Prediction of Paper Coating Mechanical Behavior Based on Particle-scale Models

The mechanical properties of pigmented coatings are important for a number of situations; including coated paper, architectural paints, and structures in flexible lithium ion batteries. Coated paper and board undergo a variety of post coating application processes which have the potential to cause serious quality problems such as cracking, picking, and crack-at-the fold (CAF). Because a large number of parameters are known to influence the results, fundamental models are needed to help describe these processes and link them to the coating formulations and to the defects. A discrete element method (DEM) computer model was developed to describe the pigment level deformation of the coating layer. The model is based on calculating the forces between particles as they move relative to each other and undergo tension or compression. For the case of tension, a non-linear stress-strain relationship was developed that is similar to the behavior seen for pure binder films – data for the pure binder are inputs into the model. In the case of compression, a repulsive force is used that is linear with strain. This thesis is the first time that a DEM was used to model bending, to include the influence of starch, and to model two coating layers. The model was compared to recent experimental results in the literature for free-standing coating films using different ratios of pigment to binder and also various combinations of latex and starch in the binder systems. The two dimensional version of the model was set up using uniform spherical particles to represent the paper coating pigments. For both tension and three-point bending, the model was able to predict cracking in accordance with the experimental data. The model’s results followed the same trends and were of the same order of magnitude as the lab data. However, differences between the two sets of data did exist, which could be attributed to such causes as issues when making the coating films in the lab, starch impacting the packing, assuming only cohesive failure, the use of spherical particles, and the assumptions made for the simulated packing. The two-dimensional model also was used to simulate the printing event via an out-of-plane tension event and by applying a moving force boundary condition. Picking correlated to both the experiments and the models for the strain-at-failure (STF) and not for the elastic modulus or for the ultimate stress. The two-dimensional model also was applied to two layer coatings. The model agreed with the literature in that the starch-rich layers of high coat weight were more prone to cracking. Furthermore, the two-layer model agreed with pilot and mill results by predicting less cracking with a thick, flexible bottom layer and a thin, stiff top layer. The three-dimensional model using the packing distribution of uniform spheres, of bimodal size distributions, and of full particle size distributions improved the predictions relative to the two-dimension cases. The results with uniform spheres showed the modulus, maximum stress, and strain-at-failure to be well predicted except for the maximum stress being underpredicted for cases near the critical pigment volume concentration (CPVC). In addition, the strain-at-failure tended to be overpredicted. When the model used the bimodal and full distributions for packing, the predictions improved. The model overpredicted the modulus and underpredicted the maximum stress, but the predictions were close in some cases, especially when using the full distribution. In addition, the STF showed good agreement between the predictions and the lab data when starch was part of the binder system. Discrepancies still exist between the model predictions and the experimental data, and these differences can be attributed to many factors including the method of packing. The model showed the modulus and the maximum stress to increase directly with the packing density. These results are in accord with the expectation that a tighter initial packing leads to higher local strains, which lead to increased modulus and stress

Nondestructive testing techniques used in analysis of honeycomb structure bond strength

DOT /Driver-Displacement Oriented Transducer/, applicable to both lap shear type application and honeycomb sandwich structures, measures the displacement of the honeycomb composite face sheet. It incorporates an electromagnetic driver and a displacement measuring system into a single unit to provide noncontact bond strength measurements

Static versus dynamic fluctuations in the one-dimensional extended Hubbard model

The extended Hubbard Hamiltonian is a widely accepted model for uncovering the effects of strong correlations on the phase diagram of low-dimensional systems, and a variety of theoretical techniques have been applied to it. In this paper the world-line quantum Monte Carlo method is used to study spin, charge, and bond order correlations of the one-dimensional extended Hubbard model in the presence of coupling to the lattice. A static alternating lattice distortion (the ionic Hubbard model) leads to enhanced charge density wave correlations at the expense of antiferromagnetic order. When the lattice degrees of freedom are dynamic (the Hubbard-Holstein model), we show that a similar effect occurs even though the charge asymmetry must arise spontaneously. Although the evolution of the total energy with lattice coupling is smooth, the individual components exhibit sharp crossovers at the phase boundaries. Finally, we observe a tendency for bond order in the region between the charge and spin density wave phases.Comment: Corrected typos. (10 pages, 9 figures

Locating the source of projectile fluid droplets

The ill-posed projectile problem of finding the source height from spattered droplets of viscous fluid is a longstanding obstacle to accident reconstruction and crime scene analysis. It is widely known how to infer the impact angle of droplets on a surface from the elongation of their impact profiles. However, the lack of velocity information makes finding the height of the origin from the impact position and angle of individual drops not possible. From aggregate statistics of the spatter and basic equations of projectile motion, we introduce a reciprocal correlation plot that is effective when the polar launch angle is concentrated in a narrow range. The vertical coordinate depends on the orientation of the spattered surface, and equals the tangent of the impact angle for a level surface. When the horizontal plot coordinate is twice the reciprocal of the impact distance, we can infer the source height as the slope of the data points in the reciprocal correlation plot. If the distribution of launch angles is not narrow, failure of the method is evident in the lack of linear correlation. We perform a number of experimental trials, as well as numerical calculations and show that the height estimate is insensitive to aerodynamic drag. Besides its possible relevance for crime investigation, reciprocal-plot analysis of spatter may find application to volcanism and other topics and is most immediately applicable for undergraduate science and engineering students in the context of crime-scene analysis.Comment: To appear in the American Journal of Physics (ms 23338). Improved readability and organization in this versio

Effects of D-amino acid oxidase inhibition on memory performance and long-term potentiation in vivo

N-methyl-d-aspartate receptor (NMDAR) activation can initiate changes in synaptic strength, evident as long-term potentiation (LTP), and is a key molecular correlate of memory formation. Inhibition of d-amino acid oxidase (DAAO) may increase NMDAR activity by regulating d-serine concentrations, but which neuronal and behavioral effects are influenced by DAAO inhibition remain elusive. In anesthetized rats, extracellular field excitatory postsynaptic potentials (fEPSPs) were recorded before and after a theta frequency burst stimulation (TBS) of the Schaffer collateral pathway of the CA1 region in the hippocampus. Memory performance was assessed after training with tests of contextual fear conditioning (FC, mice) and novel object recognition (NOR, rats). Oral administration of 3, 10, and 30 mg/kg 4H-furo[3,2-b]pyrrole-5-carboxylic acid (SUN) produced dose-related and steady increases of cerebellum d-serine in rats and mice, indicative of lasting inhibition of central DAAO. SUN administered 2 h prior to training improved contextual fear conditioning in mice and novel object recognition memory in rats when tested 24 h after training. In anesthetized rats, LTP was established proportional to the number of TBS trains. d-cycloserine (DCS) was used to identify a submaximal level of LTP (5× TBS) that responded to NMDA receptor activation; SUN administered at 10 mg/kg 3–4 h prior to testing similarly increased in vivo LTP levels compared to vehicle control animals. Interestingly, in vivo administration of DCS also increased brain d-serine concentrations. These results indicate that DAAO inhibition increased NMDAR-related synaptic plasticity during phases of post training memory consolidation to improve memory performance in hippocampal-dependent behavioral tests