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This paper presents an innovative approach for the modelling of viscous behaviour of short-fibre reinforced composites (SFRC) with complex distributions of fibre orientations and for a wide range of strain rates. As an alternative to more complex homogenisation methods, the model is based on an additive decomposition of the state potential for the computation of composite’s macroscopic behaviour. Thus, the composite material is seen as the assembly of a matrix medium and several linear elastic fibre media. The division of short fibres into several families means that complex distributions of orientation or random orientation can be easily modelled. The matrix behaviour is strain-rate sensitive, i.e. viscoelastic and/or viscoplastic. Viscoelastic constitutive laws are based on a generalised linear Maxwell model and the modelling of the viscoplasticity is based on an overstress approach. The model is tested for the case of a polypropylene reinforced with short-glass fibres with distributed orientations and subjected to uniaxial tensile tests, in different loading directions and under different strain rates. Results demonstrate the efficiency of the model over a wide range of strain rates.

Split Hopkinson Pressure Bar system (SHPB) with large-diameter and Nylon bars introducing a shear-compression loading device is used in order to investigate the dynamic behaviour of aluminium honeycomb under multiaxial loadings conditions. All shear-compression configurations including the loading angle variation from 0∘ to 60∘ are performed with an impact velocity of about 15m/s. The adapted SHPB system with the device are validated numerically and a phenomenon of separation between the input bar and the input beveled bar is observed. Numerical results suggest that this phenomenon provides a cutting of the reflected wave. An electro optical extensometer is employed in experiments. A good agreement between the numerical elastic waves and the experimental ones is obtained. Experimental results show a significant effect of the loading angle on the apparent stress-strain curves. The initial peak value and the plateau stress decrease with the increase of the loading angle. The combined shear-compression device with an enhancement at the alignment set-up provides efficient results for samples dynamically loaded. This device will be used to investigate the influence of the in-plane orientation angle on the deformation mechanisms and multiaxial behaviour of aluminium honeycomb under dynamic and quasi-static loading conditions.

In additive manufacturing (AM), one of the most popular procedures is material extrusion (MEX). The materials and manufacturing parameters used in this process have a significant impact on a printed product’s quality. The purpose of this work is to investigate the effects of infill percentage and filament orientation on the mechanical properties of printed structures. For this reason, the characterisation of polylactic acid (PLA) was done numerically using the finite element method and experimentally through mechanical tests. The experiments involved three-point bending and tensile tests. The results showed that mechanical performance is highly dependent on these processing parameters mainly when the infill percentage is less than 100%. The highest elastic modulus was exhibited for structures with filament align at 0° and 100% infill, while the lowest one was verified for specimen filament aligned at 0° and 30% infill. The results demonstrated that the process parameters have a significant impact on mechanical performance, particularly when the infill percentage is less than 100%. Structures with filament aligned at 0° and 100% infill showed the maximum elastic modulus, whereas specimens with filament oriented at 0° and 30% infill showed the lowest. The obtained numerical agreement indicated that an inverse method based only on the load–displacement curve can yield an accurate value for this material’s elastic modulus.

In this article, strain-rate sensitivity of short-fiber reinforced composites (SFRC) with complex fiber orientation is modeled. The principal aim is to allow an easier implementation than that of classical techniques, in case of complex reinforcement characteristics and nonlinear matrix behavior. The interest for such an approach is particularly acute for high-strain-rate simulations using explicit formulation. The composite behavior is computed based on an additive decomposition of the state potential between linear elastic short fiber media and a viscoelastic–viscoplastic matrix medium. Finite element simulations demonstrate model's ability to reproduce behavior trends of SFRC with distributed fiber orientations, for a wide strain-rate range. [ABSTRACT FROM AUTHOR]

The present work focuses on the dynamic crushing response of 2D re-entrant auxetic honeycomb. The aim of this work is to propose analytic formulations to predict the crushing strength of the considered structure by including design parameters (specific geometrical ratios and/or material properties). The model for dynamic impact is based on shock waves propagation analogy in a rigid, perfectly plastic, locking (R-P-P-L) material model. The formulations depend on the geometric and the material characteristics of the auxetic but also on the impact velocity. Finite Element simulations of the impact of a plate on an auxetic structure were carried out using the RADIOSS® explicit solver. The impact velocities varies from 35 m/s to 200 m/s. The numerical simulations presented in this study show good accordance between analytical and Finite Element results.