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Fracture Mechanics and Structural Integrity of Composite Materials

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (20 November 2021) | Viewed by 15327

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Special Issue Editor

Dr. Ana Martins Amaro

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Guest Editor

Department of Mechanical Engineering, University of Coimbra, 3030-788 Coimbra, Portugal
Interests: composites structures; nanocomposite; structural integrity; finite element analysis; biomechanics; impact; non-destructive analysis; mechanical properties
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Special Issue Information

Dear Colleagues,

Composite materials have been increasingly used because of their high specific strength and stiffness, good fatigue performance and corrosion resistance. However, in many cases, there are some problems in their application as consequence of the poor tolerance to damage. Composite materials are very susceptible to degradation/damage which can reduce significantly their structural integrity. For example, when submitted to impact events, like low velocity impact, which can occur in-service or during the maintenance activities. Also, composite structures can be exposed to a range of corrosive environments during their in-service life, which causes degradation in terms of material properties, where irreversible material degradation occurs and some chemical changes can be found. For example, composite pipes are largely used in the chemical industry, building and infrastructures. Fracture mechanics is used to predict and diagnose failure of a component with an existing crack or flaw. In this context, their presence magnifies the stress in the vicinity of the crack and may result in failure prior to that predicted using traditional strength-of-materials methods.

Hence, this Special Issue intends to contribute to the publication of reports containing increase the state-of-the-art related to composite materials, namely in terms of fracture mechanics and structural integrity. For this purpose, experimental and numerical studies are welcome.

It is my pleasure to invite you to publish your original research contributions and reviews in the Special Issue, “Fracture mechanics and structural integrity of composite materials”, of Applied Sciences.

Dr. Ana Paula Betencourt Martins Amaro
Guest Editor

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Keywords

Composite materials
Fracture mechanics
Crack propagation
Environmental degradation
Structural integrity
Finite element method

Published Papers (7 papers)

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Research

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12 pages, 3267 KiB

Open AccessArticle

Seawater Effect on Fatigue Behaviour of Notched Carbon/Epoxy Laminates

by Ricardo Branco, Paulo N. B. Reis, Maria A. Neto, José D. Costa and Ana M. Amaro

Appl. Sci. 2021, 11(24), 11939; https://doi.org/10.3390/app112411939 - 15 Dec 2021

Cited by 7 | Viewed by 1525

Abstract

This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were performed under uniaxial cyclic loading using a stress ratio equal to 0.1. After the tests, the optical microscopy technique allowed the examination of the failure micro-mechanisms at the fracture surfaces. The results showed that saturation appeared before 30 days of immersion and that water absorption rates were similar for natural and artificial seawater. The S–N curves showed that the seawater immersion affects the fatigue strength, but there were no relevant effects associated with the type of seawater. Moreover, it was also clear that fatigue life was similar for long lives, close to 1 million cycles, regardless of the immersion time or the type of seawater. On the contrary, for short lives, near 10 thousand cycles, the stress amplitude of dry laminates was 1.2 higher than those immersed in seawater. The failure mechanisms were similar for all conditions, evidencing the fracture of axially aligned fibres and longitudinal delamination between layers. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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18 pages, 4851 KiB

Open AccessArticle

Impact Response of Composite Sandwich Cylindrical Shells

by Paulo N. B. Reis, Carlos A. C. P. Coelho and Fábio V. P. Navalho

Appl. Sci. 2021, 11(22), 10958; https://doi.org/10.3390/app112210958 - 19 Nov 2021

Cited by 8 | Viewed by 2082

Abstract

Nowadays, due to the complexity and design of many advanced structures, cylindrical shells are starting to have numerous applications. Therefore, the main goal of this work is to study the effect of thickness and the benefits of a carbon composite sandwich cylindrical shell incorporating a cork core, compared to a conventional carbon composite cylindrical shell, in terms of the static and impact performances. For this purpose, static and impact tests were carried out with the samples freely supported on curved edges, while straight edges were bi-supported. A significant effect of the thickness on static properties and impact performance was observed. Compared to thinner shells, the failure load on the static tests increased by 237.9% and stiffness by 217.2% for thicker shells, while the restored energy obtained from the impact tests abruptly increased due to the collapse that occurred for the thinner ones. Regarding the sandwich shells, the incorporation of a cork core proved to be beneficial because it promoted an increase in the restored energy of around 44.8% relative to the conventional composite shell. Finally, when a carbon skin is replaced by a Kevlar one (hybridization effect), an improvement in the restored energy of about 20.8% was found. Therefore, it is possible to conclude that numerous industrial applications can benefit from cylindrical sandwiches incorporating cork, and their hybridization with Kevlar fibres should be especially considered when they are subject to impact loads. This optimized lay-up is suggested because Kevlar fibres fail through a series of small fibril failures, while carbon fibres exhibit a brittle collapse. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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16 pages, 4577 KiB

Open AccessFeature PaperArticle

Effect of Harsh Environmental Conditions on the Impact Response of Carbon Composites with Filled Matrix by Cork Powder

by Marco P. Silva, Paulo Santos, João Parente, Sara Valvez and Paulo N. B. Reis

Appl. Sci. 2021, 11(16), 7436; https://doi.org/10.3390/app11167436 - 12 Aug 2021

Cited by 4 | Viewed by 1808

Abstract

Composites are used in a wide range of engineering applications, as a result, exposure to hostile environments is rather common and its mechanical properties degradation is unavoidable. It is necessary to have a complete understanding of the impact of hostile environments on mechanical performance, namely critical solicitations as low velocity impacts. Therefore, this work intends to analyse the low velocity impact response of a carbon fibre/epoxy composite, and a similar architecture with an epoxy matrix filled with cork, after immersion into different solutions: diesel, H₂SO₄, HCl, NaOH, distilled water, seawater, and seawater at 60 °C. These solutions significantly affected the impact properties. In this context, the maximum load, maximum displacement, and restored energy behaviour were studied to understand the influence of exposure time. It was possible to conclude that such impact parameters were significantly affected by the solutions, where the exposure time proved to be determinant. The benefits of cork on the perforation threshold were investigated, and this parameter increased when the epoxy matrix was filled with cork. Finally, cork filled epoxy laminates also show less variation in maximum load and recovered energy than carbon/epoxy laminates. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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18 pages, 2889 KiB

Open AccessArticle

Micromechanical Analysis in Applications of Active Mono-Slip and Continuum Dislocations in the MDCM

by Temesgen Takele Kasa

Appl. Sci. 2021, 11(7), 3135; https://doi.org/10.3390/app11073135 - 1 Apr 2021

Cited by 1 | Viewed by 1212

Abstract

The key purpose of this paper is to propose a mono-slip-dependent continuum dislocation method for matrix-dominated composite structure (MDCS) analysis. The methodology focuses on dissipation energy theories utilizing a continuum dislocation method (CDM) integrated with small-strain kinematics. The mathematical modeling of the CDM comprises active mono-slip system formulations, thermodynamic dislocation analysis (TDA), free energy dissipation analysis, and the progression of dislocations. Furthermore, zero and non-zero energy dissipation due to dislocation progression is formulated by using an energy minimization technique with variational calculus. The numerical analysis, performed with Wolfram Mathematica©, is presented using zero and non-zero energy dissipation energy formulations. The outcomes indicate that the formulated approach can be effective for obtaining optimal analysis results for matrix-dominated composite (MDC) materials with a mono-slip system. In sum, this study confirms the feasibility of using the proposed approach to investigate MDCS with inclusions. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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16 pages, 8340 KiB

Open AccessArticle

Numerical Study of the Toughness of Complex Metal Matrix Composite Topologies

by Julie Lemesle, Cedric Hubert and Maxence Bigerelle

Appl. Sci. 2020, 10(18), 6250; https://doi.org/10.3390/app10186250 - 9 Sep 2020

Cited by 3 | Viewed by 2244

Abstract

Fracture toughness tests (compact tension) of a dual material composed of a structured Metal Matrix Composite (MMC) (martensitic steel and titanium carbides, named MS-TiC) surrounded by martensitic steel (MS) are simulated with a Discrete Elements Model (DEM) developed with the GranOO Workbench. The MMC structures are micro-lattices such as gyroid, octet-truss and Face and Body-Centered Cubic with Z-truss (FBCCZ). The volume fraction of these MMC inserts and their cell size are fixed, the influence of the cell orientation is studied. The aim of the study is to determine the configuration of topology (shape and cell orientation) which absorbs the most energy and is the most crack resistant. From experimental tests, the Young’s moduli and the failure stresses of the MMC material and the metal are estimated, and thanks to beam network discretization, a local stiffness and a failure criterion are evaluated to finally obtain a crack propagation path. To verify the suitability of the DEM model, a Compact Tension (CT) experimental test on MMC specimens is performed and a stress intensity factor is computed. A good agreement with an error less than 10% is obtained between experimental and simulated

K_{I c}

with values respectively equal to 35 and 37

M Pa \sqrt{m}

. From DEM simulations based on the CT tests, the FBCCZ cell absorbs the most energy at the crack propagation compared to other structures and the steel. The crack propagation length depends on the shape of the topology. The originality of the study lies in the modeling, with granular properties using DEM, of the mechanical and elastic fracture behavior of these topological structures classically solved by Finite Elements Method (FEM): the microscopic constitutive relations have been validated macroscopically by experimental tests on homogeneous MMC materials. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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12 pages, 2594 KiB

Open AccessArticle

The High-Velocity Impact Behaviour of Kevlar Composite Laminates Filled with Cork Powder

by Ana Martins Amaro, Paulo Nobre Balbis Reis, Ines Ivañez, Sonia Sánchez-Saez, Shirley Kalamis Garcia-Castillo and Enrique Barbero

Appl. Sci. 2020, 10(17), 6108; https://doi.org/10.3390/app10176108 - 3 Sep 2020

Cited by 11 | Viewed by 2459

Abstract

The literature reports benefits when the cork powder obtained from industrial by-products is used as the filler of composite laminates. For example, while the fatigue life is insensitive to the presence of cork in the resin, significant improvements are achieved in terms of to low-velocity impact strength. However, in terms of ballistic domain, the literature does not yet report any study about the effect of incorporating powdered cork into resins. Therefore, this study intended to analyse the ballistic behaviour and damage tolerance of Kevlar/epoxy reinforced composites with matrix filled by cork powder. For this purpose, high-velocity impacts were studied on plates of Kevlar bi-directional woven laminates with surfaces of 100 × 100 mm². It was possible to conclude that the minimum velocity of perforation is 1.6% higher when the cork powder is added to the resin, but considering the dispersion, this small difference can be neglected. In terms of damage areas, they are slightly lower when cork dust is added, especially for velocities below the minimum perforation velocity. Finally, the residual bending strength shows that these composites are less sensitive to impact velocity than the samples with neat resin. In addition to these benefits, cork powder reduces the amount of resin in the composite, making it more environmentally friendly. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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Graphical abstract

Review

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19 pages, 2339 KiB

Open AccessFeature PaperReview

Joining of Fibre-Reinforced Thermoplastic Polymer Composites by Friction Stir Welding—A Review

by Miguel A. R. Pereira, Ivan Galvão, José Domingos Costa, Ana M. Amaro and Rui M. Leal

Appl. Sci. 2022, 12(5), 2744; https://doi.org/10.3390/app12052744 - 7 Mar 2022

Cited by 10 | Viewed by 2971

Abstract

The objective of the current work is to show the potential of the friction stir welding (FSW) and its variants to join fibre-reinforced thermoplastic polymer (FRTP) composites. To accomplish that, the FSW technique and two other important variants, the friction stir spot welding (FSSW) and the refill friction stir spot welding (RFSSW), are presented and explained in a brief but complete way. Since the joining of FRTP composites by FSSW has not yet been demonstrated, the literature review will be focused on the FSW and RFSSW techniques. In each review, the welding conditions and parameters studied by the different authors are presented and discussed, as well as the most important conclusions taken from them. About FSW, it can be concluded that the rotational speed and the welding speed have great influence on heat generation, mixture quality, and fibre fragmentation degree, while the tilt angle only has residual influence on the process. The reduction of internal and external defects can be achieved by adjusting axial force and plunge depth. Threaded or grooved conical pins achieved better results than other geometries. Stationary shoulder tools showed better performance than conventional tools. Regarding the RFSSW, it has not yet been possible to deepen conclusions about most of the welding parameters, but its feasibility is demonstrated. Full article

(This article belongs to the Special Issue Fracture Mechanics and Structural Integrity of Composite Materials)

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