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In this paper, the crashworthiness characteristics of tapered structures with the uniform cells in cross-section subjected to oblique impacts are theoretically and numerically investigated. Benefit...

The application of piezoelectric materials in energy harvesting devices has become an interesting topic for designers in recent years. Most of the reported works consider electrical power as a major parameter throughout the design procedure. What is less discussed is considering other design factors like the fatigue life of the harvester as well as the financial costs of the device. In this research, a methodology is introduced to design an optimum harvester, taking into account the aforementioned design factors. The finite element model of a piezoelectric harvester used in roadways is developed and validated. The fatigue test constants of the piezoelectric material are extracted via a novel approach. A parametric study is conducted on the model to generate a dataset containing electrical and mechanical characteristics, where it is used as an input for training an artificial neural network to model the behavior of the harvester. In order to evaluate the level of importance of the optimization objectives, two methods are employed: the Shannon entropy method and equal weighting factors. Results show the effectiveness of the model, where considering the electromechanical characteristics of the module is important in terms of overall performance, efficiency, durability, and financial costs.

In this paper, transient coupled thermo-mechanical finite element analysis of a three-dimensional model of braking pairs (brake disk and brake pads) is accomplished in order to estimate temperatures and stresses in brake disk during a braking cycle, including braking and cooling phases, and calculate fatigue life. A nonuniform distribution of temperatures is revealed on the surface of the brake disk, gradually generating surface hot spots and hot bands with temperatures up to 800 °C that lead to an uneven distribution of thermal stresses on the frictional surfaces. According to the simulations, variations in the circumferential stress, which is mainly responsible for the cracking of the brake disk, can reach up to 400 MPa in the hot spot areas, depending on the braking configurations. The numerical results are also used to estimate the fatigue life of brake disk using the Smith–Watson–Topper model. The numerical model demonstrates a high accuracy of fatigue life estimation when evaluated by prior experimental studies, signifying the effects of hot spots in reducing the service life of brake disk. Results of the fatigue life estimation show superiority to the analytical method both in the accuracy of calculation and detection of the failure location.

The most important purpose of the present work is to propose an analytical approach for solving the governing characteristic equations of the free vibrations problem of an orthotropic cylindrical shell with its length much greater than its other dimensions half way along which exist a semi-elliptical surface crack. Governing equations of motion of the problem have been derived using classical shell theories and simplified with regard to the Donell–Mushtari–Vlasov (DMV) theory. In comparison to shell dimensions, crack size is considered to be very small, which would minimize effects of the curvature in this study. Equations have been extracted for two different types of cracks: circumferential and axial cracks. In both cases, effects of the presence of crack on overall stiffness of the structure have been included in governing motion equations utilizing some crack compliance coefficients which have been calculated through Line Spring Model (LSM). A closed form solution for the characteristic equations of the problem has been introduced using Hamilton's principle and separation of variables for the simply supported shells. A comparison has been made between obtaining results through the proposed model and those from previous studies and Finite Element model. Last but not least, effects of the various shells, materials and the crack parameters on the fundamental natural frequency of the shell have been investigated.

This article investigates free vibration of a functionally graded piezomagnetic material cylindrical nanoshell embedded in viscoelastic media under rotational, external electric and magnetic loadings. The governing equations of the nanoshell are derived based on Eringen’s nonlocal theory. It is found that, magnetic and piezoelectric properties of the structure change exponentially along the thickness. The rotational loading is calculated considering initial hoop tension. The results are obtained by applying generalized differential quadrature method to the governing equations and associated boundary conditions. Results also include those achieved for clamped-clamped and simply hinged-hinged boundary conditions. It is found that free vibration characteristics of functionally graded piezomagnetic material cylindrical nanoshell are influenced by several factors including angular velocity, length scale parameter, external voltage, external amperage, functionally graded power index, and viscoelastic media parameters.

In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton’s principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are solved using the differential quadrature method. It is shown that the vibrational characteristics of functionally graded magneto-elastic material nano/microcircular plates are significantly affected by non-dimensional angular velocity, size dependency of the Eringen’s and the modified couple stress theories, and power law index for clamped and hinged boundary conditions. Results show that a critical point occurs by increasing the angular velocity and the effect of several parameters are changed after this point.

Approximate Stress Intensity Factors (SIFs) for a semi-circular surface crack in arbitrary elastic finite and infinite bodies are presented. Utilizing General Point Load Weight Function (GPLWF) concept, an explicit expression is derived to determine SIFs for semi-circular cracks subjected to uniform, linear, and nonlinear loads. The presented formulation not only provides a solution for cracked bodies subjected to arbitrary two-dimensional stress distribution on the crack faces, but also could present SIFs for any point on the crack front. The results of the presented formulation for special cases, i.e. semi-circular cracks in a finite thickness plate subjected to complicated loadings, central and non-central semi-circular cracks in finite-length thick-walled cylinders subjected to a uniform internal pressure, and central semi-circular cracks in an infinite-length thick-walled cylinder subjected to a non-uniform internal pressure are compared with the available results in the literature and those obtained through FEM, indicating a very good accuracy. The proposed procedure will be generalized for semi-elliptical cracks in arbitrary structures and mixed mode loading in future.

For the first time in this paper, free vibration and thermal buckling of micro temperature-dependent FG porous circular plate subjected to a nonlinear thermal load are numerically studied. The governing equations are derived based on Hamilton's principal and using both classical and the first-order shear deformation theories in conjunction with the modified couple stress theory. Generalized Differential Quadrature method is applied to solve the equations with associated boundary conditions. The results reveal that the increase of size dependency and the temperature-change would lead to the increase of differences between the first natural frequencies predicted based on the two theories. In contrast, the porosity and the FG power index do have not any effect on that. While the effect of porosity on free vibration of clamped and free plates are negligible, but the effect of porosity for hinged ones is considerable as the temperature-change increase. Moreover, the critical conditions of the plates which are expressed by porosity, FG power index, size dependency, temperature-change and geometrical dimensions are presented, as well. Numerical results are in good agreement with those available in literature in some special cases.

Circumferential crack growth pattern in a thin-walled cylinder is studied. Thermo-elastic stresses in a cylinder subjected to thermomechanical loads are extracted. Closed form thermo-elastic stress intensity factor for cracked cylinder are derived using weight function method. An algorithm is developed to simulate different crack growth patterns utilizing a very high efficiency weight function method. This would lessen the taken time for the analyses compared to other numerical methods such as FEM. Results show that while the load effect on cylinder subjected to thermal load lead to the crack growth in small aspect ratio, in cylinder subjected to mechanical loads, it would lead to the growth of crack in large aspect ratio. The results show that, apart from load effects, the cylinders containing initial semi-circular crack have the longest life among the cylinders containing initial semi-elliptical crack with the same initial depth.

In this paper, magneto-hyper-viscoelastic responses of isotropic magnetorheological elastomers (MREs) subjected to uniaxial compression loadings and induced by magnetic fields are experimentally and numerically studied. Unlike many investigations on the rheological models (representing a simplified one-dimensional response of MRE), in order to prepare the input material data for three-dimensional stress and fatigue analysis of the structures enhanced by MRE, a procedure is proposed to characterize and determine material constants for a magneto-hyper-viscoelastic constitutive model. Utilizing some uniaxial compression tests in the presence and absence of the magnetic field as well as the procedure, hyper-elastic, magneto-elastic, and viscoelastic constants are determined. In order to show the predictive capabilities of the procedure, the numerical predictions of hysteresis responses of the MRE are compared with the experimental analysis. The acceptable agreements between the predictions, for which the extracted coefficients are used, and the observations indicates towards the accuracy of the proposed procedure.

During the E5 engine durability test, the failure happens in cast iron cylinder head. This is characterized as low cycle fatigue. The macro-scale cracks initiate and propagate in valve bridge region. The present investigation focuses on simulating durability test and evaluating low cycle fatigue life of the failed part. The simulation includes one pre-step as a determination of material grid and three steps as fluid, structural and fatigue analyses. In order to cover the durability test, the analysis steps are repeated at five crack speeds, 750, 1650, 2075, 2350, and 2600 rpm. The cylinder head is subjected to cyclic multi-axial variable amplitude loads. In fatigue analysis, critical plane and cumulative damage theories are utilized in order to predict fatigue life. A general script is developed and validated so as to calculate fatigue life in the whole model. The numerical results also show that the failure of critical cylinder head can be characterized as low cycle fatigue. The valve bridge region, in which high temperature exists during engine operation, is the critical area in fatigue analysis approach. The simulation results are in a good agreement with the durability test observations.

Targeted investigation of the impact fracture performance of PVB laminated glass, which is a combined analytical and numerical method for impact dynamics prediction, is presented. In this method, the relationship between the impact force and the post-cracking response of laminated glass is developed in the framework of impact dynamics to present a prediction formulation. The formulation is utilized to be applied to predict vehicle impact speed based on the crack patterns propagated on the automotive laminated glass due to the pedestrian head impact. To prepare a numerical set-up, an automotive laminated glass finite element model is proposed by inserting cohesive elements on all common surfaces of glass layers and glass-PVB interfacial. The prediction model is validated well by comparison with numerical crash patterns and ten real vehicle–pedestrian accident cases.

Market forecasts for the civilian use of unmanned aerial vehicles (UAVs) show a sustained growth in the long term. To increase awareness for operators, a three degree-of-freedom haptic interface is introduced to provide helpful operational assistance for UAV motion control. Furthermore, an adjustable feedback is implemented in the interface with different combinations of force. In this paper, the kinematics of the haptic manipulator are analyzed first. Specifically, by studying the relation between angular and linear motion, a kinematic model is established to derive the Jacobian matrix and the inverse kinematics of the manipulator. Then, the Newton-Euler equations are introduced to characterize the system dynamics. Finally, these dynamics are incorporated into the adjustable feedback control strategy which accounts for the stiffness and damping effects. The control strategy is evaluated based on the performance of human operators. It is demonstrated that by adding adjustable feedback, the operators' performance can be improved by 16% in position error and 45.7% in test completion time in comparison to non-feedback haptic devices.