Abaqus GUI’s

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Abaqus’ capabilities can be extended by Python scripts and Fortran subroutines. In the following some examples are presented of work that ALE has performed.

Material Properties of Heterogeneous Materials

ALE has developed an Abaqus tool with Graphical User Interface to obtain material properties of heterogeneous materials from the properties of the individual constituents. For example, the material properties of fibre reinforced plastics can be determined from the individual properties of the resin and the fibres. Using the tool, stiffness properties and coefficients of thermal expansion can be obtained. For fibre reinforced plastics the tool also gives the possibility to determine ply strength values.

Heterogeneous materials often show orthotropic material symmetry, i.e. the stiffness depends on the direction in which the material is loaded. Apart from the stiffness properties of the constituents, the orthotropic behaviour also depends on the shape and orientation of the inclusions. Various inclusion shapes can be handled by the tool, ranging from long fibres to spherical constituents. The inclusions can be oriented in any 3D direction.

An advanced homogenization scheme is implemented in the tool, resulting in accurate property prediction. The results have been checked by Finite Element simulations on Representative Volume Elements.

Simulation of progressive damage in composites

ALE developed progressive damage models for composites in the framework of the MAAXIMUS (More Affordable Aircraft through eXtended, Integrated and Mature nUmerical Sizing) FP7 project, led by Airbus. MAAXIMUS aims at achieving the fast development and right-first-time validation of a highly-optimised composite fuselage thanks to a coordinated effort between virtual structure development and composite technology.

A multi-scale damage model has been developed by ALE, which predicts ply-level damage evolution, based on the properties of the constituents, e.g. epoxy matrix and carbon fibre. Effects of voids and fibre misalignment can be taken into account. The model is analytical and therefore numerically efficient. Failure criteria are defined on constituent level and can be determined from ply or constituent strength data. The multi-scale damage model is implemented in Abaqus in combination with a user-friendly GUI to define the necessary properties. The multi-scale damage model relies on accurate prediction of stress and strain from the underlying finite elements. For thin shell applications ALE has implemented a so-called Solid-Like Shell (SLS) element that has all the advantages of normal shell elements, but is able to predict 3D stress and strain.

The combination of solid-like shell elements and the multi-scale damage model has been demonstrated by application in simulations of stringer-stiffened composite panel tests.  

Virtual Testing of Bolted Joints

Shear pull tests were performed on simple bolted composite specimens, to be used as input for non-linear finite element analysis of typical skin to structure connections under crash or impact loads as part of an aircraft program. The aim of the project was to create finite element models and perform accurate simulations of the experiments.

In order to speed up the process of validating a large number of joints, differing in the type of bolt, lay-up, thickness and material, an Abaqus plugin was created by ALE written in Python. The plugin generates a fully working Abaqus model, based on dimensions and properties specified by the user via a simple Graphical User Interface. It makes clever use of the presence of repetitive parts and provides an extensive selection of premade bolts, modeled on the basis of technical drawings, to include in the model. The user is free to choose the dimensions of the specimen, type, size and number of bolts, material properties and speed of the pulling load. Simulations can be performed for both single lap shear and double lap shear joints.

Besides the possibility to create and validate a large number of bolted configurations rapidly, the plugin makes it possible to design and verify new joints very easily. Moreover, bolts which are not yet included can be implemented in a convenient way. This makes the plugin a powerful tool in the design and testing phase of future aircraft.