Repair of Advanced Composites for Aerospace Applications

Mohamed Thariq Hameed Sultan, M. Rajesh, K. Jayakrishna, Mohamed Thariq Hameed Sultan, M. Rajesh, K. Jayakrishna

• Publisher: CRC Press
• Year: 2022
• Print ISBN:
  9781032061634
• eBook ISBN:
  9781000550047
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

This book focuses on the repair of polymer composites for critical components in aerospace industries. It also covers the complexities of failure and repair of composites, types of fiber reinforcement and bonding. It includes special topics on damage assessment using on-site inspection (NDT and THz techniques) and automated repair processes for reliability and repeatability. Repair of Advanced Composites for Aerospace Applications also describes the characterization, modelling and simulation of the composites' damage mechanisms with respect to specific environments and applications. Failures associated with various composite repairing techniques for aerospace applications are also covered.

Key Features:

• Addresses the composites development process including damage detection and repair for aerospace applications.
• Covers research on the multi-scale process modelling, material modelling, self-healing, repairing and their analyses.
• Concentrates on the repair of composites for weight-sensitive applications in automobiles and aerospace.
• Analyses perspectives on materials processing and material design.
• Details composite joints, their failure, and operations of aircraft component in various environments.

This book is aimed at researchers, professionals and graduate students in composite materials, manufacturing, aerospace engineering, advanced materials design and manufacturing, composite materials repair, and hybrid materials repair.

1 A Review on Polymer Nanocomposites Used in Aerospace

Benedict Thomas and Sourabh Kumar Soni

Vellore Institute of Technology, Vellore, India

DOI: 10.1201/9781003200994-1

Contents

1. 1.1 Introduction
2. 1.2 Research Works on the Exploration of CNTRCs Characteristics
   • 1.2.1 Mechanical Characteristics of CNTRCs
   • 1.2.2 Thermal Characteristics of CNTRCs
   • 1.2.3 Research Works on Exploration of Thermo-mechanical Characteristics of CNTRCs
   • 1.2.4 Research Works on Exploration of Vibrational Characteristics of PMCs Reinforced with CNTs
   • 1.2.5 Research Works on Agglomeration Effect of CNTs on PNCs Characteristics
3. 1.3 Summary
4. References

1.1 Introduction

Polymers are the most promising materials owing to their reproducibility and ease of processing. They are relatively inexpensive and widely employed in numerous engineering applications. In earlier literature, polymers are classified as (1) thermoplastics, (2) thermosets and (3) elastomers. Amalgamation of two or more materials such as polymer matrices and additives are combined to fabricate polymer composites (PMCs). There are some limitations in optimizing the characteristics of PMCs by incorporating traditional micron-scale fillers. Generally the conventional filler content in PMCs in the range of 10–70 wt% makes the resulting composite more expensive and dense. Unlike traditional PMCs comprising micro-scale fillers, the addition of nanoscale reinforcement materials (nanofillers) into a polymer creates a very short distance among the fillers; therefore, the characteristics of the resulting composites can be largely improved even with an enormously trivial nanofiller content. Owing to those improved characteristics, PMCs reinforced with nano-sized fillers are an open door as future materials in nanostructures, biomechanics, aviation and more. During the last twenty years improvement in the functionalities of PMCs with nano-scaled fillers has come to be an attractive new subject in the field of nanocomposites, literature shows, and still progressive development is going on in this field to fill the lacuna (Wernik and Meguid 2010).

In earlier literature, PMCs reinforced with carbon nanotubes (CNTs) – also known as polymer nanocomposites (PNCs) – are more popular and widely studied among nanocomposite researchers. After Ajayan et al. (1994), Qian and their co-workers (Khalili and Haghbin 2013) were the initiators to examine the influence of the addition of CNTs in polymers by conducting experimental investigations. Numerous review articles have been published on the fabrication technique (Spitalsky et al. 2010; Jin and Park 2011), mechanical characterization (Spitalsky et al. 2010; Coleman et al. 2006) and thermal conductivities (H. Chen et al. 2016) of PNCs. Findings from published articles concur that the higher interfacial bond augments the mechanical characteristics because the CNTs take a major part of the load, which is externally applied in the PNCs. Moreover, CNTs are often modified (functionalised) to increase their dispersibility and facilitate their improved interactions with the polymers (Soni et al. 2020). Available literatures suggest that functionalization processes such as oxidation, amino-functionalization, polymer grafting and silane-functionalization are a promising approach that develops covalent interaction and integrates CNTs into the polymer matrix. Owing to that, resulting nanocomposites become more uniform and don’t indicate any phase separation and agglomeration difficulty (Rahmat and Hubert 2011). In various research work physical and chemical functionalization of CNTs has been performed to increase interfacial adhesion; the same has been proven through an extensive experimental and analytical approach.

Some of the researchers observed enhancement in load transfer capability and mechanical properties, mainly due to chemical bonding among the treated CNTs and polymeric matrix (Liao and Li 2001). Pande et al. 2009 observed augmentation in the mechanical characteristics of MWCNT-reinforced PMMA polymer nanocomposites (PNCs). They also found that even trivial loading of functionalised CNTs in a PMMA matrix provide higher strength and modulus by virtue of better interaction among the reinforcement and matrix. Further, Ma et al. (2010) revealed that the homogenous exfoliation of nanotubes within the matrix depends considerably on numerous parameters such as CNT length, their entanglement phenomenon, V_CNT, viscosity of the matrix, attraction between inter-tube and dispersion methods. They also observed that the numerous CNT functionalization techniques and dispersion techniques were adopted by previous researchers to attain homogenous dispersion of nanotubes on the PMCs. After intensive review, Kim et al. (2012) found that uniform distribution in various solvents or polymer matrices is a major concern for the application of CNTs in various fieldws. Further, they presented various dispersion techniques and their effectiveness during the fabrication of nanocomposites. Following the morphological investigation of CNT/epoxy PNCs, Gojny et al. (2003) found that by using chemical functionalization techniques they effortlessly augment the dispersal of MWCNTs on the epoxy. Their findings showed enhanced interfacial interaction among the matrix and functionalised nanotubes, which results in improved mechanical characteristics of the resulting nanocomposite. Yu et al. (2006) prepared SWNT/epoxy PNC by utilising raw and purified SWNTs and conducted experimental studies to explore the influence of SWCNTs’ purity on the thermal conductivities of SW-CNTRCs. They found that purified and functionalised SWCNTs–reinforced composites have five times better thermal conductivity as compared to unpurified reinforced composites. Also, as compared to end-walled and side-walled covalent chemically modified CNTs, Spitalsky et al. (2009) found stronger molecular interaction among the physically modified CNTs and polymer matrix. More detailed investigations revealed that polymerization is also an efficient approach; however, its efficiency is limited to specific polymers. In order to overcome the preceding problem and achieve the homogenous dispersion of CNTs with good alignment in numerous polymer matrices, alignment techniques such as mechanical stretching, infiltration winding, melt spinning, dielectrophoresis, application of electrical or magnetic fields, and ultrasonic-assisted solution evaporation have been also employed during the preparation of PNCs (Bhattacharya 2016).

1.2 Research Works on the Exploration of CNTRCs Characteristics

In this section, an effort has been made to review published literature on the mechanical, thermal, thermo-mechanical and vibrational properties of CNT-reinforced PMCs. In addition, some literatures on the agglomeration effect of CNTs on composites reinforced with CNTs is also presented.

1.2.1 Mechanical Characteristics of CNTRCs

A substantial amount of experimental and numerical investigation have been carried out to analyse the mechanical characteristics of CNT-reinforced PMCs (CNTRCs). The main aim of this section is to summarise several destructive and non-destructive approaches for evaluation of mechanical properties and to present predictive strategies taken by numerous researchers to achieve the maximum advantage of CNTs reinforcement in numerous CNTs–based nanocomposites. In the preceding twenty years much intensive research on the fabrication and evaluation of the mechanical properties of numerous PNCs has been conducted and a large volume of the literatures suggests that the PNCs’ mechanical performances are significantly reliant on the interfacial interaction among the CNTs and the polymers. Exploration of PS /MWCNTs nanocomposites were performed by Qian et al. (2000). Their observation revealed that upon loading of 1 wt% MWCNTs on PS /MWCNTs nanocomposites, improvement in break stresses (25%) and E (36%–42%) were achieved as compared to blank PS composites, primarily due to homogenous dispersion of undamaged NTs on PS matrices. They also performed microstructural investigation, which shows external loads are effectively transferred to NTs due to their lesser size and larger l/d ratios.

Further, Safadi et al. (2002) conducted fabrication and orientation processes of a PS/MWCNTs composite by using spin casting and film casting techniques to investigate the basic relations between the processing conditions and their mechanical and electrical properties. Uniform dispersion of MWCNTs in solutions was achieved by a simple sonication process, and the MWCNTs’ orientation and dispersion within a PS matrix were inspected employing SEM. The researchers found higher orientation of MWCNTs near the fluid-solid interface and decreases to random orientation at the shear-free fluid-air interface. By using the Carreau equation, rheology of PS/MWNTs suspensions was modeled. Their results shows an increment in the tensile strength (TS) of the nanocomposite, which is loaded with up to 1 vol% MWCNTs. Numerous techniques were employed in literatures to fabricate CNT–reinforced polyvinyl alcohol (PVA) composites such as gel spinning, electro spinning, wet spinning (Jee et al. 2012) and melt spinning (Ferreira et al. 2017). Yang et al. (2015) prepared the PVA/MWCNT composites fibre by using the melt-spinning process to investigate the mechanical response and microstructure characteristics as a function of the draw condition. They found higher elastic and mechanical properties as compared to undrawn composite fiber; XRD analysis also revealed that by increasing the draw ratio the degree of orientation and crystallinity increases. Polypropylene (PP) thermoplastics are also a widely employed polymer owing to its low density and ease of processability as well as a decent balance among cost and properties. Manchado et al. (2005) analysed the effect of numerous SWCNTs concentrations on physical and thermal characteristics of CNT–reinforced PMCs by using DMA and calorimetric analysis. In their fabrication procedure, a shear mixing approach was used to attain homogenous dispersion of SWCNTs in isotactic polypropylene (iPP). Their results show that modulus of elasticity (E) and TS enhances with the accumulation of NTs, with a maximum content of 0.75 wt%. Also, the accumulation of a trivial amount of SWNT (less than 1 wt%) increases the rate of polymer crystallization with no considerable variations in the crystalline structure.

Epoxy is costly compared to other polymers, but due to its superior characteristics it is widely used in a range of industries, including aerospace. Earlier literature shows that epoxy is the most-studied and most-used polymer in advanced PNCs because of its prodigious properties. The foremost reason behind its popularity is its low viscosity, excellent thermo-mechanical properties, higher strength, low shrink rates, low volatility during cure and low flow rates. While investigating properties of MWCNTs/epoxy PNCs, Montazeri et al. (2010) found that acid-treated MWCNTs are uniformly dispersed as compared to untreated MWCNTs within the nanocomposites. They also perceived that the homogenous exfoliation of nanotubes (MWs) in the epoxy increases the uniformity of stress distribution and diminishes stress concentration. While investigating mechanical characteristics of PNCs, Guo et al. (2007) found augmentation in the TS and fracture strain of epoxy-based PNCs. Montazeri et al. (2011) also observed significant effect of nanotubes on the PMCs involving the viscoelastic and mechanical characteristics of the MWCNT/epoxy PNCs. Mansour et al. (2013) analyses the mechanical response of the MW-CNTRCs and found good agreement between the value of elastic modulus estimated by the nano-indentation technique (NT) and tensile testing. They found that the both hardness and modulus of MWCNTs/epoxy composites increase with higher MWCNTs concentrations.

1.2.2 Thermal Characteristics of CNTRCs

Presently, thermal characteristics are the most important parameter for upcoming technologies. The excellent thermal conductivity and thermal stability of CNTs motivated substantial research interest to use them as a filler material and enhance the thermal characteristics of polymers. Earlier literature shows that the thermal characteristics of PNCs depends on various aspects such as CNT content, uniform dispersion, aspect ratio and interfacial interactions with matrix, as shown in Figure 1.1.

Figure 1.1 Factors that affects the thermal conductivities of composites. (Chen et al. 2016).

Biercuk et al. (2002) suggested that the addition of trivial amounts of SWCNTs (1%) can enhance the thermal characteristics of...

Table of contents

• Cover Page
• Half Title Page
• Title Page
• Copyright Page
• Contents
• Preface
• Editors’ Biographies
• Contributors
• 1 A Review on Polymer Nanocomposites Used in Aerospace
• 2 A Review on Natural Fibre Reinforced Composite Under UV Concentration for Aircraft Application
• 3 A Review on Advanced Polymer Composites Used in Aerospace Application
• 4 The Mechanical Properties of Kenaf/Jute Hybrid Composites in Different Angles of Orientation
• 5 Dynamic Behaviour of Adhesively Bonded Structures in Aerospace Applications: An Overview
• 6 Introduction on Repair of Composites: Types of Repair Techniques
• 7 Adhesively Bonded Composite Joints in Aerospace Application: An Overview
• 8 Impact Testing of Graphene, Epoxy and Carbon Fibre Reinforced Coir Composites and Automatic Prediction of Graphene Composition Using ANN
• 9 Failure of Composite Structure: Modelling of Cracks in the Aerospace Composite Structure
• 10 Low Temperature Effect on Deflection Behavior of a Cracked Laminated Glass Plate
• 11 Damage Detection and Evaluation on Gamma Irradiated Oil Palm EFB/Kevlar Hybrid Composites Using NDT Methods
• 12 Mechanical Behaviour of Sandwich Composites in Automotive Applications
• Index