AISI 4340 Çeliğinin Farklı Gerinme Hızlarında ve Sıcaklıklarda Dinamik Basma Davranışı

Year 2024, Volume: 16 Issue: 2, 707 - 720, 30.06.2024

Hakan Hafızoğlu

https://doi.org/10.29137/umagd.1385551

Abstract

Bu çalışmada, AISI 4340 çelik alaşımının dinamik basma davranışı ayrık-Hopkinson ve Taylor çarpma testleri ve nümerik çalışmalarla incelenmiştir. Ayrık-Hopkinson basınç barı kullanılarak oda sıcaklığında 725, 1500, 2000 s-1 gerinme hızlarında ve 150 ve 250 °C yüksek sıcaklıklarında dinamik basma testleri yapılmıştır. Çarpma koşullarında dinamik deformasyon davranışını gözlemlemek için 245, 324 ve 336 ms-1 çarpma hızlarında Taylor çarpma testleri icra edilmiştir. Taylor çarpma testlerinde numunelerdeki gerilme ve sıcaklık dağılımının incelenmesi için Ls-Dyna 3D sonlu elemanlar yöntemi kullanılarak numerik çalışmalar yapılmıştır. Deneysel sonuçlar oda sıcaklığında yapılan dinamik basma testlerinde gerinme hızının artışı ile akma ve en fazla basma dayanımının ve toplam gerinmenin arttığını göstermiştir. Yüksek sıcaklık koşullarında yumuşama etkisi dolayısıyla her iki dayanım da düşmüş ve toplam gerinmeler artmıştır. Taylor çarpma test sonuçları tüm numunelerin mantarlanma deformasyonuna uğradığını ve çarpma hızı artışının kesme çatlakları ve deformasyon sürecinin sonunda kırılmaya neden olduğunu göstermiştir. Nümerik sonuçlar en yüksek sıcaklıkların üç çarpma hızı için de çarpma yüzeylerinde bulunduğunu göstermiştir. Ek olarak, çarpma hızının artışı çarpma yüzeylerine yakın deforme olmuş bölgelerde gerilme dağılımını artırmıştır.

Keywords

Taylor çarpma testi, ayrık-Hopkinson basıç barı, AISI 4340 çeliği

Dynamic Compression Behavior Of AISI 4340 Steel Under Various Strain Rates And Temperatures

Abstract

In this study, dynamic compression behavior of AISI 4340 steel alloy was investigated with split-Hopkinson and Taylor impact tests and numerical studies. Dynamic compression tests at strain rates of 725, 1500, 2000 s-1 at room temperature and at high temperatures of 150 and 250 °C were done using split-Hopkinson pressure bar. Taylor impact tests with the impact velocities of 245, 324 and 336 ms-1 were performed with cylindirical specimens to observe dynamic deformation behavior at impact conditions. Numerical studies using Ls-Dyna 3D finite element method were conducted to investigate temperature and stress distribution of specimens during Taylor impact tests. Experimental results revealed that as strain rate increased, yield and ultimate compressive strengths and total strains increased at room temperature at dynamic compression tests. At elevated test conditions, both strengths decreased and total strains increased due to softening effect. Taylor impact test results showed that all the specimens exhibited mushroomed deformation and increase of impact velocity led to shear crack and fracture at the end of deformation process. Numerical results indicates that highest temperatures were obtained at the impact surfaces for three impact velocities. In addition, the increase of impact velocity enhanced the stress distribution at deformed regions near impact surfaces.

Keywords

Taylor impact test, split-Hopkinson pressure bar, AISI 4340 steel

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