Monotonic and fatigue properties of thin sheet of an interstitial free steel

Author(s)

Marcelo Tadeu Milan

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT)
• Defense date: 1999-06-18

Examining board members

Waldek Wladimir Bose Filho; Fernando Luiz Bastian

• Advisor: Waldek Wladimir Bose Filho

Abstract

In the present work, the monotonic and low cycle fatigue properties of thin sheet of interstitial free steel containing titanium additions, used in the automotive industry, were investigated. Fatigue tests were conducted under deformation control (R&#949 = -1) using a grip alignment fixture. The material exhibits different fatigue behavior for the transverse and longitudinal directions (in relation to the rolling direction). A comparison between the monotonic stress-strain curve and the cyclic stress-strain curve in the transverse direction showed that the material exhibits cyclic hardening in all strain amplitudes tested. The strain-life relationship obtained for transverse direction is given by &#916&#949t/2 = 0,0186(2Nf)-0,262 + 0,235(2Nf)-0,476 with transition point in 2Nt = 1,4x105 reverses; buckling of longitudinal specimens made impossible to obtain such relationship. Several prediction methods of fatigue properties from monotonic properties were compared to the experimental results. The Four Point Correlation and the Modified Universal Slopes Methods showed a good correlation for the low cycle region. Fractographic analysis through Scanning Eletronic Microscopy showed the presence of Stage II striations, giving support to the high ductility of the material. (AU)