Dynamic Strain Sensor Research Articles

Enhanced piezoresponse of electrospun PVDF mats with a touch of nickel chloride hexahydrate salt

PVDF nanofibers are prepared using electrospinning. The effect of addition of a hydrated salt, nickel chloride hexahydrate (NiCl(2)·6H(2)O), on the phase formation is examined. Addition of the hydrated salt (NC) is found to enhance the polar β phase by about 30%. The peak to peak piezo-voltage generated for PVDF NC is almost 0.762 V, a factor of 3 higher than that for PVDF. The fiber mats exhibit a significantly enhanced dynamic strain sensor response. The voltage generated per unit micro-strain developed during the free vibration test for PVDF was 0.119 mV whereas it was 0.548 mV for PVDF NC, exhibiting a non-linearly enhanced performance vis a vis the increase in the β phase component.

Assessment of damage localization based on spatial filters using numerical crack propagation models

This paper is concerned with vibration based structural health monitoring with a focus on non-model based damage localization. The type of damage investigated is cracking of concrete structures due to the loss of prestress. In previous works, an automated method based on spatial filtering techniques applied to large dynamic strain sensor networks has been proposed and tested using data from numerical simulations. In the simulations, simplified representations of cracks (such as a reduced Young's modulus) have been used. While this gives the general trend for global properties such as eigen frequencies, the change of more local features, such as strains, is not adequately represented. Instead, crack propagation models should be used. In this study, a first attempt is made in this direction for concrete structures (quasi brittle material with softening laws) using crack-band models implemented in the commercial software DIANA. The strategy consists in performing a non-linear computation which leads to cracking of the concrete, followed by a dynamic analysis. The dynamic response is then used as the input to the previously designed damage localization system in order to assess its performances. The approach is illustrated on a simply supported beam modeled with 2D plane stress elements.

Damage identification in beam-type structures using pseudo strain energy density and grey relation coefficient

Based on pseudo strain energy density (PSED) and grey relation coefficient (GRC), an index is proposed to locate the damage of beam-type structures in time-domain. The genetic algorithm (GA) is utilized to identify the structural damage severity of confirmed damaged locations. Furthermore, a systematic damage identification program based on GA is developed on MATLAB platform. ANSYS is employed to conduct the finite element analysis of complicated civil engineering structures, which is embedded with interface technique. The two-step damage identification is verified by a finite element model of Xinxingtang Highway Bridge and a laboratory beam model based on polyvinylidens fluoride (PVDF). The bridge model was constructed with 57 girder segments, and simulated with 58 measurement points. The damaged segments were located accurately by GRC index regardless of damage extents and noise levels. With stiffness reduction factors of detected segments as variables, the GA program evolved for 150 generations in 6 h and identified the damage extent with the maximum errors of 1% and 3% corresponding to the noise to signal ratios of 0 and 5%, respectively. In contrast, the common GA-based method without using GRC index evolved for 600 generations in 24 h, but failed to obtain satisfactory results. In the laboratory test, PVDF patches were used as dynamic strain sensors, and the damage locations were identified due to the fact that GRC indexes of points near damaged elements were smaller than 0.6 while those of others were larger than 0.6. The GA-based damage quantification was also consistent with the value of crack depth in the beam model.

Compact fiber Bragg grating dynamic strain sensor cum broadband thermometer for thermally unstable ambience

An instrument for simultaneous measurement of dynamic strain and temperature in a thermally unstable ambience has been proposed, based on fiber Bragg grating technology. The instrument can function as a compact and stand-alone broadband thermometer and a dynamic strain gauge. It employs a source wavelength tracking procedure for linear dependence of the output on the measurand, offering high dynamic range. Two schemes have been demonstrated with their relative merits. As a thermometer, the present instrumental configuration can offer a linear response in excess of 500 °C that can be easily extended by adding a suitable grating and source without any alteration in the procedure. Temperature sensitivity is about 0.06 °C for a bandwidth of 1 Hz. For the current grating, the upper limit of strain measurement is about 150 µε with a sensitivity of about 80 nε Hz−1/2. The major source of uncertainty associated with dynamic strain measurement is the laser source intensity noise, which is of broad spectral band. A low noise source device or the use of optical power regulators can offer improved performance. The total harmonic distortion is less than 0.5% up to about 50 µε,1.2% at 100 µε and about 2.3% at 150 µε. Calibrated results of temperature and strain measurement with the instrument have been presented. Traces of ultrasound signals recorded by the system at 200 kHz, in an ambience of 100–200 °C temperature fluctuation, have been included. Also, the vibration spectrum and engine temperature of a running internal combustion engine has been recorded as a realistic application of the system.

A High-Resolution MEMS Piezoelectric Strain Sensor for Structural Vibration Detection

This paper presents the modeling, fabrication, and testing of a high-performance dynamic strain sensor. Using microelectromechanical systems (MEMS) technology, ZnO piezoelectric microsensors are directly fabricated on silicon and steel substrates. The sensors are intended to be used as point sensors for vibration sensing without putting an extra burden on the host structures. A model that incorporates piezoelectric effects into an RC circuit, representing the sensor architecture, is developed to describe the voltage output characteristics of the piezoelectric microsensors. It is shown that the sensitivity of microplanar piezoelectric sensors that utilize the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> effect is linearly proportional to sensor thickness but unrelated to sensor area. Sensor characterization was performed on a cantilever beam cut from a fabricated silicon wafer. The experimental data indicate that the overall sensor and circuit system is capable of resolving better than 40.3 nanostrain time domain signal at frequencies above 2 kHz. The corresponding noise floor is lower than 200 femto-strain per root hertz and the sensitivity, defined as the sensor voltage output over strain input, is calculated to be 340 V/epsiv . Micro ZnO piezoelectric sensors fabricated on steel hard disk drive suspensions also show excellent results. The sensor not only has a better signal-to-noise ratio but also detects more vibration information than the combination of two laser-Doppler-vibrometer measurements in different directions.

A quasi-distributed dynamic and static strain sensor system

A quasi-distributed dynamic and static strain sensor system consisting of 16 FBG sensors is designed by using an amplified-sponteneous emission (ASE) optical source, an optical tunable filter and a tunable laser. A resolution of about 5 has been achieved for dynamic strain measurement. The resolution for static strain measurement is about 1 μɛ.

Interrogation of Fiber Bragg Grating Dynamic Strain Sensors by Self-Mixing Interferometry

An innovative investigation of optical feedback or self-mixing interference within the cavity of a single-longitudinal-mode laser is described as an integral part of a novel interrogation scheme to be employed in a fiber Bragg grating-based sensor for strain measurement. The entire sensor device simply consists of a laser diode with an integrated photodiode which is coupled to a fiber Bragg grating under strain. A small percentage of the injected lightwave resonantly reflected off the grating structure reenters the laser cavity and modifies the emission properties of the laser, resulting in the formation of characteristic sawtooth fringes which contain the embedded strain information. The feasibility of demodulating the induced small wavelength shifts of fiber Bragg gratings under dynamic mechanical loading by self-mixing interferometry is thus presented analytically and experimentally verified. A relatively good corroboration has been achieved.

Monitoring Fatigue Crack Growth in Compact Tension Specimens Using Piezoelectric Sensors

This paper aims to report the results of an experimental study on the application of piezoelectric dynamic strain sensors for crack length measurement in fracture mechanics specimens. The performance of the piezoelectric sensors was assessed through fatigue crack propagation tests in compact tension (CT) specimens. Sensors of polarized polyvinilidene fluoride polymer (PVDF) were bonded to the back face of CT specimens, in the same manner as the electrical resistance strain gages installed for crack length measurement in the back face strain technique. The results showed that, mainly due to its high sensitivity to strain, the use of piezoelectric materials as dynamic strain sensors can contribute to the experimental investigation in the field of fracture mechanics.

Development of piezoelectric paint thick-film vibration sensors

This paper describes a programme of trials of thick-film dynamic strain sensors made using ‘piezoelectric paint’. The fabrication process is described and it is shown that the sensitivity is comparable with that of other thick-film sensors and the piezoelectric polymer polyvnylidenefluoride (PVDF). A series of dynamic and environmental tests is described. The dynamic range and bandwidth are shown to be suitable for structural vibration monitoring, and to be largely unaffected by adverse environments (rain, frost, sunlight, etc.).

Detection of bolt load loss in hybrid composite/metal bolted connections

Hybrid composite/metal connections are susceptible to bolt load loss due to viscoelastic creep and/or environmental effects. Accordingly, the focus of this research is on experimentally quantifying changes in bolt load of composite/metal hybrid connections. A proof-of-concept model was created consisting of a fiber reinforced composite panel bolted to a steel frame. A piezoelectric actuator bonded to the center of the composite panel was used to provide controlled vibration input. The response of the plate was measured using either shear accelerometers or dynamic strain sensors located at the four corners of the composite panel. The load on an instrumented bolt was decreased and three different monitoring techniques were used to detect bolt load loss, including (a) low frequency modal analysis, (b) high frequency transfer functions between the actuator and sensors and (c) high frequency transmittance functions between pairs of sensors. Experiments demonstrate that the transmittance function approach shows the most promise and was able to reliably detect a single bolt loosening. A damage index based on change in transmittance function is very sensitive to changes in bolt load.

Developments In Paint Based Piezoelectric Thick-film Strain Sensors

This paper describes developments in the manufacture of thick-film dynamic strain sensors based on piezoelectric paint for structural vibration monitoring. A new generation of paints have been developed as the vehicle for depositing piezoelectric composites as thick films. These are water based to be compatible with likely future environmental legislation and are suitable for use with conventional spraying equipment. Results of tests on strain amplitude response and frequency response are presented, showing that sensors made using these materials have a wide bandwidth and good dynamic range making them suitable for use in structural dynamics applications.

Anisotropic Dynamic Strain Sensors Based on Ferroelectric PZT Films

ABSTRACTThe present paper deals with anisotropie dynamic strain sensors based on polycrystalline Pb(Zr0.53Ti0.45W0.01Cd0.01)O3 films. The films were deposited on ceramic substrates designed to operate at radiofrequencies. The planar interdigitated Al electrodes were deposited on the film surfaces. To pole the films the sawtooth monopolar pulses of the amplitude ranging from 5 · 107 to 8 · 107 V/m were used during the heating of the films from room temperature to 300 °C and the following cooling down to room temperature (Tc = 360 °C).