Extreme Mechanics Letters最新文献

Liquid crystal elastomers (LCEs) are a novel class of materials created by combining polymeric solids with stiff, rod-like molecules known as nematic mesogens. These materials exhibit large, reversible deformations under mechanical, thermal, and optical stimuli. In this work, we develop a nonlinear beam formulation for analyzing the finite elastic deformation of beam-like structures made of LCEs under photo-actuation. This formulation applies to ideal, non-ideal, isotropic genesis, and nematic genesis LCEs. We establish the variational form of the problem based on the principle of virtual work. To solve numerical examples, we also develop a nonlinear finite element formulation based on B-spline functions. Several numerical examples are presented to demonstrate the applicability of the proposed formulation.

The pursuit of "smart" materials, drawing inspiration from biological organisms, has been a significant focal point in the realm of material science and engineering. Shape memory materials, notably Shape Memory Alloys (SMAs), have emerged as promising platforms for the development of adaptive and responsive materials that undergo transformations in response to environmental stimuli. This article explores the creation of a bioinspired morphing surface that capitalizes on the innovative amalgamation of Ecoflex and Nitinol (NiTi) wires. Inspired by biological mechanisms, this morphing surface exemplifies remarkable adaptability, seamlessly transitioning from 2D to 3D shapes with precision. A detailed mechanical characterization underscores pivotal changes in material properties, showcasing a significant reaction force increase from 0.4 N to 1 N in NiTi wires at 20 °C and 50 °C. Concurrently, the embedded NiTi wire within the Ecoflex matrix exhibits a similar force increment from 0.6 N to 1.2 N, reflecting the microstructural alterations dependent on temperature. The study also elucidates the versatility and scalability of this technology, highlighting its potential for diverse applications in aerospace, robotics, medical devices, and adaptive materials. This bioinspired morphing surface offers a versatile foundation for customizable shapes and programmable transformations, paving the way for impactful advancements in a multitude of fields.

Transcatheter aortic valve replacement (TAVR) has emerged as a promising treatment option for aortic stenosis. However, the prevalent stent used for valve placement restricts the post-release adjustment or movement of the artificial valve, increasing the potential risk to patients once accidental mispositioning occurs. Herein, we propose a 4D printing strategy to realize a proof-of-concept thermal-activated transcatheter aortic valve (TAV) stent that allows for programmable manipulation. Polylactic acid/polyurethane composites are directly printed to perform as the active units that tailor the configuration of the programmable TAV stent, accommodating to different tasks such as blood vessel navigation and topological fixation with cardiac cavity. A theoretical model is developed to explore the curvature evolutions of the active composite, realizing good agreement with experimental observations. Guided by the model, we seek out the optimized programming and activation conditions that allow for desired transformations to realize permanent fixation under intra-annular release and thermal-activated retraction under infra-annular release, inspiring the future development of TAV stents with shape memory principle.

The rapid advancement of micro-nano machining technology has led to a decrease in the dimensions of microdevices and microchips, following the principles of Moore’s law. In addition to conventional semiconductor materials like silicon, emerging nanoscale materials such as nanowires, nanotubes, and two-dimensional materials are being considered as promising alternative constituent materials. The mechanical properties of these materials have a significant impact on the performance and service life of these microdevices and microchips. However, conventional mechanical testing methods have difficulty in accurately measuring the properties of these materials at the nanoscale due to limitations in displacement control and microforce sensing. Consequently, there is an urgent need to develop a micromechanical device capable of testing nanoscale solid materials. In this study, we propose a concept based on high-resolution image sequences for the design of an integrated micromechanical device capable of synchronously measuring the force and deformation of tested specimens. The device has been fabricated using ultrafast femtosecond laser etching technology, which offers an efficient and cost-effective approach for manufacturing microstructures and is suitable for processing various materials such as metals and nonmetals. The stiffness of the device plays a crucial role in the design of the micromechanical device, and a stiffness-matching criterion is introduced to ensure appropriate design parameters. The fabricated device is employed to conduct in-situ tension experiments on SiC nanowires and multilayer molybdenum disulfide nanosheet within a scanning electronic microscope, enabling accurate measurement of their strength, modulus, and fracture strain.

Stick-slip friction exists widely in our life especially the occurrence of large earthquakes, but people cannot predict and control by a limited understanding of the mechanisms involved. In the present work, the whole process of stick-to-slip transition has been investigated through digital image correlation and acoustic emission. Two phases, namely, the nucleation and abrupt rupture phases have been discovered during the transition that are characterized well by nucleation and transient emission of dislocations, which may support the combination of pre-slip and cascade-up models. Based on the findings simple yet analytical expressions then have been obtained to predict the earthquake cycles consistent with available simulations and practical observations.