Multiscale Modeling of Textile Composite Materials

1 Introduction

1.1 Introduction to textile composites  

Recently, significant growth in the development and applications of textile composites has been seen in many engineering fields such as automotive, aerospace and civil. Textile composites not only inherit the advantages of unidirectional composites, such as light-weight and high specific strength but also possess higher interlaminar shear strength, better damage tolerance and impact resistance as compared to unidirectional composites. Besides that, textile composites also offer lower manufacturing costs, ease of handling, and better drapability that makes them more suitable for manufacturing complex shapes. However, because of the complex microstructures, it is a much more challenging task to accurately predict the effective material behaviors of textile composites. 

                                Figure 1: Basic weave structures of 2D woven fabric composites.  

1.2 Motivation of Micromechanics study :

Heterogeneous materials, such as composites, solid foams, polycrystals, or bone, consist of clearly distinguishable constituents that show different mechanical and physical material properties. While the constituents can often be modeled through anisotropic behavior, the microstructure characteristics (shape, orientation, different volume fraction) of heterogeneous material often leads to an anisotropic behavior. The goal of micromechanics is to predict the anisotropic response of the heterogeneous material on the basis of the geometries and properties of the individual phases, a task known as homogenization. Another purpose of micromechanics is that it allows predicting multi-axial properties that are often difficult to measure experimentally. A typical example is the out-of-plane properties for UD composites. 

The main advantage of micromechanics is to perform virtual testing in order to reduce the cost of an experimental setup. Indeed, an experimental setup of heterogeneous material is often expensive and involve a more significant number of permutations such as constituent material combinations, fiber and particle volume fractions, fiber and particle arrangements, and processing histories. Once the properties of the constituent are known, all these permutations can be simulated through virtual testing using micromechanics. In especially textile composites, having complex microstructures it is difficult to conduct the experimental test and a very high precision testing setup is required for textile composites even though it is difficult to predict the out-of-plane properties accurately. As a result, researchers are focusing on the micromechanical modeling of textile composites.

1.3 3D Woven Fabric Composites

Two-dimensional laminated composites are characterized by their in-plane high specific stiffness and strength. However, most of the real application is exposed to out-of-plane loading conditions that make it impossible to resort to the 2D laminates as the proper solution. Wind turbine blades, stringers, and stiffener in aircraft, pressure vessels, and construction application are some examples of application in which out-of-plane loading are imposed on the structures. Thus, the need for a composite material with enhanced "through-thickness" properties has emerged. This need requires replacing 2D laminated composites with three-dimensional (3D) textile composite structures in which binding yarn is introduced in the thickness/z-directions as shown in the figure 2. 3D woven joints and preforms are widely used in aircraft, missiles, satellites, spacecraft, helicopters, vehicles and more. By means of the low cost, fast production, and lightweight solutions, 3D woven carbon fiber composites are the products of the present and the future.

Fig.2 Repetitive 3D orthogonal woven fabric composite and it's unit-cell 

 Advantages of 3D woven composites, over a 2D laminated composites:

• Directly woven into complex net shapes.
• high fiber volume and strength.
• improved impact resistance and Compression After Impact (CAI).
• Consist of X, Y and Z yarns.
• Yarns can be controlled according to stability, strength, and shape desired in the end product.
• Possibility to choose different fiber types such as carbon fiber, aramid, glass, etc., in the weaving process.
• Practically zero delamination between the layers
.• Reduce the cost of composite parts production  

Interlaminar Fracture Properties of 3D Woven Composites:

A significant advantage of 3D woven composites over conventional 2D laminates is high resistance to delamination cracking. 2D laminates are prone to delamination cracking when subject to impact or out-of-plane loads due to their low interlaminar fracture toughness properties.

Figure 2: Mode I delamination cracking in a 3D woven composite.  

 Applications for 3D woven composites

• Turbine engine thrust reversers, rotors, rotor blades, insulation, structural reinforcement and heat exchangers
• Nose cones and nozzles for rockets• Engine mounts
• T-section elements for aircraft fuselage frame structures
• Rib, cross-blade, and multi-blade stiffened aircraft panels
• T- and X-shape elements for filling the gap at the base of stiffeners when manufacturing stiffened panels
• Leading edges and connectors to aircraft wings
• I-beams for civil infrastructure• Manhole covers