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Background In order to design thin-walled components it is necessary to consider the presence of holes and their effects. For high performance composite structures, this is still an issue, since usually only coupons are used in experimental observations and the influence of free edges and the hole affects the fatigue behavior mutually. Objective This work aims to find, through experimental trials, an empirical model that can be used to describe and predict the damage propagation, originating from a circular hole. Methods A fatigue test series is performed and the damage initiation and propagation is monitored with three-dimensional digital image correlation, with which the occurring damage can be measured. Validation of the experimentally induced damage size measured with digital image correlation is performed intermediate with an in-situ measurement with active thermography and phased array ultrasonic. The novelty of this approach is that wide specimens are used, where the influence of the free edges on the hole does not occur. Results The progression of the detected damage over the test reflects the applied loads, where higher loads cause larger damage. For all defined load levels a similar damage propagation is identified, allowing to establish an empirical model and fit it to the test data. Conclusion The proposed empirical model provides a novel approach to describe and predict damage propagation originating from a circular hole in thin-walled composite plates. In addition, it is shown that the damage propagation ceases for the selected plate configuration and thus does not lead to a complete failure. Version of record

Anaerobic digestion of microalgal biomass is one option for sustainable energy production. Therefore, several microalgae i.e. Chlorella vulgaris, C. emersonii and Acutodesmus obliquus were produced in a sleevebag photobioreactor system (maximum volume 800 L) and investigated in so-called biochemical methane potential tests (BMP). Different pre-treatments were selected in order to enhance methane (CH4) yields. A. obliquus was selected to screen for effective pretreatment methods: a combined milling and enzyme approach (+57%), ultrasonication (+53%) and milling (+51%) resulted in significantly higher CH4 yields. In the follow-up experiments, milling and ultrasonication were applied to cooled biomass of C. emersonii and A. obliquus. In both cases, ultrasonication led again to significantly higher CH4 yields (+41%) for A. obliquus and (+35%) for C. emersonii. In experiments with frozen biomass, highest CH4 yields were reached with freeze-thawed C. vulgaris biomass i.e. 406 Nm³ t-1 VSharvest. Freeze-thawed A. obliquus biomass yielded 337 Nm³ t-1 VSharvest, an increase of 47% if compared to unfrozen biomass i.e. 229 Nm³ t-1 VSharvest. Ultrasonication of frozen A. obliquus biomass increased CH4 yields for only 20% indicating that freeze-thawing strongly affects CH4 yields and provokes cell disruption by ice crystals. In addition, our work proposes that pretreatments seem to act strain-specific., Proceedings of the 23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp. 612-615

International audience; The Structural Health Control (SHC) concept is a novel and overarching approach to monitor the strength of a structure online and in realtime over its lifecycle. In the center of the SHC approach is the structural analysis of the monitored part. It provides the information to identify structural parameters as damage indicators. With this information an optimized sensor layout can be defined to monitor the damage indicators in a smart way. The monitoring system is therefore referred as SmartSHM system. This article is about the experimental validation of the SmartSHM concept within the SHC approach. The SmartSHM system is tested at a simply supported thin plate under compressive loading close to ultimate load. In the post-buckling regime bending occurs which causes high tension stresses at the plateÕs surface despite of the compressive loading. These stresses can initiate a crack due to fatigue. Therefore these regions are monitored with a SmartSHM system. Cracks were initiated to prove the functionality of the proposed SHM concept.