Browsing by Subject "TOUGHNESS"

Now showing 1 - 6 of 6
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    Flexural strength and defect behaviour of polygranular graphite under different states of stress
    (PERGAMON-ELSEVIER SCIENCE LTD) Mostafavi, M; McDonald, SA; Çetinel, H; Mummery, PM; Marrow, TJ
    The effect of stress state on the fracture behaviour of Gilsocarbon, an isotropic nuclear grade polygranular graphite, has been studied by employing four-point bend and ring-on-ring loading configurations to achieve uniaxial and equi-biaxial flexural stress states, respectively. Optical images of the specimens' tensile surface were analysed by digital image correlation to measure the full-field displacements: these were used to identify the fracture initiation sites, analyse crack geometry (surface length and opening displacements) and also to calculate the J-integral strain energy release rate associated with surface crack propagation. Surface cracks that did not propagate to failure were identified and subsequently examined by X-ray computed tomography combined with digital volume correlation: measurements were made of their three-dimensional displacement fields when subjected to an opening tensile stress using a modified (flat) Brazilian Disk test geometry. The crack opening behaviour is explained by an effect of stress state on the development of the crack tip fracture process zone, which is in agreement with the effect of stress state on the measured strain energy release rates of sub-critical crack propagation. Both are attributed to the plastic constraint effect, which varies with the stress state in materials that can undergo inelastic deformation. (C) 2013 Elsevier Ltd. All rights reserved.
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    Cracking during cold forming process of rear brake component
    (PERGAMON-ELSEVIER SCIENCE LTD) Elkoca, O; Cengizler, H
    The root cause for cracking of rear brake components occurred during cold forming process was investigated. Optical micrographs showed the abundance of extended inclusions with several rounded ones in the steel. SEM image revealed the fracture surface which contained many extended cavities formed by extended inclusions and dimples all indicating a ductile rupture. EDS analysis confirmed that the extended inclusions were MnS type while the rounded ones were formed as a result of Ca-treatment. The crack propagation along with inclusions was clearly observed on the polished planes and on the fracture surface. It was determined that MnS type inclusions were the root cause for the cracking phenomena. The abundance of extended MnS inclusions indicated insufficient inclusion modification through Ca-treatment and insufficient removal of these inclusions in failed steel. (C) 2007 Elsevier Ltd. All rights reserved.
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    Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysisCharakterisierung von warmgeschmiedetem P285NH-Stahl durch metallurgische Untersuchungen und Zuverlassigkeitsanalyse
    (WILEY-V C H VERLAG GMBH) Saklakoglu, N; Çivi, C; Hocalar, Ç; Demirok, S
    An extensive study was carried out to investigate the effect of cooling rate after hot forging process and normalization step on the hardness, strength and impact toughness and microstructure of P285NH steel. Understanding of the combined effect of cooling rate and normalization on the mechanical and microstructural properties of the steel would help to select conditions required to achieve optimum mechanical properties. The results indicated that the microstructures of all forging and cooling conditions were dominated by ferrite and pearlite phases with different morphologies and grain sizes according to various cooling rates. Conveyor cooling led to a formation of relatively fine acicular ferrite and pearlite grains in comparison to batch cooling which presented coarse polygonal ferrite with pearlite. Based on the data fluctuation of Charpy tests, the normal distribution provided a statistical analysis method for assessing the reliability. Through the statistical analysis of the distribution function, it can be concluded that normalization step is necessary for higher reliability. Both batch cooling and conveyor cooling did not give the required reliability level for safety components due to heterogeneities in the microstructure.
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    Mechanical performance of marine sandwich composites subjected to flatwise compression and flexural loading: Effect of resin pins
    (SAGE PUBLICATIONS LTD) Balikoglu, F; Demircioglu, TK; Yildiz, M; Arslan, N; Atas, A
    Mechanical performance of marine sandwich panels comprising E-glass/vinyl ester face sheets and perforated poly-vinyl chloride foam core was evaluated and compared with conventional foam core sandwich panels. Circular holes through the foam core thickness were drilled with 12 different arrangements in square patterns and the holes were filled with the resin during the infusion process which created the through-the-thickness solid resin pins. The effect of each pattern on the flatwise compression and core shear properties of the sandwich panels were experimentally investigated. The three-point bending maximum failure load of perforated foam core sandwich panels was increased over 133.8% by increasing the diameter of the resin pins at the expense of increased panel weight up to 67%. The flatwise compression stress to induce core crushing was significantly increased by reinforcing the resin pins.
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    Fracturing and adhesion behavior of hydroxyapatite formed by a citric acid and sodium citrate buffer system
    (CARL HANSER VERLAG) Aydin, I; Çetinel, H; Pasinli, A; Yuksel, M
    This study aims to examine the fracture and surface adhesion behavior of hydroxyapatite (HA) coatings created in acitric acid-sodium citrate buffer system. Coatings were implemented on the surface of Ti6Al4V. The modulus of elasticity, hardness and adhesion strength values of the presented coatings were determined, the fracture toughness values were calculated and scanning electron microscope (SEM) images were taken as well. Finally, the mechanical properties found by the tests implemented to hydroxyapatite coatings applied on Ti6Al4V, which yielded successful outcomes were compared to the mechanical properties of bone. The fracture toughness achieved in this study was found to be more compatible with the mechanical properties of the original bone itself when compared to the literature findings. Besides, the adhesion strength was found to be remarkably high.
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    Improving four-point bending performance of marine composite sandwich beams by core modification
    (SAGE PUBLICATIONS LTD) Balikoglu, F; Arslan, N; Demircioglu, TK; Inal, O; Iren, M; Atas, A
    The aim of this study was to improve four-point bending performance of foam core sandwich composite beams by applying various core machining configurations. Sandwich composites have been manufactured using perforated and grooved foam cores by vacuum-assisted resin transfer moulding method with vinyl-ester resin system. The influence of grooves and perforations on the mechanical performance of marine sandwich composite beams was investigated under four-point bending test considering the weight gain. Bending strength and effective bending stiffness increased up to 34% and 61%, respectively, in comparison to a control beam without core modification. Analytical equations were utilised for calculating the mid-span deflection, equivalent bending stiffness and ultimate bending strength of the sandwich beams. Finite element analysis was also performed to analyse the flexural response of the specimens taking into account the combined effect of orthotropic linear elasticity of the face sheet and the non-linear behaviour of the foam core.