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A short overview of different locking mechanisms is presented, in which the more recent locking phenomenon tension locking is placed. Tension locking is found during composite forming simulations and occurs when the element edges are unaligned with the fiber directions. Discontinuities in composite forming simulations show similarities with other weak discontinuities such as material interfaces and shear bands found during shear localization. Two enrichment strategies are explored to resolve tension locking in linear triangular elements.

Fibre reinforced thermoplastic tapes are subjected to high heating and cooling rates during the tape placement process. Such high cooling rates can significantly inhibit the crystallisation of the thermoplastic polymer and thereby affect its mechanical properties, such as strength or toughness. In the present work, the crystallisation of poly(phenylene sulphide) (PPS) subjected to high cooling rates was investigated using a fast scanning calorimeter. The PPS was found to be unable to crystallise when subjected to cooling rates higher than 20°C s-1. The influence of the degree of crystallinity on fracture toughness was investigated using an essential work of fracture approach. The amount of plastic work during the fracture process was found to decrease after moderate annealing.

Standard finite elements can exhibit the numerical artifact of intra-plyshear locking during forming simulations. The displacement fields of elementsare piecewise  continuous and cannot correctly capturediscontinuities in the shear field. This shear locking is illustrated insimulations of bias-extension experiments with an unaligned mesh. Two simpletests were developed as a critical indicator of intra-ply shear locking intriangular elements. A single-element-test shows the origin of the locking anda pull-out test indicates locking caused by small misalignments of theelements.

Friction stir welding (FSW) is a relatively new solid-state joining technology for metals. It shows no solidification-related joint imperfections which makes it utmost suitable for hard-to-weld highly alloyed aerospace aluminium grades, like AA 2xxx and AA 7xxx. These alloys are often cladded with a thin layer of pure aluminium for corrosion protection. Friction stir welding of such materials requires removal of the clad layer prior to welding to prevent weakening of the joint by the soft clad material. This leaves the welded region vulnerable to corrosion after the joining process. Post-weld restoration of the clad layer is required to restore the protective action of the clad layer and as such to enhance the life expectancy of the welded construction. In this work the deposition of thin layers of pure aluminium on AA 2xxx and AA 7xxx alloys is studied employing an innovative FSW tool. The tool shoulder is equipped with strategically placed internal channels that allow delivery of filler type of material into the weld zone. Depending on the channel architecture used, filler material can be deposited on top of the work piece surface and/or mixed with the work piece surface region. The cladding is done in the solid state avoiding many problems with solidification and interface reactivity often observed with other surface modification techniques, such as laser surface engineering, plasma spraying or casting. Here, the filler material is deposited on top of the work piece; the modified tool is not equipped with a tool pin. The work comprises an in depth study of the influence of process conditions on the microstructural changes in the underlying work piece and on the quality of the bonding of the clad material (99.5 % aluminium) to the work piece material. Apart from the usual process conditions, such as tool rotation speed, translation speed, down force and tool angle also the delivery pressure and rate of the filler supply system can be varied. The influence of the usual process conditions on the microstructure of the underlying work piece is similar to that observed with “traditional” FSW. Changes in hardness can be related to the amount of heat generated by the welding process. Shape and dimensions of the microstructural zones found are typical for welds made without a tool pin. The effect of the small amount of clad material deposited on top of the work piece on the temperature distribution is small. The amount of heat required to heat it up is negligible to the heat required to heat up the work piece and the tool. The quality of the bonded clad layer is dependent on the amount of heat and plastic deformation generated at the interfaces between the tool, the filler material and the work piece. Tool angle, tool shape and supply rate of the filler supply system determine the layer thickness.

In this paper, a numerical problem with contacting solid metal flows is presented and solved with an arbitrary Lagrangian-Eulerian (ALE) finite element method. The problem consists of two domains which mechanically interact with each other. For this simulation a new free surface boundary condition is implemented for remeshing of the boundary elements. It uses explicitly that the integral of the convective velocity along a boundary element remains zero. Steady state solutions are obtained only if the integral of the convective velocities along each free surface boundary element remains zero. The new remeshing option for the free surface is tested on a cladding problem employing friction stir welding (FSW). The problem describes two elasto-viscoplastic aluminum material flows which mechanically interact.

A comparison is made between Arbitrary Lagrangian–Eulerian (ALE) finite element formulations for simulation of forming processes based on an artificial dissipation scheme and a limited flux scheme. The first ALE algorithm is based on an averaging procedure used in post-processing of finite element calculations. The second ALE algorithm stems from a finite difference method for compressible fluid dynamics. Both approaches have complementary characteristics with respect to accuracy and implementation. © 1998 John Wiley & Sons, Ltd.

The developments of composites forming analyses are summarized, from a historic perspective and towards the expected future. While the recent methods are already accepted in the market, there is a number of challenges ahead in simulation methods and experimental characterisation, to reach even better predictions of defects and part distortions.

Fabric misalignment leads to unsymmetry in fibre reinforced composite laminates. This unsymmetry induces out-of-plane deformation after processing. This paper evaluates the influence of fabric misalignment on the out-of-plane deformation of flat press-consolidated thermoplastic laminates. The results of this analytical and experimentally validated study shows a strong relation between deformations and length/width ratio. In particular narrow laminates show high twisting values. The results obtained are of importance for the prediction of deformations of stamp formed thermoplastic laminates.