Sharif Digital Repository

Flow curves and microstructural changes of nanostructured Al6063 alloy produced by mechanical alloying followed by hot extrusion were investigated by means of uniaxial compression test in the temperature range between 300 and 450 °C and strain rate range between 10-2 and 1 s-1. The analysis of flow curves were performed by a hyperbolic sine law equation and the stress exponent and activation energy were determined to be 2.9 and 228 kJ mol-1, respectively. The microstructural constituents for elaboration of deformation mechanisms were observed by TEM and EBSD under FEG-SEM. The microstructural observations determine that dynamic recovery through the formation of subgrains within the grains... 

Design and development of biodegradable scaffolds with highly uniform and controlled internal structure that stimulate tissue regeneration are the focus of many studies. The aim of this work is to apply a modified three-dimensional (3D) printing process to fabricate polymer-matrix composites with controlled internal architecture. Computationally-designed plaster molds with various pore sizes in the range of 300-800. μm were prepared by employing 3D printing of a water-based binder. The molds were converted to ε-polycaprolactone (PCL) and PCL/bioactive glass (BG) composite scaffolds by solvent casting and freeze drying methods. Optical and electron microscopy studies revealed that the pore... 

Uniaxial compression test at different temperatures [573 K to 723 K (300 °C to 450 °C)] and strain rates (0.01 to 1 s−1) was employed to study the hot deformation behavior of an ultrafine-grained (UFG) Al6063 alloy prepared by the powder metallurgy route. The UFG alloy with an average grain size of ~0.3 µm was prepared by mechanical milling of a gas-atomized aluminum alloy powder for 20 hours followed by hot powder extrusion at 723 K (450 °C). To elaborate the effect of grain size, the aluminum alloy powder was extruded without mechanical milling to attain a coarse-grained (CG) structure with an average grain size of about 2.2 µm. By employing the dynamic materials model, processing maps for... 

In this work, the flow stress behavior of a metal matrix composite AA2017-10% SiCp was studied by means of the uni-axial compression test. The composite was first produced by stir casting technique and then, hot extrusion with the ratio of 18:1 was carried out to achieve a microstructure with a homogeneous distribution of SiC particles. In the next stage, the isothermal compression tests were conducted on the cylindrical specimens up to the true strain of 0.6. The experiments were performed at temperatures between room temperature to 400°C and strain rates of 0.003, 0.03 and 0.3s-1. Negative strain rate sensitivity was observed in the temperatures less than 250°C indicating the occurrence of... 

The molecular-dynamics analysis is presented for 3D compaction simulation of nano-crystalline metals under uniaxial compaction process. The nano-crystalline metals consist of nickel and aluminum nano-particles, which are mixed with specified proportions. The EAM pair-potential is employed to model the formation of nano-particles at different temperatures, number of nano-particles, and mixing ratio of Ni and Al nano-particles to form the component into the shape of a die. The die-walls are modeled using the Lennard-Jones inter-atomic potential between the atoms of nano-particles and die-walls. The forming process is model in uniaxial compression, which is simulated until the full-dense... 

The biomechanical behavior of brain tissue is needed for predicting the traumatic brain injury (TBI). Each year over 1.5 million people sustain a TBI in the United States. The appropriate coefficients for modeling the injury prediction can be evaluated using experimental data. In the present paper, using an experimental setup on bovine brain tissue, unconfined compression tests at quasi-static strain rates of ϵ 0.0004s-1, 0.008s-1 and 0.4s-1 combined with a stress relaxation test under unconfined uniaxial compression with ϵ 0.67s-1 ramp rate are performed. The fitted viscohyperelastic parameters were utilized by using obtained stressstrain curves. The finite element analysis (FEA) is... 

In this investigation, polymer concrete (PC) with three different epoxy resin contents, ordinary cement concrete (OCC), lightweight concrete (LWC), and lime-mortar soil (LMS) have been studied under uniaxial and triaxial compression tests to determine their mechanical behavior by measuring axial stress-strain and volumetric strain versus axial strain curves. According to the results, PC showed higher strength, ductility, and energy absorption than that of OCC and LWC. Then, nonlinear finite element analysis (NFEA) was implemented to predict the experimental results using hierarchical single-surface (HISS) failure criterion and disturbed state concept (DSC) to capture the elastoplastic... 

In recent years, pozzolana are being increasingly used in different types of concretes and mortars. This investigation aims to evaluate the effect of replacing 7, 14, 21, and 28% cement (by weight) with silica fume (SF), granulated blast furnace slag (GBFS), zeolite, and fly ash (FA) under elevated temperatures. Forty mix designs were built with various water-to-cement ratios and plasticizers. Three hundred and six specimens were prepared, and the flexural, uniaxial compression and tensile tests were performed on specimens after exposure to elevated temperatures between 25°C and 900°C. The X-ray diffraction (XRD) test was then performed on the two series of specimens. Accordingly, the...