• Pinto, Ricardo

Abstract

The plethora of available carbon fibre based composite material solutions is increasing drastically as new material novel combinations are implemented, particularly with the purpose of obtaining lightweight structures for space applications with very demanding mechanical properties that require multiscale damage evaluation, such an example are the new designs for deployable antenna arms with elastic hinges obtained through patterned slots. During the design process, it is imperative to predict the behaviour of the advanced composite structure to several load scenarios. The most common and globally applied tool is by taking advantage of the finite element method. However, the elastic and fracture properties of the composite under investigation must be known, as these are required to feed the numerical models. In order to obtain the mechanical properties, a significant amount of time and costly experimental test campaigns are required, mainly if there is more than one potential material candidate for the required application. As an alternative to the experimental tests, several numerical micromechanical models have emerged. These are usually very complex to implement, often require additional properties to capture the material mechanical behaviour and have a limited range of application. Unlike more evolved and complex methods, the mail goal in the work presented, is the quick assessment of different composite formulations and their performance by means of estimating the required properties as quick and simple as possible with only a scarce set of properties. The methodology proposed in the present work can be used to estimate the elastic and fracture properties of unidirectional composites as well as composites with more complex geometries such as multidirectional fabrics. The process begins with a first micromechanical model of an UD composite hexagonal unit cell modelled in the Abaqus commercial FEA package. Simple damage models are implemented as a user material for both the fibres and the matrix where the fibre is considered pure elastic until failure and the matrix damage progresses linearly after onset up to failure. Recurring to true periodic boundary conditions a set of load scenarios are ran obtaining the elastic and fracture properties of the UD composite or tow. If the ultimate objective is to obtain the properties for more complex material architectures, such as fabrics, a second model is prepared. The geometry of the fabric is generated recurring to the open source TexGen software. The elastic and fracture properties are then obtained following a similar method as previously described however, while for the matrix the damage model is the same, for the tow, the Tsai-Wu failure criteria is used with the properties obtained in the previous step as the elastic and fracture tow characteristics. By means of the present method, transversely isotropic composite material properties are determined applicable to glass or carbon fibre reinforcements in a polymer matrix. This provides enough data to suffice the implementation and use of damage models such as Hashin, Tsai-Wu, Tsai-Hill and Maximum Stress, for example to predict the mechanical response of advanced lightweight structural panels.

Topics

• impedance spectroscopy
• polymer
• Carbon
• glass
• glass
• composite
• isotropic
• finite element analysis