Mechanical Behaviour of SMC Composites and Structures

Sammanfattning: The goal of this work has been to investigate the influence of material composition and process induced fiberorientation on mechanical properties of SMC composite body panels. It has also been a goal to study methods to predict the properties. This requires basic understanding of the relationship between the microstructure and the properties of this type of material and the models used for prediction of the properties. The background behind this work is an interest from industry to use composite panels instead of sheet metals. However, there are some drawbacks for composites and one is that because of insufficient predictability composite designs are usually over dimensioned. Three types of SMC materials have been analysed regarding composition, microstructure and mechanical properties. These materials were of type standard SMC (Std-SMC) and low density and high flex SMC (Flex SMC). Micromechanics have been used to model the stiffness and the model has been implemented in FEM program to be able to predict properties of a geometry with known state of fiberorientation. In the first paper, stiffness of a conventional SMC material was modelled based on composition and fiber orientation using micromechanics. The model was implemented in the FEM program ABAQUS and global stiffness of the geometry for a loadcase was calculated. This was compared with a conventional calculation where the material is assumed planar random. In the second paper, Damage mechanics and toughness of a new type of SMC material, Flex-SMC, were analysed and compared with Std-SMC. The underlying mechanisms for differing in behaviour were clarified. The results were that the strain at onset of damage for Flex SMC is higher than for Std-SMC due to that resistance to strain magnification of its matrix is higher. Toughness is dependent on fiber orientation and degree of pull-outs of fibers. In the third paper, commercial masterbatch for TPO-nanocomposite were evaluated and the weight saving potential in a concept body panel were compared with pristine polymer as well as alternative materials. The nanocomposite, even though mainly only being intercalated, were 5-19% lighter than alternative materials in this comparison. The general conclusions are that the influence of fiberorientation on mechanical properties and damage mechanics of SMC is substantial. The LD- and flex additives changes the properties and the reasons for it has been investigated. If the state of fiber orientation is known, it is possible to use a micromechanical model implemented in FEM to predict mechanical properties of components and so far it has been shown that global stiffness could be calculated.

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