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The outer skins of aerospace structures, which are frequently experiencing variations of temperature, are threatened by thermally induced vibration. Vibration in space has dangerous effects on the safety of structures and may result in structural failure. So, the construction of an active control system to suppress thermally induced vibrations is necessary. Active thermally induced vibration control of homogenous isotropic beams, and plates through magnetostrictive layers are presented here. Negative velocity feedback with a constant gain is employed to make appropriate strain in the magnetostrictive actuator layer. Ultimately, a closed-form solution is presented for thermally induced vibration control of the hybrid magnetostrictive-Aluminum beams and plates. Effects of material properties, thickness of magnetostrictive layers, and control gain on vibration suppression have been evaluated.

In engineering practice, dynamic vibration absorber is an effective method to control vibration of beam structure. The mathematical model of beam coupled with spring–mass systems under elastic edge constraints is established in this paper. In addition to Fourier cosine series, supplementary sine functions are introduced to represent the displacement function of the beam. The spring–mass system is considered by increasing degrees of freedom when constructing the mass matrix and stiffness matrix. The efficiency of solving equivalent mass is greatly improved in the comparison with FEM, which is important when designing dynamic vibration absorber. Subsequently, we conduct parametric analysis of the control effect about the dynamic vibration absorber based on the current mathematical model. The procedure of designing distributed dynamic vibration absorber of beam structure under various boundary condition is also presented. To verify the validity of the current mathematical model and design procedure, a cantilever beam experiment was conducted. The findings presented in the current research may be useful for researchers in the process of multi-line spectrum vibration control of beam structure.

An adequate ductile fracture locus has to be developed to reasonably model crack initiation and propagation in high velocity impact. Most of the fracture loci in the literature were proposed on the basis of tensile tests while in high velocity impact cracks usually occur in the region where shear and compression are dominant. In this paper, perforation response of a thin beam struck by a rigid, blunt projectile moving at a high velocity is simulated using, respectively, uniform fracture strain, Johnson-Cook's, and Bao-Wierzbicki's fracture locus for 2024-T351 aluminum alloy. The former two predict that materials in the impacted area of the beam beneath the rigid mass fail layer by layer, which is not consistent with experimental observations. By contrary, Bao-Wierzbicki's fracture locus, which was developed from up-setting, shear and tensile tests, and covers the whole range of the stress triaxiality, is capable of capturing all of the features occurring in the whole failure process. Numerical results reveal that the beam would fail by shear plugging at a high impact velocity and by tensile tearing at a velocity near the ballistic limit.

This paper examines the dynamic stability of an elastic beam on the elastic foundation, in which the stress wave effect is taken into account. Based on Euler–Bernoulli beam theory, the dynamic response of the elastic beam on the elastic foundation to a small transverse perturbation is analyzed. By considering the stress wave propagation in the beam and the constraint of the elastic foundation, the critical bifurcation condition of elastic beam is derived, and the critical axial load of the elastic beam is predicted. Furthermore, the effects of the elastic foundation and the beam length on buckling condition are discussed by using numeric examples. Finally, an approximate solution of critical axial load for elastic beam on the elastic foundation is provided, which may be used to investigate elastic beam buckling problem.

Based on the theory of elasticity, bending and free vibrational analyses of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beam embedded in piezoelectric layers are carried out, using the state-space differential quadrature method (DQM). Applying the DQM to the governing differential equations and boundary conditions along the longitudinal directions, new state equations about state variables at discrete points are derived. By using the state-space technique across the thickness direction, semi- analytical closed form solutions are derived. The method is validated by comparing numerical results for beams without piezoelectric layers. Both the direct and the inverse piezoelectric effects are investigated and the influence of piezoelectric layers on the mechanical behavior of beam is studied. Furthermore, the effects of CNT volume fraction, kind of CNT distribution, length to thickness ratio and edge boundary conditions on the mechanical behavior of the beams are examined.

Buckling and vibration analysis of cantilever functionally graded (FG) beam that reinforced with carbon nanotube (CNT) is the purpose of this paper. The beam is graded in the thickness direction, and compressive axial force impressed the beam. The volume fractions of randomly oriented agglomerated single-walled CNTs (SWCNTs) are assumed to be graded in the thickness direction. To determine the effect of CNT agglomeration on the elastic properties of CNT-reinforced FG-beam, a two-parameter micromechanics model of agglomeration is employed. In this paper, an equivalent continuum model based on the Eshelby–Mori–Tanaka approach is obtained. The stability and motion equations are based on the two-dimensional elasticity theory and Hamilton’s principle. The generalized differential quadrature method (GDQM) that has high accuracy is used to discretize the equations of stability and motion and to implement the boundary conditions. To study the accuracy of the present analysis, a compression is carried out with a known data. Convergence rate, the influence of graded agglomerated CNTs, and the effect of axial forces exerted on the beam, on the natural frequencies of reinforced beam by randomly oriented agglomerated CNTs are investigated.

Continuum damage-healing mechanics (CDHM) is used for phenomenological modeling of self-healing materials. Self-healing materials have a structural capability to recover a part of the damage for increasing materials life. In this paper, a semi-analytic modeling for self-healing concrete beam is performed. Along this purpose, an elastic damage-healing model through spectral decomposition technique is utilized to investigate an anisotropic behavior of concrete in tension and compression. We drive an analytical closed-form solution of the self-healing concrete beam. The verification of the solution is shown by solving an example for a simply supported beam having uniformly distributed the load. Finally, a result of a self-healing concrete beam is compared to elastic one to demonstrate the capability of the proposed analytical method in simulating concrete beam behavior. The results show that for the specific geometry, the self-healing concrete beam tolerates 21% more weight, and the deflection of the entire beam up to failure load is about 27% larger than elastic solution under ultimate elastic load for both I-beam and rectangular cross-section. Comparison of Continuum Damage Mechanics (CDM) solution with CDHM solution of beam shows that critical effective damage is decreased by 32.4% for a rectangular cross-section and by 24.2% for I-shape beam made of self-healing concrete.

The novel concept presented in this paper is the use of fiber reinforced polymers (FRP) to control the performance of new and existing reinforced concrete (RC) structures during and after moderate to strong earthquakes. This study was conducted in three major steps. First, an overview of the different concepts considered to improve both the pre- and post-earthquake performances of new infrastructures is presented. Second, a mechanical model for FRP-RC structure damage control is defined. Third, based on the proposed definition for controllable structures and using the post-yield stiffness and permanent deformations as seismic performance measures, the results of scaled tests of different structural elements are examined. For virgin beams, strengthening new RC beams or those with initial damage using hybrid FRP are presented, and the results of using wet bonding between FRP and concrete as a new technique for the construction of structures are briefly discussed. In addition, the effectiveness of FRP jacketing in existing non-ductile RC bridge columns with different deficiencies for quick recoverability after an earthquake is scrutinized using a large experimental database. Finally, to achieve a recoverable and more durable structure, the performance of steel bars wound with different types of FRP as reinforcement is highlighted.

Low-level laser therapy (LLLT) has been clinically utilized for many indications in medicine requiring protection from cell/tissue death, stimulation of healing and repair of injuries, pain reduction, swelling and inflammation. Presently, the use of LLLT to treat stroke, traumatic brain injury and cognitive dysfunction are attracting growing interest. Near-infrared light is capable of penetrating into the cerebral cortex, allowing noninvasive treatments to be carried out with few treatment-related adverse events. Optimization of LLLT treatment effect is a crucial issue of this field; however, only a few experimental tests on mice for wavelength selection have been reported. We addressed this issue by low-cost, straightforward and quantitative comparisons on light dosage distribution within visible Chinese human head by Monte Carlo modeling of near-infrared light propagation. Optimized selection in wavelength, beam type and size were given based on comparisons among frequently used setups (i.e., wavelengths: 660, 810 and 980 nm; beam type: Gaussian and flat beam; beam diameter: 2, 4 and 6 cm). This study provided an efficient way for guiding the optimization of LLLT setup and selection on wavelength, beam type and size for clinical brain LLLT.

In this paper, a mathematical model for beams with partially delaminated layers is presented to investigate their behavior. In this formulation account is taken of lateral strains. The principal advantage of the element is that it allows the modeling of delamination anywhere in the structure. Numerical results of the present model are presented and its performance is evaluated for static problems.

The electric impedance of a segmented beam with surface piezoelectric actuators is studied. The two layer piezoelectric actuators are in parallel in the electric circuit. The dynamics of the piezo-laminated segment and the elastic segments in the whole beam are presented by the 5 × 5 and 4 × 4 impedance matrix, respectively. Considering the mechanical-electric boundary conditions and the continuum conditions among these beam segments, the electric impedance of the whole system is obtained by solving its linear impedance equations. The experiment on a free-free segmented beam is done, the measured electric impedance of the system agrees with the theoretical value. For the resonance frequencies of such system, the relative errors between the measured and the theoretical values are smaller than 1.62% in the frequency range of 2800Hz. The parameter study of piezoelectric elements shows the change of the system impedance has the same trend with the change of their elastic modulus and absolute value of piezoelectric strain constant. However, the change of the system impedance has the opposite trend with the change of its dielectric constant.

In vehicle crashworthiness simulation analysis, anti-crash performance of the front bumper beam assembly of auto body made of 22MnB5 by hot forming and high strength steel by cold forming is compared. Software PAM-CRASH is employed to analyze the energy absorption and the acceleration value of beams with different profiles and thicknesses during the frontal impact process. And the structure of the hot forming bumper beam is optimized to get more light-weight effect. The results show that the use of hot forming beam can not only improve the energy absorption, but also can effectively reduce the weight of the body in white.

The non-linear behaviour of rubbing cylindrical rotors have been studied in several papers. In such systems rich dynamics have been found for frequencies above the natural frequency. Below natural frequency the solution was found to be stationary. In this paper the influence of blades is studied. A Jeffcott rotor with three blades is used and the contacts are described by large displacement beam theory. The model shows that no stationary point will exist and complex behaviour will occur below the natural frequency. For the studied rotor, failure due to high stresses will occur at driving frequencies below 50% of the natural frequency and instability at 80% of the natural frequency. The paper shows that the dynamics of bladed rotors differs from the dynamics of rubbing circular rotors. If a bladed rotor is used it is essential to study a model with blades. Otherwise the general conclusions on the dynamics can be wrong.

About 30 years ago, I was among several students mentored by Professor Yang at Stony Brook to enter the field of particle accelerator physics. Since then, I have been fortunate to work on several major accelerator projects in USA and in China, guided and at times directly supported by Professor Yang. The field of accelerator physics is flourishing worldwide both providing indispensable tools for fundamental physics research and covering an increasingly wide spectrum of applications beneficial to our society.