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In this paper, the assessments of structural health monitoring (SHM) for metallic structures are presented. Tests were conducted on three specimens for fatigue crack testing and damage inde...

In this paper, the bending singularity at the apex of V-notch in an anisotropic thick plate is investigated. The Stroh-like formalism is used to model the anisotropy of the material. Based on the Ressiner-Mindlin plate theory and the eigenfunction expansion method, the characteristic equation for bending singularity order is derived and the order can be determined numerically. The numerical results show that the singularity orders strongly depend on the plate angle a. In addition, the singularity orders also depend on the principal orientation of the anisotropic material. The singularity orders for the case of are stronger than for that of. In the case of, to reduce the anisotropy is helpful to release the singularity at the notch tip. For the other case of, it is preferable to increase the anisotropy to reduce the singularity. The disappearance conditions of the bending singularity can be found based on the numerical results.

In this paper, the wave propagation in phononic crystal composed of auxetic star-shaped honeycomb matrix with negative Poisson&rsquo, s ratio is presented. Two types of inclusions with circular and rectangular cross sections are considered and the band structures of the phononic crystals are also obtained by the finite element method. The band structure of the phononic crystal is affected significantly by the auxeticity of the star-shaped honeycomb. Some other interesting findings are also presented, such as the negative refraction and the self-collimation. The present study demonstrates the potential applications of the star-shaped honeycomb in phononic crystals, such as vibration isolation and the elastic waveguide.

In this paper, the mode II strain energy release rates (SERR) of a cracked sandwich beam (CSB) subjected to a three-point loading are investigated. Due to the stiff face sheets and soft core, the displacements in the sandwich beam have the zigzag distribution through the thickness. A literature survey reveals that SERR of the CSB can be determined by the first-order shear deformation theory (FSDT). However, the accuracy of the results in FSDT is limited due to the lack of zigzag phenomenon. In this paper, we re-solve the CSB based on the refined zigzag theory (RZT), in which the kinematics of the displacements are assumed to have zigzag characteristic. The kinematic variables of the displacements can be determined from solving the governing equations of RZT in conjunction with the boundary conditions and continuity conditions of the CSB, and then SERR can be calculated by the compliance method. We show that for sandwich beams with slender aspect ratio (large L/h) or with thin face sheet (large rh), the FSDT can provide a satisfactory results due to the insignificant zigzag displacements. Otherwise for small L/h or small rh, the RZT should be used to take the significant zigzag displacements into consideration. For a given crack length, the FSDT give a result that the SERR is independent of the beam length. By using the RZT, it is found that the SERR depends on the beam length for a given crack length, especially for long crack length that a/L is ranged from 0.4 to 0.5. The material properties of the core materials on SERR are also investigated. By comparing with the finite element method (FEM), the deflections, compliances and SERRs in the CSB obtained by RZT are more accurate than those by FSDT. It is found that, for the cases of the core with very small shear modulus, the RZT gives correct results that are validated by FEM. For such cases, the FSDT gives incorrect calculations for SERR due to the lack of the zigzag model. The results arose in this study show the superior advantages of the use of the RZT in the SERR calculation of CSB specimen.

A novel natural frequency self-tuning energy harvester is presented, which utilizes the presence of the nonlinearity model and the well-weighted swing disk to maximize the power output and the frequency bandwidth for a wheel rotating at any speed. Kinetic energy harvesters are frequency selective, meaning that they have high power transmission efficiency only when they are excited at their natural frequency. The well-weighted swing disk with nonlinear effects can render the energy harvester more broadband, that is, it has a more steady power generation at various wheel speeds than the ill-weighted swing disk has. We integrate magnets in a novel circular Halbach array and coils into the design to augment the magnetic strength on one side of the array where the coils are placed. Therefore, the gradient of the average magnetic flux density for the circular Halbach array disk is larger than that of the multipolar magnetic disk. The dynamic models with electromechanical couplings have been established and are analyzed. In the experiments, the power output of the prototype at an optimum external resistance was approximately 300–550 µW at about 200–500 rpm and precisely matches the numerical results.

In this paper, a distributed parameter electromechanical model for bimorph piezoelectric energy harvesters based on the refined zigzag theory (RZT) is developed. In this model, the zigzag function is incorporated into the axial displacement, and the zigzag distribution of the displacement between the adjacent layers of the bimorph structure can be considered. The governing equations, including three equations of motions and one equation of circuit, are derived using Hamilton's principle. The natural frequency, its corresponding modal function and the steady state response of the base excitation motion are given in exact forms. The presented results are benchmarked with the finite element method and two beam theories, the first-order shear deformation theory and the classical beam theory. Comparing examples shows that the RZT provides predictions of output voltage and generated power at high accuracy, especially for the case of a soft middle layer. Variation of the parameters, such as the beam thickness, excitation frequencies and the external electrical loads, is investigated and its effects on the performance of the energy harvesters are studied by using the RZT developed in this paper. Based on this refined theory, analysts and engineers can capture more details on the electromechanical behavior of piezoelectric harvesters.

Based on stochastic crack growth model, the effects of material variations on aircraft inspection schedules are investigated in this paper. Fatigue tests are performed to obtain the log standard deviation of fatigue lives due to material variations. The test materials are 7475-T7351, 7050-T7451, 2024-T851 and 2124-T851. The effects of material variation on inspection schedule are significant. For a large material variation, the inspection schedule should be shortened for conservative consideration. The effects of sample size on the material variation under 50% and 95% confidence levels are investigated numerically. The results of this study provide a guideline to allocate resources of fleet planning more realistically by compromising between the cost (or time) of fatigue experiments and aircraft inspections.

IA piezoelectric strip with semi-infinite electrode is investigated. Two combinations of mechanical–electrical loadings are considered. They consist of the anti-plane deformation with in-plane electrical field and the in-plane electroelastic field. Based on the Fourier transform and the Wiener–Hopf technique, the electroelastic local stress fields are found to exhibit the square root singularity near the electrode tip. The energy density factor criterion is applied to examine the fracture behavior near the electrode tip.

This paper presents the formulation of piezoelectric elasticity under generalized plane deformation derived from the three-dimensional theory. There are four decoupled classes in the generalized plane deformation formulation, i.e. when l 3 ( μ )= l 2 * ( μ )=0, l 3 ( μ )= l 3 * ( μ )=0, l 3 * ( μ )= l 2 * ( μ )=0 or l 3 ( μ )= l 3 * ( μ )= l 2 * ( μ )=0. Only the inplane fields of the first class and the antiplane field of the second class include the piezoelectric effect. Several examples of wedge problem often encountered in smart structures, such as sensors or actuators are studied to examine the stress singularity near the apex of the structure. The bonded materials to the PZT-4 wedge are PZT-5, graphite/epoxy or aluminum (conductor). The influencing factors on the singular behavior of the electro-elastic fields include the wedge angle, material type, poling direction, and the boundary and interface conditions. The numerical results of the first case are compared with Xu's graphs and some comments are made in detail. In addition, some new results regarding the antiplane stress singularity of the second class are obtained via the case study. The coupled singularity solutions under generalized plane deformation are also investigated to seek the conditions of the weakest or vanishing singular stress fields.

This study presents the design and analysis of a two-axis scanner driven by lead-zirconate-titanate (PZT) ceramic. The proposed device consists of a silicon-based MEMS scanning mirror and a bulk-type piezoelectric actuator. The MEMS process involves three masks. The experimental results showed that the fast and slow frequencies at resonance are 29.6 kHz and 4.8 kHz, respectively. For the fast scan, the scanning angle is 46.9 degrees at a driving voltage of 10 V. For the slow scan, the scanning angle is 22.6 degrees at a driving voltage of 20 V. A multi-DOF vibration model was developed to analyze the scanning characteristics of the device. The numerical simulations, including the resonance frequency, scanning angle and the mode coupling phenomenon, were validated with the experimental observations. This study also develops a laser projection module integrated with the scanning device. The module can receive a video content with a resolution of 720 p and project a 16:9 image that is 19 inches in diagonal at a projection distance of 600 mm.

This paper presents the development of a wheel-mounted eccentric ring energy harvester that is driven by centripetal and gravitational forces during wheel rotation. The natural frequency of the eccentric ring matches the wheel rotation frequency at any car speed because its character length is designed equal to the wheel radius. Consequently, the eccentric ring oscillates with a relatively large swing angle at the wheel speed to generate high levels of power. The nonlinear dynamic behavior of the eccentric ring is investigated to ensure that the proposed design produces steady swing angles, especially at high wheel speeds. Herein, the jump phenomenon of the dynamic motion of the eccentric ring is analyzed by using the Duffing equation and the linearization process. The discriminant value obtained from the analysis confirms that no jump phenomenon occurs at all wheel speeds if the eccentric ring is properly designed. In the experiment, the eccentric ring is integrated with magnets and a coil set to generate 318?442??W at constant wheel speeds between 300 and 500?rpm. This shows that the proposed device is a potential power source for low-power wheel-mounted electronics, such as pressure sensors, accelerometers, and thermometers.

Based on the generalized Lekhnitskii formulation and Mellin transform, the thermo-electro-elastic fields of a piezoelectric bonded wedge are investigated in this paper. From the potential theory in a wedge-shaped region, a general form of the temperature change is proposed as a particular solution in the generalized Lekhnitskii formulation. The emphasis is on the singular behavior near the apex of the piezoelectric bonded wedge, including singularity orders and angular functions, which can be computed numerically. The interface between two materials can be either perfectly bonded, namely type A, so that the continuity of electric displacements holds, or a thin electrode, namely type B, so that the electric potential is grounded. Case studies of PZT-5H/PZT-4 and graphite-epoxy/PZT-4 bonded wedges reveal that, in most cases, the type B continuity condition has more severe singularities than type A due to the mixed boundary point of the electrostatics at the apex of the wedge. The results of this study show that the reduction or disappearance of singularity orders is possible through the appropriate selection of poling/fiber orientations and wedge angles.