07/26/2021
By Sokny Long
Ph.D. Candidate: Vahidreza Alizadeh
Defense Date: Monday, Aug. 2, 2021
Time: 9 – 11 a.m. EST
Location: This will be a virtual defense via Zoom. Those interested in attending should contact vahidreza_alizadeh@student.uml.edu and committee advisor, alireza_amirkhizi@uml.edu, at least 24 hours prior to the defense to request access to the meeting.
Committee Chair (Advisor): Alireza V. Amirkhizi, Associate Professor, Department of Mechanical Engineering, UMass Lowell
Committee Members:
• Scott Stapleton, Assistant Professor, Department of Mechanical Engineering, UMass Lowell
• Christopher J. Hansen, Associate Professor, Department of Mechanical Engineering, UMass Lowell
• Joey Mead, Interim Associate Dean, Department of Plastics Engineering, UMass Lowell
Brief Abstract:
Elastomers and their composites have been used in harsh and extreme loading conditions such as cavitation erosion, blast, and ballistics. Examples of such applications include polyurea (PU) under cavitation erosion and blast, polyethylene (PE) and its composites under ballistic impact, and transparent polycarbonate (PC) for eye protection. These materials undergo large deformations at a high rate without immediate failure and provide an intriguing possibility for novel protection mechanisms and designs. However, fundamental mechanisms that derive such desirable outcomes have not yet been well understood.
This research aims to identify the mechanisms that contribute to the response of lightly cross-linked elastomers, in particular polyurea variants and its composites at high-rate and large deformation conditions, such as under cavitation erosion. To pursue this, two scientific aims were followed. The first aim is to identify the mechanical and chemical characteristics of polyurea that influence their behavior in high rate and large deformation conditions. To address this aim, , standard formulations and novel hybrid variants along with polyurea-based particulate-reinforced composites were synthesized and fully characterized thermomechanically both in their elastic and inelastic deformation regime. These variants were engineered to have superior properties believed to affect the cavitation erosion response the most, such as high yield plateau level with large ductility. The variants were then tested in cavitation erosion conditions, and results proved their improved performance compared to the standard formulations reported in the literature.
Elastomeric components including coatings undergo complex loadings configurations and histories. Therefore, numerical predictive models that can accurately represent and predict the mechanical behavior with such complexities are essential for design of optimum material candidates and geometries. The second scientific aim of this research is to develop a constitutive model, for lightly cross-linked elastomers applicable for high deformation rates with proper temperature and pressure update and plasticity, and to calibrate and validate it with the experimental findings. The numerical subroutine, which incorporates all the physical elements of the constitutive model components, is coded and is compatible with research and commercial finite element software packages. The results from this scientific aim are broadly applicable to all lightly cross-linked elastomers experiencing large deformations at high rates.
All interested students and faculty members are invited to attend the online defense via remote access.