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Reis P.N.B.,University of Beira Interior | Ferreira J.A.M.,University of Coimbra | Richardson M.O.W.,GTG CTA Ltd
Applied Composite Materials | Year: 2011

This paper presents the results of a study on glass-fibre-reinforced polypropylene composite in which the fatigue damage was investigated in terms of residual stiffness and temperature rise. Thermographic and acoustic emission techniques were used to aid the interpretation the fatigue damage mechanisms. Different laminates were tested. For one series, all the layers have one of the two fibre directions oriented with the axis of the plate. For the other two series layer distribution was obtained with the following laminate orientation in respect to the axis of the sheet: +45°/0°/-45°/0°/+45°/ 0°/-45° and +30°/-30°/+30°/0°/+30°/-30°/ +30°. It was possible to conclude that the residual stiffness and temperature rise can be used to predict final failure of a structure and/or component. With thermographic technique it is possible to obtain temperature maps and the precise site where the failure will occur. © 2010 Springer Science+Business Media B.V.


Reis P.N.B.,University of Beira Interior | Ferreira J.A.M.,University of Coimbra | Zhang Z.Y.,University of Portsmouth | Benameur T.,University of Monastir | Richardson M.O.W.,GTG CTA Ltd.
Composites Part B: Engineering | Year: 2014

Composite materials have been widely used in several engineering applications. However, there are very few studies about the effects of nanoclays on the impact strength of laminates after exposure to the fire. Therefore, this paper intends to study this subject and the impact performance was analysed by low velocity impact tests carried out at different incident impact energy levels. For better dispersion and interface adhesion matrix/clay, nanoclays were previously subjected to a silane treatment appropriate to the epoxy resin. The exposure to the fire decreases the maximum load and increases the displacement in comparison with the respective values obtained at room temperature. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and flexural stiffness. Finally, a decrease of the elastic recuperation can be found, independently of the benefits introduced by the nanoclays. © 2013 Elsevier Ltd. All rights reserved.


Reis P.N.B.,University of Beira Interior | Santos P.,University of Beira Interior | Ferreira J.A.M.,University of Coimbra | Richardson M.O.W.,GTG CTA Ltd
Journal of Reinforced Plastics and Composites | Year: 2013

Present work intends to study the improvement of impact performance on sandwich composites by the addition of nanoclays. For this purpose, nanoclays Cloisite 30B were previously subjected to a silane treatment in order to improve their dispersion and interface adhesion. Different incident impact energy levels were used and, for both sandwiches, the maximum load, displacement or elastic recuperation shows to be very dependent of the impact energy. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and impact bending stiffness. Finally, sandwiches enhanced by nanoclays presented higher maximum impact loads, lower displacements, the best performance in terms of elastic recuperation and maximum residual flexural strength. © The Author(s) 2013.


Ferreira J.A.M.,University of Coimbra | Reis P.N.B.,University of Beira Interior | Costa J.D.M.,University of Coimbra | Richardson M.O.W.,GTG CTA Ltd
Journal of Composite Materials | Year: 2013

The fatigue behaviour of Kevlar fibre-reinforced composites is a subject not often studied and requires a better understanding. The objective of this study is to characterize the fatigue strength of a Kevlar/epoxy laminate composite as well as the benefits obtained using a nanoclay-filled epoxy matrix. The filler used was an organoclay Cloisite 30B after applying an appropriate silane treatment and other proprietary chemicals to improve the dispersion and interface adhesion. Twelve ply laminates, all in the same direction, of woven bidirectional Kevlar 292, were prepared by hand lay-up, using an SR 1500 epoxy resin. The composite sheets were produced by a vacuum moulding process. The addition of nanoclays reduced static strength and increased the stiffness in both tension and bend loading. Filled composites exhibited tensile fatigue strengths 12% higher than unfilled matrices, but in three-point bending the fatigue strength of filled composites was lower. © The Author(s) 2012 Reprints and permissions.


Reis P.N.B.,University of Beira Interior | Ferreira J.A.M.,University of Coimbra | Santos P.,University of Beira Interior | Richardson M.O.W.,GTG CTA Ltd. | Santos J.B.,University of Coimbra
Composite Structures | Year: 2012

Kevlar fibres have been widely used as impact-resistant reinforcement in composite materials. The paper studies the impact behaviour as well as damage tolerance of Kevlar/filled epoxy matrix. Two different fillers, cork powder and nanoclays Cloisite 30B, were used in order to improve the impact response of these laminates. For better dispersion and interface adhesion matrix/clay nanoclays were previously subjected to a silane treatment appropriate to the epoxy resin. The fillers adding increases the maximum impact load but the opposite tendency was observed for the displacement. Nanoclays promote higher maximum impact loads, lower displacements, the best performance in terms of elastic recuperation and the maximum residual tensile strength. © 2012 Elsevier Ltd.


Reis P.N.B.,University of Beira Interior | ZhangFerreira J.A.M.,University of Coimbra | Zhang Z.Y.,University of Portsmouth | Benameur T.,University of Monastir | Richardson M.O.W.,GTG CTA Ltd.
Composites Part B: Engineering | Year: 2013

Kevlar fibres have been widely used as impact-resistant reinforcement in composite materials. However, there are very few works about the effects of nanoclays on the impact strength of Kevlar/epoxy laminates. Therefore, this paper intends to study the ideal amount of nanoclays to obtain the best impact performance. Nanoclays Cloisite 30B were dispersed in the epoxy system of at 1.5%, 3% and 6% in weight. For better dispersion and interface adhesion matrix/clay, nanoclays were previously subjected to a silane treatment appropriate to the epoxy resin. The laminates manufactured with epoxy resin filled by 6 wt.% of nanoclays shown the best performance in terms of elastic recuperation and penetration threshold. The opposite tendency was observed for the displacement at peak load. However marginal benefits can be found when compared the results obtained for laminates filled by 3% and 6% of nanoclays. © 2012 Elsevier Ltd. All rights reserved.


Silva H.,University of Coimbra | Silva H.,Polytechnic Institute of Viseu | Ferreira J.A.M.,University of Coimbra | Capela C.,University of Coimbra | And 2 more authors.
Composites Part A: Applied Science and Manufacturing | Year: 2014

Increasing interlaminar fracture toughness (IFT) has long been an important goal in the fiber reinforced composites field. For that purpose some research has recently explored the use of nanoparticle reinforced matrices to improve interlaminar strength. In this present paper a small quantity of nanoclays (NC) and multiwalled carbon nanotubes (MWCNT) were used in order to enhance the IFT of glass fiber/epoxy composite laminates. The composites sheets were produced by a vacuum molding process. Mode I, Mode II, and Mixed-Mode I/II tests were performed to determine critical strain energy release rates, using double cantilever beam, end-notched flexure, and Mixed-Mode Bending specimens, respectively. Significant improvements in IFT were obtained for all loading modes by the incorporation of NC into the epoxy resin, whilst MWCNT produced only moderate improvements. For Mode I, IFT improvement by the incorporation of nanoparticle fillers, reached about 31% for 3 wt% of NC and 17% for 1 wt% of MWCNT. In Mode II the increase was about 50% for 3 wt% of NC and 30% for 1 wt% of MWCNT. The dispersion of small quantities NC and MWCNT into matrices significantly improved Mixed-Mode IFTs for all loading mode ratios G II/G. The total fracture toughness G increased under Mode II loading components and linear Mixed-Mode fracture criteria reproduced the Gc versus Mode ratios GII/G and GI versus GII relationship. © 2014 Elsevier Ltd. All rights reserved.


Ferreira J.A.M.,University of Coimbra | Reis P.N.B.,CCTA UBI | Costa J.D.M.,University of Coimbra | Richardson M.O.W.,GTG CTA Ltd
Journal of Thermoplastic Composite Materials | Year: 2013

This paper presents the results of a current study on the mechanical properties of a polypropylene matrix resin, enhanced using nanoclay filler with a special silane treatment. The study was centred on the effect of adding nanoclay and of water immersion on static and fatigue behaviour. Specimens filled up to 3% in weight were produced by an injection moulding process. The filler improved significantly bending quasi static and dynamic stiffness, and also marginally the bending strength. Surprisingly, the immersion in water for 40 days increases the bending stiffness and the bending strength. The addition of 3% w/w nanoclay promoted a negative effect in Gc. All material configurations exhibited a faster and intense stress release from the first cycles of fatigue. The 3% nano-enhanced composites exhibited higher fatigue strength than unfilled materials. © The Author(s) 2011.

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