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    Effect of cooling rate on microstructure, mechanical and wear properties of Mg-2Zn and Mg-2Zn-1Mn alloys
    (Taylor & Francis Ltd, 2024) Elen, Levent; Elen, Nurhan Cevik
    In this study, the wear characteristics of Mg-2Zn and Mg2Zn-1Mn alloys in both dry and corrosive conditions, as well as their mechanical properties dependent on cooling rate, were examined. It has been determined that MgZn, Mg2Zn3 and MgZn2 phases are formed together with the alpha-Mg main matrix in the microstructure of the alloys. The highest tensile strength (188.6 MPa) was observed in section B of Mg-2Zn alloy. With this, section A of the Mg-2Zn-1Mn alloy showed the lowest wear value (0.00144 mm3/N.m) following dry wear. However, under corrosive wear conditions, the lowest wear rate (0.0008 mm3/N.m) was exhibited at B section in Mg-2Zn-1Mn alloy. In the SEM images of the abrasive tips used in the wear tests, it was determined that the scratches occurred along the wear direction, and as a result of the EDX analysis, alloying elements were transferred from the alloys to the abrasive tip. Dans cette etude, on a examine les caracteristiques d'usure des alliages Mg-2Zn et Mg-2Zn-1Mn dans des conditions seches et corrosives, ainsi que leurs proprietes mecaniques dependantes de la vitesse de refroidissement. On a determine que les phases MgZn, Mg2Zn3 et MgZN2 se forment ensemble avec la matrice principale Mg-alpha dans la microstructure des alliages. Les sections C des deux alliages montraient les valeurs de durete maximales, qui resultaient de la vitesse de refroidissement. Cependant, on a observe la resistance a la traction la plus elevee (188.6 MPa) dans la section B de l'alliage Mg-2Zn. Avec cela, on a observe la limite d'elasticite la plus elevee (69.7 MPa) dans la section A de l'alliage Mg-2Zn-1Mn. En meme temps, la section A de l'alliage Mg-2Zn-1Mn montrait la valeur d'usure la plus faible (0.00144 mm3/N center dot m) apres usure par voie seche. Cependant, dans des conditions d'usure corrosives, la section B de l'alliage Mg-2Zn-1Mn exhibait le taux d'usure le plus faible (0.0008 mm3/N center dot m). Dans les images du MEB des pointes abrasives utilisees lors des essais d'usure, on a determine que les rayures se produisaient dans le sens de l'usure et, a la suite de l'analyse EDX, les elements d'alliage etaient transferes des alliages vers la pointe abrasive.
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    Investigation of the effects of central rectangular gap located in the adhesive layer on failure load and joint stiffness
    (Springer Heidelberg, 2022) Oz, Ozkan; Ozer, Halil; Elen, Nurhan Cevik
    The purpose of this study is experimentally and numerically to reveal the effects of rectangular gap located in the middle of the adhesive layer on the failure load of the single lap joint with various adhesives. The presence of a rectangular gap in the bondline center can be considered both as an adhesive defect and, when gap limits are set correctly, it can also be considered as an adhesive saving. What is intended to be done in this study is to reveal these limits correctly. The effects of the gap length, adhesive type on the von Mises equivalent stress distribution and failure load in the recessed joints were analyzed numerically. For this purpose, four different gap lengths and three different adhesives were considered. The tensile stiffness investigations for the recessed joints were performed. In addition, the effect of the gap length on the failure load of the recessed joints with various adhesives was investigated experimentally. As a result, in the design of recessed joint, although the effect of other parameters considered was also involved, it was seen that especially the adhesive property was clearly the main design parameter.
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    Tribological properties of hemp fiber reinforced polylactic acid bio-composites: effect of different types of modification methods
    (Iop Publishing Ltd, 2023) Elen, Nurhan Cevik; Yildirim, Musa; Kanbur, Yasin
    In this study, green composites are prepared with 30 wt.% hemp fibers reinforced polylactic acid (PLA) to enhance the impact and tribological properties. Different surface treatments of alkali and silane, compatibilizer of maleic anhydride (MA), and blends of thermoplastic polyurethane (TPU) and poly (butylene succinate) were applied to improve interfacial adhesion between fibers and matrix. Hemp-reinforced PLA bio-composites were fabricated and characterized by hardness, impact strength, wear, and friction properties. The tribological tests of the injection-molded components were performed under two different loads (10 N and 20 N) as dry-sliding linearly reciprocating motion per ASTM G133. Modified composites gave better tribological properties than unmodified composites. While no remarkable improvement was observed in the hardness value of untreated fiber-reinforced composite, alkali-treated composite reached up to 43% improvement in hardness value. In general, as the load increased, weight loss increase was observed in all composites. Unmodified bio-composite exhibited a very low weight loss and specific wear rate (SWR) compared to neat PLA under 10 N load. The SWR of the MA bio-composite had the lowest value for both loads (10 N and 20 N) compared to the other bio-samples. The TPU blended bio-composite exhibited the highest impact strength (22.96 kJ m(-2)) after pure PLA (26.5 kJ m(-2)). Therefore, due to surface treatments and blends applied to the fibers, some composites' hardness and wear resistance were increased while the impact strength and friction coefficient was decreased. Especially silane surface treatment and MA compatibilizer application increased the wear resistance of composites. When the scanning electron microscope images were examined, it was revealed that the fiber and matrix interface bonding was good, and the fibers were firmly embedded in the matrix. Furthermore, forming a protective thin film layer formed by the polymer debris from the surface during dry-sliding increased the wear performance of the bio-composites.