Review of Fracture Analysis of Natural Fiber Polymer Reinforced Composites: An Experimental Study

Review of Fracture Analysis of Natural Fiber Polymer Reinforced Composites: An Experimental Study

Santhosha M, Raghavendra N T, Manjunatha G M

Department of Mechanical Engineering, BIET, Davanagere 577004, India

Abstract: The incorporation of natural fibers into polymer composites has gained significant attention in recent years due to their eco-friendly nature and potential to replace traditional synthetic reinforcements. This review paper presents a comprehensive analysis of fracture behavior in natural fiber polymer reinforced composites through an extensive examination of experimental studies. The review focuses on various natural fiber types, composite processing techniques, fracture testing methods, fracture toughness evaluation methods and the influence of different parameters on the fracture properties of these composites. The findings offer valuable insights into the mechanical performance and fracture mechanics of natural fiber polymer composites and provide guidance for their application in various engineering fields.

INTRODUCTION:

The introduction sets the stage by outlining the growing interest in natural fiber polymer reinforced composites as an environmentally sustainable alternative to conventional composites. The significance of fracture analysis in understanding the mechanical behavior of these materials is emphasized, along with the potential advantages of utilizing natural fibers [1]. Natural Fiber Polymer Reinforced Composites includes natural fibers, such as those derived from plants (e.g., jute, flax, hemp, bamboo) and animals (e.g., wool), are used as reinforcement within a polymer matrix. These composites combine the benefits of both natural fibers and synthetic polymers, offering improved mechanical properties, lower environmental impact, and potential cost savings compared to traditional synthetic fiber composites [2].

Considering an overview of the increasing interest in sustainable and eco-friendly materials, which has led to the exploration of natural fibers as reinforcements for polymer composites. Types of Natural Fibers: Discuss various natural fibers commonly used in these composites, including their properties, sources, and advantages [3]. Examples include jute, sisal, flax, hemp, kenaf, bamboo, and coir. Explore different types of polymers (thermoplastics, thermosets, biopolymers) used as matrices for these composites. Each type of polymer has unique properties that can influence the final properties of the composite [4]. Natural fibers can be classified in various ways based on their origin. Here are a few common classifications of natural fibers [5,6]:

Plant Fibers: These fibers are derived from various parts of plants, such as stems, leaves, and seeds. Examples include flax, jute, hemp, kenaf, and bamboo.

Animal Fibers: These fibers come from animals and can include materials like wool and silk.

Mineral Fibers: These fibers are derived from naturally occurring minerals or rocks, such as basalt fibers.

NATURAL FIBER COMPOSITE PROCESSING:

This section delves into the diverse range of natural fibers employed in polymer composites, such as jute, hemp, sisal, bamboo, coir, and others. Each fiber's unique properties and suitability for reinforcement in specific polymer matrices are discussed [7]. Additionally, the various composite processing techniques, including hand layup, Vacuum bagging, compression molding, injection molding, and extrusion, are explored in terms of their impact on the final composite's fracture behavior [8].

FRACTURE TESTING METHODS IN NATURAL FIBER COMPOSITES:

The review extensively covers different fracture testing methods used to characterize natural fiber polymer composites, such as tensile tests, flexural tests, impact tests, and fracture toughness tests. The advantages and limitations of each method are highlighted, offering valuable insights into their appropriateness for specific applications and experimental scenarios. Fracture testing methods are crucial for assessing the mechanical behavior and performance of natural fiber composites. These methods help in understanding how these materials behave under different loading conditions, including how they fracture or fail. Here are some commonly used fracture testing methods for natural fiber composites:

Tensile Testing (ASTM D3039/D3039M, ASTM D638): Tensile testing involves subjecting a specimen to an axial load to measure its tensile strength, modulus of elasticity, and elongation at break. For natural fiber composites, this test helps determine the composite's resistance to stretching and its ability to withstand forces pulling it apart [9].

Flexural Testing (ASTM D790): Flexural testing, also known as three-point or four-point bending, assesses the bending strength, modulus of elasticity, and flexural properties of composites. It provides insights into the material's response to bending loads, which is relevant for applications where the material might be subjected to bending or bending-induced stresses [10].

Impact Testing (ASTM D256, ASTM D6110): Impact tests evaluate a material's resistance to sudden loads or impacts. For natural fiber composites, these tests help determine their toughness and ability to absorb energy during impact events [11].

Fracture Toughness Testing (ASTM E399, ASTM D5045): Fracture toughness testing assesses a material's ability to resist crack propagation. This is particularly important for natural fiber composites, as it provides insights into their resistance to crack growth and their behavior under stress concentrations [12].

Shear Testing (ASTM D3846, ASTM D4255): Shear tests assess the shear strength and shear modulus of composite materials. Shear loading is relevant in applications where the material experiences force parallel to its plane.

Fatigue Testing (ASTM D3479, ASTM D7791): Fatigue testing involves subjecting a material to repeated loading and unloading cycles to assess its endurance limit and fatigue life. This is important for applications where the material will be exposed to cyclic loading.

Microscopic Analysis (Scanning Electron Microscopy – SEM): Microscopic analysis techniques like SEM allow for the examination of fracture surfaces at a microscopic level. This can provide insights into the mode of failure, fiber-matrix interactions, and other details of the fracture process [13].

Acoustic Emission (AE) Testing: This is an NDT method used to analyze the crack behaviour. AE testing involves monitoring the acoustic signals generated during material deformation and failure. It can provide information about crack initiation, propagation, and other failure mechanisms [14].

It's important to select the appropriate testing method based on the specific properties and behaviors you want to investigate in natural fiber composites. Keep in mind that these methods might have specific standards associated with them (such as ASTM standards), which provide guidelines for test setup, specimen preparation, and data analysis.

FRACTURE TOUGHNESS EVALUATION METHODS IN NATURAL FIBER COMPOSITES:

Fracture toughness evaluation methods are essential for understanding how materials, including natural fiber composites, respond to crack propagation and failure. Fracture toughness provides insights into a material's resistance to crack growth and its ability to withstand applied stresses without catastrophic failure. In the context of natural fiber composites, which combine natural fibers with polymer matrices, fracture toughness evaluation is crucial for assessing their performance in structural appliations. Here's a review of fracture toughness evaluation methods in natural fiber composites:

Mode I Fracture Toughness (ASTM D5528, ASTM D5045): Mode I fracture toughness, also known as the opening mode, involves the propagation of a crack in the plane of the material under tensile loading. In natural fiber composites, this mode reflects the material's resistance to crack opening and fiber-matrix interface debonding. Testing methods such as the Single Edge Notched Tension (SENT) test or the Double Cantilever Beam (DCB) test are commonly used [15].

Mode II Fracture Toughness (ASTM D7905): Mode II fracture toughness, or the sliding mode, examines crack propagation perpendicular to the applied tensile load. This mode is relevant for assessing the interlaminar shear strength and the material's resistance to delamination. End-Notched Flexure (ENF) and End-Loaded Split (ELS) tests are used to measure Mode II fracture toughness [16].

Mixed-Mode Fracture Toughness: Natural fiber composites can experience combined modes of fracture. Tests that can be used to evaluate mixed-mode fracture toughness include the Mixed-Mode Bending (MMB) test and the Four-Point Bending Shear (4PBS) test. These methods simulate loading conditions that involve a combination of opening and sliding modes [17,18].

Numerical Simulation and Finite Element Analysis (FEA): Numerical methods, like FEA, can simulate fracture behavior by modeling crack propagation and stress distribution. FEA allows researchers to study the effect of various factors on fracture toughness, such as fiber orientation, matrix properties, and loading conditions [19].

Notch Toughness Testing: Notch toughness tests involve creating notches or pre-cracks in specimens to simulate stress concentrations. The Charpy and Izod tests, common in polymer materials, are also used to assess the notch toughness of natural fiber composites [20,21].

Energy Absorption Capacity: Assessing the energy absorption capacity of a material during crack propagation can provide insights into its fracture resistance. Energy-based approaches, such as the Essential Work of Fracture method, are used to quantify this property [22].

It's important to consider the specific characteristics of natural fiber composites, such as fiber-matrix interactions, anisotropy, and potential environmental influences, when choosing and interpreting fracture toughness evaluation methods. A combination of experimental testing and theoretical modeling can provide a comprehensive understanding of the fracture behavior of natural fiber composites and guide their application in various industries [23].

INFLUENCE OF PARAMETERS ON FRACTURE BEHAVIOR:

This section focuses on the influence of various parameters on the fracture properties of natural fiber polymer composites. Factors like fiber volume fraction, fiber orientation, matrix type, interfacial adhesion, and environmental conditions are discussed in depth, providing a comprehensive understanding of their effects on fracture toughness, crack propagation, and ultimate failure of the composites [24,25].

Conclusion:

The conclusion concisely summarizes the key findings from the review and emphasizes the importance of fracture analysis in understanding the mechanical behavior of natural fiber polymer composites. The potential of these composites in diverse engineering applications is highlighted, and recommendations for future research and development are provided.

The review paper concludes with an overview of the potential applications of natural fiber polymer reinforced composites based on their fracture behavior. It also identifies research gaps and proposes future directions for further enhancing the mechanical properties and fracture resistance of these materials. Potential challenges and opportunities for industrial adoption are discussed, encouraging further research in this area.

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