An extended Hamilton principle as unifying theory for coupled problems and dissipative microstructure evolution

An established strategy for material modeling is provided by energy-based principles such that evolution equations in terms of ordinary differential equations can be derived. However, there exist a variety of material models that also need to take into account non-local effects to capture microstructure evolution. In this case, the evolution of microstructure is described by a partial differential equation. In this contribution, we present how Hamilton’s principle provides a physically sound strategy for the derivation of transient field equations for all state variables. Therefore, we begin with a demonstration how Hamilton’s principle generalizes the principle of stationary action for rigid bodies. Furthermore, we show that the basic idea behind Hamilton’s principle is not restricted to isothermal mechanical processes. In contrast, we propose an extended Hamilton principle which is applicable to coupled problems and dissipative microstructure evolution. As example, we demonstrate how the field equations for all state variables for thermo-mechanically coupled problems, i.e., displacements, temperature, and internal variables, result from the stationarity of the extended Hamilton functional. The relation to other principles, as the principle of virtual work and Onsager’s principle, is given. Finally, exemplary material models demonstrate how to use the extended Hamilton principle for thermo-mechanically coupled elastic, gradient-enhanced, rate-dependent, and rate-independent materials. © 2021, The Author(s)

An extended Hamilton functional for the thermodynamic topology optimization of hyperelastic structures

We present our work on a new variational approach for thermodynamic topology optimization of hyperelastic structures: building upon our previous works, we follow a thermodynamic approach for deriving a field equation that describes the evolution of the density. The problem of topology optimization is consequently solved without the need of expensive optimization routines. Furthermore, our new formulation can also be applied to hyperelastic structures which show a remarkable difference to structures optimized for small deformations. Important aspects like tension/compression asymmetry and buckling are inherently included in the topology optimization approach due to the large deformation formulation

Continuum multiscale modeling of absorption processes in micro- and nanocatalysts

In this paper, we propose a novel, semi-analytic approach for the two-scale, computational modeling of concentration transport in packed bed reactors. Within the reactor, catalytic pellets are stacked, which alter the concentration evolution. Firstly, the considered experimental setup is discussed and a naive one-scale approach is presented. This one-scale model motivates, due to unphysical fitted values, to enrich the computational procedure by another scale. The computations on the second scale, here referred to as microscale, are based on a proper investigation of the diffusion process in the catalytic pellets from which, after continuum-consistent considerations, a sink term for the macroscopic advection–diffusion–reaction process can be identified. For the special case of a spherical catalyst pellet, the parabolic partial differential equation at the microscale can be reduced to a single ordinary differential equation in time through a semi-analytic approach. After the presentation of our model, we show results for its calibration against the macroscopic response of a simple standard mass transport experiment. Based thereon, the effective diffusion parameters of the catalyst pellets can be identified. © 2022, The Author(s)

Efficient and robust numerical treatment of a gradient-enhanced damage model at large deformations

The modeling of damage processes in materials constitutes an ill-posed mathematical problem which manifests in mesh-dependent finite element results. The loss of ellipticity of the discrete system of equations is counteracted by regularization schemes of which the gradient enhancement of the strain energy density is often used. In this contribution, we present an extension of the efficient numerical treatment, which has been proposed by Junker et al. in 2019, to materials that are subjected to large deformations. Along with the model derivation, we present a technique for element erosion in the case of severely damaged materials. Efficiency and robustness of our approach is demonstrated by two numerical examples including snapback and springback phenomena. © 2021 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd

Qualifizierung laser-additiv gefertigter Komponenten für den Einsatz im Werkzeugbau der Massivumformung

Shortened product life cycles and a raised degree of customization require an increased use of flexible manufacturing processes for production. Due to this, additive manufacturing technology is constantly gaining significance within production. Therefore, in this thesis the possibility of using laser-based additive manufacturing processes in toolmaking for bulk metal forming is investigated. The focus is on the resulting material properties, as these are significant for use in toolmaking. In particular, the behavior under tensile and compressive loads as well as the hardness are analyzed. The corresponding structure is identified by using microscopy. The analyzed structures are manufactured by Laser Beam Melting in powder bed and Laser Metal Deposition welding. Furthermore, the influence of a post-heat-treatment is part of the investigations. Based on the results, the potential of additive manufacturing for toolmaking for bulk metal forming is derived and the use of an additively manufactured tool is proven for a selected production sequence through use in serial production.Verkürzte Produktlebenszyklen und ein erhöhtes Maß an Individualisierung erfordern den vermehrten Einsatz flexibler Fertigungsprozesse. Vor diesem Hintergrund gewinnt die Technologie der additiven Fertigung im Produktionsumfeld stetig an Bedeutung. In dieser Arbeit wird deshalb die Möglichkeit des Einsatzes laserbasierter additiver Fertigungsverfahren im Werkzeugbau der Massivumformung untersucht. Der Fokus liegt dabei auf den resultierenden Materialeigenschaften, da diese ausschlaggebend für den Einsatz im Werkzeugbau. Insbesondere werden das Verhalten unter Zug- und Druckbelastung sowie die Härte analysiert. Die Identifikation des zugrundeliegenden Gefüges findet mittels Mikroskopie statt. Die Fertigung der analysierten Körper erfolgt durch Laserstrahlschmelzen im Pulverbett und Laser-Pulverauftragschweißen. Des Weiteren ist der Einfluss einer thermischen Nachbehandlung Bestandteil der Untersuchungen. Auf Basis der erarbeiteten Ergebnisse wird das Potential der additiven Fertigung für den Werkzeugbau in der Massivumformung abgeleitet und der Einsatz eines additiv gefertigten Werkzeugs für eine ausgewählte Fertigungsfolge durch die Verwendung im Serienbetrieb nachgewiesen

Automatic extraction of cause-effect-relations from requirements artifacts

Background: The detection and extraction of causality from natural language sentences have shown great potential in various fields of application. The field of requirements engineering is eligible for multiple reasons: (1) requirements artifacts are primarily written in natural language, (2) causal sentences convey essential context about the subject of requirements, and (3) extracted and formalized causality relations are usable for a (semi-)automatic translation into further artifacts, such as test cases. Objective: We aim at understanding the value of interactive causality extraction based on syntactic criteria for the context of requirements engineering. Method: We developed a prototype of a system for automatic causality extraction and evaluate it by applying it to a set of publicly available requirements artifacts, determining whether the automatic extraction reduces the manual effort of requirements formalization. Result: During the evaluation we analyzed 4457 natural language sentences from 18 requirements documents, 558 of which were causal (12.52%). The best evaluation of a requirements document provided an automatic extraction of 48.57% cause-effect graphs on average, which demonstrates the feasibility of the approach. Limitation: The feasibility of the approach has been proven in theory but lacks exploration of being scaled up for practical use. Evaluating the applicability of the automatic causality extraction for a requirements engineer is left for future research. Conclusion: A syntactic approach for causality extraction is viable for the context of requirements engineering and can aid a pipeline towards an automatic generation of further artifacts from requirements artifacts.Comment: ASE '20: Proceedings of the 35th IEEE/ACM International Conference on Automated Software Engineerin

Pamir-Gebirge, Tadschikistan. Tadschikisch-Deutsche Pamir Expedition. Die Arbeiten des Jahres 2019

During late summer 2019, archaeological sites and museums in Tajikistan were visited to study prehistoric gemstones and metal artefacts using portable XRF. Besides objects made of gold, silver, lead and copper alloys, jewelry of lapis lazuli and turquoise were examined to establish a geochemical fingerprint. This will help to pinpoint the raw material sources of Chalcolithic and Bronze Age metal and stone trade in Central Asia and beyond. During field surveys in the Pamirs high-altitude mountains, lapis lazuli sources were visited and settlement patterns and former land use, in relation to the lapis lazuli occurrences were documented. The campaign is part of the DFG-Project »RESAF – Resources and Antique Mining in Afghanistan«

Comparison of real-time elastography and multiparametric MRI for prostate cancer detection: A whole-mount step-section analysis

OBJECTIVE. The purpose of this study was to compare prostate cancer detection rate of real-time elastography (RTE) with that of multiparametric MRI to evaluate the advantages and disadvantages of the two methods. SUBJECTS AND METHODS. Thirty-nine patients with biopsy-proven prostate cancer underwent both RTE and multiparametric MRI to localize prostate cancer before radical prostatectomy. RTE was performed to assess prostate tissue elasticity, and hard lesions were considered suspicious for prostate cancer. Multiparametric MRI included T2-weighted MRI, diffusion-weighted MRI (DWI), and contrast-enhanced MRI (CE-MRI) with an endorectal coil at 1.5 T. After radical prostatectomy, whole-mount step sections of the prostate were generated, and the prostate cancer detection rates with both modalities were analyzed for cancer lesions measuring 0.2 cm 3 or larger. RESULTS. Histopathologic examination revealed 61 cancer lesions. RTE depicted 39 of 50 cancer lesions (78.0%) in the peripheral zone and 2 of 11 (18.2%) in the transitional zone. Multiparametric MRI depicted 45 of 50 cancer lesions (90.0%) in the peripheral zone and 8 of 11 (72.7%) in the transitional zone. Significant differences between the two modalities were found for the transitional zone and anterior part in prostates with volumes greater than 40 cm3 (p \u3c 0.05). Detection rates for high-risk prostate cancer (Gleason score ≥ 4 and 3) and cancer lesions with volumes greater than 0.5 cm3 were high for both methods (93.8% and 80.5% for RTE, 87.5% and 92.7% for multiparametric MRI). Volumetric measurements of prostate cancer were more reliable with T2-weighted MRI than with RTE (Spearman rank correlation, 0.72 and 0.46). CONCLUSION. RTE and multiparametric MRI depicted high-risk prostate cancer with high sensitivity. However, multiparametric MRI seems to have advantages in tumor volume assessment and for the detection of prostate cancer in the transitional zone and anterior part within prostates larger than 40 cm3. American Roentgen Ray Society