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Published in:
2025 | OriginalPaper | Chapter
9. Application of Fracture Mechanics to Composites
Author : Bahram Farahmand
Published in: Fundamentals of Composites and Their Methods of Fabrications
Publisher: Springer Nature Switzerland
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Abstract
This chapter examines the application of fracture mechanics to polymer matrix composites (PMCs), emphasizing their distinct behaviors under monotonic and cyclic loading conditions. Unlike metallic alloys, which are homogeneous and isotropic, PMCs exhibit unique failure mechanisms that necessitate a deeper understanding for effective structural life assessment. The chapter delves into the linear elastic fracture mechanics (LEFM) approach, which focuses on the crack tip stress intensity factor and the energy required for crack propagation. It discusses the conventional stress-life and strain-life approaches, contrasting them with LEFM to highlight the importance of considering preexisting defects in composite materials. The chapter also explores various nondestructive inspection methods, such as ultrasonic testing and thermography, to detect initial flaw sizes and monitor crack growth. It provides detailed insights into the Griffith energy balance and Irwin stress intensity factor approaches, essential for assessing crack behavior under applied loads. The chapter further elaborates on the methods for obtaining mode I fracture properties and the challenges associated with testing composite materials. It includes case studies on delamination growth and matrix crack propagation, offering practical examples and analytical tools for life assessment. Additionally, the chapter addresses the importance of fracture allowables and the use of software like NASGRO and AFGRO for predicting the number of cycles to failure. It concludes with a summary of the key findings and the significance of fracture mechanics in enhancing the durability and reliability of composite structures, paving the way for their broader application in various industries.
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Abstract
Understanding the fracture behavior of composite materials is essential for ensuring the safety and reliability of primary structures that have applications in industries. This chapter provides a comprehensive overview of the application of fracture mechanics to composite materials when subjected to both modes I and II, as well as the mixed-mode loading conditions. This assessment begins by presenting the fundamental principles of fracture mechanics and their applicability to composite materials. It explores the unique challenges associated with predicting the remaining fatigue life of composites, considering factors such as anisotropic nature of material, fiber orientation, matrix properties, and environmental conditions. The role of manufacturing processes and defects in influencing fatigue and fracture is also discussed, highlighting the need for quality control and proper nondestructive inspection methods. This work also discusses experimental techniques and testing procedures for obtaining the fracture toughness and fatigue crack growth rate data of composite parts subjected to both mode I and II. These data can be utilized in estimating the number of cycles to failure when components are exposed to cyclic load environments. It explores the applicability of linear elastic fracture mechanics in assessing fracture behavior of composite structures. Furthermore, several scenarios concerning crack behavior were assessed. Crack growth in the matrix, when defects are parallel and perpendicular to the fibers under mode I is discussed. The case of crack arrest at the interface, the bridging mechanisms where fibers are untouched, and the presence of defects because of delamination are also presented in this chapter. It further discusses ongoing research efforts aimed at improving prediction accuracy, the question of which parameter should be used when plotting fatigue crack growth results, developing standardized testing procedures, and advancing the understanding of the complex interactions between various factors influencing fatigue crack/damage growth behavior in composites under mode I, and II, as well as mixed-mode loading conditions.
