Large strain and small-scale biaxial testing of sheet metals

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2016

Öğrenci: YADİGAR SEYMEN

Danışman: MERT EFE

Özet:

Small-scale and multi-axial testing of sheet metals, particularly of lightweight alloys and advanced high strength steels (AHSS) are becoming important as these materials exhibit forming behavior sensitive to their unique microstructural features and strain paths. As an alternative to large-scale standard tests, in this study, a novel biaxial tensile test apparatus for miniature cruciform samples is introduced. The compact and portable apparatus includes a custom-built optical microscope and high-resolution digital imaging and correlation equipment for in-plane and in-situ strain measurements at the microstructure scale. The small strain and premature fracture problems common to the cruciform tests are solved by optimizing the sample design and by meticulously controlling the manufacturing steps and surface finish. Strain analyses reveal a key mechanism responsible for large strains and fracture at the center. This mechanism suppresses the local neck formation and allows uniform deformation under equibiaxial conditions until fracture. When normalized with the strain hardening exponent of the sample material (Al 6061-T6), the effective strain value before fracture, , surpasses the reported values for similar materials tested by cruciform and standard methods.