غلامحسین فرهی
دانشکده مهندسی مکانیک، دانشگاه صنعتی شریف
[ 1 ] - بررسی تجربی و عددی تأثیر فرایند ساچمه‌زنی شدید بر افزایش عمر خستگی آلومینیوم ۳۵۶A
بسیاری از قطعات مکانیکی در عمل تحت بارگذاری خستگی قرار دارند و بسیاری از شکست‌ها و از کار افتادگی‌های مکانیکی نیز بر اثر این نوع بارگذاری است. زمانی‌که یک چرخه‌ی بارگذاری خاص در دوره‌های زمانی متوالی تکرار می‌شود پدیده‌ی خستگی و عمر خستگی مطرح می‌شود. این پدیده به شکست قطعات در تنشی کمتر از تنش تسلیم ماده منجر می‌شود. امروزه، برای افزایش عمر خستگی روش‌های بسیاری پیشنهاد شده است. بسیاری از این...
[ 2 ] - بررسی کاهش سختی سطحی موضعی و آزادسازی تنش داخلی فولاد روتور
آزادسازی تنش فولاد روتور که به‌صورت موضعی دچار افزایش سختی شده، با تعیین پارامترهای عملیات حرارتی همچون دما و زمان مورد توجه قرار گرفته است. پس از تعیین ارتباط بین سختی اندازه‌گیری شده و تنش پسماند داخلی ماده، با حل یک تحلیل المان محدود حرارتی ـ سازه‌یی و جفت‌کردن آن با پدیده‌ی خزش، مشخصات و روش اجرای عملیات حرارتی به‌منظور حذف تنش‌های داخلی مشخص شد. در روش دوم کاهش مستقیم سختی موضعی با توجه به...
[ 3 ] - اثرتنش‌های پسماند بر رفتار خستگی قطعات دوار
این نوشتار به بررسی اثرات تنش پسماند ناشی از ماشین‌کاری بررفتار خستگی پره کمپرسور یک موتور توربینی می‌پردازد. از آن‌جا که کوپل تنش‌های پسماند با تنش‌های وارده و بارهای نوسانی روی عمر نمونه تأثیر دارد، ابتدا نقاط حساس تنشی روی پره که از نتایج تحلیل اجزاء محدود به دست آمد، تعیین شد. سپس تنش‌های پسماند در این نقاط با استفاده از روش سوراخ‌کاری اندازه‌گیری و در ادامه تنش‌های دینامیکی وارده بر پره با...
[ 4 ] - A review of thermal barrier coating effects on diesel engine performance and components lifetime
In the present paper, a complete literatures review of thermal barrier coating applications in diesel engines is performed to select a proper type and to find coating effects. The coating system has effects on the fuel consumption, the power and the combustion efficiency, pollution contents and the fatigue lifetime of engine components. Usually there are several beneficial influences by appl...
[ 5 ] - Effect of Residual Stress on Failure of Tube-to-tubesheet Weld in Heat Exchangers
In a shell and tube heat exchanger, the failure of tube-to-tubesheet welds results in high-pressure water jet which erodes the refractory in front of the tubesheet. Finite element method was employed to simulate the welding process and post weld heat treatment (PWHT) to find the factors affecting the failure in tube-to-tubesheet weldments. Residual stresses in two different geometries of tube-t...
[ 6 ] - A Study on the Contact Ellipse and the Contact Pressure During the Wheel Wear through Passing the Tracks including Several Sharp Curves
Wheel wear has been a concern in the railway for several decades. Studying the form change of the wheel/rail contacts in particular railways consisting of sharp curves helps to identify the risk of severe or catastrophic wear to minimize maintenance costs in order to be competitive in the transportation business. In this paper, the wheel/rail contact was studied on the particular railways. The ...
[ 7 ] - Modelling of Conventional and Severe Shot Peening Influence on Properties of High Carbon Steel via Artificial Neural Network
Shot peening (SP), as one of the severe plastic deformation (SPD) methods is employed for surface modification of the engineering components by improving the metallurgical and mechanical properties. Furthermore artificial neural network (ANN) has been widely used in different science and engineering problems for predicting and optimizing in the last decade. In the present study, effects of conv...
[ 8 ] - Experimental and Finite Element Studies on Free Vibration of Automotive Steering Knuckle
The main aim of this research is to determine the best material for manufacturing of steering knuckle in order to reduce the weight using aluminum alloy and Metal Matrix Composite (MMC). To achieve this purpose, the Modal test has been performed to study vibrational behavior of steering knuckle. CAD Model has been prepared by using coordinate measuring machine (CMM). Finally, the Finite Element...
[ 9 ] - Analytic Approach to Free Vibration and Buckling Analysis of Functionally Graded Beams with Edge Cracks using four Engineering Beam Theories
A complete investigation on the free vibration and stability analysis of beams made of functionally graded materials (FGMs) containing open edge cracks utilizing four beam theories, Euler-Bernoulli, Rayleigh, shear and Timoshenko, is performed in this research. It is assumed that the material properties vary along the beam thickness exponentially and the cracked beam is modeled as two segments ...
[ 10 ] - The Effect of Various Parameters on Out-of-phase Thermo-mechanical Fatigue Lifetime of A356.0 Cast Aluminum Alloy
In this paper, the effect of various parameters on out-of-phase thermo-mechanical fatigue (OP-TMF) lifetime of A356.0 cast aluminum alloy is investigated. The studied parameters include maximum temperature, dwell time, and the thermo-mechanical loading factor. OP-TMF tests are conducted considering realistic running conditions of diesel engine cylinder heads. The maximum temperature varies betw...
[ 11 ] - Fatigue Life of Repaired Welded Tubular Joints
In this study, the effect of repair on fatigue life of tubular joints is investigated. Six cracked specimens precedently subjected to fatigue loading undergone to weld repair. Two of those specimens were shot peened before primary fatigue loading. It is shown that repair gives rise to about 150% increase in fatigue life for original specimens while the increase of fatigue life for shot-peened ...
[ 12 ] - Side Effects of Shot Peening on Fatigue Crack Initiation Life
Shot peening beneficial effects on fatigue life of mechanical components are well known. However, there are some reports in the literature that indicate inappropriate shot peening parameters tend to reduce the fatigue life. It is therefore, the purpose of this study to find a logical quantitative justification for these observations. Using finite element method, a dynamic elastic-plastic simula...
[ 13 ] - NUMERICAL INVESTIGATION OF CRACK ORIENTATION IN THE FRETTING FATIGUE OF A FLAT ROUNDED CONTACT
The growth of slant cracks by fretting fatigue of a half plane in contact with a flat rounded pad was studied. The mode I and mode II stress intensity factors for cracks of various lengths and directions were calculated using the semi-analytical method of the distribution of dislocations, and their cumulative effect on the crack growth was investigated using the strain energy density criterion....
[ 14 ] - Thermal Analysis of Laser Hardening for Different Moving Patterns
Transient thermal field in laser surface hardening treatment of medium carbon steel was analyzed by employing both three-dimensional analytical model and finite element model. In finite element model the laser beam was considered as a moving plane heat flux to establish the temperature rise distribution in the work-piece, while in analytical model laser beam was considered as an internal heat s...
[ 15 ] - Efficiency of Anti-Hourglassing Approaches in Finite Element Method (TECHNICAL NOTE)
one of the simplest numerical integration method which provides a large saving in computational efforts, is the well known one-point Gauss quadrature which is widely used for 4 nodes quadrilateral elements. On the other hand, the biggest disadvantage to one-point integration is the need to control the zero energy modes, called hourglassing modes, which arise. The efficiency of four different an...
[ 16 ] - Crack Behavior of the Aluminum Alloy 2024 Under Fretting Conditions
The initial stage of fretting fatigue crack growth is significantly influenced by tangential force induced by fretting action along the contact surface where a mixed-mode crack growth is involved. Fretting crack behavior of aluminum alloy 2024 was studied, taking into account the problem of contact asperities. Finite element was used for the determination of the stress field near the contact su...
[ 17 ] - Influence of Residual Stress on Fatigue Life of Hot Forged and Shot Blasted Steel Components
Hot forging is a common manufacturing process for the production of large quantities of engineering components. Residual stresses are developed in forged components as a result of various aspects of the manufacturing process, including subsequent cooling, and heat treatment. Residual stresses can significantly affect the deformation and fatigue failure of materials. Hot forged EN15R steel bars ...
[ 18 ] - Dynamic and Quasi-Static Tensile Properties of Structural S400 Steel
The study of mechanical behavior of the structural steel S400 under quasi- static and dynamic loading has been the subject of this investigation. In oder to obtain different stress - triaxiality conditions the specimens were notched with 1, 1.5, 2 and 3.5 mm notch radius. The results of fractography show as the velocity of tension increases, ductility reduces and a ductile-brittle transition oc...
[ 19 ] - The Dc Electrical Potential Method for the Measumment of Fretting Cracks
As fretting fatigue cracks are initiated at an early stage of life, the fretting fracture process is dominated by the stable growth of cracks. Hence the measurement of crack length is very important. This paper demonstrates the suitability of the DC potential drop technique for the measurement of fretting cracks. A calibration has been established for monitoring crack growth in BS L65 copper al...
[ 20 ] - Surface Hardness Measurment and Microstructural Characterisation of Steel by X-Ray Diffraction Profile Analysis
An X-ray diffraction line will broaden considerably when steels change into martensitic structure on quenching. The results presented in this paper show that X-ray diffraction technique can be employed for a rapid and nondestructive measurement of hardness of hardened steel. Measurement on various quenched and tempered steels showed that the breadth of its diffraction peak increased with increa...
[ 21 ] - Analysis of Resistance Spot Welding Process Parameters Effect on the Weld Quality of Three-steel Sheets Used in Automotive Industry: Experimental and Finite Element Simulation
In the present research, the effects of spot-welding process parameters on the nugget diameter and electrode penetration depth of spot-welded joints were investigated. To achieve this, a spot-welded joint of three-thin sheet low carbon steels (same thicknesses of 0.8 mm) was simulated as an electerical-thermal-mechanical coupling of 3D finite element model. After validating the finite element s...