Longitudinal strain ratcheting and stress relaxation in interference‐fitted single‐holed plates were investigated both experimentally and numerically. In the experimental part single‐holed plates made from Al‐alloy 7075‐T6 were force‐fitted with oversized pins to create 1% and 2% nominal interference fit sizes. Then these plates (specimens) were instrumented with dynamic strain gauges in longitudinal direction around the hole to measure the strain during interference fit and strain ratcheting during subsequent cyclic loading. In the numerical part, 2D finite element code has been written to simulate the interference fit process and subsequent cyclic loading to obtain strains and stresses around the force fitted hole. To predict the strain ratcheting, Ohno–Wang kinematic hardening model was applied for simulation of stress/strain path. The strain ratcheting predicted from the finite element code and experimental test results were compared. The results showed that there is a good agreement between the measured and numerically evaluated strains, and the strain ratcheting is bigger for higher cyclic load level, but it is smaller for larger interference size.

This paper analyses the non-stationary free vibration and nonlinear dynamic behavior of the viscoelastic nano-plates. For this purpose, a sizedependent theory is developed in the framework of the consistent couple stress theory for viscoelastic materials. The previously presented modified couple stress theory was based on some consideration making it partially doubtful to apply. This paper uses the recent findings for the mentioned problem and develops it to analyze the nonlinear dynamic behavior of nanoplates with nonlinear viscoelasticity. The material is supposed to follow the Leaderman integral nonlinear constitutive relation. In order to capture the geometrical nonlinearity, the von-Karman strain displacement relation is used. The viscous parts of the size-independent and size-dependent stress tensors are calculated in the framework of the Leaderman integral and the resultant virtual work terms are obtained. The governing equations of motion are derived using the Hamilton principle in the form of the nonlinear second order integro-partial differential equation with coupled terms. These coupled size-dependent viscoelastic equations are solved using the forthorder Runge-kutta and Harmonic balance method after simplifying by the expansion theory. The short-time Fourier transform is performed to examine the system free vibration. In addition, frequency-and forceresponses of the nanosystem subjected to distribute harmonic load are presented. The obtained results show that the viscoelastic model-based vibration is non-stationary unlike the elastic model. Moreover, the damping mechanism of the viscoelasticity is amplitude dependent and the contribution of the viscoelastic damping terms at higher forcing conditions becomes noticeable.

In this study, the nonstationary oscillation, secondary resonance and nonlinear dynamic behavior of viscoelastic nanoplates with linear damping are investigated based on the modified strain gradient theory extended for viscoelastic materials. The viscous component of the nonclassical and classical stress tensors are evaluated on the basis of the Leaderman viscoelastic model. Then, incorporating the size-dependent potential energy, kinetic energy and an external excitation force work, the governing equations of the oscillations are obtained based on the Hamilton’s principle. The governing formula is obtained as a nonlinear second-order integro-differential partial equation. This size-dependent viscoelastic formula is solved using analytical Harmonic balance method (HBM) and the fourth-order Runge–Kutta technique after applying the expansion theory. Additionally, the stability of the steady-state response is examined by means of HBM. Then, the secondary resonance conditions due to the super-harmonic motion are determined by performing frequency response, force response, Poincare map and phase portrait analyses. In addition, the nonstationary transient vibration of viscoelastic nanosystem is analyzed by performing Hilbert–Huang transform.

Patched-clamped oscillating lipid membranes are used as biosensors acting based on the flexoelectric effects of large dipole moments. The variations in the flexoelectric signal from the bilayer lipid membrane can be used to sense the absorbed particles on it. In this study, a size-dependent model based on strain gradient theory is developed for an initially curved lipid bilayer attached to the inner surface of a rectangular capillary. The flexoelectricity and strain gradient viscoelastic effects are considered in this model. Furthermore, the von-Karman strain terms are used to model the deformation of the lipid bilayer more accurately. First, the density of the internal energy, kinetic energy, and external force work are obtained and then the governing equations are derived from Hamilton’s principle. The static bending and dynamic response of the nanosystem are studied. In order to solve the dynamic motion equations, the multiple scale method is applied to study the size-dependent electromechanical responses of the lipid bilayer. The results show that for smaller length-scale parameters, the static deflection predicted by the model with flexoelectricity is remarkably higher than the deflection anticipated by the model without the flexoelectricity. However, the deflections of both models approach each other with increasing the length-scale parameter. In addition, for the dynamic response, the flexoelectricity increases the resonance frequencies of lipid membranes up to 4–9 times in comparison to the model without flexoelectric effects. Moreover, the flexoelectricity reduces the dynamic response amplitudes, drastically.

In this paper, cyclic loading behavior of carbon steel pressurized piping elbows are described. Effects of internal pressure and bending moment amplitude on the ratcheting rate are investigated. The AF kinematic hardening model is used to predict the plastic behavior of the elbows. Material parameters and stress-strain data have been obtained from several stabilized cycles of specimens that are subjected to symmetric strain cycles. The results show that the maximum ratcheting strain occurred mainly in the hoop direction at flanks. Hoop strain ratcheting was found at intrados for individual specimen. Ratcheting strain rate increases with increase of the bending loading level at the constant internal pressure. The results show that the initial rate of ratcheting is large and then it decreases with the increasing cycles. The FE model predicts the hoop strain ratcheting rate to be near that found experimentally in all cases that 1 l M M ≤ .