Nano and submicrometric fibers of poly(D,L-lactide) (PDLLA or PLA) were spun from solutions using a solution blow spinning (SBS) apparatus. Fiber morphology and diameter were investigated by scanning electron microscopy as a function of polymer concentration, feed rate, and air pressure. A more systematic understanding of the SBS process parameters was obtained, and a quantitative relationship between these parameters and average fiber diameter was established by design of experiments and response surface methodology. It was observed that polymer concentration played an important role in fiber diameter, which ranges from 70 to 2000 nm, and its distribution. Lower polymer concentration tended to increase the formation of bead-on-string structures, whereas smooth fibers were formed at higher concentrations. Fiber diameter tended to increase with polymer concentration and decrease with feed rate. Based on these results, optimal conditions could be obtained for solution-blow spun fibers.

The properties of mixtures of poly(lactic acid) (PLA) and poly(ethylene oxide) (PEO) were studied in polymer solutions by dilute solution viscometry, and in-solution blow-spun nanofibers were studied by microscopy (scanning electron and transmission electron microscopy) and thermal and spectral analysis. Three mixtures of PLA and PEO (3:1, 1:1, and 1:3) were solution-blended in chloroform. Dilute solvent viscometry indicated that the 3:1 mixture of PLA and PEO had a higher miscibility coefficient value than the other mixtures. The neat polymers and mixtures were solution-blow-spun into nanofibers. The fiber diameters were smallest in the neat polymers. Transmission electron micrographs revealed a core/sheath structure for the sample mixtures. X-ray analysis indicated that the crystallinity was positively correlated with the PEO content. Fibers from the mixtures had contact angle measurements similar to those of the neat PEO. Fourier transform infrared and Raman spectroscopy of the mixtures indicated interactions between ester and ether groups, which were attributed to dipole-dipole interactions between the ester groups of PLA and the ether groups of PEO.

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Materials accumulate energy around voids and defects under external loading, causing the formation of microcracks. With increasing or repeated loads, those microcracks eventually coalesce to form macrocracks, which in a brittle material can cause catastrophic failure without apparent permanent deformation. At the continuum level, a stochastic phase-field model is employed to simulate failure through introducing damage and fatigue variables. The damage phase-field is introduced as a continuous dynamical variable representing the volumetric portion of fractured material and fatigue is treated as a continuous internal field variable to model the effects of microcracks arising from energy accumulation. We formulate a computational-mathematical framework for quantifying the corresponding model uncertainties and sensitivities in order to unfold and mitigate the salient sources of unpredictability in the model, hence, leading to new possible modeling paradigms. Considering an isothermal isotropic linear elastic material with viscous dissipation under the hypothesis of small deformations, we employed Monte Carlo and probabilistic collocation methods to perform the forward uncertainty propagation, in addition to local-to-global sensitivity analysis. We demonstrate that the model parameters associated with free-energy potentials contribute significantly more to the total model output uncertainties, motivating further investigations for obtaining more predictable model forms, representing the damage diffusion.