farrahi

Study of the wheel and rail wear phenomenon can provide the optimal use of wheel profile which results cost efficiency, dynamic stability, travel comfort, and safety to prevent the derailment especially in curves. In this paper, the experimental data is recorded in the from the field measurements worn wheels of a passenger wagon in the “Southern line” of Iran’s railway system and is combined with the dynamic simulations to study the effects of severe wheel flange wear on the dynamics of wagon. The results show that the amount of wheel wear (especially the wheel flange) directly impacts the dynamic behavior of the wagon in curves. In addition, based on the history of wear index and the peak derailment ratio, the appropriate range of the wheel flange thickness in order to repair or replace the worn wheels is suggested in the range of 25 to 27 mm.

In this paper, the effect of penicillin G benzathine (PGB) drug as a green corrosion inhibitor on mild steel in 1.0 M hydrochloric acid solution has been investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency (IE) was found to increase with increasing inhibitor concentration. Potentiodynamic polarization measurements indicated that PGB is a mixed type inhibitor. The results of potentiodynamic polarization and EIS measurements demonstrated that the adsorption of PGB on mild steel in 1.0 M HCl follows Langmuir isotherm. The calculated values of free energy indicated that both physical and chemical adsorption take place. The IE values obtained from EIS measurements show a reasonable agreement with those obtained from potentiodynamic polarization method.

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-to-tubesheet weldment were calculated through uncoupled thermal-structural analysis. The results showed that the values of residual stresses are higher in heat exchanger of site 1 than site 2 due to more weld passes and geometry of connection. Also, the maximum stress in site 1 occurs at the shellside face of tubesheet while it is on the weld toe in site 2. High tensile residual stresses, especially in Site 1, reduce the tubesheet life. Therefore, performing an efficient PWHT is vital. The PWHT simulation indicated that the process designed is effective for both sites by reducing the residual stress significantly. In addition, the effect of stress concentration was examined on both sites. Moreover, the stress concentration factor in site 1 is as twice as in site 2 and it is the main reason for more failures in site 1.

The present paper investigates the effect of changes in wheel primary angles such as Camber and Toe angles on the fatigue life of vehicle steering knuckle under multi-input random non-proportional 3D stress components. In order to develop real loading conditions for the steering knuckle, the localizing equivalent road as a combination of some rough roads (ISO road classification B-F for highway out of town, urban highway, urban asphalt, soil road, and flagstone, respectively) based on statistical data collected from different cities by utilizing a general questionnaire including road type and vehicle velocity was considered. Then, the various actual load histories obtained through multi-body dynamics analysis of a full vehicle model were applied on several points of the component. The fatigue life of steering knuckle was predicted by using some prominent multi-axial fatigue criteria for non-proportional loading, rain-flow cycle counting algorithm, and Palmgren-Miner damage accumulation rule. Finally, the effect of different values of wheel angles on the fatigue life of the steering knuckle was examined. The results showed that the highest and lowest fatigue life of steering knuckle are related to the values of 2 positive and negative degrees of camber angle, respectively. The stress level is reduced in the various equivalent load histories by changing the toe angle to 0.2 negative, resulting in an increase in the fatigue life of steering knuckle.

The effect of three different sheet thicknesses of friction stir spot welding on lap-shear specimens of Al 6061-T6 alloy was experimentally analyzed. Different fatigue life evaluation models were applied to estimate the fatigue behavior of the friction stir spot welding in different thicknesses. Experimental results show a clear correlation between static strength and fatigue behavior of different welding conditions. Results of tensile and fatigue tests demonstrated the sheets with 2mm indicated the optimum thickness which were studied in this research. At the same cycles, fatigue results of different thicknesses showed considerable differences in the low cycles in comparison with the higher ones. The evaluation models of Pook, Zhang and three-dimensional finite element models were investigated in the different sheet thicknesses. The three-dimensional finite element model evaluated fatigue behavior better than the other models at different sheet thicknesses.

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 experimental measurement of wheel profiles was used as an input to Hertz Contact Theory (HCT). It was found that: 1) for these railways the wheel flange is highly worn; 2) a 5th order polynomial function is appropriate to model the wear behavior of the critical wheel; 3) the minimum and maximum contact ellipse surface areas occur in Sd=22.29 mm and Sd=32 mm, respectively; 4) the maximum and minimum surface areas of the contact ellipse occur at points in which the contact pressure are minimum and maximum, respectively; and finally 5) the flange thickness region between 25 to 29 mm can be chosen as an appropriate range for the wheel maintenance purposes.

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 conventional shot peening (CSP) and severe shot peening (SSP) on properties of AISI 1060 high carbon steel were modelled and compared via ANN. In order to networks training, the back propagation (BP) error algorithm is developed and data of experimental test results are employed. Experimental data illustrates that SSP has superior influence than CSP to improve the properties. Different networks with different structures are trained with try and error process and the one which had the best performance is selected for modeling. Testing of the ANN is carried out using experimental data which they were not used during networks training. Distance from the surface (depth), SP intensity and coverage are regarded as inputs and microhardness, residual stress and grain size are gathered as outputs of the networks. Comparison of predicted and experimental values indicates that the networks are tuned finely and adjusted carefully; therefore, they have good agreement.

Steering Knuckle is a basic part of vehicle which joins suspension and steering system, wheel and brake to the chassis. It experiences several loads subjected to different conditions, for example, multi-axial loads and vibration. Hence, the knowledge of its dynamics and vibrational behavior is very important. Several materials are used to produce steering knuckle, for example, SG Iron, white and grey cast iron. However, nowadays there is a tendency to use aluminum alloy by automakers. Material replacement which results in weight reduction and using advanced materials are highly preferable. One suggestion is the use of Metal Matrix Composite which has higher strength to weight ratio and better performance than a metal. The main aim of this research is to determine the best material for manufacturing of steering knuckle in order to reduce the weight by applying aluminum alloy and Metal Matrix Composite. 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 analysis has been performed to evaluate natural frequencies and mode shapes of knuckle. The obtained FEM results have been compared with experimental data to validate the simulation. Three groups of materials (iron, aluminum alloy and metal matrix composite with different fiber volume ratio) have been investigated to determine the best material for manufacturing. DIN 1.7035, unreinforced alumina and MMC-Al 15% Ti-C have been reported as the best materials in each groups. MMC materials has higher vibrational rigidity and by using it, about 63.65 percent weight reduction is possible. FEM results for different models including CMM and smooth model have been compared with test data. The CMM model is closer to reality and it contains all details such as barcode, data and surface defects. It is obvious that meshing of smooth surface is easier than CMM model, but some details will be ignored which could affect the results. However, it has been shown that use of CMM model creates about 5.21% errors related to test data in comparison of 2.58% when the smooth model is used.

Wheel wear is one of the major costs in railway tracks consisting of sharp curves. In this paper wear behavior of the S1002 profiles of wheels in the «Southern Line» of Iran’s railway, which consists of a large number of distinct and/or consecutive sharp curves, is studied using the field data measuring technique. Based on wear behavior analysis of all wheels, an optimal wagon maintenance technique called “first and second limits” is suggested to minimize the wagon’s cost per traveled distance. The results show that: 1) A severe wheel flange wear occurs for all wheels in comparison to the wheel tread wear in normal tracks. 2) A wagon’s detachment for repair of critical wheels on its four axles occurs at the traveled distances of 40, 000, km, 54000 km, 71000 km, and 75000 km, respectively (much less than the normal traveled distance of 500, 000 km). 3) A fifth order polynomial function can be appropriated to represent the wear behavior of the wheels. 4) By implementing the suggested technique, the cost per traveled distance decreased by 38. 64%, and the travelled distance increased by 45%.

In this article, fatigue, oxidation and creep damages in the A356.0 aluminum alloy (including an aluminum-silicon-magnesium alloy, which has been used in diesel internal combustion engines) have been investigated under isothermal and un-isothermal cyclic loadings. In order to calculate different damages, Sehitoglu’s model was utilized, in which the total damage in materials under hightemperature cyclic loadings include the fatigue damage, the oxidation damage and the creep damage. Material constants in this model for the mentioned alloy were calculated by experimental data from isothermal fatigue tests (or low-cycle fatigue tests at constant room temperature and at 250°C) and non-isothermal fatigue tests (or out-of-phase thermo-mechanical fatigue tests) were performed on test specimens. Obtained results showed that the main damage under out-of-phase thermo-mechanical fatigue loadings was the oxidation and under high-temperature low-cycle fatigue loadings was the creep phenomenon. In addition, the model used for the A356.0 aluminum alloy had generally a proper accuracy and in lower strains (higher lifetimes), the error was increased. The standard error for Sehitoglu’s model under thermo-mechanical and low-cycle fatigue tests was 0.006 and 0.005%, respectively and the relative error for the total damage was 21 and 10%, respectively.

In this article, failure and fracture mechanisms in an aluminum alloy (which has been used in diesel internal combustion engines), with and without ceramic thermal barrier coatings, have been investigated under isothermal and non-isothermal fatigue loadings. In this research, the base material is an aluminum-silicon-magnesium alloy and the thermal barrier coating includes a metallic bond coat layer with 150 µm thickness and a top coat layer, made of zirconia stabilized 8%wt. yttria with 350 µm thickness, which is applied on the substrate by the plasma thermal spray method. In order to study the failure and the sensitivity analysis, isothermal fatigue tests (or low-cycle fatigue tests at constant temperatures) and non-isothermal fatigue tests (or out-of-phase thermo-mechanical fatigue tests) were performed on test specimens. Then, fracture mechanisms in the aluminum alloy, were investigated by the scanning electron microscopy. After checking the fatigue damage and the failure analysis, the sensitivity of the material lifetime was studied based on different parameters (the temperature and the strain). Based on obtained results, the fracture surface of the aluminum alloy had dimples and therefore, its fracture was ductile. In thermal barrier coating, the damage mechanism was the separation between the substrate and the bond coat layer. The highest sensitivity was related to the strain parameter in fatigue tests of the aluminum alloy (with and without coating).

This paper presents vibration and buckling analysis of functionally gradedbeams with different boundary conditions, using reproducing kernel particle method(RKPM). Vibration of simple Euler–Bernoullibeam using RKPM is already developed and reported in the literature. Modeling of FGM beams using theoretical method or finite element technique is not evolved with accurate results for power law form of FGM with large power of “n” value so far. Accuracy of the RKPM results is very good and is not sensitive to n value. System of equations of motion is derived using Lagrange’s method under the assumption of Euler–Bernoulli beam theory. Boundary conditions of the beam are taken into account using Lagrange multipliers. It is assumed that material properties of the beam vary continuously in the thickness direction according to the power-law form. RKPM is implemented to obtain the equation of motion and consequently natural frequencies and buckling loads of the FGM beam are evaluated. Results are verified for special cases reported in the literature. Considering the displacement of the neutral axis, buckling loads with respect to length and material distribution are evaluated. For the special case of homogenous beam, RKPM matches theoretical evaluation with less than one percent error.

This research aimed to study the phenomenological pattern of obsessive-compulsive symptoms. In a cross-sectional study، 255 patients with obsessive-compulsive disorder were selected by Convenience sampling and were evaluated by Yale-Brown Obsessive Compulsive Scale in terms of symptoms and severity of OCD. Obsessions of contamination، aggressive، compulsions of washing/cleaning and checking had the highest percentage of frequency، and Obsessions of hoarding، sexual and compulsions of counting and hoarding had the lowest percentage of frequency among the thirteen groups of obsessive-compulsive symptoms. Single patients had religious obsession and repetition compulsion more than married patients. Concerns with the dirt and germs and excessive or ritualized hand washing were the most prevalent obsessive-compulsive symptom. Also، some differences were observed between the male and female patients. The obtained results showed that the phenomenological pattern of the obsessive-compulsive symptoms observed in this sample of the Iranian patients with OCD had some similarities and differences with the phenomenological pattern observed in other studies and societies.

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 here. It is assumed that the material properties vary along the beam thickness exponentially and the cracked beam is modeled as two segments connected by two mass-less springs, extensional and rotational spring. Afterward the equations of motion for the free vibrations and buckling analysis are established and solved analytically for clamped-free boundary conditions. A detailed parametric study is also performed to examine the influences of the location and depth of the crack, material properties and slenderness ratio of the beam on the free vibration and buckling characteristics of cracked FGM beams for each of the four engineering beam theories.

Researches have shown that Information and communication technology (ICT) can increase knowledge and skills of employees. The purpose of this paper is to reach an interactive empowerment model of the human capital of the revolutionary guards on the basis of information and communication technology (ICT). The method of this research has been descriptive-correlational, and from the standpoint of purpose, it can be classified among applied and developmental researches. The sample in the mentioned organization includes managers and experts of the department staff. For testing the hypotheses and the conceptual model of the research structural equations model, correlation tests, confirmatory factor analysis have been used. The results indicate that there a meaningful relation between information and communication (ICT) and empowerment of human capital. Also, the results show that human capital as a mediator variable intensifies the influence of information and communication (ICT) on the empowerment of employees in the mentioned organization.

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 between 200 to 275°C and the thermo-mechanical loading factor, which is the ratio of mechanical strain to thermal strain, is considered between 75 to 150%. The dwell time (or holding time) changes between 5 to 180 sec. at maximum temperature. The fracture surfaces of specimens are studied using Scanning electron microscope (SEM). These SEM images reveal that A356.0 alloy has a ductile behavior. The cyclic softening phenomenon is also observed during stress-strain hysteresis loops. The TMF tests results demonstrate that the dwell time bears no significant effect upon the lifetime. However, large influences for maximum temperature and the thermo-mechanical loading factor are depicted in the lifetime of A356.0 alloy.

Neonatal mortality rate is an important index of development in different communities and respiratory distress syndrome is one of the important causes. This study aimed to determine the status and effective demographic factors of neonatal mortality due to respiratory distress syndrome in Rural Area of Ahvaz city Iran. It was a case control study of all neonatal death which had recorded health center rural area in Ahwaz city, Iran (54people) during 2010-2011 as case group. The control group (54 neonates alive) was selected as same birth date, age and residence for each case. Data was collected by a self-administrate questionnaire and interview with their mother to find the cause of death. All data has entered in spss software and analyzed by using chi-square, T-test. The results showed that neonatal mortality was for male 52.4% and female 47.6%. The most important causes of death were retard fetal growth (44.4%), respiratory distress syndrome (27.7%) and cardiovascular anomalies (16.6%). The findings reported significant correlation between neonatal mortality with, birth intervals and birth weight. Improve pregnancy care, prevention of preterm deliveries, interventional programs for high risk groups, preparing the medical team for premature births and NICU equipment may have a critical role in reducing of neonatal mortality.

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 and repaired specimens is around 105%. The in depth residual stresses are measured on the repaired joints before and after fatigue loading. It can be stated that repair made a remarkable improvement into fatigue behaviour of tubular joints examined in this investigation. However, if repair is not possible, shot peening can be a good alternative to improve the fatigue life of welded joint but if repair is planned, shot peening may not be financially or technically justifiable.

An analytical solution is presented that reconstructs residual stress field from limited and incomplete data. The inverse problem of reconstructing residual stresses is solved using an appropriate form of the airy stress function. This function is chosen to satisfy the stress equilibrium equations together with the boundary conditions for a domain within a convex polygon. The analytical solution is demonstrated by developing a reference solution from which selected “measurement” points are used. An artificial error is then randomly added to “measurement” points for studying the stability of the reconstruction method utilizing Tikhonov-Morozov regularization technique. It is found that there is an excellent agreement between the model prediction and limited set of residual stress data in the sense of least-square approximation.

The objective of this article is to simulate the thermal and mechanical behavior of the diesel engine cylinder head. This finite element analysis was performed in the ABAQUS software. Thus، to identify the material behavior، results of low cycle fatigue tests at various temperatures (stress- mechanical strain hysteresis curve at the mid-life cycle) were used and material constants of the two-layer elastic-viscoplastic model were extracted. Fatigue tests were performed in the strain-controlled tensile-compressive condition on the aluminum-silicon-magnesium alloy (A356. 0). Then، by using these material constants at 25، 200 and 250°C، thermal and mechanical stresses of the cylinder head were calculated. The validation result illustrated that the elastic-viscoplastic model has a proper accuracy to predict the hysteresis behavior of the aluminum alloy. Finite elements results showed the location of cracking between valves. In addition، the calculated viscous strain cannot be eliminated، although it is less than the plastic strain.

In the present paper، a new low cycle fatigue lifetime prediction model for magnesium alloy is presented and low cycle fatigue experimental results of magnesium specimens were used to achieve this target. In such this case، an energy approach was applied to consider both stress and strain effects. This model had less material constants in comparison to other classical theories and had higher accuracy، since in the energy method، a plastic energy-lifetime relation was used، in which the plastic strain energy was equal to a multiple of plastic strain and stress numbers. In addition، the effect of the mean stress was considered in the fatigue lifetime prediction model by using a correction factor. Results of mentioned model demonstrated a proper agreement to experiments. At last، an applicable example was presented including a low cycle fatigue analysis of a diesel engine cylinder head، made of magnesium alloy، by using presented lifetime prediction model.

This paper presents the coating thickness effect on the stress distribution of a coated cylinder head. A typical thermal barrier coating was applied on a diesel engine cylinder head. Thus، the residual stress which occurred during the plasma thermal spraying was also considered. The coating system consisted of two layers; a metallic bond coat and a ceramic top coat. The bond coat thickness is considered as 50 to 250 µm and the top coat thickness was considered as 200 to 800 µm. The stress distribution was found by the finite element analysis using the ABAQUS software. Then، stress distributions were compared for various coating thicknesses. Finally، optimized values for each layer are suggested.

The beneficial effects of shot peening on fatigue life of mechanical components are wellknown. 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 elasticplastic simulation of shot peening was presented. Effect of shot velocity and size on surface morphology after shot peening were examined. Fatigue crack initiation life calculation of shot peened specimens revealed that beneficial effect of shot peening significantly vanishes in the case of high velocities and bigger shots.

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. The results showed dominance of mode I fracture on crack growth, and based on the observation of strain energy density factor versus crack orientation, the results also suggest that depending on the crack length, the most critical orientations of cracks are at 00 to 200 outward the contact zone. Good agreement was observed between the results of this semi-analytical approach, and the corresponding results from finite element method, for selected crack lengths and orientations.

The premature breakage in some four cylinder diesel engine crankshafts was reported. All crankshafts were failed from the same region. Failures had been occurred in the first crankpin, the nearest crankpin to the flywheel. Dynamic analysis and finite element modelling were carried out to determine the state of stress in the crankshaft. FEM results revealed that the first crankpin fillet is the most vulnerable point to fracture. Soderburg diagram of the studied crankshaft showed that the service operation point, which stands for mean and alternating stresses of the critical region (first crankpin fillet) was located in the safe region. Therefore, it can be concluded that fatigue fracture has not occurred in the crankshaft. SEM images of the fractured surface also showed cleavage fracture and put in evidence that the failure was brittle fracture. No sign of fatigue failure was observed. The fracture may be caused by an overload. However, the results suggest re-evaluation of the design and manufacturing. The fillet rolling may play an important role in this matter. Optimization of the fillet rolling process by changing process parameters has been recommended to the manufacturer. This recommendation has been adopted by the manufacturer and no further fracture has been reported since.