Experimental characterization of phenolic-impregnated honeycomb sandwich structures for transportation vehicles

In the present paper the main outcomes of an experimental characterization on phenolic impregnated honeycomb sandwich structures are presented. The experimental investigations addressed both the static and dynamic properties of novel sandwich material, manufactured expressly for transportation industry and both the structural and impact behavior of the sandwich configuration. Moreover in order to fulfill design requirements, the prediction of the material properties and structural behaviors of sandwich structures due to environmental degradation have been assessed using accelerated aging tests. The outcomes herein presented provide information for the modification of design parameters to minimize the influences of the environmental factors and the adverse effect of in-service impact events.     

The interaction of ultrasound with imperfect interfaces: Experimental studies of model structures

Model specimens are prepared, each of which may be viewed as two sections of similar material joined imperfectly at a planar interface. Measurements of the ultrasonic reflection from, mode conversion at, and/or transmission through these imperfect interfaces, are reported. The interface structures include distributions of pores, contacts, and inclusions. Included are both near-periodic and random cases. As the frequency is increased, the measured reflection coefficients generally show an initially linear increase from zero, followed by a maximum which may exhibit multiple peaks, and a subsequent decay. These results are interpreted in terms of a quasi-static model and an independent scattering model for ultrasonic interactions with imperfect interfaces.     

光触发增强葡萄糖氧化酶催化活性的等离子体囊泡用于程序化光热-饥饿疗法

在肿瘤的饥饿治疗及协同治疗中,基于葡萄糖氧化酶(GOx)的纳米诊疗剂展现出具大的应用前景.自组装等离子体金囊泡(GV),由于具有独特的光学性能、巨大空腔和强局域表面等离子体共振等特性,可作为协同治疗的多功能纳米载体.本文中,我们开发了一种装载GOx的GV(GV-GOx)用于光触发释放GOx,同时增强GOx的催化活性,从而实现程序化光热-饥饿治疗.在近红外激光照射下,由于GV具有等离子体耦合效应, GV-GOx可以产生很强的局部高热,引起封装的GOx释放,同时高热可提高GOx催化活性,从而增强肿瘤的饥饿效应.此外,高光热效应可促进细胞对GV-GOx的摄取,并可通过活体光声/光热双模态成像对协同治疗进行有效监测.令人印象深刻的是,协同光热/饥饿疗法能完全消融4T1荷瘤小鼠的肿瘤,抗肿瘤效果明显优于单一疗法,且没有明显的系统毒性.本工作展示了一种光触发的纳米平台,可用于癌症协同治疗.     

Scalable Fabrication of Superhydrophobic Coating with Rough Coral Reef-Like Structures for Efficient Self-Cleaning and Oil-Water Separation: An Experimental and Molecular Dynamics Simulation Study

Superhydrophobic coating has a great application prospect in self-cleaning and oil-water separation but remains challenging for large-scale preparation of robust and weather-resistant superhydrophobic coatings via facile approaches. Herein, this work reports a scalable fabrication of weather-resistant superhydrophobic coating with multiscale rough coral reef-like structures by spraying the suspension containing superhydrophobic silica nanoparticles and industrial coating varnish on various substrates. The coral reef-like structures effectively improves the surface roughness and abrasion resistance. Rapid aging experiments (3000 h) and the outdoor building project application (3000 m²) show that the sprayed superhydrophobic coating exhibits excellent self-cleaning properties, weather resistance, and environmental adaptability. Moreover, the combined silica-coating varnish-polyurethane (CSCP) superhydrophobic sponge exhibits exceptional oil-water separation capabilities, selectively absorbing the oils from water up to 39 times of its own weight. Furthermore, the molecular dynamics (MD) simulation reveals that the combined effect of higher surface roughness, smaller diffusion coefficient of water molecules, and weaker electrostatic interactions between water and the surface jointly determines the superhydrophobicity of the prepared coating. This work deepens the understanding of the anti-wetting mechanism of superhydrophobic surfaces from the perspective of energetic and kinetic properties, thereby paving the way for the rational design of superhydrophobic materials and their large-scale applications.     

Crack deflection analyses of different peel stopper designs for sandwich structures

This paper relates to a newly developed peel stopper concept for sandwich structures. The proposed concept is a specially designed core insert, which has the ability to confine face sheet debonding/delamination (peeling) by deflecting a delamination crack front away from the face/core interface into the bulk of the sandwich core, and thereby constraining the debonding/delamination to a limited prescribed area. In this paper various peel stopper designs are analysed for their ability to deflect cracks away from propagating along a face–core interface. The crack deflection ability of the studied peel stopper designs leads to design guidelines, which describes the minimum requirements regarding the relation between the two interface toughnesses. The analysis further reveals that compliant peel stopper wedges are preferred because they lead to the lowest interface toughness ratio requirement. This has been confirmed through an experiment with a sandwich beam subjected to three-point bending loading. The experiment has shown that the ability of a peel stopper to deflect cracks is highly dependent on the stiffness of the wedge.     

Experimental study and finite element analysis of the elastic instability of composite lattice structures for aeronautic applications

The work presented in this paper is focused on the finite element modelling (FEM) of the failure behaviour of lattice composite hollow structures that have been subjected to an external hydrostatic pressure. Furthermore, the development of an experimental procedure to measure the aforementioned resistance, and to test the FEM model is also presented. Carbon fibres composite hollow cylinders with a lattice structure and with different geometries were produced and tested. In order to develop a design tools for such structures, all the experiments performed were computer simulated using finite element modelling. The results obtained with FEM simulation provide further insight to analyze and investigate the failure mechanism. The elastic instability of the studied structures was therefore analyzed and the influence of element geometry on the collapsing resistance thereof was considered. As a result of the study it has been possible to locate three different failure modes which where strictly related to the length of the cylinders. Both the shape of the broken tube and the lever of failure stresses were correctly predicted by the FEM model.     

填充吸波泡沫的碳纤维复合材料格栅结构吸波性能计算

采用空间回路网法计算得到填充吸波泡沫的碳纤维复合材料格栅结构的电磁散射性能。根据格栅结构的周期性排布特征,采用Floquet 定理分析结构的周期性边界条件,将计算模型简化为一个周期单元进行电磁场分布计算。通过计算结果分析结构在不同频率、不同单元体尺寸下的吸波性能。计算表明：对于含吸波泡沫的复合材料格栅结构,其吸波性能明显好于未填充结构;格栅单元中所填充的泡沫厚度以及泡沫体积分数是影响格栅结构吸波性能的2个主要因素。     

Experimental study of hydrogen embrittlement on AISI 304 stainless steels and Rayleigh wave characterization

Many failures due to hydrogen embrittlement or hydrogen damage are widely reported in oil and refinery industry. Despite many ultrasonic testing methods have been developed to assess hydrogen embrittlement, they are applied well to serious hydrogen attack instead of earlier degradation. This paper aims to characterize nascent hydrogen embrittlement of AISI 304 austenitic stainless steels under cathodic hydrogenation using Rayleigh wave. After cathodic hydrogen charging of AISI 304 stainless steel, XRD and metallographic examination show that martensite transformation occurs within the subsurface region of the specimens. Microhardness testing indicates that hydrogen leads to hardening of the material. It is found that Rayleigh wave are better to inspect local degradation than bulk waves. Rayleigh wave velocity of 5 MHz and 10 MHz decreases significantly with cathodic charging time, while longitudinal wave velocity changes not. Acoustic velocity change is due to elastic modulus reduction resulting from hydrogen-induced phase transformation in the subsurface region.     

预应力FRP加固工程结构技术研究进展

围绕国内外预应力FRP加固技术的研究现状以及最新进展,从预应力FRP加固混凝土结构、预应力FRP加固钢结构、预应力FRP加固中关键技术的研究等方面进行了综述。试验研究表明：预应力FRP加固混凝土能显著提高构件的开裂荷载、屈服荷载和极限荷载,改善受弯构件在长期荷载的力学性能,提高构件的疲劳寿命;预应力CFRP加固钢梁后,其屈服荷载和极限荷载相对于对比梁都有明显的提高,其提高的程度随着预应力CFRP的用量和预应力水平的提高而增大;预应力CFRP加固对钢梁的刚度提高作用也比较明显,对低强度的钢材,提高效果更明显;采用预应力FRP加固工程结构的关键问题在于预应力的施加体系、预应力控制值、预应力损失和端部的锚固。     

Review of the mathematical background to the development of realistic load histories for fatigue testing relevant to tubular structures in the North Sea

Following the discovery of oil and gas, fixed welded tubular steel platforms were first installed in the North Sea in 1966. They are subjected to significant fatigue loads due to wave action. A report on proposed standard load histories was published in 1976. These were based on theoretical calculations. In 1979, increasing interest led to the formation of the Wave Action Standards History (WASH) Working Group. Strain gauge data for platforms in the North Sea were made available to the Working Group so later standard load histories were based on service data rather than theoretical calculations. Mathematical techniques used are reviewed, and some load histories are described as case studies. A framework was developed that could be used to formulate a particular standard load history but left open the option of incorporating alternative features, with relatively little additional work.     

Stability and structures of the CFCC-TmC phases: A first-principles study

The η-M₆C, γ-M₂₃C₆, and π-M₁₁C₂ phases (M = Cr, Mn and Fe) have complex cubic lattices with lattice parameters of approximately 1.0 nm. They belong to the CFCC-TmC family (complex face-centered cubic transition metal carbides), display a rich variety of crystal structures, and play in important role in iron alloys and steels. Here we show that first-principles calculations predict high stability for the γ-M₂₃C₆ and η-M₆C phases, and instability for the π-M₁₁C₂ phases, taking into account various compositional and structural possibilities. The calculations also show a wide variety in magnetic properties. The Cr-containing phases were found to be non-magnetic and the Fe-phases to be ferromagnetic, while the Mn-containing phases were found to be either ferrimagnetic or non-magnetic. Details of the local atomic structures, and the formation and stability of these precipitates in alloys are discussed.     

The universal scissor component: Optimization of a reconfigurable component for deployable scissor structures

Deployable scissor structures are well equipped for temporary and mobile applications since they are able to change their form and functionality. They are structural mechanisms that transform from a compact state to an expanded, fully deployed configuration. A barrier to the current design and reuse of scissor structures, however, is that they are traditionally designed for a single purpose. Alternatively, a universal scissor component (USC)—a generalized element which can achieve all traditional scissor types—introduces an opportunity for reuse in which the same component can be utilized for different configurations and spans. In this article, the USC is optimized for structural performance. First, an optimized length for the USC is determined based on a trade-off between component weight and structural performance (measured by deflections). Then, topology optimization, using the simulated annealing algorithm, is implemented to determine a minimum weight layout of beams within a single USC component.     

On the application of the probability transformation method for the analysis of discretized structures with uncertain proprieties

The aim of this work is to show a novel approach for the analysis of random systems. This approach, based on the application of the Probabilistic Transformation Method (PTM), is here developed for the study of uncertain structural systems. These systems are characterized by the fact that some of their geometrical and/or mechanical properties can be characterized only by a probabilistic point of view. In particular, the goal of the proposed approach is the evaluation of the probability density function (pdf) of a single response quantity avoiding the onerous operation of the variable saturation, which is necessary when the classical PTM is applied.     

Cyclical parthenogenesis algorithm for layout optimization of truss structures with frequency constraints

Structural optimization with frequency constraints is seen as a challenging problem because it is associated with highly nonlinear, discontinuous and non-convex search spaces consisting of several local optima. Therefore, competent optimization algorithms are essential for addressing these problems. In this article, a newly developed metaheuristic method called the cyclical parthenogenesis algorithm (CPA) is used for layout optimization of truss structures subjected to frequency constraints. CPA is a nature-inspired, population-based metaheuristic algorithm, which imitates the reproductive and social behaviour of some animal species such as aphids, which alternate between sexual and asexual reproduction. The efficiency of the CPA is validated using four numerical examples.     

水平拼缝部位增强叠合板式剪力墙抗震性能试验研究

近年来,装配式剪力墙在实际工程中得以广泛应用。在其施工过程中,水平向相邻的两块预制墙板通常通过预留的后浇带装配在一起。该方法仍然需要大量的现场浇筑作业。因此,干式连接成为了进一步提高装配式结构施工效率和抗震性能的优化方案之一。该文针对一种新型装配式干式连接剪力墙的数值模拟及其设计方法开展了研究。建立了单层装配式干式连接剪力墙的有限元模型,并对其模拟了与前序拟静力试验相同的加载方案。模拟结果与试验结果吻合较好,从而验证了模型的有效性。基于以上建模方法,建立了2个具有不同参数的10层干式连接剪力墙的有限元模型,开展了Pushover分析,优化了干式连接件在高层结构中的设计。根据数值分析结果,提出了装配式干式连接剪力墙在高层建筑结构中基于振型的设计公式。     

Experimental study on the stitching reinforcement of composite laminates with a circular hole

Experimental study is carried out on the stitching reinforcement of composite laminates containing a circular hole. First, the tensile strength and stiffness are measured, and their dependence on stitching parameters such as stitching needle span, row spacing, edge distance and stitching type are analyzed. Next, the strain distribution and concentration are investigated analytically and experimentally for different stitching parameters, external load and edge location of the hole. It is shown that the results of stitching reinforcement are quite different for composite laminates with a circular hole, which could provide proper stitching parameters for designers.     

Experimental and numerical study of compression after impact of sandwich structures with metallic skins

A finite element model is proposed to determine the residual print of sandwich structures with Nomex honeycomb core and metallic skins indented by a spherical indenter and to simulate its behavior when this indented structure is subjected to lateral compressive loading (known as CAI/ Compression after impact). The particularities of this model rely on representing the honeycomb with a grid of non-linear springs which its behavior law calibrated from uniform compression test. This simple model, after integrating the cycle behavior law of honeycomb, allows predicting the geometry of residual print with a good precision. This model is then developed to propose a complete computation from indentation, residual print geometry to lateral compressive loading after indentation (CAI). This model also allows predicting numerically the residual strength of structure in CAI and the elliptical evolution of residual print geometry during CAI loading. A good correlation with test results is obtained except for the very small residual print depth.