Mechanical modelling of solid woven fabric composites 73 yarn into smaller,piecewise straight yarn slices)that assumed an isostrain state within the unit cell.Hence,as in the Hahn and Pandy model,the iso- strain model is applied.In the calculation for the strength,TexCad uses a curved beam-on-elastic-foundation model for yarn crimp regions together with an incremental approach in which stiffness properties for the failed yarn slices are reduced,based on the predicted yarn slice failure mode.Only on-axis tensile loadings and in-plane shear loadings were modelled and reported.Certainly,the most questionable assumption in this strength model is the calculation of the local stress fields in yarn and matrix slices based on the isostrain assumption.Basically,TexCad is well documented and easy to use.It is a thorough implementation of the isostrain approach which could be extended easily to analyse complex 3-D woven fabric com- posites.It will perform stiffness and failure analyses as correctly as can be expected for an isostrain model. Model of Paumelle,Hassim and Lene Paumelle et al.[23,24]developed a finite element method for analysing plain weave fabric composite structures.The periodic medium homoge- nization method is implemented.Basically,by applying periodic boundary conditions on the surface of the unit cell and by solving six elementary loading conditions on the unit cell,the complete set of elastic moduli of the homogenized structure can be computed.At the same time,the method pro- vides a good approximation of the local distribution of force and stress fields acting in the composite components and at their interface.These microscopic stress fields give a strong indication of the types of damage that will occur.To the best of our knowledge,Paumelle et al.have not yet 8 reported an extension of this finite element model to predict damage propa- gation or to analyse 3-D woven preforms.Moreover,outlined below are some problems encountered in a practical finite element analysis of solid woven fabric composites. First,this approach requires large computer calculation power and memory because of the 3-D nature and the complexity (size)of the yarn architecture.Second,a correct finite element model includes the generation of the fabric geometry and the finite element mesh of nodes and elements. Most of the time spent is related to the creation and the verification of a correct geometric model [25].Finally,there are major problems in analysing and interpreting the results in a 3-D domain of a rather complex geometry [26: Model of Blackketter Here,we will discuss in some detail the research work of Blackketter [27]. In our opinion,this work is certainly one of the first and most importantyarn into smaller, piecewise straight yarn slices) that assumed an isostrain state within the unit cell. Hence, as in the Hahn and Pandy model, the iso￾strain model is applied. In the calculation for the strength, TexCad uses a curved beam-on-elastic-foundation model for yarn crimp regions together with an incremental approach in which stiffness properties for the failed yarn slices are reduced, based on the predicted yarn slice failure mode. Only on-axis tensile loadings and in-plane shear loadings were modelled and reported. Certainly, the most questionable assumption in this strength model is the calculation of the local stress fields in yarn and matrix slices based on the isostrain assumption. Basically, TexCad is well documented and easy to use. It is a thorough implementation of the isostrain approach which could be extended easily to analyse complex 3-D woven fabric com￾posites. It will perform stiffness and failure analyses as correctly as can be expected for an isostrain model. Model of Paumelle, Hassim and Léné Paumelle et al. [23,24] developed a finite element method for analysing plain weave fabric composite structures. The periodic medium homoge￾nization method is implemented. Basically, by applying periodic boundary conditions on the surface of the unit cell and by solving six elementary loading conditions on the unit cell, the complete set of elastic moduli of the homogenized structure can be computed.At the same time, the method pro￾vides a good approximation of the local distribution of force and stress fields acting in the composite components and at their interface. These microscopic stress fields give a strong indication of the types of damage that will occur. To the best of our knowledge, Paumelle et al. have not yet reported an extension of this finite element model to predict damage propa￾gation or to analyse 3-D woven preforms. Moreover, outlined below are some problems encountered in a practical finite element analysis of solid woven fabric composites. First, this approach requires large computer calculation power and memory because of the 3-D nature and the complexity (size) of the yarn architecture. Second, a correct finite element model includes the generation of the fabric geometry and the finite element mesh of nodes and elements. Most of the time spent is related to the creation and the verification of a correct geometric model [25]. Finally, there are major problems in analysing and interpreting the results in a 3-D domain of a rather complex geometry [26]. Model of Blackketter Here, we will discuss in some detail the research work of Blackketter [27]. In our opinion, this work is certainly one of the first and most important Mechanical modelling of solid woven fabric composites 73 RIC3 7/10/99 7:37 PM Page 73 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:11 AM IP Address: 158.132.122.9