SUMMARYA new global search method for general contact systems is developed and implemented in the DYNA3D program, along with a rectnt contact interface algorithm. The concept of 'position codes' for efficient global contact searching is presented. With the position code algorithm, the problem of sorting and searching in three dimensions is transformed to a process of sorting and searching within a one-dimensional array. The cost of contact searching is of the order of N log, N, where N is the number of nodes in the system. The proposed algorithms are uncomplicated and the implementation into any finite element code is straightforward. Numerical experiments are presented in order to examine the behaviour of the algorithms in different aspects.

The pressing of hard metal components is analysed with numerical methods. The analysed components are selected from produced components for which the density distribution in the material after pressing has been measured. The expected results from the analyses are the density distribution and the springback after unloading and ejection of the components. The highly non-linear quasistatic problem is analysed with the use of explicit integration of the equations of motion. A contact constraint method based on direct integration of the equations of the contact interface is used in the analyses. The contact and friction algorithms have been developed in earlier work and are further verified by analyses of a test problem that has an analytical solution. The behaviour of the powder is described by a special cap plasticity material model developed for powder applications. In one example the results obtained using the cap model are compared with results obtained with a multisurface plasticity model. The parameters of the constitutive models are fitted to triaxial experimental data through optimization methods. The presented methods are evaluated by comparing the results with experimental data from density measurements where a technique based on gamma ray absorption is used. The density distributions are qualitatively in good agreement with experimental results. The springback obtained in the simulation of unloading and ejection is in good agreement with measured values.

SUMMARYA thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin-walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature-dependent elastic-plastic model with a non-linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one-sided forming and quenching experiment.

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To improve the modelling of the behaviour of steel profiles in the forming and quenching process, the influences of high-temperature plastic deformation and applied stress on the martensitic transformation were investigated in a B-bearing steel by dilatometric measurements and compression tests. The plastic deformation of austenite was found to enhance ferrite formation so significantly that the dilatation due to the low-temperature transformation decreases even at a cooling rate of 280°C/s. The presence of ferrite in the microstructure results in markedly lower hardness and flow stress than the completely martensitic microstructure. Possibilities to avoid ferrite formation have been discussed. Stress applied during the martensitic transformation increases diametric dilatation by as much as 200 % under axial compression, which seems to result from the preferred orientation of the martensite formed. However, subsequent to a hightemperature plastic deformation, the influence of applied stress remains much smaller.