Owing to their inherent multiscale characteristics, cracks in fiber-reinforced composites initiate and propagate normally at the microscale level during loading, spanning spatial scales up to the macroscopic fracture failure of the material. Motivated by this phenomenon, this study proposes a collaborative multiscale phase-field (CMPF) approach to model the trans-scale fracture propagation of fiber-reinforced composites. The CMPF model includes a region-based phase-field model for characterizing matrix cracking, fiber breaking, and interface debonding at the microscale; a two-modes phase-field model for characterizing the axial and transverse fracture modes at the macroscale; and a bridging model for exchanging information (fracture modes, nonlinear stress–strain relationship, and strain levels) between the macro- and micro-models. Specifically, the real-time attenuation mechanical properties of the composite caused by crack propagation are first obtained at the microscopic scale and then transferred to the macroscopic two-modes phase-field model to map the trans-scale fracture propagation. The CMPF model is implemented within a finite-element package for numerical calculations and then applied to analyze the tensile-fracture behavior of needled carbon/carbon composites, which is a typical type of fiber-reinforced composite. The calculated results show that the transverse fracture mode nucleates successively within the needled region and then in a 90° nonwoven cloth layer, whereas the axial fracture mode arises within a 0° nonwoven cloth layer. The source of the transverse fracture is matrix cracking and that of the axial fracture is fiber breaking at the microscopic scale. In addition, the fracture properties and overlap of the needled region significantly affect the propagation paths of cracks, thus changing the strength and toughness of the composite. This CMPF model offers a promising approach for modeling and understanding the trans-scale fracture mechanisms of fiber-reinforced composites.
Molecular dynamic studies of the micromechanical response of titanium–aluminum layered twin structures and graphene
Tinghong Gao, Hong Huang, Jin Huang, Qian Chen, Qingquan Xiao
doi:10.1016/j.mechmat.2024.105050
钛铝层状孪晶结构与石墨烯微力学响应的分子动力学研究
The nanotwin structure and graphene (Gr)-reinforced phase can significantly enhance the mechanical properties of the material. However, there have been relatively few studies on the mechanisms underlying the strengthening resulting from the interaction between these two components in titanium–aluminum (TiAl) alloy materials. Here, molecular dynamics (MD) simulations were employed to investigate the mechanical properties and microstructural evolution of nanotwinned TiAl/Gr (nt-TiAl/Gr) composites under uniaxial loading. The study investigated the influence of Gr layer number and temperature on composite properties. Results demonstrate that the twin boundary structure interacts with graphene, enhancing mechanical properties synergistically. Relative to pure nt-TiAl, the maximum tensile strength increased by 7.42%, 24.66%, and 35.86% for varying Gr layers. Furthermore, the mechanical properties of nt-TiAl/Gr composites exhibit an inverse correlation with temperature, where maximum tensile strength decreases with temperature elevation. The synergy between Gr and the twin structure significantly inhibits dislocation diffusion and diminishes dislocation nucleation, thus improving the properties of the composite.
Composite honeycomb sandwich panels (CHSPs) have been widely used in the aerospace industry owing to their lightweight and superior mechanical properties. However, these CHSPs are susceptible to impact damage, leading to a significant reduction in compressive strength and potentially jeopardize aircraft safety. It is crucial to investigate repair methods for CHSPs with impact damage. This paper aims to evaluate the repair performance of CHSPs with impact damage through an analysis of their compressive failure behaviors. To accomplish this, both experimental tests and advanced numerical models are employed. The numerical models for the intact, damaged and stepped-scarf repaired CHSPs are established using the progressive failure analysis model, cohesive zone model and sandwich plate theory. A good agreement is observed between the experimental results and numerical predictions of compressive failure behaviors. Moreover, the validated numerical models are successfully utilized for determining optimum repair parameters by parametric analysis of the repaired CHSPs. The establishment of these numerical models offers an accurate and cost-effective evaluation of repair performance for CHSPs with impact damage, highlighting the novelty and main contribution of this paper.
The increasing attention towards 3D-printed fibre-reinforced thermoplastic composite structures is due to their superior characteristics, ability to produce intricate architectures, repeatability, and short lead times. This experimental study aims to investigate the mechanical and dynamic behaviours of 3D-printed composite structures under tensile and impact tests. Different types of specimens are designed, including Onyx layers, triangular infill patterns (30% and 40% infill density), and continuous carbon fibre layers (two, four, six, and eight layers). Scanning electron microscopy (SEM) and X-ray micro-computed tomography (μCT) analyses are conducted to visualise the morphological characterisation and observe the delamination and damage of the composite structures. The results of the study reveal that the inclusion of carbon fibre reinforcement layers increases the stiffness and tensile strength of the composite structures. Furthermore, the addition of fibre layers in the composite panels provides critical support in damage resistance against impact loading. In contrast, sandwich structures without reinforcement layers are fatally punctured by the impact force, resulting in significant damage on both the impacted and bottom surfaces. The composite sandwich panels with fewer fibre-reinforced layers and lower infill density become softer and absorb impact energy better.
Experimental investigation into demountable dry connections for fully precast frame structures through shaking table tests
Ruijun Zhang, Tong Guo, Aiqun Li
doi:10.1016/j.tws.2024.112014
全预制框架结构可拆卸干连接振动台试验研究
To fulfill the objective of reducing pollution and carbon emission while advancing the development of high-performance structural systems aligned with green building principles, an innovative demountable dry connection fully precast frame structure system was introduced in this paper. The structure is easy to assemble, can significantly enhance construction efficiency, and facilitates the upgrading and earthquake-damaged replacement of components during service. To comprehensively investigate the dynamic characteristics of this novel precast frame structure, a half-scale specimen structure was manufactured and tested on a shaking table. The seismic performance of the structure was evaluated by collecting and analyzing the data on acceleration, displacement, and strain, as well as observing the deformation and cracking of the structure. The results show that the structure performs well as designed with confined damage, and can achieve the performance target of withstanding minor earthquakes without damage and surviving severe earthquakes without collapsing. After experiencing strong earthquakes, the damage was concentrated on the concrete beams, and the damaged components were easy to demount and replace, which could extend the service life of the structure, ensure the sustainability of the structural seismic resistance, and present an effective solution for achieving environmentally conscious, green, and low-carbon construction practices.
Elastic Properties Prediction of Two- and Three-Dimensional Multi-Material Lattices
Parham Mostofizadeh, Robert A. Dorey, Iman Mohagheghian
doi:10.1016/j.tws.2024.112015
二维和三维多材料晶格的弹性特性预测
Advances in multi-material additive manufacturing have opened unprecedented new opportunities for the design and manufacture of lightweight multifunctional structures. The ability to create complex topologies, at a relatively fine resolution, in addition to controlling the material composition on a voxel basis have significantly expanded the design space. To explore this large design space efficiently, accurate and cost-effective modeling tools are essential. In this paper, mechanics-based models for predicting the elastic properties of multi-material 2D and 3D lattice structures are developed or extended. The outcomes are compared with the predictions obtained from finite element models and experimental data. The results reveal that the adapted analytical models demonstrate good accuracy in predicting the elastic modulus of multi-material lattices for relative densities up to approximately 25% while have considerably less computational cost compared to finite element using solid elements (providing the most accurate results in comparison with experiment). Careful consideration of the accuracy of the predictions is necessary for the use of these models for lattices with high relative density values. Besides, several homogenization-based models were studied to investigate their applicability to multi-material lattice structures when the assumption of scale-separation is considered valid. The capability of these models in predicting the whole elasticity tensor and the potential of multi-material lattices in manipulating the anisotropy are demonstrated. Finally, the introduced prediction frameworks are compared in order to provide an overview of their respective advantages and disadvantages in the case of multi-material lattice structures.
Elastic wave demultiplexer with frequency dependent topological valley Hall edge states
Zheng Wu, Jiyue Chen, Weihan Wang, Jie Xu, Shixuan Shao, Rongyu Xia, Zheng Li
doi:10.1016/j.tws.2024.111997
具有频率相关拓扑谷霍尔边缘态的弹性波解复用器
Valley Hall topological insulators (VHTIs) hold great promise for enhancing the manipulation of elastic wave propagation by their intrinsic topologically protected mechanism. Different from most of VHTIs designed by the deterministic Dirac degeneracy, a more flexible design of VHTIs is proposed by the accidental Dirac degeneracy to steer elastic wave propagation. Based on the accidental Dirac degeneracy, a kind of hexagonal phononic crystal is designed to independently control the topological phase transitions at different frequency ranges. Consequently, a two-channel topological demultiplexer is designed with the function of frequency separation for flexural waves, and its effectivity is verified by numerical simulations and experimental testing. Comparing with traditional designs of demultiplexers, the VHTIs-based demultiplexer possesses a series of advantages in robust performance, easy fabrication and low energy leakage, and sheds light on developing new generation of elastic wave devices.
Review on the protective technologies of bridge against vessel collision
Wen Zhe Zhang, Jin Pan, Javier Calderon Sanchez, Xiao Bin Li, Ming Cai Xu
doi:10.1016/j.tws.2024.112013
桥梁船舶碰撞防护技术综述
The collisions between bridges and ships might cause severe damage to both of them, which is impossible to avoid completely, although several specifications or requirements need to be followed in the design of bridges and during the navigation of ships passing bridge. Many researches on protective technology had been conducted to reduce the potentially disastrous consequences. These technologies can be broadly categorized into two main types: the technologies of collision avoidance, which try to reduce the collision possibility by warning the passing ship that might impact the bridge; and passive collision protections, which use protective structures to minimize the damage of bridge and ship due to impact. The purpose of the present paper is to systematically summarize both classifications and then provide insights into their characteristics, advantages, disadvantages, and suitable conditions for application. Additionally, the related approaches originally designed for other applications but with potential relevance are also discussed, such as ship-ship collision avoidance. This review can serve as meaningful guidance and reference for future research and realistic engineering applications.