Sharif Digital Repository

A numerical analysis is improved to study the effect of vibration on temperature history, heat generation, and mechanical properties during the friction stir welding process with different welding speeds. In this investigation, smoothed particle hydrodynamics (SPH) was applied to improve the 3D numerical analysis for simulation of the friction stir welding (FSW) process and friction stir vibration welding (FSVW) under different welding speeds. According to the experimental analysis, the grain size of the FSVW-ed sample is finer compared with that of the FSW-ed sample. The analysis was validated through a comparison of the simulated thermal cycles with the experimental results. There was a... 

This study aims at understanding the metallurgical and mechanical response of Hastelloy X nickel-based superalloy to the thermal cycle of gas tungsten arc welding (GTAW), post welding solution treatment (ST), and aging. In the as-weld condition, the weldment was characterized by the formation of the M6C carbide, sigma phase, and micro-solidification cracks in the interdendritic zones of the weld metal, and constitutional liquation of M6C carbide in the heat-affected zone. It is demonstrated that neither the weld metal nor the heat-affected zone could adversely affect mechanical properties of the welded joint in as-weld condition. However, to alleviate the microstructural heterogeneity,... 

Nucleic acid amplification using polymerase chain reaction (PCR) method has been widely used in different fields such as agricultural science, medicine, pathogen identification, and forensics to name a few. Today, it seems inevitable to have a robust, simple PCR system for diagnostics at the point-of-care (POC) level. Many photonic PCR systems have been proposed in the literature that benefit from plasmonic photothermal heating to achieve the common PCR thermal cycling. However, non-homogeneous temperature distribution is a challenge in some of them. In the present work, to achieve more efficient gene amplification, the effect of adding TiO2 nanoparticles has been investigated in a photonic... 

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 study, the thermal cycles and the grain structure in the weld heat-affected zone (HAZ) are predicted. At the first stage, a combined heat transfer and fluid flow model is employed to assess the temperature fields during and after welding of 304 stainless steel and then, the evolution of grain structure is conducted using the predicted temperature distribution and an analytical model of grain growth. The grain sizes of the CGHAZ (coarse grain heat affected zone) achieved from the model are basically in agreement with those obtained from experimental measurement under different heat inputs in the range of 0.33-1.07 MJ/m. Both the experimental data and the calculated results show that... 

In this work, temperature field and weld pool geometry during gas tungsten arc welding of 304 stainless steel are predicted by solving the governing equations of heat transfer and fluid flow under quasi-steady state conditions. The model is based on numerical solution of the equations of conservation of mass, momentum, and energy in the weld pool. Weld pool geometry, weld thermal cycles, and various solidification parameters are then calculated by means of the model predictions. The model considers the effects of various process parameters including welding speed and heat input. It is found that the weld pool geometry, predicted by the proposed model, is in reasonable agreement with the... 

In the present study, the temperature and the velocity fields during gas tungsten arc welding of commercial pure aluminum were simulated using the solution of the equations of conversation of mass, energy and momentum in three dimensions and under steady-state heat transfer and fluid flow conditions. Then, by means of the prediction of temperature and velocity distributions, the weld pool geometry, weld thermal cycles and various solidification parameters were calculated. To verify the modeling results, welding experiments were conducted on two samples with different thicknesses and the geometry of the weld pool was measured. It is found that there is a good agreement between the predicted... 

A mathematical model is developed to assess the solidification behaviour of the weld pools. To do so, during gas tungsten arc welding of commercial pure aluminium, equations of conversation of mass, energy and momentum are numerically solved considering three-dimensional steady state heat transfer and fluid flow conditions. The weld pool geometry, weld thermal cycles and various solidification parameters are calculated using temperature and velocity fields acquiring from the utilised model. The solidification behaviour of the weld pool at the weld centreline and the fusion line is then studied using the solidification parameters including temperature gradient G, solidification rate R and the...