Browsing by Author "Tahir, Furqan"

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Effect of aging on the mechanical behavior of aluminum-steel composites processed by accumulative roll bonding
(Elsevier, 2021) Tahir, Furqan; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Tahir, Furqan
Severe plastic deformation (SPD) processes have been widely used to provide ultrafine-grained (UFG) structures along with enriched strength in various metals. This study focuses on accumulative roll bonding (ARB), an SPD method, which was employed to fabricate aluminum and interstitial free steel composite, while the effect of heat-treatment was investigated by the resulting mechanical behavior. Improvement in strength and ductility levels was attained with increasing aging time, indicating the formation of precipitates among aluminum layers. Substantial enhancements in tensile strength and elongation of 420 MPa and 18%, respectively were exhibited after 24hr aging time. Interface strength raised consistently throughout the aging treatments which was about 270 MPa under shear.
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Manufacturing and mechanical behavior of lightweight composites by accumulative roll bonding
(2021-08-18) Tahir, Furqan; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Başol, Altuğ Melik; İpekoğlu, M.; Department of Mechanical Engineering; Tahir, Furqan
Severe plastic deformation (SPD) methods have received significant attention in fabricating a combination of similar and dissimilar metal composites. Accumulative roll bonding (ARB) is one of the SPD techniques employed to produce high strength, fine-grained, and multi-layered metal matrix composites (MMCs). The current work is characterized into two parts. The major part deals with the fabrication of different combinations between titanium and interstitial free (IF) steel interlayered with aluminum alloy (Al2024). While the second part studies the effect of post-ARB heat treatment on Al2024-IF steel composite. Microstructural evaluation and mechanical characteristics of processed composites were examined by optical microscope (OM), scanning electron microscope (SEM), and mechanical tests. Surface and bulk properties were analyzed through microhardness, uniaxial tensile, and shear punch test (SPT). Finally, experiment results were validated using numerical analysis. For the first case of titanium-IF steel composites, the optical micrographs indicated the reduction in layer thickness and grain size after each rolling cycle. Necking was initiated in some layers of the processed composite after the third (final) ARB cycle, suggesting the interlocking of layers and consequently stronger bonding. SEM figures from fracture surfaces revealed the delamination of layers from interfaces in early cycles, that lessened in the final cycle due to high strain exerted after each rolling cycle. Significant improvement was noticed in hardness levels as the number of ARB cycles increased. Enhancement levels for titanium and IF steel layers were up to 1.4 and 2.6 times, respectively after the ARB process. The tensile strength of the titanium-IF steel composite rolled at 400°C exceeded over 670MPa after three cycles. Typical to SPD processes, the ductility was reduced to less than 5% in all cases after three ARB cycles. Enhancement levels in tensile strength of each layer of the final composite compared to the initial metals were similar to hardness. SPT results showed the improvement in shear strength of the sample with the increasing number of cycles, a maximum shear strength of around 440MPa was achieved after three cycles. For the second part of aluminum-IF steel composite, microstructure observation revealed that long aging imparted partial coarsening of the average grain size in a three-cycle ARBed sample. Furthermore, the ductility was recovered after aging without losing tensile strength due to the occurrence of precipitation hardening along with recovery in individual layers. A maximum ultimate tensile strength (UTS) and ductility of around 420MPa and 18%, respectively, was obtained after aging at 150°C for 24h. SPT results showed a similar response as the tensile test, and maximum shear strength was reached up to 270MPa at the peak-aged condition. The ARB process, in the case of titanium-IF steel composite, was modeled by employing finite element analysis through ANSYS workbench. The effective plastic strain and effective stress (von-Mises) were calculated through the thickness of ARBed samples. A close agreement between experimental findings and numerical simulations was observed.
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Manufacturing and mechanical behavior of titanium-steel composite by accumulative roll bonding
(Trans Tech Publications Ltd, 2021) Tahir, Furqan; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Tahir, Furqan
Metal matrix composites have attracted interest for use in several engineering applications and this study focuses on the fabrication titanium and interstitial free steel composite and its mechanical performance. Accumulative roll bonding (ARB) was employed as a severe plastic deformation method to fabricate the multi-layered composite up to three cycles where an aluminum alloy is utilized as an interlayer material. Improvement in hardness and strength levels was achieved with an increased number of ARB cycles. Although, the composite obtained after three cycles indicated a brittle behavior, a decent tensile response of around 650 MPa and 10% ductility was demonstrated after two ARB cycles.