Cemented carbides are hard materials used in tough materials machining as well as in situations where other tools would wear away. These are one of the most successful composite engineering materials ever produced. The advantage of cemented carbides is that their structure and composition can be engineered to have properties tailored to specific applications and operations. These materials allow faster and more precise machining and will leave a better surface finish. Carbide tools can also withstand higher temperatures than standard high speed steel tools. Considering their application and known range of properties, main disadvantage of cemented carbides is appearance of their sudden fracture during machining process. This is caused by the low toughness at dynamic rates and overcoming this problem is yet to be researched further. In order to understand these limitations and provide suggestions for the improved design of the material, combined experimental and numerical analysis is currently being performed. Cohesive strength values numerically determined using Dugdale cohesive zone model are compared to flexural strength obtained experimentally. Reduction in flexural strength was then analysed and explained, relating it to the flaw size on the tensile surface of the specimen.
In this study structural strength and fatigue life estimation of Y32 bogie frame were examined by finite element method. A static structural and fatigue life simulation were performed according to TS EN 13749 standard. The results of the static structural and fatigue life simulations depicted that Y32 bogie manufactured by Tuvasas achieved the regulations.
Ti-TiAl₃ in situ composites with 10 wt.% Nb were successfully prepared from Ti, Al, and Nb metallic powders by powder metallurgy processing technique of electric current activated/assisted sintering. The current and process time used for producing metallic-intermetallic composites were 2000 A and 90 s, respectively. In terms of fracture toughness, effects of addition of ductile niobium phase to Ti-TiAl₃ composites were investigated. According to SEM-EDS and XRD results, the synthesized composites mainly consisted of TiAl₃ matrix and dispersive Nb reinforcing phases, as well as ductile Ti phases. Hardness and fracture toughness values of the samples were measured by Vickers hardness tester under loads of 100 g and 10 kg, respectively. Fracture toughness value of TiAl₃ intermetallic composites was increased with Nb ductile phase addititon from 1.69± 0.05 MPa m^{1/2} to 5.23± 0.3 MPa m^{1/2}.
The high cycle and very high cycle fatigue properties of the titanium alloy Ti-6Al-4V with a duplex microstructure were investigated at room temperature. High cycle fatigue tests were performed in the range from 10⁴ to 10⁷ cycles by rotating bending at the frequency of 30 Hz. The very high cycle fatigue tests were carried out in the range from 10⁷ to 10¹⁰ cycles in tension-compression on an ultrasonic fatigue testing machine at the frequency of 20 kHz. The stress amplitude was found to decrease with increasing number of cycles in the whole range from 10⁴ up to 10⁹ cycles and only at the highest number of cycles (N_{F}=10⁹) the alloy exhibits the fatigue limit of 460 MPa. The detail fractographic analysis was performed to characterize the fatigue failure mechanisms. Both subsurface and surface crack initiation were observed in very high cycle fatigue region. No inclusions, but only local chemical inhomogeneity in microstructure was observed at the locations of subsurface fatigue crack initiation in alpha-grains.
In this study, the variation of the magnetic flux distribution in a magnetised ferromagnetic material which has in homogeneity as a crack is studied. An orthogonal fluxgate magnetic field sensor was used in the inspection of cracks. In the fluxgate sensor, the sensing element (Co_{0.94}Fe_{0.06})_{72.5}Si_{12.5}B_{15} amorphous ferromagnetic wire was placed inside a pickup coil winding with 50 μm copper wire and connected to a signal generator and the output from pick-up coil was detected using a lock-in amplifier. The surface profile of magnetic materials with a crack was obtained using a specially designed 3-dimensional moving system. A large decrease in the output voltage of the sensor was observed when the sensor was moved on the top of the crack, after the further movement of the sensor the output voltage came back to the previous value.
The determination of fracture toughness of aluminium alloy aviation parts, exposed to cyclic mechanical loading, is an important engineering issue. The service life and crack resistance of such unprotected metallic parts is limited under corrosive operating conditions. The resistance against fracture cracking and corrosion resistance can be increased by the surface coatings. The scientific research of fracture toughness of coated metallic parts is being carried out in a comprehensive way. In this research, fracture toughness behaviour of high velocity oxy-fuel (HVOF) spray coated and conventional hard chrome plated aluminium-zinc alloy parts were compared and the results are discussed. The fracture surfaces are investigated and fracture toughness values are calculated. Electron microscopy analysis revealed significant differences in crack growth morphology and toughness values. As a result, the fracture toughness value is higher in hard chrome plated parts.
Being a light metallic engineering material with low density, high specific stiffness and strength, aluminium alloys are promising materials in the fields of aerospace, military and automotive industries. Consumption of aluminium alloys in the forms of sheets and plates has generally increased in global markets over the past 45 years. Rolling directions affect the anisotropy and mechanical properties of the aluminium alloys. In this work, the plane strain fracture toughness K_{IC} values of 7075 aluminium alloy were measured in plates of three directions and six orientations (L-T, T-L, T-S, S-T, L-S, S-L), using the standard (ASTM E399) compact tension specimens. The results indicate that dependence of fracture toughness of 7075-T651 aluminium alloy on rolling direction is obvious and that K_{IC} values of T-S and L-T orientations are the highest.
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