Volume 62, Issue 3

Nanocrystalline nickel-iron layers are produced electrochemically on copper discs by varying the current density and then annealed in a vacuum furnace at a temperature range between 200 and 800 °C. Grain size, iron content, texture and microstrain of the microstructure are primarily characterized by X-ray diffraction (XRD). Instrumented indentation tests and microbending tests for mechanical characterization are carried out. The iron contents of the investigated layers are 5.7, 8.8, 13.5 and 17.7 wt.-%. By varying the annealing temperature, the reduction of the microstrains is initiated at 200 °C and ends at a temperature of about 280 °C. Primary recrystallization starts slightly higher at 220 °C and is completed at 300 °C. With higher iron content, the indicated temperatures shift to slightly higher values. Indentation modulus, Young's modulus, indentation hardness and strength change considerably after the annealing treatment. Fracture strain at the edge, as a measure of ductility, decreases immediately after annealing at 200 °C to 0 %. Low annealing temperatures occurring before the beginning of primary recrystallization lead to an increase in indentation hardness and 0.01-% offset bending yield strength R p0.01 ∗ as compared to the electrochemically deposited initial state. After annealing at high temperatures, the mechanical parameters are mostly below the initial values for electrochemical deposition. Hall-Petch (HP) behavior is observed for R p0.01 ∗, both for the electrochemically deposited specimens down to almost 6 nm and for the specimens annealed at high temperatures. Specimens annealed at low temperatures deviate from the HP straight line to higher values. In this case, an increase in strength is assumed to be due to the very small nanocrystalline (nc) grain sizes, segregation at the grain boundaries and a decrease in dislocation density. Indentation hardness measurements show almost no dependence on D −0.5 for the electrochemically deposited specimens and also for annealed specimens below 30nm grain size. Above 30nm, the indentation hardness values are considerably higher than for the HP straight line. Overall, the hardness and strength values of the nc specimens, electrochemically deposited or additionally annealed, are significantly higher than those of the microcrystalline (mc) specimens.

This article is on the optimum design of driver seats in commercial vehicles, which are expected to provide high comfort to drivers during long travel distances. This comfort is usually achieved through a pneumatic actuation and suspension motion that provides alignment with the road. Moreover, the seat which directly hosts the driver is supposed to ensure safety and best working conditions. The result is that seat weight increases considerably when all comfort, safety, and reliability features are incorporated. But, weight is an important factor in automotive transportation as it results in increased cost and also undesired emission values. For this reason, even the smallest reduction in the weight of commercial vehicles can lead to high amounts of savings. In this study, weight reduction and structural strengthening are targeted together with the help of topography optimization. Optimizations were made, and in these studies, the desired lightness and target strength levels were achieved. As a result of the study, optimization, weight reduction, strengthening, product performance, production cost and material cost outputs were considered and remodeled for better quality. An ECE R14 seat belt pulling test was simulated as an ultimate solution, and the expected results were obtained yet again. With the help of optimization and simulation tools, the appropriateness of the outcomes was assessed at the end of the study and found to achieve a 7 % reduction in weight and 13 mm displacement improvement.

In this paper, a novel hybrid optimization algorithm is introduced by hybridizing a Harris hawks optimization algorithm(HHO) and simulated annealing for the purpose of accelerating its global convergence performance and optimizing structural design problems. This paper is the first research study in which the hybrid Harris hawks simulated annealing algorithm (HHOSA) is used for the optimization of design parameters for highway guardrail systems. The HHOSA is evaluated using the well-known benchmark problems such as the three-bar truss problem, cantilever beam problem, and welded beam problem. Finally, a guardrail system that has an H1 containment level as a case study is optimized to investigate the performance of the HHOSA. The guardrail systems are designed with different cross-sections and distances between the posts. TB11 and TB42 crash analyses are performed according to EN 1317 standards. Twenty-five different designs are evaluated considering weight, the guardrail working width, and the acceleration severity index (ASI). As a result of this research, the optimum design of a guardrail is obtained, which has a minimum weight and acceleration severity index value (ASI). The results show that the HHOSA is a highly effective approach for optimizing real-world design problems.

As a result of the requirements imposed by international organizations and governments on fuel emissions, there is a growing interest in the design of lightweight vehicles with low-fuel emissions. Metaheuristic methods have been widely used for the optimum design of vehicle components in recent years for which successful results have been reported. Encouraged by such results obtained from the methods mentioned, the Henry gas solubility optimization algorithm (HGSO), a recently developed optimization method, is used to solve the shape optimization of a vehicle brake pedal to prove how HGSO can be used for solving shape optimization problems. This paper is the first application of the HGSO in connection with real-world optimization problems in the literature. The results show HGSO's ability to design better optimal components in the automotive industry.

Fatigue testing experiments and computer-simulations have been conducted for notched specimens of two cutting-tool materials: high speed steel (M42 HSS) and cemented carbide composite (WC-10Co). The effects of varying loads and notches on the fatigue lives of M42 HSS and WC-10Co, including a comparative study of the fatigue behavior of the two cutting-tool materials, have been reported. The fatigue behavior of the two cutting-tool materials has been investigated by developing their S-N curves as well as through an examination of the fracture surfaces of the materials. A fatigue life of 10 7 cycles corresponding to a fatigue limit of 430 × 10 6 N × m −2 was determined for M42 HSS. It has been found that a reduction of stress amplitude by 60 × 10 6 N × m −2 results in an increase of fatigue life by around 175 percent for the notched specimens of cemented carbide. The computer simulation studies involved the use of ANSYS finite element analysis (FEA) as well as SolidWorks software packages. Both experimental and simulation results were found to be in agreement. These research findings might enable engineers to select a suitable cutting tool material with a notch for application under cyclic stressed machining.

Bone cement is a polymer used as filler material for the attachment of bone to implants in cemented joint replacements. Stronger interdigitation of the bone cement with both the implant and the bone provides a more durable surgical intervention. In previous studies published in the literature to date, tensile, shear and multi-axial stress occurring on the interfaced surfaces of the cement due to static and dynamic loads acting on the femur have been tested. This study investigated the impact strength of both implant-cement and cement-bone interfaces in a cemented implant. The effects of different implant materials, blasting sand particle size and cement mantle thickness on impact strength were investigated. It was determined that the surface roughness values of the implant materials increased as larger blasting sand particles were applied. As the surface roughness increased, the interfacial impact strength also increased. The impact strength of the cement-bone interface was higher than that of the implant-cement interface. The optimum mantle thickness in terms of impact strength was found to be 2 mm. Under impact force, failure will occur at the implant-bone cement interface.

Two round bar tensile samples (without notch and with notch) and two temperatures, namely 100 °C and 150 °C, have been used to observe the effect of notch and temperature on stress corrosion cracking in steel. The stress corrosion cracking sensitivity index of the tensile strength and elongation was calculated by means of data from a stress-strain curve. The fracture surface of the high strength steel was analyzed by scanning electron microscopy (SEM). In this way, the effect of notch and temperature on stress corrosion crack of the steel was determined. The results of a constant load tensile stress corrosion test show that at the same stress level and temperature, the stress corrosion cracking performance of an unnotched round bar tensile specimen was better than that of the notched specimen, and the unnotched steel had better corrosion resistance. Simultaneously, it was observed that the samples at 100 °C exhibited a lower stress corrosion cracking sensitivity index at the same stress level compared to the higher temperature (150 °C), which means that the steel showed a better corrosion resistance at a temperature of 100 °C. The fracture morphology analysis shows that the fracture surface of the unnotched round bar tensile samples had a dimple fracture, but the notched round bar tensile samples had a characteristic intergranular fracture due to the combined action of stress and the corrosive solution. Temperature increased the corrosion's velocity and the stress concentration in the notch causing an increase in dislocation after plastic deformation were the main reasons for the increase in stress corrosion sensitivity of the steel. It can be seen that these two factors, the temperature and the notch both increased the stress corrosion cracking sensitivity of the steel in organic salt drilling fluid, but the notch had a greater influence.

The measurement of wear volume in tribological tests is a critical step in wear characterization. There are many methods and instruments for wear volume measurement reported in the literature and most of them have already been commercialized. These commonly determine wear volume by means of tactile or optical methods, requiring costly and/or specifically developed instruments. In this study, an alternative method for determining wear volume, obtained after a sliding test with a pin-on-disk type apparatus, using focus variation microscopy is reported. A reflective-type light microscope, equipped with a digital camera, together with a range of computer software was used for the line profiling of wear scars, rather than a specialized focus variation microscope. In this study the relatively “shallow” depth of field at the high magnification of the light microscope was precisely used for determining surface line profiles on both slightly and heavily worn specimen surfaces after a series of tribological wear tests. Results of the study method were compared with both profilometric measurements obtained from a 3D optical microscope and with those obtained using a previously reported method. This comparison showed that the method under development and tested in this study yielded successful measurements, comparable to those obtained using the much more expensive 3D optical microscope.

In the dry galvanizing process, pipes are subjected to chemical treatment and then dried in a continuous drying furnace which is followed by the galvanizing kettle. However, drying furnaces used in a dry galvanizing process, lead to some problems. The impossibility of achieving a uniform temperature distribution along the pipe in conventional drying furnaces and the negative impacts thereof on the product quality make it inevitable to seek new approaches towards pipe drying. In this study, instead of in a drying furnace, the fluxed pipes were dried at the line by means of induction heating. By using an induction heating system, the pipes were heated up much more uniformly than by the conventional drying method. It is observed that the temperature change along the pipe surface varied by ±5 °C while it was 15–20 °C in the conventional system. In addition, the problem of black spots, seen very frequently at galvanizing plants, was eliminated completely.

The present work reports new results about developments in the flash butt welding of CT-90 (Coiled Tubing-90) steel. In this study, the flash-butt welding process, microstructures and mechanical properties of the weldet joint are investigated. The main findings are as follows: upset current has a significant effect on microstructures and the mechanical properties of a welded joint. When the upset current value is 357.9 A, polygonal ferrite and pearlite occur in the weld metal, and the mechanical properties of joint are at their best with a yield strength (YS) in the joint of 635 MPa, ultimate tensile strength (UTS) of the joint at 706 MPa, impact-absorbed energy of the weld at 112 J × cm −2 , and with the impact-absorbed energy of the heat affected zone at 166 J × cm −2 .

Prediction of unstable fractures or growth of existing cracks represents the fundamental problems in fracture mechanics. Experimental measurement of the propagation force of pre-cracks obtained by fatigue plays an important role in this prediction. The stress intensity factor at the crack tip (K IC ), crack tip opening displacement (CTOD) and the crack tip opening angle (CTOA) are the most recognized parameters used in fracture mechanics [1]. This paper is focused on the determination of the fracture toughness, CTOD in the weld and the interface between heat affected zone/fusion line of the API 5L X65M steel pipe lines having a diameter of 42″ (1066.8 mm), a wall thickness of 31.75 mm, welded by the MAG process. To determine the crack tip opening displacement (CTOD), specimens subjected to bend in three-points (SENB = single edge notched bend) were used.

Multi directional turning tools can perform various operations such as cutting, grooving and profile turning with high performance on their own. Tool change and setting times are reduced considerably with the use of these tools. This study discusses surface roughness and wear behavior for different cutting speeds, chip breaker types and nose radii in the rough turning of AISI 4140 steel with physical vapor deposition coated cemented carbide multi directional turning tool. Experimental results based on Taguchi's L8 orthogonal array are assessed through the analysis of variance, main effects and interaction plots. As a result, optimum roughness and an roughness increase percentage are obtained at 0.803 μm and 19.92 %, respectively.

In the present work, joining of dissimilar aluminum alloys AA6061 and AA8011 was carried out by FSW butt joint. The Taguchi L 9 orthogonal array design of experiments was adopted for the experiments to estimate optimal process parameters such as rotational speed, welding speed and axial force using Minitab 18. In ANOVA analysis, the priority of input parameters and the contribution percentage of each factor were determined through response and analysis of variance tables. From the ANOVA analysis data, tensile strength, impact strength and hardness of substantial values were optimized. Further thermal analyses of optimized values were examined through COMSOL Multiphysics 5.3b model which also successfully predicted the maximum welding temperature obtained from pin and work piece interaction of each position during welding. In this investigation the transient temperature levels of the weld zone during welding and after welding were investigated. Likewise the curves of transient temperatures were plotted with the aid of Origin Pro 2018.

In order to study the influence of steel fiber on the damage characteristics of concrete under uniaxial tension, based on the improved G-P algorithm, the acoustic emission event rate correlation dimension (hereinafter referred to as correlation dimension) curves of steel fiber reinforced concrete under uniaxial tension failure before and after peak stress were obtained, and the evolution characteristics of the correlation dimension of concrete with different steel fiber contents analyzed. According to the correlation dimension, the R value, the F value and the variance (σ 2 ) were proposed to measure the effect of steel fiber on the micro-failure characteristics of concrete. The results show that before peak stress, the correlation dimension first increases and then decreases with an increase in the stress level; the mean correlation dimension increases with an increase in steel fiber; the addition of steel fiber reduces the R value by 36.13 % to 65.04 % compared with plain concrete, but has little effect on the F value. After peak stress, with a decrease in the stress level, the correlation dimension decreases with some fluctuation; and the variance of correlation dimension decreases with the increase of steel fiber; whereas the order degree of the system microstructure, measured by the correlation dimension, increases with an increase in steel fiber. These results can be used for structural health monitoring and the non-destructive testing of steel fiber reinforced concrete, which have an important value for enriching the early warning of fracture failure in steel fiber reinforced concrete based on acoustic emission technology.