In this paper, a functionally graded foam model is proposed in order to improve the energy absorption characteristics offered by uniform foams. In this novel model, the characteristics of the foam (e.g., density) are varied through the thickness according to various gradient functions. The energy absorption ability of the novel foam is explored by performing finite element simulations of physical impact tests on flat specimens of the functionally graded foam materials. Energy absorbing capacity with respect to parameters including gradient functions, density difference, average density, and impact energy, is explored in detail. It is illustrated that the functionally graded foam is superior in energy absorption to the uniform foam and that convex gradients perform better than concave gradients. The performance of such foams can be improved more if the density difference is enlarged. These findings provide valuable suggestions in the design of high performance energy absorption polymeric foams.

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Designing the energy absorption capacity of functionally graded foam materials

A new approach and material architecture is presented in order to overcome the inherent brittleness and unstable failure characteristic of conventional high performance composites. The concept is the use of thin-ply hybrid laminates. Fracture mechanics calculations were carried out to determine the critical carbon layer thickness for stable pull-out in a three layer unidirectional hybrid laminate, which can provide a pseudo-ductile failure. Unidirectional hybrid composites were fabricated by sandwiching various numbers of thin carbon prepreg plies between standard thickness glass prepreg plies and tested in tension. Specimens with one and two plies of thin carbon prepreg produced pseudo-ductile failure, whereas ones with three and four plies failed with unstable delamination. An explanation of the different failure modes is given in terms of the different energy release rates for delamination in various specimens. The observed damage characteristics agreed well with the expectations according to the estimated critical carbon layer thickness.

Demonstration of pseudo-ductility in high performance glass-epoxy composites by hybridisation with thin-ply carbon prepreg

With the advent of high performance thermoplastic polymers, structural applications for thermoplastic composites are increasing rapidly. Thermoplastic matrix composites possess distinct advantages vis-a-vis thermoset matrix composites in terms of recyclability, high specific strength and specific stiffness, corrosion resistance, enhanced impact toughness, cost effectiveness, and flexibility of design. Since 1990s, the number of material forms and combinations in fibre reinforced thermoplastic polymers has increased exponentially, thereby expanding application avenues in transportation, automotive, mass transit, marine, aerospace, military and construction sectors. In this paper we review the state of the art in processing of fibre reinforced thermoplastics. We start with a brief description of thermoplastic polymers used in structural applications followed by material forms and methods of impregnation of the reinforcement with polymer. Long fibre based processing methods are described next. A desc...

Processing of fibre reinforced thermoplastic composites

All three classes of fibre reinforced composite materials (polymer, metal and ceramic matrix) may be produced by flow of liquid matrix into the open spaces left within pores of a fibre preform. Even though several specific issues arise from the nature of each composite matrix class, governing phenomena apply to all infiltration processes, and include in particular: (i) capillary phenomena, (ii) transport phenomena, and (iii) the mechanics of potential fibre preform deformation. These phenomena and their governing laws are reviewed for the case of isothermal infiltration with no phase transformations. Four basic functional quantities, which need to be known to model the processes, are identified, and addressed in turn. The paper concludes with some examples of modelling methodologies and comparison with experimental data.

Infiltration processing of fibre reinforced composites: governing phenomena

Polypropylene/glass fibre 3D-textile reinforced composites for automotive applications

The use of commingled yarns is one of the more promising routes for producing structural thermoplastic composites. The textile processes available enable faster manufacturing and tailoring of the fiber architecture of preforms. Development of this technology is pushed by significant interest from, for example, the transportation industry. This paper reviews work done on commingled materials, including yarn manufacturing and preforming, modeling of impregnation and consolidation, and mechanical properties of the composites.

Manufacturing of Thermoplastic Composites from Commingled Yarns-A Review:

The transient permeabilities and steady-state permeabilities of five different architectural glass fabrics were measured using one-dimensional experiments. The fabric architectures include 3-dimensional structure, random distributed fiber mat with stitches and knitted fabrics. The influence of the test liquids on the permeability measurements was investigated us3ing corn syrup, vinyl ester resin and epoxy resin. The experimental results show that the influence of the test liquids on permeability measurement is small if the simulated test fluids are properly selected. The relationship between permeability and porosity was also investigated. The experimental results indicate that the relationship between permeability and porosity can be expressed as an approximated exponential function. The permeability decreases dramatically as the porosity is reduced to about 0.65. The transient permeability of all fabrics used in the experiments exhibits the characteristic that it increases as the flow front moves forwar...

Permeability Characterization of Different Architectural Fabrics

The response to mechanical loads of unidirectional commingled warp knitted and woven glass fibre reinforced polyethylene terephthalate laminates has been characterized. The mechanical properties of the two materials were determined under tension, in-plane shear and flexure. The flexural fatigue properties were determined for the woven laminates by means of three-point bending tests with a loading ratio of R=0.1 at stress levels of 50–90% of the ultimate static strength. The Mode I, Mode II and mixed mode (Mode I : II ratios 4 : 1, 1 : 1 and 1 : 4) interlaminar fracture toughnesses of the laminates were determined by means of the double cantilever beam and mixed mode bending tests, respectively. The main fractographic features, as determined by a scanning electron microscopy examination, of the Mode I dominated failures were a brittle matrix failure and larger amounts of fibre pull-out. As the Mode II loading component increased, the amount of fibre pull-out was reduced and the features of the matrix appeared to be more sheared. Cusps were found on the fracture surfaces of specimens tested in pure Mode II and mixed mode I : II=1 : 4. Cusps are normally not found in thermoplastic matrix composites. © 1998 Kluwer Academic Publishers

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Fracture and fatigue performance of textile commingled yarn composites

The mechanical properties and the response to mechanical load of continuous glass fiber reinforced polyethylene terephthalate (GF/PET) laminates have been characterized The laminates were manufactured by compression molding stacks of novel woven and warp knitted fabrics produced from commingled yarns The laminate quality was examined by means of optical and scanning electron microscopy Few voids were found and the laminate quality was good Resin pockets occurred in the woven laminates, originating from the architecture of the woven fabric The strength of the fiber/matrix interface was poor Some problems were encountered while manufacturing the laminates These led to fiber misalignment and consequently resulted in tensile mechanical properties that were slightly lower than expected Flexural failures all initiated as a result of compression, and it is possible that the compression strength of the matrix material, rather than its tensile strength, might limit the ultimate mechanical performance of the composites Flexural failures for both materials were very gradual The warp knitted laminates were stronger and stiffer than the woven laminates The impact behavior was also investigated; the woven laminates exhibited superior damage tolerance compared with the warp knitted laminates

Fabrication and mechanical response of commingled GF/PET composites

The Mode I, Mode II and mixed mode (Mode I:II ratios of 4:1, 1:1 and 1:4) fracture behavior of novel textile glass fiber reinforced polyethylene terephthalate (GF/PET) laminates has been investigated. The laminates were manufactured by compression molding two different fabrics produced by weaving and warp knitting commingled GF/PET yarns. The initiation fracture toughness of the woven laminates in pure Mode I and Mode II were slightly higher than those of the warp knitted laminates. For the mixed modes, the difference between the fracture toughness of the two materials was smaller. An extensive scanning electron microscopy (SEM) investigation of the fracture was conducted to identify any characteristic failure mechanisms. The main fractographic features of the Mode I dominated failures were a brittle matrix failure and large amounts of fiber pull-out. As the Mode II loading component increased, the amount of fiber pull-out was reduced and the matrix had a more sheared appearance. A relatively large amount...

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Roshan Shishoo

Papers

Manufacturing of Thermoplastic Composites from Commingled Yarns-A Review:

Permeability Characterization of Different Architectural Fabrics

Fracture and fatigue performance of textile commingled yarn composites

Fabrication and mechanical response of commingled GF/PET composites

Interlaminar Fracture of Commingled GF/PET Composite Laminates