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Residual Stress Determination of Multi-pass Welding Process, Stress Relieving Procedures and Its Effect on Crack Propagation
, M.Sc. Thesis Sharif University of Technology ; Farahi, Gholamhossein (Supervisor)
Abstract
One of the most important issues in welding is residual stresses. It is desirable to produce less residual stresses when possible and to reduce them which remain in the structure. At the present, various methods have been developed to reduce the residual stresses. The most important methods are heat treatment, shot peening, and grinding. The main problem in using these methods is cost, and for large structures these methods are often impractical. In recent decades, a technique called vibratory stress relief has been developed. It is used for large structures without limitation of size and weight; besides, the cost of this process is much less in comparison with other conventional methods...
Effect of processing parameters on electrical, mechanical and magnetic properties of iron-resin soft magnetic composite
, Article Powder Metallurgy ; Volume 50, Issue 1 , 2007 , Pages 86-90 ; 00325899 (ISSN) ; Madaah Hosseini, H. R ; Miraghaei, S ; Sharif University of Technology
2007
Abstract
In the present paper, a practical thermal treatment process has been introduced to stress relieve the iron powders in a soft magnetic composite. The composites were pressed and treated at different pressures and temperatures. Also, some of the samples were treated for various periods of time at 200°C. Density, electrical resistivity and transverse rupture strength of the samples were measured and fracture surfaces were studied by SEM. A series of tests were performed to determine the DC magnetic properties of the samples. It has been shown that there are optimum amounts of resin content and compaction pressure and temperature, rather than time is the dominant factor in stress relief of the...
Welding characteristics of ultrahigh strength steel in annealed and quench-tempered conditions
, Article Journal of Materials Engineering and Performance ; Volume 19, Issue 7 , 2010 , Pages 963-969 ; 10599495 (ISSN) ; Barzegari, M ; Kokabi, A. H ; Madaah Hosseini, H. R ; Sharif University of Technology
Abstract
In this research, the welding characteristics of a new UHSLA steel, 35NiCrMoV123, have been studied in two general conditions (annealed and quench-tempered). Carbon equivalent value of 35NiCrMoV123 steel is near 0.9 which classifies it as a "very difficult to weld" steel. The effects of welding heat treatment cycle (preheat, interpass, and postheat) on metallurgical and mechanical properties of weldments have been investigated by tensile, impact toughness, and hardness tests, as well as optical microscopy observations. It has been observed that by employing high-temperature stress relief (600 °C), welding could be performed in annealed condition successfully. Also, the results indicate that...
Structural and corrosion characterization of hydroxyapatite/zirconium nitride-coated AZ91 magnesium alloy by ion beam sputtering
, Article Applied Surface Science ; Volume 401 , 2017 , Pages 172-180 ; 01694332 (ISSN) ; Afshar, A ; Mojtahedzadeh Larijani, M ; Yousefpour, M ; Sharif University of Technology
Abstract
The adhesion of hydroxyapatite (HA) as a coating for the AZ91 magnesium alloy substrate can be improved by using the sputtering method and an intermediate layer, such as ZrN. In this study, HA coatings were applied on ZrN intermediate layers at a temperature of 300 °C for 180, 240, 300, 360, and 420 min by ion beam sputtering. A profilometer device was used to study the HA coating thickness, which changed from 2 μm for the 180-min deposition to 4.7 μm for 420-min deposition. The grazing incidence X-ray diffraction analysis method and the Williamson–Hall analysis were used for structural investigation. As the deposition time increased, the crystalline size increased from 50 nm to 690 nm....
A comparative study on the fatigue life of the vehicle body spot welds using different numerical techniques: Inertia relief and modal dynamic analyses
, Article Frattura ed Integrita Strutturale ; Volume 14, Issue 52 , 2020 , Pages 67-81 ; Farrahi, G. H ; Kashyzadeh, K. R ; Azadi, S ; Jahani, K ; Sharif University of Technology
Gruppo Italiano Frattura
2020
Abstract
Owing to the expensive and time-consuming nature of durability experiments, finite element based durability analysis is quite prevalent in the automotive industry. Numerical fatigue life analyses are typically divided into two different categories, the quasi-static methods which are faster and the dynamic methods which are more accurate. The aim of this paper is to compare the inertia relief and modal dynamic approaches in terms of formulation, accuracy and computation time. The chosen case study is the fatigue life of the vehicle body which is considered the main load-bearing component in a vehicle. By utilizing multi-body dynamics model and driving the vehicle on different standardized...