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    THE EFFECT OF COLEMANITE ADDITION ON THE MICROSTRUCTURAL AND MECHANICAL CHARACTERISTICS OF IPP
    (2020) Soykan, Uğur; Veliyeva, Fidan
    The objective of this study was to investigate the effect of the addition of the colemanite having 45µm size on the significantcharacteristic features of the isotactic polypropylene (IPP). The microstructural properties (diffraction pattern, a,b and c unitcell parameters and grain size) and mechanical behaviors (tensile strength, Young's Modulus, impact strength and percentelongation of the samples relative to the colemanite content (5, 10, 15, 20 and 30 wt.%) were studied in details. The optimumamount of colemanite was determined in order to obtain IPP based composites having improved properties. The obtainedsamples were characterized by using XRD and conventional mechanical tests. The results showed that the content level of thecolemanite considerably affected the fundamental properties of IPP. As for microstuructural properties, it was observed fromthe XRD patterns that all composite samples mainly showed only ? form (monoclinic arrangement) in the crystalline domainswithout any ? form (hexagonal arrangements). Moreover, the finding revealed that a and b the unit cell parameters of IPPbased composites increased initially, reached the maximum values with the products containing 10% of colemanite, and thenthe consistent decrement trend was observed with the further increase in the colemanite content in the products. Conversely, cunit cell parameter almost remained relatively unchanged. Furthermore, the mechanical test measurements depicted that thereinforcements were achieved in the tensile, Modulus and impact strengths of the composite materials, while the percentelongation of the products decreased with the increasing of the colemanite content. 7.4%, 24.9% and 6.7% increases wererecorded in the tensile strength, Modulus and impact strength at the product with 10% colemanite, respectively. Theimprovements were probably stemmed from that the presence of micro size colemanite particles gave rise to increment in theorientations and alignments of IPP chain in the matrix.
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    EXAMINATION OF VANADIUM EFFECT ON GENERAL MECHANICAL CHARACTERISTICS OF Bi-2223 MATERIALS VIA SEMI-EMPIRIC MODELS
    (2020) Soykan, Uğur; Veliyeva, Fidan; Yildirim, Gürcan
    In the current work, we semi-empirically investigate the load-independent Vickers hardness values of vanadium added Bi2223 compounds in the plateau limit regions evaluated from the experimental microhardness graphics (Vickers hardnessparameters versus applied indentation test loads) to determine the role of vanadium particles on the general mechanicalcharacteristics with the aid of six mechanical modeling approaches, namely law of Meyer, proportional sample resistance,elastic/plastic deformation, modified proportional sample resistance, Hays-Kendall and indentation-induced cracking models.Throughout the study, the samples are prepared with the different molar rations varying from x=0 to 0.3 by the conventionalceramic method in the normal atmospheric pressure at the room temperature conditions. All the model findings show that themechanical performances tend to constantly reduce with increasing the vanadium concentration level embedded in the Bi-2223superconducting crystal system. This is in accordance to the fact that the concentration level of vanadium remarkably damages themain structural problems and permanent irreversible deformations. In this respect, it is not wrong to verify that the vanadiuminclusions unstabilize the inherit durable tetragonal phase of Bi-2223 inorganic solids, resulting in the regression in themechanical durability (resistance towards to the applied loads) in case of the applied test loads. Moreover, the modelsindicate that every material prepared exhibits the conventional indentation size effect (related to the formation of elastic andplastic deformations in the host crystal structures simultaneously due to the recovery of systems) but within the suppressiontrend. Shortly, all the semi-empiric models preferred in the present work are found to be useful descriptors to define thesuitable relationship between the ion-addition mechanism in the crystal lattice and mechanical durability/performances ofvanadium-added Bi-2223 materials. We should, of course, declare here that Hays–Kendall approach is gathered to be the best approach model for the load-independent Vickers hardness values in the plateau limit regions.
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    A VALUABLE VIEW ON EVALUATION OF GENERAL MECHANICAL PERFORMANCES PERTAINING TO Bi-2223 SUPERCONDUCTING CERAMICS WITH VANADIUM ADDITION
    (2020) Soykan, Uğur; Veliyeva, Fidan; Yildirim, Gürcan
    In this research, our scientific group investigates the effect of vanadium addition in the Bi-2223 superconducting matrix onthe general mechanical performance features by the help of experimental microhardness measurements conducted by a smallindenter between the well-defined stress loads of 0.245 N and 2.940 N. Moreover, we determine the key mechanical designparameters including the elastic moduli with the hardness, stiffness coefficients, fracture toughness, yield strength, brittlenessindex and its opposite behavior (ductility) in the applied test loads given using the experimental data deduced from themicroindentation tests. According to the experimental findings, it is oberved that the presence of vanadium content in the Bi2223 crystal structure surpasses seriously the general mechanical performance and related parameters due to the degradation inthe quality of grain boundary couplings, crystal structure and basic structural quantities as a consequence of the increment in thestructural problems, permanent plastic deformations, crack-producing flaws and dislocations. In other words, the augmentationof vanadium compounds in the Bi-2223 superconducting lattice brings about the considerable enlargement in the responsibilityto the static indentation loads. Namely, the sensitive level to the applied loads increases rapidly with the vanadium concentration.We also search the variation of graphs between the Vickers hardness parameters and applied test loads. In this respect, all thematerials prepared in this work exhibit the standard ISE (indentation size effect) characteristics but within the decrement trendas the vanadium content level increases. In more detail, the impurity atoms damage harshly the ISE feature of Bi-2223 type-IIsuperconducting ceramics. Additionally, we discuss the change of plateau limit regions coincided with the permeant artificialstructural problems in the graphics. The vanadium leads to shorten the applied test load values for the plateau limit regions ofBi-2223 materials, stemmed from the enhancement the general structural problems. To conclude, the vanadium inclusions areploughed to improve the general mechanical performance features and key mechanical design parameters.