Nonlinear Analysis of Shape Memory Devices With Duffing and Quadratic Oscillators

In this paper, we investigate the linear and nonlinear response of shape memory alloy (SMA)-based Duffing and quadratic oscillator under large deflection conditions. In this study, we first present thermomechanical constitutive modeling of SMA with a single degree-of-freedom system. Subsequently, we solve equation to obtain linear frequency and nonlinear frequency response using the method of harmonic balance and validate it with numerical solution as well as averaging method under the isothermal condition. However, for nonisothermal condition, we analyze the influence of cubic and quadratic nonlinearity on nonlinear response based on method of harmonic balance. Analysis of results leads to various ways of controlling the nature and extent of nonlinear response of SMA-based oscillators. Such findings can be effectively used to control external vibration of different systems.

A novel DOPO-containing flame retardant for epoxy resin

A novel halogen-free flame retardant (6,6′-(((methylenebis(4,1-phenylene))bis(azanediyl))bis((4-hydroxy-3-methoxyphenyl)methylene))bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide)(DP-DDM))) was synthesized via a one-pot procedure based on the Pudovik reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide and imine directly resulting from 3-methoxy-4-hydroxybenzaldehyde with 4,4′-methylenedianiline (DDM). The thermal curing behaviors of epoxy resins with different contents of DP-DDM were investigated by differential scanning calorimetry under a nonisothermal condition, aimed to suggest an optimized curing procedure in accordance with the property of DP-DDM. These DP-DDM-modified epoxy thermosets under optimized curing procedure showed high glass transition temperature and thermal degradation activation energy. Moreover, their high flame-retarding performance has been found: the epoxy thermosets with a relatively low addition amount of DP-DDM (on account of the phosphorus content of 0.75 wt%) can reach UL 94 V-0 (Instrumental analysis and measurements) rating with limiting oxygen index value of 34.5.

Heat Transfer to a Nonisothermal Rotating Disk With a Turbulent Boundary Layer

Three approaches are presented for the prediction of heat transfer from a nonisothermal disk rotating in a fluid of infinite extent at such high speeds that the induced flow is turbulent. These include the analysis of Dorfman, the analysis of Davies (extended to nonisothermal conditions) assuming the eddy diffusivity of radial momentum is equal to the eddy diffusivity of heat, and a modified Davies analysis assuming the eddy diffusivity of tangential momentum is equal to the eddy diffusivity of heat. A comparison of these three predictions with available heat and mass transfer data suggests that Dorfman’s analysis when appropriately modified gives the best representation for the isothermal rotating disk. For the nonisothermal disk having a power-function wall-temperature distribution, Tw − Te = Brm, both the Dorfman analysis and the tangential momentum analogy give what appears to be a reasonable estimate of the influence of the nonisothermal condition, while the radial momentum analogy overestimates the influence. Until additional data are obtained, it is recommended that the modified Dorfman prediction be used to estimate heat transfer from a nonisothermal disk in the presence of turbulent flow.