Browsing by Subject "General interface"
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Item Open Access Bounds on size effects in composites via homogenization accounting for general interfaces(Springer, 2020-01) Firooz, Soheil; Javili, Ali; Chatzigeorgiou, G.This manuscript provides novel bounds and estimates, for the first time, on size-dependent properties of composites accounting for generalized interfaces in their microstructure, via analytical homogenization verified by computational analysis. We extend both the composite cylinder assemblage and Mori–Tanaka approaches to account for the general interface model. Our proposed strategy does not only determine the overall response of composites, but also it provides information about the local fields for each phase of the medium including the interface. We present a comprehensive study on a broad range of interface parameters, stiffness ratios and sizes. Our analytical solutions are in excellent agreement with the computational results using the finite element method. Based on the observations throughout our investigations, two notions of size-dependent bounds and ultimate bounds on the effective response of composites are introduced which yield a significant insight into the size effects, particularly important for the design of nano-composites.Item Open Access Generalized interfacial energy and size effects in composites(Elsevier Ltd, 2017) Chatzigeorgiou, G.; Meraghni, F.; Javili, A.The objective of this contribution is to explain the size effect in composites due to the interfacial energy between the constituents of the underlying microstructure. The generalized interface energy accounts for both jumps of the deformation as well as the stress across the interface. The cohesive zone and elastic interface are only two limit cases of the general interface model. A closed form analytical solution is derived to compute the effective interface-enhanced material response. Our novel analytical solution is in excellent agreement with the numerical results obtained from the finite element method for a broad variety of parameters and dimensions. A remarkable observation is that the notion of size effect is theoretically bounded verified by numerical examples. Thus, the gain or loss via reducing the dimensions of the microstructure is limited to certain ultimate values, immediately relevant for designing nano-composites. © 2017 Elsevier LtdItem Open Access Homogenization of composites embedding general imperfect interfaces(Bilkent University, 2019-06) Firooz, SoheilThe objective of this work is to present a systematic study on the overall behavior of composites embedding general interfaces between the constituents. The zero-thickness interface model represents a finite-thickness interphase between the constituents. The term general interface refers to an interface model that allows for both displacement and traction jumps, unlike cohesive or elastic interface models. To set the stage, a comprehensive study on homogenization is carried out to examine the effects of various representative volume elements (RVE) and boundary conditions on the overall response of composites. Next, we extend the homogenization framework to account for interfaces hence, capturing size effects in both particulate and fiber composites. Two new analytical approaches are developed to determine the overall size-dependent response of composites. The first approach extends the composite sphere assemblage (CSA), composite cylinder assemblage (CCA) and the generalized self-consistent method (GSCM) resulting in bounds and estimates on the macroscopic properties of composites. In the second approach, we generalize the Mori{Tanaka method that not only determines the effective properties but also provides the state of the stress and strain in each phase of the medium including the interface. The proposed analytical results are thoroughly verified via a series of numerical examples using the finite element method.Item Open Access Homogenization of composites with extended general interfaces: comprehensive review and unified modeling(ASME, 2021-08-03) Javili, Ali; Steinmann, P.; Firooz, S.Interphase regions that form in heterogeneous materials through various underlying mechanisms such as poor mechanical or chemical adherence, roughness, and coating, play a crucial role in the response of the medium. A well-established strategy to capture a finite thickness interphase behavior is to replace it with a zero-thickness interface model characterized by its own displacement and/or traction jumps, resulting in different interface models. The contributions to date dealing with interfaces commonly assume that the interface is located in the middle of its corresponding interphase. This paper revisits this assumption and introduces an extended general interface model, wherein a unifying approach to the homogenization of heterogeneous materials embedding interfaces between their constituents is developed within the framework of linear elasticity. Through utilizing a weighted average operator, we demonstrate that the assumption of enforcing the interface to coincide with the midlayer is not required and thereby develop a new class of interfaces where the interface is allowed to take any arbitrary position between its bulk neighbors. The proposed novel interface model can recover any of the classical interface models. Next, via incorporating this extended general interface model into homogenization, we develop bounds and estimates for the overall moduli of fiber-reinforced and particle-reinforced composites as functions of the interface position and properties. Finally, we carry out a comprehensive numerical study to highlight the influence of interface position, stiffness ratio, and interface parameters on the overall properties of composites. The developed interface-enhanced homogenization framework also successfully captures size effects, which are immediately relevant to emerging applications of nanocomposites due to their pronounced interface effects at small scales.Item Open Access On effective behavior of microstructures embedding general interfaces with damage(Springer, 2019-05) Saeb, S.; Steinmann, P.; Javili, AliThe interface between constituents of a multiphase material exhibits properties different from those of the bulk and can lead to major alternation of the material response. Interface effects are particularly important for multiphase nano-materials where the area-to-volume ratio is significantly large. In this contribution, we study the influence of a degrading general interface. That is, we allow for the initiation and accumulation of damage on a generalized interface accounting for both jumps of the displacement and the traction across the interface. The applicability of the proposed framework is demonstrated through several numerical examples. We present a parametric study on the influence of a broad range of interface material parameters on the overall behavior of various microstructures subject to volumetric loading and unloading. The numerical results illustrate that the resistance along the interface plays a key role in the resulting damage mechanism and could potentially prevent the detachment of the inclusion from the matrix regardless of the resistance across the interface or bulk material parameters. This behavior is observed and shown for both two- and three-dimensional examples. Moreover, the size-effect due to the general interface model is examined and compared against other interface models. Finally, the influence of the boundary conditions on the effective response and damage initiation of several microstructures is studied.Item Open Access Understanding the role of general interfaces in the overall behavior of composites and size effects(Elsevier, 2019) Firooz, Soheil; Javili, AliThe objective of this contribution is to investigate the role of generalized interfaces in the overall response ofparticulate composites and the associated size effects. Throughout this work, the effective properties of com-posites are obtained via three-dimensional computational simulations using the interface-enhancedfinite ele-ment method for a broad range of parameters. The term interface corresponds to a zero-thickness model re-presenting the interphase region between the constituents and accounting for the interfaces at the micro-scaleintroduces a physical length-scale to the effective behavior of composites, unlike the classicalfirst-orderhomogenization that is missing a length-scale. The interface model here is general in the sense that both tractionand displacement jumps across the interface are admissible recovering both the cohesive and elastic interfacemodels. Via a comprehensive computational study, we identify extraordinary and uncommon characteristics ofparticle reinforced composites endowed with interfaces. Notably, we introduce the notion ofcritical sizeat whichthe overall behavior, somewhat surprisingly, shows no sensitivity with respect to the inclusion-to-matrix stiffnessratio. Our study, provides significant insight towards computational design of composites accounting for in-terfaces and in particular, nano-composites.