Filtern
Dokumenttyp
- Zeitschriftenartikel (6)
- Beitrag zu einem Sammelband (1)
- Vortrag (1)
Sprache
- Englisch (8)
Schlagworte
- Micromechanics (8) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (1)
The fracture toughness in the fiber-matrix composite by means of the single fiber pull-out test can be achievable, if it is possible to measure the compliance of partial debonded fiber, which necessitates a stable crack propagation and the determination of the corresponding crack length. A combination of high stiff test equipment and a simultaneous monitoring of the photo-elastic pattern of the embedded fibers with the help of polarization microscope enables to measure crack length and determination of Gc [Hampe, A and Marotzke, C. (1997). The Energy Release Rate of the Fiber/Polymer Matrix Interface: Measurement and Theoretical Analysis, J. Reinf. Plast. and Compo., 16: 341-352.]. This method is well-known for glass fiber-amorphous polymer composite. In this investigation, we tried to implement the same technique to C-fiber with amorphous and semi-crystalline polymer composites. The energy release rate (ERR) of the fiber-matrix interface was evaluated for the carbon fiber-reinforced in polycarbonate (PC) by interfacial crack propagation arising in the single fiber pullout test. Further, the crack propagation at the fiber-matrix interface with different matrix morphology was discussed with the use of photo-elastic pattern observed with the aid of polarization microscope.
The strength of unidirectional elastic fibre composites is shown to depend on the loading rate as the viscoelastic nature of the matrix results in a fall in breaking load as the rate is reduced. The simulation of the accumulation of fibre breaks leading to failure, takes into account all physical phenomena involved fibre failure, including the stochastic nature of fibre strength, stress transfer through the matrix between reinforcements, interfacial debonding and the viscoelastic nature of the matrix. The kinetics of composite failure are seen to involve the initial formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The rate at which this occurs depends on the viscoelastic properties of the matrix. These results have been shown to closely mirror the behaviour of carbon fibre composite pressure vessels.
Explaining Deviatoric Residual Stresses in Aluminum Matrix Composites with Complex Microstructure
(2020)
The residual stresses in multiphase metal Matrix composites with both random planar-oriented short fibers and particles were studied by neutron diffraction and by a model based on the reformulation of classic Maxwell’s homogenization method. Contrary to common understanding and state-of-the-art models, we experimentally observed that randomly oriented phases possess non-hydrostatic residual stress. The recently developed modeling Approach allows calculating the residual stress in all phases of the composites. It rationalizes the presence of deviatoric stresses Accounting for the interaction of random oriented phases with fibers having preferential orientation.
Failure of composite materials is initiated by fracture processes on microscale, especially by interfacial debonding. Failure processes taking place on microscale are studied by single fiber experiments. This is, single fibers embedded in tensile specimen are loaded under various off-axis angles. Starting at microdefects interface cracks propagate circumferentially as well as longitudinally, depending on the loading angle. In addition, finite element simulations of interfacial crack propagation around single fibers as well as fibers embedded in a hexagonal composite are shown based on linear elastic fracture mechanics. The course of the energy release rate is given in dependence of the fiber volume fraction.
Microstructural analysis and mechanical properties of concrete reinforced with polymer short fibers
(2018)
The paper focuses on the development of a methodology for quantitative characterization of a concrete containing polymer fibers and pores. Computed tomography (CT) characterization technique is used to provide input data for Finite Element Method (FEM) simulations and analytical modeling based on micromechanical homogenization via the compliance contribution tensor formalism. Effective elastic properties of reinforced concrete are obtained experimentally using compression testing, analytically in the framework of Non-Interaction approximation and numerically performing direct FEM simulations on specimen with reconstructed microstructure. It is shown that CT produces results suitable for implementation in numerical and analytical models. The results of analytical and numerical modeling are in a good agreement with experimental measurements providing maximum discrepancy of ∼ 2.5%.
Microstructure-property connections for porous ceramics: The possibilities offered by micromechanics
(2016)
Microstructure of porous ceramics is highly “irregular”: it comprises pores and microcracks of diverse shapes and orientations.
This makes their quantitative modeling challenging, and one
often resorts to empirical relations containing Fitting Parameters and having somewhat uncertain range of applicability. We review the substantial progress made in modeling of “irregular” microstructures that does not seem to have been sufficiently utilized in the context of ceramics. We discuss the possibilities offered by micromechanics in developing microstructure–property relations for porous microcracked ceramics. After an overview of relevant micromechanics topics, we focus on several issues of specific interest for ceramics: nonlinear stress–strain behavior, effective elastic properties, and thermally induced microcracking. We discuss extraction of microscale Parameters (such as strength of the intergranular cohesion, density of cracks and pores, etc.) from macroscopic data and identify the extent of uncertainty in this process. We also argue that there is no quantitative correlation between fracturing process and the loss of elastic stiffness.
The High-Fidelity Generalized Method of Cells (HFGMC) is one technique, distinct from traditional finite-element approaches, for accurately simulating nonlinear composite material behavior. In this work, the HFGMC global system of equations for doubly periodic repeating unit cells with nonlinear constituents has been reduced in size through the novel application of a Petrov-Galerkin Proper Orthogonal Decomposition order-reduction scheme in order to improve its computational efficiency. Order-reduced models of an E-glass/Nylon 12 composite led to a 4.8–6.3x speedup in the equation assembly/solution runtime while maintaining model accuracy. This corresponded to a 21–38% reduction in total runtime.Thesignificant difference in assembly/solution and total runtimes was attributed to the evaluation of integration point inelastic field quantities; this step was identical between the unreduced and order-reduced models. Nonetheless, order-reduced techniques offer the potential to significantly improve the computational efficiency of multiscale calculations.