The particle finite element method (PFEM) is a Lagrangian method that avoids large mesh distortion through automatic remeshing when the computational grid becomes too distorted. The method is well adapted for flows with deforming interfaces and moving boundaries. However, the \(\alpha \)-shape technique used to identify these boundaries presupposes a mesh of approximately uniform size. Moreover, the \(\alpha \)-shape criterion is purely geometric and, thus, leads to violations of mass conservation at boundaries. We propose a new algorithm for mesh refinement and adaptation in two dimensions to improve the ratio accuracy to computational cost of the PFEM. A local target mesh size is prescribed according to geometric and/or physics-based criteria, and particles are added or removed to approximately enforce this target mesh size. Additionally, the new boundary recognition algorithm relies on the tagging of boundary nodes and a local \(\alpha \)-shape criterion that depends on the target mesh size. The method allows thereby reducing mass conservation errors at free surfaces and improving the local accuracy through mesh refinement and simultaneously offers a new boundary tracking algorithm. The new algorithm is tested on four two-dimensional validation cases. The first two cases, i.e., the lid-driven cavity flow at Reynolds number 400 and the flow around a static cylinder at Reynolds numbers below 200, do not feature a free surface and mainly illustrate the mesh refinement capability. The last two test cases consist in the sloshing problem in a reservoir subjected to forced oscillations and the fall of a 2D liquid drop into a tank filled with the same viscous fluid. These last two cases demonstrate the more accurate representation of the free surface and a corresponding reduction of the error in mass conservation.

A simulation method is developed herein based on the particle finite element method (PFEM) to simulate processes with surface tension and phase change. These effects are important in the simulation of industrial applications, such as welding and additive manufacturing, where concentrated heat sources melt a portion of the material in a localized fashion. The aim of the study is to use this method to simulate such processes at the meso-scale and thereby gain a better understanding of the physics involved. The advantage of PFEM lies in its Lagrangian description, allowing for automatic tracking of interfaces and free boundaries, as well as its robustness and flexibility in dealing with multiphysics problems. A series of test cases is presented to validate the simulation method for these two effects in combination with temperature-driven convective flows in 2D. The PFEM-based method is shown to handle both purely convective flows and those with the Marangoni effect or melting well. Following exhaustive validation using solutions reported in the literature, the obtained results show that an overall satisfactory simulation of the complex physics is achieved. Further steps to improve the results and move towards the simulation of actual welding and additive manufacturing examples are pointed out.

ESAFORM is an association with the mission to stimulate applied and fundamental research in the field of material forming. Its annual conference, the International ESAFORM Conference on Material Forming, is used to achieve one of the main goals of ESAFORM: to spread scientific and technological information related to material forming within academic and industry. The next conference will be held online on 14-16 April 2021.

Friction Melt Bonding (FMB) allows to weld aluminium and steel plates in a lap-joint configuration. FMB produces a melt pool in the aluminium plate, which is visually inaccessible as it is trapped between the two plates. As the melt pool boundaries are initially unknown and evolve during the process, numerical simulation is essential to support quantitative research on the FMB process or to predict behaviour in out-of-laboratory conditions. To simulate the FMB process, this work proposes a partitioned methodology that combines PFEM (Particle Finite Element Method) and FEM. PFEM is used for modelling the aluminium plate, including phase change and convective flow within the melt pool. FEM, on the other hand, is used for the steel plate and the accompanying equipment, as they do not present complex multiphysics phenomena such as phase change and evolving boundaries. A 2D model was used for the experimental comparison, as numerous simulations were required to set up the thermal model. Results were compared against experimental measurements. A good agreement between numerical and experimental results was achieved, both for the melt pool geometry and the temperature of a thermocouple. In addition, the effect of ignoring the convective flow inside the melt pool was also studied. In this regard, results show moderate differences in melt pool geometries between flowing and a non-flowing melt pool models.