Papers by Keyword: Bi-Material Interfaces

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Authors: Jan Klusák, Zdeněk Knésl
Abstract: Conditions of damage initiation in bi-material structures are analysed in the paper. The considerations are derived from the knowledge of the stress state caused by the existence of the sharp notch and the bi-material interface. The step change of material properties and the geometrical discontinuity at the interface leads to a singular peak of stress that is similar to the stress singularity near the crack tip in homogeneous material. That fact urges to use generalized linear elastic fracture mechanics for assessment of conditions of crack initiation. In the paper crack initiation direction and quantification of the external load connected with crack initiation are discussed. Within the stability assessment, possible directions of crack initiation should be considered and tested in both material components and at their interface as well. Knowing the critical applied stresses, one can decide among the damage eventualities.
Authors: Luboš Náhlík, Lucie Šestáková, Pavel Hutař
Abstract: The objective of the paper is to investigate the direction of a further crack propagation from the interface between two elastic materials. The angle of crack propagation changes when the crack passes the interface. The suggested procedure makes it possible to estimate an angle of propagation under which the crack will propagate into the second material. The assumptions of linear elastic fracture mechanics and elastic behavior of the body with interfaces are considered. The finite element method was used for numerical calculations. The results obtained might contribute to a better understanding of the failure of materials with interfaces (e.g. layered composites, materials with protective coatings) and to a more reliable estimation of the service life of such structures.
Authors: Luboš Náhlík, Pavel Hutař, Zdeněk Knésl
Abstract: The article deals with the behaviour of a fatigue crack propagating across a bi-material interface. A stability criterion for the crack touching the bi-material interface, taking into account the residual stresses closing the crack faces is formulated. The linear elastic fracture mechanics is assumed to apply and the finite element method is used in the calculations. The criterion proposed is applied to determine the fatigue threshold stress for crack propagation across the interface. It is shown that the threshold values for crack propagation are influenced by the residual stresses closing the crack and by the specific combination of the elastic constants of the materials used. The results contribute to a better understanding of the failure of structures with bi-material interfaces (protective layers, composite materials, etc.).
Authors: Michael T. Heitzmann, Meng Hou, Martin Veidt, Luigi Jules Vandi, Rowan Paton
Abstract: The morphology of the interface between a commercial epoxy prepreg resin (HexPly M18/1) and Polyetherimide (PEI) is studied. Different cure cycles prescribed by the supplier were investigated to determine the influence of temperature and pressure on interface formation. Atomic Force Microscopy (AFM) was used as the main means of investigation. A phase-separated interphase spanning 9-10μm was observed for the PEI/epoxy prepreg interface. It was found that the temperature profile of the cure cycle strongly influences the formation of this interphase. Rapid formation of these relatively large interphase areas suggests that mechanisms other than diffusion are responsible for this phenomenon.
Authors: Jun Long Peng, Jiao Tang, Zhen Yu Ouyang
Abstract: The interface fracture process of most layered or bonded structures is commonly under the control of mixed mode cracking where the interface shear and normal fracture components exist simultaneously when the hybrid joints are bonded with different adherend materials. In this work, a simple and novel method is proposed to realize and characterize the pure mode I interface fracture for the hybrid joints with dissimilar substrates. The theoretical and experimental results indicate that the present method may be considered as a standard test method for the characterization of hybrid joints with dissimilar materials.
Authors: Luboš Náhlík, Pavel Hutař, Zdeněk Knésl
Abstract: The paper is devoted to fatigue crack propagation in layered materials. The influence of plasticity induced crack closure on threshold values for fatigue crack propagation through interfaces between different materials layers is studied. The main aim was to estimate the influence of the loading ratio R on threshold values for crack propagation through a bi-material interface as a function of the elastic mismatch of both materials. The finite element method (FEM) is used for numerical calculations. Results obtained for different loading ratios, materials, boundary conditions and magnitude of applied loading can be generalized and used for the design of composite bodies with different material layers.
Authors: Luboš Náhlík, Pavel Hutař, Zdeněk Knésl
Abstract: The objective of this paper is to investigate the transverse fatigue cracking of layered structures. To this end a fatigue crack propagation rate for a crack growing perpendicularly through the interfaces between individual layers of the structure is estimated. The suggested procedure takes into account the influence of different material properties of the layers on the stress field around the fatigue crack and the change of the stress singularity exponent in the special case of a crack touching the material interface. The assumptions of linear elastic fracture mechanics and elastic behaviour of the composite are considered. It is shown that the existence of the interfaces can have a negative influence on the residual fatigue life of layered structures.
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