@article{ramasubramanian_wang_2007, title={A computational micromechanics constitutive model for the unloading behavior of paper}, volume={44}, ISSN={["1879-2146"]}, DOI={10.1016/j.ijsolstr.2007.05.002}, abstractNote={In this study, a computational micromechanics material model for the unloading behavior of paper and other nonwoven materials is presented. The asymptotic fiber and bond (AFB) model for paper elastic–plastic behavior [Sinha, S.K., Perkins, R.W., 1995. Micromechanics constitutive model for use in finite element analysis, In: Proceedings of the 1995, Joint ASME Applied Mechanics and Materials Summer Meeting, Los Angeles, CA, USA, Jun 28–30, 1995] has been extended to model the unloading process through a computational algorithm and implemented using the UMAT subroutine in ABAQUS finite element code. For every unloading increment, the material model assumes elastic unloading with a slope equal to the initial elastic modulus. The Jacobian matrix of the constitutive model is updated at every unloading increment by applying the incremental form of AFB model for a planar element with an elastic fiber and bond condition. A uniaxial tensile and a biaxial Mullen burst loading–unloading experiments were carried out for a paperboard sample and simulated using the model. The stress–strain curve and residual strain for the uniaxial loading were in good agreement with experimental results. The finite element model of the burst test with the AFB unloading material model predicted the general shape of the pressure versus deflection curve. However, the model over predicted the residual deflection by more than 50%. The loading portion of the pressure–deflection curve had a significant offset from experimental curves, and the nonlinearity in the unloading curve towards the end was not predicted. The discrepancies with experimental results are attributed to the burst test itself, model parameter estimation inadequacies, boundary conditions used in the FEA, and neglecting time-dependant effects. Nevertheless, the model can be useful in parametric studies relating microstructure to unloading behavior in structural problems.}, number={22-23}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Ramasubramanian, M. K. and Wang, Yun}, year={2007}, month={Nov}, pages={7615–7632} }
@article{hubbe_rojas_argyropoulos_wang_song_sulic_sezaki_2007, title={Charge and the dry-strength performance of polyampholytes. Part 2. Colloidal effects}, volume={301}, DOI={10.1016/j.colsurfa.2006.11.053}, abstractNote={Polyampholytes, which are macromolecules that contain both positive and negative ionizable groups, can provide superior strength improvements for paper manufacture, compared to the addition of simple polyelectrolytes. Colloidal effects, which were measured in solution and in fiber suspensions, were consistent with observed bonding effects. The same colloidal effects were found to correlate with the effects of pH and of the density of the ionizable groups on the polyampholytes. Tests were carried out with a series of polyampholytes having a constant ratio of cationic to anionic monomeric groups and molecular mass. Their charge density varied in the ratio 1:2:4:8. The greatest strength gains were obtained at intermediate charge density and under conditions of pH favoring instability of the aqueous polymer mixtures. Colloidal phenomena were elucidated by turbidimetric tests, sediment volumes of treated fiber suspensions, flocculation tendencies of treated fiber suspensions, and zeta potentials of probe particles.}, journal={Colloids and Surfaces. A, Physicochemical and Engineering Aspects}, author={Hubbe, M. A. and Rojas, O. J. and Argyropoulos, Dimitris and Wang, Y. and Song, J. and Sulic, N. and Sezaki, T.}, year={2007}, pages={23–32} }
@article{wang_hubbe_rojas_argyropoulos_wang_sezaki_2007, title={Charge and the dry-strength performance of polyampholytes. Part 3: Streaming potential analysis}, volume={301}, ISSN={["1873-4359"]}, DOI={10.1016/j.colsurfa.2006.11.052}, abstractNote={Results reported in Part 1 of this series showed that paper strength improvements could be optimized by varying pH and the overall content of ionic groups in random terpolymers containing a fixed molar ratio of acidic and basic monomeric groups. Further treatment of kraft fiber slurries with polyaluminum chloride (PAC), after polyampholyte addition, yielded significant strength benefits. The present paper shows how these results can be explained in terms of the streaming potential (SP) of glass fibers, which were used as a model substrate. The data suggest that aluminum ions interact both with the anionic carboxyl groups of the polyampholytes and with anionic silanol groups at fiber surfaces. The streaming potential of the treated surfaces could be changed by varying the pH, the overall density of charged groups of the polyampholytes, the ratio of cationic to anionic groups on the polymer and by post-treatment with polyaluminum chloride.}, number={1-3}, journal={COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS}, author={Wang, Yun and Hubbe, Martin A. and Rojas, Orlando J. and Argyropoulos, Dimitris S. and Wang, Xingwu and Sezaki, Takao}, year={2007}, month={Jul}, pages={33–40} }
@misc{lucia_wang_nafisi_netzel_schanze_1995, title={DIRECT OBSERVATION OF ULTRAFAST C-C BOND FRAGMENTATION IN A DIAMINE RADICAL-CATION}, volume={99}, ISSN={["0022-3654"]}, DOI={10.1021/j100031a002}, abstractNote={Nanosecond and picosecond transient absorption studies were carried out on fac-(bpy)Re{sup 1}(CO){sub 3}(DA){sup +} (1), where bpy is 2,2{prime}-bipyridine and DA is the 1,2-diamine-substituted pyridine erythro-l-[p-[4-(pyridyl)methyl]-anilino]-2piperidino-1, 2-piperidino-1,2-diphenylethane. Photoexcitation of the d{pi} (Re) {pi}(bpy) metal-to-ligand charge-transfer excited state in 1 initiates the following sequence: (1) forward electron transfer from the 1,2-diamine unit to the photoexcited (bpy)Re(CO){sub 3}{sup -} chromophore to produce the ligand-to-ligand charge transfer (LLCT) state, (bpy{sup -})Re{sup 1}(CO){sub 3}(DA{sup +}); (2) C-C bond fragmentation of the diamine radical cation unit. Nanosecond transient absorption spectral data indicate that the {alpha}-amino radical which is the primary product of the C-C bond fragmentation is produced during the 10 ns laser excitation pulse. Picosecond pump-probe studies of 1 allow direct determination of the kinetics of back electron transfer in the LLCT state (1 x 10{sup 8} s{sup -1}) and for C-C bond fragmentation in the diamine radical cation (3 x 10{sup 8} s{sup -1}). 36 refs., 2 figs.}, number={31}, journal={JOURNAL OF PHYSICAL CHEMISTRY}, author={LUCIA, LA and WANG, YS and NAFISI, K and NETZEL, TL and SCHANZE, KS}, year={1995}, month={Aug}, pages={11801–11804} }