Journal of Engineering Mechanics

Composite materials and structures often exhibit thermal stresses and deformations due to their thermal expansion mismatch. For a layered laminate, the stress transfer mechanism involves both bending and interfacial shearing, which have been evaluated by Stoney’s equation and shear lag models, respectively. However, the two theories cannot consider both effects simultaneously due to their distinct assumptions. Because bending and shearing effects coexist in the physical problem, higher accuracy and fidelity can be achieved by considering both mechanisms. This paper presents an analytical formulation to solve this boundary value problem by constructing two separate trial functions from Navier’s equation. The analytical solution was proposed with an assumption of a perfectly bonded interface, and the corresponding coefficients were determined with the principle of stationary potential energy. The proposed model was applied to thermomechanical analysis of thin-film photovoltaic cells on smart window blinds, and good agreement was achieved between the theoretical prediction and finite-element results. A parametric study was also conducted to guide the design of solar window blinds and general bilayered composites.

Tensile test data for structural steels are ubiquitous. However, the information monotonic loading provides with respect to the material’s characteristics is limited. Notably, features of inelastic response to cyclic loading, such as the Bauschinger effect, cannot be determined without testing with a load reversal protocol. This study aimed at addressing this shortcoming by formulating a constrained optimization problem that provided best-fit material parameters to a tensile test while simultaneously imposing representative cyclic properties for structural steels. Recommendations on constraints were given. Results demonstrated that improvements can be achieved when compared to: (1) direct fits to tensile data and (2) input model parameters from the same steel material but from different batches calibrated to a wide range of strain-based protocols. Given the available data, it is concluded that simpler models with one backstress tend to perform best with the proposed constraints.

Additive manufacturing technologies such as fused filament fabrication (FFF) allow the production of metastructures with global properties that can be tailored to their specific application. This study simulated and optimized an auxetic re-entrant structure with a stiffness gradient for enhanced energy absorption with low acceleration peaks under different low-velocity impact conditions. The finite-element method (FEM) was used, and appropriate constitutive models were fitted to static and dynamic tensile and compressive data of acrylonitrile butadiene styrene (ABS) tested under various strain rates. A Johnson–Cook plasticity model demonstrated the best compromise between accuracy and computational efficiency. A simulation strategy using explicit FEM was developed to simulate additively manufactured auxetic metastructures under impact conditions. There was good agreement between the model prediction and the experimentally observed structural response. A parametric optimization was implemented to enhance the energy absorption capability with low acceleration peaks of a graded auxetic re-entrant structure for different impact velocities.

This paper studies the dynamic performance of two kinds of time-domain piecewise linear stiffness systems, a piecewise positive-stiffness system (PPS) and a piecewise negative-stiffness system (PNS). The PPS is formulated by involving a positive-stiffness spring in the drifting stage of structural motion, whereas the PNS is formulated by introducing a negative-stiffness spring in the recentering stage of structural motion. To investigate the performance of the piecewise stiffness systems (PSSs), some fundamental analyses are conducted on the PPS and PNS compared with their respective continuous positive-stiffness system (CPS) and continuous negative-stiffness system (CNS), which have demonstrated the superior performance of the PPS over the continuous stiffness systems (CSSs). A PSS shows additional damping effect on the resonance responses and maintains part of the stiffness property compared with a CSS. Second, for the convenience of performance evaluation, the equivalent linearization of the PSS is studied to determine the equivalent stiffness and the equivalent damping of the equivalent linear system (ELS) of the PSS. The equivalent stiffness is derived after obtaining the equivalent period of the PSS, and the equivalent damping is obtained based on the equivalent energy in one cycle of steady-state harmonic vibration. Third, the accuracy of the ELS is analyzed by comparing the resonance frequency ratio and the resonance response ratio. Finally, the displacement reduction effect of the PSS is investigated under excitations from different soil conditions to consider the influence of the frequency of excitations.

Approximate analytical solutions that can be applied effectively to describe the wave transformation of a solitary wave propagating past a partially submerged stationary body of rectangular shape with two attached side porous walls are introduced in this paper. Laboratory measurements of the free-surface elevation were also performed to validate the analytical predictions. The velocity potentials in the upstream and downstream of the fluid domain are formulated using the Fourier integral approach. Applying the boundary and matching conditions, including Darcy’s law–based porous wall conditions, and the concept of the orthogonality of eigenfunctions, the unknown coefficients are analytically derived. The results of free-surface elevations and hydrodynamic forces are presented. It is found that the transmitted wave profiles predicted from the present analytical model match well with the experimental data and other published numerical results, while the calculated reflected wave elevations are shown to slightly overestimate the wave peak. The physical parameters that affect the wave transformation and hydrodynamic forces on structures are investigated. With the addition of the extended porous walls, the overall reflection coefficient increases slightly for smaller amplitude waves; however, the overall transmission coefficient is reduced significantly for all wave conditions. The hydrodynamic force decreases with an increase in porous-effect parameters. An increase of the body draft or the body thickness can also enhance the reduction of the transmitted wave amplitude.

Stay cables on cable-stayed bridges are inherently low-damped flexible structural members. In order to improve their energy-dissipating capacities, external dampers are installed to control undesired cable vibrations. Typically, external dampers are mounted near the cable anchorage and their performance reduced in the case of longer cables. In addition to this, damper performance is also reduced by the presence of neoprene rubber bushings, which are provided to reduce the bending stresses due to live loadings. In this study, a concept of negative stiffness in an external damper is suggested to improve the damping of stay cables equipped with rubber bushings. An analytical approach is used to explore the modal behavior of a cable-damper system mounted with neoprene rubber bushings. The solution is expressed in the approximate (asymptotic approach) as well as the exact approach. An expression for effective damper location and design damping curves are proposed for the benefit of designers and researchers. The lower-bound limit of a negative-stiffness damper is also derived, and its effect on damper performance is explored. Damping contour plots are developed to select the required level of damping from the available system parameters.

Particle dampers have good performance of vibration control and noise reduction, and they have been widely studied and applied in the field of high-frequency vibration control, such as aviation and mechanical engineering. However, the vibration characteristics of civil engineering structures are usually low frequency and low amplitude, which restricts the performance of particle dampers. A new type of particle damper, namely the multiple unidirectional single-particle damper (MUSPD), is advanced based on the comparative analysis of the construction characteristics, damping performance, and damping mechanism of a single-particle damper and multiparticle damper. Based on the analysis of the damping mechanism of MUSPD and the integral consideration of the stress state of particles, the mechanical model of MUSPD is established, and an efficient numerical calculation method with variable step size is proposed. For harmonic excitation, the relationship between the optimal motion distance of a particle and other parameters is established by theoretical analysis. In addition, the optimization analysis method of MUSPD subjected to ground motions is proposed, and the rationality and accuracy are all verified. The results show that MUSPD has a better damping effect than a classical particle damper. Because the MUSPD belongs to acceleration (force)-related dampers, the energy of the controlled structure will be transferred as long as the particles collide with the controlled structure, and the frequency richness and randomness of the ground motion spectrum enhance the probability of particles colliding with the controlled structure. Moreover, the site effect has no obvious influence on the damping effect of MUSPD, and it is more suitable for middle- and low-rise structures.