Materials Testing

Czichos, Horst

doi: 10.1515/mt-2022-2003pmid: N/A

doi: 10.1515/mt-2023-frontmatter1pmid: N/A

Reisgen, Uwe; Olschok, Simon; Rasbach, Erik; Krichel, Thomas

doi: 10.1515/mt-2022-0364pmid: N/A

AbstractMajor 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.

Hosseini Mehrab, Alireza; Amirfakhrian, Seyedmahdi; Esfahani, M. Reza

doi: 10.1515/mt-2022-0210pmid: N/A

AbstractThis 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.

Yang, Xingwang; Liu, Fuguang; Shi, Chunfeng; Liu, Gang; Li, Yong

doi: 10.1515/mt-2022-0244pmid: N/A

AbstractMicrocracks 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.

Uzay, Çağrı

doi: 10.1515/mt-2022-0083pmid: N/A

AbstractBoron 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.

Kalay, Onur Can; Yuce, Celalettin; Doğan, Oğuz; Yılmaz, Tufan Gürkan; Karpat, Esin; Kopmaz, Osman; Karpat, Fatih

doi: 10.1515/mt-2022-0255pmid: N/A

AbstractGears 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.

Wang, Yifan; Yu, Jun; Wang, Zhanshan

doi: 10.1515/mt-2022-0217pmid: N/A

AbstractSelective 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 AlSi10Mg 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.

Negemiya, Arun; Selvarajan, Rajakumar; Sonar, Tushar

doi: 10.1515/mt-2022-0209pmid: N/A

AbstractThe 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.

Wang, Dongxiao; Lin, Baosen; Jing, Yi; Zhu, Qiangqiang; Li, Jianping; Misra, R. Devesh K.

doi: 10.1515/mt-2022-0239pmid: N/A

AbstractIn 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.