimental results. The aim of this study is to evaluate the capability of the extended nite element method to predict the crack propagation path under a mixed mode loading situation. All of the studied situations consist of plane mixed mode I-II. The extended finite element method was implemented on Abaqus software using the Paris law subroutine as propaga- tion criterion. The natural neighbour radial point interpolation method was also used to model the problems. Additionally, experimental data was obtained and compared with the numerical results. The experimental tests were performed in two dierent types of specimens, compact tension and three point bend. For both cases the initial geometry, which is standardized, suered changes in order to induce the mixed mode loading. Equivalent stress intensity factor was analysed considering the most common ap-proaches: Richard/Henn, strain energy release rate, Tanaka and Chen. A comparison between them was performed taking into account the ratio of mode I and mode II stress intensity factors. Also da=dN = f(Ke) curves were determined for all equivalent stress intensity factors formulations. Results were compared among themselves and with the mode I original Paris law for the used material. Reasonable agreement between numerical and experimental results was achieved for most of the cases studied. It should be noticed that heterogeneities are always part of the materials and were not considered in the numerical models, which may be one of the reasons for the differences found. It was also concluded that the geometrical changes in the specimens did not induced a signsignificant mode II loading.
Conventional smoothed particle hydrodynamics (SPH) methods suffer from disadvantages, such as dif... more Conventional smoothed particle hydrodynamics (SPH) methods suffer from disadvantages, such as difficult initial particle configuration, uneven distribution of generated particles, and low computational efficiency when applied to numerical simulation of shaped charge blasting. In this research, to overcome these problems, a modified SPH method that generates the particle configuration through self-adaptive optimization is developed by the combined application of MATLAB and LS-DYNA. e results presented in this paper demonstrate that the modified configuration method solves the problem of uneven distribution of particles in complex geometry domains by providing a more uniform smoothed particle distribution than the conventional SPH method. Furthermore, the results from the application of these two methods to the bidirectional-shaped charge blasting problem reveal that the defects in the particle configuration in the conventional SPH method lead to the development of main cracks in both the shaped and the unshaped directions. However, with the self-adaptive optimization method, the main cracks develop only in the shaped direction. In addition, the equivalent stress difference between the shaped and unshaped directions, 0.7 ms after detonation, is 120 MPa with the modified method. is is 85 MPa more than that with the conventional method.
Corrugated plates play very important role in various engineering applications. The occurrence of... more Corrugated plates play very important role in various engineering applications. The occurrence of crack in the body of corrugated plate might results in catastrophic failure. In the present paper there are different profiles of corrugated plates (trapezoidal, sinusoidal and triangle) that are studied. In each profile the stress intensity factor and shape factor were calculated for various crack orientations, various corrugation angles and different curvature radius for the same profile. They are all subjected to different loading conditions using Extended Finite Element Method (XFEM). It is found the stress intensity factor when load applied parallel to corrugation direction is higher when load applied perpendicular to corrugation direction. Also found that the stress intensity factor increase by 115% when curvature radius increases with the load applied perpendicular to corrugation. This study also found and explained that the stress intensity factor increases slightly when the corrugation angle of triangle corrugated plate increases. In all cases studied, the trapezoidal corrugated plate shows the lower values of stress intensity factor compared to the sinusoidal and triangle corrugated plates.
In this paper, we focus on the stress-strain behavior prediction of the bimodal bulk Al5083 serie... more In this paper, we focus on the stress-strain behavior prediction of the bimodal bulk Al5083 series which are comprised of Ultra-Fine Grains (UFG) separated by Coarse Grain (CG) regions. This material is selected due to the availability of the required data in the literature. The CGs in the UFG matrix effectively prevents microcracks from propagation, leading to enhance ductility and toughness while the strength remains high. In this work, initially the dependency of stress-strain behavior of the model on the CG distribution in constant volume fraction is investigated by extraction of RVEs from optical microscopy (OM) images of the real material. Then, XFEM is implemented for bimodal materials considering various fracture criteria for brittle and ductile phases in maximum traction and cohesive law. The solution convergence of such a problem with irregular geometry, plasticity and crack initiation propagation without any defined pre-cracks demanded extreme effort that accomplished by refining and arranging meshes and adding damage stabilizations. As a result of the above procedures, the sensitivity of the modeling procedure to various RVEs is obtained, the crack initiation-propagation pattern in microscale is predicted and consequently , the global stress-strain behavior result is obtained. It is shown that the predicted results are in good agreement with the available experimental results.
CMES - Computer Modeling in Engineering and Sciences, 2019
A dual-support smoothed particle hydrodynamics (DS-SPH) that allows variable smoothing lengths wh... more A dual-support smoothed particle hydrodynamics (DS-SPH) that allows variable smoothing lengths while satisfying the conservations of linear momentum, angular momentum and energy is developed. The present DS-SPH is inspired by the dual-support, a concept introduced from dual-horizon peridynamics from the authors and applied here to SPH so that the unbalanced interactions between the particles with different smoothing lengths can be correctly considered and computed. Conventionally, the SPH formulation employs either the influence domain or the support domain. The concept of dual-support identifies that the influence domain and the support domain involves the duality and should be simultaneously in the SPH formulation when variable smoothing lengths are used. The DS-SPH formulation can be implemented into conventional SPH codes with minimal changes and also without compromising the computational efficiency. A number of numerical examples involving weakly compressible. fluid are presented to demonstrate the capability of the method.
Critical point is a factor that causes chassis fatigue failure. In this study, critical
buckling ... more Critical point is a factor that causes chassis fatigue failure. In this study, critical buckling load analysis of truck chassis with arc-length method and the effect of replacing conventional steel with two stainless steels in critical point of truck chassis have been investigated. critical point analysis of stress that may cause the fatigue failure, the FE software, ABAQUS, is employed. The obtained results from the linear analysis of buckling showed that changing of the chassis materials did not bring about considerable changes in the values of critical loads. Post buckling response showed that the imperfection of very small values causes a significant decrease of the critical buckling loads. These reductions make stressful points in chassis. Investigation showed that when conventional steel is used in chassis, the amount of displacement and stress is critical in Stressful points. This amount of displacement and stress can cause fatigue failure in chassis and reduce the longevity of chassis.
Performing various experimental, theoretical, and numerical investigations for better understandi... more Performing various experimental, theoretical, and numerical investigations for better understanding of behavioural characteristics of metals under impact loading is of primary importance. In this paper, application of smoothed particle hydrodynamics (SPH) method in impact mechanics is discussed and effective parameters on impact strength of an aluminum plate are investigated. To evaluate the accuracy of smoothed particle hydrodynamics method for simulating impact, Recht and Ipson model is first provided thoroughly for both Rosenberg analytical model and smoothed particle hydrodynamics method, and then plots of initial velocity-residual velocity and initial velocity-absorbed energy for target of aluminum 6061-T651 are presented. The derived information and simulation results expresses that the maximum error percentage of smoothed particle hydrodynamics method in compared with Rosenberg analytical model is within an acceptable range. Therefore, the results of smoothed particle hydrodynamics method verify the Rosenberg analytical model with high accuracy. Results reveal that higher initial impact velocity decreases the time of projectile penetration, and so penetration depth and length as well as the local damage rate of plate increases.
The 6061-T651 aluminium alloy is one of the most common aluminium alloys for marine components an... more The 6061-T651 aluminium alloy is one of the most common aluminium alloys for marine components and general structures. The stress intensity factor (SIF) is an important parameter for estimating the life of the cracked structure. In this paper, the stress intensity factors of a slant-cracked plate, which is made of 6061-T651 aluminum , have been calculated using extended finite element method (XFEM) and finite element method (FEM) in ABAQUS software and the results were compared with theoretical values. Numerical values obtained from these two methods were close to the theoretical values. In simulations of crack growth at different crack angles, the crack propagation angle values were closer to the theoretical values in XFEM method. Also, the accuracy and validity of fatigue crack growth curve were much closer to the theoretical graph in XFEM than the FEM. Therefore, in this paper the capabilities of XFEM were realized in analyzing issues such as cracks.
CMES - Computer Modeling in Engineering and Sciences, 2017
Radius of ceramic cone can largely contribute into final solution of analytic models of penetrati... more Radius of ceramic cone can largely contribute into final solution of analytic models of penetration into ceramic/metal targets. In the present research, a modified model based on radius of ceramic cone was presented for ceramic/aluminum targets. In order to investigate and evaluate accuracy of the presented analytic model, obtained results were compared against the results of the Florence's analytic model and also against numerical modeling results. The phenomenon of impact onto ceramic/aluminum composites were modeled using smoothed particle hydrodynamics (SPH) implemented utilizing ABAQUS Software. Results indicated that, with increasing initial velocity and ceramic thickness and decreasing support layer thickness, the radius of ceramic cone decreases; this ends up increasing residual velocity of the projectile and penetration time and extending the area across which the pressure is distributed. These findings indicate enhanced levels of target energy absorption and the required energy for bending and tensioning the target. As such, it can be observed that, at the same thickness and areal density, the ceramic target has its efficiency enhanced with increasing ceramic thickness and decreasing the support layer thickness. Finally, the results revealed that the associated data with SPH confirm the modified analytic model at higher accuracy than the Florence's analytic model.
XXV Congresso Nacional de Estudantes de Engenharia Mecânica , 2018
Este projeto busca analisar computacionalmente os campos de tensões e deformações de um chassi e ... more Este projeto busca analisar computacionalmente os campos de tensões e deformações de um chassi e feixe de molas da suspensão traseira de um veículo utilitário esportivo (SUV). Neste caso, será analisado um chassi do tipo escada, muito utilizados em utilitários esportivos. Tal componente será modelado em plataforma CAD e analisado via Método dos Elementos Finitos (MEF). Os efeitos causados pelos esforços aos quais o modelo estará submetido, serão minimizados no sentido de melhorar a resistência mecânica do projeto. Neste sentido, será realizada a modelagem do chassi, aprimorando a malha para então fazer análises estática, modal e de fadiga. O mesmo processo será aplicado a um feixe de molas, parte da suspensão traseira do SUV.
this Dissertation arises due to the need for validation of the Extended Finite Element Method, si... more this Dissertation arises due to the need for validation of the Extended Finite Element Method, since in the area of mechanical engineering there are still some hightech companies using classical methods to evaluate some of its components, which translates into efficiency loss with increased production time and higher costs of materials and personnel. The objective of this Dissertation consists in validating the Extended Finite Element Method by comparing the results obtained by classic model for a given material with an exterior geometry and loading predetermined. The Dissertation is within the scope of Linear Elastic Fracture Mechanics and consists of shaping a crack located in a hollow shaft using the Abaqus software. After validating the use of the Extended Finite Element Method, the same procedure is used to propagate a crack in a shaft of an aircraft engine crankshaft in order to determine the useful life of the engine by the spread of crack fatigue through the Paris law.
American Journal of Engineering and Applied Sciences, 2021
In this study, a Finite Element Method (FEM) analysis is presented for the loss of stability in e... more In this study, a Finite Element Method (FEM) analysis is presented for the loss of stability in elastic states of very slender pinned without friction box-section thin-walled column axially compressed. From the FEM buckling linear stress analyses are determined the compressing critical forces for 36 cases, presented in tables and as the surface functions in dependence on the slenderness ratio and cross-section. Also are presented graphs obtained from the FEM post-buckling linear stress analysis for the elastic central line, slope, deflection and states of the stresses and strains of the box-section column 202812500 mm made of steel, by the assumption that a maximal deflection equals the half of a side dimension. The obtained from the FEM computing function and surface graphs are compared and then discussed with graphs corresponding to Euler's and Technical Stability Theory (TSTh) results. Finally are compared graphs of the stresses and strains of box-section thin-walled column 202812500 obtained from FEM and TSTh, but under compressing critical force determined according to TSTh.
Pre-freezing is an important stage in freeze-drying processes. For the lyophilization of a cell, ... more Pre-freezing is an important stage in freeze-drying processes. For the lyophilization of a cell, freezing not only plays a role for primary dehydration, but it also determines the amount of residual (intracellular or extracellular) water, which in turn can influence the solution properties and the choice of operation parameters. The freezing of human platelets in lyoprotectant solution is theoretically investigated here. A two-parameter model and an Arrhenius expression are used to describe cell membrane permeability and its temperature dependency. It is assumed that the intracellular solution is composed of four components: sodium chloride, trehalose, serum protein and water, while the extracellular solution consists of three components. Non-ideal solution behaviors are predicted using measured data. The concentration of maximally freeze-concentrated solution is estimated on the basis of an assumption of solute hydration. The impacts of lyoprotectant composition and extracellular sub-cooling on intracellular super-cooling and residual water content in the cell are analyzed. The values of activation energy of hydraulic permeability at low temperatures are tested to study their impact on the critical cooling rate. As the mass fraction extracellular lyoprotectant (trehalose+bovineserum albumin) increases from 5 wt% to 20 wt%, the intracel-lular water content at the end of freezing does not change, but the intracellular solution undergoes much higher super-cooling degree. Increasing the mass ratio of trehalose to bovine serum albumin does not change the intracellular water content , but can mitigate intracellular super-cooling. While 0.05 mol/kg trehalose is loaded into platelet, the total quantity of residual water at the end of freezing may raise by 4.93%. The inclusion of dimethyl sulfoxide (Me 2 SO) in protectant may bring negative impacts to the drying stage by increasing the residual water content and lowering the drying temperature.
Coconut fibre reinforced polymer composites are gaining popularity in the field of engineering du... more Coconut fibre reinforced polymer composites are gaining popularity in the field of engineering due to the many benefits that come with them such as low cost of production, easy fabrication, enhanced strength compared to other polymer composites. Of late, there has been an increase in the use of composites that are naturally based because they have many benefits. In line with this, the current research is focused on the mechanical properties of coconut fiber reinforced epoxy composites. The effect of the fibre content on the flexural and compressive characteristics of the epoxy composites was investigated. Chemical treatment of the coconut fibres was performed using 50% bleaching concertation. The composites were fabricated in random orientations withe fibre length of 10 mm as recommended by the literature. Scanning Electron Microscopy (SEM) was used to examine the fractured surfaces. The main findings are that the increase in the volume fraction of the coconut fibre in the epoxy composites increases the flexural and compressive strengths. SEM showed that the main failure mechanisms were brittle nature in the epoxy regions and pullout and breakage of fibres in the coconut region.
Journal of Aircraft and Spacecraft Technology , 2020
A plane quadrangular element with geometric anisotropy has been developed to perform 2D Finite El... more A plane quadrangular element with geometric anisotropy has been developed to perform 2D Finite Elements Analyses in cases where high stress concentrations, varying with very different laws along two orthogonal directions, are present. The element has been implemented into a finite element code. To validate the element behavior, analyses in the adhesive of a single lap joint and in a bimaterial interface have been performed, comparing the stress fields obtained with those get from different methodologies (analytical, experimental and numerical with very fine meshes). It has been found that, using the same number of nodes, the analyses with the developed element returned better results with respect to the ones obtained with standard geometric isotropic elements
CMES-Computer Modeling in Engineering and Sciences, 2020
Ceramics are extensively used in protective structures which are often subjected to projectile im... more Ceramics are extensively used in protective structures which are often subjected to projectile impacts. During an impact process of a ceramic target by a projectile, fragmentation occurs in both the target and the projectile. It is challenging to simulate such events and predict residual mass and velocity of the projectile. In this work, we attempt to use smoothed particle hydrodynamics (SPH) in LS-DYNA to reproduce fragmentation of the target and the projectile and predict residual mass and velocity of the projectile during a projectile impact of a ceramic target. SPH models for an alumina ceramic tile impacted by a blunt tungsten heavy alloy projectile are established. SPH simulation results of residual mass and velocity of the projectile as well as ejecta and bulge movements of the ceramic tile are obtained and compared with experimental data and simulation results of other numerical approaches. It is found that SPH simulation can properly reproduce the impact fragmentation of the target and the projectile, and shows advantages over existing numerical approaches in the prediction accuracy of residual mass and velocity. Moreover, effects of some numerical aspects of SPH, including particle spacing, contact treatment and parameters in artificial viscosity and smoothing length, on simulation results are identified. A simple approach using identical smoothing length and balanced artificial viscosity is proposed to reduce particle spacing sensitivity. The observed parametric effects and the proposed approach will provide guidance to set appropriate parameters values for SPH simulation of impact fragmentation.
CMES - Computer Modeling in Engineering and Sciences, 2020
Supercritical carbon dioxide (Sc-CO2) jet rock breaking is a nonlinear impact dynamics problem in... more Supercritical carbon dioxide (Sc-CO2) jet rock breaking is a nonlinear impact dynamics problem involving many factors. Considering the complexity of the physical properties of the Sc-CO2 jet and the mesh distortion problem in dealing with large deformation problems using the finite element method, the smoothed particle hydrodynamics (SPH) method is used to simulate and analyze the rock breaking process by Sc-CO2 jet based on the derivation of the jet velocity-density evolution mathematical model. The results indicate that there exisits an optimal rock breaking temperature by Sc-CO2. The volume and length of the rock fracture increase with the rising of the jet temperature but falls when the jet temperature exceeds 340 K. With more complicated perforation shapes and larger fracture volumes, the Sc-CO2 jet can yield a rock breaking more effectively than water jet, The stress analysis shows that the Sc-CO2 rock fracturing process could be reasonably divided into three stages, namely the fracture accumulation stage, the rapid failure stage, and the breaking stabilization stage. The high diffusivity of Sc-CO2 is identified as the primary cause of the stress fluctuation and W-shaped fracture morphology. The simulated and calculated results are generally in conformity with the published experimental data. This study provides theoretical guidance for further study on Sc-CO2 fracturing mechanism and rock breaking efficiency.
The knowledged of the mechanical behavior of structures subjected to cyclic loading is a very imp... more The knowledged of the mechanical behavior of structures subjected to cyclic loading is a very important issue. It allows engineers to do a proper design, therefore the relevant mechanical properties and behavior must be well known and understood; This includes mixed-mode fracture mechanics problems. The present research consists of a study about the path of fatigue crack propagation under mixed mode loading situations. Known geometries were modied to promote mode II crack propagation; the study involved numerical simulations which were compared with experimental results. The aim of this study is to evaluate the capability of the extended nite element method to predict the crack propagation path under a mixed mode loading situation. All of the studied situations consist of plane mixed mode I-II. The extended finite element method was implemented on Abaqus software using the Paris law subroutine as propaga- tion criterion. The natural neighbour radial point interpolation method was also used to model the problems. Additionally, experimental data was obtained and compared with the numerical results. The experimental tests were performed in two dierent types of specimens, compact tension and three point bend. For both cases the initial geometry, which is standardized, suered changes in order to induce the mixed mode loading. Equivalent stress intensity factor was analysed considering the most common ap-proaches: Richard/Henn, strain energy release rate, Tanaka and Chen. A comparison between them was performed taking into account the ratio of mode I and mode II stress intensity factors. Also da=dN = f(Ke) curves were determined for all equivalent stress intensity factors formulations. Results were compared among themselves and with the mode I original Paris law for the used material. Reasonable agreement between numerical and experimental results was achieved for most of the cases studied. It should be noticed that heterogeneities are always part of the materials and were not considered in the numerical models, which may be one of the reasons for the differences found. It was also concluded that the geometrical changes in the specimens did not induced a signsignificant mode II loading.
Conventional smoothed particle hydrodynamics (SPH) methods suffer from disadvantages, such as dif... more Conventional smoothed particle hydrodynamics (SPH) methods suffer from disadvantages, such as difficult initial particle configuration, uneven distribution of generated particles, and low computational efficiency when applied to numerical simulation of shaped charge blasting. In this research, to overcome these problems, a modified SPH method that generates the particle configuration through self-adaptive optimization is developed by the combined application of MATLAB and LS-DYNA. e results presented in this paper demonstrate that the modified configuration method solves the problem of uneven distribution of particles in complex geometry domains by providing a more uniform smoothed particle distribution than the conventional SPH method. Furthermore, the results from the application of these two methods to the bidirectional-shaped charge blasting problem reveal that the defects in the particle configuration in the conventional SPH method lead to the development of main cracks in both the shaped and the unshaped directions. However, with the self-adaptive optimization method, the main cracks develop only in the shaped direction. In addition, the equivalent stress difference between the shaped and unshaped directions, 0.7 ms after detonation, is 120 MPa with the modified method. is is 85 MPa more than that with the conventional method.
Corrugated plates play very important role in various engineering applications. The occurrence of... more Corrugated plates play very important role in various engineering applications. The occurrence of crack in the body of corrugated plate might results in catastrophic failure. In the present paper there are different profiles of corrugated plates (trapezoidal, sinusoidal and triangle) that are studied. In each profile the stress intensity factor and shape factor were calculated for various crack orientations, various corrugation angles and different curvature radius for the same profile. They are all subjected to different loading conditions using Extended Finite Element Method (XFEM). It is found the stress intensity factor when load applied parallel to corrugation direction is higher when load applied perpendicular to corrugation direction. Also found that the stress intensity factor increase by 115% when curvature radius increases with the load applied perpendicular to corrugation. This study also found and explained that the stress intensity factor increases slightly when the corrugation angle of triangle corrugated plate increases. In all cases studied, the trapezoidal corrugated plate shows the lower values of stress intensity factor compared to the sinusoidal and triangle corrugated plates.
In this paper, we focus on the stress-strain behavior prediction of the bimodal bulk Al5083 serie... more In this paper, we focus on the stress-strain behavior prediction of the bimodal bulk Al5083 series which are comprised of Ultra-Fine Grains (UFG) separated by Coarse Grain (CG) regions. This material is selected due to the availability of the required data in the literature. The CGs in the UFG matrix effectively prevents microcracks from propagation, leading to enhance ductility and toughness while the strength remains high. In this work, initially the dependency of stress-strain behavior of the model on the CG distribution in constant volume fraction is investigated by extraction of RVEs from optical microscopy (OM) images of the real material. Then, XFEM is implemented for bimodal materials considering various fracture criteria for brittle and ductile phases in maximum traction and cohesive law. The solution convergence of such a problem with irregular geometry, plasticity and crack initiation propagation without any defined pre-cracks demanded extreme effort that accomplished by refining and arranging meshes and adding damage stabilizations. As a result of the above procedures, the sensitivity of the modeling procedure to various RVEs is obtained, the crack initiation-propagation pattern in microscale is predicted and consequently , the global stress-strain behavior result is obtained. It is shown that the predicted results are in good agreement with the available experimental results.
CMES - Computer Modeling in Engineering and Sciences, 2019
A dual-support smoothed particle hydrodynamics (DS-SPH) that allows variable smoothing lengths wh... more A dual-support smoothed particle hydrodynamics (DS-SPH) that allows variable smoothing lengths while satisfying the conservations of linear momentum, angular momentum and energy is developed. The present DS-SPH is inspired by the dual-support, a concept introduced from dual-horizon peridynamics from the authors and applied here to SPH so that the unbalanced interactions between the particles with different smoothing lengths can be correctly considered and computed. Conventionally, the SPH formulation employs either the influence domain or the support domain. The concept of dual-support identifies that the influence domain and the support domain involves the duality and should be simultaneously in the SPH formulation when variable smoothing lengths are used. The DS-SPH formulation can be implemented into conventional SPH codes with minimal changes and also without compromising the computational efficiency. A number of numerical examples involving weakly compressible. fluid are presented to demonstrate the capability of the method.
Critical point is a factor that causes chassis fatigue failure. In this study, critical
buckling ... more Critical point is a factor that causes chassis fatigue failure. In this study, critical buckling load analysis of truck chassis with arc-length method and the effect of replacing conventional steel with two stainless steels in critical point of truck chassis have been investigated. critical point analysis of stress that may cause the fatigue failure, the FE software, ABAQUS, is employed. The obtained results from the linear analysis of buckling showed that changing of the chassis materials did not bring about considerable changes in the values of critical loads. Post buckling response showed that the imperfection of very small values causes a significant decrease of the critical buckling loads. These reductions make stressful points in chassis. Investigation showed that when conventional steel is used in chassis, the amount of displacement and stress is critical in Stressful points. This amount of displacement and stress can cause fatigue failure in chassis and reduce the longevity of chassis.
Performing various experimental, theoretical, and numerical investigations for better understandi... more Performing various experimental, theoretical, and numerical investigations for better understanding of behavioural characteristics of metals under impact loading is of primary importance. In this paper, application of smoothed particle hydrodynamics (SPH) method in impact mechanics is discussed and effective parameters on impact strength of an aluminum plate are investigated. To evaluate the accuracy of smoothed particle hydrodynamics method for simulating impact, Recht and Ipson model is first provided thoroughly for both Rosenberg analytical model and smoothed particle hydrodynamics method, and then plots of initial velocity-residual velocity and initial velocity-absorbed energy for target of aluminum 6061-T651 are presented. The derived information and simulation results expresses that the maximum error percentage of smoothed particle hydrodynamics method in compared with Rosenberg analytical model is within an acceptable range. Therefore, the results of smoothed particle hydrodynamics method verify the Rosenberg analytical model with high accuracy. Results reveal that higher initial impact velocity decreases the time of projectile penetration, and so penetration depth and length as well as the local damage rate of plate increases.
The 6061-T651 aluminium alloy is one of the most common aluminium alloys for marine components an... more The 6061-T651 aluminium alloy is one of the most common aluminium alloys for marine components and general structures. The stress intensity factor (SIF) is an important parameter for estimating the life of the cracked structure. In this paper, the stress intensity factors of a slant-cracked plate, which is made of 6061-T651 aluminum , have been calculated using extended finite element method (XFEM) and finite element method (FEM) in ABAQUS software and the results were compared with theoretical values. Numerical values obtained from these two methods were close to the theoretical values. In simulations of crack growth at different crack angles, the crack propagation angle values were closer to the theoretical values in XFEM method. Also, the accuracy and validity of fatigue crack growth curve were much closer to the theoretical graph in XFEM than the FEM. Therefore, in this paper the capabilities of XFEM were realized in analyzing issues such as cracks.
CMES - Computer Modeling in Engineering and Sciences, 2017
Radius of ceramic cone can largely contribute into final solution of analytic models of penetrati... more Radius of ceramic cone can largely contribute into final solution of analytic models of penetration into ceramic/metal targets. In the present research, a modified model based on radius of ceramic cone was presented for ceramic/aluminum targets. In order to investigate and evaluate accuracy of the presented analytic model, obtained results were compared against the results of the Florence's analytic model and also against numerical modeling results. The phenomenon of impact onto ceramic/aluminum composites were modeled using smoothed particle hydrodynamics (SPH) implemented utilizing ABAQUS Software. Results indicated that, with increasing initial velocity and ceramic thickness and decreasing support layer thickness, the radius of ceramic cone decreases; this ends up increasing residual velocity of the projectile and penetration time and extending the area across which the pressure is distributed. These findings indicate enhanced levels of target energy absorption and the required energy for bending and tensioning the target. As such, it can be observed that, at the same thickness and areal density, the ceramic target has its efficiency enhanced with increasing ceramic thickness and decreasing the support layer thickness. Finally, the results revealed that the associated data with SPH confirm the modified analytic model at higher accuracy than the Florence's analytic model.
XXV Congresso Nacional de Estudantes de Engenharia Mecânica , 2018
Este projeto busca analisar computacionalmente os campos de tensões e deformações de um chassi e ... more Este projeto busca analisar computacionalmente os campos de tensões e deformações de um chassi e feixe de molas da suspensão traseira de um veículo utilitário esportivo (SUV). Neste caso, será analisado um chassi do tipo escada, muito utilizados em utilitários esportivos. Tal componente será modelado em plataforma CAD e analisado via Método dos Elementos Finitos (MEF). Os efeitos causados pelos esforços aos quais o modelo estará submetido, serão minimizados no sentido de melhorar a resistência mecânica do projeto. Neste sentido, será realizada a modelagem do chassi, aprimorando a malha para então fazer análises estática, modal e de fadiga. O mesmo processo será aplicado a um feixe de molas, parte da suspensão traseira do SUV.
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materials and personnel. The objective of this Dissertation consists in validating the
Extended Finite Element Method by comparing the results obtained by classic model for
a given material with an exterior geometry and loading predetermined. The Dissertation
is within the scope of Linear Elastic Fracture Mechanics and consists of shaping a
crack located in a hollow shaft using the Abaqus software. After validating the use of
the Extended Finite Element Method, the same procedure is used to propagate a crack in
a shaft of an aircraft engine crankshaft in order to determine the useful life of the engine
by the spread of crack fatigue through the Paris law.
The present research consists of a study about the path of fatigue crack propagation under mixed mode loading situations. Known geometries were modied to promote mode II crack propagation; the study involved numerical simulations which were compared with experimental results.
The aim of this study is to evaluate the capability of the extended nite element method to predict the crack propagation path under a mixed mode loading situation. All of the studied situations consist of plane mixed mode I-II. The extended finite element method was implemented on Abaqus software using the Paris law subroutine as propaga-
tion criterion. The natural neighbour radial point interpolation method was also used to model the problems. Additionally, experimental data was obtained and compared with the numerical results.
The experimental tests were performed in two dierent types of specimens, compact tension and three point bend. For both cases the initial geometry, which is standardized, suered changes in order to induce the mixed mode loading.
Equivalent stress intensity factor was analysed considering the most common ap-proaches: Richard/Henn, strain energy release rate, Tanaka and Chen. A comparison between them was performed taking into account the ratio of mode I and mode II stress intensity factors.
Also da=dN = f(Ke) curves were determined for all equivalent stress intensity factors formulations. Results were compared among themselves and with the mode I original Paris law for the used material.
Reasonable agreement between numerical and experimental results was achieved for most of the cases studied. It should be noticed that heterogeneities are always part of the materials and were not considered in the numerical models, which may be one of the reasons for the differences found. It was also concluded that the geometrical changes in the specimens did not induced a signsignificant mode II loading.
buckling load analysis of truck chassis with arc-length method and the effect of
replacing conventional steel with two stainless steels in critical point of truck chassis
have been investigated. critical point analysis of stress that may cause the fatigue
failure, the FE software, ABAQUS, is employed. The obtained results from the linear
analysis of buckling showed that changing of the chassis materials did not bring about
considerable changes in the values of critical loads. Post buckling response showed
that the imperfection of very small values causes a significant decrease of the critical
buckling loads. These reductions make stressful points in chassis. Investigation showed that when conventional steel is used in chassis, the amount of displacement and stress is critical in Stressful points. This amount of displacement and stress can cause fatigue failure in chassis and reduce the longevity of chassis.
Método dos Elementos Finitos (MEF). Os efeitos causados pelos esforços aos quais o modelo estará submetido, serão minimizados no sentido de melhorar a resistência mecânica do projeto. Neste sentido, será realizada a modelagem do chassi, aprimorando a malha para então fazer análises estática, modal e de fadiga. O mesmo processo será aplicado a um feixe de molas, parte da suspensão traseira do SUV.
materials and personnel. The objective of this Dissertation consists in validating the
Extended Finite Element Method by comparing the results obtained by classic model for
a given material with an exterior geometry and loading predetermined. The Dissertation
is within the scope of Linear Elastic Fracture Mechanics and consists of shaping a
crack located in a hollow shaft using the Abaqus software. After validating the use of
the Extended Finite Element Method, the same procedure is used to propagate a crack in
a shaft of an aircraft engine crankshaft in order to determine the useful life of the engine
by the spread of crack fatigue through the Paris law.
The present research consists of a study about the path of fatigue crack propagation under mixed mode loading situations. Known geometries were modied to promote mode II crack propagation; the study involved numerical simulations which were compared with experimental results.
The aim of this study is to evaluate the capability of the extended nite element method to predict the crack propagation path under a mixed mode loading situation. All of the studied situations consist of plane mixed mode I-II. The extended finite element method was implemented on Abaqus software using the Paris law subroutine as propaga-
tion criterion. The natural neighbour radial point interpolation method was also used to model the problems. Additionally, experimental data was obtained and compared with the numerical results.
The experimental tests were performed in two dierent types of specimens, compact tension and three point bend. For both cases the initial geometry, which is standardized, suered changes in order to induce the mixed mode loading.
Equivalent stress intensity factor was analysed considering the most common ap-proaches: Richard/Henn, strain energy release rate, Tanaka and Chen. A comparison between them was performed taking into account the ratio of mode I and mode II stress intensity factors.
Also da=dN = f(Ke) curves were determined for all equivalent stress intensity factors formulations. Results were compared among themselves and with the mode I original Paris law for the used material.
Reasonable agreement between numerical and experimental results was achieved for most of the cases studied. It should be noticed that heterogeneities are always part of the materials and were not considered in the numerical models, which may be one of the reasons for the differences found. It was also concluded that the geometrical changes in the specimens did not induced a signsignificant mode II loading.
buckling load analysis of truck chassis with arc-length method and the effect of
replacing conventional steel with two stainless steels in critical point of truck chassis
have been investigated. critical point analysis of stress that may cause the fatigue
failure, the FE software, ABAQUS, is employed. The obtained results from the linear
analysis of buckling showed that changing of the chassis materials did not bring about
considerable changes in the values of critical loads. Post buckling response showed
that the imperfection of very small values causes a significant decrease of the critical
buckling loads. These reductions make stressful points in chassis. Investigation showed that when conventional steel is used in chassis, the amount of displacement and stress is critical in Stressful points. This amount of displacement and stress can cause fatigue failure in chassis and reduce the longevity of chassis.
Método dos Elementos Finitos (MEF). Os efeitos causados pelos esforços aos quais o modelo estará submetido, serão minimizados no sentido de melhorar a resistência mecânica do projeto. Neste sentido, será realizada a modelagem do chassi, aprimorando a malha para então fazer análises estática, modal e de fadiga. O mesmo processo será aplicado a um feixe de molas, parte da suspensão traseira do SUV.