11/21/2022
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a doctoral dissertation proposal defense by Nahal Aliheidari on “Long-Term Environmental Durability Assessment of Fiber-Reinforced Composite/Adhesive Joints.”

Candidate Name: Nahal Aliheidari
Degree: Doctorate
Date: Monday, Nov. 28, 2022
Time: 2 to 4 p.m.
Location: Ball Hall 323 and virtual via Zoom.

Committee:

  • Advisor Amir Ameli, Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
  • Davide Masato, Chair, Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
  • Akshay Kokil, Assistant Teaching Professor, Plastics Engineering, University of Massachusetts Lowell

Brief Abstract:

Adhesives such as epoxies are extensively used as structural components in wind turbines. As the service life of a wind turbine is in the range of decades and it can experience harsh environments (e.g., hot, humid, saline), the long-term durability and reliability of these structural adhesives are vital. Water ingress over this long time causes degradation in composite/adhesive joints such that adhesive failure has become one of the leading causes of the blade’s malfunction.

There is extensive research on fracture mechanics in the modeling and design of WT’s adhesive joint. There are also reports on accelerated aging of stress- and strain-based test specimens applicable to WT. However, there is a lacking effort on aging via the accelerated open-faced method and its applicability to the prediction of long-term fracture performance in WT’s adhesive joints. In this research, we propose a framework that enables the assessment and eventually prediction of joint’s strength upon environmental degradation. The framework unites fracture mechanics with open-faced accelerated hygrothermal aging and finite element modeling.

The proposed project will investigate a) composite surface treatment, b) water absorption/desorption characterization of adhesives, c) fracture testing and evaluation using end-notched flexural joints, and d) integration of the hygrothermal and fracture behaviors into a finite element model. The gravimetric measurements for two different adhesives were conducted to measure and model the water absorption/desorption behavior. The open-faced accelerated aging approach and fracture mechanics will be used to measure the loss of fracture toughness (Gc) in adhesive joints. Envelopes of Gc representing a range of degradation (governed by temperature, relative humidity, and time of exposure) will be created and correlated to an Environmental Index (EI) defined by the adhesive’s hygrothermal behavior and exposure time. The integrated Gc-EI envelopes will be used together with a finite element cohesive zone model (FE-CZM) to predict the strength loss of joints at a given level of degradation.

All interested students and faculty members are invited to attend the defense in person or via remote online access. Those interested in attending should contact Nahal_aliheidari@student.uml.edu and committee advisor, amir_ameli@uml.edu, at least 24 hours prior to the defense to request access to the meeting.