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- MakaleYalnız künye2023Scopus SJRQ3Comparison of Mechanical Properties Obtained for Armor Steels: Conventional Methods vs. Nanoindentation
Ekmekci, Dursun; Cora, Ömer Necati
The mechanical properties of three armor steels, namely Ramor 500, Ramor 550, and Armox Advance, were acquired by nanoindentation and conventional methods, and then the results were compared. To this goal, samples were extracted from different (e.g., undeformed and deformed) zones of the ballistically tested armor plates. Then, nanoindentations were performed at 10-mN maximum load and different maximum indentation depths (50-150 nm). In addition to the hardness and modulus of elasticity values of the examined materials, residual stress values of the samples were calculated through the equations suggested in the literature. These values were then compared with the residual stress measurements obtained with the conventional x-ray diffraction (XRD) - sin2ψ method. Moreover, Charpy V-notch impact tests were performed to calculate the fracture toughness of armor steel samples. Microstructural analysis (e.g., optical microscope, scanning electron microscope, atomic force microscope), surface roughness, and micro-hardness (micro-Vickers) measurements were also obtained. It was noted that hardness values for the Ramor 500 and Ramor 550 armor steels were in the range of 5.5-9 GPa, whereas the hardness values of Armox Advance samples were obtained in the 8.6-10.2 GPa range at a 50-nm indentation depth. The residual stress values obtained with nanoindentation were found to be in quite good agreement with the one obtained through XRD. It was proven that nanoindentation can be used to acquire several mechanical properties through considerably less sample preparation procedure, in an automated, and a more representative manner because of the measurements obtained at multiple points.
- MakaleYalnız künye2013Scopus SJRQ2Effects of different curvature patches on the strength of double-strap adhesive joints
Akpinar, Salih
In general, the damage in adhesively bonded joints initiates from and propagates through the ends of the overlap area due to high stress concentration in that area. The reduction of these stress concentrations results in an increase in the strength of the joints. For this reason, the rounding of the overlap region before bonding and then applying compression during the bonding process will exert compressive residual stresses on the adhesive layer in the overlap end regions. It is known that the residual stresses formed in this process increase the failure strength of the joint and hence delay the initiation of the damage. In this study, the effects of overlap length (L = 50,75, and 100 mm), patch thickness (h = 1.6, 3.2, and 5 mm) and patch materials (AA2024 aluminum alloy, AISI 304 steel, AISI 1040 steel) on bond strength were experimentally investigated for adhesively bonded double-strap joint (DSJ) and curvature double-strap joint (CDSJ) subjected totensile loading. The experimental study showed that the overlap length, patch thickness and patch materials have considerable influence on the failure strength and displacement capacity of the joints.
AtıfScopus31WoS29
İncele - MakaleYalnız künye2013Scopus SJRQ2Increasing single-lap joint strength by adherend curvature-induced residual stresses
Temiz, Ş.; Akpinar, S.; Aydin, M.D.; Sancaktar, E.
Single-lap joint (SLJ) geometry is the most widely used type of adhesive joint geometry. In this joint, peel stresses occur at the overlap ends due to load eccentricity and the presence of shear-free adhesive termination surfaces. These peel stresses, along with the transverse tensile stresses which occur along the overlap longitudinal axes, and adhesive shear stresses, ultimately cause joint failure. Obviously, reductions in these stresses should result in higher joint strength and increased load capacity. To this end, we exploited elastic spring-back capability of (steel) metal adherends by initially forming curved segments of varying arc lengths and radii at overlap ends. These adherends with curved-end sections were then bonded in single-lap configuration, simply by applying sufficient bonding pressure to elastically flatten the curved segments to result in typically flat overlap sections subsequent to adhesive cure and the removal of bonding pressure. Since the elastic adherend overlap ends tend to revert back to their initial curved form, they exert compressive residual stresses on the adhesive layer in the overlap end regions. We determined that the compressive residual stresses induced in this fashion considerably increased the load capacity of SLJs subjected to tension.
AtıfScopus18WoS18İncele