29 research outputs found
Micromechanical finite element modeling of long fiber reinforced thermoplastics
No full textLong fiber reinforced thermoplastics are promising candidates for the mass production of lightweight components. In order to predict their microstructure-dependent mechanical properties, a novel procedure for the generation of a representative volume element is developed. The approach mimics the pressing process during the fabrication of the material by compression molding. The model is experimentally validated with respect to different mechanical properties, including elasticity, creep and damage
An anisotropic creep model for continuously and discontinuously fiber reinforced materials
No full textMicromechanical finite element modeling of long fiber reinforced thermoplastics
No full textLong fiber reinforced thermoplastics are promising candidates for the mass production of lightweight components. In order to predict their microstructure-dependent properties, a novel procedure for the generation of a representative volume element is developed. The approach mimics the pressing process during the fabrication of the material by compression molding. The model is experimentally validated with respect to different mechanical properties, including elasticity, creep and damage
Creep resistance of load application inserts for hybrid thermoplastic sandwich structures
No full textCCLA
An anisotropic creep model for continuously and discontinuously fiber reinforced thermoplastics
No full textObjective of the present study is the definition and implementation of a constitutive creep model for fiber reinforced thermoplastics. Both, unidirectionally as well as discontinuously long fiber reinforced materials are considered. Assuming that creep deformation is restricted to the thermoplastic matrix, a three term Kelvin Voigt formulation is employed as a base material model. For continuously unidirectionally fiber reinforced materials, the thermoplastic matrix is superimposed with a standard linear elastic model. For discontinuously long fiber reinforced thermoplastics, an anisotropic generalization of the original, isotropic Kelvin-Voigt model is proposed. Both models are implemented into a finite element program and validated against an experimental data base consisting of tensile creep experiments on neat matrix material, unidirectionally fiber reinforced material as well as discontinuously long fiber reinforced material with different fiber volume fractions. Different fiber orientations as well as different temperatures are considered. As a structural example for further validation, creep experiments on loading points for hybrid thermoplastic sandwich structures are performed and simulated numerically. In all cases, the experimental results and the numerical prediction are found in a good agreement.19
Anisotropic creep analysis of fiber reinforced load point support structures for thermoplastic sandwich panels
No full text161174The present contribution is concerned with a numerical analysis of creep in load point support structures for sandwich panels made from different fiber reinforced thermoplastic materials. Whereas the face sheets consist of laminates of unidirectional carbon fiber reinforced plies, the support structures for the load points consist of discontinuously long fiber reinforced thermoplastics manufactured in a compression molding process. The sandwich core is a thermoplastic foam. For the numerical creep analysis of such structures under long-term loading, an anisotropic viscoelastic material model is formulated. In different versions, the model is applicable either to unreinforced thermoplastics, or to thermoplastics with discontinuous or continuous fiber reinforcement. The material model is implemented into a finite element system. The model is validated against an experimental data base on both, coupon and structural level
Bauteilberechnung unter Wasserstoffatmosphäre auf Basis der FKM-Richtlinien
No full textIm Rahmen der Energiewende erfährt der Druckwasserstoff als Energieträger eine stetig steigende Relevanz. Um eine praxistaugliche Wasserstoff-Infrastruktur zu schaffen, bedarf es einer Vielzahl von neu zu entwickelnden Komponenten, um eine sichere Speicherung, Betankung und Transport zu gewährleisten. Um diese Bauteile auszulegen, werden neue Berechnungskonzepte benötigt, die materialspezifisch die Schädigungsmechanismen unter Wasserstoff-Atmosphäre in geeigneter Art und Weise abbilden können. Für spezielle Anwendungen (z.B. Pipelines, Druckbehälter) existieren zwar erste Regelwerke, die einen Wasserstoffeinfluss in vereinfachter Form berücksichtigen. Darüber hinaus besteht ein erheblicher Bedarf an maßgeschneiderten Berechnungsprozeduren für eine breite Vielzahl an Bauteilen und Materialien, die den Medieneinfluss des Wasserstoffs sachgerecht berücksichtigen. Die ideale Basis hierfür stellen die bei vielen kleinen und mittelständischen, sowie Groß-Unternehmen bereits fest etablierten FKM-Richtlinien dar, die allgemein für Maschinenbaukomponenten anwendbar sind. Das präsentierte IGF-Projekt "Bauteilberechnung unter Wasserstoffeinfluss" stellt dabei dabei die Vorstufe zur Entwicklung einer Berechnungs-Richtlinie dar. Auf Basis der existierenden Berechnungsabläufe der FKM-Richtlinien werden Beispielbauteile analysiert, die statischen und Ermüdungslasten unter Wasserstoffatmosphäre ausgesetzt sind. Die Anwendbarkeit der existierenden Richtlinien, sowie zukünftig benötigte Anpassungen werden anhand experimentell validierter Berechnungsbeispiele diskutiert
Component Dimensioning in Hydrogen Environment
No full text625632For the ongoing energy transition, high pressure hydrogen is a highly relevant energy carrier. In order to provide a practical and robust hydrogen infrastructure, a vast variety of components needs to be developed to ensure a save hydrogen storage and transport. Dimensioning of these parts with respect to their structural durability requires new dimensioning schemes and guidelines to be developed which account for material specific damage mechanisms under hydrogen environment. An ideal basis represents the well-established FKM guideline issued by the German Research Association Mechanical Engineering (FKM). The guideline is applicable for a wide range of mechanical engineering components and is particularly popular for small and medium enterprises. Within this work, the dimensioning scheme based on FKM guideline is applied for exemplary structural parts in hydrogen environment. Based on literature data and experiments conducted within the project, the fatigue strength assessment scheme acc. to the FKM guideline is modified and finally used for the assessment of a sample component from austenitic stainless steel. In our work, we analyze the applicability of the guidelines based on this dimensioning use case and discuss how the FKM approach needs to be adapted to consider the hydrogen effects on a general basis.7
3D microstructure modeling of long fiber reinforced thermoplastics
No full textS.136-145A novel procedure for the generation of a representative volume element for long fiber reinforced thermoplastics and materials with a similar microstructure is presented here. It is characterized by a maximum fiber aspect ratio of approx. 5000 and a maximum fiber volume fraction up to 25%. The modeling procedure is based on characteristic values describing the microstructure in a statistical sense, which are the fiber orientation distribution, the fiber length distribution and the fiber volume content. The resulting mesh for finite element analysis represents the microstructure with a relatively low element count, modeling each fiber only by a single element per cross section. Hence, the model is computationally very efficient and allows the analysis of comparably large structures which include the complete fiber length spectrum of the investigated material. The procedure is validated against the elastic properties of three material variants with different fiber volume fractions, incorporating their experimental measured fiber orientation and length distributions.10
Principle strategies for the fatigue assessment of steels based on machine learning approaches
No full text94101Machine learning (ML) approaches gain more and more importance for fatigue assessment of materials and industrial parts. In this work an extensive database of more than 22.000 single fatigue test and 1100 fatigue test series (SN-curves) of different steels are used to build a generalized approach for the fatigue prediction based on machine learning. For this, different strategies are used: First, on SN-curve level, the fatigue life assessment based on SN-curves, where the SN-curve parameters (slope, fatigue strength) were determined by ML and used for the fatigue life prediction later; and second, the fatigue life prediction based on specimens, where the characteristics of single specimen of the fatigue tests series (stress amplitude, roughness, hardness, …) are used (specimen level). Different ML approaches like an artificial neural network (ANN) or random forest approach are used. A higher accuracy of the direct fatigue life prediction is shown. Slightly higher accuracy was determined using an ANN. This work shows the limitation using mainly commercial, older data sources for ML-based fatigue assessment with a certain degree of inconsistency that affect the prediction accuracy of this approaches.7
