Numerical prediction of three-dimensional fiber orientation in Hele-Shaw flows

A numerical technique is developed to determine the three-dimensional fiber orientation in complex flows. The fiber orientation state is specified in terms of orientation tensors, which are used in several constitutive models. This method is applied to quasi-steady state Hele-Shaw flows in order to predict the flow-induced fiber orientation during injection molding at zero volume fraction limit. At the inlet, a number of fibers are introduced at a specified rate into the flow and each fiber location is traced during the mold filling. Along these determined paths, the independent components of fourth order orientation tensors are solved, describing the orientation state. The numerical grid generation technique, which is suitable for complex mold shapes, is employed for the flow solution. Orientation ellipsoids are calculated from the second order tensors and are used to present the fiber orientation results. The numerical solutions are obtained for channel and converging flows. Planar, longitudinal, and transverse orientation results are generated from the orthogonal projections of the orientation ellipsoids.     

Polarized wave electromagnetic shielding of anisotropic carbon nanomodifier‐based LLDPE composites

The polarized wave electromagnetic shielding (EM SE) of nanocomposites containing 10 vol% of carbon nanomodifiers in a semicrystalline matrix is reported. Heat‐treated carbon nanofibers, Pyrograf^® III PR‐19 heat treatment (HT) and multiwalled carbon nanotubes (MWNT) HT were dispersed in a linear low‐density polyethylene matrix to produce flow‐induced orientation of the nanomodifiers in the spun microfilaments. Consequently, the electrical conductivity of the resulting nanocomposites exhibited anisotropic behavior due to the nanomodifier orientation. The in‐plane conductivity in the longitudinal direction (PR‐19 HT comp.: ～0.02 S/m; MWNT HT comp.: ～3 S/m) was at least an order of magnitude higher than that along the transverse direction. As measured with a rectangular waveguide (WR510, 1.45–2.2 GHz), the PR‐19 HT‐ and MWNT HT‐oriented nanocomposites (1‐mm thick) displayed EM SE values of 0.7 dB and 3.0 dB, respectively, when the nanomodifiers were transversely oriented with the polarized electric field. In contrast, when the orientation of the nanomodifiers was parallel with the field, EM SE values of 3.2 and 9.0 dB were obtained, respectively. The higher EM SE values are consistent with high conductivities observed in the direction of preferred orientation of the modifiers. POLYM. ENG. SCI., 55:299–307, 2015. © 2014 Society of Plastics Engineers     

Investigation of ammonium polyphosphate dilution with ground eggshells and lignin through the study of natural fibre composite flammability

The interactions of Calcium carbonate (e.g., eggshell powder) and Lignin with ammonium polyphosphate (APP) when used as fire retardants were investigated. Three mixing ratios - 1:3, 1:1, and 3:1, were used with natural fibre reinforced composites containing a hemp mat and an epoxy matrix manufactured using a light resin transfer moulding (L-RTM) process. The thermal decomposition of the retardant mixtures and composites was investigated using thermogravimetric analysis (TGA). The findings showed that even though the decomposition reactions of APP with eggshell powder and lignin mixtures interacted and overlapped, the same interactions could not be seen in the composites. In the composite form while the residue was affected by the retardant, the decomposition reactions were driven primarily by the hemp and epoxy. Flammability of the composites was studied by testing to 20, 35, 50, and 75 kW/m² with a cone calorimeter, and determining the critical heat flux. While the samples with eggshell powder had higher ignition times, the critical heat flux for ignition was 13 kW/m² for all sample groups except for a ratio of 1:3 APP to eggshell powder, which was 14 kW/m². The lowest burning rates (mass loss and heat release) occurred in composites containing only APP, however, the addition of eggshell powder or lignin at even a ratio of 3:1 APP to either provided a notable reduction.     

Computer-Aided Design of Composite Systems

The use of complex materials, such as composites, for fabrication of structural components exacts a price of increased complexity in design and analysis of these structures. In order to economically and efficiently facilitate complex structural design and analysis, computer-aided design techniques are being employed throughout the industrial community. This paper illustrates a system of computer-aided design techniques and software (CADOT) for the design and analysis of engineering structures and solids that are constructed of sheet molding, injection molding, and/or laminated composite technologies.     

Longitudinal prediction of child outcomes from differing measures of parenting in a low-income sample.

This study examined predictions from preschool parenting measures to middle childhood cognitive and socioemotional child outcomes to explore whether parenting assessment methodologies that require more time, training, and expense yield better predictions of child outcomes than less intensive methodologies. Mother-child dyads (N=278) in low-income African American families were assessed when the child was in preschool, using maternal report, the Home Observation for Measurement of the Environment-Short Form (P. Baker & F. Mott, 1989; R. Bradley & B. Caldwell, 1984), and structured observational measures of parenting. Child outcomes reported by children, mothers, teachers, and direct assessment were collected 4 years later. All parenting methodologies showed some predictive value; however, observational parenting measures showed the strongest and most consistent predictions of child outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detecting sequential patterns and determining their reliability with fallible observers.

On the basis of recent work by W. Gardner (1995), implications of fallible observers for observational research are discussed. Analysis shows that for identically fallible observers, values for kappa are lower when codes are few and their simple probabilities variable than when codes are many and roughly equiprobable; thus no one value of kappa can be regarded as universally acceptable. Additional analysis shows that fallible measurement degrades indices of sequential pattern more when codes are few and their simple probabilities variable. Finally, a simulation study establishes likely values for intraclass correlation reliabilities for sequential indices generated by various circumstances and suggests principled ways to select both lengths of sequences and acceptable levels of kappa for observational studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Intervention Selection Bias: An Underrecognized Confound in Intervention Research.

Selection bias can be the most important threat to internal validity in intervention research, but is often insufficiently recognized and controlled. The bias is illustrated in research on parental interventions (punishment, homework assistance); medical interventions (hospitalization); and psychological interventions for suicide risk, sex offending, and juvenile delinquency. The intervention selection bias is most adequately controlled in randomized studies or strong quasi-experimental designs, although recent statistical innovations can enhance weaker designs. The most important points are to increase awareness of the intervention selection bias and to systematically evaluate plausible alternative explanations of data before making causal conclusions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)