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    Behavior of dry and saturated soils under impact load during dynamic compaction

    , Article 16th International Conference on Soil Mechanics and Geotechnical Engineering: Geotechnology in Harmony with the Global Environment, ICSMGE 2005, Osaka, 12 September 2005 through 16 September 2005 ; Volume 3 , 2005 , Pages 1245-1248 ; 9059660285 (ISBN); 9789059660281 (ISBN) Pak, A ; Shahir, H ; Ghassemi, A ; Sharif University of Technology
    Dynamic compaction is a widely used soil improvement method in dry and/or saturated soils. Despite its vast application, its design basis is still empirical and the mechanisms that are involved in the procedure are not fully understood. A fully coupled dynamic finite element code has been developed in order to clarify the ambiguities in the process and predict the strain/displacement field in the ground, determine depth and degree of improvement, and also calculate the pore pressure variation during the process. This model can be used as a rational design tool for dynamic compaction projects  

    Numerical Modeling of Dynamic Compaction Operation in Sandy Soils Deposits in Order to Provide a Design Approach

    , M.Sc. Thesis Sharif University of Technology Jahangiri, Ghodrat (Author) ; Pak, Ali (Supervisor)
    Dynamic compaction is a widely used soil deep improvement method in dry and/or saturated soils. Despite its vast application, numerical and /or experimental modeling studies of dynamic compaction due to impact are little. In order to clarify the ambiguities in process and to present a comprehensive design approach, numerical modeling of dynamic compaction in dry soils with PISA (A fully coupled dynamic finite element code: Program for Incremental Stress Analysis) has been done. Because the geometry and loading configuration are symmetric around the falling tamper (load centerline), a two-dimensional axisymmetric simulation has been used. Here for sake of simplicity, initial velocity of... 

    Molecular Dynamics Simulation of Polymer Nano-Composites Reinforced by Graphene Sheets under Impact Loading

    , M.Sc. Thesis Sharif University of Technology khakbiz, Sadegh (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
    Mechanical properties such as Young's and bulk modulus and strength of material is improved by adding Nano fillers to polymer substrates. Hence by adding Nano fillers such as graphene and carbon nanotubes to polymer substrates it is possible to achieve better properties in resultant nano composites. The aim of this study is to investigate the improvement in polymer-based composites properties by adding graphene Nano fillers for shock absorption. In this study, molecular dynamics method is used to model the molecular behavior of the material. First, a sample cell that have the properties of the whole material, is modeled, then by applying impact loading in modeling software, the response of... 

    Experimental and Theoretical Analysis of Plastic Deformation of Metals under Impact Loading Using Taylor Impact Test

    , M.Sc. Thesis Sharif University of Technology Khayyer Dastjerdi Toroghi, Ahmad (Author) ; Naghdabadi, Reza (Supervisor)
    In most of the engineering applications, the mechanical behavior of materials in high strain rate deformations differs from their behavior in quasi-static deformations. In some engineering problems like impact loading on structures, metal forming and explosive forming, the range of strain rate is about . Taylor impact test is one of the experiments used for characterizing the dynamic behavior of materials in high strain rate deformations. In the Taylor impact test a rigid cylindrical projectile is impacted normally onto a hard and massive surface (anvil), the projectile deforms by mushrooming at the impact end. With plastic wave propagation analysis, the plastic deformation of projectile is... 

    Dynamic Response of Concrete Funicular Shells under Impulse Loads

    , M.Sc. Thesis Sharif University of Technology Sabermahany, Hadi (Author) ; Vafai, Abolhassan (Supervisor) ; Mofid, Massoud (Co-Advisor)
    Reinforced concrete shells are widely used to cover the small to large area with more aesthetics at minimum cost. Shell structures carries load through their shape rather than material strength. Funicular shells are special type of shells that their shape is obtained so that stresses be compressive under a special load (for shell, this load is its dead weight). This study deals with forced vibration of funicular shells on a rectangular ground plan under impulse loads using shallow shells theory. Two boundary conditions, simply supported and clamped, are considered. Displacement components are product of position and time functions. The analysis is based on the expansion of displacement... 

    Numerical study of the coupled hydro-mechanical effects in dynamic compaction of saturated granular soils

    , Article Computers and Geotechnics ; Volume 37, Issue 1-2 , 2010 , Pages 10-24 ; 0266352X (ISSN) Ghassemi, A ; Pak, A ; Shahir, H ; Sharif University of Technology
    Dynamic compaction is a widely used method for improvement of loose granular deposits. Its applicability in saturated layers generally considered to be less effective because of the fact that part of the applied energy is absorbed by pore water. Up to now the majority of numerical simulations have focused on the analysis of dynamic compaction in dry/moist soils. In this paper, a fully coupled hydro-mechanical finite element code has been developed and employed to evaluate the dynamic compaction effects on saturated granular soils. After verification of the results by comparing the numerical results with those measured in a real field case of DC treatment in a highway, some sensitivity... 

    Impact crushing behavior of foam-filled paraboloid shells using numerical and experimental methods

    , Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 1912-1921 ; 10263098 (ISSN) Shams, S ; Haddadpour, H ; Tuzandejani, H ; Hosseini, S. A. A ; Vatanparast, M ; Zahab, S ; Sharif University of Technology
    Sharif University of Technology  2017
    This paper deals with the dynamic response and energy absorption of foam-filled aluminum parabolic tubes under axial impact loading. The numerical crush analysis of empty and foam-filled tubes is performed using non-linear finite element techniques. The effects of geometrical (wall thickness) and material parameters (foam density and Young's relaxation modulus) on the impact response and energy absorption capacity of foam-filled tube are investigated using numerical models. The results show that the foam properties have significant effect on the crushing behavior, force and impact acceleration magnitude, and energy absorption capacity. Furthermore, there is a critical foam density beyond... 

    Dynamic simulation of biomechanical behaviour of the pelvis in the lateral impact loads

    , Article Journal of Healthcare Engineering ; Volume 2018 , 2018 ; 20402295 (ISSN) Hatami, M ; Wang, D ; Qu, A ; Xiangsen, Z ; Wang, Q ; Baradaran Kazemian, B ; Sharif University of Technology
    The objective of this study was to develop and validate a novel 3D dynamic model of a pelvic side-impactor system. The biomechanical responses of a pelvic flexible model (having.mnf file suffix) under the lateral impact load for predicting the bone fracture mechanism are investigated as well. The 3D solid model of the side-impactor system was imported into MSC/ADAMS software for analyzing the dynamic model, and the pelvic flexible model was extracted from the CT images of a Chinese female volunteer. The flexible model of the pelvis system was developed considering a wide range of mechanical properties in the bone complex and soft tissue to achieve a realistic biomechanical response during a... 

    Investigation and Analysis of Response Behavior of Tension Leg Platform under Impulse and Limit Loads (In order to Investigate the Phenomenon of Tendon Disconnection)

    , M.Sc. Thesis Sharif University of Technology Belvasi, Navid (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    Given the increasing development of exploitation of deepwater oil and gas resources, access to realistic solutions for analyzing and designing offshore platforms is a major factor in facilitating the exploitation of oil and gas resources in these areas. There is a huge amount of oil reservoirs in deep water beds, and Tension leg platform (TLP), as a compliant structure, are suitable for oil extraction in deep water.The advantage of using these platforms is the ability to rotate and move at a rate of rotational and transient freedom. Surge motion The TLP is a 120-second long period; In high-amplitude and low period waves, the platform faces a tendon rupture due to high waves forces and bad... 

    A Strain Rate Constitutive Model for Fiber Reinforced Concrete Based on Split Hopkinson Pressure Bar Tests

    , Ph.D. Dissertation Sharif University of Technology Bagher Shemirani, Alireza (Author) ; Naghdababi, Reza (Supervisor)
    In this thesis, experimental and numerical investigations are performed on dynamic behavior of fiber reinforced concrete (FRC) by split Hopkinson pressure bar (SHPB) and penetration tests. In the experimental part, effects of parameters such as quasi-static compressive strength of matrix (36 and 48 MPa), strain rate (3*10-5 up to 100 s-1), type of fibers (crimped steel, hooked-end steel, micro polypropylene and micro polypropylene) and volume fraction of the fibers (0%, 1% and 2%) are studied by employing SHPB apparatus on testing more than 150 specimens. Also, different types of FRC panels with 5 cm thickness were casted to perform 20 penetration tests with compressed gas gun apparatus. The... 

    Behavior Evaluation of Pre-stressed Concrete Slabs Strengthened by FRP laminates under Impact Loads

    , M.Sc. Thesis Sharif University of Technology Jarrahbashi, Amir Hossein (Author) ; Khaloo, Alireza (Supervisor)
    The investigation of non-prestressed concrete components subjected to impact loadings has been reported in the literature. However, the knowledge on the impact-resistant capacity of pre-stressed concrete components is very limited. In this study, behavior of pre-stressed concrete slabs strengthened by FRP sheets is investigated. The behavior of strengthened pre-stressed concrete slabs under impact load is analyzed using finite elements method. The effects of FRP strengthening of pre-stressed concrete slabs to resist impact loads have been studied using ANSYS software. Pre-stressed concrete slabs have been modeled without/with different FRP strengthening measures. Pre-stressed concrete slab... 

    Behavior Evaluation of Reinforced Concrete Slabs Strengthened by FRP laminates under Impact Loads

    , M.Sc. Thesis Sharif University of Technology Jarrahbashi, Alireza (Author) ; Khaloo, Alireza (Supervisor)
    Precise numerical models to predict responses and damage of FRP strengthened RC slabs to impact loads are limited in the literature. The behavior of (RC) slabs strengthened by FRP sheets is investigated. The behavior of strengthened RC slabs under impact load is analyzed using finite elements method. In this study, the effects of FRP strengthening of RC slabs to resist impact loads have been performed using ANSYS software. RC slabs without/with different FRP strengthening measures have been simulated in this study. RC slab without strengthening and RC slab strengthened with FRP sheets applied to the tension face of the slab have been included in the model. Each slab is subjected to repeated... 

    Experimental Studies and Finite Element Analysis of Polymer Nanocomposites Reinforced with Graphene Sheets under Impact Loading

    , M.Sc. Thesis Sharif University of Technology Zarei Darani , Sajad (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
    In the experimental approach, graphene and Graphene Oxide (GO) were synthesized through a chemical method. In order to study the quality of GO, characterization tests were performed. Then, reinforced polymer with GO and graphene was made. Moreover, tension, compression and Split- Hopkinson pressure bar tests were performed on standard samples of reinforced polymer nanocomposite. The experimental data show that nanoparticles have a destructive effect in very low and high percentages for extension test as well as in high percentages for compression test. On the other hand, graphene is more effective than GO on improving material properties. Furthermore, comparison of compression results in... 

    Biomechanical response of intact, degenerated and repaired intervertebral discs under impact loading – Ex-vivo and In-Silico investigation

    , Article Journal of Biomechanics ; Volume 70 , March , 2018 , Pages 26-32 ; 00219290 (ISSN) Nikkhoo, M ; Wang, J. L ; Parnianpour, M ; El-Rich, M ; Khalaf, K ; Sharif University of Technology
    Elsevier Ltd  2018
    Understanding the effect of impact loading on the mechanical response of the intervertebral disc (IVD) is valuable for investigating injury mechanisms and devising effective therapeutic modalities. This study used 24 porcine thoracic motion segments to characterize the mechanical response of intact (N = 8), degenerated (Trypsin-denatured, N = 8), and repaired (Genepin-treated, N = 8) IVDs subject to impact loading. A meta-model analysis of poroelastic finite element simulations was used in combination with ex-vivo creep and impact tests to extract the material properties. Forward analyses using updated specimen-specific FE models were performed to evaluate the effect of impact duration. The... 

    Dynamic and static fracture analyses of graphene sheets and carbon nanotubes

    , Article Composite Structures ; Volume 94, Issue 8 , 2012 , Pages 2365-2372 ; 02638223 (ISSN) Niaki, S. A ; Mianroodi, J. R ; Sadeghi, M ; Naghdabadi, R ; Sharif University of Technology
    Dynamic and static fracture properties of Graphene Sheets (GSs) and Carbon nanotubes (CNTs) with different sizes are investigated based on an empirical inter-atomic potential function that can simulate nonlinear large deflections of nanostructures. Dynamic fracture of GSs and CNTs are studied based on wave propagation analysis in these nanostructures in a wide range of strain-rates. It is shown that wave propagation velocity is independent from strain-rate while dependent on the nanostructure size and approaches to 2.2×10 4m/s for long GSs. Also, fracture strain shows extensive changes versus strain-rate, which has not been reported before. Fracture stress is determined as 115GPa for GSs and... 

    Failure analysis of a gas turbine compressor

    , Article Engineering Failure Analysis ; Volume 18, Issue 1 , 2011 , Pages 474-484 ; 13506307 (ISSN) Farrahi, G. H ; Tirehdast, M ; Masoumi Khalil Abad, E ; Parsa, S ; Motakefpoor, M ; Sharif University of Technology
    During the shut down period, a 32. MW gas turbine experienced a severe failure accompanied by a loud noise near its second natural frequency at 4200. rpm. After opening the turbine casing, it was revealed that the disks of stages 16 and 17 of the compressor had been fractured and all of the stationary and rotary blades of stages 14-18 of the compressor had been detached from the dovetail region of the disks. The degree of damage was such that repairing the compressor was not economical, and thus, the compressor was no longer able to be used. Diagnostic work was carried out using different finite element models and fractography analysis. Analysis showed that multiple cracks had been initiated... 

    Vibration isolation of foundations subjected to impact loads by open trenches using physical models

    , Article 16th International Conference on Soil Mechanics and Geotechnical Engineering: Geotechnology in Harmony with the Global Environment, ICSMGE 2005, Osaka, 12 September 2005 through 16 September 2005 ; Volume 3 , 2005 , Pages 1497-1500 ; 9059660285 (ISBN); 9789059660281 (ISBN) Jafarzadeh, F ; Sharif University of Technology
    Surface waves generated during vibration of machine foundations are sometimes troublemaking and cause some damages to the nearby sensitive structures or people. Considering the function of the machines located on the foundations the dynamic loading could be harmonic or impact type. The main part of the generated energy is transferred to the ground by Rayleigh surface waves. One of the most reliable and economic methods for reduction of the effects of these generated waves is using open trenches around the dynamic sources, so called active isolation in literature. In this paper applicability and affecting parameters of the open trenches around the impact dynamic source is studied using... 

    Dynamic performance of concrete slabs reinforced with steel and GFRP bars under impact loading

    , Article Engineering Structures ; Volume 191 , 2019 , Pages 62-81 ; 01410296 (ISSN) Sadraie, H ; Khaloo, A ; Soltani, H ; Sharif University of Technology
    Elsevier Ltd  2019
    Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar's material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs,...