As shown in previous studies within other scientific fields, the material behavior of polymethyl methacrylate (PMMA) is viscoelasticviscoplastic. However, in dental biomaterial science it is mostly considered as linear elastic or elastic-plastic. The aim of the present study was to evaluate, whether the assumption of elastic or elastic-plastic material behavior for PMMA is a practicable simplification or a potential source of error, especially considering clinical loading conditions. Telio-CAD was tested in three-point bending tests with different test velocities to examine the material behavior at different initial loading rates. Additionally, a dynamic-mechanicalthermal-analysis at different frequencies and temperatures was used. Here, a significant influence of loading rate and temperature as well as stress relaxation and creep were observed. To describe the rate-dependency of the elastic modulus, a new model was created, from which the elastic modulus can be calculated with a given strain rate. This model was validated using linear elastic finite element analysis.
Material characteristics can change significantly with increasing chewing velocity. As these in-vitro examinations are very timeconsuming and cost-intensive, the application of finite element analysis (FEA) offers a suitable alternative for predicting the material behavior of complex specimen geometries under clinically relevant loads. Although FEA is applied within numerous dental investigations, there are only few studies available in which a nonlinear FEA is validated with real experiments. Therefore, the aim of the present study was to predict the mechanical behavior of a clinically close three-unit temporary bridge composed of polymethyl methacrylate (PMMA) in the left upper jaw with nonlinear FEA and to verify the prediction through validation experiments. In conclusion, simplifying assumptions of linear elastic material properties for polymeric materials should be avoided in FEA studies, because rate dependencies, stress relaxation and plastic flow are not considered. Additionally, precise preliminary investigations for material characterization are necessary.
Durch fraktographische Analysen der Bruchflächen spröder Werkstoffe ist es anhand der im Versagensursprung entstehenden Bruchspiegel möglich, eine Aussage über die Bruchspannung zu treffen. Im vorliegenden Artikel wird diese Methodik auf nicht-ideal-spröde Werkstoffe am Beispiel von PMMA (Acrylglas bzw. Plexiglas ® ) angewendet und eine Vorgehensweise zur Bestimmung der materialabhängigen Bruchspiegelkonstanten vorgestellt. Hierzu werden an über 50 Zugproben die Bruchspiegelradien vermessen und ausgewertet. Mittels digitaler Bildkorrelation wird das nicht lineare Spannungs-Dehnungs-Verhalten von PMMA ermittelt und daraus die Versagensspannungen bestimmt. Zur Validierung der Bruchspiegelanalyse an PMMA wird die resultierende statistische Bruchspannungsverteilung mit der aus einer digitalen Bildkorrelation gewonnenen Verteilung verglichen. Das vorgestellte Verfahren erlaubt es, die Bruchspannung auch für komplexe Bauteilgeometrien nach bereits erfolgtem Versagen zu bestimmen.Fractographic fracture stress analysis of acrylic glass. Fractographic analyses of the fracture surfaces in brittle materials allow an evaluation of the fracture stress on basis of fracture mirrors which appear in the origin of failure. In the present work, this methodology is applied to non-ideal brittle materials like PMMA (acrylic glass or Plexiglas ® ). A procedure is presented for determining the material-dependent fracture mirror constant. For this purpose, the fracture mirror radii are measured and evaluated on more than 50 tensile specimens. Hereby, the non-linear stress-strain behaviour of PMMA and the fracture stresses are determined experimentally by digital image correlation. In order to validate the fracture mirror analysis on PMMA, the resulting statistical fracture stress distribution is compared to the distribution from digital image correlation. The presented method allows to determine the fracture stress even for complex component geometries after failure.Schlagwörter: Acrylglas, Fraktographie, Bruchspiegel, Bruchspannung, Versagenswahrscheinlichkeit
Thin-walled polymeric components are used in many applications. Hence, knowledge about their fracture behavior in bulk is beneficial in practice. Within this study, the double cantilever beam (DCB) and out-of-plane double cantilever beam (ODCB) tests are enhanced to enable the testing of such bulk specimens in mode I and mode III on the basis of the J-integral. This paper then presents and discusses the experimental results following the investigation of a semicrystalline polymer (polyoxymethylen) under quasi-static load conditions. From the experiments, fracture energies of similar magnitude in both mode I and mode III were determined. In mode III, pop-in fracture was observed. Furthermore, the fracture surfaces were investigated regarding the mode I and mode III dominant crack growth mechanisms, based on the morphology of the tested material. For specimens tested in mode I, no signs of plastic deformation were observed, and the fracture surface appears flat. In mode III, some samples display a twisted fracture surface (twisting angle close to 45°), which indicates local mode I crack growth. A transfer of the presented methodology to other (more ductile) polymeric materials is deemed possible without further restrictions. In addition, the presented setup potentially enables an investigation of polymeric bulk specimens in mixed mode I+III.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.