TY - JOUR A1 - Freese, Jens de A1 - Holtmannspötter, Jens A1 - Raschendorfer, Stefan A1 - Hofmann, Timo T1 - End milling of Carbon Fiber Reinforced Plastics as surface pretreatment for adhesive bonding - effect of intralaminar damages and particle residues JF - The Journal of Adhesion N2 - In this study, the use of dry end milling of carbon fiber reinforced plastics (CFRP) as surface pretreatment for high-strength (structural) adhesive bonding was investigated. Surfaces were pretreated using different milling parameters; subsequently, they were adhesively bonded and tested. In comparison with sanding and other industrial standard pretreatment methods, the measured adhesive strength was significantly lower. Detailed surface investigations utilizing field-emission scanning electron microscopy could identify two major effects for lower adhesion strength. Intralaminar damages and microparticle residues on the created surface reduced the strength of the CFRP adhesive joints. This eventually explains results from investigations on milling pretreated repairs. By application of power ultrasound cleaning equipment and coating with low viscosity epoxy primers, the authors showed a way to overcome the discovered drawbacks and to improve bond strength significantly. Surface roughness measurements showed that the arithmetical mean roughness R(a)can be used as an effective value for assessment of mechanical pretreated CFRP surfaces as well as for the quality of necessarily following cleaning processes. KW - aeronautical KW - BONDED JOINTS KW - butt joints KW - composites KW - epoxides KW - Epoxy KW - GRAPHITE/EPOXY COMPOSITE KW - ORTHOGONAL CUTTING MECHANISMS KW - repair KW - surface treatment Y1 - 2020 U6 - https://doi.org/10.1080/00218464.2018.1557054 VL - 96 IS - 12 SP - 1122 EP - 1140 PB - TAYLOR & FRANCIS ER - TY - JOUR A1 - Holtmannspötter, Jens A1 - Czarnecki, Jürgen von A1 - Feucht, Florian A1 - Wetzel, Michael A1 - Gudladt, Hans Joachim A1 - Hofmann, Timo A1 - Meyer, J. C. A1 - Niedernhuber, Michal T1 - On the Fabrication and Automation of Reliable Bonded Composite Repairs JF - Journal of adhesion N2 - For structures made of carbon fiber-reinforced plastics (CFRP), fast, robust, and reliable repair technologies are mandatory for economical usage. In this paper, the authors explain their strategy and experiences. An automated process is proposed to achieve the challenging goals. A general overview on the origin, effects, and analysis of contaminants in CFRP structures and the relationship to the achievable strength of adhesive bonds are given. For the repair of composite structures using adhesive bonding, surface pretreatment is a key factor in terms of reliability and strength. Different surface treatment processes such as grinding, grit blasting, plasma and pulsed lasers treatments are discussed. Furthermore, the possibilities and technical implementation of an automated milling process for the repair of composite structures are presented. This change from manual production to automation tremendously improved the quality and duration of the repair and allows the creation of a uniform surface for adhesive bonding. Further integration of novel technologies is discussed and will further support and enhance the repair in the near future. KW - ADHESION KW - Adhesive bonding KW - Automation KW - Carbon fiber KW - composites KW - FIBER-REINFORCED PLASTICS KW - repair KW - Scarfing KW - Surface preparation Y1 - 2015 U6 - https://doi.org/10.1080/00218464.2014.896211 VL - 91 IS - 1-2 SP - 39 EP - 70 PB - Taylor&Francis ER - TY - GEN A1 - Judenmann, Anna A1 - Pongratz, Christian A1 - Ehrlich, Ingo A1 - Höfer, Philipp A1 - Holtmannspötter, Jens T1 - Additive Fertigung von endlosfaserverstärkten Kunststoffstrukturen T2 - Münchner Leichtbauseminar 2022, 26. October 2022, 16. November 2022, 30 November 2022, Munich/Neubiberg/Garching N2 - Additive Fertigung hat sich in zahlreichen industriellen Anwendungen etabliert und bildet eine wichtige Schlüsseltechnologie. Im Gegensatz zu metallischen Werkstoffen, haben additiv gefertigte Bauteile aus Kunststoffen geringere Festigkeit und Steifigkeit, sodass sich ihre Verwendung als lasttragende Strukturen schwierig gestaltet. Insbesondere der Einsatz von endlosen Verstärkungsfasern kann die mechanischen Eigenschaften additiv gefertigter Strukturen signifikant verbessern und die Fertigung hochbelastbarer Faserverbundstrukturen im 3D-Druckverfahren ermöglichen. Daher gilt es aktuell notwendige Anlagen und Prozessketten für den Fertigungsprozess aber auch Vorgehensweisen für die belastungsoptimierte Auslegung der Faserverläufe innerhalb des Bauteils zu entwickeln, um so das Themengebiet „Endlosfaserverstärkter 3D-Druck“ weiter voranzutreiben. Für mehr räumliche Freiheit bei der Positionierung der Druckbahnen können industrieroboterbasierte Systeme eingesetzt werden, um so das Potenzial gerichteter Bauweise von Faserverbundstrukturen auch im additiven Fertigungsprozess vollumfänglich ausschöpfen zu können. Dabei ermöglicht ihr Einsatz auch eine räumliche Ablage der Faserverstärkung, wobei für die Materialablage ein geeigneter 3D-Druckkopf erforderlich ist. Für die Implementierung der Faserverstärkung ist zudem eine dem Lastfall entsprechende Auslegung des Bauteils sowie die Ermittlung einer sinnvollen Faserpositionierung innerhalb des Bauteils erforderlich, wobei unterschiedliche Variablen aus den Bereichen Material, Struktur und Fertigungsprozess berücksichtigt werden müssen. Im Rahmen des Vortrages werden die Herausforderungen der Technologieentwicklung des endlosfaserverstärkten 3D-Drucks aufgegriffen sowie auf eine belastungsorientierte Faserpositionierung näher eingegangen. Aktuelle Erkenntnisse werden diskutiert sowie eine Entwurfsmethodik für die Prozesspfadgenerierung vorgeschlagen. KW - additive manufacturing KW - continuous fiber KW - composites KW - toolpath Y1 - 2022 ER - TY - JOUR A1 - Niedernhuber, Michael A1 - Holtmannspötter, Jens A1 - Ehrlich, Ingo T1 - Fiber-oriented repair geometries for composite materials JF - Composites, Part B N2 - In this paper, the idea of fiber-oriented repair geometries for carbon fiber reinforced plastics (CFRP) is investigated. It considers the differing mechanical properties of unidirectional fiber reinforced material by excluding overlapping regions perpendicular to the fiber direction of the particular layer. A mechanical and numerical comparison of tensile strength of stepped joints with continuous step lengths per ply and stepped joints with reduced step lengths in plies with fiber orientation differing from load direction is performed. Finite element simulations show similar shear stresses. Mechanical tests of CFRP laminates with stepped joints show no significant deviation in tensile strength, in spite of a joint length reduction of nearly 40%. This leads to the possibility of a significant reduction of repair area. Y1 - 2016 U6 - https://doi.org/10.1016/j.compositesb.2016.03.027 VL - 94 SP - 327 EP - 337 ER - TY - CHAP A1 - Judenmann, Anna A1 - Holtmannspötter, Jens A1 - Ehrlich, Ingo T1 - Additive Manufacturing of Continuous Fiber-Reinforced Composites T2 - Proceedings of the Munich Symposium on Lightweight Design 2022 Y1 - 2023 ER - TY - CHAP A1 - Niedernhuber, M. A1 - Ehrlich, Ingo A1 - Holtmannspötter, Jens ED - Ziemann, Olaf ED - Mottok, Jürgen ED - Pforr, Johannes T1 - Fiber-Oriented Repair of Fiber Reinforced Plastics: Investigations on Tensile Specimens T2 - 4th Applied Research Conference - ARC 2014, 5th July 2014, Ingolstadt Y1 - 2014 SP - 298 EP - 302 PB - Shaker CY - Aachen ER -