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Article Citation - WoS: 29Citation - Scopus: 38An Experimental Study of Cutting Performances of Worn Picks(Springer Wien, 2016) Dogruoz, Cihan; Bolukbasi, Naci; Rostami, Jamal; Acar, CemilThe best means to assess rock cuttability and efficiency of cutting process for using mechanical excavation is specific energy (SE), measured in full-scale rock cutting test. This is especially true for the application of roadheaders, often fitted with drag-type cutting tools. Radial picks or drag bits are changed during the operation as they reach a certain amount of wear and become blunt. In this study, full-scale cutting tests in different sedimentary rock types with bits having various degree of wear were used to evaluate the influence of bit wear on cutting forces and specific energy. The relationship between the amount of wear as represented by the size of the wear flats at the tip of the bit, and cutting forces as well as specific energy was examined. The influence of various rock properties such as mineral content, uniaxial compressive strength, tensile strength, indentation index, shore hardness, Schmidt hammer hardness, and density with required SE of cutting using different levels of tool wear was also studied. The preliminary analysis of the data shows that the mean cutting forces increase 2-3 times and SE by 4-5 times when cutting with 4 mm wear flat as compared to cutting with new or sharp wedge shape bits. The grain size distribution of the muck for cutting different rock types and different level of bit wear was analyzed and discussed. The best fit prediction models for SE based on statistical analysis of laboratory test results are introduced. The model can be used for estimating the performance of mechanical excavators using radial tools, especially roadheaders, continuous miners and longwall drum shearers.Article Citation - WoS: 22Citation - Scopus: 27The Stress Response and Onset of Yield of Rotating Fgm Hollow Shafts(Springer Wien, 2006) Akis, T.; Eraslan, A. N.An analytical model is developed to study the stress response and the yielding of rotating functionally graded hollow shafts in the framework of generalized plane strain. The modulus of elasticity and the uniaxial yield limit of the shaft material are assumed to vary radially in nonlinear forms. It is shown that different modes of plasticization may take place. Analytical expressions for the critical values of the material parameters leading to different modes of plastic deformation and the corresponding elastic limit rotation speeds are derived by the use of Tresca's yield criterion.Article Citation - WoS: 16Citation - Scopus: 16Elastic Analysis of Variable Profile and Polar Orthotropic Fgm Rotating Disks for a Variation Function With Three Parameters(Springer Wien, 2017) Essa, Saad; Argeso, HakanAnalytical solutions are developed for the analysis of elastic polar orthotropic functionally graded annular disks rotating with constant angular velocity. The formulations are carried out by presuming a state of plane stress and small deformations. The elasticity moduli and thickness are varied radially by a nonlinear function controlled by three parameters, while the radial variation of density may be defined by any form of continuous function. Poisson's ratios are taken to be constant. Annular disks having traction-free inner and outer surfaces, and annular disks mounted on a circular rigid shaft having traction-free outer surface are studied separately. The analytical solutions are verified numerically by the use of a computational model based on the nonlinear shooting method. An analysis that inspects the effects of the degree of orthotropy is presented. Elastic limit angular velocities are determined according to Hosford's yield criteria. Stress, displacement and strain profiles are compared within the elastic range.Article Citation - WoS: 93Citation - Scopus: 101On the Plane Strain and Plane Stress Solutions of Functionally Graded Rotating Solid Shaft and Solid Disk Problems(Springer Wien, 2006) Eraslan, AN; Akış, Tolga; Akis, T; Akış, Tolga; Civil Engineering; Civil EngineeringClosed form solutions to functionally graded rotating solid shaft and rotating solid disk problems are obtained under generalized plane strain and plane stress assumptions, respectively. The nonhomogeneity in the material arises from the fact that the modulus of elasticity of the material varies radially according to two different continuously nonlinear forms: exponential and parabolic. Both forms contain two material parameters and lead to finite values of the modulus of elasticity at the center. Analytical expressions for the stresses at the center are determined. These limiting expressions indicate that at the center of shaft/disk: (i) the stresses are finite, (ii) the radial and the circumferential stress components are equal, and (iii) the values of the stresses are independent of the variation of the modulus of elasticity. It is also shown mathematically that the nonhomogeneous solutions presented here reduce to those of homogeneous ones by an appropriate choice of the material parameters describing the variation of the modulus of elasticity.Article Citation - WoS: 18Citation - Scopus: 20Periodicity in Precipitation and Temperature for Monthly Data of Turkey(Springer Wien, 2021) Akdi, Yilmaz; Unlu, Kamil DemirberkIn this study, we model and forecast monthly average temperature and monthly average precipitation of Turkey by employing periodogram-based time series methodology. We compare autoregressive integrated moving average methodology and harmonic regression. We show that harmonic regression performs better than the classical methodology in both time series. Also, we find that the monthly average temperature and monthly average precipitation have two different periodic structures of 6 months and 12 months which coincide with the seasonal pattern of the time series.
