Sharif Digital Repository

In this research, cold compaction behavior and pressureless sinterability of WC, WC-10%wtCu and WC-30%wtCu powders were investigated. WC and WC/Cu powders were milled in a planetary ball mill for 20h. The milled powders were cold compacted at 100, 200, 300 and 400 MPa pressures. The compressibility behavior of the powders was evaluated using the Heckel, Panelli-Ambrosio and Ge models. The results showed that the PanelliAmbrosio was the preferred equation for description the cold compaction behavior of the milled WC and WC-30%wtCu powders. Also, the most accurate model for describing the compressibility of WC-10%wtCu powders was the Heckel equation. The cold compacts were sintered at 1400oC.... 

In the present research, results of buckling analysis of 384 finite element models, verified using three different test results obtained from three separate experimental investigations, were used to study the effects of five parameters such as D/t, L/D, imperfection, mesh size and mesh size ratio. Moreover, proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD, ISO 19902, and NORSOK N-004 have been compared to FE and experimental results. One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

This paper presents the results of an experimental and analytical study on the improvements gained in the axial compressive behavior of confined concrete. Among several parameters affecting compressive ductility of confined concrete, including confinement mechanical volumetric ratio, shape and size effect, number of confinement layers, strength of plain concrete and ductility of confining material, the latter was found to play the most important role in determining the ultimate strain and post peak behavior of concrete. Axial compressive tests were performed on small-scale circular or square section concrete columns, which were retrofitted either by CFRP jacket or by two types of... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

This paper presents an evaluation of two distinct techniques to improve energy absorption capability of an accordion cellular structure with close-to-zero Poisson's ratio. For this purpose, fiber-reinforcement and foam-filling methods were employed to address the material enhancement and to obtain light and tough structures with high specific energy absorption. Employing an innovated additive manufacturing based on material extrusion process, specimens of glass fiber-reinforced PLA were produced in both in-plane directions to compare with the un-reinforced counterpart. In continue, some of the 3D printed samples were strengthened by means of polyurethane foam in their hollow structure. The... 

The nonlinear finite element method with eight noded isoparametric quadrilateral element for concrete and two noded element for reinforcement is used for the prediction of the behavior of reinforcement concrete structures. The disturbed state concept (DSC) including the hierarchical single surface (HISS) plasticity model with associated flow rule with modifications is used to characterize the constitutive behavior of concrete both in compression and in tension which is named DSC/HISS-CT. The HISS model is applied to shows the plastic behavior of concrete, and DSC for microcracking, fracture and softening simulations of concrete. It should be noted that the DSC expresses the behavior of a... 

This paper presents the results of an experimental study on the application of strapping technique for retrofit of concrete compressive specimens. In this technique, standard strapping devices, which are used in the packaging industry, are applied to post-tension high strength metal strips around the concrete columns. Experimental program included axial compressive tests on 72 cylindrical and prismatic compressive specimens, which were actively confined by pre-stressed metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete, mechanical volumetric ratio of confining strips, post-tensioning force in... 

This paper presents analytical part of an investigation on the application of prestressed strips for concrete confinement. In this paper, an analytical model is proposed to predict the compressive stress-strain curve of strapped concrete as a function of the confinement level. The model was calibrated based on the experimental data of compressive tests which were described in part A of this paper. Various parameters are considered in the proposed model including volumetric ratio, yield strength and ultimate strain of confining material, shape of cross section, strength of plain concrete. Three key points were defined on the stress-stress curve of strapped concrete columns and applied in... 

Concrete-filled polyethylene (PE) tubes (CFPT) are composite systems using the polyethylene tubes as confinement for the marine structures in the splash zone to extend the service life of structures subjected to harsh environments. However, thermal cycles in marine environments can affect the behavior of such composite systems. This paper evaluates the effect of concrete infill strength (30 MPa and 60 MPa), the number of thermal cycles (50, 100, and 150 cycles) ranging from 25 °C to 60 °C, and thermal cycle type (type A and B) on the compressive and bond response of CFPTs. Characteristics of control and conditioned concrete infill, PE tubes, and CFPTs were obtained by means of compression... 

In this article, a constitutive model in the framework of continuum damage mechanics is proposed to simulate the elastic behavior of concrete in tension and compression states. We assume two parts for Gibbs potential energy function: elastic and damage parts. In order to obtain the elastic-damage constitutive relation with the internal variables, two damage thermodynamic release rates in tension and compression derived from the elastic part of Gibbs potential energy are introduced. Also, two anisotropic damage tensors (tension and compression) are defined which characterize the tensile and compressive behaviors of concrete. Furthermore, two different linear hardening rules for tension and... 

The performance of cellular solids in biomedical applications relies strongly on a detailed understanding of the effects of pore topology on mechanical properties. This study aims at characterizing the failure mechanism of scaffolds based on nodal connectivity (number of struts that meet in joints) and geometry of the pores. Plastic models of scaffolds having the same relative density but different cubic and trigonal unit cells were designed and then fabricated via three dimensional (3-D) printing. Unit cells were repeated in different arrangements in 3-D space. An in-situ imaging technique was utilized to study the progressive deformation of the scaffold models. Different nodal...