Molecular Weight Controls Interactions between Plastic Deformation and Fracture in Cold Spray of Glassy Polymers

Abstract

Polymer cold spray has gained considerable attention as a novel manufacturing process. A promising aspect of this technology involves the ability to deposit uniform polymer coatings without the requirements of solvent and/or high-temperature conditions. The present study investigates the interplay between shear instability, often considered to be the primary mechanism for bond formation, and fracture, as a secondary energy dissipation mechanism, collectively governing the deposition of glassy thermoplastics on similar and dissimilar substrates. A hybrid experimental-computational approach is utilized to explore the simultaneous effects of several interconnected phenomena, namely the particle–substrate relative deformability, molecular weights, and the resultant yielding versus fracture of polystyrene particles, examined herein as a model material system. The computational investigations are based on constitutive plasticity and damage equations determined and calibrated based on a statistical data mining approach applied to a wide collection of previously reported stress–strain and failure data. Results obtained herein demonstrate that the underlying adhesion mechanisms depend strongly on the molecular weight of the sprayed particles. It is also shown that although the plastic deformation and shear instability are still the primary bond formation mechanisms, the molecular-weight-dependent fracture of the sprayed glassy polymers is also a considerable phenomenon capable of significantly affecting the deposition process, especially in cases involving the cold spray of soft thermoplastics on hard substrates. The strong interplay between molecular-weight-dependent plastic yielding and fracture in the examined system emphasizes the importance of molecular weight as a critical variable in the cold spray of glassy polymers, also highlighting the possibility of process optimization by proper feedstock selection.

Cold Spray Deposition of Nylon-6 on Glass Fiber-Reinforced Composites

“…Numerical values for the model parameters used in the current simulations are given in Table . Note that the validity of the Johnson–Cook plasticity model in polymer cold spray has been discussed in several prior investigations. , …”

“…Note that the validity of the Johnson−Cook plasticity model in polymer cold spray has been discussed in several prior investigations. 43,44…”

Polyurea/Aminopropyl Isobutyl Polyhedral Oligomeric Silsesquioxane-Functionalized Graphene Nanoplatelet Nanocomposites for Force Protection Applications

“…This capability is essential to effectively absorb and dissipate a broader spectrum of loading frequencies. Overall, the energy absorption and impact strength of polymers can be subject to the modulation induced by factors such as their chemical structure, 7 molecular weight, 8,9 and presence of organic and/or nonorganic, nanosized additives, including carbon nanotubes (CNTs), 10 nanosilica, 11 cellulose nanocrystals (CNCs), 12 graphite oxide, 13 graphene oxide (GO), 14,15 and graphene nanoplatelets (GNPs). 16,17 Extensive research efforts have been conducted to explore the impact of both GNPs and their derivatives on the mechanical properties of PU thanks to their outstanding intrinsic properties and more availability than other nanostructured carbon allotropes, i.e., one-dimensional nanotubes and zero-dimensional fullerenes.…”

“…This capability is essential to effectively absorb and dissipate a broader spectrum of loading frequencies. Overall, the energy absorption and impact strength of polymers can be subject to the modulation induced by factors such as their chemical structure, molecular weight, , and presence of organic and/or nonorganic, nanosized additives, including carbon nanotubes (CNTs), nanosilica, cellulose nanocrystals (CNCs), graphite oxide, graphene oxide (GO), , and graphene nanoplatelets (GNPs). , …”

“…Therefore, achieving a homogeneous dispersion of GNPs in a polymer solution (preventing GNP aggregation and restacking) is crucial . One approach to achieve this is the chemical modification of GNPs that would promote stronger polymer–nanofiller interactions (better compatibilization) and, hence, lead to enhanced mechanical properties of the final nanocomposite product. ,,,− , As reported in the literature, hydrogen atoms and sp 2 -carbon-containing groups could potentially be active sites for GNP functionalization with different chemical modifiers, such as aluminum triisopropoxide, 3-amino-propyltrimethoxysilane, acids, ,,− metal oxides, − metal nanoparticles, − amines, − and POSS. − Among these modifiers, POSS is conceived as a suitable one based on its well-defined hybrid nanostructure and favorable and flexible chemistry, thanks to its inorganic siloxane cages and peripheral organic groups. Specifically, POSS comprises a crystalline silica cagelike core, which is surrounded by eight organic groups connected by Si–O–Si bonds.…”