Master of Science in Mechanical Engineering (MSME)
A shape memory polymer (SMP) is a smart material capable of maintaining two distinct shapes depending on its temperature. A SMP is soft at temperatures above its glass transition temperature but hard below it. When copolyester thermoplastic additives are dispersed in a SMP, it becomes a SMP-based particulate composite capable of self-healing at both the molecular level and the structural level. This makes it very desirable for industrial applications. Upon damage to the composite, the surfaces at the damage interface have to come into contact for efficient healing; the shape memory effect, coupled with a confined recovery (healing) process, ensures this. This study examined the effect of the surface roughness at the damage interface on the efficiency of the healing process. Also studied was the effect of the compressive stress at the point of contact during the healing process on the healing efficiency. The particulate composite (CP-PSMP) consisted of polystyrene shape memory polymer (PSMP) as the matrix and copolyester thermoplastic additives (CP) as the reinforcement. Compressive programming at 10 % pre-strain was performed on the CP-PSMP, which was then tested for its pre-flexural strength. Next, the surfaces were varied using sandpapers of different embedded particle diameters, and the CP-PSMP was healed at 10 MPa using the close-then-heal (CTH) self-healing mechanism. The recovered flexural strength was then obtained and the healing efficiency computed as a fraction of the recovered flexural strength to the pre-healing flexural strength. Healing efficiencies were found to be higher for CP-PSMP with smoother surfaces. The highest healing efficiency of 39 % was found in CP-PSMP with average and root-mean-squared roughness profile parameters, Ra and Rq, of 0.425 and 0.617 μm respectively. Another set of tests revealed that healing was more efficient at higher compressive stresses. Efficiencies at higher compressive stresses (20 – 80 MPa) ranged from 78 % to 118 %. Next, the effects of sanding on healing efficiency was examined by comparing the healing efficiencies of two sets of CP-PSMP with similar Ra and Rq values—one of which was treated with sandpaper. The sanded CP-PSMP samples were 24 % more efficient in healing.
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Okoro, Ifeanyi Janarus, "Effect of surface roughness on the efficiency of self-healing polymers" (2013). LSU Master's Theses. 2865.