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• A novel non-intrusive sensitivity-based nonlinear finite element model updating method is proposed. • The nonlinear response sensitivity is computed using real and imaginary perturbation synchronously. • The nonlinear finite element model is updated using time history responses. • A cantilever beam with steel slice is conducted to illustrate the experimental application of the proposed method. This paper presents a novel non-intrusive sensitivity-based nonlinear finite element model updating method in which the local nonlinearity of structure is considered. The sensitivity analysis is conducted to determine the sensitivity of a dynamic response with respect to different nonlinear parameters using the real and imaginary perturbation method in one single calculation. The use of the imaginary perturbation is capable of second-order accuracy in imaginary perturbation sensitivity analysis of the nonlinear finite element model updating procedure. The nonlinear parameters in the finite element model are estimated by using the improved sensitivity-based optimization algorithm. A nonlinear multi-degree-of-freedom oscillator and a cantilever beam with multiple nonlinear supports are studied to verify the accuracy of the proposed method. The effects of measurement noise and initial parameters on the performance of the presented approach are further investigated. Then, the proposed approach is verified by an experimental test of a cantilever beam with a steel slice. The updated nonlinear finite element model is further evaluated by the structure subjected to new excitations. Results show that the proposed method can effectively update the nonlinear finite element model even in the presence of contaminated measurement data and different initial parameters in the finite element model. [ABSTRACT FROM AUTHOR]

The discreteness of strength seriously restricts the wider use of Carbon/Carbon (C/C) composites. The strength of C/C composites is studied by using statistical analysis methods. Here, a novel statistical analysis method named B-distribution is proposed to examine the shear strength of C/C composite pins. The method is implemented using a Bayesian inference scheme with a Markov Chain Monte Carlo sampler. Then, the shear-strength distributions of the C/C composites in different directions are calculated by the B-distribution and four traditional statistical models (three-parameter Weibull, two-parameter Weibull, log-normal, and gamma). These are critically analysed by a Kolmogorov-Smirnov (K–S) test and a maximum likelihood test. Next, the effect of the loading direction on the shear strength of C/C composite pin is statistically analysed. The results show that the B-distribution is the most appropriate statistical distribution for the experimental data. Additionally, it is found that the high reliability shear strengths of C/C composite pin in the 30° and 45° directions are relatively higher, and the high reliability shear strengths of C/C composite pin are relatively lower in the 75° and 90° directions. [ABSTRACT FROM AUTHOR]

The statistical energy analysis (SEA) is applied to predict the transient energy response of structures with time-varying parameters for the first time. With the energy governing equations derived by considering time-varying SEA parameters and energy flow item caused by time-varying damping loss factor, SEA method is firstly applied to predict transient energy response of time-varying systems. Then, numerical examples of a time-varying two-oscillator system, a time-varying L-shaped fold plate and a complex time-varying vibro-acoustic structure are investigated to demonstrate the effectiveness and accuracy of SEA method for time-varying system. The Newmark-beta method and finite element method are used to verify the accuracy of predicted transient energy response. Results show that SEA method for time-varying system is capable of predicting transient energy response of time-varying structures with sufficient accuracy and also applicable for transient analysis of complex time-varying structures with a small computational cost. [ABSTRACT FROM AUTHOR]

The out-of-plane crushing resistance of fractal-like honeycombs with self-similar hierarchy are investigated numerically and analytically. The hierarchical honeycombs are developed via replacing each three-edge vertex of a regular hexagonal honeycomb by a smaller hexagon. Hierarchical honeycombs with higher orders are constructed by repeating this process. Theoretical solutions are derived based on the Super Folding Element (SFE) theory to predict the mean crushing forces (MCFs) of the hierarchical honeycombs. Numerical simulations are also conducted in conjunction with the theoretical solutions. Crushing resistances of three groups of hierarchical honeycombs with different relative densities are explored subsequently. Good agreement between results obtained using theoretical and numerical methods indicates that the theoretical predictions are reliable. The results show that hierarchy can significantly improve the crushing resistance of honeycombs. It is found that the MCFs of first to fourth order hierarchical honeycombs are improved by 71%, 114%, 201% and 309% compared with the regular honeycomb under the same relative density, respectively. It reveals that the amplification of the MCF from one generation to the next approaches a constant (ξ n  ≈ 1.26) when the hierarchical order is sufficiently large. The potential maximum achievable amplifications of the MCF for hierarchical honeycombs of different relative densities are also discussed. [ABSTRACT FROM AUTHOR]

In order to pursue better crashworthiness and higher energy absorption efficiency, a new type of multi-cell honeycomb (quadri-arc) was designed and followed by a series of numerical studies on in-plane dynamic crushing behavior and energy absorption property under different impact loading. Meanwhile, simulations of a regular circular single-cell honeycomb were also conducted as comparisons. Three distinct deformation modes were identified from the observation of deformation profiles: quasi-static, transition and dynamic, respectively. Simulations indicate that deformation modes are not only influenced by impact velocity but also sensitive to relative density of the honeycomb, based on which a deformation map was summarized. Furthermore, the plateau stress and energy absorption of the quadri-arc honeycomb as well as the circular honeycomb were explored and compared, during which effects of impact velocity and relative density of the honeycomb were discussed in detail. The results show that a much higher plateau stress and better energy absorption efficiency for the quadri-arc honeycomb are predicted compared to the circular honeycomb, especially in the quasi-static case. The investigation suggests that design of the quadri-arc multi-cell will enhance the crashworthiness and energy absorption capacity of honeycombs. [ABSTRACT FROM AUTHOR]

Indentation response and energy absorption property of honeycomb sandwich panels subjected to drop-weight impact under a spherical impactor were investigated. Experiments were conducted using a pendulum-impact system. A three-dimensional finite element model with micro-structure considered was built and validated. In conjunction with experimental and numerical methods, analytical models of indentation response and energy balance specifically aimed to solve problems of low-velocity impact of a spherical indenter on sandwich panels were deduced. Results show that a hemispherical residual dent caused by bending of top face-sheet and core crushing is left on top face-sheet after impact. It also concludes that more than 80% of impact energy is absorbed mostly by top face-sheet and honeycomb core. The main form of energy dissipation is plastic dissipation. In addition, parametric studies were carried out to explore effects of impact energy on impact behavior by altering impact velocity or impactor mass. Different effects are observed for the two approaches and some useful semi-empirical formulations based on both experimental and numerical results are overfitted to estimate the residual dent depth and energy absorbed during a drop-weight impact event on a honeycomb sandwich panel under a spherical impactor. [ABSTRACT FROM AUTHOR]

A numerical investigation was performed to further understand the physical significance of bird striking on a rotary jet-engine fan. A new numerical bird model considering more geometric characteristics than traditional ones was established first, during which the smooth particles hydrodynamic (SPH) method and an equation of state (EOS) were employed. The numerical method and material model were indicated to be reasonable by a validation analysis. Then, a preliminary study of a rigid target struck by a realistic bird from four different orientations including head, tail, bottom and wing sides as well as a traditional hemispherical-ended cylinder model were simulated. It was found that bird geometry and impact orientation had significant effects on impact response and kinetic energy loss of the bird. Furthermore, the same load conditions were conducted on a rotary jet-engine fan and followed by a series of parametric studies, including impact force history, kinetic energy loss of the bird, deformations of the blade tips and von Mises stresses of the blade roots. The results showed that both bird geometry and impact orientation had significant and non-ignorable influence on bird striking on a rotary jet-engine fan and bottom side was the most dangerous case. Considering more geometric characteristics of the bird and impact orientation in studies of bird strike problems was proved to be meaningful and necessary. [ABSTRACT FROM AUTHOR]

Abstract: Structural stability is an vital aspect for structural health monitoring of transmission lines. This paper presents a novel method to evaluate the structural status of transmission line based on dynamic and stability analysis. A newly built long-span transmission tower-line system that crosses the Huaihe River in China with a span of 1083m was studied as an example. Finite element model of the transmission tower-line system was constructed. Nonlinear buckling analysis for both the tower and tower-line system were performed to determine the critical wind loads. Dynamic properties of both the tower and tower-line system under different levels of wind loads were analyzed. Numerical results show the law that modal frequency of low order modes decreases when the wind velocity increases before the structural instability happens for both cases. Therefore, for the structural health monitoring of transmission lines, frequency decrease of low order mode is an useful indicator to predict the happening of structural instability. This conclusion could be taken as the reference in the design of structural health monitoring system for transmission lines. [Copyright &y& Elsevier]

Abstract: Structural damage localization plays an important role in structural damage identification. An cumulative structural damage localization method based on evidence theory is studied in this paper. An algorithm for cumulative fusion of primary localization information is presented. In the numerical study, a fixed-end beam is inspected. Two damage cases are studied, one with single damage and the other with multiple damages. White noises are added to the beam mode shapes of the first five orders to simulate the measurement noises. First, Modal Strain Energy Change Ratio (MSECR) method is used to localize the damage elements using the noise-contaminated mode shapes. Then, the locations determined by MSECR are taken as primary information and fused cumulatively. In both the single-damage-case and the multiple-damage-case, the fused results show that damaged elements are accurately identified. Furthermore, the damage elements are distinguished much more clearly than those identified from MSECR. [Copyright &y& Elsevier]

• The shear failure stress of C/C composites increases with increasing strain rate. • Under quasi-static loading, the C/C composites damage with fibers fracture successively and the shear stress-strain curve shows a "pseudo-plastic" characteristic, while brittle fracture features subjected to dynamic loading. • A viscoelastic constitutive model incorporated with a damage model based on the Weibull distribution function is proposed. To understand the strain rate sensitivity of carbon/carbon (C/C) composite pins' shear behaviors, quasi-static and dynamic experiments are conducted using an electric universal testing machine and a drop weight impact testing machine. A scanning electron microscope (SEM) is used to observe the shear fracture surfaces. The results show that the shear failure stress increases with increasing strain rate. Under quasi-static loading, the C/C composites damage with fibers fracture successively, and the shear stress-strain curve shows a "pseudo-plastic" characteristic, while brittle fracture features subjected to dynamic loading. In order to explain such differences, a viscoelastic constitutive model incorporated with a damage model based on the Weibull distribution function is proposed. Parameters of the constitutive model are estimated based on the experimental data. After that, the theoretical shear failure stresses are obtained by calculating the maximum shear stress of the constitutive model for different shear strain rates. The fitted model and theoretical failure stress match well with the experimental data. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Assembling sandwich serpentine structures with soft functional materials creates an effective way to high-performance stretchable devices. In order to achieve better design criteria for the application of serpentine-shaped stretchable systems, this paper explores the mechanics governing the deformation mechanisms of the sandwich serpentine structures. Firstly, detailed three-dimensional (3-D) numerical simulations were conducted to well capture the deformation modes. Secondly, a theoretical model was developed within the simplified 1-D formulation. Numerical and theoretical investigations reveal the important features of the underlying materials (including the representative low-modulus elastomers) and mechanics aspects of the polymer/metal/polymer sandwich serpentine interconnects system with strain-isolating layers, and their dependence on key design variables (including the material selection and thickness of both the isolation layer and the serpentine clad). Three distinct deformation modes of the sandwich serpentine structures were observed and discussed: 1) Global buckling; 2) Local wrinkling; and 3) Planar bending. By theoretically analyzing the wrinkling wavelengths, we propose a simple design criterion for the strain-isolating layers that indicates a transition from local wrinkling to global buckling, with the increasing thickness of the isolation layer. Results will be useful to mechanical design of stretchable systems with high levels of the elastic stretchability. • Systematic simulations were conducted for sandwich serpentine structures mounted on soft substrates with isolating layers. • Three deformation modes were differentiated by various designs: 1) Local wrinkling, 2) Global buckling, 3) Planar bending. • The wrinkling/buckling transition point obtained from FEA results agrees well with the wavelengths by theoretical analysis. • We proposed a useful design criterion to improve the stretchability of sandwich serpentine interconnects. [ABSTRACT FROM AUTHOR]

• A dynamic sensitivity-based nonlinear finite element model updating method is proposed. • The direct differential method is presented for calculating the nonlinear dynamic responses and its sensitivities synchronously. • A scheme for responses points selection and its effect on the updating accuracy are analyzed. To obtain the numerical model for predicting the nonlinear dynamic responses with high accuracy, a dynamic sensitivity-based model updating approach by using the time-domain responses is proposed in this paper. The sensitivity analysis of time-domain response is derived by using the direct differentiation method. The objective function of the nonlinear model updating is constructed by minimizing the discrepancy between the measured and the calculated time-domain responses. The time-domain responses and the corresponding dynamic sensitivities are calculated synchronously. The repeated nonlinear dynamic analysis can be avoided to obtain dynamic sensitivity, which is independent of the perturbation step. Numerical examples of a Duffing-Van der Pol oscillator, a magnetometer boom, and a cantilever plate with multiple nonlinear supports are adopted to verify the method. Crucial issues about the measured noise and the selection of the targeted responses are also considered and discussed. The validation results show that the proposed method is effectively applied to model updating of nonlinear structure using time-domain response with good anti-noise performance, and the scheme for response points selection is reliable for guaranteeing the accuracy. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The efficient Wave-Based Method (WBM) is extended to predict the bending vibration response of thin-walled rectangular plates under thermal load. Governing equations of dynamic plate bending problems considering thermal effects are first introduced. The general solution and particular solution of governing equation are derived by the separate variable method and residue theorem, respectively. Then novel wave functions and particular solution function are selected to establish the wave-based model of dynamic plate bending problems under thermal load. The accuracy of WBM is verified by finite element method (FEM) for a simply supported plate and a clamped plate. Then the influence of thermal load on the dynamic bending responses of a clamped plate is investigated. Simulation results prove that WBM achieves higher convergence rate than FEM. The thermal load significantly changes the structural dynamic behaviors. When both the temperature-dependent material properties and thermal stresses are considered, the increase of environment temperature leads to the resonant peak of displacement response shifts toward lower frequency. • The WBM is developed to predict the bending vibration response of thin-walled structures under thermal environment. • Novel wave functions and particular solution function are derived to establish the wave-based model. • The proposed method is validated on two cases with different boundary conditions. • The developed WBM achieves high accuracy and reduces computing time effectively. • The influence of thermal environment on the dynamic bending responses is investigated. [ABSTRACT FROM AUTHOR]

• A modeling method of curvilinearly stiffened plates suitable for both thin and thick plates is established and verified by experimental and existing numerical results. • Similar accuracy can be obtained when fewer mesh is used than finite element software. • The stiffeners can be arranged on the plate in any form without changing the mesh of the plate. Curvilinearly stiffened plates can have superior mechanical properties than traditional straight-line stiffened plates. To avoid the shear locking problem in the modeling of stiffened thick plates by Reissner-Mindlin theory when the thickness of plate decrease, discrete shear triangle element was introduced by employing the discrete shear constraints on each side. The discrete shear triangle element is employed for the plate and the Timoshenko beam theory is employed for the curvilinearly stiffeners, respectively. The FE equations are established through displacement interpolation function of plate and the displacement compatibility conditions at the plate-stiffened interfaces. The plate and stiffener are modeled separately in the present method, which allows the nodes of stiffener element not coincide with nodes of the plate's shell-element. Based on the newly proposed modeling technique, the statics, vibration and buckling behavior of curvilinearly stiffened plates are investigated. Numerical and experimental investigations are conducted to verify the mechanical properties of proposed model for stiffened plates. Results from the proposed method show good agreements with the numerical and experimental results. The present method can conduct static and dynamic analysis for both stiffened thick and thin plates and guarantee the accuracy of calculation with less number of elements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Triangular lattices were hierarchically incorporated into a regular hexagonal honeycomb to substitute each vertex of the regular honeycomb. To investigate the crushing behaviors of the newly constructed vertex-based hierarchical honeycombs, finite element (FE) analyses were carried out subsequently for both in-plane and out-of-plane crushing. Effect of the hierarchical organizational parameter on deformation mode, crushing response and energy absorption capacity were discussed respectively. The results showed that the hierarchy significantly affected the crushing behaviors of the honeycomb differently for in-plane and out-of-plane crushing. The hierarchy had a far greater influence on the deformation mode for in-plane crushing than out-of-plane crushing. Compared with that of the regular honeycomb, hierarchy not always improved the honeycomb in terms of plateau stress and specific energy absorption (SEA). The maximum plateau stress and SEA of the hierarchical honeycombs increased by up to approximately 127% and 109% respectively under crushing along L direction (in-plane ribbon direction); 122% and 108% respectively under crushing along W direction (in-plane width direction); and 30% and 34% respectively under crushing along T direction (out-of-plane direction). • A novel type of vertex-based hierarchical honeycombs with triangular substructures was introduced. • Hierarchy significantly affected the crushing behaviors for in-plane and out-of-plane crushing differently. • Hierarchy not always improved the honeycombs in terms of plateau stress and energy absorption capacity. • The maximum improvement of crashworthiness performed much better for in-plane crushing than out-of-plane crushing. [ABSTRACT FROM AUTHOR]

Uncertainties to varying degrees often exist in the analysis and design problems of vibro-acoustic systems. This paper investigates the high-frequency vibro-acoustic analysis problem with large levels of fuzzy parameters. By employing the level-cut strategy, the energy balance equations with fuzzy parameters are firstly transformed into the interval forms. Then, by combining the perturbation method, the Sherman-Morrison-Woodbury formula, and the statistical energy analysis, a modified perturbation statistical energy analysis (MPSEA) is proposed to predict the uncertainty propagation of the energy flow in vibro-acoustic systems with fuzzy parameters. Further, the sub-interval technique is introduced in MPSEA to improve its accuracy for the systems with large levels of fuzzy parameters. Numerical simulations of a plate-cavity system and a launcher fairing model with fuzzy parameters are presented to demonstrate the efficiency and accuracy of proposed method. Results indicate that the proposed MPSEA with a suitable number of sub-intervals is capable of predicting the energy flow in vibro-acoustic system with large fuzzy parameter accurately and efficiently. [ABSTRACT FROM AUTHOR]

In the modal test of lightweight structures, the measured data is easily polluted by mass loading effects of transducers. A method is proposed to eliminate the influence of sensors for accurately estimating the frequency response functions (FRFs) of structures. Considering the situation that the multiple accelerometers lead to changes in the dynamic stiffness matrix, the corrected FRFs are derived from the original measured signals based on the Sherman-Morrison-Woodbury formula. The salient feature of the proposed strategy is that the adverse effects of sensors can be eliminated in only one step. Numerical simulations are conducted by employing a six-degrees of freedom spring-mass system, modal frequencies and mode shapes with high accuracy are obtained by measured signals. Experimental investigation is undertaken by using a laboratory solar panel. Results show that the effects of multi-transducers mass can be removed efficiently and the corrected FRFs are in good agreement with the targeted values. The excitation and measurement points are regarded as active coordinates, and the computational efficiency can be significantly improved when the presented method is applied on active coordinates. [ABSTRACT FROM AUTHOR]

• Uncertainty of heterogeneity of composites is characterized. • The polynomial chaos is extended to describe the random field of composite parameters with spatial distributed uncertainty. • The correlation between elastic parameters is represented by using the Copula function. Considering the heterogeneity and randomness in the elastic performance of composite materials, a novel method is proposed for vibration analysis of composites with spatially distributed uncertain parameters. Firstly, the polynomial chaos expansion is used to characterizing the material field, which is expressed as the product of the deterministic coefficient and the basis function of polynomial chaos, the coefficient is expanded by using orthogonal polynomial to represent the spatially distributed heterogeneous of composites. Secondly, the correlation of elastic parameters is expressed by using Copula function. Finally, according to the non-intrusive method, the probabilistic characteristics of the composite structure with spatially distributed uncertain parameters are obtained. The method is implemented for free vibration analysis of a composite panel, results show that the variability of the standard deviation of the dynamics performance is dependent on the correlation between the elastic parameters of composites. [ABSTRACT FROM AUTHOR]

An algorithm that integrates Karhunen–Loeve expansion (KLE), finite element method (FEM), and boundary element method (BEM) is proposed to carry out a vibro-acoustic analysis under stationary and non-stationary random excitations which are uncorrelated or correlated. In the KLE, a set of orthogonal basis functions is employed to discretize the auto-covariance function of the excitations and obtain the eigenvalues and eigenfunctions of the auto-covariances. The KLE for correlated random excitation relies on the expansions of correlated random variables. During the response calculation, the FEM and BEM are employed to obtain structural and acoustic responses. A circular piston in an infinite baffle and a stiffened panel excited by stationary or non-stationary random processes are used to illustrate the proposed algorithm's accuracy. Results show that the statistics of vibro-acoustic response are accurately obtained with the proposed method and this method is also applicable for the vibro-acoustic analysis of more complex structures under various types of random excitations. [ABSTRACT FROM AUTHOR]

Uncertainties are generally included in elastic parameters of the fiber reinforced textile composites. An approach on predicting the statistical characteristics of elastic modulus of braided composites using vibration test data is proposed in this paper. The method consists of two main steps, firstly estimate the initial mean values of the orthotropic elastic parameters by adopting the homogenization method, and then identify the variability of the elastic constants using a stochastic model updating algorithm with the first-order perturbation approach, the uncertain parameters are assumed as the summation of mean value and a deviation term with zero mean. A braided composite panel is employed in numerical simulations to verify the proposed method, the random samples of experimental modal data are simulated with the Latin Hypercube Sampling technique based on a reference finite element model, which is constructed by using deterministic updated elastic parameters. Results show that the mean value and standard deviation of the uncertain effective parameters of braided composite can be identified from modal data using the proposed stochastic identification method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fatigue life at 600 °C was found to be approximately nine times higher than at 420 °C under identical stress conditions. • Multiple dynamic recrystallization (DRX) mechanisms, including continuous (CDRX) and discontinuous (DDRX), were identified. • Demonstrated that variation in fatigue life is attributed to different dominant DRX mechanisms at varying temperatures. High temperature low cycle fatigue (LCF) tests were conducted on the FGH95 nickel-based superalloy at temperatures of 420 °C and 600 °C. The experimental results indicate that the fatigue life of the FGH95 alloy at 600 °C is approximately nine times higher than that at 420 °C under identical stress conditions. This finding differs from the conclusions of previous studies on the effect of temperature on fatigue life. The microstructure of the alloy was characterised, and it was found that there were multiple dynamic recrystallisation (DRX) mechanisms present. Continuous dynamic recrystallisation (CDRX) and discontinuous dynamic recrystallisation (DDRX) were identified as the dominant mechanisms at different temperatures. These different dominant mechanisms contributed to the variation in the fatigue life of the alloys under different temperature conditions at the same stress level. [ABSTRACT FROM AUTHOR]

• The evolution mechanisms of out-of-plane performance in C/SiC riveted joint are demonstrated. • The refined simulation model considering deposited SiC matrix, mesoscale structural characteristics and interference fit is established. • The thermos-mechanical coupling effects on failure mechanisms of C/SiC riveted joints are illustrated by experiments and simulations. • Significant factors affecting jointed performance including deposition of SiC matrix and interference fit are revealed. The failure mechanisms of C/SiC riveted joints are complicated and unclear under thermo-mechanical coupling loading. This work numerically and experimentally examines the mechanical responses, failure evolutions and damage modes of C/SiC riveted joints subjected to push-out loading at room temperature and 800 ℃. The typical C/SiC riveted joints are fabricated by integrated manufacturing techniques based on CVI process, which are then adopted for push-out experiments through the combined mechanical and thermal loading system. To fully reveal the thermo-mechanical coupling damage mechanisms, a refined finite element (FE) model is established, considering deposited SiC matrix, structural characteristics of C/SiC composites and interference fit. The comprehensive results from FE model and experiments indicate the bearing capacity of C/SiC riveted joints could maintain within a certain deformation range even under broken interface between rivet and plate, which benefits from the designed interference fit. Furthermore, significant temperature-dependent mechanical responses and damage modes are observed and analyzed. This work could potentially provide the basis for designing reliable hot structures made of ceramic matrix composite. [ABSTRACT FROM AUTHOR]

The residual stress generated from temperature changes and interference fit of rivet plays a significant role in the performance of C/SiC composites. To gain a thorough understanding of the residual stress evolution mechanisms and their influences on C/SiC composites, this work carries out comprehensive experimental research combined with simulation analyzes. The results of quasi-static tension tests present that as the environmental temperature rises from room temperature to 800 °C, the stiffness of structure increases a lot, while the strength of riveted joints significantly decreases. Furthermore, it is found that the microscopic failure modes are also changed. The cyclic unloading-reloading tests for calculating the residual stress quantitatively are conducted to explain the failure evolutions of structures. The obtained results reveal an important connection between the residual stress states and the microscopic failure modes of C/SiC composites. The environmental temperature and interference riveted joint both can affect stress state around the open hole, which are significant factors determining the damage modes and structural performance. In the process of C/SiC composites design, it is necessary to pay attention to the processing parameters of rivet interference fit to meet the performance optimization under service conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Wave Based Method (WBM) is an efficient method to analyze mid-frequency dynamic problems. This work extended the WBM to the transverse vibration analysis of a thermal beam with limited uncertain information. Novel wave functions and particular solution function for the thermal beam with deterministic parameters are derived to obtain the dynamic response. Then, by employing the interval perturbation method and sub-interval decomposition technique, the Sub-Interval Perturbation Wave Based Method (SIPWBM) is developed to analyze the uncertain propagation in thermal beams for the first time. Numerical simulations for thermal beams with deterministic parameters and interval parameters are conducted, respectively. The impacts of different thermal effects on deterministic dynamic response are investigated. Simulation results prove that the developed WBM could accurately predict the low- and mid-frequency transverse dynamic response of the thermal beam with deterministic parameters. The thermal stress effect plays a leading role in the low-frequency displacement frequency responses for beams under low-level temperature load. Whereas it is necessary to consider both the temperature-dependent material property effect and thermal stress effect in the mid-frequency transverse vibration analysis of thermal beams. By using the sub-interval decomposition technique and choosing a suitable sub-interval number, the SIPWBM could predict the bounds of the mid-frequency interval dynamic response accurately and efficiently. [ABSTRACT FROM AUTHOR]

The unsteady vortex-lattice method provides a medium-fidelity tool for calculation of low-speed aerodynamic loads based on the potential-flow theory. It has long been favored in research on the aeroelasticity and flight dynamics for flexible aircraft with high aspect ratios. However, the unsteady vortex-lattice method is established in the discrete time domain which brings difficulties to modeling aeroelastic system for stability analysis. An analytical aerodynamic sensitivity calculation scheme is developed in this paper to formulate the aeroelastic equations of motion with UVLM aerodynamics. A free wake model is used to simulate accurate vortex shedding and subsequent wake propagation. Using a small perturbation method, the aerodynamic governing equations are linearized around the equilibrium condition, where the analytical sensitivities can be derived. The surface spline interpolation algorithm is adopted to implement the structure-aerodynamic coupling. Both aerodynamic sensitivities with respect to structural motions and circulation strengths of vortices are obtained. In numerical studies, a time-marching transient response analysis scheme is used to obtain the distributed aerodynamic loads and structural deformations. Analytical sensitivity results are validated by the finite difference method. The proposed analytical sensitivity calculation framework is demonstrated to be applicable to commonly used beam-based flexible wing models, as well as the shell-based finite element models with higher fidelity. The derived sensitivity formulations and related numerical implementations can build the foundation for further studies on aeroelastic optimization and stability analysis. [ABSTRACT FROM AUTHOR]

To analyze the effects of void on transverse tensile properties of composites considering thermal residual stress (TRS), finite element models with different distribution patterns and shapes for voids are established. Two different void modeling methods, with voids explicitly established and with voids modeled within elements, are compared first. For the method with voids explicitly established, circular, elliptical and arbitrary voids are considered. To reveal the effects of TRS, two different TRS analysis methods are evaluated. Results show that for the models without considering voids and TRS, the interface debonding is the dominant failure mechanism. After considering the voids, the effects of matrix damage on the crack initiation become more important. There are more variations in tensile strengths of models with voids explicitly established than those from the models with voids modeled within elements. It is also found that higher TRS values are obtained when the change of matrix properties with temperature is considered. After considering the TRS, the matrix damage contributes more to the crack initiation and the interface debonding is inhibited. Besides, the TRS results in thermal residual matrix plasticity around the void, which contributes to the premature initiation of crack around the void. [ABSTRACT FROM AUTHOR]

The nonlinear behavior of the airfoil-store system introduces complexity to its mechanical characteristics, making it essential to identify the system's nonlinear features. This study presents a novel nonlinear subspace identification approach in combination with an aerodynamic force. Based on the dynamic modeling of the airfoil storage system with random force, a linear elastic contribution related to the wind speed is introduced to two sides of motion equations, thereby transforming the original asymmetric linearity into the symmetric stiffness. A nonlinear state-space representation of the airfoil-store system is established, and the nonlinear parameters are identified by the proposed approach. Simulation examples are conducted considering different levels of nonlinearity, measurement noise, and flow speeds. The results demonstrate that the proposed method exhibits strong flexibility and robustness across various wind speeds in the airfoil-store system. It effectively identifies nonlinear stiffness, nonlinear damping, and various types of nonlinearity. [ABSTRACT FROM AUTHOR]

• The performances of FML pin joints under in-plane high-speed dynamic loads are analyzed. • The effects of ply stacking sequences on energy absorption efficiency and damage evolution of FML pin joints are revealed. • The dynamic ultimate strength of FML pin joint incorporates contributions from inertia effects. • The design guide about fiber direction in FML pin joint is constructed for an excellent energy absorption efficiency. With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage. [ABSTRACT FROM AUTHOR]

[Display omitted] • A reliability-guided frequency-domain-based digital image correlation method is proposed to solve the low computational efficiency caused by the amount of vibration collected data. • This method combines the advantages of a reliability-guided strategy and an integer-pixel search method based on the frequency domain to ensure that the seed point with the best matching effect in the calculation area is selected. • A multi-camera array system is established to obtain full-field modal anaysis. • The modal test of a solar panel is carried out by building four cameras system, which verifies the correctness of the proposed method and has certain engineering significance. A multi-camera array system was established to address the limitations of traditional measurement methods in full-field modal measurement. According to the principle of binocular vision, two cameras are utilized to form a set of three-dimensional measurement subsystems, and the subsystems are calibrated to establish unity in coordinates. To improve computational efficiency, a reliability-guided frequency-domain-based digital image correlation method is proposed to optimize pixel matching and calculation path. This method incorporates the benefits of a reliability-guided strategy and an integer-pixel search method based on the frequency domain to ensure that the seed point with the optimal matching effect in the calculation area is selected. The zero-mean normalized cross-correlation coefficient is used as the criterion for determining reliability. This approach effectively avoids the problem of error transmission and reduces the need for complex operations and repeated searches in the spatial domain, thus improving computational efficiency. The matching time is reduced, the calculation efficiency of displacement signal extraction under large data volume is improved, and the obtained response signal is substituted into the modal identification algorithm to obtain the modal parameters of the structure. Ultimately, the modal test of a solar panel is performed by constructing a four-camera system, which verifies the correctness of the proposed method and has practical engineering significance. [ABSTRACT FROM AUTHOR]

To identify the uncertain stiffness and damping of the rotor support system, and obtain the most credible interval parameters, an interval model validation for rotor support system using Kmeans Bayesian method is proposed. Interval model updating is transformed into interval lower bound and interval diameter determination. The minimization of discrepancies between predicted and experimental data is converted into minimizing the area between the cumulative distribution function (CDF) of the errors and CDF of 0. To improve the computational efficiency, the long short-term memory (LSTM) network is constructed to denote the mapping relationship between the unbalance response and support parameters. To obtain the most credible interval, the Kmeans clustering algorithm is combined with the Bayesian method to select the interval bounds with maximum credibility. Kmeans clustering algorithm is used to reduce the number of reconstructed errors while utilizing all the information on reconstruction errors. Bayesian method is used to calculate the credibility of the interval bounds. The performance of the proposed method is validated by a gas-generator rotor and a dual-disks rotor. Results show that the proposed method is effective for model validation of the rotor support parameters. [ABSTRACT FROM AUTHOR]

Distributed load information is essential for the design and monitoring of aerospace structures. A frequency domain method for the identification of correlated random fluctuating pressure is proposed in which structural responses acquired from limited strain sensors are used. The spatially-correlated power spectral density function of the random fluctuating pressure on the structure is firstly represented by Legendre polynomials w.r.t. the spatial distance multiplying their corresponding frequency-dependent coefficients. Secondly, the transfer matrix is obtained by the stochastic response analysis using distributed load in the form of Legendre polynomials. Then, the coefficients in the power spectral density function model of the pressure are identified by inversion of the transfer matrix together with a modified regularization technique. Finally, the random fluctuating pressure load is reconstructed by the superposition of the identified coefficients multiplying with Legendre polynomials. Numerical simulations on a simply-supported plate subjected to correlated stochastic distributed loads are conducted to verify the proposed method. Factors that may influence the accuracy of identification results are also discussed. To test the performance of the proposed method on complex structures, the gust-induced pressure load on a 3D wing structure is further identified using the proposed method. Results show that the proposed method is capable of identifying the correlated random fluctuating pressure on aircraft structures. [ABSTRACT FROM AUTHOR]

• Two types of new classes of hierarchical circular tubes (HCTs) are constructed. • Two deformation patterns are identified, which have different crushing behavior of the HCTs. • The mean crushing force and the specific energy absorption can be significantly improved by choosing suitable hierarchical configurations. • Partial hierarch performs better than the fully compacted one in improving the crashworthiness of the tubes. In this numerical study by means of finite element modeling, the concept of hierarchy is incorporated into thin-walled circular tubes for a configuration with optimum energy absorption. Hierarchical circular tubes (HCTs) are constructed by replacing the wall of an initially single-cell circular tube (SCT) with a series of small tubes placed next to each other (Fully packed, HCT-F) or at a distance apart (partially packed, HCT-P); the total net cross-sectional area and hence the mass is kept the same. The behavior of these new classes of hierarchical tubes under axial crushing is investigated in terms of deformation modes, crushing forces and energy absorption. Two deformation modes are identified and they have different crushing behavior of the HCTs. The initial peak force (PF) remains almost constant after micro-cell tubes are hierarchically introduced, but the mean crushing force (MCF) and hence the specific energy absorption (SEA) can be significantly improved by choosing suitable configurations. It is also demonstrated that partial hierarchy performs better in enhancing the crushing performance of the tubes compared with the full hierarchy. [ABSTRACT FROM AUTHOR]

Abstract The mechanical behavior of aluminum honeycombs subjected to quasi-static combined compression-shear loading was experimentally investigated. Two different deformation patterns were observed, deforming cell walls non-inclined (Mode I) and inclined (Mode II) respectively. For the first time, normal and shear forces of honeycombs deforming in Mode II were measured directly using a tri-axial load cell. It was found that the shear force behavior was very different for Modes I and II, with a negative shear force being observed for Mode II, which was not previously reported. Three aluminum hexagonal honeycombs with different cell configurations (cell size and wall thickness) were tested at two loading velocities of 5 × 10−4 and 5 × 10−3 m/s, three loading angles of 15°, 30° and 45°, in the two plane orientations, respectively. The effects of loading velocity, loading angle and loading plane were discussed in detail. An empirical model specifically revealing the effect of loading angle on normal plateau stress was proposed. Initial yield surface was estimated and was found to take the form of an ellipse envelop in the stress space. Graphical abstract Unlabelled Image Highlights • Two deformation patterns were observed, deforming cell walls non-inclined (Mode I) and inclined (Mode II) respectively. • For the first time, normal and shear forces of honeycombs deforming in Mode II were measured directly. • The shear force behavior was different for the two deformation patterns, with a negative value for Mode II. • Initial yield surface of honeycombs takes the form of an ellipse envelop in the stress space. [ABSTRACT FROM AUTHOR]