Sharif Digital Repository

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... 

Split Hopkinson pressure bar (SHPB) test is one of the tests used for characterizing the mechanical behavior of materials at high strain rates between and s -1. A SHPB test consists of a gas gun, a striker bar, an incident bar, a transmission bar and a specimen which is sandwiched between the incident and transmission bars. In order to achieve constant strain rate during the test which is necessary in SHPB test, the incident pulse should obey the stress-strain curve of the specimen. For shaping the incident pulse usually a thin deformable disk -called pulse shaper- is placed between the striker and incident bars. In this thesis, first we designed, implemented and calibrated the measuring... 

Increasing the application of elastomeric structures in industries has caused an interest in the researchers for nonlinear elasticity and viscoelasticity of solids. Such materials which show large deformation and rate dependent behavior are treated by visco-hyperelastic constitutive equations. Based on visco-hyperelastic constitutive equations, total stress is divided into two parts: quasi-static and viscous stress. The method for determining the visco-hyperelastic constitutive equation is strictly dependent on the chosen rheological model. In this project, a new visco-hyperelasic constitutive equation in the integral form was introduced based on the Zener model. Also, based on the internal... 

Studying the behavior of materials at high strain rate is necessary for design and analysis of structures subjected to impact loading. Therefore, design and construction of apparatuses that enable us for testing various materials under impact loading is very important. The split Hopkinson pressure bar test -one of the most important impact tests- is utilized for dynamic loading at constant strain rates ranging from 100 to 10000 1/s.
In this thesis, first we explain about the behavior of materials at high strain rates and then focus on the behavior of polymers -that are widely used in different industries- under impact loading. Also, basic concepts of polymeric Hopkinson pressure bar and... 

So far, a lot of research has been done on the hot behavior of different alloys; These studies have generally been performed using tensile, compression and torsion tests and isothermal conditions, which have greatly contributed to the understanding of the mechanisms of deformation at high temperatures. Due to the fact that in real deformation processes, it is less common for the material to experience isothermal conditions during deformation, so in this project, the aim is to investigate the behavior of 2024 aluminum-alloy in non-isothermal hot compression test. In this regard, non-isothermal hot pressure test was performed from 300℃ to 600℃ و temperature range and at different deformation... 

Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using... 

In Li-ion batteries, large volume changes of electrodes with high capacity, such as silicon electrodes during charging and discharging processes (insertion/extraction of lithium into/from the electrode), lead to restrictions on the use of this type of electrode. Given the very high capacity of silicon, predicting and modeling the behavior of silicon electrodes during electrochemical cycles is important and is also addressed in this thesis. First, using the theory of linear elasticity, relations are proposed that couple the diffusion of particles with small elastic deformation. The effect of hydrostatic stress on diffusion and stresses is investigated in lithiation processes. Then, the...