Putting Stiffness where it’s needed: Optimizing the Mechanical Response of Multi-Material Structures

Manufacturing processes are increasingly adapted to multi-material part production to facilitate lightweight design via improvement of structural performance. The difficulty lies in determining the optimum spatial distribution of the individual materials. Multi-Phase Topology Optimization (MPTO) achieves this aim via iterative, linear-elastic Finite Element (FE) simulations providing element- and part-level strain energy data under a given design load and using it to redistribute predefined material fractions to minimize total strain energy. The result us a part configuration offering maximum stiffness. The present study implements different material redistribution and optimization techniques and compares them in terms of optimization results and performance: Genetic algorithms are matched against simulated annealing, the latter with and without physics-based constraints. Both types employ partial randomization in generating new configurations to avoid settling into local rather than global minima of the objective function. This allows exploring a larger fraction of the full search space than accessed by classic gradient-based algorithms. Evaluation of the objective function depends on FE simulation, a computationally intensive task. Minimizing the required number of simulation runs is the task of the aforementioned constraints. The methodology is validated via a three point bending test scenario

2D-simulation of Material Flow During Infeed Rotary Swaging Using Finite Element Method

AbstractFE simulation was applied to study the material flow during infeed rotary swaging. The neutral plane according to the process parameters was investigated and compared with experimental results. A single forming stroke was analyzed precisely by using small time points of 10-4s. For analysis the essential steps between the first contact of wire and forging die and the last contact before the die opens again are represented. In that range the feed velocity is eliminated and the neutral plane can be observed as spatial velocity at nodes in the axial direction equal 0mm/s. During a single stroke the location, the geometry and the orientation of the neutral plane is changing

High-Temperature Mechanical Properties of Stress-Relieved AlSi10Mg Produced via Laser Powder Bed Fusion Additive Manufacturing

The present study is dedicated to the evaluation of the mechanical properties of an additively manufactured (AM) aluminum alloy and their dependence on temperature and build orientation. Tensile test samples were produced from a standard AlSi10Mg alloy by means of the Laser Powder Bed Fusion (LPBF) or Laser Beam Melting (LBM) process at polar angles of 0°, 45° and 90°. Prior to testing, samples were stress-relieved on the build platform for 2 h at 350 °C. Tensile tests were performed at four temperature levels (room temperature (RT), 125, 250 and 450 °C). Results are compared to previously published data on AM materials with and without comparable heat treatment. To foster a deeper understanding of the obtained results, fracture surfaces were analyzed, and metallographic sections were prepared for microstructural evaluation and for additional hardness measurements. The study confirms the expected significant reduction of strength at elevated temperatures and specifically above 250 °C: Ultimate tensile strength (UTS) was found to be 280.2 MPa at RT, 162.8 MPa at 250 °C and 34.4 MPa at 450 °C for a polar angle of 0°. In parallel, elongation at failure increased from 6.4% via 15.6% to 26.5%. The influence of building orientation is clearly dominated by the temperature effect, with UTS values at RT for polar angles of 0° (vertical), 45° and 90° (horizontal) reaching 280.2, 272.0 and 265.9 MPa, respectively, which corresponds to a 5.1% deviation. The comparatively low room temperature strength of roughly 280 MPa is associated with stress relieving and agrees well with data from the literature. However, the complete breakdown of the cellular microstructure reported in other studies for treatments at similar or slightly lower temperatures is not fully confirmed by the metallographic investigations. The data provide a basis for the prediction of AM component response under the thermal and mechanical loads associated with high-pressure die casting (HPDC) and thus facilitate optimizing HPDC-based compound casting processes involving AM inserts

Intrinsic aluminum CFRP hybrid composites produced in high pressure die casting with polymer based decoupling layer

Combining aluminum and carbon fiber reinforced plastic (CFRP) has been a key focus in realizing lightweight hybrid concepts. Yet for hybrid composites of these materials, the solutions to date have relied on conventionally mechanical or adhesive joining techniques. The direct joining of these two materials is problematic, due to their electrochemical intolerance and the resulting corrosive degradation. The joining technology therefore is at the center of this challenge and is investigated within a DFG-sponsored joint research project at the University of Bremen. It aims at combining aluminum and thermoplastic CFRP into an intrinsic hybrid composite. This is to be achieved in a single-step primary shaping process, avoiding conventional joining techniques like adhesive bonding or riveting. To this end, CFRP structures are to be recast with aluminum by high pressure die casting (HPDC), creating an electrochemically decoupling layer between the two materials. This decoupling layer can therefore be considered as a key factor for realizing hybrid composites. It also needs to have a high process reliability and be long-term and mechanically stable. Polyetheretherketone (PEEK) thermoplast was identified as a suitable material for that purpose, given its stability at high temperatures and electrochemical insulation effect. First test results show the possibility of incorporating CFRP accordingly by HPDC, resulting in a continuous intact decoupling layer of PEEK. The trend indicated that different thermal treatments as well as different aluminum thicknesses of the hybrid casted sample influence the joint strength. On average, in tensile shear tests a joint strength approximately in the range of current single lap adhesive bonds could be achieved