Luke, Mark (2023-05). Polymer-Particle Composite Material Failure Characterization in Quasistatic Compression and Dynamic Impact Regimes. Master's Thesis.
Thesis
This work focuses on high solids loading (>=80% weight) polymer-particle composites, a specific subset of heterogeneous materials where particles are suspended in a polymer matrix. These composites exhibit complex behaviors in mechanical environments including viscoelasticity, pressure dependent yield, and damage accumulation via matrix rupture, polymer-particle interfacial debonding, and crystal fracture. At intermediate strain rates (O 10-1000 s?-1 ), these coupled phenomena influence the rate-dependent thresholds of damage and fracture. Current literature lacks sufficient experimental data at these intermediate rates for predictive deformation model validation. Additionally, few studies investigate the critical importance of particle strength in influencing bulk material deformation and fracture. The deformation and fracture behavior of high solids loading polymer-particle composites is studied at intermediate strain rates with a unique focus on particle strength and its influence on bulk material behavior. The polymer used is a polydimethylsiloxane with particle systems of either silica sand or sodium chloride. Particle size, distribution, morphology, and strength are all characterized. Silica sand is found to be approximately an order of magnitude stronger as a particle system than sodium chloride. X-ray micro-computed tomography of the composite material system is used to characterize material heterogeneity and local particle distribution. Low-strain-rate compression testing is performed to characterize the quasistatic mechanical response of the composites. Consistent with literature, the polymer dominates material ultimate strength and strong evidence of debonding at low strains is observed. The sodium chloride composite is stiffer suggesting the role of particle shape strongly influences response in the low-strain-rate regime. Intermediate-strain-rate testing using a drop hammer test and split Hopkinson pressure bar spans the intermediate-strain-rate regime. Ductile deformation is observed at intermediate-strain-rate with debonding occurring and coalescing in surface fracture at the highest strain rates and impact energies. This first of a kind study spans the low and intermediate-strain-rate regimes with consistent composite compositions and presents a novel dataset for use in the verification and validation of the Viscoplastic-ViscoSCRAM model. Follow-on studies are needed to investigate the role of particle morphology on bulk response along with damage visualization to differentiate between debonding and particle rearrangement.
