Browsing by Subject "Cohesive interface"

Now showing 1 - 5 of 5

Open Access
Generalized interfaces via weighted averages for application to graded interphases at large deformations
(Elsevier Ltd, 2021-04) Saeb, S.; Firooz, S.; Steinmann, P.; Javili, Ali
Finite-thickness interphases between different constituents in heterogeneous materials are often replaced by a zero-thickness interface model. Commonly accepted interface models intuitively assume that the interface layer is situated exactly in the middle of its associated interphase. Furthermore, it has been reported in the literature that this assumption is necessary to guarantee the balance of angular momentum on the interface. While the interface coincides with the mid-layer of a uniform interphase, we argue that this assumption fails to sufficiently capture the behavior of graded or inhomogeneous interphases. This contribution extends the formulation of the general interface model to account for arbitrary interface positions. The issue of angular momentum balance on general interfaces is critically revisited. It is proven that the interface position does not necessarily have to coincide with the mid-layer in order to satisfy the angular momentum balance. The analysis here leads to a unique definition of the controversially discussed interface configuration. The presented general interface model is essentially based upon the weighted average operator instead of the commonly accepted classical average operator. The framework is geometrically exact and suitable for finite deformations. The significance of the interface position is demonstrated via a series of examples where the interface position is identified based on a full resolution interphase.
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.
Open Access
A note on traction continuity across an interface in a geometrically non-linear framework
(SAGE Publications, 2018) Javili, Ali
The objective of this contribution is to elaborate on the notion of “traction continuity” across an interface at finite deformations. The term interface corresponds to a zero-thickness model representing the interphase between different constituents in a material. Commonly accepted interface models are the cohesive interface model and the elastic interface model. Both the cohesive and elastic interface models are the limit cases of a generalized interface model. This contribution aims to rigorously analyze the concept of the traction jump for the general interface model. The governing equations of the general interface model in the material as well as spatial configurations are derived and the traction jump across the interface for each configuration is highlighted. It is clearly shown that the elastic interface model undergoes a traction jump in both the material and spatial configurations according to a generalized Young-Laplace equation. For the cohesive interface model, however, while the traction field remains continuous in the material configuration, it can suffer a jump in the spatial configuration. This finding is particularly important since the cohesive interface model is based on the assumption of traction continuity across the interface and that the term “traction” often refers to the spatial configuration and not the material one. Thus, additional care should be taken when formulating an interface model in a geometrically non-linear framework. The theoretical findings for various interface models are carefully illustrated via a series of two-dimensional and three-dimensional numerical examples using the finite element method.
Open Access
On effective behavior of microstructures embedding general interfaces with damage
(Springer, 2019-05) Saeb, S.; Steinmann, P.; Javili, Ali
The 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.
Open Access
Understanding the role of general interfaces in the overall behavior of composites and size effects
(Elsevier, 2019) Firooz, Soheil; Javili, Ali
The 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.