Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

Abstract

Fiber-filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the b-relaxation to the a-relaxation, or glass transition temperature, (i.e., from À100 to 180 C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the a-relaxation region, increasing in the vicinity of the b-relaxation, and then decreasing below the temperature associated with the peak in the b-relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the a-relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the b-relaxation peak.

Pressure‐volume‐temperature and glass transition behavior of silica/polystyrene nanocomposite

“…This differs from results on a 10 wt % POSS nanoparticle/epoxy system where 10 and 20% reductions in the thermal stress coefficient (as estimated by a P G) and thermal pressure coefficient c at 10 wt % POSS loading were found 4,5 in the glassy state below T g.…”

“…4,5 Although moduli and thermal expansivities normally exhibit a reciprocal relationship, [6][7][8] findings for a 10 wt % polyhedral oligomeric silsesquioxane (POSS)-reinforced epoxy resin show reductions in the thermal pressure coefficient and the thermal stress coefficient (the product of linear thermal expansion coefficient a L and Young's modulus E). 4,5 In addition, model calculations have also reported polymer nanocomposites may have exceptional properties-for example, the incorporation of nanoparticles may reduce the bulk modulus of the neat polymer. Hooper and Schweizer 9 predicted that the bulk modulus of well-dispersed spherical nanoparticle-filled polymer decreases significantly with increasing filler loading using the Polymer Reference Interaction Site Model (PRISM); at 10% filler volume loading, K decreases approximately 10% compared to the neat polymer.…”

“…These isotropic thermal residual stresses, which can lead to early failure or suboptimal performance of a material, depend on the thermal pressure coefficient c, which in turn depends on the product of the bulk modulus K (52V(@P/@V) T ) and the isobaric thermal expansion coefficient a p (51/V(@V/@T) P ). [1][2][3][4] One potential strategy to mitigate thermal residual stresses in fiber-reinforced polymeric materials may be to add nanoparticles to the polymer matrix. 4,5 Although moduli and thermal expansivities normally exhibit a reciprocal relationship, [6][7][8] findings for a 10 wt % polyhedral oligomeric silsesquioxane (POSS)-reinforced epoxy resin show reductions in the thermal pressure coefficient and the thermal stress coefficient (the product of linear thermal expansion coefficient a L and Young's modulus E).…”

“…[1][2][3][4] One potential strategy to mitigate thermal residual stresses in fiber-reinforced polymeric materials may be to add nanoparticles to the polymer matrix. 4,5 Although moduli and thermal expansivities normally exhibit a reciprocal relationship, [6][7][8] findings for a 10 wt % polyhedral oligomeric silsesquioxane (POSS)-reinforced epoxy resin show reductions in the thermal pressure coefficient and the thermal stress coefficient (the product of linear thermal expansion coefficient a L and Young's modulus E). 4,5 In addition, model calculations have also reported polymer nanocomposites may have exceptional properties-for example, the incorporation of nanoparticles may reduce the bulk modulus of the neat polymer.…”

Evaluation of cure shrinkage measurement techniques for thermosetting resins

“…A modern rheometer can be configured to measure linear shrinkage and investigate the rheological behavior of the resin [10,24]. Torque or strain controlled tests can be performed to not only determine the point of gelation but also to monitor dimensional changes of the resin as it cures.…”