Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 100272

100272 - A Multi-Physics Phase-Field Model for Studying Interaction Between Phase Transformation and Cracking in Shape Memory Ceramics 

In this research we present a modified phase-field model to investigate the interaction between phase transformation and cracking in shape memory ceramics. The chemical free energy is modified to address the shortcomings of current models in predicting the elastic response of shape memory materials. The chemical free energy is modified by adding a new term which gives more control on the evolution rate of the order parameters at the beginning of the stress-strain curve. In other words, the added term slows down the evolution rate of the order parameter, therefore, the material behaves elastically in the beginning of the stress-strain. The modified phase-field model is first tested for accurate predictions of microstructure and mechanical response in a super-elastic single crystal 3 mol% yttria-stabilized tetragonal zirconia without considering fracture. Using the unmodified phase-field model yields about 30% error between the predicted elastic modulus and actual elastic modulus. However, this error decreased to 5% by our proposed modified phase-field model. In addition, the modified phase-field model predicts a more pronounced twin-martensite experimentally observed microstructure compared to the unmodified model. Furthermore, the proposed model predicts an experimentally reported transformation stress and a plateau region in the stress-strain curve.

 Furthermore, the modified phase-field is coupled with phase-field fracture to study the interaction between phase transformation and cracking in a center-cracked super-elastic specimen under displacement-controlled loading condition. Based on the obtained results and comparing the results with the literature, the model can predict a realistic mechanical response and fracture strain, the experimentally observed microstructure, crack deflection due to phase transformation, and reverse phase transformation due to crack propagation in super-elastic shape memory ceramics. The ultimate strain (fracture strain) obtained using the modified phase-field model is about 4%.  In the experimental studies, a maximum bending strain of 8% was reported for a coarse-grained micropillar specimen in the super elastic regime. Therefore, a model prediction of the maximum strain for a cracked single crystal experiencing uniaxial tension is expected to be less than the reported maximum bending strain and this is captured in the predicted stress-strain curve using the modified phase-field model. The ultimate strain for a single crystal zirconia is reported to be 15% in the literature using unmodified phase-field model.

The modified phase-field model provides a reliable computational tool for study and design of shape memory ceramics. Such studies are difficult to conduct by experiments which show advantage of phase-field modeling in study of interactions of phase transformation and cracking.

 

Keywords: Shape memory ceramics; Phase transformation; Fracture; Super-elastic regime; Phase-field model.

 

 

Presenting Author: Amirreza Lotfolahpour Colorado School of Mines

Presenting Author Biography: My name is Amirreza Lotfolahpour,<br/><br/>I am a Ph.D. student in Mechanical Engineering at Colorado School of Mines. I joined Prof. Asle Zaeem&#39;s research group in August 2019. My research is focused on phase-field modeling of phase transformation and fracture in non-transforming and transforming ceramics (shape memory ceramics). I already published one paper based on my research and about to submit the second paper. My current research is supported by the U.S. National Science Foundation (NSF), under Award number 2054274.

Authors:

Amirreza Lotfolahpour Colorado School of Mines
Mohsen Asle Zaeem Colorado School of Mines