Mekanik otofretaj işleminde oluşan kalıntı gerilmelerin sayısal olarak incelenmesi

Öz

Otofretaj, kalın cidarlı silindirlerin basınç taşıma kapasitelerini ve yorulma ömrünü artırmak için silindirin cidar kalınlığı boyunca kalıntı gerilme oluşturma işlemidir. Uygulamada birçok teknik olmasına rağmen, ağır silah namlusu üretim sürecinde en çok mekanik ve hidrolik otofretaj işlemleri kullanılmaktadır. Bu çalışmada, bir ağır silah namlusu üzerinde mekanik otofretaj işlemi sonunda oluşan gerilmeler, bir SEA (Sonlu Elemanlar Analizi) yazılımı kullanılarak sayısal olarak hesaplanmıştır. SEA analizinde iki boyutlu (2D) eksenel simetrik bir model kullanılmıştır. Otofretajsız namlu için çalışma basıncı altındaki Von Mises gerilmesi 1350,3 MPa olarak hesaplanmıştır. Otofretajlı namlu için Von Mises eşdeğer gerilmesi namlu et kalınlığının %63’ne denk gelen konumda 1122,3 MPa’dır. Bu gerilme değerinin, namlu akma mukavemeti olan 1195 MPa’ın altında olduğu görülmektedir. Sonuç olarak, çalışma basıncı altında otofretajlı namluda Von Mises eşdeğer gerilmesi %16,88 azalmıştır. Ayrıca, mekanik otofretaj işlemi sırasında oluşan mil kuvveti sayısal ve deneysel olarak hesaplanmıştır. Mil kuvveti SEA yazılımı ile 135,58 ton olarak hesaplanırken deneysel olarak yaklaşık 142 ton olarak ölçülmüştür Sayısal ve deneysel sonuçlar karşılaştırıldığında, iki sonuç arasında %4,52'lik bir hatanın olduğu görülmektedir. Bu hata oranının oldukça makul olduğu söylemek mümkündür. Sonuç olarak, sayısal çalışmanın gerçek durum şartlarını doğru bir şekilde yansıtması açısından oldukça başarılı olduğunu söylemek mümkündür.

Anahtar Kelimeler

• Mekanik Otofretaj
• Kalıntı Gerilme
• Sonlu Elemanlar Analizi (SEA)
• Sürtünme

Numerical investigation of residual stress formation during swage autofrettage process

Abstract

Autofrettage is the process of developing residual stress through the wall thickness of the cylinder to increase the pressure carrying capacity and fatigue life of thick-walled cylinders. Although there are many techniques in practice, swage and hydraulic autofrettage processes have been mostly used in heavy gun barrel production process. In this study, the stresses developed at the end of the swage autofrettage process on a heavy gun barrel are numerically calculated by using an FEA (Finite Element Analysis) software. In FEA, a two-dimensional (2D) axisymmetric model has been used. The Von Mises stress under working pressure for non-autofrettaged barrel is calculated as 1350.3 MPa. The Von Mises equivalent stress for the autofrettaged barrel is 1122.3 MPa at 63% barrel thickness. It is seen that this stress is below the barrel yield strength of 1195 MPa. As a result, there is 16.88% reduction of Von Mises equivalent stress for autofrettaged barrel under the working pressure. In addition, the pushing force generated during the mechanical autofrettage process has been calculated numerically and experimentally. The pushing force is calculated with FEA software as 135.58T while it is empirically measured as about 142T. When the numerical and experimental results are compared, it is seen that there is an error of 4.52% between the two results. It is possible to say that this percentage error is quite reasonable. Finally, it is possible to say that the numerical study is quite successful in terms of accurately reflecting the real-world conditions.

Keywords

• Swage Autofrettage
• Residual Stress
• Finite Element Analysis (FEA)
• Friction

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