@article{FreeseHoltmannspoetterRaschendorferetal., author = {Freese, Jens de and Holtmannsp{\"o}tter, Jens and Raschendorfer, Stefan and Hofmann, Timo}, title = {End milling of Carbon Fiber Reinforced Plastics as surface pretreatment for adhesive bonding - effect of intralaminar damages and particle residues}, series = {The Journal of Adhesion}, volume = {96}, journal = {The Journal of Adhesion}, number = {12}, publisher = {TAYLOR \& FRANCIS}, doi = {10.1080/00218464.2018.1557054}, pages = {1122 -- 1140}, abstract = {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.}, language = {en} } @article{HoltmannspoetterCzarneckiFeuchtetal., author = {Holtmannsp{\"o}tter, Jens and Czarnecki, J{\"u}rgen von and Feucht, Florian and Wetzel, Michael and Gudladt, Hans Joachim and Hofmann, Timo and Meyer, J. C. and Niedernhuber, Michal}, title = {On the Fabrication and Automation of Reliable Bonded Composite Repairs}, series = {Journal of adhesion}, volume = {91}, journal = {Journal of adhesion}, number = {1-2}, publisher = {Taylor\&Francis}, doi = {10.1080/00218464.2014.896211}, pages = {39 -- 70}, abstract = {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.}, language = {en} } @inproceedings{JudenmannHoltmannspoetterEhrlich, author = {Judenmann, Anna and Holtmannsp{\"o}tter, Jens and Ehrlich, Ingo}, title = {Additive Manufacturing of Continuous Fiber-Reinforced Composites}, series = {Proceedings of the Munich Symposium on Lightweight Design 2022}, booktitle = {Proceedings of the Munich Symposium on Lightweight Design 2022}, language = {de} } @inproceedings{NiedernhuberEhrlichHoltmannspoetter, author = {Niedernhuber, Michal and Ehrlich, Ingo and Holtmannsp{\"o}tter, Jens}, title = {Fiber-Oriented Repair of Fiber Reinforced Plastics: Investigations on Tensile Specimens}, series = {4th Applied Research Conference - ARC 2014, 5th July 2014, Ingolstadt}, booktitle = {4th Applied Research Conference - ARC 2014, 5th July 2014, Ingolstadt}, editor = {Ziemann, Olaf and Mottok, J{\"u}rgen and Pforr, Johannes}, publisher = {Shaker}, address = {Aachen}, pages = {298 -- 302}, language = {en} } @misc{JudenmannPongratzEhrlichetal., author = {Judenmann, Anna and Pongratz, Christian and Ehrlich, Ingo and H{\"o}fer, Philipp and Holtmannsp{\"o}tter, Jens}, title = {Additive Fertigung von endlosfaserverst{\"a}rkten Kunststoffstrukturen}, series = {M{\"u}nchner Leichtbauseminar 2022, 26. October 2022, 16. November 2022, 30 November 2022, Munich/Neubiberg/Garching}, journal = {M{\"u}nchner Leichtbauseminar 2022, 26. October 2022, 16. November 2022, 30 November 2022, Munich/Neubiberg/Garching}, abstract = {Additive Fertigung hat sich in zahlreichen industriellen Anwendungen etabliert und bildet eine wichtige Schl{\"u}sseltechnologie. 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 Verst{\"a}rkungsfasern kann die mechanischen Eigenschaften additiv gefertigter Strukturen signifikant verbessern und die Fertigung hochbelastbarer Faserverbundstrukturen im 3D-Druckverfahren erm{\"o}glichen. Daher gilt es aktuell notwendige Anlagen und Prozessketten f{\"u}r den Fertigungsprozess aber auch Vorgehensweisen f{\"u}r die belastungsoptimierte Auslegung der Faserverl{\"a}ufe innerhalb des Bauteils zu entwickeln, um so das Themengebiet „Endlosfaserverst{\"a}rkter 3D-Druck" weiter voranzutreiben. F{\"u}r mehr r{\"a}umliche Freiheit bei der Positionierung der Druckbahnen k{\"o}nnen industrieroboterbasierte Systeme eingesetzt werden, um so das Potenzial gerichteter Bauweise von Faserverbundstrukturen auch im additiven Fertigungsprozess vollumf{\"a}nglich aussch{\"o}pfen zu k{\"o}nnen. Dabei erm{\"o}glicht ihr Einsatz auch eine r{\"a}umliche Ablage der Faserverst{\"a}rkung, wobei f{\"u}r die Materialablage ein geeigneter 3D-Druckkopf erforderlich ist. F{\"u}r die Implementierung der Faserverst{\"a}rkung 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 ber{\"u}cksichtigt werden m{\"u}ssen. Im Rahmen des Vortrages werden die Herausforderungen der Technologieentwicklung des endlosfaserverst{\"a}rkten 3D-Drucks aufgegriffen sowie auf eine belastungsorientierte Faserpositionierung n{\"a}her eingegangen. Aktuelle Erkenntnisse werden diskutiert sowie eine Entwurfsmethodik f{\"u}r die Prozesspfadgenerierung vorgeschlagen.}, language = {de} } @article{NiedernhuberHoltmannspoetterEhrlich, author = {Niedernhuber, Michal and Holtmannsp{\"o}tter, Jens and Ehrlich, Ingo}, title = {Fiber-oriented repair geometries for composite materials}, series = {Composites, Part B}, volume = {94}, journal = {Composites, Part B}, doi = {10.1016/j.compositesb.2016.03.027}, pages = {327 -- 337}, abstract = {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.}, language = {en} } @article{AfanasevHoeferHoltmannspoetteretal., author = {Afanasev, Anna and H{\"o}fer, Philipp and Holtmannsp{\"o}tter, Jens and Zimmer, Felix and Ehrlich, Ingo}, title = {Development of a continuous fiber-reinforced 3D printing process with a 6-axis robot arm: Process design and equipment}, series = {The International Journal of Advanced Manufacturing Technology}, journal = {The International Journal of Advanced Manufacturing Technology}, publisher = {Springer}, issn = {0268-3768}, doi = {10.1007/s00170-025-17263-3}, pages = {20}, abstract = {The utilisation of 3D printing processes in the fabrication of continuous fiber-reinforced composites confers a multitude of advantages, in particular flexible design based on structural requirements. In order to achieve greater flexibility, there is a necessity for 3D printing systems that allow for customisable material selection and fiber positioning. This paper presents the design of a robot-based 3D printing system that incorporates an in-situ impregnation line and flexibility regarding the machine code generation for fiber positioning. The development of the system enabled the attainment of an average fiber volume content of up to 37.12\%. In the tensile tests, material characteristics up to E1 = 24.7 GPa and strength of up to RM1 = 0.51 GPa were determined.}, language = {en} }