P Wriggers

Bio: P Wriggers is an academic researcher. The author has contributed to research in topics: Finite element method & Mixed finite element method. The author has an hindex of 1, co-authored 1 publications receiving 222 citations.

Investigations on residual stresses and deformations in selective laser melting

Abstract: For establishing Selective Laser Melting (SLM) in production technology, an extensive knowledge about the transient physical effects during the manufacturing process is mandatory. In this regard, a high process stability for various alloys, e.g. tool steel 1.2709 (X3NiCoMoTi 18-9-5), is realisable, if approaches for the virtual qualification of adequate process parameters by means of a numerical simulation based on the finite element analysis (FEA) are developed. Furthermore, specific methods to evaluate and quantify the resulting residual stresses and deformations due to the temperature gradient mechanism (TGM) are required. Hence, the presented work contains particular approaches using the FEA for the simulation of transient physical effects within the additive layer manufacturing (ALM) process. The investigations focus on coupled thermo-mechanical models incorporating specific boundary conditions and temperature dependant material properties to identify the heat impact on residual stresses and deformations. In order to evaluate the structural effects and simultaneously validate the simulation, analysis on residual stresses based on the neutron diffractometry as well as considerations concerning part deformations are presented.

Deployment dynamics of tape springs

Abstract: Tape springs are straight, thin–walled strips with a curved cross–section. Following recent proposals for large deployable structures exploiting the structural simplicity and robustness of such springs as deployment actuators, the paper investigates the dynamic deployment of a tape spring that is either coiled around a circular hub, or folded into a zig–zag pattern. It is shown that in both cases the spring deforms by forming an elastically deformed region with zero transverse curvature and uniform longitudinal curvature. The process of formation and growth of a fold belongs to a wide class of propagating instabilities. It is characterized by a high peak moment and a lower propagation moment. A compact characterization of the moment–rotation relationship for an elastic fold is presented. A key feature is that the bending moment on either side of a fold moving along a uniform tape spring, away from any end supports, is constant, whereas this moment increases near a support. Compact and accurate two–dimensional theories are developed to simulate the self–actuated deployment of tape springs. It is shown that conservative energy formulations are appropriate for coiled springs, where the velocity field is smooth, but not for springs with localized folds. To simulate the motion of such localized folds a non–conservative impulse–momentum formulation is proposed, and it is found that this model can accurately predict both the steady motion of the folds along the tape spring and their rebound against the end supports.