International Journal of Mechanical Sciences最新文献

Among the various methods for strain sensing, the metamaterial absorbers (MMAs) stand out due to their dual capabilities. Specifically, MMAs facilitate the wireless detection of deformations in the target and operate independently of any external power source. However, conventional research has a limitation in that stretchable strain sensors are unable to deform themselves autonomously, which puts constraints on being efficiently utilised in special environments where human intervention is difficult. Herein, we propose a wireless, power-independent, biaxial strain sensor equipped with self-shape and frequency recovery capability that addresses the limitations of existing wireless strain sensors through the unprecedented integration of a 4D-printed shape memory actuator and a biaxially stretchable MMA. The novel integration with the shape memory actuator enables the stretchable MMA to autonomously recover to its original shape and absorption frequency after being heated to 70 °C for a few minutes. This smart functionality enables the resulting wireless strain sensor based on the proposed idea to revert to the original state when sensing a new target without requiring human intervention. The highly sensitive biaxial sensing capability is as follows. When stretched horizontally from 0 % to 30 %, the absorption frequency of the proposed biaxially stretchable MMA demonstrates a linear change from 9.75 GHz to 7.94 GHz, exhibiting a high sensitivity of 4.3 × 10^7 Hz/%. Similarly, when stretched vertically from 0 % to 30 %, the absorption frequency linearly changes from 7.35 GHz to 6.01 GHz, indicating a sensitivity of 5.9 × 10^7 Hz/%. Accordingly, the wireless biaxial sensing capability of the proposed stretchable MMA, as well as its shape-recovery functionality facilitated by the 4D-printed actuator are highly effective for remote strain measurement in environments where direct human involvement is impractical.

Moving components exposed to electron radiation over longer durations are more prone to failure due to its complex changes from material properties to component characteristics. It involves multi-scale analysis, leading to current methods being deficient in accuracy and efficiency. In this paper, a cross-level vibration prediction method, which selects the ultrasonic motor (USM) stator as a typical component for Jupiter exploration, is proposed by incorporating the cross-scale changes of material properties based on the edge-based smoothed finite element method (ES-FEM). A cross-scale degradation model for exploring the material properties is constructed by establishing the correlation between the degradation of molecular chains and the mechanical properties of the epoxy resin. The ES-FEM is developed for investigating the vibration of the USM stator, by introducing the edge-based gradient smoothing technique (GST) to perform the strain smoothing operation in its stiffness matrix, offering superior accuracy and efficiency. The experiment of 1.2 MeV electron radiation under different electron fluences was carried out. It demonstrated that the present method can achieve higher accuracy and efficiency than the traditional one, while being closed to the experimental results with the frequency and amplitude errors of 0.03 % and 1.3 %, respectively.

Rigid foldable origami enables smooth and precise folding without stretching or bending its constituent panels and is promising for applications such as reprogrammable matter, self-folding machines, reconfigurable antennas, and deployable spacecraft. The diverse range of potential applications necessitates the need for the design and detailed analysis of different rigid-foldable origami structures, especially those with intricate motion modes. In this paper, we introduce a rigid-foldable spiral origami design that features a compression-torsion coupled motion mode. This design exhibits rich static and dynamic properties. Under static conditions, the compression-torsion coupled motion mode creates multiple self-locking positions and allows for the development of mechanical static diodes. Under dynamic conditions, the compression-torsion coupling effect in the spiral origami facilitates precise control of wave modes within the origami chain when impacted by a ball with a moderate initial velocity. In the case of large initial velocities of the ball, the spiral origami can function as a wave generator, producing rarefaction solitary waves or compressive solitary waves. The proposed spiral origami design provides an opportunity to explore new applications of rigid-foldable origami with compression-torsion coupling effects.

Shrinkage-induced cracking significantly impacts the durability of mass concrete structures. Quantitatively evaluating drying shrinkage of concrete proves challenging due to the time-consuming experiments and overlooked microstructure changes during the hydration process. To address this concern, this study initially characterized the long-term hydration products and microstructure of low-heat Portland cement (LHPC) through microstructural experiments. Subsequently, a novel high-resolution mesoscale framework is developed to investigate the drying shrinkage with hydration kinetics. High-resolution models consist of realistic-shaped aggregates are validated by the aggregate morphology and gradation parameters of core sample from mass concrete. Concurrently, the quantitative effects of internal and external factors on LHPC drying shrinkage are explored. Results indicated that LHPC possesses a denser microstructure, lower porosity, higher carbonation resistance, and 20% lower drying shrinkage compared to moderate-heat Portland cement, suggesting promising applications. Furthermore, experimental and computational findings suggested that increasing aggregate volume, controlling aggregate morphology, and adjusting curing time and humidity could be employed to reduce and manage drying shrinkage, ensuring concrete structure durability.

One of the most commonly used methods for characterizing the mechanical properties of discontinuous fiber reinforced composites (DFRC) is to establish a Representative Volume Element (RVE) model and perform finite element (FE) analysis. However, FE analysis on RVE models established by traditional sampling algorithms is often computationally expensive due to the large size of RVE that is required to be statistically representative of the composite. To address this issue, this paper proposes a new approach for constructing RVE models with more accurate description of fiber orientation, aiming to make the FE modelling more efficient by using an RVE with small size. When establishing RVE models with given target fiber orientation tensor, it is very challenging to accurately capture the orientation of fibers. In order to mitigate the error between the orientation tensor reconstructed by fibers generated in the RVE and the target orientation tensor, a group-random algorithm is proposed in the current work to generate RVE models. Unlike the traditional algorithm, in which fibers are sampled one by one in the RVE, the group-random algorithm samples a group of four fibers at one time in order to eliminate the error of the off-diagonal components of the reconstructed orientation tensor in the principal coordinate system. Then a modification tensor is further introduced to mitigate the error of the diagonal components of the reconstructed orientation tensor. Simulation results show that the orientation tensor error could be significantly reduced by the group-random algorithm even for the RVE with low number of fibers. The merits of the group-random algorithm are also witnessed by the stability and accuracy of predicting the elastic constants of composite materials through RVE modeling. It is thus concluded that the major advantage of this work is to provide an alternatively feasible strategy to substantially improve computational efficiency of RVE modelling.

Various researchers have studied jet array impingement heat transfer in impingement/effusion cooling systems. However, there is a lack of research on impingement/effusion cooling systems installed within rectangular cavities that focus on the impact of the proximity of the jet hole to the cavity sidewalls on cooling performance. The main objective of this study is to investigate the flow and heat transfer characteristics of jet array impingement with effusion holes in a rectangular cavity, considering various spacings between the cavity sidewalls and the outermost jet hole. The design parameters in this study include the ratio of the jet hole pitch to jet hole diameter of 7.1, 10.0, and 16.7, and the ratio of the distance between the jet and impingement plates to jet hole diameter of 2, 6, and 10, with the Reynolds number based on the jet hole diameter ranging from 2500 to 15,000. Heat transfer characteristics in the stagnation region and wall jet region were examined using local Nusselt number distributions on the impingement surface, measured by liquid crystal thermography. The local Nusselt number was high in the stagnation region and decreased radially from the stagnation region as the wall jet region formed. The closer the outermost jet hole is to the sidewall, the higher the Nusselt number on the impingement surface near the sidewall. Moreover, the flow structure in the rectangular cavity was numerically investigated, and the velocity vectors and streamlines showed that primary and secondary vortices were generated in the middle of two neighboring jets and near the sidewall, respectively. This study also assessed previous average Nusselt number correlations. Based on experimentally determined average Nusselt number data with 54 center unit cells and 1296 side unit cells, new correlations to predict the average Nusselt number on the impingement surface in a rectangular cavity with effusion holes were developed.

The dramatic advancement of autonomous engineering systems has fueled a surge of research interest in materials and structures embodying intelligence within the mechanical domain. Fundamental to achieving this mechanical intelligence is the ability to process information using the mechanics and dynamic characteristics of structures, such as wave propagation. While utilizing elastic waves for information processing and computing is a promising concept, a critical issue for current platforms is the lack of robust wave transmission that is insensitive to material or structural imperfections. The goal of this research is to overcome this obstacle by leveraging the extraordinary elastic wave control capabilities of higher-order topological metamaterials. More specifically, this work uncovers a novel approach that harnesses multimodal higher-order topological states to achieve robust and frequency-selective mechanical logic. Multimodal resonance is engineered into a 2D higher-order topological metamaterial to create 0D corner states that emerge in eight distinct frequency bands and have a rich collection of displacement field characteristics. A new phase-engineering strategy is synthesized that encodes binary information within the corner states to achieve eight fundamental mechanical logic gates. Crucially, this approach produces an easily detectable mechanical signal due to the temporal and spatial confinement of the higher-order topological states. The multifaceted frequency-dependent features of the corner states are innovatively employed to provide the logic gates with frequency-selective functionality and parallelize unique logic operations across multiple frequency channels. The mechanical logic uncovered in this study will pave the way for future intelligent structures that are much more resilient to cyberattacks and harsh environments, as compared to current systems that are built solely on electronics-based logic.

High-Performance Ring Parts (HPRPs) are widely used in various critical industrial fields, which require good surface quality and dimensional accuracy. The fine finishing of HPRPs is crucial in modern manufacturing. For traditional finishing methods, it is necessary to process the inner and outer surfaces separately due to the clamping. This paper reports on the floating clamp used in barrel finishing to realize the rotation of the ring workpiece by friction driven and uniform finishing of the outer surface and inner surface simultaneously. This work focuses on the finishing mechanism of the ring workpiece, which was rotated stably by friction driven. The constraint rule for the stable rotation of the ring workpiece was clarified by theoretical, simulation, and experimental methods. Subsequently, the action mode and strength of media on the inner and outer surface were studied by contact pressure distribution. Results show that the action strength of media on the inner surface is more significant than that on the outer surface. The finishing experiment is performed on the GCr15 ring workpiece under the condition that the distribution circle diameter is 70 mm, the number of support bars is 6, the angular speed of vessel is 60 rpm, and the filling level is 70 %. The surface roughness, topography, and morphology of finished and unfinished workpiece were analyzed to understand the finishing mechanism. It was found that the cutting induced by sliding is the dominant finishing mechanism of the inner surface, while the micro-ploughing and plastic deformation induced by impact are the dominant finishing mechanism of the outer surface.