Hubertus J.M. Geijselaers

The dynamic mechanical characteristics of a resonating microbridge mass-flow sensor

This paper gives an explanation of the dynamic mechanical behaviour of a resonating microbridge mass-flow sensor. A rise in the average temperature of the bridge initially results in a reduction of the resonance frequency. Upon further temperature rise, a reversal occurs and the resonance frequency starts rising too. The dynamic behaviour in this case is found to be governed by static buckling. This phenomenon is analysed, first using a finite-element model and then with an approximate analytical calculation.

Thermo-Mechanical Analysis with Phase Transformations

An elongated reaction chamber (11) has an inlet end (23), an outlet end (25), and a gas containment boundary (12) extending along its length. Waste material to be processed is injected into the reaction chamber (11) at the inlet end (23) and reaction products are removed from the reaction chamber out the outlet end (25). The reaction chamber (11) is mounted within a supply chamber (16) containing a molten reactant metal (15). The level of the molten reactant metal (15) in the supply chamber (16) resides above the level of the upper gas containment boundary (12). A circulating arrangement including a circulating paddle (17) circulates molten reactant metal (15) into the inlet end (23) of the reaction chamber (11) and through the reaction chamber to its outlet end (25). A mixing arrangement which may include fins (44) associated with the reaction chamber (11) mixes both gases and molten reactant metal in the reaction chamber to enhance exposure of unreacted gases to the molten metal. Gases exiting the reaction chamber (11) may be monitored to control the input of waste material at the inlet end (23) of the reaction chamber.

Generating the Best Stacking Sequence Table for the Design of Blended Composite Structures

In order to improve the ability of a large-scale light-weight composite structure to carry tensile or compressive loads, stiffeners are added to the structure. The stiffeners divide the structure into several smaller panels. For a composite structure to be manufacturable, it is necessary that plies are continuous in multiple adjacent panels. To be able to prescribe a manufacturable design, an optimization algorithm can be coupled with a reference table for the stacking sequences (SST). As long as the ply stacks are selected from the SST, it is guaranteed that the design is manufacturable and all strength related guidelines associated with the design of composite structures are satisfied. An SST is made only based on strength related guidelines. Therefore, there exist a large number of possibilities for SSTs. Minimized mass is a typical goal in the design of aircraft structures. Different SSTs result in different values for the minimized mass. Thus it is crucial to perform optimization based on the SST which results in the lowest mass. This paper aims to introduce an approach to generate a unique SST resulting in the lowest mass. The proposed method is applied to the optimization problem of a stiffened composite structure resembling the skin of an aircraft wing box.

A model for TRIP steel constitutive behaviour

A constitutive model is developed for TRIP steel. This is a steel which contains three or four different phases in its microstructure. One of the phases in TRIP steels is metastable austenite (Retained Austenite) which transforms to martensite upon deformation. The accompanying transformation strain and the increase in hardness provide excellent formability characteristics. The phase transformation depends on the stress in the austenite, which is not equal to the overall stress. An estimate of the local stress in the austenite is obtained by homogenization of the response of the phases using a Mean-Field homogenization method. Overall stress strain results as well as stress strain results for individual phases are compared to measurements found in literature. The model can be used in finite element simulations of forming processes.

A constitutive model for multi‐phase steels

Mean‐Field homogenization algorithms for materials involving two or more elastic‐plastic constituent phases are investigated. The Voigt, Reuss and Self consistent schemes which are directly applicable to multi‐phase systems are implemented. The shortcomings of these schemes are accuracy for the former two and computational efficiency for the latter. A new interpolative model is proposed which is aimed to be both computationally efficient and accurate. The results of the models are studied on the material point level for a prescribed uniaxial tensile deformation. It is observed that the response computed by the proposed scheme closely matches that computed by the Self Consistent approach.

Efficient Calculation of Uncertainty Propagation with an Application in Robust Optimization of Forming Processes

Robust optimization is being used in metal forming processes to select the design which is least sensitive to the presence of uncertainty in the input parameters. In most cases, a mathematical surrogate model is built via input data and resulting output obtained from finite element simulations. The influence of uncertainty in input parameters is then considered using a large number of function evaluations via Monte Carlo analysis with a given probabilistic distribution. Although this method is quite fast and simple, it needs a lot of function evaluations to increase accuracy. This random sampling is neither efficient nor reproducible. A new approach is used to calculate the uncertainty propagation analytically. Compared to conventional Monte Carlo approach this method is accurate, fast, stable, and efficient. In addition, it is possible to employ this method with different types of probability distributions and most commonly-used metamodels. To show the applicability of this method in robust optimization process, a stretch-bending process is investigated with two design and two noise variables. Comparing the results obtained by Monte Carlo and the analytical approach shows that different Monte Carlo runs lead to fluctuations around the exact analytical solution. In addition, the analytical approach reduces the evaluation time of finding the robust optimum to a great extent.

A nonlinear dynamic corotational finite element model for submerged pipes

A three dimensional finite element model is built to compute the motions of a pipe that is being laid on the seabed. This process is geometrically nonlinear, therefore co-rotational beam elements are used. The pipe is subject to static and dynamic forces. Static forces are due to gravity, current and buoyancy. The dynamic forces exerted by the water are incorporated using Morisons equation. The dynamic motions are computed using implicit time integration. For this the Hilber-Hughes-Taylor method is selected. The Newton-Raphson iteration scheme is used to solve the equations in every time step. During laying, the pipe is connected to the pipe laying vessel, which is subject to wave motion. Response amplitude operators are used to determine the motions of the ship and thus the motions of the top end of the pipe.

Simulation of Steady Laser Hardening by an Arbitrary Lagrangian Eulerian Method

One of the most practical methods for simulation of steady state thermal processing is the Arbitrary Lagrangian‐Eulerian method. Each calculation step is split into two phases. In the first phase, the Lagrangian phase, the element mesh remains attached to the material. The evolution of the state variables is monitored and the state at the end of the phase is calculated. In the second phase, the Eulerian phase, the mesh is, broadly speaking, restored to its original position with respect to a window attached to the moving heat source. The mesh is not restored to its exact original position, but some allowance is made perpendicular to the flow direction in order to capture movement of the free surfaces. In this paper a finite element model for Lagrangian simulation of thermo‐mechanical processes with phase transformations is combined with a second order discontinuous Galerkin method for modeling of Eulerian advection.