Piezoelectric energy harvester with double cantilever beam undergoing coupled bending-torsion vibrations by width-splitting method

We propose piezoelectric energy harvester (PEH) with double-cantilever-beam (DCB) undergoing coupled bending-torsion vibrations by combining width-splitting method and asymmetric mass, in order that more ambient energy could be harvested from environmental vibration with multiple-frequency excitation. The geometrical dimensions are optimized for PEHDCB, when the maximum of output peak voltages Up-max and resonance frequency difference (Δf0) between the first and second modes are chosen as optimization objectives based on orthogonal test method. The energy harvesting efficiency is evaluated by the proportion of half-power bandwidth and quality factor, and the experimental and simulation results are compared to verify reliability. The Up-max1 and Pp-max1 are increased 25.2% and 57.3% for PEHDCB under the multi-frequency excitation, when the split-width method is applied into PEH with single-cantilever-beam (SCB) undergoing coupled bending-torsion vibrations. The deviations of Up-max1 and f0 are at the ranges of 4.9–14.2% and 2.2–2.5% for PEHDCB under the different mass ratios, and the measurement reliability is acceptable considering incomplete clamping, damping and inevitable assembly effects. The energy harvesting efficiency of PEHDCB presented is much higher than that of the conventional PEHSCB from environmental vibration with multiple-frequency excitation.

A temperature-insensitive FBG acceleration sensor with sinusoid-shaped curved beams

Purpose This study aims to solve the problem of temperature cross sensitivity of fiber Bragg grating in structural health monitoring, proposing a novel acceleration sensor based on strain chirp effect which is insensitive to temperature. Design/methodology/approach A kind of M-shaped double cantilever beam structure is developed. The fiber grating is pasted in the gradient strain region of the beam, and the chirp effect is produced under the action of non-uniform stress, and then the change of acceleration is converted into the change of reflection bandwidth to demodulate and eliminate the temperature interference. Through theoretical analysis, simulation and experimental verification with rectangular beam sensor. Findings The results show that the sinusoidal curvature beam sensor is insensitive to the change of temperature and is more likely to produce chirp effect. The sensitivity is about 317 pm/g, and the natural frequency is 56 Hz. Originality/value This paper fulfils an insensitive to temperature changes sensor which has effectively solved the temperature cross-sensitivity problem in building structure health monitoring.

Acoustic emission as a valuable technique used for monitoring polymer failures

In the paper, acoustic emission (AE) system was presented as a method that can be used to monitor polymer material failures. Samples fabricated of two aluminum profiles bonded together with a thick layer of cured epoxy resin were subjected to fracture tests. Epidian 53 epoxy resin cured with Z1 curing agent as well as Epidian 5 epoxy resin cured with PAC curing agent were selected as adhesives. Acoustic emission parameters were acquired during Double Cantilever Beam (DCB) tests. The frequencies of elastic waves released during failure were then analyzed using both Fast Fourier Transformation (FFT) and Wavelet Transformation (WT) for the two materials.

Investigating the effects of loading system on the fracture behavior of DCB specimens considering T-stress

Double cantilever beam specimen is a standard specimen for assessment of mode I failure and separation in adhesively bonded joints and also composite materials. Among the several load introduction systems, the piano hinges and end loading blocks are more common. It has been accepted that the fracture toughness results of the two cases are different, but the effect of the loading system on the load-displacement data and fracture mechanisms is not entirely known yet. Therefore, in this study, the two loading concepts are compared both by precise finite element simulations and experimental tests. The adhesive layer is modeled with its own material properties, and the failure of adhesive is investigated by known LEFM procedures. The results reveal that the load block makes the double cantilever beam specimen stiffer and exhibit more non-linear behavior. Moreover, double cantilever beam with the load block system fails in higher loads and lower crack opening displacements compared with the same specimen loaded by the hinges. To study the effect of loading arrangement in more details and including the softening phase, cohesive zone model was utilized. A correction for strain energy release rate based on the parameter T was proposed, and the role of the T-stress on the traction-separation law of the cohesive zone model and the load-displacement behavior were investigated. It was concluded that the T-stress as a crack tip constraint parameter can successfully justify the difference between the two cases. Applying the correction to the traction-separation law of CZM proves the validity of proposed correction in justifying the experimental results.

Determination of mode I interlaminar fracture toughness of C/SiC composite using taped double cantilever beam and J integral

Due to the low in-plane strength of C/SiC ceramic matrix composite (CMC), arm failure may occur in the classical double cantilever beam (DCB) test for determination of the mode I interlaminar fracture toughness. A taped DCB (TDCB) is proposed to avoid this undesired failure mode. Exact and explicit J integral for the TDCB is derived and applied to measure the interlaminar fracture toughness of CMC. The present TDCB and J integral are demonstrated to be simple and reliable for determining the interlaminar fracture toughness, without visual measurement of the delamination length and complex data reduction.

CLOSED-FORM J-INTEGRAL AND ITS APPLICATIONS FOR MEASUREMENT OF MODE I INTERLAMINAR FRACTURE TOUGHNESS OF COMPOSITES

Due to the interlaminar properties of composites are low, delamination is one of the major failure modes. It threatens the safety of composite structure subjected to out-of-plane static and especially impact loadings. High interlaminar fracture toughness is demanded in the society where composite structures are widely used. However, for tough material, large deformation may occur in the determination of the interlaminar fracture toughness when using the double cantilever beam (DCB) test. Therefore, accurate determination of the fracture toughness of tough material and dynamic loading is very challenging under large deformation. J-integral is an important parameter in fracture mechanics. It’s equivalent to energy release rate under monotonic loading and widely used in the determination of interlaminar fracture toughness of composites. In this paper, it is used to determine the fracture toughness for composite DCB under large deformation and wedge-insert double cantilever beam (WDCB) test, which is widely used to determine the dynamic interlaminar fracture toughness. Exact and closed form nonlinear J-integrals are derived for the largely deformed DCB and WDCB. Compared with the alternative data reduction methods for determining interlaminar fracture toughness, the J- integral method is more accurate. In addition, the J-integral method is simple and promising, since it is unnecessary to measure the crack length in the tests.