by Mohammad Tabatabaee Ghomi

Institution: Mälardalen University
Department: School of Sustainable Development of Society and Technology
Degree: Doctorate Degree
Year: 2011
Keywords: Explosive welding, Impact- echo
Posted: 11/25/2016
Record ID: 2150637
Full text PDF: http://www.diva-portal.org/smash/record.jsf?pid=diva2%3A459130&dswid=-9899


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 loading 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 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. 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.