Volume 62, Issue 4

Components often manifest varied local behavior due to their manufacturing process. In order to be able to determine local material behavior in the best possible way, it is necessary to take specimens from the area under investigation. Due to constant developments in efficiency and lightweight construction, it is difficult to produce standard-compliant specimens from the examined area in a component. For this reason, specimens with smaller dimensions are often taken. Through the investigation of the influence of size in the area of high-cycle fatigue, it is well known that the size of a test specimen influences its lifespan. Not so much is known about the influence of specimen size on the behavior of material in the field of low-cycle fatigue (LCF). In this work, tensile, LCF and thermomechanical fatigue tests are performed using AlCu4PbMgMn with varied specimen geometries, the smallest test diameter being 3 mm, the largest 7.5 mm. The results of the tensile test show that the mean values of tensile strength for both diameters is within one percent. At LCF load and thermomechanical load, there are no or only slight deviations in deformation behavior. The low cycle fatigue behavior at RT is identical for both diameters. However, the results show that stress-strain behavior is the same for both test diameters, and fatigue behavior is the same, except in tests with high strain amplitudes and temperature.

Fused deposition modeling is a layer-by-layer 3D printing technology used to additively manufacture polymers. A major benefit of 3D-printed polymers is the option of tailoring their mechanical properties by varying the process parameters. In addition, the present study investigates the influence of the filling degree (50 % or 100 %) and the nozzle temperature during manufacturing on the mechanical properties of 3D-printed poly-ether-ether-ketone (PEEK) material. PEEK samples were built either compact (filling degree 100 %) or closed-cell porous (filling degree 50 %), using three different nozzle temperatures (390 °C, 430 °C and 470 °C). In static bending tests, the bending properties were evaluated and compared with injection molded PEEK samples. Bending strength and modulus increased up to 21.1 %, when the nozzle temperature was increased and up to 40.8 % when the volumetric filling was altered. The results indicate that nozzle temperature and volumetric filling can be altered to tailor the bending properties of 3D-printed PEEK for particular applications. However, the mechanical properties of the 3D-printed samples determined in the current study could not achieve those of the properties of the injection molded PEEK.

In this study, the stress on portal crane components at various payloads has been investigated theoretically, numerically and experimentally. The portal crane was computer-aided modeled and finite element analyses were performed so that the most stressed points at the each trolley position investigated on the main girder could be determined. In addition, the critical points were marked on the portal crane, and strain gages were attached to the those critical points so that stress values could be experimentally determined. The safety factor values at different payloads were determined by using finite element simulation. Results indicate that the most stressed component in the examined portal crane is the main girder. Experimental results indicate that the maximum stress value on the main girder is 3.05 times greater than the support legs and 8.99 times larger than the rail. Abstract In this study, the stress on portal crane components at various payloads has been investigated theoretically, numerically and experimentally. The portal crane was computer-aided modeled and finite element analyses were performed so that the most stressed points at the each trolley position investigated on the main girder could be determined. In addition, the critical points were marked on the portal crane, and strain gages were attached to the those critical points so that stress values could be experimentally determined. The safety factor values at different payloads were determined by using finite element simulation. Results indicate that the most stressed component in the examined portal crane is the main girder. Experimental results indicate that the maximum stress value on the main girder is 3.05 times greater than the support legs and 8.99 times larger than the rail.

This article presents an implementation of one of the latest optimization methods of obtaining light vehicle designs. First, the problem of coupling with a bolted rim is optimized using the butterfly optimization algorithm (BOA). Finally, the BOA is used to solve the shape optimization of a vehicle suspension arm. It is utilized from the Kriging metamodeling method to obtain equations of objective and constraint functions in shape optimization. At the end of the research effort in this paper, the weight reduction of the suspension arm by using the BOA is 32.9 %. The results show the BOA’s ability to design better optimum components in the automotive industry.

In order to present an integrated approach to optimal automobile component design, this research is focused on a shape optimization problem of a bracket using moth-flame optimization algorithm (MFO) and response surface methodology. First, the multiple disc clutch brake problem is optimized using the MFO. Finally, the design problem is posed for shape optimization of the bracket with a mass objective function and a stress constraint. Actual function evaluations are based on finite element analysis while the response surface method is used to obtain the equations for objective and constraint functions. Weight reduction of the bracket is 45.2 % using the MFO. The results show the ability of the MFO to optimize automobile components in the industry.

Porous graphitic carbon nitride nanosheets were synthesized by the thermal condensation method using various precursors such as urea and melamine. Relevant properties of as-synthesized products were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and differential thermal analysis (DTA). The overall results suggest that the formation of porous graphitic carbon nitride nanosheets with a varied morphology can be achieved using diverse precursors through this process. Based on this product yield analysis, it is suggested that melamine and the lower synthesis temperature be selected to achieve the higher yield of graphitic carbon nitride production. The present work provides a facile and economic method for controlling the morphology and properties of graphitic carbon nitride products.

In recent years, metaheuristic methods have been preferred for the optimum design of automobile components, and important results have been accomplished. In this paper, a comparison of the whale optimization algorithm (WOA), the ant lion algorithm(ALO), and the spotted hyena optimization algorithm (SHOA) are presented to show how these optimization methods have been exploited to achieve weight reduction in an automobile brake pedal while maintaining stress requirements. This research is the first in the literature elucidating the application of the SHOA for the optimum design of automobile components. Optimization using the SHOA results in a reduction of 18.1 % of brake pedal weight.

In this study, multi-layered composite pipes with varied orientation angles and subjected to internal pressure were investigated by using the 3-D finite element method (FEM) and through experimental tests. The composite pipes were made of E-glass and T300/934 carbon fiber. The studies were carried out experimentally, analytically and numerically. The T300/934 carbon fiber reinforced composite pipes and E-glass reinforced composite pipes were given numerical model codes via ANSYS 14.5 software. These models were then compared with analytical results in the literature and with the experimental results. Finite element analyses (FEA) were carried out to predict failure loads. Each layer of the composite pipes was numerically examined from various orientation angles. Hoop and shear stress wereobtained numerically for each layer. Radial strain and radial stress were achieved in the radial direction of the composite pipes. Shear extension coupling was considered because the layup angles with + θ and - θ layers were in varied radii. Subsequently, the effects of the orientation angles were examined for all models. Moreover, it was found that an embedded adhesive joint is important for industrial applications.

Compound extrusion (CE) is a newly developed plastic deformation technique which combines direct extrusion (DE) with a two-pass equal channel angular extrusion (ECAE). This paper focuses on the strength, ductility and anti-corrosion properties of an NaCl solution at certain concentrations and the wear-resistance of dry sliding AZ61 magnesium alloy prepared by CE and DE. It is found that the strength and elongation of the AZ61 alloy prepared by CE are enhanced because of grain refinement. Furthermore, AZ61 magnesium alloy made by CE displays higher corrosion and wear resistance than that prepared by DE. Experimental results prove that CE is a prospective manufacturing method for improving the mechanical properties, anti-corrosion and anti-wear of AZ61 magnesium alloy.

Silver and silver(Ag)-graphene(Gr) nanocomposite coatings were prepared via direct current, pulse current and pulse reverse current on copper electrical contacts for evaluating electrical contact performance. The effects of the addition of Gr and current types on microstructure, crystallographic orientation, mechanical properties and electrical contact performance were investigataed via a scanning electron microscope, an X-Ray diffractometer, microhardness test device and an electrical contact test device, respectively. The addition of Gr changed the Ag surface morphology and decreased grain sizes. Moreover, the addition of Gr significantly improved arc erosion resistivity and decreased the average working temperature during the contact test. In addition, pulse current and pulse reverse current provided a significant improvement in microhardness and electrical contact erosion resistance owing to increased embedded graphene amounts in silver layers.

In this study, the variation of thermal conductivity and density of 15 wt.-% boric acid - 85 wt.-% sepiolite, 30 wt.-% boric acid - 30 wt.-% sepiolite - 40 wt.-% perlite, 30 wt.-% boric acid - 30 wt.-% cordierite - 40 wt.-% perlite and 30 wt.-% boric acid - 30 wt.-% alumina - 40 wt.-% perlite compositions at 700 °C and 900 °C sintering temperatures were investigated. The results show that increasing the amount of boric acid and decreasing the sintering temperature lead to an improvement in thermal insulation properties. There is a direct relation between the thermal conductivity and density of the specimens. Both physical properties change with a change in the sintering temperature and the composition characteristics. Minimum thermal conductivity has been observed in a specimen consisting of 30 wt.-% boric acid - 30 wt.-% alumina - 40 wt.-% perlite.

Computer-based design and optimization have become increasingly important in recent years. This paper has investigated the stress concentration factors (SCF) K t for shoulder filleted shafts with a hole and without a hole. This study contains two types of shoulder filleted shafts, i. e., a stepped bar of circular cross section with shoulder filleted and a tube with filleted shafts under tension stresses. Investigations on SCF that have been carried out in experimental and theoretical studies, were updated and validated for 2 types of shafts. The charts have been converted into numerical value using high precision computer techniques. Dimensional ratios and SCF were determined using previous work charts. This study determines maximum stresses for shoulder filleted shafts by three dimensional finite element analysis (FEA) and artificial intelligence techniques. A set of SCF charts was converted into numerical values and this data was organized and stored in an Excel file. ANSYS models were created and applied the boundary conditions on the models. And also mesh optimizations were performed. Artificial neural networks (ANN) models were designed using previously collected and verified data. Previous works, ANSYS and ANN results were compared to each other. As a result, ANN model and chart results show a good agreement. The usage of ANN model does not require any mathematical formulae or converting the numerical data action for determining the K t result for shafts. ANN model usage was identified as a very useful and practical method.

Fiber reinforced plastic (FRP) plays an increasingly important role in many engineering fields due to its advantages of light weight, low cost, simple maintenance, and excellent corrosion resistance. The conventional contact methods for deformation measurement, such as strain gauge and mechanical extensometer, have some shortcomings in measuring the strain of FRP rebar specimens with spiral curved surfaces. Therefore, the non-contact three-dimensional digital image correlation (3D-DIC) technique was employed to determine the tensile mechanical properties of two types of FRP rebar specimens, i. e. glass FRP (GFRP) and carbon FRP (CFRP) specimens. Uniaxial tensile tests with three different loading rates were conducted to obtain the stress-strain curves, elastic modulus, tensile strength and percentage total extension at maximum force of these two FRP specimens. Experimental results indicate that the axial-strain field of all FRP rebar specimens present nonuniform distribution and that the stress of GFRP and CFRP rebars varies linearly with the strain. Moreover, no yielding phenomenon was observed from the stress-strain curves, which indicates that both GFRP and CFRP rebars belong to the group of typical brittle materials. The dispersion of elastic moduli obtained using 3D-DIC is better than that using a clip-on extensometer, which demonstrates the validity of 3D-DIC for the determination of tensile mechanical properties of FRP rebars with spiral curved surfaces.

Fatigue strength of cyclically stressed components can be affected by various sub-microdefects such as dislocations, vacancy and micropores. An interaction of dislocations and non-metallic inclusions, the formation of pores and various cracking mechanism have been described.