@article{WinklerHaaseSchwarzetal.2021, author = {Winkler, Christoph and Haase, Stefan and Schwarz, Ulrich and Jahreis, Markus}, title = {Piezoresistive bond lines for timber construction monitoring—experimental scale-up}, series = {Wood Science and Technology}, volume = {55}, journal = {Wood Science and Technology}, number = {4}, publisher = {Springer Nature}, issn = {0043-7719}, doi = {10.1007/s00226-021-01305-6}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-1959}, pages = {1379 -- 1400}, year = {2021}, abstract = {Several laboratory studies and experiments have demonstrated the usability of polymer films filled with electrically conductive filler as piezoresistive material. Applied to adhesives, the glue lines of wood products can achieve multifunctional—thus bonding and piezoresistive/strain sensing—properties. Based on critical load areas in timber constructions, upscaled test setups for simplified load situations were designed, especially with regard to a stress-free electrical contact. In a second step, another upscaling was done to small glulam beams. Based on an experimental test sequence, the piezoresistive reactions as well as the behaviour until failure were analysed. The results show in all cases that a piezoresistive reaction of the multifunctionally bonded specimens was measurable, giving a difference in the extent of relative change. Additionally, measured phenomena like inverse piezoresistive reactions, electrical resistance drift and the absence of a piezoresistive reaction were discussed, based on additional strain analysis by digital image correlation. A model of macroscopic and microscopic strains influencing the piezoresistive reaction of the electrically conductive bond line in wood was used to explain all experimental results. Finally, a first scale-up of piezoresistive bond lines from laboratory samples to glulam beams was possible and successful.}, language = {en} } @article{SchaeferJagerSchwarzetal.2021, author = {Sch{\"a}fer, Jesco and Jager, Christopher and Schwarz, Ulrich and Winkler, Christoph}, title = {Improving the usability of piezoresistive bond lines in wood by using impedance measurements}, series = {Wood Science and Technology}, volume = {55}, journal = {Wood Science and Technology}, number = {4}, publisher = {Springer Nature}, issn = {0043-7719}, doi = {10.1007/s00226-021-01311-8}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-1942}, pages = {937 -- 954}, year = {2021}, abstract = {Various studies on wood adhesives filled with conductive fillers for future application to structural monitoring showed a piezoresistive (resistance change with strain) response of the adhesive bond lines that is measurable under direct current. The results also showed a relatively high signal noise with low sensitivity. Using impedance spectroscopy as a measurement technique, the improvements in frequency-dependent piezoresistivity over DC (Direct Current) resistography of multifunctional bonded wood were studied. Beech specimens were bonded by one-component polyurethane prepolymer (1C-PUR) filled with carbon black and tested under shear load. The quality of the piezoresistive properties was described by calculating the signal-to-noise ratio (SNR) of the measured signal. A setup-specific frequency band with optimized SNR between 100 kHz and 1 MHz could be derived from the measurements. Several frequencies showed a signal with higher quality resulting in a higher SNR. Regardless of the variations in impedance spectra for all specimens, this frequency band provided several frequencies with improved signal quality. These frequencies give a more reliable signal with lower noise compared to the signal from DC resistography.}, language = {en} } @article{WinklerKonnerthGibckeetal.2020, author = {Winkler, Christoph and Konnerth, Johannes and Gibcke, Johannes and Sch{\"a}fer, Jesco and Schwarz, Ulrich}, title = {Influence of polymer/filler composition and processing on the properties of multifunctional adhesive wood bonds from polyurethane prepolymers I: mechanical and electrical properties}, series = {The Journal of Adhesion}, volume = {96}, journal = {The Journal of Adhesion}, number = {1-4}, publisher = {Taylor \& Francis}, issn = {0021-8464}, doi = {10.1080/00218464.2019.1652601}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5741}, year = {2020}, abstract = {Multifunctional adhesives out of a polymer matrix and electrically conductive fillers are known to typically decrease in bond strength with increasing filler content, while the electrical resistance drops extensively at the percolation threshold. Three experiments have focused on different aspects of the production of electrically conductive adhesive wood bonds, experiment I with a variation of the adhesive components, experiment II is varying the process parameters in the bonding process, and experiment III is investigating a thermal postcuring effect. Tensile shear strength (EN 302-1, requirement for structural wood bonding dry condition (A1 treatment)) and electrical resistography under direct current (DC measurements) of the bondline was used to identify major influences on tensile shear strength and the formation of the electrically conductive network. The results show high differences due to the adhesive polymer selection, the filler type and some of the process parameters. As an example, it was revealed that the bond strength of multifunctional adhesive wood joints can be increased by integrating increasing contents of carbon nanotubes in polyurethane prepolymers, if the polymers do not contain fibrous fillers before the dispersion.}, language = {en} } @article{WinklerSchaeferJageretal.2020, author = {Winkler, Christoph and Sch{\"a}fer, Jesco and Jager, Christopher and Konnerth, Johannes and Schwarz, Ulrich}, title = {Influence of polymer/filler composition and processing on the properties of multifunctional adhesive wood bonds from polyurethane prepolymers II: electrical sensitivity in compression}, series = {The Journal of Adhesion}, volume = {96}, journal = {The Journal of Adhesion}, number = {1-4}, publisher = {Taylor \& Francis}, issn = {0021-8464}, doi = {10.1080/00218464.2019.1652602}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5756}, year = {2020}, abstract = {Electrically conductive fillers enhance the functionality of adhesive bondlines by inducing a strain-dependent electrical resistance. Applied as sensor elements in engineered timber, these multifunctional adhesive bondlines are influenced by a lot of process parameters, including the dispersion process, manufacturing parameters and postcuring conditions. Additionally, the sensitivity of these sensor elements is counteracted by instabilities of the piezoresistivity. A setup and analysing method of the piezoresistive response have been developed, which includes sensitivity as well as instability effects. With this setup, the quality of the piezoresistive bondline has been assessed by three experiments, varying 10 influencing factors. The piezoresistive response was investigated in compression perpendicular to the bondline. It was shown that the electrical sensitivity in compression and stability of the piezoresistive bondline can be influenced by polymer formulation, filler type, filler content as well as the press temperature, glue spread, dispersion technique and thermal postcuring.}, language = {en} } @article{WinklerRodriguezAgudoSchwarzetal.2021, author = {Winkler, Christoph and Rodriguez Agudo, Jos{\´e} Alberto and Schwarz, Ulrich and Sch{\"a}ffler, Michael}, title = {Prozessnahe Rheologie am Beispiel von Verpackungsklebstoffen}, series = {adh{\"a}sion KLEBEN \& DICHTEN}, journal = {adh{\"a}sion KLEBEN \& DICHTEN}, publisher = {Springer Nature}, issn = {1619-1919}, doi = {10.1007/s35145-021-0472-z}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5340}, pages = {24 -- 29}, year = {2021}, language = {de} } @article{WinklerSchwarzSenge2020, author = {Winkler, Christoph and Schwarz, Ulrich and Senge, Bernhard}, title = {Materialwissenschaftliche Analyse des Abbindeverhaltens von Holzklebstoffen am Beispiel von 1K-PUR}, series = {Chemie Ingenieur Technik}, volume = {92}, journal = {Chemie Ingenieur Technik}, number = {6}, publisher = {Wiley}, issn = {0009-286X}, doi = {10.1002/cite.201900171}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5323}, pages = {759 -- 768}, year = {2020}, abstract = {Das Abbinden von Holzklebstoffen wird bisher anhand von Parametern bewertet, die kaum eine prozesstechnische Optimierung erm{\"o}glichen. Mithilfe von Oszillationsmessungen und einem an dem Klebeprozess angepassten Versuchsaufbau kann dieser jedoch detailliert erfasst werden. Am Beispiel durchgef{\"u}hrter Timesweep-Messungen kann der Klebeprozess in charakteristische Bereiche molekularer und struktureller Abl{\"a}ufe eingeteilt werden. Diese Methode wird anhand eines Polyurethan-Prepolymers zum F{\"u}gen von Holzwerkstoffen dargestellt und analysiert.}, language = {de} } @article{WinklerRodriguezAgudoSchwarzetal.2021, author = {Winkler, Christoph and Rodriguez Agudo, Jos{\´e} Alberto and Schwarz, Ulrich and Sch{\"a}ffler, Michael}, title = {Process-Oriented Rheology of Packaging Adhesives}, series = {adhesion ADHESIVES + SEALANTS}, journal = {adhesion ADHESIVES + SEALANTS}, publisher = {Springer Nature}, issn = {2192-2624}, doi = {10.1007/s35784-021-0359-2}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5333}, pages = {19 -- 24}, year = {2021}, language = {en} } @article{WinklerKruegerSarnaghietal.2022, author = {Winkler, Christoph and Kr{\"u}ger, Robert and Sarnaghi, Ani Khaloian and Kluge, Patrick and van de Kuilen, Jan-Willem and Schwarz, Ulrich}, title = {Mechanische Eigenschaften von Sch{\"a}lfunierlagen in Sperrh{\"o}lzern}, series = {Holztechnologie}, journal = {Holztechnologie}, number = {1}, issn = {0018-3881}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-4597}, pages = {25 -- 36}, year = {2022}, abstract = {In dieser Publikation wird der Frage nachgegangen, ob mit Klebstoff beschichtete Furniere gegen{\"u}ber nativen Furnieren geeigneter sind, um Kennwerte zur Berechnung und Simulation von Sperrh{\"o}lzern zu erhalten. Der Frage wurde mittels experimentellen Versuchen, analytischer Berechnung und Simulation nachgegangen und die Ergebnisse anhand von Buchenfurnier, teils beschichtet mit Phenol-Resorzin-Formaldehyd-Klebstoffen, dikutiert. Die Ergebnisse zeigen, dass beschichtete Furniere eine bessere {\"U}bereinstimmung mit BErechnungsans{\"a}tzen und Simulationen von Sperrh{\"o}lzern als native Furniere bieten und auch einem vereinfachten Ansatz eines Laminats aus Furnieren mit separaten Klebstoffschichten {\"u}berlegen sind.}, language = {de} }