Low amplitude, low frequency elastic measurements using Dynamic Mechanical Analyzer (DMA) spectroscopy

2011 ◽  
Vol 226 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Ekhard K. H. Salje ◽  
Wilfried Schranz
Keyword(s):  
Low Frequency ◽  
Dynamic Mechanical Analyzer ◽  
Dynamic Mechanical ◽  
Low Amplitude

scholarly journals Dynamic Mechanical Analysis on Delaminated Flax Fiber Reinforced Composites

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2559 ◽  
Author(s):  
Yiou Shen ◽  
Jiayi Tan ◽  
Luis Fernandes ◽  
Zehua Qu ◽  
Yan Li
Keyword(s):  
Dynamic Mechanical Analysis ◽  
Loss Factor ◽  
Composite Laminate ◽  
Low Frequency ◽  
Mechanical Analysis ◽  
Fiber Reinforced ◽  
Dynamic Mechanical ◽  
Reinforced Composite ◽  
Local Flexibility ◽  
Low Amplitude

It is well-known that the presence of the delamination in a plant fiber-reinforced composite is difficult to detect. However, the delamination introduces a local flexibility, which changes the dynamic characteristics of the composite structure. This paper presents a new methodology for composite laminate delamination detection, which is based on dynamic mechanical analysis. A noticeable delamination-induced storage modulus reduction and loss factor enhancement have been observed when the delaminated laminate was subjected to a forced oscillation compared to the intact composite laminate. For delamination area of 12.8% of the whole area of the composite laminate, loss factor of approximately 12% increase was observed. For near-to-surface delamination position, loss factor of approximately an 18% increment was observed. The results indicate that the delamination can be reliably detected with this method, and delamination position shows greater influence on the loss factor than that of the delamination size. Further investigations on different frequencies and amplitudes configurations show that the variation of loss factor is more apparently with low frequency as well as the low amplitude.

Investigation of frequency dependent mechanical properties of porous materials using dynamic mechanical analyzer and frequency-temperature superposition theory

2021 ◽  
Vol 263 (2) ◽  
pp. 4851-4862
Author(s):  
Attila Schweighardt ◽  
Balazs Vehovszky
Keyword(s):  
Frequency Dependence ◽  
Storage Modulus ◽  
Acoustic Analysis ◽  
Fluid Motion ◽  
Low Frequency ◽  
Dynamic Mechanical Analyzer ◽  
Dynamic Mechanical ◽  
Frequency Measurements ◽  
Temperature Superposition ◽  
Frequency Temperature

In acoustic design of engineering applications - such as in the acoustic analysis of passenger vehicles - poroelastic materials are of great importance. One of the most influencing properties in determining their noise-reduction potential is the storage modulus. The purpose of this study is to examine the frequency dependence of storage modulus of selected porous acoustic materials at least up to 1000 Hz. This is executed by using the combined use of dynamic mechanical analyzer and frequency-temperature superposition theory. All other methods for measuring the storage modulus fall short in determining frequency-dependence above 100 Hz: quasi-static mechanical analyzer is mostly used for determining an averaged constant value deduced from low-frequency measurements, while the usage of an electromagnetic shaker capable for high-frequency excitation may include effects of fluid motion inside the pores, thus significantly modifying the results. Frequency-temperature superposition enables to determine the storage modulus values in a wide frequency range, based on low-frequency measurements, where fluid-structure interaction is negligible. It was found that the modulus varied significantly up to and beyond 1000 Hz, and thus, acoustical characterization of these materials can be significantly improved using the proposed method. The work concludes with recommendations to improve the accuracy of the results.

scholarly journals Multiscale Characterization of E-Glass/Epoxy Composite Exposed to Extreme Environmental Conditions

2021 ◽  
Vol 5 (3) ◽  
pp. 80
Author(s):  
George Youssef ◽  
Scott Newacheck ◽  
Nha Uyen Huynh ◽  
Carlos Gamez
Keyword(s):  
Power Distribution ◽  
Epoxy Composite ◽  
Fire Retardant ◽  
Sandwich Composite ◽  
Dynamic Mechanical Analyzer ◽  
Fire Event ◽  
Balsa Wood ◽  
X Ray ◽  
Dynamic Mechanical ◽  
Composite Skins

Fiber-reinforced polymer matrix composites continue to attract scientific and industrial interest since they offer superior strength-, stiffness-, and toughness-to-weight ratios. The research herein characterizes two sets of E-Glass/Epoxy composite skins: stressed and unstressed. The stressed samples were previously installed in an underground power distribution vault and were exposed to fire while the unstressed composite skins were newly fabricated and never-deployed samples. The mechanical, morphological, and elemental composition of the samples were methodically studied using a dynamic mechanical analyzer, a scanning electron microscope (SEM), and an x-ray diffractometer, respectively. Sandwich composite panels consisting of E-glass/Epoxy skin and balsa wood core were originally received, and the balsa wood was removed before any further investigations. Skin-only specimens with dimensions of ~12.5 mm wide, ~70 mm long, and ~6 mm thick were tested in a Dynamic Mechanical Analyzer in a dual-cantilever beam configuration at 5 Hz and 10 Hz from room temperature to 210 °C. Micrographic analysis using the SEM indicated a slight change in morphology due to the fire event but confirmed the effectiveness of the fire-retardant agents in quickly suppressing the fire. Accompanying Fourier transform infrared and energy dispersive X-ray spectroscopy studies corroborated the mechanical and morphological results. Finally, X-ray diffraction showed that the fire event consumed the surface level fire-retardant and the structural attributes of the E-Glass/Epoxy remained mainly intact. The results suggest the panels can continue field deployment, even after short fire incident.

Frequency Response Analysis of Piecewise Nonlinear Vibration Isolator

2005 ◽  
Author(s):  
Patrick Stahl ◽  
G. Nakhaie Jazar
Keyword(s):  
Low Frequency ◽  
High Amplitude ◽  
Relative Displacement ◽  
Response Analysis ◽  
Frequency Response Analysis ◽  
State Behavior ◽  
Vibration Isolators ◽  
Short Period ◽  
Secondary Suspension ◽  
Low Amplitude

Non-smooth piecewise functional isolators are smart passive vibration isolators that can provide effective isolation for high frequency/low amplitude excitation by introducing a soft primary suspension, and by preventing a high relative displacement in low frequency/high amplitude excitation by introducing a relatively damped secondary suspension. In this investigation a linear secondary suspension is attached to a nonlinear primary suspension. The primary is assumed to be nonlinear to model the inherent nonlinearities involved in real suspensions. However, the secondary suspension comes into action only during a short period of time, and in mall domain around resonance. Therefore, a linear assumption for the secondary suspension is reasonable. The dynamic behavior of the system subject to a harmonic base excitation has been analyzed utilizing the analytic results derived by applying the averaging method. The analytic results match very well in the transition between the two suspensions. A sensitivity analysis has shown the effect of varying dynamic parameters in the steady state behavior of the system.

Oxygen Consumption by the Sea Anemone Calliactis Parasitica (Couch)

1980 ◽  
Vol 88 (1) ◽  
pp. 367-374
Author(s):  
A. E. BRAFIELD
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Concentration ◽  
Low Frequency ◽  
High Amplitude ◽  
Total Oxygen ◽  
Strip Chart ◽  
Calliactis Parasitica ◽  
Cycle Lengths ◽  
Mean Cycle ◽  
Low Amplitude

Oxygen consumption by Calliactis parasitica, measured in a continuousflow polarographic respirometer, yielded a slope of 0·92 when plotted against body weight on log scales. This high value is discussed in terms of the sea anemone's basically laminate nature. Strip-chart records of the oxygen concentration of water which had just passed a specimen of Calliactis commonly showed rhythmic fluctuations, either of low amplitude and high frequency or high amplitude and low frequency (mean cycle lengths 11 and 34 min respectively). The fluctuations are explained in terms of rhythmic muscular contractions which irrigate the enteron for respiratory purposes. Analysis of the slow fluctuations indicates that the endoderm is responsible for about 18% of the total oxygen consumption. The oxygen concentration of water in the enteron, measured and recorded continuously, was 4–27% of the air-saturation level. These strip chart records also frequently showed rhythmic fluctuations (mean cycle length 12 min), apparently resulting from the muscular contractions.

Electrical Resistive Spiking of Fungi

2021 ◽  
pp. 1-7 ◽  
Author(s):  
Andrew Adamatzky ◽  
Alessandro Chiolerio ◽  
Georgios Sirakoulis
Keyword(s):  
Electrical Resistance ◽  
Electronic Devices ◽  
Low Frequency ◽  
High Amplitude ◽  
Average Amplitude ◽  
Average Width ◽  
C 23 ◽  
C 30 ◽  
Low Amplitude

We study long-term electrical resistance dynamics in mycelium and fruit bodies of oyster fungi P. ostreatus. A nearly homogeneous sheet of mycelium on the surface of a growth substrate exhibits trains of resistance spikes. The average width of spikes is c. 23[Formula: see text]min and the average amplitude is c. 1[Formula: see text]k[Formula: see text]. The distance between neighboring spikes in a train of spikes is c. 30[Formula: see text]min. Typically, there are 4–6 spikes in a train of spikes. Two types of electrical resistance spikes trains are found in fruit bodies: low frequency and high amplitude (28[Formula: see text]min spike width, 1.6[Formula: see text]k[Formula: see text] amplitude, 57[Formula: see text]min distance between spikes) and high frequency and low amplitude (10[Formula: see text]min width, 0.6[Formula: see text]k[Formula: see text] amplitude, 44[Formula: see text]min distance between spikes). The findings could be applied in monitoring of physiological states of fungi and future development of living electronic devices and sensors.

Three-dimensional mode growth in boundary layers with tuned and detuned subharmonic resonance

1995 ◽  
Vol 352 (1700) ◽  
pp. 453-471 ◽  
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Phase Speed ◽  
Subharmonic Resonance ◽  
Oblique Waves ◽  
Periodic Disturbances ◽  
Wave Numbers ◽  
Interaction Order ◽  
Tollmien Schlichting ◽  
Low Amplitude

This work involves the use of controlled periodic disturbances to excite a plane Tollmien-Schlichting (TS) wave at one frequency ( f 2D) along with pairs of oblique waves with equal but opposite wave angles at a different frequency ( f 3D) in order to study the resonant growth of 3D modes in a Blasius boundary layer. In our earlier work (Corke & Mangano 1989; Corke 1990), the frequency of the oblique modes was exactly the subharmonic of the plane Tollmien-Schlichting (TS) mode. These modes were also phase-speed locked so that in terms of their streamwise wave numbers, α2D=1/2 α3D. This so-called ‘tuned’ subharmonic resonance leads to the enhanced growth of the otherwise linearly damped oblique waves, as well as the growth of higher harmonic 3D modes with frequencies and wave numbers: (3/2 f2d, 3/2 α2D, ±β3D), (5/2 f2d, 5/2 α2D, ±β3D), (f2d, α2D, ±2β3D) and (0, 0, ±2β3D). Even when the initial 3D oblique waves have frequencies which are close to the TS subharmonic frequency, a ‘detuned’ subharmonic resonance leads to the enhanced growth of the 3D mode. In addition, it promotes the growth of numerous discrete modes produced by successive sum and difference interactions. These interacted modes are also three dimensional, with higher amplification rates that increase with the interaction order. The growth of these modes accounts for the rapid spectral filling, and low-frequency modulation commonly observed in natural subharmonic transition. Starting from a ‘tuned' resonance, this scenario then provides a mechanism for the generation of a broad spectrum at the later stages of subharmonic mode transition. However, the results also suggest that with ‘natural’ transition, starting from low-amplitude broadband disturbances, the most likely 2D/3D resonance will be ‘detuned’.

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