今日更新：International Journal of Solids and Structures 1 篇，Journal of the Mechanics and Physics of Solids 3 篇，International Journal of Plasticity 1 篇，Thin-Walled Structures 3 篇
International Journal of Solids and Structures
Machine learning predictions on the compressive stress–strain response of lattice-based metamaterials
Lijun Xiao, Gaoquan Shi, Weidong Song
doi:10.1016/j.ijsolstr.2024.112893
格基超材料压缩应力-应变响应的机器学习预测
Predicting the stress–strain curve of lattice-based metamaterials is crucial for their design and application. However, the complex nonlinear relationship between the mesoscopic structure of lattice materials and their macroscopic mechanical behavior makes prediction challenging. In this study, beam element models of over 20,000 lattice structures were established using Python scripts, and calculations were performed in ABAQUS to obtain training and testing datasets. The spatial features of each lattice-based metamaterial were then encoded into a graph, a data structure recognizable by machine learning algorithm. Utilizing machine learning methods, a Structure to Sequence Neural Network was constructed and trained, achieving rapid prediction of the compressive stress–strain curves for lattice-based metamaterials. Afterwards, several lattice structures were randomly selected and 3D printed. The accuracy of the simulation results as well as machine learning predictions was validated through quasi-static compression experiments. It is revealed that the proposed Neural Network model outperforms the traditional Artificial Neural Networks as the errors are reduced while the Coefficient of Determination is higher. The results demonstrate the accurate fitting between the complex spatial features of the lattice-based metamaterials and their stress–strain curves, which provides a potential methodology for inverse optimization of the lattice-based metamaterials in the future.
The emergence of heterogeneous nanostructured materials (HNMs) offers exciting opportunities to achieve outstanding mechanical properties. Among these materials, gradient nanotwinned (GNT) Cu is a prominent class of HNMs, demonstrating superior strengths by gaining extra strengths compared to non-gradient counterparts. Its layered gradient structure provides a simplified quasi-one-dimensional model system for understanding the extra strengthening effects of structural gradients and resulting plastic strain gradients. This paper presents a comprehensive report for recent experimental and modeling studies on the mechanics of GNT Cu, covering advances in controlled material processing, back stress measurement, deformation field characterization, dislocation microstructure analysis, and strain gradient plasticity modeling. These studies unveil the spatiotemporal evolution of both plastic strain gradients and extra back stresses originating from structural gradients. Direct connections are established between the sample-level extra strength of GNT Cu and the synergistic strengthening effects induced by local nanotwin structures and their gradients. We emphasize the critical role of the representative volume element size in assessing the effects of plastic strain gradient and extra back stress. Moreover, lower-order strain gradient plasticity models are validated through experimental characterizations of GNT Cu, paving the way for future investigation into the mechanics of gradient nanostructured metals. Finally, we provide an outlook on research needs for understanding the mechanics of gradient nanostructured metals and, more broadly, HNMs, towards achieving exceptional mechanical properties.
The applications of soft materials in various fields often require interfacial adhesion to sustain prolonged static or cyclic loads, whereas most existing adhesives are susceptible to fatigue failure. Unlike in a quasistatic debonding process, which depends more on the average resistance, the key to preventing fatigue crack propagation is to build up high energy barriers locally. Herein, we invoke three types of structural designs to induce large energy barriers at the interface to achieve fatigue-resistant adhesion. By varying the local bending stiffness of the backing layer, locally altering the fracture mode through kirigami patterns, or hindering crack initiation with simple edge notches, we enhanced the fatigue thresholds of various adhesives against peeling by several orders of magnitude, reaching record-breaking values. To verify the proposed mechanism and reveal the details of these remarkable enhancements, we develop theoretical models to study the peeling processes. Based entirely on structural design, the proposed mechanism is non-material-specific and universally applicable to various intermolecular interactions under any harsh environment, such as high temperature, high humidity, and physiological environments. We envision that the strategy and methodologies presented can pave the avenue of future adhesion designs for both durability and reliability.
Bending Stiffness of Ionically Bonded Mica Multilayers told by its Bubbles
Baowen Li, Wang Tan, Chun Shen, Yuyang Long, Zhida Gao, Jiajun Wang, Wanlin Guo, Jun Yin
doi:10.1016/j.jmps.2024.105723
离子键合云母多层膜的弯曲刚度由其气泡决定
Revealing the bending stiffness of layered materials is crucial for guiding their applications with notable out-of-plane deformation, such as in flexible electronics. To this end, dedicated methods have been developed, but usually involving precise manipulation of atomically thin flakes or cross-section characterization with atomic resolution, hindering their widespread adoption. Here, we utilize mica as a case study to demonstrate that bubbles spontaneously formed during mechanical exfoliation provide a facile but reliable approach for investigating its bending mechanics. Through topographical analysis of bubbles with widely distributed sizes, a bending stiffness is extracted following a nonlinear plate theory. The less bending stiffness than the ideal non-linear plate solution indicates a moderate interlayer slip, as confirmed by molecular dynamics simulations. The interlayer shear coefficient for mica is higher than that for multilayer graphene, which is attributed to its strong interfacial shear strength inheriting from its interlayer ionic bonding.
As deformation twins have a profound impact on the plastic flow and mechanical properties of metallic materials, enhancing deformation twinning in face-centered cubic (FCC) metallic materials has long served as a unique microstructure design strategy to attain an extraordinary strength-ductility synergy. Deformation twinning, however, rarely occurs in pure FCC Al and its alloys since its generalized planar fault energies (GPFEs) are almost unaffected by most soluble alloying elements such as Mg, Zn and Cu. Here we successfully tune the GPFEs of a nanocrystalline Al-Mg alloy by alloying with Zr, Fe or Y element, and enable deformation twinning in the Zr-, Fe- and Y-containing alloys. Based on a combined analysis of microscopic observations, modeling and ab initio calculations, we find a strong grain-size-dependent twinning (i.e., twinning occurs in preferable grains having sizes in the range ∼20-40 nm), as well as only one single twinning plane (i.e., twinning occurs in single, parallel atomic planes) for twin formation rather than intersecting twinning planes (i.e., twinning occurs in multiple, unparallel atomic planes) usually observed in coarse-grained FCC materials. This interesting twinning behavior is further observed to be accompanied by grain rotations, producing defective twin boundaries. Our experimental results extend the current understanding of the plastic deformation mechanisms in nanograined metallic materials, and will guide microstructure design of twinnable nanograined Al alloys with an improved strength-ductility synergy.
Isogeometric material optimization for shape control of bi-directional functionally graded plates with piezoelectric layers
Liangliang Ma, Chao Wang, Yun Chong, Wenfeng Hu, Lei Zeng
doi:10.1016/j.tws.2024.112067
压电层双向功能梯度板形状控制的等几何材料优化
This paper proposes an effective numerical method for shape control of bi-directional functionally graded plates (2D-FGPs) with piezoelectric layers. Isogeometric analysis (IGA) based on non-uniform rational B-splines (NURBS) related to third-order shear deformation theory (TSDT) is employed for the static analysis of the 2D-FGPs with piezoelectric layers. The B-spline basis functions are utilized to represent the distribution of the ceramic volume fractions, where the control points placed along the plane corresponding to the ceramic volume fraction and the applied voltages are taken as the design variables. In addition, an improved moth flame optimization algorithm is utilized to solve the optimization problem of minimizing the static shape error, which effectively balances the exploratory and exploitative capabilities of the algorithm. Various numerical examples of square, skew, and dart-shaped 2D-FGPs are analyzed to validate the proposed method and demonstrated the superior mechanical performance of 2D-FGPs over 1D-FGPs.
Dynamic modeling and vibration suppression evaluation of composite honeycomb hemispherical shell with functional gradient protective coating
Hui Li, Jichuan Cao, Jintong Han, Jinghan Li, Yao Yang
doi:10.1016/j.tws.2024.112066
功能梯度防护涂层复合材料蜂窝半球形壳动力学建模及抑振评价
The vibration reduction performance of composite honeycomb hemispherical shells (CHHSs) coated with functional gradient protection coating (FGPC) are investigated in this work. Using the first-order shear deformation theory and the power-law distribution rule, the virtual spring technique, the regional decomposition method, and the Newmark-Beta approach, etc., a dynamic model of the FGPC-CHHSs under base excitation is formulated to solve the inherent characteristics and displacement responses in time and frequency domains. After a set of convergence analyses are completed to ascertain an appropriate segment number and the stiffness values of virtual springs employed in the predictive model, the forecasted vibration parameters are verified using the literature and experimental results that are performed on uncoated and coated shells. The maximal natural frequency errors of the current model compared to the experimental results are 3.8 % and 4.8 %, and the displacement response errors under different excitation amplitudes are less than 10.3 % and 12.7 %, respectively, which demonstrate the correctness of such a model. Finally, the impact of key structural and material parameters on the vibration behaviors of the FPGC-CHHSs is evaluated. To improve their vibration suppression capability, it is recommended to choose a high gradient index of coating material and a large thickness ratio of the FGPC to the overall shell with a reasonable moduli ratio of Material A to Material B of the FGPC to improve vibration reduction capability. This study offers a practical model tool and several important design recommendations for vibration prediction and dynamic attenuation of honeycomb sandwich hemispherical shell structures in aerospace engineering.
In recent years, as space is being explored more frequently, various spacecraft have been launched into space. Space debris and radiation in the universe as well as the irregular activities of the sun, such as solar flares and solar storms, can have serious effects on spacecraft. Protective shields are a favorable measure to protect spacecraft from space debris, radiation, and other damage. In this study, a protective shield for spacecraft is first proposed inspired by the behavior of mollusks. The concept of origami is then introduced for the folding and unfolding scheme design. The protective shield has a certain thickness, although its thickness is not significant and can be considered a thin-walled structure, it cannot be treated as zero-thickness origami since even a small thickness can cause issues such as motion interference. This study proposes three guidelines for thickening panels. Through the derivation of spatial geometry, a method to make the spatial curved surface thickening is presented. This method perfectly solves the compatibility problem of vertices in thickening, while making each panel manufacturable. After that, based on space vectors, a computational method for determining whether motion interference occurs in thick-panel curved origami is proposed, and the conditions for preventing motion interference are given. The accuracy and effectiveness of the proposed methods are verified by numerical simulations, and the complete unfolding and folding process of the deployable protective shield is also demonstrated. The methods proposed in this paper are all general and can be easily generalized to further and more complex situations. Finally, a case is shown where the deployable protective shield can be applied to a spacecraft like the Spitzer Space Telescope.
