Synthesis, characterization and analytical modelling of mechanical behavior of a conducting polymer actuator

Electrochemical synthesis of a tri-layer polypyrrole based actuator optimized for performance was reported. The 0.05 M pyrrole and 0.05 M tetrabutylammonium hexaflurophosphate in propylene carbonate (PC) yielded the optimum performance and stability. The force produced ranged from 0.2 to 0.4mN. Cyclic deflection tests on PC based actuators for 3 hours indicated that the displacement decreased by 60%. PC based actuator had a longer operating time, exceeding 3 hours, compared to acetonitrile based actuators. A triple-layer model of the polymer actuator was developed based on the classic bending beam theory by considering strain electrode material. A tri-layer actuator was fabricated [4, 6], by initially sputter coating a PVDF film with approximately 100nm of gold layer, resulting in a conductive film with a surface resistance of 8-10Ω. The PVDF film was about ~145µm thick had an approximate pore size of 45μm. A solution containing 0.05M distilled pyrrole monomer, 0.05M (TBAPF6) and 1% (w/w) distilled water in PC (propylene carbonate) solution was purged with nitrogen for 15 minutes. The continuity between PPy and PVDF. Results predicted by the model were in good agreement with the experimental data.

Microstructure and mechanical properties of nitrided and chromized short steel fiber reinforced aluminum based P/M composites

The present investigation is on the microstructure evolution and hardness of powder metallurgically processed Al- 0.5 wt.%Mg base 10 wt.% short steel fiber reinforced composites. The 0.38 wt.% C short steel fibers of average diameter 50µm and 500-800µm length were nitrided and chromized in a fluid bed furnace. Nitriding was carried out at 525°C for 90, 30 and 5 min durations. Chromizing was performed at 950°C for 53 and 7 min durations, using thermal reactive deposition (TRD) and diffusion technique. The treated fibers and resulting reaction interfaces were characterized using metallographic, microhardness and XRD techniques.

Effects of multiple laser shock processing (LSP) impacts on mechanical properties and wear behaviors of AISI 8620 steel

The aim of this paper was to address the effects of multiple laser shock processing (LSP) impacts with different pulse energy on mechanical properties and wear behaviors of AISI 8620 steel. Wear analyses were conducted by means of calculation of volume loss and scanning electron microscope (SEM) of the wear surface. Surface profiles, roughness and micro-hardness were measured. The micro-structures in the surface layer of the untreated and LSPed samples (treated by multiple LSP impacts) were investigated by using transmission electron microscopy (TEM) observations. Experimental results and analyses indicated that multiple LSP impacts can remarkably improve the wear resistance of AISI 8620 steel, and the wear mechanism of multiple LSP impacts on AISI 8620 steel was also entirely revealed. The wear process of the unpolished sample subjected to multiple LSP impacts can be described as follows: the wear rate was big at the beginning of sliding dry wear, but then decreased after the micro-indention in the sample surface was polished to the disappear. This phenomenon can be attributed to the fact that multiple LSP impacts generate many micro-indents in the sample surface.

Effects of Si on microstructural evolution and mechanical properties of hot-rolled ferrite and bainite dual-phase steels

Based on the thermo-mechanical controlled process, the effects of Si on microstructural evolution, tensile properties, impact toughness, and stretch-flangeability of ferrite and bainite dual-phase (FBDP) steels were systematically investigated. The addition of Si from 0 to 0.95% promoted the formation of fine and equiaxed ferrite grains, and high Si (0.95%) also resulted in the formation of blocky martensite islands and retained austenite. Yield and tensile strengths, and uniform and total elongations all increased with increasing Si content. Therefore, the tensile strength and ductility balance was improved by Si addition due to the increasing strain-hardening rate. The fractured morphologies after hole-expansion showed that the excellent stretch-flangeability of FBDP steels was associated with the micro-cracks propagating through in ferrite phase as well as the elongated ferrite grains along the direction perpendicular to the crack. 0.95% Si steel had a similar high combination of tensile strength and impact toughness to 0.55% Si steel, and especially 0.95% Si steel exhibited an excellent combination of tensile strength and stretch-flangeability.

Utilizing polypropylene fibers to improve physical and mechanical properties of concrete

The influence of polypropylene fibers has been studied in different proportioning and fiber aspect ratios to improve physical and mechanical properties of fiber-reinforced concretes. Fibers are used in two different lengths (12 mm and 19 mm) and proportions (0.1% and 0.3%) in concrete mixture design. Hardened concrete properties, such as 7- and 28-day compressive strength, splitting tensile strength, flexural strength, water and air absorption, and restrained shrinkage cracking were evaluated.

No statistically significant effects were observed for polypropylene fibers on the compressive strength of concrete, while toughness indexes, splitting tensile and flexural strength and durability parameters showed an increase in the presence of polypropylene fibers. Increased fiber availability (fiber aspect ratio) in the concrete matrix, in addition to the ability of longer polypropylene fibers to bridge on the micro cracks, are suggested as the reasons for the enhancement in mechanical properties. Finally, crack width in fiber-reinforced concrete is calculated analytically with fiber property variables (fiber type, length, diameter and proportion). Results are compared with experimental values and concluded that with an increase in fiber length and/or decrease in fiber diameter crack width, decrease significantly.

Shrinkage induced stretchable micro-wrinkled reduced graphene oxide composite with recoverable conductivity

A novel thermo-mechanical shrinking method is reported to fabricate a three dimensional (3D) stretchable and highly conductive micro-wrinkled reduced graphene oxide (MWrGO) supported on an elastic polydimethylsiloxane (PDMS) substrates. This 3D rGO architecture not only increases the specific area for more electrons to pass through but also bestows stretchability to the conductive pathway. The structural change of micro-wrinkles has been monitored by an in situ straining microscopy. The electrical conductivity of the samples remained fairly constant and stayed above 25 S/m under low deformation (no more than 30% strain) for up to 500 mechanical stretching-release cycles. Additionally, the MWrGO/PDMS composite can be stretched bi-axially because the shrinking process itself is isotropic. This MWrGO based stretchable composite with stable electrical properties and long life span could form a new platform of stretchable electronics.

Effect of strain ageing on the mechanical properties of partially damaged structural mild steel

ABSTRACT
This paper addresses the strain ageing effects on the mechanical properties of the partially damaged structural mild steel. Since repairing partly damaged structures may not occur immediately, the strain ageing effect can significantly influence the structural behaviour. The changes due to this effect have not so far been considered in the civil engineering design guidelines. In order to investigate strain ageing effects, two-stage experimental tests are carried out on the mild-steel specimens. In the first stage, partial damage is made using quasi-static loading. During the second stage, the strength and ductility of the specimens are examined after 2 and 7 days ‘ageing’ at room temperature and the results are compared with the corresponding no-age samples. The microstructure of the specimens is examined using scanning electron microscopy (SEM). To illustrate the effect of strain ageing on the global behaviour of steel structures, a numerical example is provided in which strain ageing impacts on loading capacity and deflection of a steel beam. Finally, the stress–strain relation of partially damaged mild-steel material incorporating strain ageing effects is expressed by calibrating the parameters of Ramberg–Osgood model.

Notes on vibration control of a micro/macromanipulator mounted on a flexible structure

The objective of this study is to describe the design and the implementation of an experimental set-up used to study the dynamics, the experimental identification, and the active vibration control of a flexible structure mounted manipulator system. The system consists of a three-degree-of-freedom cylindrical manipulator system with a flexible link on its tip. A two-degree-of-freedom polar rigid manipulator is mounted on the flexible macromanipulator. The dynamic modelling and experimental modal analysis identification in the frequency domain are being applied to design active digital control strategies for the micro-manipulator system to damp the mechanical vibrations of the flexible structure on the tip of the macro-manipulator system.

On an Active Control for a Structurally Nonlinear Mechanical System, Taking Into Account an Energy Pumping

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Control and chaos for vibro-impact and non-ideal oscillators

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

On energy transfer between linear and nonlinear oscillators

In this paper energy transfer in a dissipative mechanical system is analysed. Such system is composed of a linear and a nonlinear oscillator with a nonlinearizable cubic stiffness. Depending on initial conditions, we find energy transfer either from linear to nonlinear oscillator (energy pumping) or from nonlinear to linear. Such results are valid for two different potentials. However, under resonance and absence of external excitation, if the mass of the nonlinear oscillator is adequately small then the linear oscillator always loses energy. Our approach uses rigorous Regular Perturbation Theory. Besides, we have included the case of two linear oscillators under linear or cubic interactions. Comparisons with the earlier case are made. (c) 2008 Elsevier Ltd. All rights reserved.

Harmonical oscillator and electro-mechanical analogy: an interdiscinary experiment to high precision mass variation measurements

De forma geral, os cursos de física clássica oferecidos nas universidades carecem de exemplos de aplicações nas áreas de química e biologia, o que por vezes desmotivam os alunos de graduação destas áreas a estudarem os conceitos físicos desenvolvidos em sala de aula. Neste texto, a analogia entre os osciladores elétrico e mecânico é explorada visando possívies aplicações em química e biologia, mostrando-se de grande valia devido ao seu uso em técnicas de medição de variação de massa com alta precisão, tanto de forma direta como indireta. Estas técnicas são conhecidas como técnicas eletrogravimétricas e são de especial importância em aplicações que envolvem biossensores. Desta forma, o texto explora o estudo da analogia eletromecânica de forma interdisciplinar envolvendo as áreas de física, química e biologia. Baseado nessa analogia é proposto um experimento que permite a sua aplicação em diferentes níveis conceituais dessas disciplinas, tanto em abordagem básica como mais profunda.

Preparation and Characterization of Novel Micro- and Nanocomposite Hydrogels Containing Cellulosic Fibrils

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Environmental ageing studies of chemically modified micro and nanofibril phenol formaldehyde composites

Cellulose micro and nano fibrils were extracted from banana macro fibres and chemically modified using sodium hydroxide, formic acid, 3-methacryloxy propyltrimethoxy silane. These untreated and chemically treated fibrils were incorporated into PF resin and the specimens were prepared. The composites were subjected to long-term water ageing, thermal ageing soil burial and outdoor weathering. The mechanical properties are reduced under all ageing conditions. The present study investigates the effects of different types of ageing on macro fibre, microfibril and nanofibril reinforced PF composites. The effect of chemical modifications of fibres on the degradability of the composites at different environments also has been analysed. © 2013 Elsevier B.V.