Polymer Testing 21 (2002) 27–33 www.elsevier.com/locate/polytest Test Method The use of a three-point support ﬂexural test to predict the stiffness of anisotropic composite plates in bending J.P. Nunes * , A.S. Pouzada, C.A. Bernardo Department of Polymer Engineering, Universidade do Minho, 4800-058 Guimara ˜es, Portugal Received 17 January 2001; accepted 20 March 2001 Abstract Anisotropic polymeric matrix composite discs supported on three points were subjected to a non-destructive bending test to study their behaviour in complex ﬂexural loading situations. The results show that the ﬂexural behaviour of the composites depends on several factors, such as ﬁbre orientation, laminate stacking, surface waviness and moulding temperature. The experimental data were compared with those obtained from the ﬁnite element program software Algor. Differences up to 13% were found between the experimental and simulated values of the ﬂexural stiffness. In spite of that, it was concluded that the non-destructive test used is a useful tool to predict the behaviour of anisotropic composites and to validate the results obtained from computer FEM analysis.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Anisotropic composite plates; Flexural stiffness; Three-point bending test 1. Introduction The ﬂexural stiffness of anisotropic composite plates subject to pure bending in any direction is usually calcu- lated using engineering constants that are directly derived from the laminate normalised ﬂexural com- pliance matrix [1,2]. Depending on support conditions, complex states of stress may result on loaded composite plates and shells. Some of these bending stress states can be especially severe in the case of long ﬁbre composites that have low stiffness across the ﬁbre direction. Further- more, as non-predictable multidirectional solicitations are generated in the plate, the overall ﬂexural behaviour of this type of composite is difﬁcult to predict using ana- lytical methods. It is therefore important to envisage reliable methods to estimate that behaviour. It is also of importance to generate methods to evaluate optimal ﬁbre * Corresponding author. Tel.: +351-253-510-245; fax: +351- 253-510-249. E-mail address: jpn@dep.uminho.pt (J.P. Nunes). 0142-9418/02/$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S0142-9418(01)00040-X orientations and laminate stacking sequences that will help to produce better performing composites. In this work, anisotropic discs of two different com- posite materials were loaded at the centre and subjected to three-point support bending tests to assess and com- pare their ﬂexural stiffnesses. The discs were com- pression moulded at four different temperatures to inves- tigate the inﬂuence of the processing temperature on the ﬂexural behaviour. Then, in order to assess the inﬂuence of the ﬁbre direction on the ﬂexural stiffness, they were bent with the continuous ﬁbre direction varying with respect to the position of the supports. Finally, the properties of the laminate plies were determined and used in the ﬁnite element software program Algor (Algor Inc., Pittsburgh, USA) to generate data for com- parison with the experimental results. It was concluded that non-destructive bending tests are useful tools to pre- dict the behaviour of anisotropic composites in complex bending situations and to optimise their design.