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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.4, #2)

Fractal Analysis and Simulation of Surface Roughness of Ceramic Particles for Composite Materials by X. Kuang; Z. Zhu; G. Carotenuto; L. Nicolais (pp. 69-81).

An analytical model is presented for the determination of the fractal dimensions of particles which are widely used as reinforcement in nanocomposites. The model is used to characterize the surface irregularity or roughness. It was found that fractal dimensions of both the contour and surface of particles depend only on the relative particles size ratio between secondary particles and subunits. It is proposed that, in practical applications, the fractal dimension of a certain reinforcement particle can be obtained by a combination of this model and a state-of-the-art instrument that can determine the sizes of primary and secondary particles by image analysis. It is possible to relate the fractal dimension with the adhesion and other physical and chemical properties at the interface between particles and matrix.

Keywords: nanocomposites; roughness; fractal dimension

Fractal analysis and simulation of surface roughness of ceramic particles for composite materials by X. Kuang; Z. Zhu; G. Carotenuto; L. Nicolais (pp. 69-81).

Keywords: nanocomposites; roughness; fractal dimension

A method to apply structure relevant impact damage to small structure relevant specimens for damage tolerance studies by L. C. Ubels; J. F. M. Wiggenraad (pp. 83-94).

An approach is presented to represent stiffened composite panels by small but ‘structure relevant’ (SR) specimens in compression tests to study failure mechanisms. The necessary support conditions to be applied during low velocity impact tests were determined for the SR specimens in order to obtain damage that is similar to the damage found in stiffened panels. Fractography revealed that the locations of the major delaminations in the SR specimens due to impact were the same as in stiffened panels. These delaminations occurred where they were expected, suggesting that they can be ‘placed’ deep inside a laminate for optimum damage tolerance. Initial compression tests on stiffened panels confirmed the high damage tolerance of the configuration considered.

Keywords: impact; delamination; damage tolerance; design; structural response; testing

A Method to Apply Structure Relevant Impact Damage to Small Structure Relevant Specimens for Damage Tolerance Studies by L. C. Ubels; J. F. M. Wiggenraad (pp. 83-94).

Keywords: impact; delamination; damage tolerance; design; structural response; testing

Damage Mechanisms in Composite/Composite Bonded Joints Under Static Tensile Loading by A. Roy; C. Mabru; J. L. Gacougnolle; P. Davies (pp. 95-119).

This paper presents an experimental study of the initiation and development of damage in composite/composite joints. The materials studied are glass fibre reinforced polyester laminates and these are bonded together using an epoxy adhesive. Two types of joint interface are examined, assemblies between woven roving layers and between mat layers. The experimental techniques employed are dye impregnation, extensometry, visual observation and photoelasticimetry. It is shown that the nature of the surface layer does not influence the damage initiation load but does affect subsequent crack propagation.

Keywords: composite/composite bonded lap joints; crack evolution; experimental characterisation of damage; dye impregnation; extensometric measurements; optical observations; photoelasticimetry; static tensile loading

Damage mechanisms in composite/composite bonded joints under static tensile loading by A. Roy; C. Mabru; J. L. Gacougnolle; P. Davies (pp. 95-119).

Spatial distribution of yarns and mechanical properties in 3D braided tubular composites by Y. Q. Wang; A. S. D. Wang (pp. 121-132).

This paper outlines a method which links the following analytically simulated events in sequence: (1) braiding of a 3D preform of tubular cross-section—characterized by a set of braiding parameters defining the braiding setup and braiding steps; (2) geometric description of the yarn topology in the braided preform—in explicit terms of a set of topological parameters defined by the preform shape and the braiding parameters; (3) description of the exact yarn distribution after preform consolidation with a binding matrix—the values of the topological parameters are related to the exterior dimensions and surface features of the consolidated preform; and (4) forecasting the mechanical properties in the final composite—via a suitable micromechanics model that takes into account the spatial yarn distribution in the composite and properties of the constituents.It is shown that these sequential events form a closed-loop linkage which connects the properties of the final composite all the way to the initial preform braiding setup design; the analytically derived interrelationships in each link can provide for design simulations of three dimensionally braided, complex-shaped and property-specific composite articles.In order to obtain explicit interrelationships, the 4-step 1×1 braiding procedure is utilized in the analytical development. For the same reason, a graphite yarn and an epoxy resin with known properties are used in illustrative examples. There can be more than one braiding setup design for a preform to have the same shape and overall dimensions; but the yarn structure and properties in the final composite can differ widely if different braiding setups are used. Hence an optimization for a composite shape to meet the prescribed requirements may be conducted using the developed closed-loop.

Keywords: textile composites; design of 3D braided preforms; yarn structures; composite properties; close-loop design optimization

Spatial Distribution of Yarns and Mechanical Properties in 3D Braided Tubular Composites by Y. Q. Wang; A. S. D. Wang (pp. 121-132).

This paper outlines a method which links the following analytically simulated events in sequence: (1) braiding of a 3D preform of tubular cross-section – characterized by a set of braiding parameters defining the braiding setup and braiding steps; (2) geometric description of the yarn topology in the braided preform – in explicit terms of a set of topological parameters defined by the preform shape and the braiding parameters; (3) description of the exact yarn distribution after preform consolidation with a binding matrix – the values of the topological parameters are related to the exterior dimensions and surface features of the consolidated preform; and (4) forecasting the mechanical properties in the final composite – via a suitable micromechanics model that takes into account the spatial yarn distribution in the composite and properties of the constituents.It is shown that these sequential events form a closed-loop linkage which connects the properties of the final composite all the way to the initial preform braiding setup design; the analytically derived interrelationships in each link can provide for design simulations of three dimensionally braided, complex-shaped and property-specific composite articles.In order to obtain explicit interrelationships, the 4-step 1×1 braiding procedure is utilized in the analytical development. For the same reason, a graphite yarn and an epoxy resin with known properties are used in illustrative examples. There can be more than one braiding setup design for a preform to have the same shape and overall dimensions; but the yarn structure and properties in the final composite can differ widely if different braiding setups are used. Hence an optimization for a composite shape to meet the prescribed requirements may be conducted using the developed closed-loop.

Keywords: textile composites; design of 3D braided preforms; yarn structures; composite properties; close-loop design optimization

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.4, #2)

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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.4, #2)