65,179 research outputs found
Buckling of beams with finite prebuckling deformation
No full textThe prebuckling deformation of structures is usually very small in conventional concepts, and is always neglected in the conventional buckling theory (CBT) and numerical method (CNM). In this paper, we find a class of structures from the emerging field of stretchable electronics, of which the prebuckling deformation becomes large and essential for determining the critical buckling load. Although great progress has been made for the buckling theory in the past hundred years, it is still challenging to analyze the buckling problems with finite prebuckling deformation (FPD buckling) straightforwardly. Here, the experimental stretch of a series of serpentine interconnects was firstly conducted as a representative example to show the FPD buckling behaviors and inapplicability of the CBT and CNM. The CNM can yield a huge error of 50% on the critical buckling load for the case with thickness-to-width ratio of the cross section h/b=0.6. Most importantly, a systematic and straightforward theory (FPD buckling theory) is developed to analyze the FPD buckling behaviors of beams with the coupling of bending, twist and stretch/compression. As a comparison, various theoretical and numerical methods are applied to three classic problems, including lateral buckling of a three-point-bending beam, lateral buckling of a pure bending beam and Euler buckling. Our FPD buckling theory for beams is able to give a good prediction, while the CBT (by Timoshenko et al.) and CNM (by commercial program packages) yield unacceptable results (with 70% error for a three-point-bending beam with h/b = 0.8, for example). Discussion on the FPD buckling of bulk structures is deferred to a following paper. (C) 2019 Elsevier Ltd. All rights reserved
Measured Output Voltages of Piezoelectric Devices Depend on the Resistance of Voltmeter
No full textPiezoelectric mechanical energy harvester (MEH) has been developed as an important emerging variant of piezoelectric devices. Experiments in the literature show that the voltage-time curves of piezoelectric devices encompass both positive and negative characteristics even though the strain in the piezoelectric material is always positive during the applied cycling load. This does not agree with the results predicted by the piezoelectric theory of open circuit. Here, both the experiments and theory are performed to understand this important problem. A zirconate titanate (PZT) MEH is fabricated and the output voltages are recorded with three voltmeters. It is found that the measured voltages depend on the resistance of voltmeter. The peak value of voltage increases with the increase of the resistance of voltmeter, which is contrary to the established knowledge that the measurement results are independent of the instruments used. A theoretical model considering the voltmeter with finite resistance is established. The charge is allowed to go through the voltmeter and switch the directions during increasing and releasing of strain. The results by this model agree well with those from the experiments. The findings suggest that the resistance of voltmeter should be reported for voltage measurement of the piezoelectric devices.Piezoelectric mechanical energy harvester (MEH) has been developed as an important emerging variant of piezoelectric devices. Experiments in the literature show that the voltage-time curves of piezoelectric devices encompass both positive and negative characteristics even though the strain in the piezoelectric material is always positive during the applied cycling load. This does not agree with the results predicted by the piezoelectric theory of open circuit. Here, both the experiments and theory are performed to understand this important problem. A zirconate titanate (PZT) MEH is fabricated and the output voltages are recorded with three voltmeters. It is found that the measured voltages depend on the resistance of voltmeter. The peak value of voltage increases with the increase of the resistance of voltmeter, which is contrary to the established knowledge that the measurement results are independent of the instruments used. A theoretical model considering the voltmeter with finite resistance is established. The charge is allowed to go through the voltmeter and switch the directions during increasing and releasing of strain. The results by this model agree well with those from the experiments. The findings suggest that the resistance of voltmeter should be reported for voltage measurement of the piezoelectric devices
Buckling of Bulk Structures With Finite Prebuckling Deformation
No full textThe prebuckling deformation of structures is neglected in most of the conventional buckling theory (CBT) and numerical method (CNM), because it is usually very small in conventional concepts. In the preceding paper (Su et al., 2019), we found a class of structures from the emerging field of stretchable electronics, of which the prebuckling deformation became large and essential for determining the critical buckling load, and developed a systematic buckling theory for 3D beams considering the effects of finite prebuckling deformation (FPD). For bulk structures that appear vastly in the advanced structures, a few buckling theories consider the effects of the prebuckling deformation in constitutive equations by energy method, which are significantly important but not straightforward and universal enough. In this paper, a systematic and straightforward theory for the FPD buckling of bulk structures is developed with the use of two constitutive models. The variables for the prebuckling deformation serve as the coefficients of the incremental displacements, deformation components, and stress in the buckling analysis. Four methods, including the CBT, CNM, DLU (disturbing-loading-unloading method) method and FPD buckling theory, are applied to the classic problems, including buckling of an elastic semi-plane solid and buckling of an elastic rectangular solid, respectively. Compared with the accurate buckling load from the DLU method, the FPD buckling theory is able to give a good prediction, while the CBT and CNM may yield unacceptable results (with 70% error for the buckling of an elastic semi-plane solid)
Energy-Efficient Train Operation: Conclusions and Future Work
No full textThis chapter gives the basic conclusions about energy-efficient train operation covering energy-efficient train driving, energy-efficient train timetabling, regenerative braking, energy storage systems and power supply networks. Future work that will develop energy-efficient train operation further include the interaction of connected driver advisory systems (C-DAS) and automatic train operation (ATO) with railway traffic management systems, cooperative train control in platoons of virtually coupled trains, digital twin technology and particularly its application to power supply systems, and the interaction between the railway network with the electrical power grid and renewable energy generation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Plannin
Stretchable Strain Sensors Based on Deterministic-Contact-Resistance Braided Structures with High Performance and Capability of Continuous Production
No full textOwing to their potential applicability in wearable devices and intelligent robots, stretchable strain sensors have been widely investigated. However, fabricating sensors with high sensitivity, wide sensing range, high repeatability, robustness, and capability for continuous production remains challenging. Herein, a deterministic-contact-resistance braided structure (DCRBS)-based stretchable strain sensor is proposed. The polyester yarns in the sensor tightly trap the silver fibers with the latex thread substrate to form a periodic Y structure to avoid slippage of the fibers, thereby facilitating deterministic contact and separation between the silver fibers during cyclic stretching. Owing to this braided structure, the strain sensor exhibits high repeatability (repeatability error = 3.74%), high sensitivity (gauge factor up to 140), wide sensing range (50%), and high robustness (washability, insensitivity to micro-defects). Additionally, the strain sensor can be continuously mass produced using mature raw materials and processing technology. Because of its demonstrated excellent performance, the strain sensor can find applications in human motion monitoring, rehabilitation medicine, and robotic control.</p
Relating Research and Teaching: comparing experiences and beliefs
No full textThe relationship between research and teaching has possible benefits and inherent tensions. It is a recurrent topic of discussion by faculty including engineering educators. Exploring a potentially beneficial relationship and is of interest and possible value to engineering faculty, our students, and our stakeholders. Institutions and departments have developed a range of approaches including research-led, research informed, or just plain scholarly. This paper examines the relationship between research and teaching in the undergraduate curriculum. It compares and contrasts evidence of the beliefs and experiences of the engineering faculty and the engineering student. It presents and analyses the result of surveys which gathered qualitative and qualitative data to explore the inter-relationship of research and teaching; in the curriculum; and as it is delivered and experienced in the lab, seminar room and lecture hall. This research builds on existing work developed in a preliminary study which examined ways in which synergies between research and teaching could be achieved, particularly in the ‘hard/applied’ areas of the curriculum. It analyses data from the ‘research-intensive’ and the ‘teaching-intensive’ perspective
A traction-free model for the tensile stiffness and bending stiffness of laminated ribbons of flexible electronics
No full textLaminated ribbons have been widely adopted for structures of flexible electronics to simultaneously achieve the electronic functions and mechanical performances. Their effective tensile stiffness and bending stiffness, which are extensively used as fundamental parameters
in the mechanical analysis, are usually obtained by the plane-strain hypothesis for simplicity. However, it is found that the practical condition is usually closer to the traction free, even for the cases with a relatively large width. Here, a traction-free model is proposed to analytically obtain the effective tensile stiffness and bending stiffness of laminated ribbons,
which can be used directly in the mechanical analysis of flexible electronics. The prediction of the traction-free model agrees very well with the precise result obtained by 3D finite element analysis (FEA) for the cases that are in the range of structure designs of flexible electronics. It is found that the tensile/bending stiffness of traction-free model is between the plane-stress model and plane-strain model, but is closer to the plane-stress model. The use of the plane-strain model sometimes may yield a considerable error in the mechanical analysis of flexible electronics. The parameter study shows that this model is very important for the problems with advanced materials, such as metamaterials with negative Poisson’s ratio. This work provides a theoretical basis for the mechanical analysis of flexible electronics.</p
Simulation of fully coupled hydro-mechanical behavior based on an analogy between hydraulic fracturing and heat conduction
No full textThe hydraulic fracturing process involves complex coupling problems of the deformation and fracturing of solid and fluid flow in fractures. In this paper, a simple numerical tool for simulating the coupled hydro-mechanical behavior is developed by using an analogy between hydraulic fracturing and heat conduction. Using this analogy, the numerical implementation can be simply realized in the framework of a commercial finite element package ABAQUS with two user material subroutines to fully characterize the complex coupling problems of hydraulic fracturing. It is thus considerably simplified without any new development of user-defined element and fluid-solid solver but directly with the commercial finite element package. The proposed numerical tool along with the virtual crack method for elastic-brittle material is firstly verified by the classical 2D plain strain KGD analytical solution and then applied to several representative hydraulic fracturing problems and laboratory tests to illustrate its advantageous features. The present method is aiming to develop a useful numerical tool to study the coupled hydro-mechanical behavior of hydraulic fracturing. However, it is not limited to any specific materials and can be extended to other constitutive models that featured with the fully coupling problems of fluid and solid due to its simplicity
Education for Cataloging in Spanish Universities: A Descriptive and Critical Study
No full textObjective: This is a critical descriptive study of the situation of cataloging as an academic discipline within Library and Information Science studies in Spain. Material and methods: The descriptive analysis of the sectional contents of the general and specific guidelines of the degrees of Diplomado (three-year degree) and Licenciado (fiveyear degree) in LIS and the curricular programs of the Spanish university schools or departments. Variables analyzed: The denomination and content descriptors of the course offerings and credit hours. The test-retest method was used, with a qualitative processing of data. Results: General data is given about the studies in LIS: their introduction, the universities that offer them, and the degrees awarded. Cataloging is considered an obligatory core subject matter, and is represented by several courses that present important differences insofar as their denominations, their credits, and their character from one curricular program to the next. The average credit requisite for obligatory courses in cataloging in Spain is 14 (1 credit = 10 class hours), and 19.7 if electives are also considered. At present, this discipline is undergoing a reform that will produce important changes as a result of the adaptation of university studies to the common framework of the European Union
Introduction to Energy-Efficient Train Operation
No full textRailway, as one of the most energy-efficient transport, plays an essential role in improving the world’s energy and environmental sustainability. Statistics about rail share of transport activities and the corresponding energy consumption will demonstrate the energy efficiency of railway and indicate the potential of developing railway transport. Therefore, this chapter will provide an overview of the railway's energy consumption and traffic volume shares. Statistics presented in this chapter show that railway energy consumption decreased in these decades while its transport volume kept stable, and the traffic volume share of the railway is extremely large in urban transport. To achieve the goal of carbon neutralization, the European Union and many countries have conducted research projects on railway energy conservation. The technologies developed in these projects include energy-efficient train driving, integrated timetabling, using regenerative braking energy, etc. A summary of these technologies is also given, along with their potential energy savings, which range from 1 to 25%. This book will analyse and illustrate the whole systems processes of train operation with optimisation solutions. The structure of the following chapters will be presented at the end.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Plannin
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