A modified phenomenological model for PAAm hydrogel with hardening effect under cyclical loading

• Main Author: Goh, Jing Xuan
• Other Authors: Li Hua
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/168106
• Institution: Nanyang Technological University

In this study, an improvement is suggested upon existing phenomenological models to more accurately reflect the Mullins effect, strain hardening phenomenon, and residual stretch associated with PAAm hydrogel. Our modifications to existing research allowed for better predictions of hydrogel fatigue fracture behaviour, which has important implications for the durability and reliability of hydrogel-based technologies. The root mean square value improved by 69% in comparison to the model proposed by Wang [1]. This work attempts to create the best model for capturing the stress-stretch characteristic of PAAm hydrogel over a prolong cycle. The study begins with a brief introduction to hydrogel and an overview of current simulation and modelling techniques. A literature review is then presented, summarizing current attempts to develop a fatigue fracture model. This study chooses to focus on phenomenological model, which has shown superior predictive ability compared to the physical model. Among the sparse literature of phenomenological model on hydrogel, Wang model [1] is currently considered one of the most accurate models in predicting double-network hydrogel after prolonged cycles. However, after implementing Wang model [1] into MATLAB fitted with PAAm hydrogel data, the predictive error was found to be high, possibly due to the model's inability to accurately capture the strain hardening effect. In this paper, the knowledge from all previous phenomenological models is consolidated. Based on the experimental results of PAAm hydrogel, two proposed modifications were suggested to modify the softening parameter, both of which resulted in better approximations compared to the Wang phenomenological model [1]. At the time of writing, there was no known publication that models fatigue fracture for PAAm hydrogel using a phenomenological approach. This study contributes by introducing a new softening variable to more accurately capture the characteristics of PAAm hydrogel in a multiple tensile loading experiment, resulting in a reduced error compared to actual experimental data. In addition, the derived MATLAB code provided in this paper presents an opportunity for further research onto different platform such as ABAQUS to visualise the stresses experienced in PAAm hydrogel.