Cellulose has been investigated as a promising green material. Piezoelectricity is the embedded property of this material.
Sandwiched layer of electro-spun cellulose may produce enhanced mechanical and electrical properties because of the
nano-scaled electro-spun cellulose layer. Mechanical tests are executed to observe the strength of cellulose composite.
Scanning electron microcope is investigated to observe the formation of layers and cross section of composite. Electrical
properties such as capacitance are measured as a function of temperature to assess the dielectric constant of this material.
The voltage creep behavior on actuation performance of cellulose based electro-active paper (EAPap) has been studied.
Because the actuation of EAPap is originated from both the inner ionic movement in cellulose and its piezoelectric
behavior, the actuation can be affected by the external field. When the external field applied, cyclic hysteresis of P-E
loop is observed. In order to investigate the detail of actuation behavior of EAPap actuator, the detail actuation response
- called voltage creep- is required. The voltage creep which can reduce the response and the actuating accuracy of
actuator is one important issue in order to control the micro/nano scaled positioning of smart material devices. In this
paper, we present the voltage creep phenomena of EAPap, which will give more detail information to understand EAPap
as well as other polymer based smart materials.
Understanding of creep effects on actuating mechanisms is important to precisely figure out the behavior of
material. Creep behaviors of cellulose based Electro-Active Paper (EAPap) were studied under different constant loading
conditions. We found the structural modification of microfibrils in EAPap after creep test. Structural differences of as-prepared
and after creep tested samples were compared by SEM measurements. From the measured creep behaviors by
different loading conditions, two different regions of induced strain and current were clearly observed as the
measurement time increased. It is consider that local defects may occur and becomes micro-dimple or micro-crack
formations in lower load cases as localized deformation proceeds, while the shrinkage of diameter of elongated fibers
was observed only at the high level of loading. Therefore, cellulose nanofibers may play a role to be against the creep
load and prevent the localized structural deformations. The results provide useful creep behavior and mechanism to
understand the mechanical behavior of thin visco-elastic EAPap actuator.
Material properties of Electro-active paper (EAPap) actuator were investigated under different environmental conditions
such as humidity and temperature. Understanding of humidity and temperature effects on the material behavior of
EAPap during visco-elastic deformation regime provided useful information on structural changes of EAPap by
environmental factors. The pulling test results showed that the humidity and temperature heavily impact the mechanical
properties of EAPap. Electro-mechanical coupling effects were investigated by applying electric field during the pulling
test. Change of elastic modulus under different electric fields provides directional dependency of EAPap and strong
shear electro-mechanical coupling. Creep behavior of cellulose paper was studied to figure out mechanical strength of
EAPap under different ambient conditions. Tests under different humidity levels with fixed temperature and different
temperatures with fixed humidity provided the coupled hygrothermal effects on the performance of EAPap.
In this paper, mechanical properties and piezoelectric effects of cellulose based Electro-Active Paper (EAPap) actuators were investigated. Typical pulling tests of cellulose paper, which is a basic material of EAPap actuator, showed distinct elastic modulus and bifurcation point followed by plastic modulus at ambient conditions. The mechanism of this distinct phenomenon was examined to obtain better understanding of EAPap actuator. After that, in-plane strain of EAPap actuator under constant electric field was experimentally investigated to understand piezoelectricity of EAPap. EAPap samples were made by coating very thin gold electrodes on both sides of cellophane film. When external DC voltages were applied, in-plane contractions were induced due to the converse piezoelectric effect of EAPap. It was observed that the EAPap sample with 45° orientation exhibited the largest in-plane strain compared to other orientation samples.
Vibration-based damage identification using embedded sensitivity functions is discussed. These sensitivity functions are computed directly from experimental frequency response functions and reflect changes in the forced response of structural systems when mass, damping or stiffness parameters are changed. The theory of embedded sensitivity functions is reviewed and applied to characterize damage in a simulated three degree-of-freedom system and a full-scale exhaust system with nonlinear characteristics. Linear damage is shown to be properly detected, located and quantified in theory and practice for structures with one damage mechanism by comparing embedded sensitivity functions with finite difference frequency response functions in undamaged and damaged test data. It is also shown using the exhaust system that false indications of damage due to nonlinear amplitude dependence can be avoided by developing nonlinear baseline models. Experimental results indicate that the technique is most effective when changes to frequency response functions are no larger than 10% to avoid distortions in the estimated perturbations due to variations in the sensitivity functions.