Emmanuelle Vidal-Sallé

A hyperelastic approach for composite reinforcement large deformation analysis

A hyperelastic constitutive model is developed for textile composite reinforcement at large strain. A potential is proposed, which is the addition of two tension and one shear energies. The proposed potential is a function of the right Cauchy Green and structural tensor invariants whose choice corresponds to textile composite reinforcement mechanical behavior which exhibits weak elongations in the fiber directions and large angular variations in the fabric plane. The model is implemented in a Vumat user routine of ABAQUS/Explicit. Some elementary tests are performed in order to identify the model and verify its validity. It is then used to simulate the hemispherical punch forming of balanced and unbalanced fabrics. A correct agreement is obtained with experimental forming processes.

Analysis of the stress components in a textile composite reinforcement

When a continuum approach is considered for textile reinforcements, the internal loads are described by a stress tensor. The mechanical behaviour of the textile material is very much dependent on the fiber directions, and the frames defined from warp and weft directions are preferred to write the stress components. The exterior loads in these frames permit to define tensile and pure shear states. Nevertheless, these frames are generally not orthogonal. The relationships between the exterior loads and the different stress components are analyzed in the present paper, and, in particular, the relationship between direct stress components and longitudinal loads on one hand, and shear stress components and transversal loads on the other hand. When dealing with textile materials, the exterior loads in the direction of the fibres and transverse to the fibres define the pure tensile and pure shear state. It is shown that the covariant stress component matrix is diagonal in a pure tensile loading and that the first mixed direct stress components are equal to zero in a pure shear loading. In these cases, the direct relationship between the stresses and the loadings are given. This is applied to the cases of the picture frame test, the biaxial tensile test or of a combined tension-shear test.

A shear stress dependent ductile damage model

Abstract Prediction of ductile damage is an important challenge for finite element modelling of thermo-mechanical forming processes. Existing plasticity theories intended for the prediction of the void growth are mainly formulated with the normal mean stress, without any influence of the deviatoric stress tensor. In order to take into account shear stress effects during the void growth, a yield function including the mass conservation and its corresponding flow rule is discussed and identified with a modified Rice and Tracey model.

Friction law for hydrostatic mixed lubrication regime

Abstract The accuracy of the finite element simulation of bulk forming processes is connected to the interface friction law. For quasi-static processing operations, the well-known plastic wave friction model, applied to unlubricated contacting interfaces of metallic workpieces with rigid tools, is a versatile link between the Coulomb–Amonton and the constant friction laws. An improvement of the plastic wave friction model is proposed for mixed lubricating conditions when the load is carried by the asperities in direct contact and by the lubricant. The main assumption of this new constitutive relation uses the compressibility of the trapped lubricant in the pockets created inside the tool asperity with the rising plastic wave. This new friction law is used for the simulation of different ring-compression tests carried out by Tan et al. [J. Mater. Proc. Technol. 80–81 (1998) 292].

Simulation and tomography analysis of textile composite reinforcement deformation at the mesoscopic scale

The preforming stage of the LCM composite manufacturing process leads to fibrous reinforcement deformations which may be very large especially for doubly curved shapes. The knowledge of the mesoscopic deformed geometry is important for reinforcement permeability computations and for damage prediction analyzes of the composite. A simulation method for woven composite fabric deformation at mesoscopic scale is presented in this paper. A specific continuum hypo-elastic constitutive model is proposed for the yarn behaviour. The associated objective derivative is based on the fibre rotation. Spherical and deviatoric parts of the transverse behaviour are uncoupled. X-ray tomography is used to obtain experimental undeformed and deformed 3D geometries of the textile reinforcements. It provides, in particular, fibre distribution within the yarn. A comparison between deformed geometries obtained by mesoscopic simulation and by tomography is presented for bi-axial tension and in-plane shear deformation.

A Friction-Test Benchmark with Twintex PP

This paper presents an update on a friction benchmark, that was proposed during the 13th ESAFORM conference. The goal is to compare different friction test set-ups [1–4] by determining the coefficient of friction (CoF) for Twintex® PP. The benchmark instructions are based on the ASTM standard D1894 [5] but also account for different friction velocities, pressures and temperatures. At the time of writing five research groups contributed to the benchmark, each with a custom designed test set-up, differing in size, mechanism, force control and temperature regulation. All tests will be conducted with woven glass reinforced polypropylene, from the same Twintex® batch. Conclusions will be drawn about the comparability of different testing methods by recognizing and analyzing systematically deviating results.

Modelling the structures and properties of woven fabrics

Abstract: Modelling the mechanical properties of woven fabrics has been a goal of researchers for many decades. Nowadays, numerical simulations permit different approaches at different scales. This chapter gives a non-exhaustive view of the proposed approaches and tools for modelling mechanical properties of woven fabrics. Two main aspects are dealt with: (1) macroscopic modelling that is used for textile structure deformation analyses, especially forming simulations, and (2) mesoscopic modelling, that is modelling on the scale of the unit woven cell. The specific experimental tests used for woven fabrics are described. X-ray tomography analyses are performed to validate simulations of unit cell deformations. Mesoscopic modelling is an efficient method of providing input data on the macroscopic behaviour of textile preforms and for resin flow analysis in the resin transfer moulding (RTM) processes.

Friction Measurement on Dry Fabric for Forming Simulation of Composite Reinforcement

Forming processes are highly influenced by all the interface conditions between the tooling and the workpieces. For thermo-mechanical processes like hot forging or cutting processes friction is widely studied for a long time but for composite parts, it is not the case because the problem is not so crucial: forming forces are generally weak enough to allow the part be realized with any forming device; surface quality is not highly affected by the friction conditions; for pre-impregnated fabrics, the viscous or even fluid matrix acts like a lubricant and avoids defects due to sticking between fibre reinforcement and metallic tools. Nevertheless, friction seems to have an important role when precise simulations are expected. Up to now, few studies have been focussed on friction during composite forming processes. The aim of the present study is to make a contribution on that topic for an experimental point of view using an high precision device able to measure small friction forces. The relative fibre orientations can be monitored in order to explore the whole range of geometrical configurations. The final goal is to develop an efficient tool for finite element simulations of dry and pre-impregnated fibre fabrics accounting for the main specificity of fabrics, that is to say their strong anisotropy.

Identification of Fibre Degradation due to Friction during the Weaving Process

In order to be able to properly evaluate the in-use mechanical properties of high performance composite materials, it is useful to identify all the critical operations of the forming process which can degrade the row materials (i.e. the yarns for continuous fibre reinforcements). Those degradations begin during the weaving process which is the main topic of the present paper. The weaving operation has been proved to be particularly critical, especially when the weaving parameters are not correctly tuned. For glass fibre reinforcements, the travel followed by both the warp and weft yarns inside the weaving loom is observed and several zones are identified as particularly critical: the contact between warp yarns and heddles, between yarns and the beater, between yarns … For each zone, the loading has been reproduced in laboratory devices in order to quantify its effect on the final resistance of the yarn. In parallel, the friction parameters have been measured for several friction configurations: friction between yarns in several directions, friction between yarns and various metallic parts of the loom. The objective is the identification of a forming window in terms of yarn tension, the shed opening, the beater for… This work is realised with the financial support of the French National Agency for Research (ANR) in the framework of project ANR- 09-MAPR-0018 (NUMTISS)

Impact of density gradients on the stress level within a green ceramic compact during drying

Abstract: Internal water content and mechanical stress distributions during convective drying were simulated for a homogeneous and a heterogeneous (with density gradients) annular compact of a green ceramic agglomerate. A diffusive model for water transfer and an elastic model for structural mechanics were applied. Based on experimental measurements, the material apparent density was numerically implemented as a function of spatial coordinates and the key material properties (moisture diffusivity and the Youngs modulus) were implemented as functions of material density. The heterogeneous compact (with density peaks at the top edges) exhibited three times larger circumferential tensile stress at the top external radius corner than that exhibited by the homogeneous one.