Volume 65, Issue 1

Major components of electrical machines are iron cores made of stacked electrical steel sheets. In this paper, pulsed laser beam welding in vacuum is used to join the individual electrical steel sheets. Three different non-grain-oriented electrical steel alloys are investigated and joined by individual spot welds. The influence of pulsed laser beam welding in atmosphere as well as in vacuum on the welding result and the tensile strength of the welded joint is discussed. The results show that the insulation coating of the electrical sheets has significant effects on the grain structure as well as the hardness of the weld spots. These effects can be reduced with decreased working pressure, which reduces the power loss of iron cores. The reduction of the working pressure and the associated reduction of the vapor plume, which appears to reduce the energy input into the component depending on the material and coating, results in an increase of the melt volume and the joint cross sectional area. The tensile strength of the performed welds was tested and interpreted with respect to the influencing process parameters.

This paper investigates and compares the experimental results of fracture characteristics in various polypropylene fiber-reinforced concretes (high strength concrete, lightweight concrete, and engineered cementitious composite) on 90 three-point bend (notched and un-notched) beams. Five widely used fracture mechanics testing methods, such as work of fracture method, stress-displacement curve method, size effect method, J integral method, and ASTM E399, were used to investigate the fracture behavior. Results have demonstrated that fracture energy and fracture toughness improved as the dosage of polypropylene fibers increased in concretes. However, this improvement was different in concretes owing to various results of fracture mechanics testing methods and different properties of each concrete. Aggregates played significant role in the performance of polypropylene fibers on the fracture behavior of concretes. Among testing methods, the ASTM E399 showed the lowest values for the fracture toughness of concretes. Both work of fracture and stress-displacement curve methods exhibited appropriate results for the fracture energy of polypropylene fiber-reinforced concrete composites. The accuracy of size effect method was acceptable for determining size-independent fracture parameters of plain high strength and lightweight concretes. Furthermore, the J integral method showed more relevant results for the fracture toughness of polypropylene fiber-reinforced engineered cementitious composite.

Microcracks are always present in the deposited metal of 10MnNi2MoVA steel weld seam, which affects the safety of the power plant steam pipeline. It is important to investigate the effect of heat input on the hot cracking sensitivity of the EA395-9 weld metal. In this work, the deposition of the weld metal of EA395-9 was prepared, then the hot cracking tendency of the weld with the different heat input was analyzed and observed. The results show that the moderate welding heat input can help to avoid hot cracking.

Boron nitride (BN) nanostructures are a relatively new type of filler and highly convenient for aerospace applications due to its high strength, excellent thermal resistance, and acting as radiation shielding. Cubic BN (c-BN) nanoparticle is a structural form in crystalline shape and offers outstanding characteristics because it can provide additional improvements through the thickness of laminated composites. This study investigates the effects of c-BN nanoparticle addition on the wear properties of carbon fiber-reinforced polymer (CFRP) composites. The polymer matrix was modified with c-BN nanoparticles at weight ratios of 1, 2, 3, and 4%, respectively, and then reinforced with carbon fibers. The Vickers microhardness measurements showed that dispersion of c-BN nanoparticles into the matrix dramatically enhanced the surface hardness of the composite structures. Additionally, tribological examination revealed that friction coefficient values of the composites were extraordinarily reduced due to the presence of c-BN nanoparticles. The improved wear resistance was also exhibited with wear track profiles. Scanned electron microscopy images have confirmed the experimental findings. The c-BN nanoparticles can be used as secondary reinforcement for CFRP composites, and these hybrid systems could be strong material candidates for several industries like aviation, aerospace, and electronics due to their excellent wear properties.

Gears are widely used machine elements to transmit power and motion in the industry. During the power transmission, the gears are subjected to cyclic loads. Thus the fatigue resistance of the gears should be deeply investigated. In particular, this issue is gaining much more importance in the space and aviation fields. In this study, the fatigue life of gears made of 9310-VIM-VAR steel used in the aviation field was determined experimentally, and the crack propagation paths obtained were numerically verified. To this end, the SAE J1619 standard single-tooth bending fatigue test apparatus was redesigned and manufactured in order to adapt it to the helicopter gears. Totally 28 single-tooth bending fatigue tests were carried out for various loading conditions. Accordingly, the S–N curves for the helicopter gears were created. The experimental results were verified by the finite element fatigue crack propagation analysis in terms of the initial crack location, crack initialization angle, and crack propagation paths. Conducted experiments and numerical studies are found as compatible with each other.

Selective laser melting allows aluminum-silicon alloy mirrors further lightweight for aerospace applications. The reflective surfaces based on Selective laser melting aluminum-silicon alloy substrates are commonly machined by single point diamond turning. However, many surface defects on single point diamond turning machined surfaces may limit their direct applications in optical system. In the paper, single point diamond turning parameters (cutting depth, feed rate, and cutting speed) are optimized orderly to improve its surface quality. The single point diamond turning machined surface morphologies are measured by using white light profilometer. In our selective laser melting AlSi 10 Mg substrate, scratches and holes mainly damaged single point diamond turning surface. Scratches are caused by inclusions while holes are generated by gas pores and inclusions. Single point diamond turning parameters optimization reduces the density of such surface defects, but these defects cannot be eliminated totally.

The main objective of this investigation is to study the effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints. The dissimilar joints of Ti6Al4V titanium alloy and AISI 304 steel were developed using the different levels of bonding time (30, 45, 60, 75 and 90 min) in a vacuum chamber at a bonding temperature of 900 °C and compressive pressure of 14 MPa. The microstructure of joints was analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The elemental analysis of joint interface was studied using the SEM energy dispersive spectroscopy (EDS). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The ram tensile tests and lap shear tests were performed to assess the bonding strength and lap shear strength of dissimilar joints. Results showed that the dissimilar joints of Ti6Al4V alloy–AISI 304 steel developed using the diffusion bonding time of 75 min showed higher lap shear strength of 151 MPa and bonding strength of 244 MPa due to the better coalescence of the joining surfaces and evolution of optimum width of diffusion region having minimum embrittlement effects.

In this study, two AZ91 samples were produced by compression at 200 °C and 350 °C, respectively. The microstructure of the samples and their effect on deformation were studied. The results show that the deformation mechanism is slipping, twinning and shear banding at low temperature due to the low compression temperature. The stacking fault energy of alloy can be increased by the increase of adiabatic temperature, the dislocations gather at the shear band, resulting in the increase of hardness, which is not conducive to deformation. At high temperature, there were a large number of fine second phases precipitated at the shear bands. This second phase provides nucleation site for recrystallization, and dislocation energy storage in the shear band provides energy for recrystallization, resulting in recrystallization nucleation and growth at the shear bands. Discontinuous dynamic recrystallization weakened texture intensity.

The main objective of this investigation is to enhance the tensile shear fracture load (TSFL) bearing capability and minimize softening in heat affected zone (HAZ) of resistance spot welded DP-1000 steel spot joints for automotive applications. The lap tensile and cross tensile shear fracture load tests (LTSFL and CTSFL) were conducted. The process parameters were optimized using numerical and graphical optimization techniques to maximize the TSFL capability of spot joints. The microstructure of spot joints was studied using optical microscopy and correlated to TSFL and hardness of spot joints. Results showed that DP-1000 steel spot joints made using the welding power of 70 W, welding time of 1.0 s, electrode pressure of 4.25 MPa showed maximum LTSFL of 22 kN and CTSFL of 9.1 kN. The parametric optimization showed 46.66, 45.77, 22.33 and 9.87% increase in LTSFL, CTSFL, nugget zone hardness and HAZ hardness of DP-1000 steel spot joints. The higher TSFL and nugget hardness of spot joints is mainly attributed to the evolution of finer martensitic sandwiching ferrite phases in nugget zone and lower softening of HAZ than other joints. Welding power showed significant influence on TSFL of spot joints followed by welding time and electrode pressure.

In this study, the effect of particle additive on buckling behaviour in laminated hybrid composite plates was investigated numerically and experimentally for patched samples. In the experimental study, carbon-aramid woven fabric was chosen as the hybrid material and composite plate production was carried out in a temperature-controlled vacuum infusion production unit. The circular holed specimens were patched on one face with the wet patch and the adhesion performance under buckling load was investigated. The buckling test results for composite plates with and without nanoparticle added to patch matrix material were compared. In numerical study, the buckling analysis of composite plates patched with nano-additive and without nano-additive wet patch method was performed with the finite element method. The numerical results obtained in the nonlinear buckling analysis for plates and the experimental results were compatible with each other. Addition of 1 wt% carbon nano tube (CNT) and graphene to the patch material with fiber angle parallel to the loading direction increased the damage loads by 22.5 and 12.6 wt%, respectively, compared to the non-additive patch. Adding 2 wt% CNT increased damage loads by 50%, while adding 2 wt% graphene reduced damage loads only 1%.

Particularly in the automotive industry and the sector of liquid–gas storage, austenitic steels with a high energy absorption capacity are used. The light metals frequently used do not meet all requirements. Therefore, especially for components involved in crash situations, the cost-effective alternative with outstanding properties is used. In this respect, the high-manganese TWIP steels are of great interest, specifically due to their strength and ductility. Also in other research areas, the high-strength steels are moving into the focus of attention. For example, the properties of welded high-manganese steels at low temperature applications, such as those encountered during storage and transport of liquefied gases, are to be investigated. For this purpose, high-speed tensile tests are used to experimentally determine how the material behaves at different low temperatures and high strain rates. The investigations carried out provide results that can be used to draw conclusions about the strain rate and temperature dependence of the mechanical characteristics. These dependencies are shown as well.

In this present work, mechanical engineering optimization problems are solved by employing a novel optimizer (HFDO-DOBL) based on a physics-based flow direction optimizer (FDO) and dynamic oppositional-based learning. Five real-world engineering problems, viz. planetary gear train, hydrostatic thrust bearing, robot gripper, rolling bearing, and multiple disc clutch brake, are considered. The computational results obtained by HFDO-DOBL are compared with several newly proposed algorithms. The statistical analysis demonstrates the HFDO-DOBL dominance in finding optimal solutions relatively and competitiveness in solving constraint design optimization problems.

In this study, the powder hardness and substrate surface hardness on the coating formation in the cold spray process was investigated. The AA6082 aluminum alloy hardened by the shot-peening process was used as the base material. Two different metallic powders and a ceramic particle powder were used as powder materials with different hardness. Thus, the powder particles from different materials were sprayed onto the surface under the same spraying process conditions. In order to obtain a workpiece surface with different hardness values, shot-peening treatment was applied to the substrate material at different treatment times. According to the microstructural examination, the harder metallic coating powder has accumulated more and the lower hardness metallic coating powder has accumulated less when the substrate material hardness increases. Al 2 O 3 particles in the layer formed were distributed close to homogeneous. Furthermore, the size of Al 2 O 3 particles near the contact surface has become much finer especially in the long-term shot peened samples due to their higher hardness. From the indentation experiments, the elastic behavior and recovery amount of the composite coating layer increased due to the increase of the substrate surface hardness, and the stress distributions were performed less after the load was removed.