Fracture Behavior of Nanocomposites and Reinforced Laminate Structures

This chapter explores the characterization of mechanical and fracture behavior in nanocomposites and reinforced laminated structures. Nanocomposites, materials incorporating reinforcements on the nanoscale, offer potential for significant enhancements in properties compared to traditional composites. Reinforced laminated structures, often utilizing fiber-based reinforcements, are widely used in engineering applications due to their high strength-to-weight ratio. However, understanding their deformation and fracture under stress is crucial for optimal design and performance. This chapter explores various testing methodologies, such as tensile tests and fracture mechanics experiments, to characterize these material properties. The data obtained can then be applied to optimize the design of nanocomposites and laminated structures for real-world applications in sectors like aerospace and automotive engineering.

The recent design of advanced engineering components based on high-performance composites has increased the scientific attention towards accurate theoretical and computational models to simulate the mixed-mode delamination and fracturing phenomena, involving mechanical nonlinearities of materials and interfaces.

In a context where fiber reinforced polymer (FRP) composites are largely adopted as reinforcements in masonry and concrete substrates, in the first part of this chapter, we study the bond behavior in FRP-to-concrete structural systems, even accounting thermal variations affecting the interfacial stresses and material properties of adhesives, by means of an extended contact algorithm in a classical finite element environment, capable to handle both closure and opening of bodies at their interfacial level.

Among more recent sustainable and reversible retrofitting systems, the so-called composite-reinforced mortar (CRM) with inorganic binders within a matrix is a valid alternative to FRPs, since it ensures a higher compatibility with substrates because of the high vapor permeability of mortar. Thus, the second part of this chapter is devoted to the numerical study of the fracturing behavior in CRM single-lap shear tests, as provided by a cohesive zone (CZ) modeling and concrete damage plasticity (CDP) modeling, in a classical finite element setting. The selected specimens are characterized by the presence of mortar with mechanical properties approximated analytically, according to different polynomial or exponential functions. Different fracturing modes are explored numerically for such CRM specimens, in their matrix and reinforcement phases. A systematic investigation is, thus, performed numerically, discussing about the reliability of the proposed tool to predict the response of the overall reinforcement system, rather than costly experimental tests. The proposed results could represent valid numerical solutions for further experimental and/or analytical investigations in the field.

The last part of this chapter proposes a theoretical study of the mixed-mode interfacial response of functionally graded coatings (FGCs) on different substrates, here modelled as asymmetric double cantilever beams, accordingly to experimental tests, while resorting to an enhanced beam theory (EBT), in which subcomponents are partially connected by a continuous arrangement of elastic-brittle interfacial springs, either in tangential or normal directions. Based on the Timoshenko beam theory, the differential equations of the problem are defined directly in terms of unknown interfacial modes I and II stresses, whereas analytical distribution laws account for different material functional graduations in the thickness direction of specimens. Such variation is verified to affect the local and global response in terms of interface stresses, internal actions, energy quantities, and load-displacement curves, with a high accuracy, as checked against classical single beam theories (SBTs).

This chapter delves into the intricate realm of nanocomposites and reinforced laminate structures, offering a thorough exploration of their fracture behavior. With a specific focus on Mode I, Mode II, and Mixed Mode I/II fracture modes, the chapter embarks on unraveling the fundamental principles governing the integrity of these advanced materials. Through meticulous analysis, it navigates the distinct characteristics and implications associated with each fracture mode, shedding light on the nuanced interactions within laminated structures. The discussion extends to the influential factors shaping fracture mechanics in this context, considering aspects such as material composition, structural design, and environmental conditions. By providing a comprehensive introduction to these diverse fracture modes, the chapter aims to establish a solid foundation for understanding the underlying mechanics that govern nanocomposites and reinforced laminate structures. This groundwork not only contributes to the theoretical understanding of fracture behavior but also sets the stage for practical applications in various engineering and material science disciplines. As the complexities of advanced materials continue to evolve, this chapter serves as a crucial reference for researchers, engineers, and practitioners seeking a nuanced comprehension of the fracture mechanics intrinsic to laminated structures.

The purpose of this study is to create a useful and easy-to-understand machine learning-based model for predicting mixed-mode I/II fracture load. To this end, a database composed of specimen test configuration, material, ultimate stress, thickness, crack length, crack angle, mode I fracture toughness, mode I stress intensity, mode II stress intensity, T-stress, and mixed-mode I/II fracture load was used for the training and testing. As the problem is greatly dimensional, Gaussian Process Regression technique was chosen and optimized. The effect of variability in the input space on the output response was characterized using Monte Carlo technique. At the same time, the impact of the size of training set on the effectiveness of prediction model was also pointed out. The coefficient of determination (R²), Mean-Absolute-Error (MAE), and Root-Mean-Squared-Error (RMSE) were used as quality metrics during learning and determining the most suitable prediction model. Finally, the prediction capability was investigated and discussed. Besides, uncertainty investigation was conducted to quantify the confidence interval. For practical application, a Graphical User Interface (GUI) was developed and provided for interested users. This study showcases the effectiveness and wide-ranging applicability of data-driven fracture predictions, in contrast to conventional physics-based criteria.

In many engineering applications, laminated structures are vulnerable to cracking under various loading scenarios. For structural integrity and design, it is essential to comprehend fracture behavior under different modes. The common fracture modes in laminates are mode I,mode II and mixed mode I/II. Cracks propagate in three major ways; mode I is perpendicular to the applied tensile stress, mode II is parallel to the applied shear stress, and mode I/II combines elements of the two modes. This lays the groundwork for investigating laminated constructions’ fracture behavior and mechanics under various loading scenarios.

The idea of fracture modes in laminated structures is presented in this study, with particular attention to Mode I (opening), Mode II (in-plane shear), and Mixed Mode I/II. By utilizing the critical energy release rate, the fracture toughness of the joints was assessed. The double-cantilever beam specimen was used for mode-I tests, the end-notch flexure specimen was used for mode-II tests, and a combination of the two aforementioned specimens was used for mixed-mode tests (three mixity ratios). In order to assess and identify the method’s advantages and disadvantages, the cohesive zone modeling approach was also used to simulate the fracture behavior of the bonded joints. Each mode is clearly illustrated via images. Understanding fracture modes is crucial because of their effects on estimating the fracture toughness of a material: Knowing the dominant mode aids in estimating the resistance to crack propagation. Building structures to support particular loads: maximizing the predicted mode in the selection of materials, ply orientation, and reinforcing tactics. Finding the weak spots in laminated constructions identifying failure-prone locations according to the expected mode. This basic understanding facilitates a deeper comprehension and precise prediction of fracture behavior in layered structures by acting as a springboard for additional research into the concepts of fracture mechanics, particular materials, and testing techniques.

This work’s focus goal is to carry-out a computational modeling of the path taken by cracks in linear elastic materials under mixed-mode loadings and investigate the impact of a hole’s presence on the fatigue life and propagation of fatigue cracks in a MCTS under conditions of steady magnitude loading. The mixed-mode fatigue life of compact tension specimens with varying configurations has been assessed using the Paris law model in accordance with inference of linear elastic fracture mechanics. The methodology entails a precise assessment of stress intensity factors, the trajectory of fracture propagation, and a progressive crack extension study and fatigue life assessment. The ANSYS is applied for precise prophecy of the fracture propagation routes and the corresponding fatigue life under steady magnitude loading conditions. The book chapter focuses on the effects on the various configurations of holes in the metal specimens and predict the fatigue crack extension in the specimens.

In light of the rapid advancements in large-scale continuous fiber-reinforced polymer (FRP) composites processed via additive manufacturing (AM) for high-performance structural applications, there is a need to assess the fatigue performance of these structures. AM is being rapidly adopted due to reduced costs and time of material processing with applications spanning aeronautics, space exploration, energy (wind turbine blades, tidal wave energy converters, and composite overwrapped pressure vessels for hydrogen storage), marine, automotive, nuclear, and consumer goods. Unlike metals, fatigue in composites is multi-modal and multiscale due to inherent material heterogeneity, anisotropy, and hierarchy. Additionally, the environment, process-induced defects, and in-service damage can drastically influence composite fatigue life.

In this book chapter, a review of the state of the art in the fatigue characterization of AM-FRP composites has been presented with particular emphasis on the effect of process defects and composite microstructure/morphology on fatigue damage incipience and progression. Traditional stress-life approaches have been contrasted with non-traditional techniques such as infrared thermography, conductivity drop, and other rapid and reliable fatigue assessment techniques. Some guidelines will be presented for material design and testing to reduce the qualification and certification times for emerging AM-FRP composites.

In the current work, the mechanical and fracture toughness properties of 6082 Al alloy have been improved by rolling the alloy to 40% and 70% thickness reductions at cryogenic and room temperatures, respectively. Every cryorolled sample undergoes ageing at various temperatures, i.e., 140°, 160°, and 190 °C to improve the strength, ductility, and fracture toughness. Finite element software (Abaqus) is used to evaluate the behavior of crack growth. The deformation plasticity model, which takes the material’s yield strength into consideration, models the material’s path between its elastic and plastic ranges using a single polynomial function. The results show that the crack progression in 90% CR alloy is found a smaller amount as compared to 40% RTR, 40% CR, 70% RTR, 70% CR, and 90% RTR for the similar geometry, loading and boundary situations as a result of higher dislocations density and construction of sub-grain structures in the CR alloy.

Fracture behavior of aerospace grade fiber/epoxy composites aircraft structure deals until now with several questions, where the major issues are from in-service damage. Foreign impacts, climate phenomena (hail, ash abrasion, lightning strike) and multiaxial loads, combined with the variability of the manufacturing process, are the prime source of components’ debonding, delamination, matrix fracture, and fiber pull-out and cracking. These failure mechanisms are complex requiring new solutions for monitoring tasks and repair procedures.

As in the aerospace sector, the primary objective is to provide comfort and safety to passengers and payload; the Building Block Approach has been used to test, from coupons to whole structures, the composite materials on aircrafts and space vehicles. Recent advances on the first level have reached by developing high toughness matrix and surface fibers’ treatments, to improve ILSS or G_IC. The analysis of singularity details such as ply drop-offs, bolted/fastened/glued joints or edge effects takes place from second to fourth levels. It is at those stages where multifaceted fracture occurs, expecting to have a failure probability of 10E−6 by flight hour. In this chapter, multiple study cases from coupons to subassemblies are illustrated to give a complete picture of the fracture performance of aerospace fiber/epoxy composites.

Aerospace-grade fibers and nano-composites are widely utilized in the field for their high durability and impact resistance. These fibers and epoxy bonds allow an immense strength-to-weight ratio and superior stiffness with rigidity. As this fiber undergoes cyclic loading and tension due to environmental effects, it exhibits modes of failure and delamination. Depending on its usability, they have undergone various amounts of testing and loading conditions. The most common fracture behaviors comprise 3-mode failure behavior. To avoid such fracture behavior and undergo structural failure, electromagnetic interference (EMI) and thermal shielding are implemented on the fiber composites. This provides strengthening and resistive ability for the materials. The researchers shall work on the combination of I-II and I-III modes of failures during the application of loads and conclude on the characteristic performance of the fiber. This study is carried out for the prediction of the crack path based on modular KI-KIII stress intensity factors with the help of Finite Element Analysis. The analysis is based on determining the mixed mode fracture toughness envelope and maximum tangential stress criterion to determine the directional crack tip.

This chapter delves into the fracture behavior of nanomaterial-enhanced carbon fiber-reinforced polymer (CFRP) composites. It explores how traditional fracture mechanisms like matrix cracking and fiber-matrix debonding are altered by nanomaterials. The chapter highlights how these nanomaterials can bridge cracks, strengthen interfaces, and potentially introduce additional functionalities, ultimately enhancing fracture resistance. Computational modeling techniques like FEA and multiscale modeling are discussed as valuable tools for analyzing crack propagation and understanding the influence of nanomaterials. Promising future research directions for material development, including exploring novel nanomaterials and optimizing production methods, are outlined. The chapter concludes by comparing traditional and nanomaterial-enhanced CFRPs, emphasizing the advancements in fracture resistance and durability achieved through nanomaterial incorporation.

The aviation industry is constantly striving for improved safety and operational efficiency, and one of the most important aspects of maintenance and reliability management is accurately predicting the remaining useful life (RUL) of aircraft structures. Parameters influencing RUL of aeroplane structures subjected to fatigue loading are investigated in this work. The manufacturing quality, usage profile, load spectrum, flight hours, environmental factors, maintenance history, upgrades, structural monitoring systems, operational procedures, and aging impacts are among the factors taken into account. Deep learning models are trained and validated using an extensive dataset that includes historical data on aircraft usage, maintenance records, and structural health monitoring. The temporal dependencies present in the data are captured using recurrent neural networks (RNNs) and other networks like LSTMs, which allow for the modeling of intricate relationships between the various components influencing RUL. To offer more accurate RUL predictions, the study highlights the importance of using both internal and external variables in a holistic approach to predictive modeling. The identification of systematic plan that affect structural integrity is made easier by the integration of advanced analytics and machine learning approaches.

The present work’s objective is to inspect the fracture-fatigue behaviour of the 6082 Al alloy, an aluminium-silicon-magnesium alloy by rolling 6082 Al alloy plates at normal temperature, and cryogenic temperature results in thickness reductions of 40%, 70%, and 90%, respectively. Through experimental research, the impact of cryorolling on the high cycle fatigue behaviour of aluminium 6082 alloy has been investigated and compares these results by finite element software (Ansys). It has been noted that the fatigue life of 90% CR samples, as opposed to 90% RTR samples, is found to be maximal for a given degree of alternating stress because the CR samples have more sub-grain structures and a larger disorder density.

This project investigates the effect of thermal exposure on the life of a novel composite material made of carbon fiber-reinforced polymer (CFRP) and high-density polyethylene (HDPE). The material is fabricated using a hot-press method and cut into specimens for mechanical and microstructural testing according to ASTM D3039 standards. The specimens are subjected to different temperatures (25 °C, 50 °C, 75 °C, and 100 °C) for 3 and 6 days in an industrial oven before conducting tensile testing and field emission scanning electron microscopy (FESEM) analysis. This project aims to understand the degradation mechanisms and performance characteristics of the material under thermal conditions and to provide useful information for the design and development of advanced composite materials with potential applications in aerospace, automotive, marine, and civil engineering industries.

Engineering is the material embodiment of scientific principles for greater common good. Therefore, material science provides the foundation for innovation across all domains of engineering and helps the development of new technologies. Artificial intelligence (AI) and machine learning (ML) are being utilized more and more to develop novel materials, creative testing techniques, or models that anticipate the properties of materials. Estimating the remaining useful life (RUL) of contemporary materials, such as nanocomposites and reinforced laminated systems, is crucial for ensuring the robustness and stability of structural elements in a range of applications. Both nanocomposites and reinforced laminated structures have unique mechanical properties, structural integrity, and usage. Utilizing these properties, external conditions, and extent of usage, ML models can be developed for physical data-driven parameters, giving a comprehensive approach to RUL predictions. Data-driven models use past material performance data to identify intricate degradation trends. To find important indicators impacting RUL, feature engineering and selection techniques are investigated.

Drawing inspiration from nature’s remarkable self-healing prowess, this chapter explores the development of a revolutionary class of bio-inspired nanocomposites and laminates. These advanced materials hold immense potential for applications requiring self-repair functionality. The chapter explores into the design and engineering of bio-based components embedded within the nanocomposites. These components mimic the sophisticated self-healing mechanisms observed in biological systems, enabling the material to autonomously repair damage. The laminates are meticulously crafted to facilitate self-healing at the critical interfaces between distinct layers. This synergistic approach, combining biomimetic components and strategic laminate design, is anticipated to yield a new generation of materials boasting exceptional self-healing properties. The chapter offers a comprehensive overview of the cutting-edge advancements related to self-healing composites. It sheds light on the promising applications of shape memory alloys and shape memory polymers when incorporated into composites reinforced with advanced carbon nanotubes (CNTs). These composites exhibit remarkable self-healing capabilities.

Laminated structures represent a critical class of composite materials with widespread applications across various industries due to their customizable mechanical properties and versatility. This manuscript provides a comprehensive exploration of laminated structures and fracture mechanics, aiming to enhance understanding and application in engineering practice. The manuscript begins with an introduction that explains the importance of laminated structures in various industries, including sports equipment manufacturing, automotive, aerospace, and civil engineering. It then goes on to discuss the benefits of combining different materials to achieve better mechanical performance. The principles of fracture mechanics are discussed in detail, with a focus on stress intensity factor, energy release rate, and fracture toughness as the three main factors influencing the start and spread of cracks. The manuscript further delves into the distinct modes of fracture, namely, Mode I (opening mode), Mode II (in-plane shear mode), and Mixed Mode III (anti-plane shear mode), elucidating their behaviors and influences on laminated structures under various loading conditions. In addressing the factors influencing fracture in laminated structures, the manuscript synthesizes material properties, layer orientation, interface characteristics, residual stresses, environmental effects, loading conditions, and crack tip geometry, offering insights crucial for fracture analysis and structural design. The manuscript also clarifies several fracture criteria that are frequently used to predict failure in laminated structures, such as the fracture toughness criterion, critical stress intensity factor criterion, strain energy density criterion, and energy release rate criterion. Through meticulous examination and comparison of fracture criteria across different modes of fracture, this manuscript provides engineers and researchers with a comprehensive framework for assessing fracture behavior and designing resilient laminated structures. Ultimately, the manuscript underscores the importance of understanding fracture mechanics in ensuring the reliability, safety, and performance of laminated structures across diverse applications.

The fracture behavior of 3D printed nanocomposites in mixed mode loading conditions is investigated in this study. Nanocomposites, owing to their tailored microstructures and enhanced mechanical properties, are increasingly employed in various engineering applications. However, their fracture mechanics, particularly under mixed mode loading, remains relatively unexplored. This research employs experimental and computational methods to analyze the crack growth and fracture toughness of 3D printed nanocomposites under different modes of loading, focusing on the interaction between various reinforcing nanoparticles and the polymer matrix. The findings reveal significant insights into the fracture mechanisms, critical energy release rates, and crack path deviations observed in mixed mode conditions. Such understanding is crucial for optimizing the design and performance of nanocomposite materials in structural applications where complex loading conditions are prevalent.

The study of fracture mechanics in fiber/epoxy composites represents a cornerstone in the quest for enhancing the structural integrity and reliability of aerospace components. This abstract delves into the complexities and significance of understanding the fracture behavior of these advanced materials, encompassing fundamental principles, critical fracture parameters, environmental considerations, and advanced modeling techniques. Through meticulous investigation and analysis, researchers have elucidated the mechanisms governing crack initiation and propagation in fiber/epoxy composites, shedding light on key fracture parameters such as interlaminar and intralaminar fracture toughness, cohesive zone parameters, and fatigue crack growth rates. Furthermore, the impact of environmental factors, including moisture absorption, temperature variations, chemical exposure, and UV radiation, on composite performance is examined, highlighting the importance of mitigating environmental degradation to ensure long-term durability. Leveraging advanced modeling techniques such as finite element analysis, cohesive zone modeling, and multiscale modeling, researchers can simulate and predict composite behavior with unprecedented accuracy, enabling informed decision-making and optimization of composite designs. As the aerospace industry continues to evolve, the insights gleaned from this abstract pave the way for future advancements in materials science, engineering, and structural integrity, shaping the trajectory of aerospace innovation and exploration.

Non-destructive testing (NDT) stands as a crucial practice for ensuring the reliability and structural integrity of various materials and components without causing any harm. The evolution of NDT marks a significant advancement, empowering the evaluation and measurement of vital properties within materials or structures while preserving their innate effectiveness and functionality. The interdisciplinary applications of NDT span across industries like aerospace, manufacturing, construction, and energy, playing a key role in guaranteeing the safety and durability of structures and materials. This section explores the historical use of conventional NDT methods for flaw identification, emphasizing the substantial advancements in accuracy and efficiency driven by ongoing technological progress. It systematically investigates the principles, limitations, and applications of these traditional NDT methods, with a specific focus on their effectiveness in detecting 2D faults, cracks, and defects. Furthermore, the section provides a comprehensive overview of current studies and developments in the field, providing insights into the current state of defect and fracture detection. By emphasizing the synergies between innovative approaches and traditional methods, the discussion seeks to contribute to a broader understanding of NDT in composite materials. The exploration of the integration of conventional and advanced methodologies offers valuable perspectives on the transformative potential of emerging technologies in defect identification, adding to the ongoing discourse on the dynamic landscape of NDT.