Semester of Graduation

August 11, 2023

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical and Industrial Engineering

Document Type

Thesis

Abstract

Polymer composite materials are attractive due to their high specific stiffness and strength-to-weight ratio. The use of thermoset shape-memory polymers (TSMPs) as a matrix provides additional advantages such as high recovery stress to assist in crack closing. Additionally, their intrinsic drawbacks including relatively low modulus and low strength can be overcome by incorporating fiber reinforcement. This study aims to analyze the fatigue life and damage progression of glass-fiber (GF)-reinforced thermally responsive shape memory epoxy composite laminates, before and after compression programming. Composite panels were made from 8 harness satin (HS) GF plies in a [0/90] layup and manufactured using vacuum bagging and oven-assisted curing process (2.5 mm-thick laminates). Bending fatigue tests were performed at room temperature under displacement control mode (20.32 mm (0.8 in) or 10.16 mm (0.4 in), ~30 Hz frequency) on unprogrammed dog bone specimens to understand failure mechanisms under flexural fatigue. Dog bone specimens underwent different cyclic intervals, from 5000 cycles to failure (30000 to 36000 cycles) for 0.8 inches displacement test. Damage analysis at each cyclic interval was performed using scanning electron microscopy (SEM), which indicated delamination, matrix microcracking, and fiber failure as dominant failure modes, as the number of cycles increased. A similar damage analysis was carried out on programmed TSMP composite specimens that underwent up to 133000 cycles. SEM analysis revealed moderate delamination, compared to unprogrammed specimens at lower cycles, indicating compression programming has potential to increase fatigue life of laminates. Finally, a series of specimens were also tested at cyclic intervals (20000 cycles intervals at 10.16 mm displacement), on which damage healing was manually applied through a heated press after each interval. SEM analysis showed that most of the damage was healed, which can help specimens reach a longer fatigue life. The outcomes of this study presented a better understanding of damage mechanisms of TSMP composites under flexural fatigue, as well as the potential of compression programming and external damage healing to extend fatigue life.

Date

7-11-2023

Committee Chair

Dr. Genevieve Palardy

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