On nonlinear thermo-electro-elasticity

Electro-active polymers (EAPs) for large actuations are nowadays well-known and promising candidates for producing sensors, actuators and generators. In general, polymeric materials are sensitive to differential temperature histories. During experimental characterizations of EAPs under electro-mechanically coupled loads, it is difficult to maintain constant temperature not only because of an external differential temperature history but also because of the changes in internal temperature caused by the application of high electric loads. In this contribution, a thermo-electro-mechanically coupled constitutive framework is proposed based on the total energy approach. Departing from relevant laws of thermodynamics, thermodynamically consistent constitutive equations are formulated. To demonstrate the performance of the proposed thermo-electro-mechanically coupled framework, a frequently used non-homogeneous boundary-value problem, i.e. the extension and inflation of a cylindrical tube, is solved analytically. The results illustrate the influence of various thermo-electro-mechanical couplings

How to Assess Sustainable Planning Processes of Buildings? A Maturity Assessment Model Approach for Designers

Over the past decades, it has become apparent that increasing demands in the construction industry have repeatedly led to project delays and increased project costs in practice. These demands have increased as a result of international and national action plans that have been developed to achieve the climate target paths and, therefore, the necessary reduction of CO2 emissions in the construction industry. We address this problem by developing a sustainable construction maturity model (SCOMM) to answer the following research question: “What is a holistic quality assurance tool for the early design phase of buildings to monitor (sustainable) planning practices in order to achieve better certification results?”. The model includes a self-assessment procedure for the building design process, based on Software Process Improvement and Capability dEtermination (SPiCE) and the German Sustainable Building Council (DGNB) building certification system. The results show that systemic interactions between sustainability criteria can be identified in the early design phase, allowing the quality of planning practices to be evaluated and early project management to be implemented to achieve the best certification results. Our findings will enable clients and users of the construction industry to better manage the complexity of the sustainable design process and avoid undesirable developments in building projects

A complete thermo–electro–viscoelastic characterization of dielectric elastomers, Part I: Experimental investigations

Dielectric elastomers are a class of solid polymeric materials that are sufficiently soft to deform under the application of an electric field due to the interaction of quasi-static electric charges. Their potential to undergo large deformations renders them promising candidates for the design of energy harvesters, sensors and soft actuators. For their application however, the influence of additional thermal effects should be taken into account as the base materials frequently show a distinct thermal sensitivity that drastically influences their mechanical response. This contribution presents the results of a wide range of experiments conducted on the popular dielectric elastomer VHB 4905™ under a combination of mechanical, thermal and electric loading scenarios. These experiments are performed in such a way that the obtained results are well suited for the identification of the necessary material parameters appearing in a thermo–electro–viscoelastic constitutive model that will subsequently be presented in the second part of the contribution

Numerical modeling of nonlinear photoelasticity

When molecular photo-switches, such as azobenzene or norbornadiene, are embedded into a sufficiently soft polymer matrix the resulting compound can undergo a mechanical deformation induced by light of a specific wavelength. These photo-sensitive compounds have the potential to be applied as soft actuators without the need for hard wired electronics or a separate energy source. Such characteristics are especially attractive in the design of micro-scale robots but also other applications such as high-speed data transfer or the conversion of photonic energy into a mechanical response holds great promise. Despite these almost futuristic possibilities, photo-sensitive polymers have not yet experienced a sufficient attention in industrial applications. One important factor to increase the acceptance of this group of soft smart materials is the formulation of a rigorous constitutive modeling approach in combination with numerical simulation methods. Thus, in this contribution we present a photo-mechanical modeling approach, departing from the fundamentals published previously. We briefly introduce the necessary constitutive equations which are subsequently utilized in combination with the respective balance laws into a finite element implementation. Finally, the capabilities of the numerical solution approach are illustrated by a simple two-dimensional bench-mark example and subsequently extended to a more complex three-dimensional problem

Towards a thermo-magneto-mechanical coupling framework for magneto-rheological elastomers

Magnetorheological elastomers (MREs) are a relatively new class of smart materials that can undergo large deformations resulting from external magnetic excitation. These are promising candidates in producing sensors and actuators. Due to their inherent chemical compositions, most polymeric materials are highly susceptible to temperature. While performing experiments on MREs that are exposed to magneto-mechanically coupled loads, maintaining a constant temperature profile is a non-trivial task for various reasons, e.g., i) experiments need to be performed in a temperature chamber that can maintain a prescribed temperature throughout a test, and ii) additional temperature gradients can be generated internally. In this paper, a thermo-magneto-mechanically coupled constitutive model is devised that is based on the total energy approach frequently used in MREs modelling and computation. Relevant constitutive equations are derived exploiting basic laws of thermodynamics that result in a thermodynamically consistent formulation. We demonstrate the performance of the proposed thermo-magneto-mechanically coupled framework with the help of two non-homogeneous boundary value problems. In both problems an axisymmetric cylindrical tube is deformed under thermo-magneto-mechanically coupled loads. In the first example the mechanical deformation is a combination of axial stretch and radial inflation whereas in the second example the cylinder is put under a mechanical load of torsion around the cylinder axis combined with an axial stretch. In both examples a circumferential magnetic field and a radial temperature gradient are applied. The results capture various thermo-magneto-mechanical couplings with the formulation proposed for MRE

Feldscheune Chrummacher/Rötler – Eptingen, VBF-Inventar Nr. 20/21 – Schlussbericht der Renovationsarbeiten

Sie gehören zu den belebenden Elementen unserer Kulturlandschaft, die Feldscheunen, die Heuschober und die Weidställe. Und sie sind gleichzeitig traditionelle Denkmäler wie Kirchen und Pfarrhäuser. Die Scheunen und Ställe stellen zusammen mit den bäuerlichen Wohnbauten unsere regionaltypische Architektur dar. Erbaut wurden die meisten in der Zeit der Dreifelderwirtschaft. Auf dorffernen Grundstücken wurden zu Zeiten des Flurzwangs kleine Heuschober erstellt. Aus diesen wurden dann im Winter das Heu geholt. Auch entstanden Weidställe in höheren Lagen. Oft wurden solche Heuschober von mehreren Mitbesitzern genutzt. Durch die Aufhebung des Flurzwangs entstanden Anfangs des 18. Jahrhunderts die ersten Aussenhöfe. Oft an der Stelle der alten Scheunen und Ställe, dort eben, wo auch Quellen in der Nähe waren. In der weiteren Entwicklung des Landwirtschaftsbetriebe siedelten immer mehr Höfe aus und bauten grosse Scheunen. Die Mechanisierung in der Landwirtschaft brachten ebenfalls einen grossen Schub an Rationalisierung und diese Maschinen konnten nicht in den alten Scheunen unterbracht werden. Die alten Bauten brachten und bringen somit kaum einen Nutzen für die Landwirte. Sie sind eher, bedingt durch notwendigen baulichen Unterhalt, eine finanzielle Last. Für viele sind Feldscheunen emotionale Orientierungspunkte in der Landschaft. Jedes Mal, wenn eine verschwindet, verschwindet ein Stück Landschaft in der Erinnerung. Der Verein Baselbieter Feldscheunen hat sich zum Ziel gesetzt, Wege zum Erhalt dieser wertvollen Kleinbauten zu finden. Dabei legt der Verein die Priorität auf die besonders schützenswerten Scheunen und Ställe. Solche, die durch ihre besondere Lage, durch ihre Geschichte und durch besonders eindrückliche handwerkliche Bauteile und Konstruktionen herausragen. Damit will der Verein dieses geschichtliche bäuerliche Kulturerbe schützen und auch im Bewusstsein wach halten. Pro Jahr soll mindestens eine Feldscheune renoviert werden

Fast Mapping of Terahertz Bursting Thresholds and Characteristics at Synchrotron Light Sources

Dedicated optics with extremely short electron bunches enable synchrotron light sources to generate intense coherent THz radiation. The high degree of spatial compression in this so-called low-alpha optics entails a complex longitudinal dynamics of the electron bunches, which can be probed studying the fluctuations in the emitted terahertz radiation caused by the micro-bunching instability ("bursting"). This article presents a "quasi-instantaneous" method for measuring the bursting characteristics by simultaneously collecting and evaluating the information from all bunches in a multi-bunch fill, reducing the measurement time from hours to seconds. This speed-up allows systematic studies of the bursting characteristics for various accelerator settings within a single fill of the machine, enabling a comprehensive comparison of the measured bursting thresholds with theoretical predictions by the bunched-beam theory. This paper introduces the method and presents first results obtained at the ANKA synchrotron radiation facility.Comment: 7 pages, 7 figures, to be published in Physical Review Accelerators and Beam

Shrinking risk profiles after deworming of children in Port Elizabeth, South Africa, with special reference to Ascaris lumbricoides and Trichuris trichiura

Risk maps facilitate discussion among different stakeholders and provide a tool for spatial targeting of health interventions. We present maps documenting shrinking risk profiles after deworming with respect to soil-transmitted helminthiasis among schoolchildren from disadvantaged neighbourhoods in Port Elizabeth, South Africa. Children were examined for soil-transmitted helminth infections using duplicate Kato-Katz thick smears in March 2015, October 2015 and May 2016, and subsequently treated with albendazole after each survey. The mean infection intensities for Ascaris lumbricoides were 9,554 eggs per gram of stool (EPG) in March 2015, 4,317 EPG in October 2015 and 1,684 EPG in March 2016. The corresponding figures for Trichuris trichiura were 664 EPG, 331 EPG and 87 EPG. Repeated deworming shrank the risk of soil-transmitted helminthiasis, but should be complemented by other public health measures

Disease, activity and schoolchildren's health (DASH) in Port Elizabeth, South Africa: a study protocol

BACKGROUND: An in-depth epidemiological investigation on intestinal parasite infections in an impoverished area of Port Elizabeth, South Africa provides a unique opportunity for research on its impact on children's physical fitness, cognitive performance and psychosocial health. Additionally, we will screen risk factors for the development of diabetes and hypertension in adulthood. METHODS/DESIGN: A 2-year longitudinal cohort study will be conducted, consisting of three cross-sectional surveys (baseline and two follow-ups), in eight historically black and coloured (mixed race) primary schools located in different townships in Port Elizabeth, South Africa. Approximately 1000 Grade 4 primary schoolchildren, aged 8 to 12 years, will be enrolled and followed. At each survey, disease status, anthropometry and levels of physical fitness, cognitive performance and psychosocial health will be assessed. After each survey, individuals diagnosed with parasitic worm infections will be treated with anthelminthic drugs, while children with other infections will be referred to local clinics. Based on baseline results, interventions will be tailored to the local settings, embedded within the study and implemented in half of the schools, while the remaining schools will serve as controls. Implementation of the interventions will take place over two 8-week periods. The effect of interventions will be determined with predefined health parameters. DISCUSSION: This study will shed new light on the health burden incurred by children in deprived urban settings of South Africa and provide guidance for specific health interventions. Challenges foreseen in the conduct of this study include: (i) difficulty in obtaining written informed consent from parents/guardians; (ii) administration of questionnaires in schools where three languages are spoken (Afrikaans, Xhosa and English); (iii) challenges in grasping concepts of psychosocial health among schoolchildren using a questionnaire; and (iv) loss to follow-up due to the study setting where illiteracy, mobility and violence are common. Finally, designing the health interventions together with local principals and teachers will allow all concerned with the research to bolster a sense of community ownership and sustained use of the interventions after the study has ceased