The rapid advancement of low-power microelectronic technologies has stimulated growing interest in vibration-based energy harvesting as a promising alternative to conventional batteries. While batteries are widely used at these scales, their replacement becomes highly challenging for systems deployed within inaccessible or remote locations. The major drawback of linear harvesters is their limited frequency bandwidth. This limitation, together with the wide frequency spectrum of ambient excitations, significantly diminishes the energy conversion efficiency of linear harvesters. To address this challenge and improve the performance of such systems in practical environments, it is essential to broaden their frequency bandwidth. Among the various approaches for broadening the frequency bandwidth, employing nonlinear techniques has proven to be highly effective in enhancing the efficiency of vibration energy harvesters. This study proves the theoretical modeling of frequency bandwidth analysis in a piezoelectric energy harvester for a series of experimental cases considering magnetic nonlinearity and impact-induced nonlinearity. Applying both approaches together increases the system efficiency by about 80 % compared to using either method separately. Furthermore, the influence of key system parameters—including magnetic strength, input acceleration amplitude, electrical resistance, and initial gap—on the system's dynamic behavior is investigated. Finally, an efficiency index is introduced to assess the harvester's efficiency relative to the conventional design.
Plate and shell structures combine smart functionality, low weight, high specific strength, and strong resistance to corrosion and fatigue, making them indispensable in aerospace, electronics, chemical and civil engineering, nanostructures, and renewable-energy applications. Conventional three-dimensional elasticity theory often introduces excessive degrees of freedom, reducing computational efficiency and limiting its engineering applicability. These limitations have motivated the systematic development of advanced plate and shell theories. This paper classifies existing plate and shell theories according to their underlying modeling assumptions: (i) equivalent single-layer theories, suited to homogeneous structures or laminates with weak interlayer variations; (ii) layer-wise theories, designed for multilayer composites with pronounced interlayer differences; (iii) mixed-field theories, which capture transverse shear effects through coupled displacement and stress fields; and (iv) hyper-dimensional theories, which incorporate thickness stretching through out-of-plane displacement components. Drawing on a broad range of case studies, this review examines the static, dynamic, linear, and nonlinear responses of plate and shell structures under multiscale, multiregion, and multiphysics coupling. It emphasizes that reliable mechanical models require theory selection to be guided by the structural characteristics and service conditions of the problem.
In practical engineering applications, uncertainties in beam vibration systems induced by manufacturing tolerances and environmental variations are inevitable. However, conventional vibration response analysis typically assumes that parameters such as material properties and geometry are deterministic. To quantify the effect of multi-parameter uncertainty on the response of beam vibration systems, this study introduces an efficient and high-precision partition of unity finite element method for beam vibration analysis within the framework of the direct probability integral method, thus developing a novel stochastic response analysis scheme for beam vibration systems. The proposed scheme features a strong capability to capture waveform information within each element, a small system matrix size, and the ability to efficiently and accurately reflect the patterns of stochastic responses. Numerical examples show that the statistical characteristics of the beam vibration system response obtained using the proposed scheme agree well with those from the Monte Carlo simulation method, whilst exhibiting good computational accuracy and efficiency. Furthermore, the elastic modulus and the beam height exert a relatively significant effect on the statistical characteristics of the system response, and the effect of material properties is greater than that of geometric properties under multi-parameter coupling.
In this paper, a mechanism-based continuum damage model for the in-plane analysis of masonry structures is presented. Each of the considered damage mechanisms is characterized by a damage criterion ruled by few mechanical parameters easily obtainable from small-scale tests on masonry components. In the proposed model, the most prominent ones, involving opening/sliding of the joints and failure of the bulk, are taken into account. A decomposition of the strains into mechanism-relevant contributions is introduced, leading to the definition of a set of five damage variables governed by cohesive-frictional laws. An ad-hoc damage activation strategy is devised to guarantee that the active damage mechanisms are independent of each other. Accordingly, the evolution of each single damage variable can be independently evaluated following its closed-form evolution law. The set of the active damage variables rules the evolution of the constitutive matrix coefficients, resulting in a secant orthotropic damage model. The numerical implementation of the proposed damage model resorts to a mixed strain–displacement finite element formulation, already proved effective to deal with mesh dependency issues. The proposed model is tested on several masonry shear wall benchmarks and compared with a state-of-the-art damaging block-based model adopted as reference. A good agreement is obtained between the two models in terms of peak loads, post-peak evolution and damage mechanisms evolutions.
Sea ice exhibits pronounced temperature-driven variations in stiffness and conductivity, making it effectively a functionally graded material (FGM). Classical homogeneous beam models neglect these gradients and linearise the kinematics, contributing to large discrepancies in flexural strength estimates used in ice-structure interaction design. This work presents a non-linear thermomechanical Euler–Bernoulli FGM formulation that captures through-thickness property variations, von Kármán strain effects, and distributed gravity-buoyancy loading. Analytical solutions are obtained for cantilever and three-point bending configurations while retaining axial-bending coupling. The analytical results are compared against numerical solutions of the governing non-linear boundary-value problem to verify their correct solution. When compared with classical homogeneous theory, the model predicts up to 69% differences in flexural stress maxima depending on temperature gradients and geometry, demonstrating that thermal-mechanical coupling is essential for accurate representation of sea ice beams. The analysis shows that beam length strongly influences sensitivity to gravitational loading. The proposed formulation provides an analytical benchmark for evaluating how through-thickness property gradients affect flexural stress estimates in idealised beam configurations.
Inspired by the fire-making tool (the Iroquois pump drill), a new two-degree-of-freedom (2-DOF) string-driven rotational energy harvester (SREH) is proposed, which can efficiently harvest energy from ambient vibrations at ultra-low frequency (0.2 Hz). The proposed SREH is composed of a 2-DOF string-driven rotor and a magnet-coil transduction unit. The 2-DOF string-driven rotor consists of a rotor, a lid, an elastic string, an inelastic string, and support springs, capable of effectively converting ultra-low frequency vibrations into high-speed rotation (328 rpm). The magnet-coil transduction unit can transfer the kinetic energy to electricity. Numerical and experimental results both show that the proposed SREH can deliver stable electrical outputs under harmonic excitation (1-5 Hz). Under an excitation frequency of 5 Hz and an excitation amplitude of 7.5 mm, the proposed harvester can generate a power of 1.55 mW. Furthermore, with flywheel energy storage mechanism, the proposed harvester can generate a power of 0.64 mW under an impact excitation of 0.2 Hz. In addition, under manual pressing excitation (approximately 6 Hz), the proposed device is capable of generating a power of 1.54 mW and rapidly charging a 1 mF capacitor from 0 V to 1.58 V within approximately 8 s. The results exhibit the great potential of the string-driven harvester for efficiently scavenging ultra-low frequency vibration energy.
A viscoelastic model of a material with brick-and-mortar architecture is proposed in this paper. This model can be used to simulate the uniaxial mechanical behavior of natural bone tissue and man-made bone-like materials. Using the unit cell approach and the formulation in the time domain, we derive the closed-form responses of bone and bone-like materials under different loading paths. These closed-form solutions enable us to investigate the influence of microstructures on the effective properties of the bone and bone-like materials, including the instantaneous modulus and viscosity; the asymptotic modulus and viscosity; the relaxation; the creep; the toughness; and the energy dissipation. Our study shows the different effects of the volume fraction and the aspect ratio of the inclusion. It also exhibits the effect of the staggering patterns of matrix and inclusion on the mechanical features of the bone-like material under the stress- and strain-controlled cases. This research supports the design of bone-like materials with specified performance theoretically and it also provides a foundation for future computational design of bone-like materials.
With a folded-beam quasi-zero-stiffness (QZS) resonant cell as the core component, tunable absorber and isolator modules are proposed for low-frequency vibration control. The folded-beam QZS unit serves as a mechanically tunable elastic element, while a central mass acts as the inertial component, enabling local resonance tuning through pre-compression without changing the basic structural configuration. Unlike conventional passive vibration-control structures, the proposed QZS resonant cell is treated as a mechanically tunable core component that can be integrated into both absorber and isolator modules. The tunable absorber module allows flexible installation and frequency adjustment, whereas the tunable isolator module embeds QZS resonant cells into a load-bearing frame, enabling tunable low-frequency isolation for heavy-load applications while preserving structural support capability. Numerical and experimental results show that the attenuation frequency can be shifted toward lower frequencies by increasing the pre-compression within an appropriate range, while multi-unit absorber combinations can enhance single-frequency attenuation or broaden the effective attenuation band. The proposed design offers a compact, mechanically tunable, and modular solution for low-frequency vibration control.
The dynamic mechanical behavior and performance prediction of titanium alloys under extreme service conditions are of fundamental and applied interests. In particular, Ti–6Al–4V has been extensively studied under various loading conditions, but a comprehensive constitutive description across wide strain rate and temperature ranges is still lacking for this alloy. This work systematically investigates the dynamic response, deformation mechanisms, and constitutive modeling of Ti–6Al–4V alloy across a exceptionally wide range of strain rates and temperatures. Quasi-static (QS, 10−3−10−1s−1), split Hopkinson pressure bar (SHPB, 103−104s−1, 133−−673 K), Taylor impact (TI, ∼104s−1), and plate impact (PI, ∼106s−1) loading are applied, revealing characteristic strain-rate-hardening and thermal-softening trends. Combined with post-mortem characterization, the loading-dependence of bulk properties and microstructural evolution is elucidated. Plastic deformation is dominated by dislocation slip and deformation twinning. Dislocation accumulation and twinning are enhanced under cryogenic temperatures and high strain rates. Based on the comprehensive experimental dataset, a modified Johnson-Cook–Cowper–Symonds (JC–CS) constitutive model is established via an experiment-constrained, iterative numerical optimization scheme. This work provides essential data and an accurate constitutive model for improving performance prediction and design of titanium alloy components, as well as a reliable approach for obtaining wide-range constitutive models in general.
Traditional homogeneous materials are prone to performance degradation and failure under repeated impact loading due to their isotropic mechanical properties. Inspired by the trabecular structure of the human femur, this work designed and fabricated a novel femur-inspired porous microlattice core using additively manufactured aluminum alloy. The femur-inspired porous microlattice structure exhibits low-density and high-porosity characteristics, enabling effective energy dissipation through elastoplastic deformation while combining lightweight design with high strength and toughness. A finite element impact model of the protective material was established, and repeated high-velocity impact tests were conducted. Under a high-velocity impact velocity of 100 m/s, the dynamic responses of the femur-inspired porous microlattice core and a conventional honeycomb core during one to three repeated impacts were comparatively analyzed. Based on parameters including explosion-proof putty stress, component energy, and rear face sheet intrusion displacement, the damage evolution of the core structure and rear face sheet was progressively investigated, thereby systematically revealing the dynamic response and protective mechanisms of the femur-inspired porous microlattice structure. The results show that the rear face sheet intrusion displacement of the femur-inspired structure agrees well with the simulation results, with a maximum error of only 17.02%. Compared with the conventional honeycomb core, the femur-inspired porous microlattice core exhibited rear face sheet intrusion displacements of 0.92 mm, 2.13 mm, and 3.42 mm during the first, second, and third impacts, respectively, which were 57.1%, 43.35%, and 32% lower than those of the conventional honeycomb core, demonstrating superior repeated impact resistance. This work provides a new technical approach for developing high-performance composite sandwich structures with repeated impact resistance.
Graphene-reinforced aluminum (Gr-Al) composites hold great promise for high-performance structural applications in aerospace and other fields due to their excellent mechanical properties. However, existing constitutive models are mostly limited to specific graphene contents or single aluminum alloy systems, failing to meet the demand for universal performance prediction. To address this gap, this study develops a generalized constitutive model via a comprehensive framework integrating experimental testing, multiscale finite element analysis, and theoretical modeling. Key results indicate that graphene significantly enhances the mechanical properties of aluminum matrices, with the enhancement effect showing a nonlinear relationship with graphene weight fraction. The proposed constitutive model, which integrates the matrix enhancement coefficient, graphene volume fraction efficiency factor, and graphene third-order elastic modulus, effectively characterizes the plastic deformation evolution of the composites. Validated across multiple aluminum alloy systems with different graphene loadings, the model exhibits robust adaptability with a goodness-of-fit R2 exceeding 97.70% for all tested combinations below 0.7 wt%. This work provides a unified theoretical tool for the performance prediction and structural optimization of Gr-Al composites, featuring significant theoretical significance and engineering application value.
Additively manufactured (AM) lattice structures offer significant potential for lightweight aerospace components. However, their application to engineering structures with complex contours remains limited by two major challenges: geometry-consistent conformal lattice generation and reliable representation of manufacturing-induced geometric imperfections. To address these challenges, this study proposes an integrated modeling framework consisting of a Shape-Function-Based Mapping Method (SFMM) and a Hermite-Interpolation-Based Imperfection Modeling Method (HIIMM). SFMM establishes an element-wise geometric mapping between regular lattice structures and complex 3D domains, enabling geometry-consistent conformal infill while preserving structural continuity, boundary compatibility, and topological connectivity. HIIMM introduces manufacturing-induced geometric imperfections, including strut center-axis offsets and cross-sectional radius variations, directly into 3D solid strut geometries through a parameterized and physically interpretable formulation. Together, the proposed framework enables efficient solid-element modeling of lattice structures with manufacturing-induced geometric imperfections for subsequent mechanical analysis. Numerical case studies demonstrate that, compared with the conventional Boolean-operation-based modeling method, SFMM produces smoother stress transfer, improved structural integrity, and enhanced load-bearing performance. Furthermore, compression experiments and finite element simulations show good agreement in the global force–displacement response, validating the predictive capability of the proposed methodology. The proposed framework provides an effective modeling approach for the conformal design and mechanical evaluation of additively manufactured lattice structures with complex engineering contours while explicitly accounting for manufacturing-induced geometric imperfections.
This paper presents an enhanced method for sequential identification of boundary condition and constitutive parameters, incorporating advanced measurement uncertainty-based sensitivity analysis through Identifiability Classes. The approach is further optimized by implementing an a priori selection of regularization weight, significantly accelerating the identification process. Additionally, the use of an elastic (linear) model is explored for initial boundary condition parameter estimation, enabling rapid approximate results. The methodology is applied to a previously studied tensile test, demonstrating its robustness through the use of intentionally offset constitutive parameters. The results confirm the method effectiveness in achieving accurate identification while maintaining computational efficiency. The combination of Identifiability Classes with measurement uncertainty-informed regularization provides a robust framework for developing models that accurately match experimental observations.
Recently, infrared thermography has emerged as a highly promising non-destructive method for rapid fatigue limit determination. However, the influence on the fatigue limit evaluation results still remains unexplored. In this study, the continuous multi-stage loading fatigue tests of the 316L laser-welded joints, under the frequencies of 10 Hz, 20 Hz, and 30 Hz, ranging from 210 MPa to 290 MPa, were carried out. An infrared camera was employed to measure the real-time temperature of the welded joints, and the thermographic data under various frequencies were processed to obtain the fatigue limit. The findings indicate that the fatigue limit of the welded joints under 10 Hz, 20 Hz, and 30 Hz was determined to be 266.02 MPa, 257.6 MPa, and 251.32 MPa, respectively, even though the temperature rise response under the same load increases with frequency. Additionally, the conventional staircase tests, which have a higher frequency of 79 Hz, demonstrate a fatigue limit value of 240 MPa with an error of 10.84%, 7.33%, and 4.72% of the counterpart in 10 Hz, 20 Hz, and 30 Hz. This reinforces the idea that frequency has an insignificant effect on fatigue limit evaluation. Additionally, the fracture fatigue entropy (FFE) under three frequencies was computed, and the findings demonstrate that FFE is independent of the test frequency. The Granato-Lücke dislocation model was introduced to discuss the possible self-heating mechanism, and the associated dislocation motion of the weld zone under a stress over the fatigue limit is confirmed by the EBSD and TEM characterization. This study may provide a basis for the use of infrared thermography to estimate fatigue limits in industrial applications.
Classical continuum theories are inadequate for describing the mechanical behaviour of materials possessing distinct microstructural features. By incorporating independent micro-rotations and couple stresses through additional kinematic and dynamic variables, the micropolar continuum provides a more comprehensive framework to analyse such materials In the present work, the focus is on assessing the capability of the model to effectively characterise the behaviour of anisotropic solids subjected to plane wave propagation. The impact of anisotropy on dispersion relations is analysed through a detailed numerical parametric investigation of a two-dimensional domain employing three distinct material parameter sets. Analytical dispersion relations are derived for stabilised formulations of the non-ordinary state-based peridynamic (NOSBPD) model in two-dimensional settings. The resulting dispersion curves are presented to demonstrate the influence of the horizon parameter δ and the nonlocal influence function. The results provide valuable insights into the wave propagation characteristics of anisotropic micropolar materials.
Multilayered aluminum-matrix composites constitute a subclass of functionally graded materials whose mechanical properties can be systematically tailored to meet specific design requirements. In this study, experimental and numerical investigations are performed to characterize Mode I and mixed-mode I/II fracture behavior and crack growth in graded AlSi12–Al2O3 composites containing a notch oriented along the gradient direction. Mode I fracture tests are conducted on four-layer, disk-shaped compact specimens subjected to tensile loading, with Al2O3 volume fractions of 0 (pure matrix), 10, 20, and 30 percent. Crack propagation on both specimen surfaces is monitored in situ, and full-field displacement measurements are obtained using Digital Image Correlation. The experiments reveal a pronounced nonlinear crack-front propagation induced by material composition gradient along the crack front. Fracture consistently initiates in the layer with the highest content of ceramic particles, propagates within this layer, and subsequently extends into adjacent layers. Distinct fracture surface morphologies are observed using scanning electron microscopy, ranging from brittle features in ceramic-rich layers to progressively more ductile characteristics in layers with lower ceramic content. An elastic–plastic phase-field model is employed to examine the influence of stacking sequence on fracture load capacity as well as on crack-front formation and evolution under both Mode I and mixed-mode I/II loading conditions. The phase-field model is calibrated against experimentally measured fracture loads, and the characteristic length-scale parameter is identified accordingly. The simulations successfully reproduce the experimentally observed nonlinear crack-front morphology and demonstrate that the stacking sequence considerably affects the maximum load-bearing capacity and crack front geometry under both pure Mode I and mixed-mode loading.
