Overview
FrançaisABSTRACT
This article provides an overview of the fracture mechanics applied to translaminar fracture of composite laminates. This phenomenon is particularly important in the field of the damage tolerance certification of composite structures. After a brief review of the fracture mechanics concepts, the different experimental tests to evaluate these characteristics will be presented and discussed. A detailed presentation of the different translaminar damages will be therefore done then a few characteristic levels of fiber failure toughness will be discussed. Finally the energy dissipated during a crash, the specific energy absorption (SEA), will be addressed.
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Read the articleAUTHORS
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Christophe BOUVET: Professor Institut Clément Ader (ICA), ISAE-SUPAERO, Toulouse, France
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Benoit VIEILLE: Professor Materials Physics Group (GPM) INSA Rouen Normandie, Rouen, France
INTRODUCTION
Composite materials are being used more and more in structural applications, particularly in fields where good specific mechanical properties (i.e. mechanical properties reduced, or divided, by density) are required. This is particularly true in the transport sector, and more specifically in the aeronautics and space industries, and increasingly in other sectors such as the automotive, naval and rail industries. One of the main advantages of composite materials is, of course, their low weight, which makes for lighter structures and, consequently, lower vehicle fuel consumption, thereby reducing the ecological impact of our journeys.
This article focuses on the translaminar fracture of long-fibre-reinforced polymer matrix composite laminates. The mode of failure depends mainly on the stacking sequence (or draping) of the laminate, i.e. the orientation of the fibers in each ply. The spatial distribution of the fibers will then condition the material's ability to dissipate mechanical energy during damage growth within a laminated composite. The methods to be used to assess this energy dissipation during fracture will therefore be guided by the contribution of the various plies to translaminar fracture. Depending on the configuration encountered, the general objective is :
quickly identify applicable experimental techniques;
quantify material quantities intrinsic to fracture, such as fracture toughness (a function of fracture mode), crack growth and energy restitution rate.
In the first part, we will review the main concepts of fracture mechanics, which will help us to understand the rest of the article. In particular, the notions of failure modes, stress intensity factor, energy restitution rate and toughness will be recalled. The various experimental tests used to measure toughness, as well as the associated standards, will also be presented. In practice, these methods are based on specimens with a specific geometry (depending on the stress mode: tension, compression, bending) and a "pre-defect" (notch or hole). The advantage of a pre-defect machined into the material is that it concentrates stresses in a damage growth zone, which in turn promotes various dissipative damage mechanisms.
In the second part, the main damage modes in laminated composite structures will be presented. In particular, the aim is to gain a better understanding of the types of damage that lead to translaminar failure, and to grasp its full complexity. The mechanisms of translaminar failure will be presented according to the loading mode (tension, compression, crushing, shear), with particular emphasis on the parameters (matrix type, reinforcement architecture, etc.) influencing...
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KEYWORDS
composite structures | energy release date | translaminar failure | crack | toughness
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Mechanics of fiber rupture in laminated composites
Bibliography
Bibliography
Standards and norms
- Standard test method for mode I interlaminar fracture toughness of unidirectional continuous fiber reinforced composite materials - ASTM D5528-33 - 2013
- Standard test method for measurement of fracture toughness - ASTM E1820-18 - 2018
- Standard test method for translaminar fracture toughness of laminated and pultruded polymer matrix composite materials - ASTM E1922-15 - 2015
- Standard test method...
Regulations
Federal Aviation Administration 25 (FAR25) – Advisory Circular 25.571, Damage tolerance and fatigue evaluation of structure (1978)
Joint Airworthiness Requirements 25 (JAR25) – Part 1: requirements, Part 2: acceptable means of compliance and interpretations (for composite structures: JAR25 § 25.603 and ACJ 25.603) (1978)
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