DETERMINATION OF MATERIAL RESPONSE AND OPTIMIZATION OF JOHNSON-COOK DAMAGE PARAMETERS OF ALUMINIUM 7075 ALLOY

The effects of rolling direction and notch radius on the mechanical response of aluminium 7075-T651 alloy were investigated and the Johnson-Cook damage parameters of aluminium 7075-T651 alloy on both rolling directions were determined. Specifically, mechanical responses of aluminium 7075- T651 along the rolling direction and perpendicular to the rolling direction were obtained from monotonic tensile tests. 56 tensile tests in total were performed on notched specimens with 3 different notch radiuses and smooth specimens. Tensile tests were repeated 7 times for each case to ensure the consistency and to obtain the closest mechanical response to the real mechanical response with minimum error. Experimental findings revealed that being perpendicular to the rolling direction deteriorates the elongation at failure dramatically but can increase the mechanical properties in elastic region. The final areas of the fractured samples, used for the calculation of Johnson-Cook damage parameters, were measured by an optical microscope. The Johnson-Cook damage parameters of aluminium 7075-T651 alloy for different applications were computed by Levenberg-Marquardt optimization method. Collectively, this study opens the venue for accurate damage simulations of aluminium 7075-T651 along the rolling direction and perpendicular to the rolling direction for different applications.

Alüminyum 7075 Alaşiminin Malzeme Davranişinin Tespiti ve Johnson-Cook Hasar Parametrelerinin Optimizasyonu

Alüminyum 7075-T651 alaşımının mekanik davranışına hadde yönünün ve çentik yarıçapının etkileri incelenmiş ve bu alaşımın iki farklı hadde yönü için Johnson-Cook hasar katsayıları hesaplanmıştır. Spesifik olarak, hadde yönünde ve hadde yönüne dik olarak hazırlanmış alüminyum 7075-T651 alaşımının mekanik davranışları çekme testleri sonucunda belirlenmiştir. 3 farklı çentik yarıçapındaki numunelere ve çentiksiz numunelere olmak üzere toplamda 56 adet çekme testi gerçekleştirilmiştir. Her bir çekme testi tutarlılığı sağlamak ve gerçek mekanik davranışa en yakın sonucu en düşük hata ile elde etmek adına 7 kere tekrarlanmıştır. Deneysel bulgular hadde yönüne dik olmanın uzamayı azalttığını fakat elastik bölgedeki mekanik özellikleri arttırabildiğini göstermektedir. Johnson-Cook hasar katsayılarının hesaplanmasında kullanılan kırılmış yüzey alanları optik mikroskop ile ölçülmüştür. Alüminyum 7075-T651 alaşımının Johnson-Cook hasar katsayıları farklı uygulama alanları için Levenberg-Marquardt optimizasyon methodunu kullanarak hesaplanmıştır. Bu sebeple, bu çalışma hadde yönünde ve hadde yönüne dik olarak hazırlanmış alüminyum 7075-T651 alaşımının farklı uygulama alanlarındaki hassas hasar simulasyonları için yol gösterici bir alan açmaktadır.

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