In this study, single and duplex aging treatment was applied to the metastable beta titanium alloy of titanium-15 vanadium-3 aluminum-3 chromium-3 tin with cryogenic treatment. The single-step aging treatment was applied for 20 h at 450°C and 10 h at 550°C. The cryogenic treatment was carried out at −196°C for 24 h, followed by single-step or duplex aging treatment. The results obtained show that the cryogenic treatment causes the formation of martensitic alpha phases. Following the cryogenic treatment, martensitic alpha phases were observed in the sample, which was subjected to aging treatment at 450°C for 20 h, whereas these phases disappeared completely in the sample treated at 550°C for 10 h. Preaging treatment applied after cryogenic treatment prevented the formation of precipitate-free zones by providing a finer and uniform distribution of α phases. Cryogenic treatment followed by preaging treatment at 250°C for 24 h led to the formation of dense metastable prephases. This resulted in a 10% increase in tensile strength, 4% elongation, and 5% hardness compared to preaging at 300°C for 10 h after cryogenic treatment. The optimum mechanical properties in single-step sample groups were obtained in samples aged 20 h at 450°C. In duplex-aged samples, optimum mechanical properties were obtained in cryogenic treatment followed by 250°C/10 h + 450°C/20 h duplex aging treatment.

In this study, the hybrid approach of the Quadrature Element Method (QEM) has been employed to generate solutions for point supported isotropic plates. The Hybrid QEM technique consists of a collocation method with the Galerkin finite element technique to combine the high accurate and rapid converging of Differential Quadrature Method (DQM) for efficient solution of differential equations. To present the validity of the solutions, the results have been compared with other known solutions for point supported rectangular plates. In addition, different solutions are carried out for different type boundary conditions, different locations and number of point supports. Results for the first vibration modes of plates are also tested using a commercial finite element code, and it is shown that they are in good agreement with literature.

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

Gears are widely used in motion transmission in machines. For this reason, they work in very difficult conditions. Some damage may occur in the gears depending on the operating conditions. These damages are bending fatigue, pitting, micropitting, scuffing, and wear. This study investigates surface fatigue damages by keeping fixed the material of test gear teeth, rotation speed, lubricating oil, and the applied load, and changing the operating temperatures of oil. In experimental studies, pre-and post-test weights of gear teeth samples were established, surface roughnesses were measured, and micrograph examinations were carried out on teeth surface. As a result, surface roughness and wear were established to increase in proportion to the rise in temperature of oil. Maximum pitting size was measured at about 870 µm at 90 ºC oil temperature, and the lowest pitting size was measured as approximately 450 µm in tests performed at 30 ºC.

 α phases precipitate higher size with the increase of aging temperature  Aging temperature determines the fatigue crack propagation rate of single-step and duplexaged samples  • The pre-aging temperature determined the fatigue behavior of the alloy Metastable β titanium alloys have been widely used in the aerospace industry since the 1960s due to their high strength and low weight. Metastable β titanium alloys differentiate from all other titanium alloy groups thanks to their high heat treatment efficiency. In the literature, significant improvements have been achieved in the mechanical properties of the metastable β alloys with cryogenic and aging treatments. Ti-15V-3Al-3Sn-3Cr metastable β titanium alloy is preferred, especially in the aerospace industry in airframe and fasteners due to its strip producibility and good formability. Considering the loading conditions and application areas to which the alloy is exposed, it becomes essential to investigate the fatigue crack propagation behaviors of the alloy. Figure A. Microstructure analysis of the heat-treated samples, a) Kry+450/8, b) Kry+300/10-450/8, c) Kry+550/8, d) Kry+300/10-550/8.Purpose: There have been a few studies about the effect of the cryogenic treatment on titanium alloys' microstructural and mechanical properties in the literature. However, studies in which cryogenic treatment is applied to metastable β titanium alloys are quite limited. Therefore, in this study, cryogenic treatment with or without single-step and duplex aging treatment was applied to the alloy. In addition, tensile, microhardness, and fatigue crack propagation tests were applied to heat-treated sample groups. Thus, fatigue crack propagation behavior of the samples that were aged after the cryogenic treatment for the first time in the literature was examined. Theory and Methods:Cryogenic treatment was applied at -196°C for 24 hours. Single-step and duplex aging treatments were applied after the cryogenic treatment. Aging treatments were applied at both high (85-195°C below β transition temperature) and low (200-450°C) aging temperatures. The tensile, microhardness and fatigue crack propagation tests were applied to heat-treated sample groups. Results:α phases were precipitated at a finer size in the duplex aged samples, and precipitation-free zones were not observed in the microstructure. In addition, significant increases in strength values were obtained without a decrease in the elongation of the alloy in the aged samples after the cryogenic treatment. Compared to singlestep aged samples, crack propagation rate was obtained lower due to uniform precipitation of finer α phases in the duplex aged samples. Conclusion:Maximum strength versus maximum elongation was obtained in Kry+300/10-450/8 specimens subjected to duplex aging after cryogenic treatment. Also, fatigue crack propagation resistance of the duplex aged samples was found higher than the single-step aged samples.