Numerical thermo-elasto-plastic analysis of residual stresses on different scales during cooling of hot forming parts

In current research, more and more attention is paid to the understanding of residual stress states as well as the application of targeted residual stresses to extend e.g. life time or stiffness of a part. In course of that, the numerical simulation and analysis of the forming process of components, which goes along with the evolution of residual stresses, play an important role. In this contribution, we focus on the residual stresses arising from the austenite-to-martensite transformation at microscopic and mesoscopic level of a Cr-alloyed steel. A combination of a Multi-Phase-Field model and a two-scale Finite Element simulation is utilized for numerical analysis. A first microscopic simulation considers the lattice change, such that the results can be homogenized and applied on the mesoscale. Based on this result, a polycrystal consisting of a certain number of austenitic grains is built and the phase transformation from austenite to martensite is described with respect to the mesoscale. Afterwards, in a two-scale Finite Element simulation the plastic effects are considered and resulting residual stress states are computed

An Investigation of Plume Rise from Titan IV Rocket Launches

Space launches at Cape Canaveral Air Station (CCAS) and Vandenberg Air Force Base (vAFB) produce exhaust ground clouds from the solid rocket boosters and liquid hypergolic fuels containing several toxic substances. In order to estimate the health effects that would be imposed upon the public by scheduled launches, range safety officials rely on the Rocket Exhaust Effluent Diffusion Model to predict ground level concentrations of these substances. A drawback to the REEDM is its underprediction of the initial ground clouds stabilization height. This underprediction causes an overprediction of the ground level toxic substance concentrations. This thesis focused on increasing the accuracy of the clouds stabilization height. Therefore, a model was developed incorporating conservation principles of volume, momentum, and buoyancy to predict stabilization height values. As part of the model a predictive function for the coefficient of entrainment was developed based on meteorological conditions. This rate of entrainment is a critical factor in accurately predicting the rise behavior of ground exhaust clouds

Sensitivity analysis of statistical measures for the reconstruction of microstructures based on the minimization of generalized least-square functionals

For the simulation of micro-heterogeneous materials the FE2-method provides incorporation of the mechanical behavior at the microscale in a direct manner by taking into account a microscopic boundary value problem based on a representative volume element (RVE). A main problem of this approach is the high computational cost, when we have to deal with RVEs that are characterized by a complex geometry of the individual constituents. This leads to a large number of degrees of freedom and history variables at the microscale which needs a large amount of memory, not to mention the high computation time. Therefore, methods that reduce the complexity of such RVEs play an important role for efficient direct micro-macro transition procedures. In this contribution we focus on random matrix-inclusion microstructures and analyze several statistical measures with respect to their influence on the characterization of the inclusion phase morphology. For this purpose we apply the method proposed in Balzani and Schr¨oder (2008); Balzani et al. (2009a), where an objective function is minimized which takes into account differences between statistical measures computed for the original binary image of a given real microstructure and a simplified statistically similar representative volume element (SSRVE). The analysis with respect to the capability of the resulting SSRVEs to reflect the mechanical response in some simple independent virtual experiments allows for an estimation of the importance of the investigated statistical measures

PlantyOrganic; Voortgang 2013

2013 was het tweede jaar waarin de systeemontwikkeling "PlantyOrganic" in praktijk is gebracht. Op de zes percelen zijn de gewassen geteeld die voorzien waren en zijn metingen verricht aan bodem en gewas. Met uitzondering van de aardappelen hadden in 2013 alle gewassen de voorvrucht die in het ontwerp was voorzien. De gebruikte meststoffen waren geheel afkomstig vanuit het eigen systeem, zoals in het ontwerp was voorzien. De totaal gegeven hoeveelheden stikstof waren ca. 45 % hoger dan waar in het ontwerp van uit is gegaan. De bodemstikstof is getoetst met metingen die in het stikstofmodel NDICEA zijn ingevoerd. De match tussen metingen en berekeningen is voldoende tot goed, met een enkele uitzondering. De gewassen groeiden goed, met hoge opbrengsten in de peen en de haver, en een tegenvallende opbrengsten in de tarwe. De tarwe heef last gehand van stikstofgebrek, waarvoor we nog geen goede verklaring hebben. In de bloemkool heeft stikstofgebrek in de laatste groeifase een negatieve invloed gehad op de kwaliteit, waardoor het niet afgezet kon worden. Alle percelen zijn groen de winter in gegaan. Tot nu toe is geen onderzoek aan beschikbaarheid van fosfaat en kali gedaan. Door de nul-aanvoer van mineralen van buiten het bedrijf is de balans negatief. Op termijn kan deze kringloop gesloten worden door regionale terugvoer van fosfaat en kali met bv. GFT compost of rioolslib. Planty Organic kan een zeer geschikte proeflocatie worden voor onderzoek naar de mobilisatie van fosfaat (en kali) onder omstandigheden van een lage aanvoer en/of een lage bodemchemisch gemeten beschikbaarheid

PlantyOrganic: Results 2013

2013 was the second year of the "PlantyOrganic" system development in practice. The six-year rotation is laid out and measurements took place at soil and crop. With the exception of the potatoes in 2013 all crops had the pre-crop as foreseen in the design. The fertilizers used were completely produced in the own system, as foreseen in the system design. The amounts of nitrogen applied were about 45 % higher than in the design. Soil nitrogen is measured and used as input in the nitrogen model NDICEA. There was a sufficient match between measured and calculated level of soil mineral nitrogen. The crops performed well, with a high yield in carrots and oats, and a disappointing yield in wheat. In wheat nitrogen was limiting for the yield, we do not yet have a satisfactory explanation. In cauliflower a lack of nitrogen ijn the last phase of the growth had a negative effect on the quality and the crop could not be sold. All plots went green into the winter. Until now no research has been done on the availability of phosphate and potassium. Because there is no supply of these minerals from outside the system, the balance is negative. In time the circle could be closed by means of regional re-use of minerals, for example by the application of household waste compost. PlantyOrganic can become a very good research location for research on the mobilisation of phosphate (and potassium) in circumstances of low supply and/or low chemically analysed availability

Validation of thermoplastic composites forming simulations

This work was supported by the Student Grant Scheme at the Technical University of Liberec through project nr. SGS-2023-3378. This publication was supported by the Ministry of Industry and Trade (MPO) within the framework of institutional support for long-term strategic development of the research organization – provider MPO, recipient VUTS, a.s

Numerical characterization of residual stresses in a four-point-bending experiment of textured duplex stainless steel

The resulting shapes in production processes of metal components are strongly influenced by deformation induced residual stresses. Dual-phase steels are commonly used for industrial application of, e.g., forged or deep-drawn structural parts. This is due to their ability to handle high plastic deformations, while retaining desired stiffness for the products. In order to influence the resulting shape as well as component characteristics positively it is important to predict the distribution of phase-specific residual stresses which occur on the microscale of the material. In this contribution a comparative study is presented, where two approaches for the numerical simulation of residual stresses are applied. On the one hand a numerically efficient mean field theory is used to estimate on the grain level the total strain, the plastic strains and the eigenstrains based on macroscopic stress, strain and stiffness data. An alternative ansatz relies on a Taylor approximation for the grain level strains. Both approaches are applied to the corrosion-resistant duplex steel X2CrNiMoN22-5-3 (1.4462), which consists of a ferritic and an austenitic phase with the same volume fraction. Mean field and Taylor approximation strategies are implemented for usage in three dimensional solid finite element analysis and a geometrically exact Euler–Bernoulli beam for the simulation of a four-point-bending test. The predicted residual stresses are compared to experimental data from bending experiments for the phase-specific residual stresses/strains which have been determined by neutron diffraction over the bending height of the specimen