No abstract

In this paper, the mechanical response of composites consisting of ductile matrix reinforced by platelets-like particles is derived with imperfect interfaces. Due to its flexibility to study imperfect interfaces with limited number of model parameters, the linear spring model LSM is considered.Moreover, the interfacial contribution to the strain concentration tensor within each material phase and inside the average strain filed is described by a modified Mori-Tanaka scheme. The material nonlinearity is established by the J 2 plasticity and Lemaitre-Chaboche damage model. A generalised mid-point rule is used to solve rate equations yielding to anisotropic consistent (algorithmic) tangent operators. To avoid spurious macroscopic stress-strain response, an isotropisation procedure is adopted during the computation of a modified Eshelby's tensor. Numerical results are performed on graphene platelets GPL-reinforced polymer PA6 composite. They confirm the possibility to achieve high stiffness with low values of GPL aspect ratio. The accumulated plastic strain and the damage variable within the matrix are influenced by the GPL volume fraction which is also involved in the softening of the overall response when imperfection is considered at the interface.

This work investigates the crashworthiness response for a hierarchical modelling of hybrid composite material consisting of short-glass fibres reinforced graphene platelets polyamide PA6 matrix. A multi scale approach, using both mean-field homogenisation and finite element FE techniques, is employed to derive the overall response. Graphene is considered as platelets GPL embedded within an elasto plastic matrix phase. The 2-phases composite response is therefore computed under the Mori-Tanaka micromechanics scheme by accounting for the GPL spatial orientation. The modelling of the 3phases short glass fibres/graphene polymer composite consists on a double-scale approach combining the 2-phases graphene polymer composite as matrix phase in which are embedded the glass fibres. Numerical characterisations involving tensile, compression, fracture toughness and Charpy impact tests enable the determination of damage/failure thresholds for crashworthiness applications. The full crash box is simulated by implementing the constitutive 3-phases composite using a user-defined Digimat/LS-DYNA linkage. Numerical results, which are compared to those from conventional steel and glass fibres composites, show the contribution of the GPL volume fraction in the improvement of the specific energy absorption SEA.

This work presents a multiscale framework for the elasto-plastic response of platelets-like inclusions reinforced nanocomposite materials. The solution of the heterogeneous material problem is solved by a kinematic integral equation. An imperfect interface is introduced between the particles and the matrix through a linear spring model LSM, leading to a modified Eshelby's tensor. The interfacial contribution, related to the strain concentration tensor within each material phase and inside the average strain field, is described by a modified Mori-Tanaka scheme. The non-linear response is established in the framework of the J 2 flow rule. An expression of the algorithmic tangent operator for each phase is obtained and used as an uniform modulus for homogenisation purpose. Numerical results are conducted on graphene platelets GPL-reinforced polymer PA6 composite for several design parameters such as GPL volume fraction, aspect ratio and the interfacial compliance. These results clearly highlight the impact of the aspect ratio as well as the volume fraction by a softening in the overall response when imperfection is considered at the interface. Finally, a multiscale simulation is performed on a three bending specimen showing the capability of the developed constitutive equations to be implemented in a finite element FE code. fillers (such as glass or carbon fibres). Graphene has been used to enhance mechanical properties of metal matrix composites [2] for instance in aluminum composite materials where a small amount of graphene nanosheets GNS or even reduced graphene oxide rGO could therefore increase the overall composite physical properties greatly [3]. From a multiscale view point, an approach, for deriving such properties, lies in the combination of molecular mechanics theories and continuum models. The graphene properties are often derived at atomistic scale and the nano particles are treated as equivalent continuum particles [4,5] that are embedded in the matrix phase through conventional homogenisation techniques.Despite graphene has been used to increase stiffness, toughness and thermal conductivity of polymer resins by a large margin [6-9], there are still much technological challenges to overcome mainly in the material modelling. This is characterised by the lack of sufficient knowledge on graphene composites for structural applications describing interfacial properties between graphene and polymer matrix under severe loading conditions. It is well-known that the interface characterises the load transfer between the particles/fibres and the matrix. Therefore, it represents an influential parameter that can significantly change the overall properties. Indeed, interface is subjected to defects (debonding, dislocations and cracks) between reinforcements and the matrix and can be identified as one of the predominant damage mechanics in particle and fibre-reinforced composites [10].Then, the accuracy of the composite response needs a proper accounting for the properties of the interface. Several micromechanics m...

No abstract