European Journal of Mechanics A-Solids最新文献

Despite the superelastic deformation of NiTi has been documented and analyzed elaborately, its shape-memory behavior during stress-biased thermal cycling has not been thoroughly unveiled. This paper examines the evolution of transformation pattern in NiTi upon thermal cycling over a wide range of biasing stress. For the present shape-memory NiTi, both forward and reverse transformations proceed via the growth of localized deformation band (LDB) under low biasing stress (${\sigma }_{\text{bias}}$ ≤ 150 MPa), while LDB only appears during forward transformation and reverse transformation is uniform under high biasing stress (${\sigma }_{\text{bias}}$ ≥ 200 MPa). This is the first time that delocalization (conversion of deformation mode from localization to homogeneity) is observed during stress-biased thermal cycling. We clarify that the intrinsic undercooling/overheating of martensitic transformation results in unstable thermomechanical response, and it is the origin of localization in shape-memory NiTi. It is found that transformation-induced plasticity (TRIP), which is dominated by dislocation slip and deformation twining, not only causes irreversibility in the present shape-memory NiTi but also leads to delocalization through stabilization of intrinsic thermomechanical response of reverse transformation.

Inspired by the cross-sectional view of leaf tissue, a bidirectional gradient hierarchical double tube (BGHDT) was proposed and its crashworthiness performance was investigated by finite element simulation. The results indicate that the proposed BGHDT has better energy absorption capacity than the conventional hexagon tube under the same mass condition. The folding wavelength of BGHDT is shorter than that of conventional hexagonal tubes, resulting in a larger number of folds. Compared with conventional hexagon tubes, the energy absorption of BGHDT with 3rd hierarchical level increases by 139.39% and its peak crush force (PCF) decreases by 16.29% at the same mass. Finally, the effects of wall thickness and the number of connecting units on the crashworthiness performance of BGHDT are systematically studied.

Helical compression springs are known for their linear force-length relation. However, it is often observed that not ground springs admit a very different mechanical behavior than expected due to the spatial behavior of the end coils. Their behavior is neglected by the standard formula determining the global stiffness of the spring, resulting in errors. Spring makers and customers currently use the standard formulations to design springs. This practice significantly affects the complex spring making process. Operators must experimentally retrieve the desired stiffness by modifying machine inputs, leading to the simultaneous loss of both tuning time and raw materials. The proposed robust and reliable optimization algorithm considers the manufacturing uncertainties and the material variabilities and proposes a target spring design that ensures the highest probability of meeting all constraints. It integrates modern equations for the principal outputs of spring sizing, which are significantly more precise than standard equations, and tends to propose a spring with the lowest possible mass. The algorithm has been successfully confronted with industrial applications. As result, the proposed solution spring sizing is significantly more reliable and robust than the most commonly used software in the spring industry.

Unlike traditional energy dissipation structures that dissipate energy through irreversible plastic deformation or collapse, metamaterials based on friction energy dissipation have attracted attention due to their reusability. This article proposed a novel energy dissipation metamaterial by integrating friction energy dissipation mechanism into negative Poisson's ratio (NPR) structures. The integration of friction energy dissipation mechanism can simultaneously enhance the effective stiffness and NPR effect. The mechanical properties of the proposed structure were investigated using theoretical analysis, experiments, and finite element (FE) simulations. The influence of variables such as internal concave angle, friction coefficient, and number of reinforcing ribs was discussed. The results indicate that both unit cell and honeycomb structure can repeatedly dissipate energy within the elastic range. Compared with the traditional concave hexagonal structure, the effective stiffness and NPR effect were enhanced. This work provides a novel idea for the design of NPR energy dissipation structures.

Sandwich nanostructures incorporating piezoelectric and magneto-electro-elastic properties have emerged as promising candidates for next-generation smart devices and composites. Due to their exceptional design, fabrication, and energy conversion capabilities, these structures are extensively utilised as sensors and actuators in nano-electromechanical systems. Accordingly, in this article, the free vibration behaviour of a multifunctional laminated (MFL) nanoplate with piezoelectric PZT5-H and magnetostrictive CoFe₂O₄ (cobalt-ferrite) face layers and a graphene-reinforced core layer is investigated by applying a higher-order sinusoidal shear deformation theory (HSDT). In addition, two different material cases consisting of Ti6Al4V and ZrO₂ materials and two foam models, uniform and symmetric, are considered for the foam core layer. Hamilton's principle is used to obtain the plate's governing equations. Navier's solution approach is utilised to get the natural frequencies of the laminated nanoplate under thermal load and electric and magnetic fields. A parametric study is performed to determine the effects of volumetric graphene content, the foam model and its pore ratio, face/core material content, external electric and magnetic potential, and thermal load on the free vibration response of the MFL nanoplate. The obtained numerical results can be a reference point for future research on layered porous MEE structures, especially for micro/nano-sized systems.

The combination of beams with piezoelectric patches has become a prevalent energy harvesting tool due to its ease of use. Typical energy harvesting systems are usually linear, and their efficiency is not satisfying due to low-frequency bandwidth. In this paper, a quad-stable piezoelectric vibration energy harvester is analyzed both numerically and experimentally. The primary purpose of this investigation is to analyze the static and dynamic characteristics of a proposed quad-stable system to consider its potential for application in broadband energy harvesting comprehensively. The harvester system consists of a slotted cantilever beam, a piezoelectric patch, a pair of tip-mass blocks, and a double-sided clip. The cantilever beam is subjected to pre-displacement constraints made by a mutual self-constraint at the free end of it. The nonlinear behaviors of the harvester system, including snap-through and softening phenomena, are analyzed using the assumed modes and finite element method (FEM). The harvester's vibration equation is solved numerically and through an FE model which is made by an in-house finite element software. A prototype is designed and fabricated to validate the mathematical model and FE simulation. The experimental force-displacement diagram of the harvester displays distinct discontinuities, reflecting abrupt transitions occurring while switching its stable states. The prototype dynamics are analyzed by harmonic base excitation with different amplitude levels in two conditions, including the presence and absence of the piezoelectric patch. The results obtained from the mathematical and FEM model demonstrate a satisfactory correlation with the experimental data. Furthermore, the experimental data reveal the occurrence of the snap-through phenomenon, accompanied by a significant widening of the frequency bandwidth at relatively high amplitude levels. The system has the ability to provide an average output electrical power of 0.288 mW for an electrical resistance of 3.262 kΩ at the excitation frequency of 12.695 Hz and base acceleration amplitude of 3g.

In this research, the underwater sound absorption performance of porous media saturated with water is investigated through long straight tubes (LSTs) with circular cross-section and sintered fibrous metals (SFMs) containing complex pores, and effective underwater sound absorption capability is demonstrated theoretically, numerically and experimentally. Specifically, the theoretical model for LSTs, verified by direct numerical simulations (DNSs), reveals that much smaller pore diameter and much larger layer thickness of porous material is needed to gain high waterborne sound absorption coefficient than to obtain large airborne sound absorption coefficient. Besides, to examine the sound absorption capacity of realistic porous materials, SFMs backed with a finite cavity are experimentally measured under 7 different hydrostatic pressures in a water-filled tube, and numerically characterized via multi-physics couplings. Insensitivity of effective sound absorption capability to high pressure is established, which stems from the different underwater wave energy consumption mechanism (i.e. viscous-thermal effect) of porous materials from conventional rubber kind of underwater sound absorption materials. Physically, porous materials possess great potential in developing the next generation of high-performance underwater sound absorption materials.

Compared to traditional lightweight corrugation and cellular cores, the novel cellular cores auxetic metamaterials with negative and zero Poisson's ratios possess distinctive mechanical deformation traits, making them suitable for modeling lightweight sandwich structures. Therefore, the concept of combining auxetic metamaterial cellular with folded corrugation is proposed to construct a new type of corrugated honeycomb hybrid cores for studying the sound insulation and energy absorption characteristics of the stiffened sandwich doubly-curved shells, wherein the honeycomb core possesses a full range of Poisson's ratio characteristic and is composed of cellular cores exhibiting positive, negative, and zero Poisson's ratios (PPR, NPR, and ZPR). The Hamilton's principle is hired to derive the governing equations and considers fluid-structure coupling by applying normal velocities continuity conditions at the fluid-structure interface, which is further analytically solved using Navier's techniques, and the sound transmission loss (STL) is described analytically. The accuracy of these results is validated through comparisons with both experimental measurements conducted in an impedance tube and simulated outcomes generated by the COMSOL commercial software. The properties of stiffened sandwich doubly-curved shells with corrugated honeycomb hybrid cores are meticulously evaluated and compared, and the results show that the hybrid cellular core type significantly impacts the STL, wherein the average STL of the corrugation ZPR cellular hybrid cores stands at 42.06 dB within the broad low-frequency range of 380–2422 Hz, which has increased by 9.11% and 8.31% compared to the values of the corrugation NPR and traditional PPR cellular hybrid cores, the specific energy absorption (SEA) of the corrugation ZPR cellular hybrid cores is 13.06 kJ/m³, which has increased by 16.19% and 18.08% compared with the corrugation NPR and PPR cellular hybrid cores, respectively, indicating that the corrugation ZPR cellular hybrid cores have better sound insulation and energy absorption characteristics than the corrugation NPR and PPR cellular hybrid cores.

Negative stiffness mechanical metamaterials have shown great promise for various applications and are progressing toward programmability. The key challenge in designing programmable metamaterials lies in achieving efficient tunability. However, due to the limitations of current tuning strategies, many existing programmable metamaterials fall short of expectations. Here, we introduce a strategy that facilitates efficient response transformation and performance tuning across scales for negative stiffness mechanical metamaterials. The implementation of this novel tuning approach requires only the adjustment of a serial spring's stiffness which is much easier and more practical than controlling the non-linear contributions of the buckling parts. A systematic theoretical model has been developed to illustrate this innovative approach, and the results have been validated through simulations and experiments. This research can serve as a reference for designing programmable negative stiffness mechanical metamaterials (NSMMs).

Polymer nanocomposites (PNCs) have shown great potential to meet the ever-growing requirements of modern engineering applications. Nowadays, molecular dynamics (MD) simulations are increasingly employed to complement experimental work and thereby gain a deeper understanding of the complex structure–property relations of PNCs. However, with respect to the thermoplastic’s mechanical behavior, the role of its average molar mass ${\overline{M}}_n$ is rarely addressed, and many MD studies only consider uniform (monodispersed) polymers. Therefore, this contribution investigates the impact that ${\overline{M}}_n$ and the dispersity $\text{Đ}$ have on the stiffness and strength of PNCs through coarse-grained MD. To this end, we employed a Kremer–Grest bead–spring model and observed the expected increase in the mechanical performance of the neat polymer for larger ${\overline{M}}_n$. Our results indicated that the unimodal molar mass distribution does not impact the mechanical behavior in the investigated dispersity range $1.0\le \text{Đ}\le 1.09$. For the PNC, we obtained the same ${\overline{M}}_n$-dependence and $\text{Đ}$-independence of the mechanical properties over a wide range of filler sizes and contents. This contribution proves that even simple MD models can reproduce the experimentally well researched effect of the molar mass. Hence, this work is an important step in understanding the complex structure–property relations of PNCs, which is essential to unlock their full potential.