Sharif Digital Repository

The present study investigates experimentally the effects of different shot peening treatments, including conventional, severe, over, and re-shot peening on microstructure, mechanical properties, and fatigue behavior of AISI 1050 mild carbon steel. Different shot peening treatments were performed using various effective parameters by considering the influences of increasing Almen intensity and coverage. Optical microscopy and field emission scanning electron microscopy observations and X-Ray diffraction measurements were carried out to analyze grains refinement in each shot peening treatment. Microhardness and residual stress measurements were taken from shot peened surfaces to the core... 

Offshore platforms have had diverse applications in the marine industry, for example, oil or gas platforms can provide facilities to store the oil and gas before transport those to refineries. Offshore wind turbines are another well-known use of the offshore platform for generating power. As platforms encounter various strong forces from water and wind currents, the materials used for these structures are mainly steel or concrete. These platforms are classified into different types, according to the depth of water and their applications. In addition, offshore platforms, as artificial reefs may be used for decades at different marine conditions. Consequently, their design and maintenance are... 

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... 

The main aim of the present paper is to assess the fatigue lifetime of ductile cast iron knuckles as one of the critical components of an automotive steering system. To this end, a real driving path, including various maneuvers, such as acceleration, braking, cornering, and moving on various types of road roughness, was considered. Different load histories, which are applied on various joints of the component (i.e., lower control arm, steering linkage, and Macpherson strut), were extracted through Multi-Body Dynamics (MBD) analysis of a full vehicle model. The achievements of previous studies have proved that the steering knuckle fails from the steering linkage and due to the rotational... 

Ultrasonic Testing (UT) is one of the well-known Non-Destructive Techniques (NDT) of spot-weld inspection in the advanced industries, especially in automotive industry. However, the relationship between the UT results and strength of the spot-welded joints subjected to various loading conditions is unknown. The main purpose of this research is to present an integrated search system as a new approach for assessment of tensile strength and fatigue behavior of the spot-welded joints. To this end, Resistance Spot Weld (RSW) specimens of three-sheets were made of different types of low carbon steel. Afterward, the ultrasonic tests were carried out and the pulse-echo data of each sample were... 

In the present study, the main purpose is investigation of the coatings thickness effect on the fatigue life of AISI 1045 steel. Herein, two different coatings of warm galvanization and hardened chromium have been used on the specimens. Fatigue tests were performed on specimens with different coating thicknesses of 13 and 19 µm. In the high-cycle level, S–N curves are extracted with 13 points for each sample. The results show that the galvanized coating is the most appropriate coating with low thickness, but with significant increasing of coating thickness, the best choice is hardened chromium coating. However, artificial neural network (ANN) has been used as an efficient approach instead of... 

In the present research, the authors have attempted to examine the compressive strength of conventional concrete, which is made using different aggregate sizes and geometries considering various curing temperatures. To this end, different aggregate geometries (rounded and angular) were utilized in various aggregate sizes (10, 20, and 30 mm) to prepare 108 rectangular cubic specimens. Then, the curing process was carried out in the vicinity of wind at different temperatures (5◦ C < T < 30◦ C). Next, the static compression experiments were performed on 28-day concrete specimens. Additionally, each test was repeated three times to check the repeatability of the results. Finally, the mean... 

Severe shot peening (SSP) process is widely used for surface nanocrysallization of a bulk material that demonstrates excellent mechanical properties compared with its coarse-grained equivalents. In this study, a plastically deformed surface was produced with nanostructured grains on different materials of AISI 1045, 1050, and 1060 carbon steels by means of SSP. Shot peening was applied with a wide range of Almen intensities and coverages. Optical microscopy, scanning electron microscopy, field emission scanning electron microscopy, high resolution transmission electron microscope observations, and X-ray diffraction analysis were employed to analyze the mechanism of grain refinement... 

In the present study, the main purpose is to detect the most key factors of shot peening (SP) process on the microhardness, grain size, and residual stress of AISI 1060 high carbon steel. The specimens were treated using various types of SP process namely conventional shot peening and severe shot peening. Several experiments were performed to study metallurgical and mechanical properties of AISI 1060 steel. Almen intensity and surface coverage from one side and microhardness, grain size, and residual stress from the other side were considered as input and output parameters for the design of experiment methodology, respectively. The L18(21and31) mixed level of Taguchi orthogonal array design... 

Petrochemical components, especially superheater internal parts, work under very harsh conditions and in destructive environments, such as proximity to the high temperature caused by the fire, surrounded by corrosive gases, effects of hydrogen released by burning gas or incomplete burning. All these factors along with loading factors and other destructive phenomena such as creep at high temperatures directly affect the mechanical behavior of components. In other words, because of these conditions, the components will have different mechanical behavior compared to the non-operated components. In the present research, a case study was conducted on the failed bolts supporting long U-shaped... 

One of the major challenges in the manufacturing parts, especially metals, is turning with good/excellent surface quality, which has a significant effect on the fatigue strength of the industrial components. Selecting incorrect or unsuitable values of machining parameters leads to vibration instability in the cutting tool and as a result, excessive roughness is created on the product’s surface. Therefore, one of the ways to reduce the roughness factor and increase the product fatigue life is to control the relative slip and vibration between the cutting tool and the workpiece. To achieve this goal, the authors attempted to investigate the simultaneous effects of tool overhang and cutting... 

The main purpose of the present research is to investigate the shunting phenomenon in a three-sheet RSW joint usingfinite element simulation. To this end, a three-sheet resistance spot weldingjoint was simulatedas an electrical-thermal-mechanical couplingproblem.Tovalidate the presentedsimulation, the finite element results were compared with the experimental results, including nugget size and geometric shapein theresistance spot weldingjoint.Afterwards, the multi-spot welds of three-sheet low carbon steels with the same thicknesses were analyzed considering the sequential distance of 45 mm. Various techniques, includingnewspot-welddiametermeasurement, electrical current density, electrical... 

In the present paper, a steering knuckle of a passenger car that serves as a highly critical component from the safety point of view, is considered to evaluate accuracy some of categories of the multiaxial fatigue criteria, through comparing their predictions with the experimental results. This component is subjected to the highest road- and steering-induced random and non-proportional loads that are exerted on several points of the component. The mechanical properties and fatigue strengths are determined experimentally and the fatigue life assessment tests are performed by the authors. Quantometric analyses and scanning electron microscope (SEM) have been employed to detect the failure... 

During the spot welding process, it is always possible to be made defects, and the most important reasons for defects can be due to incorrect settings of current, force, and time. In other words, at different time intervals depending on the working conditions of the welding machine (i.e., both manual and robotic machines), such as the erosion of the electrode head, it is necessary to optimize the welding parameters and apply the essential changes in the next settings. The presence of various defects reduces the quality and strength of spot welds and eventually structures, which is one of the main concerns in automotive, aerospace, and marine industries. Therefore, in the present research,... 

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 simulation presented in this study by comparison with the experimental results for the spot diameter, various cases of spot welds were analyzed based on the design on experiment (i.e., Taguchi method). Six variables including electrode force, electric current, and quadrilateral times (squeeze, up-slope,... 

In the present paper, the author has attempted to examine fatigue life of automotive safety components under axial variable amplitude loading conditions. To this end, the time components of stress tensor in the critical area of the knuckle and Liu-Zenner criterion were used to calculate the time history of equivalent stress. Then, the probability distribution function (PDF) of stress was extracted by applying the stress level counting technique. The Fourier curve fitting method was employed in order to formulate the PDF. Subsequently, the fatigue life of the component was estimated using the probabilistic approach. Finally, the results of the higher order of Fourier curve fitting and... 

This article presents the static performance of composite steering knuckle due to drive on an equivalent road, including different types of roughness and maneuvers. To achieve this purpose, the driving of a full-vehicle model was simulated using the multi-body dynamics (MBD) method, and the imposed loads on connection points of the steering knuckle to different components of the suspension system were extracted considering various maneuvers. Next, CATIA software was used to prepare a smooth model of the steering knuckle by employing coordinate measuring machine (CMM) data. Stress analysis was performed under the maximum value of the loading history in finite element (FE) software.... 

Abstract: This study investigates and compares the effects of different shot peening treatments including conventional and severe shot peening on microstructure, mechanical properties, fatigue behavior, and residual stress relaxation of AISI 1060 steel. Shot peening treatments were applied with two Almen intensities of 17 and 21 A and a wide ranges of coverage (100%–1500%). Various microstructural observations were carried out to analyze the evolution of microstructure. Microhardness, residual stress and surface roughness measurements and also axial fatigue test were performed. Moreover, the extent of the residual stress relaxation during cyclic loading was investigated by means of XRD... 

Abstract: This study investigates and compares the effects of different shot peening treatments including conventional and severe shot peening on microstructure, mechanical properties, fatigue behavior, and residual stress relaxation of AISI 1060 steel. Shot peening treatments were applied with two Almen intensities of 17 and 21 A and a wide ranges of coverage (100%–1500%). Various microstructural observations were carried out to analyze the evolution of microstructure. Microhardness, residual stress and surface roughness measurements and also axial fatigue test were performed. Moreover, the extent of the residual stress relaxation during cyclic loading was investigated by means of XRD... 

Vehicle speed control is one of the most important factors at increasing safety, reducing the number and severity of road accidents. Also, other factors such as inappropriate designing, the overuse of speed bumps, nonconformity to the prevailing standards of the world in construction, maintenance, and repair of roads can cause damage to the car suspension and consequently brings the discomfort of car occupants when crossing the actual road under different driving conditions (various speeds and maneuvers). In the present paper, the effect of different vehicle velocities on the comfort of occupants was investigated empirically. To this end, a passenger vehicle was driven at different constant...