A Review of Damage Tolerant Design, Certification and Repair in Metals Compared to Composite Materials

A review of some of the various fatigue models introduced over the years for both metallic materials, in particular aluminium alloys followed by fatigue and durability concerns associated with composite materials. The move towards light weight and high stiffness structures that have good fatigue durability and corrosion resistance has led to the rapid move from metal structures to composite structures. With this brings the added concern of certifying new components as the damage mechanisms and failure modes in metals differ significantly than composite materials such as carbon fiber reinforced polymers (CFRP). The certification philosophy for composites must meet the same structural integrity, safety and durability requirements as that of metals. Hence this is where the challenge now lies. Substantial work has been conducted in the reparability of composite structures through bonding using various adherend thicknesses and joint types and has been shown to have higher durability than mechanically fastened repairs for thin adherends however these are currently unacceptable repair methods as they cannot be certified. Repairs are designed on the basis that the repair efficiency can be predicted and should be designed conservatively with respect to the various failure modes and include the surrounding structure.

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Ultrasonic C-scan techniques for the evaluation of impact damage in CFRP

Materials Testing ◽

10.1515/mt-2020-0020 ◽

2021 ◽

Vol 63 (2) ◽

pp. 131-137

Author(s):

Mário Santos ◽

Jaime Santos ◽

Paulo Reis ◽

Ana Amaro

Keyword(s):

Composite Structures ◽

Impact Damage ◽

Image Resolution ◽

Fiber Reinforced Polymers ◽

Carbon Fiber Reinforced Polymers ◽

Low Frequencies ◽

Reinforced Polymers ◽

Contour Defects ◽

Service Application ◽

Pulse Echo

Abstract In the present work, different ultrasonic C-scan approaches were used to evaluate Carbon Fiber Reinforced Polymers (CFRP) submitted to impacts of low energy, in order to evaluate their effectiveness for the detection and characterization of small defects. In particular, as to the question how useful could be the air-coupled C-scan approach, using low frequencies, for in-service application. For that goal, several samples with different stacking sequences and thicknesses were impacted with 1.5 and 3 J. Then, ultrasonic C-scan images were produced by immersion pulse-echo (in amplitude and time-of-flight (TOF)) and immersion through-transmission, and also by air-coupling through-transmission. The immersion C-scan images were produced using 5, 10 and 20 MHz probes and the air-coupled C-scan was made using two 400 kHz probes. The obtained images for the considered samples show that all used methods are able to detect the defects and give acceptable information about their size and shape. However, if the way of delamination evolving over thickness is of interest, the images by TOF should be used. As expected, good image resolution with sharp contour defects require high frequencies. Nevertheless, the air-coupled C-scan demonstrated similar capabilities to detect defects, with the advantage that the coupling medium is air, thus widening the range of applications, such as real-time damage monitoring of composite structures. As a disadvantage, the air C-scan system requires high power emission signals, and also great amplification of the received signals, to face the considerable attenuation in the air.

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Study on Mechanical Bearing Strength and Failure Modes of Composite Materials for Marine Structures

Journal of Marine Science and Engineering ◽

10.3390/jmse9070726 ◽

2021 ◽

Vol 9 (7) ◽

pp. 726

Author(s):

Dong-Uk Kim ◽

Hyoung-Seock Seo ◽

Ho-Yun Jang

Keyword(s):

Composite Materials ◽

Failure Mode ◽

Composite Structures ◽

Failure Modes ◽

Offshore Structures ◽

Fiber Reinforced ◽

Bearing Strength ◽

Fiber Reinforced Plastic ◽

Reinforced Plastic ◽

Mechanically Fastened

With the gradual application of composite materials to ships and offshore structures, the structural strength of composites that can replace steel should be explored. In this study, the mechanical bearing strength and failure modes of a composite-to-metal joining structure connected by mechanically fastened joints were experimentally analyzed. The effects of the fiber tensile strength and stress concentration on the static bearing strength and failure modes of the composite structures were investigated. For the experiment, quasi-isotropic [45°/0°/–45°/90°]2S carbon fiber-reinforced plastic (CFRP) and glass fiber-reinforced plastic (GFRP) specimens were prepared with hole diameters of 5, 6, 8, and 10 mm. The experimental results showed that the average static bearing strength of the CFRP specimen was 30% or higher than that of the GFRP specimen. In terms of the failure mode of the mechanically fastened joint, a cleavage failure mode was observed in the GFRP specimen for hole diameters of 5 mm and 6 mm, whereas a net-tension failure mode was observed for hole diameters of 8 mm and 10 mm. Bearing failure occurred in the CFRP specimens.

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Eddy current modeling in linear and nonlinear multifilamentary composite materials

Open Physics ◽

10.1515/phys-2018-0026 ◽

2018 ◽

Vol 16 (1) ◽

pp. 183-187 ◽

Cited By ~ 1

Author(s):

Hocine Menana ◽

Mohamad Farhat ◽

Melika Hinaje ◽

Kevin Berger ◽

Bruno Douine ◽

...

Keyword(s):

Composite Materials ◽

Frequency Domain ◽

Eddy Currents ◽

Ac Loss ◽

Fiber Reinforced Polymers ◽

Carbon Fiber Reinforced Polymers ◽

Reinforced Polymers ◽

Differential Formulation ◽

High Anisotropy ◽

Proposed Model

Abstract In this work, a numerical model is developed for a rapid computation of eddy currents in composite materials, adaptable for both carbon fiber reinforced polymers (CFRPs) for NDT applications and multifilamentary high temperature superconductive (HTS) tapes for AC loss evaluation. The proposed model is based on an integro-differential formulation in terms of the electric vector potential in the frequency domain. The high anisotropy and the nonlinearity of the considered materials are easily handled in the frequency domain.

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Enhancement of Mechanical Integrity of Advanced Composites using PMAA-Electropolymerised CF Fabrics

MATEC Web of Conferences ◽

10.1051/matecconf/201818801007 ◽

2018 ◽

Vol 188 ◽

pp. 01007

Author(s):

Dionysios A. Semitekolos ◽

Panagiotis Goulis ◽

Despoina I. Batsouli ◽

Elias P. Koumoulos ◽

Loukas Zoumpoulakis ◽

...

Keyword(s):

Carbon Fiber ◽

Carbon Fibers ◽

Structural Integrity ◽

Fiber Reinforced Polymers ◽

Nanoindentation Test ◽

Mechanical Interlocking ◽

Hot Press ◽

Carbon Fiber Reinforced Polymers ◽

Reinforced Polymers ◽

Advanced Composites

The aim of the present study is the development of new composite materials that show improved mechanical and structural integrity. In order to accomplish this goal, a novel functionalization method of the carbon fibers for the reinforcement of the composites surface was investigated. Through the electrografting of methacrylic acid onto the surface of the carbon fiber, this treatment aims to selectively modify the surface of the carbon fabrics, in order to create active groups that can chemically react with the epoxy resin, under heat and pressure. By this way, better adhesion as mechanical interlocking between the resin and the reinforcement can be achieved. The surface treatment was examined qualitatively by means of Infrared spectroscopy, Scanning Electron Microscopy and Raman spectroscopy. The carbon fiber reinforced polymers were manufactured via the hot-press technique and they were subsequently submitted to flexural, shear and nanoindentation test. Finally, the internal structural integrity was tested through micro-Computing Tomography.

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A structural chemistry look at composites recycling

Materials Horizons ◽

10.1039/d0mh01085e ◽

2020 ◽

Vol 7 (10) ◽

pp. 2479-2486

Author(s):

Carlos A. Navarro ◽

Cassondra R. Giffin ◽

Boyang Zhang ◽

Zehan Yu ◽

Steven R. Nutt ◽

...

Keyword(s):

Composite Materials ◽

Carbon Fiber ◽

Large Scale ◽

Civil Engineering ◽

Structural Materials ◽

Structural Chemistry ◽

Fiber Reinforced Polymers ◽

Engineering Applications ◽

Carbon Fiber Reinforced Polymers ◽

Reinforced Polymers

Composite materials, especially carbon fiber-reinforced polymers, are a class of structural materials now commonly used in aircraft, marine, and other applications, with emerging large-scale use in the automotive and civil engineering applications.

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Additive Manufacturing of Structural Cores and Washout Tooling for Autoclave Curing of Hybrid Composite Structures

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4040428 ◽

2018 ◽

Vol 140 (10) ◽

Cited By ~ 4

Author(s):

Daniel-Alexander Türk ◽

Andreas Ebnöther ◽

Markus Zogg ◽

Mirko Meboldt

Keyword(s):

Composite Structures ◽

Mechanical Performance ◽

Fiber Reinforced Polymers ◽

Carbon Fiber Reinforced Polymers ◽

Reinforced Polymers ◽

Three Point Bending ◽

Lightweight Structures ◽

Autoclave Curing ◽

Lightweight Structure ◽

Temperature And Pressure

This paper presents a study combining additive manufactured (AM) elements with carbon fiber-reinforced polymers (CFRP) for the autoclave curing of complex-shaped, lightweight structures. Two approaches were developed: First, structural cores were produced with AM, over-laminated with CFRP, and co-cured in the autoclave. Second, a functional hull is produced with AM, filled with a temperature- and pressure-resistant material, and over-laminated with CFRP. After curing, the filler-material is removed to obtain a hollow lightweight structure. The approaches were applied to hat stiffeners, which were modeled, fabricated, and tested in three-point bending. Results show weight savings by up to 5% compared to a foam core reference. Moreover, the AM element contributes to the mechanical performance of the hat stiffener, which is highlighted by an increase in the specific bending stiffness and the first failure load by up to 18% and 310%. Results indicate that the approaches are appropriate for composite structures with complex geometries.

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