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  • 1.
    Tabatabaee Ghomi, Mohammad
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Impact wave process modeling and optimization in high energy rate explosive welding2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Impact waves are used in many different industries and are classified according to whether they cause plastic or elastic deformations. In the plastic deformation mode, these waves can be used to produce special electrical joints. In the elastic deformation mode, they can be used to detect leakage or to measure the thickness of pipes. Both modes have applications in offshore technology. In this thesis the application of impact waves in the plastic deformation mode and explosive welding are discussed. In the explosive welding (EXW) process a high velocity oblique impact produced by a carefully controlled explosion occurs between two or more metals. The high velocity impact causes the metals to behave like fluids temporarily and weld together. This process occurs in a short time with a high rate of energy.

    EXW is a well known method for joining different metals together. It is a multidisciplinary research area and covers a wide range of science and technology areas including wave theory, fluid dynamics, materials science, manufacturing and modeling. Many of the important results in EXW research are obtained from experimentation.

    This thesis is mainly based on experimental work. However, it begins with a review of the fundamental theory and mechanisms of explosive welding and the different steps of a successful welding operation. Many different EXW tests are done on horizontal and vertical surfaces with unequal surface areas, and on curved surfaces and pipes. The remainder of the thesis evaluates the results of these experiments, measures the main parameters, and shows the results of simulations to verify the experimental results. The thesis ends with a number of suggestions for improving and optimizing the EXW process. One of these improvements is a model for joining metallic plates with unequal surface areas. An Al-Cu joint based on this model is used in the ALMAHDI aluminum factory, a large company in southern Iran that produces more than 200,000 tons of aluminum per year. Improved methods are also suggested for joining curved surfaces. These methods may have extensive applications in pipelines in oil and gas industries, especially in underwater pipes.

  • 2.
    Tabatabaee Ghomi, Mohammad
    Mälardalen University, School of Sustainable Development of Society and Technology.
    MODELLING AND SIMULATION OF ELASTIC & PLASTIC BEHAVIOUR OF PROPAGATING IMPACT WAVE: Impact- echo and Explosive welding process development2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A force that is applied dynamically in a short period of time is called an impact force (shock wave). Due to the concentrated application of force on a small area in a fraction of a second, unique applications have emerged that other types of loadings are not capable of performing. Explosions, an impact of a hammer, impact of waves on a shore wall, or the collision of two automobiles are examples where impact waves occur. In this research the effects of impact on solid materials and the motion of stress waves due to the impact are studied and some of their industrial applications are described.

     

    The primary objective of this work is further development of some elastic and plastic impact wave methods, aiming to reduce the energy consumption of explosive welding (EXW) as well as the cost of NDT technologies. Many numerical simulations and a vast amount of experimental work were employed to reach this goal.

     

    The impact wave creates elastic deformations that move the particles of the body. In this research we focused on dimensional measurement by calculating the time of wave travel between the source of energy and a discontinuity in the part studied. The impact echo (IE) method can be used for determining the location and extent of all kinds of flaws, such as cracks, de-lamination, holes and de-bonding in concrete structures, columns and hollow cylinders with different cross-sections and materials. In the present study, simulation of the impact-echo method was carried out numerically using direct and indirect methods. In the direct method a steel ball directly impacts on the upper surface of a concrete plate-like structure, whereas in the indirect method the impact impulse transmits to the concrete plate via a steel bar, in order to adapt the method for situations where there is no access to the plate being measured. In each method a two-dimensional finite element analysis (in axisymmetric geometry) was performed for the thickness measurement of concrete plates using the LS-DYNA program. Numerical results are presented for different values of plate thickness and different projectile speeds for both the direct and the indirect method and the indirect results are validated by comparison with the results obtained by the direct method. The method was validated against experimental measurements.

     

    A high energy impact wave produces plastic deformations in metals. In this research explosive welding was studied as an application of high energy impact waves. A new method for joining different, non-compatible metals (Al and Cu-based materials) was introduced. This method may be extended for use in offshore applications. Many 3-D numerical simulations were performed using the ABAQUS explicit commercial software. The model was validated against experimental measurements.

     

    The outcome of this research work could be summarized as follows:

    a)  Introducing an indirect IE method in NDT technology for thickness measurement in particularly inaccessible structures.

    b)  Introducing a new, grooved method in EXW technology to join surfaces made of different materials, in particular Al-Cu joints.

    The results could be employed to reduce the energy consumption and cost associated with EXW and IE technologies. The methodology can be used in many other applications in all kinds of process industries.

  • 3.
    Tabatabaee Ghomi, Mohammad
    et al.
    Mälardalen University, School of Business, Society and Engineering. Technology Development Institute (TDI) and ACECR Researcher, Tehran, Iran .
    Mahmoudi, Jafar
    Mälardalen University, School of Business, Society and Engineering.
    Darabi, M
    Technology Development Institute (TDI) and ACECR Researcher, Tehran, Iran.
    Concrete Plate Thickness Measurement Using the Indirect Impact-Echo Method2013In: NDT & E international, ISSN 0963-8695, Vol. 28, no 2, 119-144 p.Article in journal (Refereed)
    Abstract [en]

    A new method for measuring the thickness of concrete plates indirectly is proposed. In this approach, a steel ball impacts on a steel bar and the generated stress waves transfer to the concrete plate. Numerical simulations of the process were carried out using different plate thicknesses. The results indicate that the impact response of the concrete plate for a dominant thickness frequency in the indirect method agrees with the results obtained in the classic direct method in which the impactor collides directly on the specimen being tested. The results also show that the proposed method can be used to measure the thickness of concrete plates with reasonable accuracy. The behaviour of stress waves in the steel bar was investigated and revealed to be consistent with previous research.

  • 4.
    Tabatabaee Ghomi, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Darabi, Mehdi
    echnology Development Institute (TDI), ACECR, Iran .
    Steel Plate Thickness Measurement using Impact-Echo Method2011In: Proceedings of the IASTED International Conference on Applied Simulation and Modelling, ASM 2011, 2011, 168-173 p.Conference paper (Refereed)
    Abstract [en]

    In this study we use impact echo method for measuring the thickness of steel plates. Numerical simulation of steel plates by the purpose of thickness measurement was performed on the different plate thicknesses. The impact echo method is usually using for concrete structures. In this study we applied this method for steel plates and the results indicated that this method also could be report truly the thickness of the steel plates.

  • 5.
    Tabatabaee Ghomi, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Khalkhali, A
    Iran Univ Sci & Technol, Sch Automot Engn, Tehran, Iran.
    Liaghat,, G
    Tarbiat Modares Univ, Tehran, Iran.
    Explosive Welding of Unequal Surface using Groove Method2012In: Transactions of the Canadian Society for Mechanical Engineering, ISSN 0315-8977, Vol. 36, no 2, 113-125 p.Article in journal (Refereed)
    Abstract [en]

     Bond strength of welded joints is an important factor in the explosive welding process. In such welding process, stress waves produced by explosive energy propagate at the, free surface and produce tension stresses. These waves result in spalling and scabbing at the edges of metals and reduce the tensile bond strength of explosive welding. The most common method for solving this problem is cutting and sizing the edges. However, this is not possible when the two metal parts to be joined are of unequal surfaces (a small plate to a large plate). This paper focuses on applying a new technique (Groove Method) for solving the strength problem at the edges for obtaining uniform welding. In this way, experimental and numerical analyses are performed to evaluate the Groove Method. The obtained results show the success and effectiveness of the groove method suggested in this paper.

  • 6.
    Tabatabaee Ghomi, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Liaghat, Gholamhossein
    Removing leakage from oil and gas low pressure pipes by explosive welding method2011In: Journal of Petroleum and Gas Exploration Research, ISSN 2276-6510, Vol. 1, no 1, 34-42 p.Article in journal (Refereed)
    Abstract [en]

    Explosive welding occurs under high velocity oblique impact, and it is possible to use explosiveenergy to form a conventional cold pressure weld. One of the advantages of this method is that itcan be used to weld different materials with different shapes. Explosive welding can be used for themaintenance of pipes and vessels, in repairing leaks especially in under water pipes in the oil andgas industries. We describe a new explosive welding method for repairing leaks in metal pipes thatis very economical and easy to apply.

  • 7.
    Tabatabaee, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Mälardalen University, School of Sustainable Development of Society and Technology.
    An advanced method for Aluminium - iron - copper bonding using explosive welding method2008In: PROCEEDINGS FROM SCIENTIFIC CONFERENCE ON GREEN ENERGY AND IT, 2008Conference paper (Refereed)
  • 8.
    Tabatabaee, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Mälardalen University, School of Sustainable Development of Society and Technology.
    FEM method simulation of Aluminium - iron - copper bonding using explosive welding method2008Conference paper (Refereed)
  • 9.
    Tabatabaee, Mohammad
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Mahmoudi, Jafar
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Finite element simulation of explosive welding2008Conference paper (Refereed)
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