Sadegh ghorbanhosseini

Grade:  Master

Thesis Title:

Implementation of Ductile-Brittle Damage model for cyclic loading in Al 2024.

Year: Sept. 2011- Feb. 2014.

Abstract:

Damage mechanics is one of the most important parts of mechanical engineering to determine mechanical component’s lifetime and their vulnerable sections. This branch of mechanical engineering is very efficient to model microvoids and microcracks in industrial processes. For this topic various models are presented in the context of damage mechanics for different materials up to now, respectively. But these days investigating the damage behavior of materials with double behavior (ductile and brittle) is highly regarded. These materials show different failure behavior reflects under various loading extensions so that is a reason for dual behavior of these materials. Due to high strength of these materials, they are used in different industrial processes under various loading condition like aerospace industry. The 2024-T351 aluminum alloy is one of these materials that extensively used for fabricating aircraft parts. This aluminum alloy shows a relatively low ductility at room temperature and is generally heat treated in various conditions to suit particular applications. According to Kintzel experimental observations, the material response of the 2024-T351 aluminum alloy is highly direction-dependent showing a material behavior between ductile and brittle. In particular, in its corresponding (small transversal) S-direction, the material behavior can be characterized as quasi-brittle. This kind of aluminum alloy is one of ductile-brittle materials that have high strength to weight ratio. For modeling of such a mechanical response, a novel, fully coupled isotropic ductile-brittle continuum damage mechanics model is proposed by Kintzel. Most of works that were presented in the damage mechanics field were taken under uniform load and the Kintzel ductile-brittle damage model was not implemented under cyclic loading. Because of this, in this study due to the various efficiency of ductile-brittle material, the Kintzel ductile-brittle damage model under cyclic loading was implemented. The purpose of this work is to predict the cyclic lifetime of the considered alloy, based on the local approach of damage evolution using continuum damage modeling (CDM). The present study numerically analyzes the damage mechanism of a 2024-T351 aluminum alloy plate (short transverse direction) subjected to cyclic uniaxial stress state to validate its implementation with Kintzel experimental results at first. Furthermore this implementation was used for a case study in the aerospace industry. Evaluation of aircraft’s wing performance under air pressure is defined as a case study in this study. This study demonstrates that ductile-brittle materials show high strength in different load case. Furthermore by knowing the small magnitude of composition factor for brittle damage, the effect of brittle damage on the total damage is small in comparison with the ductile damage, and the effect of strain on the brittle damage is less than ductile damage.

Keywords:

Damage mechanics, Kintzel, Ductile-brittle damage, 2024-T351 aluminum alloy, Cyclic loading.