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Öğe The effects of stacking sequence on drilling machinability of filament wound hybrid composite pipes: Part-2 damage analysis and surface quality(ELSEVIER SCI LTD, 2020) Gemi, Lokman.; Morkavuk, Sezer.; Köklü, Uğur.; Yazman, Şakir.In the first part of this two-part study, filament wound hybrid composite pipes with various stacking sequences were manufactured and mechanical properties such as hardness, ring tensile strength, and burst strength were experimentally investigated. After determining mechanical properties, drilling tests were performed to research machinability characteristics. The second part of the study consists damage analysis and surface quality examination including ring test damage analysis, push-out delamination analysis, borehole damage examination and borehole surface quality. The experimental data suggested that cutting parameters, stacking sequence, and the use of back-up were impactful on the formation and propagation of various types of damages. Especially, the effect of stacking sequence was remarkable. A larger delamination area was formed in Glass-Glass-Carbon (GGC) sample after the ring tensile tests compared to Glass-Carbon-Glass (GCG) and Carbon-Glass-Glass (CGG) samples. In all cases, the utilization of back-up lead to decrease of delamination with 9-40% reduction in surface roughness. When the back-up is not used during drilling, an excessive push-out delamination occurred in all drilling tests. Moreover, CGG samples represented lower push out delamination. In addition, position of the hole depending on the winding angle plays a key role on damage formation and surface quality.Öğe Transient conjugated heat transfer in thick walled pipes with axially periodic surface temperature in downstream region(SPRINGER INDIA, 2019) Ateş, Ali.Thermal entrance region transient conjugate heat transfer is investigated involving fluid axial heat conduction for laminar pipe flows. Constant outer wall temperature boundary condition is assumed in the upstream region of a thick walled, two regional pipe. In the downstream region, the outer wall temperature is considered changing spatially in a periodical manner. The problem is solved numerically by a finite difference method. A parametric analysis is conducted in order to determine the effects of Peclet number, wall thickness ratio, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio and axial frequency on heat transfer characteristics. It is seen that, the results are highly dependent on the parameter values and the most effective ones are the Peclet number and the wall thickness ratio. It is observed that heat is transferred towards upstream due to the axial conduction in the wall and in the fluid and with increasing values for high axial frequency.Öğe Experimental investigation of shear capacity and damage analysis of thinned end prefabricated concrete purlins strengthened by CFRP composite(ELSEVIER SCI LTD, 2019) Gemi, Lokman; Aksoylu, Ceyhun; Yazman, Şakir; Özkılıç, Yasin Onuralp; Arslan, Musa HakanPrefabricated structures supported with purlins are exposed to numerous damages due to the excessive snow loadings as vertical loadings. The thinned regions of the purlins are responsible with the failure of the structure since the shear cracks usually initiate at these regions and propagate along with the purlins, and as a result, a total collapse may occur. In this study, carbon fiber reinforced polymer (CFRP) composites with four different configurations (P-2-P-5) were employed for strengthening prefabricated purlins in order to increase the strength of the purlin against shear damage generated under vertical loading. The load carrying capacities and damage patterns of the purlins were compared. The failure of the reference purlin (P-1) was occurred as a shear damage at the thinned regions before reaching its bending capacity. However, the failure characteristic of the CFRP reinforced purlins was dominated by the bending damage and the vertical loading capacity of the purlins were increased up to 59% depends on the CFRP wrapping. Damage analysis of the CFRP composite was also performed. Various damage modes of the structure such as cover separation, air voids, delamination, debonding, fiber bundles breakage, matrix cracks, fiber bundles debonding, fiber breakage and buckling were observed and explained thoroughly.Öğe Evaluation of flexural strength of different denture base materials reinforced with different nanoparticles(WILEY, 2019) Karci, Muhammet.; Demir, Necla.; Yazman, Sakir.Purpose To evaluate the effect of adding Al2O3, SiO2, and TiO2 nanoparticles in ratios of 1, 3, and 5 wt% to different acrylic resins on flexural strength. Materials and Methods A total of 210 specimens were prepared in 30 groups (n = 7/group) (Control, 1% Al2O3, 3% Al2O3, 5% Al2O3, 1% SiO2, 3% SiO2, 5% SiO2, 1% TiO2, 3% TiO2, 5% TiO2). The specimens were polished with 200-, 400-, and 600-grit abrasive paper to provide a standard surface before testing and then suspended in distilled water for 30 days. Flexural strength was measured via three-point bending tests. Subsequently, SEM analysis was performed for one specimen from each group. Homogeneity of data was assessed by Kolmogov-Smirnov test followed by two-way ANOVA and Tukey HSD tests (alpha = 0.05). Results There was a significant increase in the flexural strength of polymethylmethacrylate (PMMA) after addition of 1% nanoparticles in both heat-polymerized and autopolymerized acrylic resins (p < 0.05). The flexural strength values of the groups to which Al2O3 and TiO2 nanoparticles were added exceeded those of the group with SiO2 addition (p < 0.05). The electron microscopy images revealed that the nanoparticles were more homogeneously dispersed in PMMA with higher flexural strength. Conclusions The mechanical properties of PMMA can be improved by the addition of nanoparticles to PMMA; however, the flexural strength values of PMMA decrease with the addition of nanoparticles at higher percentages (3-5%). Hence, the ideal filler ratio corresponds to 1%.Öğe Effect of silica/graphene nanohybrid particles on the mechanical properties of epoxy coatings(SPRINGER HEIDELBERG, 2019) Özcan, Ümit Esra; Karabörk, Fazliye; Yazman, Şakir; Akdemir, AhmetEpoxy resins are used as coating materials, but the practical use of epoxy coatings in industries is limited due to their weak mechanical properties. In the present paper, different amounts of silica nanoparticles (SiO2) and graphene nanoplatelets (GNPs) were introduced separately and together into an epoxy coating matrix as reinforcements. Graphene, a newly discovered carbon allotrope, has been found to improve the mechanical properties of the polymer composites in which it is dispersed. Silica particles are also known to improve the mechanical properties of composites. In this study, mechanical, physical and thermal properties of the epoxy coatings are considered as multidimensional by the macro- and microanalyses. The experimental results showed that after the addition of GNPs into the epoxy matrix, the flexibility and impact resistance of the coatings increased by 8.3 and 157.1%, respectively, in relation to neat epoxy. The microhardness increased by 53.8% and penetration depth, which is indicative of the scratch resistance, decreased by 29.7%, with the addition of SiO2-GNPs nanohybrid. A remarkable synergistic effect was observed between the GNPs and SiO2, which improved the hardness and the scratch resistance of the epoxy coatings.
