Characterization of Fatigue Damage in Composite Laminate Using Lamb Wave Velocities

Composite laminates suffer from fatigue damage under cyclic loads and one direct result is the stiffness degradation due to transverse matrix cracks in off-axis plies. Since the Lamb wave velocities are decided by the stiffness properties of materials, it is reasonable to use Lamb wave to characterize the fatigue damage in composite laminates. For this to be achieved, an explicit solution for 0-frequency S0 and SH0 mode phase velocities is deduced in this work, based on which a damage evolution law is further proposed combined with shear-lag model and Paris model. The proposed damage evolution law was then used to characterize the fatigue damage in both cross-ply GFRP laminates ([0/903/0/903]s) and quasiisotropic GFRP laminates ([45/0/-45/90]2s), where the experimental S0 phase velocity was obtained by a laser ultrasonic scanning system. The illustrated results in Fig. 1 and Fig. 2 show good agreements between numerical calculations and experimental data. With the proposed damage evolution law, it is possible for future work to be done to inspect and predict the residual fatigue life of composite laminates using Lamb wave velocities

Semi-Active Vibration Control Based on Switched Piezoelectric Transducers

Non

Interfacial stiffness dependence of the effective magnetostriction of particulate magnetostrictive composites

AbstractTerfenol-D composites attract much attention recently due to their large magnetostriction, small eddy energy loss and large operation frequency bandwidth. Binder layer in the composite usually mechanically weakens the composite and reduces the effective properties. A typical kind of magnetostictive composite is composed of Rare Earth metallic compound powder, matrix material and resin binder. The binder, which is usually flexible and forms mechanically weak interface in the composite, inevitably influences the overall magnetostriction of composites. In this paper, a theoretical model was developed to treat a simple deformation case of this kind of mechanically weak interface, in which the flexible layer has low stiffness to withstand deformation but no de-bonding or cracking. An infinite magnetostrictive plane with a circular inclusion was considered, where the matrix and inclusion are all general magnetostrictive materials which can be modeled by the standard square constitutive relation of magnetostriction. The binder layer of a certain thickness was modeled as a set of springs with no thickness but with an equivalent stiffness. The mathematical formulation was brought into the complex variable framework. The magnetoelastic field was solved and the effective magnetostriction was explicitly obtained. Comparisons with experimental results were also presented. In terms of this analysis, the interfacial stiffness has significant influences on the overall magnetostriction of composite. Increasing the interfacial stiffness can lead to large magnetostriction of composites. The measure for improving the interfacial stiffness includes increasing the binder modulus and reducing its thickness

A low-power circuit for piezoelectric vibration control by synchronized switching on voltage sources

In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results.Comment: 11 page

Signal processing and health assessment techniques in structural health monitoring

Considering the practical necessity of realizing the aircraft structure health monitoring (SHM), not only some advanced sensors must be adopted, an appropriate signal processing method is also necessary, in order to achieve the goals of signal characteristic extraction and health assessment. Based on the fact that piezoelectric (PZT) sensor signals extracted from the monitored structure carry a lot of useful health related information, this paper proposes to utilize the power characteristics of PZT signals for health assessment of the aircraft structure. The Hilbert-Huang Transform (HHT) algorithm is employed to calculate the power characteristic vector, after that, the self-organizing map (SOM) is used to map the corresponding characteristics into a confidence value (CV) which represents the health state of the monitored structure. The experimental results demonstrate that the proposed method is reliable

Nonlinear vibrations of beams with spring and damping delayed feedback control

The primary, subharmonic, and superharmonic resonances of an Euler–Bernoulli beam subjected to harmonic excitations are studied with damping and spring delayed-feedback controllers. By method of multiple scales, the non-linear governing partial differential equation is transformed into linear differential equations directly. Effects of the feedback gains and time-delays on the steady state responses are investigated. The velocity and displacement delayed-feedback controllers are employed to suppress the primary and superharmonic resonances of the forced nonlinear oscillator. The stable vibration regions of the feedback gains and time-delays are worked out based on stablility conditions of the resonances. It is found that proper selection of feedback gains and time-delays can enhance the control performance of beam’s nonlinear vibration. Position of the bifurcation point can be changed or the bifurcation can be eliminated

PO-107 Applied Research on Heart Rate Variability in Monitoring Sports Fatigue of Boxing Athletes

Objective Based on the diagnosis of sports fatigue using physiological and biochemical indicators, to detect the changes of heart rate variability (HRV) index before and after heavy load training in boxing athletes, and observe the effect of heavy load training on cardiac autonomic nerves. The purpose of this study was to investigate the application of HRV to monitor boxing athletes’ sports fatigue. Methods 16 athletes from Shanghai men's boxing team were recruited. The coach organized a 4-week heavy load training, on Monday morning before and after heavy load training, to evaluate whether athletes have exercise fatigue by testing white blood cell (WBC), red blood cell (RBC), hemoglobin (Hb), blood testosterone (T), cortisol (C), testosterone/cortisol ratio (T/C), creatine kinase (CK), blood urea (BU) and morning pulse. Heart rate variability (HRV) indicators were detected simultaneously. The data were analyzed by SPSS 19.0 statistical software. Pearson correlation analysis was used to compare the correlation between HRV and physiological and biochemical indexes. The paired sample T test was used to compare the differences between the indicators, P<0.05, P<0.01 was statistically significant. Results After heavy load training, when compared with indexes before heavy load training, T and T/C ratios decreased significantly (-38%, -52.7%, p<0.01), C and morning pulse increased significantly (+32.4%, +20.4%, p<0.05), BU and CK had an increasing trend but no statistical significance (+16.5%, +52.7%, p>0.05), while WBC, RBC and Hb showed no statistical significance (p>0.05), these changes in physiological and biochemical indexes can diagnose sports fatigue of boxing athletes after heavy load training. SDNN of HRV index was significantly correlated with morning pulse (p<0.05), RMSSD was significantly correlated with CK (p<0.05), LF was significantly correlated with Hb (p<0.05), and LF/HF was significantly correlated with T, C, T/C, morning pulse, CK (p<0.05). After heavy load training, LF and LF/HF of HRV index in boxing athletes were significantly increased than that before heavy load training (1744.7±1526.3 ms2 vs. 1134.5±1003.3 ms2, 2.5±1.3 vs. 1.6±1.0, p<0.05), the other HRV indexes showed no statistical significance (p>0.05). Conclusions The LF and LF/HF changed significantly when boxing athletes appeared sports fatigue, suggesting that the sympathetic nervous system had enhanced activity and increased tension, the imbalance between Sympathetic and parasympathetic tend to predominate in sympathetic activity. LF and LF/HF are sensitive HRV indicators for monitoring sports fatigue in boxing athletes

Nonlinear dynamics of shape memory alloys actuated bistable beams

The phenomenon of bi-stable behaviour has been widely used in the structural design, as it can provide large deformation by switching between two stable equilibrium positions. This paper aims to investigate the intrinsic nonlinear dynamic characteristics of an actively controlled bistable beam using a simplified spring-mass model. The dynamic model for an active (heated) SMA wire driven bistable beam is established based on a polynomial constitutive equation to describe the thermomechanical behaviour of the shape memory alloy. The actively controlled bistable beams are designed, fabricated and experimentally tested to achieve the morphing behaviour snapping-through form one position to another. The results obtained from the experimental testing and the theoretical simulation are compared to validate the proposed model. Dynamic behavior of the proposed SMA wires actuated bistable beam under varying external excitation is investigated to show the influence of the thermomechanical loadings. Analysis of the experimental data and simulation results shows that the SMA wires actuated bistable structure can be well-performed for the bistable switching. It also approved that the different behaviours of the system, including periodic responses, complex responses and chaos can be accurately predicted using the proposed simplified model

Exploiting the instability of smart structure for reconfiguration

Aiming to verify the concept of using heteroclinic connections to reconfigure smart structures, a multistable buckled beam with integrated Shape Memory Alloy (SMA) wires is utilized as a high fidelity model. The Shape Memory Alloy (SMA) wires are resistively heated to provide the actuation force to stabilize the unstable configuration and the transition of the beam from one unstable equilibrium condition to the other. This concept provides a means of reducing the energy requirement for transitions between configurations of the structure, which is an energy-efficient reconfiguration scheme between equal-energy unstable (but actively controlled) equilibria. This letter presents a detailed design of the system, and how the active (heated) SMA wires control the structure stay in unstable configuration and drive the structure to achieve reconfiguration. Exploiting the instability of the smart structure has significant interests in many power reduction applications, including active flow control, reconfiguration of large deployable aerospace structures, and MEMS devices