Influence of leaky vacuum bags on the quality of composite parts made from prepreg material

Leakage in vacuum bags for fibre composite production is a frequently occurring defect, especially in the manufacture of components using the open mould process. The previous limit values for assessing the leak tightness of a vacuum set up are mostly historical and based on empirical values. In this paper, the effects of leaks that have been introduced in a defined manner into a vacuum bag are investigated. The physical processes that occur during curing within the leaking vacuum structure are analysed optically as well as by means of ultrasonic testing and thickness measurement and a better understanding of the effects on laminate quality is generated. It is found that there is a difference between leakages in the vacuum bag only and leakages that affect both the vacuum and release film

Kristallklar - Vorhersage der Kristallinität von thermoplastischen Bauteilen in Konsolidierungsprozessen

"Es war einmal vor langer, langer Zeit in einer weit entfernten Galaxis..." könnte der erste Satz dieses Artikels heißen. Aber das wäre wohl ein etwas zu epischer Start für das hier adressierte Thema virtueller Prozesssimulationen. Diese sind, unter Einsatz von digitalen Zwillingen zur Vorhersage von Systemereignissen, aus der Produktionsforschung und -entwicklung nicht mehr wegzudenken. Sie spielen z. B. bei der Entwicklung von Fertigungstechnologien für thermoplastische Faserverbundstrukturen in Verbindung mit der Reduktion der Fertigungsenergie eine wesentliche Rolle. So können energieintensive Konsolidierungsprozesse mit Hilfe von thermoplastischen Materialmodellen analysiert und vorab optimiert werden. Eine Plattform für virtuelle Prozesssimulationen stellt der digitale Zwilling des Forschungsautoklavs im CFK-NORD in Stade dar. Hier kann nicht nur Energie, sondern auch eine Menge Zeit im Fertigungsprozess gespart werden

Computational methods for leakage localisation in a vacuum bag using volumetric flow rate measurements

The localisation of leakages during the vacuum bagging process of a composite is currently time intensive and reliant on human labour. The purpose of this article is to explore four computational methods for leakage localisation using volumetric flow rate (VFR) data to increase the automation of the process. The data used in this article is based on experiments on a square vacuum bag with four vacuum ports. The first method is based on potential flow theory to simulate the flow. In the second method, numerical regression was applied to find a relation between the VFRs and port-leakage distances. The third method consisted of calculating the fractional VFRs for every point on a grid and finding the grid point whose values most closely correspond to the observed fractional VFRs. The last method involved training a machine learning algorithm with experimental data. After the development of the methods, their performance was tested over the entire single-leakage dataset and compared. The results were in the same order of magnitude for all methods, with an area of 10^5 mm² for the 95% confidence interval and a distance of 10² mm for the average error. Further research is required for application to different vacuum bag shapes and multiple leakages cases. The method with the highest adaptability and performance is the method based on potential-flow theory. Machine learning and the potential-flow method is further applicable to multiple leakage localisation

Bed material transport estimate in large gravel-bed rivers using the virtual velocity approach

This paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel-bed rivers of northern Italy. Displacement length and virtual velocity of spray-painted tracers were measured in the field. Also, the thickness of the sediment active layer during floods was measured using scour chains and post-flood morphological changes as documented by repeated survey of channel cross-sections. The effects of eight and seven floods were studied on the Tagliamento and Brenta Rivers, where 259 and 277 spray-painted areas were surveyed, respectively. In the Tagliamento River 36% of the spray-painted areas experienced partial transport, whereas in the Brenta River this accounted for 20%. Whereas, full removal/gravel deposition was observed on 37% and 26% of these areas on the Tagliamento and Brenta Rivers, respectively. The mean displacement length of particles, the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress. The virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes. Annual coarse sediment transport was calculated up to 150 for the Tagliamento, and 30 × 103 m3 yr−1 for the Brenta. The outcomes of this work highlight the relevance of partial transport condition, as it could represent more than 70% of the total bed material transported during low-magnitude floods, and up to 40% for near-bankfull events. Results confirm that bed material load tends to be overestimated by traditional formulas

Scaling relationships between bed load volumes, transport distances, and stream power in steep mountain channels

Bed load transport during storm events is both an agent of geomorphic change and a significant natural hazard in mountain regions. Thus, predicting bed load transport is a central challenge in fluvial geomorphology and natural hazard risk assessment. Bed load transport during storm events depends on the width and depth of bed scour, as well as the transport distances of individual sediment grains. We traced individual gravels in two steep mountain streams, the Erlenbach (Switzerland) and Rio Cordon (Italy), using magnetic and radio frequency identification tags, and measured their bed load transport rates using calibrated geophone bed load sensors in the Erlenbach and a bed load trap in the Rio Cordon. Tracer transport distances and bed load volumes exhibited approximate power law scaling with both the peak stream power and the cumulative stream energy of individual hydrologic events. Bed load volumes scaled much more steeply with peak stream power and cumulative stream energy than tracer transport distances did, and bed load volumes scaled as roughly the third power of transport distances. These observations imply that large bed load transport events become large primarily by scouring the bed deeper and wider, and only secondarily by transporting the mobilized sediment farther. Using the sediment continuity equation, we can estimate the mean effective thickness of the actively transported layer, averaged over the entire channel width and the duration of individual flow events. This active layer thickness also followed approximate power law scaling with peak streampower and cumulative stream energy and ranged up to 0.57min the Erlenbach, broadly consistent with independent measurements

Assessment of a numerical model to reproduce event-scale erosion and deposition distributions in a braided river

Becky Goodsell and Eric Scott are thanked for field assistance. Antony Smith assisted with figure production. The field campaign wa funded by NERC Grant NE/G005427/1 and NERC Geophysical Equipment Facility Loan 892. Richard Williams was funded by NERC Grant NE/G005427/1during fieldwork and by a British Hydrological Society Travel Grant whilst visiting NIW

Ecosystem Consequences of Contrasting Flow Regimes in an Urban Effects Stream Mesocosm Study 1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73638/1/j.1752-1688.2009.00336.x.pd

Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges

Citation: Ruiz-Villanueva, V., Piégay, H., Gurnell, A. A., Marston, R. A., & Stoffel, M. (2016). Recent advances quantifying the large wood dynamics in river basins: New methods and remaining challenges. Reviews of Geophysics. doi:10.1002/2015RG000514Large wood is an important physical component of woodland rivers and significantly influences river morphology. It is also a key component of stream ecosystems. However, large wood is also a source of risk for human activities as it may damage infrastructure, block river channels, and induce flooding. Therefore, the analysis and quantification of large wood and its mobility are crucial for understanding and managing wood in rivers. As the amount of large-wood-related studies by researchers, river managers, and stakeholders increases, documentation of commonly used and newly available techniques and their effectiveness has also become increasingly relevant as well. Important data and knowledge have been obtained from the application of very different approaches and have generated a significant body of valuable information representative of different environments. This review brings a comprehensive qualitative and quantitative summary of recent advances regarding the different processes involved in large wood dynamics in fluvial systems including wood budgeting and wood mechanics. First, some key definitions and concepts are introduced. Second, advances in quantifying large wood dynamics are reviewed; in particular, how measurements and modeling can be combined to integrate our understanding of how large wood moves through and is retained within river systems. Throughout, we present a quantitative and integrated meta-analysis compiled from different studies and geographical regions. Finally, we conclude by highlighting areas of particular research importance and their likely future trajectories, and we consider a particularly underresearched area so as to stress the future challenges for large wood research. ©2016. American Geophysical Union