Dependence of the electrical conductivity and elastomeric properties on sample preparation of blends of polyaniline and natural rubber

Blend films (free-standing) containing 20% in volume of polyaniline (PANI) in 80% of natural rubber (NR) were fabricated by casting in three different ways: (1) adding PANI-EB (emeraldine base) dissolved in N-methyl-2-pyrrolidone (NMP) to the latex (NRL), (2) adding PANI-EB dissolved in in-cresol to NR dissolved in xylol (NRD), (3) overlaying the surface of a pure NR cast film with a PANI layer grown by in situ polymerization (NRO). All the films were immersed into HCl solution to achieve the primary doping (protonation) of PANI before the characterization. The main goal here was to investigate the elastomeric and electrical conductivity properties for each blend, which may be applied as pressure and deformation sensors in the future. The characterization was carried out by optical microscopy, dc conductivity, vibrational spectroscopy (infrared absorption and Raman scattering), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile stress-strain curves. The results suggest that the NRL blend is the most suitable in terms of mechanical and electrical properties required for applications in pressure and deformation sensors: a gain of conductivity without losing the elastomeric property of the rubber. (c) 2005 Wiley Periodicals, Inc.

High sensitivity low cost capacitive strain gage

This paper describes a high senstivity low cost capacitive strain gage sensor. The theory, design, and sensor construction details are presented. It consists of eight capacitive sensors connected in two full bridges. The capacitive strain gage sensor structure was designed in order to produce high sensitivity and low dependence with temperature. By using a simple signal conditioning circuit constituted by a differential amplifier, a band-pass filter, and a precision rectifier the device can measure forces with resolution of 0.009 N and precision of 98.7%. It is rugged, presents linear response, and good repeatability. It presents sensitivity of 8.7 V/N and fall time of 12 ms.

Theoretical approach including friction for determining strain limits in punch stretching of anisotropic sheet metals

A new analytical theory including friction was developed to assess strain limits in punch stretching of anisotropic sheet metals. This new approach takes into consideration the anisotropic behaviour of sheet materials and could explain the mechanical behaviour of a variety of anisotropic sheet materials. The theory explains the sheet metal failure so for the drawing as the stretching region of the forming limit curve, particularly for materials that present the strain-ratio dependence of limit strain ε 1, where dε 1/dρ is not always greater than zero. dε 1/ dρ or dε 1/dε 2 could be equal to or smaller than zero for a range of materials. Therefore, this new theory can explains such experimental observations, besides to assuming that membrane element relations near the pole, for the case of punch stretching are dependent of sheet metal properties as the process history and also suggests that the onset of local necking is controlled by shear. Thus, theoretical results obtained through this new approach are compared with experimental results available in the literature. It is demonstrated the effect of friction on a FLC curve for both regions, drawing and stretching. © 2010 American Institute of Physics.