Open Access

REVIEW

Influence of Key Parameters on the Crack Growth Resistance Curve (R-Curve) Behavior of End-Notched Flexure (ENF) Specimens of Laminated Composites: A Review

Mazaher Salamat-Talab^1,*, Hossein Kazemi^1,2, Mehdi Safari¹
1 Department of Mechanical Engineering, Arak University of Technology, Arak, Iran
2 School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran
* Corresponding Author: Mazaher Salamat-Talab. Email:

Journal of Polymer Materials https://doi.org/10.32604/jpm.2026.074982

Received 22 October 2025; Accepted 09 April 2026; Published online 22 May 2026

Abstract

Polymeric composite laminate materials have gained a prominent position in advanced industries because of their outstanding mechanical, thermal, and chemical properties. However, the lack of through-thickness reinforcement and the stress inconsistencies at the fiber-matrix interface result in weak out-of-plane properties and increase the delamination likelihood. Delamination is often a concealed form of damage that significantly diminishes the mechanical properties and long-term durability of laminated composites. Therefore, it is essential to recognize that, due to the significant shear stresses encountered in practical applications, a thorough understanding of delamination behavior under mode II loading is necessary. Also, this understanding cannot be achieved without a detailed analysis of the crack growth resistance curve (R-curve). Therefore, this review, in the first place, provides a comprehensive overview of the theoretical background and significance of the R-Curve in the mode II condition and analyzes the standard experimental methods and commonly used data reduction models, i.e., compliance calibration method (CCM) and the compliance-based beam method (CBBM), which are developed to determine this curve. Following this, conventional approaches to improving delamination resistance in laminated composites, such as stitching, Z-pinning, matrix toughening, and fiber surface treatment, are discussed, emphasizing their respective advantages and disadvantages. Afterwards, the review focuses on more efficient strategies to improve the R-Curve of laminated composites, specifically through modifications in stacking sequences and, most notably, the use of interlayers. Overall, the review of related studies indicated that incorporating optimized interlayers, especially hybrid or specially structured types, can significantly improve mode II ILFT, resulting in fully rising R-Curves. It should be noted that the primary goal of all strategies is to enhance the mode II ILFT by increasing the interaction and friction between layers in laminated composites. This improvement enables various toughening mechanisms to work together, including fiber bridging, fiber breakage, crack pinning, and crack arresting.

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Keywords

Composite laminate materials; crack growth resistance curve; delamination; interlayer; mode II interlaminar fracture toughness

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