Composite materials

Summary

A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or physical properties and are merged to create a material with properties unlike the individual elements. Within the finished structure, the individual elements remain separate and distinct, distinguishing composites from mixtures and solid solutions. Typical engineered composite materials include: Reinforced concrete and masonry Composite wood such as plywood Reinforced plastics, such as fibre-reinforced polymer or fiberglass Ceramic matrix composites (composite ceramic and metal matrices) Metal matrix composites and other advanced composite materials There are various reasons where new material can be favoured. Typical examples include materials which are less expensive, lighter, stronger or more durable when compared with common materials, as well as composite materials inspired from animals and natural sources with low carbon footprint. More recently researchers have also begun to actively include sensing, actuation, computation, and communication into composites, which are known as robotic materials. Composite materials are generally used for buildings, bridges, and structures such as boat hulls, swimming pool panels, racing car bodies, shower stalls, bathtubs, storage tanks, imitation granite, and cultured marble sinks and countertops. They are also being increasingly used in general automotive applications. The most advanced examples perform routinely on spacecraft and aircraft in demanding environments. The earliest composite materials were made from straw and mud combined to form bricks for building construction. Ancient brick-making was documented by Egyptian tomb paintings. Wattle and daub is one of the oldest composite materials, at over 6000 years old. Concrete is also a composite material, and is used more than any other synthetic material in the world. , about 7.

Photocured Nanocellulose Composites: Recent Advances

Yves Leterrier, Aigoul Schreier, Mohammed Arif Poothanari, Julien Bras

This perspective gives an overview of recent progress in thefield of photocured polymer composites based on variousforms of nanocelluloses, with a focus on cellulose nanofibrils. The manufacturing processes and performances of these nanocellulosecomposites are detailed, comprising solvent-assisted mixing processes, emulsification, coating and casting processes, preformimpregnation, and 3D printing. Attention is also paid to life-cycle engineered approaches to improve their sustainability. Thesematerialsfind applications in numerous domains, primarily as protective coatings but also as diffusion barrier composites andfilmsfor packaging and encapsulation of electronics, as composite hydrogels for biomedical applications, and as membranes for battery technologies.

AMER CHEMICAL SOC2022

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Micromechanical homogenization is often carried out with Fourier-accelerated methods that are prone to ringing artifacts. We here generalize the compatibility projection introduced by Vond.rejc et al. (2014) [24] beyond the Fourier basis. In particular, we formulate the compatibility projection for linear finite elements while maintaining Fourier-acceleration and the fast convergence properties of the original method. We demonstrate that this eliminates ringing artifacts and yields an efficient computational homogenization scheme that is equivalent to canonical finite-element formulations on fully structured grids. (C) 2021 The Author(s). Published by Elsevier Inc.

ACADEMIC PRESS INC ELSEVIER SCIENCE2022

A large number of aging road and railway riveted metallic bridges suffer from fatigue problems. Stringer-to-floor-beam double-angle bridge connections are among the most fatigue-prone details due to the many cyclic distortion-induced stresses from axle loads. Increasing service loads and corrosion put these components at a higher risk of fatigue cracking. As the replacement of existing structures is costly, lengthy, and thus in some cases almost impossible, the development of retrofitting techniques is of great importance. However, fatigue strengthening of angle connections in bridges is a challenging task. The geometric complexities of these details hinder the development of applicable retrofitting techniques, and the multiaxial stress state in connections complicates fatigue analysis.The first objective of this work is to develop an applicable retrofitting system for strengthening the stringer-to-floor-beam double-angle connections in bridges, considering the fact that the traditional retrofitting techniques such as stop holes, welding additional elements or the softening of connections are not capable of effectively tackling the problem. In recent decades, the application of carbon fiber-reinforced polymer (CFRP) composites has attracted much interest for the fatigue strengthening of metallic structures owing to their superior properties such as high strength, light weight, high corrosion and fatigue resistance. The strengthening system developed in this study consists of a new adhesive-free mechanical wedgeâbarrel anchor for prestressed CFRP rods and a friction-based clamping system. Extensive finite element simulations are performed to optimize the design of the strengthening system. In addition, the static and fatigue performance of the developed system is experimentally investigated in laboratory tests. The ultimate tensile strength of the strengthening system is found to be greater than the nominal strength of the CFRP rods, which ensures achieving the full capacity of the CFRP rod strength. In addition, the fatigue tests show neither failure of the CFRP rods nor prestressing loss due to slippage in the anchorage components.The second objective is to determine the high-cycle fatigue thresholds for the prediction of crack initiation in angle connections subjected to multiaxial stresses. The critical plane approach is employed as an advanced approach for multiaxial high-cycle fatigue analysis. In addition, the effect of prestressed strengthening is incorporated into multiaxial fatigue models. Using identified proper critical plane-based multiaxial fatigue thresholds, a design approach is proposed for the fatigue strengthening of angle connections subjected to distortion-induced multiaxial stresses. Finally, the third objective is to apply the developed retrofitting system to strengthen the connections of a 92-year-old riveted railway bridge in Switzerland as a demonstration of a field application. The results of the short-term measurements demonstrate the effectiveness of the retrofitting system in improving the high-cycle fatigue behavior of the bridge connections through the reduction of the mean values of the stress components. The post-installation long-term measurements show no prestressing loss in the CFRP rods, indicating that no slippage occurs in the strengthening system components.

EPFL2021