M. Langseth

Joining of aluminium using self-piercing riveting: Testing, modelling and analysis

The paper presents a study on identification and modelling of self-piercing rivet connections in aluminium. Failure loads of self-piercing rivets have been investigated under combined opening and shear static loading conditions using a new test set-up and simple specimen geometry with only a single rivet. These results were used to identify rivet model parameters in the code LS-DYNA using inverse modelling. Static and dynamic tests were conducted on double-hat sections made of aluminium sheets jointed with self-piercing rivets at the flanges to validate the chosen rivet model. The numerical analyses of these components provided a direct check of the accuracy and robustness of the numerical model.

An experimental investigation on the behaviour of self-piercing riveted connections in aluminium alloy AA6060

Abstract This paper presents an experimental study on the behaviour of self-piercing riveted connections in aluminium alloy AA6060 under quasi-static loading conditions. Factorial design is used in the planning of the experimental programme as well as in the results interpretation. The test specimens were made of two U-shaped plates joined in the centre by a single self-piercing rivet. The experimental programme is focused on the influence of important model parameters such as thickness of the plates, geometry of the specimens, material properties of the plates and loading conditions. The programme was divided into two parts. In the first part, a 23 factorial design was used to investigate the influence of the thickness, thematerial properties and the width of the specimens. In the second part, the interaction between the thickness and the material properties of the top and bottom plates on the response of the connections was investigated. The single-rivet specimens were tested under three different loading directions, i.e. 0° (pure shear), 45° and 90° (pure pull-out) and a failure envelope, relating the normal and shear forces acting on the rivet, was generated. Furthermore, the applicability of the design rules in the European standard on cold-formed aluminium structures (prEN 1999-1-4) was evaluated. Finally, a three-dimensional numerical model of the single-rivet specimen was generated using the explicit finite element code LS-DYNA. From the numerical simulation, a failure criterion was generated and compared with the corresponding experimental curve.

The behaviour of an offshore steel pipeline material subjected to bending and stretching

Guidelines have been worked out on how to design sub-sea pipelines in fishing-rich areas subjected to the possible interference by trawl gear or ship anchors. One topic of special interest for the offshore industry is pipelines first subjected to impact from an anchor before being dragged along the seabed. After removal of the load, the pipe will be straightened due to rebound and present axial forces. The material in the deformed impact zone will experience a complex stress and strain history, which subsequently can cause cracking, leading to leakage or full failure. To study these topics, full-scale testing is not straightforward and thus a simplified approach is chosen as a first step in the present study. Motivated by the observed local curvature in impacted pipelines, three-point bending tests of plate strips cut from a typical offshore pipeline have been carried out and the strips subsequently stretched to a straight position. One objective of these tests was to investigate whether cracking in the plate strip could occur after such a loading sequence. Material tests with specimens taken in different directions and at different locations in the actual pipe were carried out to calibrate an appropriate constitutive relation (taking anisotropy and kinematic hardening into account) and a simplified fracture criterion. Numerical simulations of the complete loading sequence were finally carried out and the predicted response was validated against the experimental data.