Abstract A sandwich structure comprises layered composite materials formed by bonding two or more thin facings or face sheets to a relatively thick core material. Topics discussed in this article include: sandwich panel failure modes, nomenclatures and definitions, strength checks, stiffness and internal loads, flat panels under pressure loading, curved sandwich panels, local strength analysis methods, and flat panel stability.
Abstract Hygrothermal behavior of cured composite materials relates to the combined and commonly synergistic effects of moisture absorption and temperature on various physical, chemical, and mechanical properties. This article concentrates on polymer-matrix composites and is limited to the effects of moisture absorption after an established cure of the material has been completed. It presents general considerations in assessing hygrothermal behavior. The article focuses on hygrothermal testing and conditioning, discussing the physical and chemical effects on the composite. It also presents the variation of mechanical properties in composites.
Abstract Vacuum bag autoclave molding for producing composite parts is the oldest and most mature composite manufacturing process. This process can be used for various resin systems, monolithic and sandwich constructions, and geometries. For these reasons, the bag autoclave molding process is still a widespread and reliable process. The process has several steps, each of which is discussed in this article, including debulking, bagging, the curing procedure with autoclave operations, and debagging. Considerations for optimizing cost and quality are also discussed.
Abstract Lightweight structural cores were first used in aircraft in the 1940s to reduce weight and increase payload and flight distance. This article focuses on the three primary types of lightweight structural cores: honeycomb, balsa, and foam. In many applications, lightweight structural cores are used in sandwich panels. The article also presents an overview of various techniques available for modeling sandwich structures, providing the basic concept of a sandwich panel, where the facings carry the bending loads, and the honeycomb core carries the shear loads.
Abstract Recycling of synthetic fiber composites—primarily fiberglass and carbon-fiber systems—is a growing priority as end-of-life materials accumulate across aerospace, automotive, and wind energy industries. This article surveys the three principal recycling approaches—mechanical, thermal, and chemical—with emphasis on carbon-fiber-reinforced thermoplastic and thermoset composites, and reviews end-use applications for recycled materials including permeable pavement, porous asphalt, and commodity plastic reinforcement. Life-cycle analysis findings confirm that all recycling strategies offer environmental advantages over landfilling, with mechanical recycling remaining the most commercially viable option.
Abstract Delamination, a separation of the fiber-reinforced layers stacked together to form laminates, is one of the most commonly observed failure modes in composite materials. This article presents an overview of the characterization, analysis, and prediction of delamination in composites. It describes the common causes of delamination during manufacturing and in service.
Abstract Recycling and disposal of metal-matrix composites (MMCs) is a significant cost and environmental consideration given the high material costs relative to conventional alloys. This article focuses primarily on aluminum-matrix composites, describing recycling procedures for various scrap types, salt-flux and argon-degassing techniques for separating reinforcement phases from the matrix, and quality control measures including chemistry verification and oxide management. Disposal options for recovered aluminum and spent reinforcement phases are summarized, and emerging methods such as rotary salt furnaces and centrifugal separation are noted for other MMC systems.
Abstract Thermoplastic composites (TPCs) are becoming increasingly popular in the aerospace, automotive, and urban air mobility sectors. This is largely due to their ability to meet industry demands for high-production rates of complex parts made from advanced sustainable materials. This article offers an overview of thermoplastic welding principles and briefly describes the main welding techniques currently used to join TPC structures in the aerospace industry. Additionally, it emphasizes the advantages of using simulation tools to model thermoplastic welding processes, illustrated through a case study.
Abstract Composites with three-dimensional (3D) fiber reinforcements were first developed in the late 1960s and the early 1970s for specific high temperature applications to replace metallic alloys, offering weight-saving benefits and cost reduction. This article presents the development stages, advantages, and disadvantages of 3D woven composites. It focuses on the 3D woven preforms and their composites. Then, the mechanical behavior of 3D woven composites is discussed in detail for some specific loading cases. The article also presents several cases in the aerospace industry of 3D components that reached technology-readiness level 5 or higher, highlighting the differentiating advantages and unique properties of 3D woven composites.
Abstract As with most engineering materials, the failure of composite materials, no matter how complex, can be divided into three discrete causes: improper design, improper manufacturing, and improper use of the end product. This article discusses these three failure causes from a broad perspective so that composite designers, manufacturers, and users can readily see some of the more common issues associated with these unique materials and more efficiently organize their thoughts and actions when investigating a specific failure.
Abstract This article provides a general overview of bio-based resins, first examining biological sources for feedstocks of bio-based resin components, followed by a detailed description of five major resin classes (phenolic, furane, unsaturated polyester, epoxy, and benzoxazine resins) and their bio-based alternatives. It also describes the methods used to synthesize and modify the bio-based resins based on the biological feedstock, manufacturing processes, and properties of neat resins in comparison to fiber-reinforced composites. Then, the current work on novel bio-based vinyl ester, acrylic, and bismaleimide resins is highlighted. The article also reviews the work on the use of renewable resources to produce bio-resins with respect to composite applications, because only the development of bio-based resins leads to the production of sustainable green composites.
Abstract This article reviews the use of collaborative robots (cobots) for surface preparation of composites, covering multiple aspects, including challenges, technology, benefits, applications, and future trends. It provides an overview of cobots and their integration into the field of surface preparation in composite manufacturing. The article explores the importance of surface preparation, surface preparation methods, the challenges involved, and how cobots can address them. Additionally, it presents real-world case studies, future trends, and best practices for implementing cobots in surface-preparation processes.
Abstract Impact represents one of the most critical threats to composite materials. This article discusses load-displacement curve and related damages, including classifications of impact velocity. It provides an overview of residual strength model after impact. The article highlights the high-velocity impact behavior of composite materials. It explains the development of hybrid composite laminates to enhance the impact damage resistance of composite laminates.
Abstract The digital twin of a manufactured part is enabled by high-quality process feedback data integrated within a digital environment. This article describes this process, using the example of a novel sensing technology mounted to the head of an automated fiber placement (AFP) machine for in-process inspection and digitization of the as-fabricated component. It details the critical building blocks to create the as-built AFP component digital twin through lay-up surface digitization during the process using a head-mounted profilometer. The most challenging factors for sensor selection for AFP lay-up surface digitization are described. The article provides an overview of synchronizing data streams among sensors and the AFP machine. An example of schematic data treatment workflow for AFP process digitization is also provided.
Abstract To unlock the full potential of lightweight laminates, software applications have been developed that transform general computer-aided design (CAD) systems into a high-performance composite engineering environment for designing and manufacturing composite parts. Composite engineering software includes CAD, computer-aided engineering, and computer-aided manufacturing modules. Design functionality may include core sample and ply stacking analysis, producibility and flat-pattern evaluations, laminate surface offset, and engineering documentation. These functionality areas are discussed in more detail in this article.
Abstract Designers have more freedom when using composite construction than they do when using other materials, because with composites, they are free to select different fibers, flakes, or particles and to combine them with a choice of various resins, ceramics, or metals. This article addresses the basic guidelines considered in designing a composite structure. It describes polymer-matrix composites processing methods. The article discusses several computer programs for analyzing composite laminates. It shows some recommendations for choosing the best material for producing tools.
Abstract This article describes the process, stages, shape categories, advantages, and applications of composite pultrusion. It explains three critical technology areas: product composition, material forming, and control of process temperature. The article also provides additional details of processing equipment and tooling, material composition, and process control essential for a basic understanding of the pultrusion process. It also focuses on the types of matrix resins andexplains the three basic types of thermoplastic processing: reactive, melt, and mingled fiber. It provides a detailed discussion on the properties of pultruded products.
Abstract This article focuses on the differences between the testing of composite materials and the testing of isotropic materials; the building-block approach to composites testing; identification of the purposes of the planned test results; and the use and application of basic statistics. In addition to grouping material property tests by building-block level, collections of material property test data can be grouped by purpose into the five categories of screening, qualification, acceptance, equivalence, and structural substantiation.
Abstract This article presents the materials and manufacturing of automotive composites. Sustainable composites cover abroad range of materials and technologies, including composite recycling, bio-based polymer matrices, natural fiber reinforcements, and bio-based fillers. The opportunities, challenges, and progress in these areas are discussed. Some fiber-reinforced composite implementations in both low- and high-volume automotive applications are also discussed.
Abstract Certification of composite structures — broadly defined as producing design definitions, test data, and analyses to demonstrate compliance with applicable regulations and requirements — varies significantly across industries but shares common underlying principles. This article surveys certification frameworks for composite structures in a range of applications, including FAA- and DoD-regulated aircraft, rotorcraft, eVTOL vehicles, launch vehicles, spacecraft, pressure vessels, automobiles, railway vehicles, maritime vessels, civil infrastructure, and wind turbines. Emphasis is placed on the FAA type certification process, the building-block approach to structural substantiation, and the unique testing and analysis demands imposed by the material-specific characteristics of composites.
