Chemical and Physical Interaction Mechanisms and Multifunctional Properties of Plant Based Graphene in Carbon Fiber Epoxy Composites

Graphene has generated substantial interest as a filler due to its exceptional strength, flexibility, and conductivity but faces obstacles in supply and implementation. A renewable, plant-based graphene nanoparticle (pGNP) presents a more accessible and sustainable filler with the same properties as mineral graphenes. In this study, the mechanisms of graphene reinforcement in carbon fiber reinforced plastic (CFRP) were examined, along with the resulting improvements to mechanical strength, resistance to crack propagation, electrical and thermal conductivity at elevated temperatures. pGNP, produced from renewable biomass, was shown to have a graphitic structure with flakes 3-10 layers thick and a median lateral size of 240 nm with epoxide and carboxyl functional groups. pGNP was sprayed on carbon fiber/epoxy prepreg at loadings from 1.1 g/m2 to 4.2 g/m2 . An even particle dispersion was achieved using a spray application in a water/alcohol suspension with the addition of surfactants and dispersion aides. Results show interlaminar pGNP improved Mode I fracture toughness at crack initiation by 146% at 20°C and 126% at 90°C, with fracture toughness improved by 53% and 52% during propagation at 20°C and 90°C, respectively. Mode II fracture toughness was not changed at 20°C and improved 55% at 90°C. pGNP addition increases flexural modulus by 15%, flexural strength by 17%, and interlaminar shear strength by 17%, as well as electrical conductivity by 397% (κ₂₂) and thermal conductivity by 27% (k₁₁), with these improvements observed at 1.1- 2.3 g/m2 spray loadings. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and dynamic mechanical analysis (DMA) show polymer crosslinking with graphene surface groups and the resulting restriction of side chain movement. These restrictions improve composite performance at ambient and elevated temperatures, extending the damage process zone and increasing fracture toughness, as well as improve particle/matrix interaction, leading to improved conductivity

Manufacturing of coir fibre-reinforced polymer composites by hot compression technique

This present chapter describes the manufacturing technique and properties of coir fibre-reinforced polypropylene composites manufactured using a hot press machine. The effects of basic chromium sulphate and sodium bicarbonate treatment on the physical and mechanical properties were also evaluated. Chemical treatment and fibre loading generally improved the mechanical properties. Five-hour basic chromium sulphate and sodium bicarbonate-treated coir-polypropylene had the best set of properties among all manufactured composites. Chemical treatment also improved water absorption characteristics. This proves that chemical treatment reduced the hydrophilicity of the coir fibre. Overall the hot compression technique was proved to be successful in manufacturing good quality coir reinforced polypropylene composites

Life cycle monitoring of composite aircraft components with structural health monitoring technologies

Life cycle monitoring could considerably improve the economy and sustainability of composite aircraft components. Knowledge about the quality of a component and its structural health allows thorough exploitation of it’s useful life and offers opportunity for optimization. Current life cycle monitoring efforts can be split in two main fields 1) process monitoring and 2) structural health monitoring with little overlap between them. This work aims to propose an integral monitoring approach, enabling entire life monitoring with the same sensor. First, the state of the art of both composite manufacturing as well as structural health monitoring technologies is presented. Piezoelectric sensors have been ruled out for further investigation due their brittleness. Fiber optical sensors and electrical property-based methods are further investigated. Distributed fiber optic sensors have been successfully used in composite manufacturing trials. Two processes were demonstrated: vacuum assisted resin transfer molding and resin infusion under flexible tooling. Due to their flexibility, optical fibers can survive the loads occurring during manufacturing and deliver valuable insights. It is shown for the first time numerically and experimentally, that fiber bed compaction levels and volume fractions can be calculated from the optical frequency shift measured by the optical fiber sensors. The same sensor was used for subsequent structural health monitoring. This proves that the gap between process monitoring and structural health monitoring can be closed with mutual benefits in both areas. The final chapter presents a novel electrical property-based sensing technique. The sensors are highly flexible and manufactured with a robot-based 3D-printing method. They are shown to reliably work as strain sensors and crack detectors. This work presents a thorough investigation of available and novel sensing technologies for process monitoring and structural health monitoring settings. The results obtained could pave the way to more efficient aircraft structures.Open Acces

Joining of Dissimilar Materials

Material manufacturers and engineering structure designers are currently focusing new ways to exploit the benefits of light-weight, hybrid materials with improved properties at a low cost. The ability to join dissimilar materials is enabling the design engineers to develop light-weight and efficient automobiles, aircraft and space vehicles. The objective of this PhD research study was to produce alternative and efficient joining solutions for automotive and aerospace applications. The joining of dissimilar material was experimented to obtain light-weight Fibre Reinforced Polymer (FRP) sandwich composites, Al-foam sandwich (AFS) composites, hybrid dynamic FRP epoxy/polyurethane composites and the joining of Ti6Al4V alloy with and without surface modification to Ceramic Matrix Composite (CMC) and itself. The joining of Al-foam and Al-honeycomb to FRP skins was performed. The experimental results show that higher flexural properties can be achieved by replacing Al-honeycomb with low-cost Al-foam as a core material in the sandwich structures. Compared to FRP-honeycomb sandwich panels, FRP-Al foam sandwich panels display ~25 % and ~65 % higher flexural strength in a long and short span three-point bending tests respectively. AFS composites with complete metallic character, to withstand high-temperature application conditions, were produced by soldering/brazing techniques using Zn-based and Al-based joining alloys. A post-brazing thermal treatment was designed to recover the mechanical properties of AFS composites, lost during the soldering/brazing process. The microstructural analysis of the Al-skin/Al-foam interface revealed that the diffusion of joining materials into the joining substrates (Al-sheet and Al-foam) was achieved. Around 80% higher bending load before failure was observed when the AFS specimens produced with Zn-based joining alloys were subjected to flexural load compared to those produced with Al-based joining alloys. Hybrid dynamic Carbon Fibre Reinforced Polymer (CFRP) composites with enhanced impact properties were produced by exploiting the reversible cross-linking functionalities of dynamic epoxy and dynamic PU resin systems. By joining dynamic CFRP-epoxy and dynamic CFR-PU laminates, hybrid dynamic composite in three different configurations and a non-hybrid composite were obtained. The four dynamic composites were characterised for structural, thermal, flexural and impact properties. The damage initiation upon impact was observed at around 95% higher energy level in the hybrid configuration (CFRP-4), compared to the non-hybrid configuration. The hybrid configuration CFRP-3 responded with around 55% higher perforation threshold energy compared the non-hybrid configuration. Preliminary work on Adhesive joining of the Ti6Al4V alloy to itself was performed to analyse the effect micro-machining on adhesion and the effect of shape/design of micro-slots on an adhesive joint strength. Three types of micro-slots: V, semi-circle and U-shaped micro-slots were produced on Ti6Al4V sheet surface by using an in-house developed Micro-Electro-Discharge Machining (Micro-EDM) setup. Ti6Al4V alloy specimens with and without micro-machined surfaces were bonded together using a commercial epoxy adhesive. The Single Lap Offset (SLO) shear test results revealed that the micro-slot oriented perpendicular to the applied load displayed ~23 % higher joining strength compared to when the micro-slots were oriented parallel to the applied load. U-shaped micro-slots configuration displayed ~30 % improvement in the joint shear strength compared to the specimens with un-modified surfaces. The fractured surfaces analysis revealed mix (adhesive-cohesive) with cohesive dominated failure in bonded specimens with micro-machined surfaces compared to the as-received where pure adhesive failure was observed. The joining of CMCs (C/SiC and SiC/SiC) to Ti6Al4V alloy was experimented using active brazing alloy (Cusil-ABA) and Zr-based brazing alloy (TiB590) in a pressure-less argon atmosphere. The CMC-Ti6Al4V joint strength was further improved by modifying the surface of Ti6Al4V alloy using an in-house built Micro-EDM setup. Around 40% higher joining strength was recorded when the Zr-based brazing alloy was used as a joining material compared to the conventional active brazing alloy, Cusil-ABA. Improvement in the joining strength was noticed when the Ti6Al4V surface was modified prior to joining

Processing of interpenetrating composites

Interpenetrating composites are emerging as a new class of materials due to their potential for displaying multifunctional properties. They consist of three-dimensionally interpenetrating matrices of two different phases. In the present work the primary focus has been on ceramic/polymer composites though some work has also been done on ceramic/metal systems. The ceramic/polymer composites have been produced by infiltrating alumina foams with polyester resin. The foams are made by mechanically agitating ceramic suspensions to entrain gases and then setting the structure via the in-situ polymerisation of the organic monomers. This resulted in the foams having a very open and interconnected structure that could be easily infiltrated using simple, low pressure systems. Both positive and negative pressures have been investigated, the former yielded higher final densities since the later encouraged the entrapment of gas within the liquid polymer that remained in the composite. [Continues.

Improving the Paintability of Sheet Molding Compounds for High-Volume Production

Sheet Molding Compounds (SMC) present a promising alternative for sheet metal in automotive exterior body panel applications. They offer excellent specific mechanical properties, improved design freedom and a cost-efficient manufacturing process. However, the paintability of SMCs is challenging and this issue has kept the material from a more widespread application, in spite all inherent advantages. This work investigates the underlying reasons of paint defect occurrence and proposes novel solutions to improve upon state-of-the-art technology. Through the modification of conventional SMC an improved surface compound is proposed. This can be combined with a novel manufacturing process, denoted Co-Compression-Molding, which enables the molding of two individual compounds in a single step. The work offers insight into appropriate molding parameter selection to ensure a flawless compression molding process. Additional processing steps are proposed to further improve manufacturing, such as thermography for the early detection of sub-surface voids, and post-processing via electron beam curing.:1 Introduction 1.1 Motivation and Objectives 1.2 Solution Approach 2 State of the Art 2.1 Automotive Production 2.1.1 Paint Processes 2.1.2 Quality Assessment Techniques 2.2 Sheet Molding Compounds 2.2.1 Manufacturing and Composition 2.2.2 Mechanical Properties 2.2.3 Conventional Methods of Surface Improvement 2.2.4 Recycling Methods 2.3 Compression Molding 2.3.1 Mold Flow of Sheet Molding Compounds 2.3.2 Compound Rheology 2.3.3 Inherent Porosity 2.3.4 Co-Molding Process 2.3.5 Alternative Approaches and Auxiliary Processes 3 Reduced Fiber Weight Fraction Compounds 3.1 Porosity as the Source of Defects 3.2 Compounding and Compression Molding 3.3 Compound Characterization 3.3.1 Fiber Network Permeability 3.3.2 Rheology and Flowability 3.3.3 Physical Properties 3.3.4 Pore Content and Porosity Elimination 3.4 Effect on Paintability 4 Co-Compression Molding 4.1 Hybrid Material Flow 4.2 Materials 4.3 Molding Trials and Testing 4.3.1 Flat Plaque Testing 5 Auxiliary Processes 5.1 Thermography 5.1.1 Materials 5.1.2 Experiments 5.2 Electron Beam Curing 5.2.1 Residual Reactivity 5.2.2 Irradiation and Post-Curing 6 Full-Scale Trials 6.1 Class-A Panel 6.2 Semi-Structural Component 6.3 Technology Demonstrator 6.3.1 Cost Comparison 6.4 Application Guidance 6.4.1 Reduced Fiber Fraction Compounds 6.4.2 Co-Compression Molding 6.4.3 Application of Auxiliary Processes 7 Summary Bibliography Appendix A Evolution of Vehicle Curb Weight B Porosity Structure of Normal Density Compound C Surface Veil Distortion During Compression Moldin

Material Selection for a Composite Hip Joint

The use of biomaterials in orthopedic surgery has been successfully acceptable in the current medical practice. Total hip joint replacement (THR) is one of the most popular and successful operations in orthopedics. Total hip replacement (THR) has been using metal prosthesis for many years. However, the use of metal implants has two major disadvantages. The first disadvantage is that the stiffness of the metallic prosthesis is relatively high compared to the surrounding, load carrying bone. The elastic moduli of titanium and cobalt-chromium alloy are 110 and 210 GPa, respectively. Whereas the elastic modulus of cortical bone ranges from 15 to 25 GPa. This mismatch between the bone and the stiffness of the implant will cause the degradation of the bone-implant interface, which will lead eventually to loosening and prosthesis fracture. The second disadvantage of metallic prosthesis is the release of harmful metal ions, which may cause hypersensitivity to the patient. To overcome the stiffness problem and other related metal implants complications, recent advances in design and manufacturing technologies proposed the use of composite materials as an alternative to the metallic implants. The use of composite materials in orthopedic surgery offers a variety of new implant designs. Outstanding mechanical properties; radiolucency, biocompatibility and low weight are the major advantages compared with metals in clinical use today. Composite materials are known as low stiffness materials with mechanical properties close to the properties of bone. The strength and stiffness of composite materials can be varied easily when compared to metals. For example, the strength varies from 70 MPa to 1900 MPa and stiffness varies from 1.0 GPa to 170 GPa. Such tailorability in strength and stiffness could provide a state of stress in the femur closer to physiological level. Thus, it will eliminate the problems of bone-prosthesis loosening and prosthesis fracture. The main goal of this thesis is to investigate the performance of woven composites for a hip prosthesis made from hybrid materials. For such a purpose, field investigation was conducted locally to establish a realistic ground for the total hip replacement procedures in the U.A.E. This field investigation revealed that the THR cases performed in the U.A.E. are exponentially increasing every year. This increase in the THR cases requires an immediate solution for the problem. For the purpose of this design, two types of fibers were used to manufacture the specimens. The first type of fiber is the E-glass fiber. The second type of the fiber is the hybrid carbon-aramid fiber reinforced vinyl ester resin. Two types of processing techniques were used to manufacture specimens. The techniques were hot press molding and vacuum infusion. The specimens were then divided into three groups and each group contains eight specimens. Some specimens were kept immersed in a physiological solution for eight weeks, while others were used as virgin specimens. The evaluation process included mechanical test, weight gain calculation for the glass fiber and the scanning-electron microscopy (SEM) study. In this study, we found that immersion in the physiological solution caused reduction in strength and modulus of the composite materials manufactured by vacuum infusion technique. On the other hand, weight reduction did not occur for the glass fiber manufactured by hot press molding. This is due to the lack of adequate resin available in the fiber-matrix interface. Scanning-electron microscopy (SEM) study examined and showed the fractures\u27 surfaces occurred to the specimen. Fatigue tests performed on conditioned specimens have shown that the main failure mechanism can be attributed to the poor interface between the fiber and the matrix

Wireless Sensors and Actuators for Structural Health Monitoring of Fiber Composite Materials

This work evaluates and investigates the wireless generation and detection of Lamb-waves on fiber-reinforced materials using surface applied or embedded piezo elements. The general target is to achieve wireless systems or sensor networks for Structural Health Monitoring (SHM), a type of Non-Destructive-Evaluation (NDE). In this sense, a fully wireless measurement system that achieves power transmission implementing inductive coils is reported. This system allows a reduction of total system weight as well as better integration in the structure. A great concern is the characteristics of the material, in which the system is integrated, because the properties can have a direct impact on the strength of the magnetic field. Carbon-Fiber-Reinforced-Polymer (CFRP) is known to behave as an electrical conductor, shielding radio waves with increasing worse effects at higher frequencies. Due to the need of high power and voltage, interest is raised to evaluate the operation of piezo as actuators at the lower frequency ranges. To this end, actuating occurs at the International Scientific and Medical (ISM) band of 125 kHz or low-frequency (LF) range. The feasibility of such system is evaluated extensively in this work. Direct excitation, is done by combining the actuator bonded to the surface or embedded in the material with an inductive LF coil and setting the circuit in resonance. A more controlled possibility, also explored, is the use of electronics to generate a Hanning-windowed-sine to excite the PWAS in a narrow spectrum. In this case, only wireless power is transmitted to the actuator node, and this lastly implements a Piezo-driver to independently excite Lamb-waves. Sensing and data transfer, on the other hand, is done using the high-frequency (HF) 13.56 MHz. The HF range covers the requirements of faster sampling rate and lower energy content. A re-tuning of the antenna coils is performed to obtain better transmission qualities when the system is implemented in CFRP. Several quasi-isotropic (QI) CFRP plates with sensor and actuator nodes were made to measure the quality of transmission and the necessary energy to stimulate the actuator-sensor system. In order to produce baselines, measurements are prepared from a healthy plate under specific temperature and humidity conditions. The signals are evaluated to verify the functionality in the presence of defects. The measurements demonstrate that it is possible to wirelessly generate Lamb-waves while early results show the feasibility to determine the presence of structural failure. For instance, progress has been achieved detecting the presence of a failure in the form of drilled holes introduced to the structure. This work shows a complete set of experimental results of different sensor/-actuator nodes