The bias-extension test is a rather simple experiment aiming to determine in-plane shear properties of textile composite reinforcements. However the mechanics during the test involves fibrous material at large shear strains and large rotations of the fibres. Several aspects are still being studied and are not yet modeled in a consensual manner. The standard analysis of the test is based on two assumptions: inextensibility of the fibers and rotations at the yarn crossovers without slippage. They lead to the development of zones with constant fibre orientations proper to the bias-extension test. Beyond the analysis of the test within these basic assumptions, the paper presents studies that have been carried out on the lack of verification of these hypothesis (slippage, tension in the yarns, effects of fibre bending). The effects of temperature, mesoscopic modeling and tension locking are also considered in the case of the bias-extension test.
This work deals with the modeling of the material flow in Friction Stir Welding (FSW) processes using particle tracing method. For the computation of particle trajectories, three accurate and computationally efficient integration methods are implemented within a FE model for FSW process: the Backward Euler with Sub-stepping (BES), the 4-th order Runge–Kutta (RK4) and the Back and Forth Error Compensation and Correction (BFECC) methods. Firstly, their performance is compared by solving the Zalesak’s disk benchmark. Later, the developed methodology is applied to some FSW problems providing a quantitative 2D and 3D view of the material transport in the process area. The material flow pattern is compared to the experimental evidence.
This paper presents synthetically the most recent models for description of the anisotropic plastic behavior. The first section gives an overview of the classical models. Further, the discussion is focused on the anisotropic formulations developed on the basis of the theories of linear transformations and tensor representations, respectively. Those models are applied to different types of materials: body centered, faced centered and hexagonal-close packed metals. A brief review of the experimental methods used for characterizing and modeling the anisotropic plastic behavior of metallic sheets and tubes under biaxial loading is presented together with the models and methods developed for predicting and establishing the limit strains. The capabilities of some commercial programs specially designed for the computation of forming limit curves (FLC) are also analyzed.
Composite materials and their related manufacturing processes involve many modeling and simulation issues, mainly related to their multi-physics and multi-scale nature, to the strong couplings and the complex geometries. In our former works we developed a new paradigm for addressing the solution of such complex models, the so-called Proper Generalized Decomposition based model order reduction. In this work we are summarizing the most outstanding capabilities of such methodology and then all these capabilities will be put together for addressing efficiently the simulation of a challenging composites manufacturing process, the automated tape placement.
This experimental work concerns the study of the preforming of a specific highly double curved geometry with a triple point (case corner) by the sheet forming process using powdered interlock reinforcement (G1151®). Three different punches (square box, prism, tetrahedron) were used in this study, each of them presenting highly double curved geometry with a case corner. A specific sheet forming device specially designed for the preforming of textile reinforcement was used. The expected shapes with the three punches have been obtained with an optimized blank-holder pressure. No classical defaults such as wrinkling or yarn damage are present in the useful zone of the preforms. However, a new default, not observed for spherical or hemispherical shape has been identified. It concerns the out of plane buckling of yarns. This phenomenon not observed on the square box is visible on some faces and edges of the prismatic and tetrahedron shapes. For the square box, it is easily possible to control the orientation of the yarn within the preform in the faces, whereas this is not possible for triangular faces of the prismatic and tetrahedron shapes. The square box punch is therefore more adapted to preform the highly doubled curved shape with the case corner.
Incremental sheet metal forming in general and Single Point Incremental Forming (SPIF) specifically have gone through a period of intensive development with growing attention from research institutes worldwide. The result of these efforts is significant progress in the understanding of the underlying forming mechanisms and opportunities as well as limitations associated with this category of flexible forming processes. Furthermore, creative process design efforts have enhanced the process capabilities and process planning methods. Also, simulation capabilities have evolved substantially. This review paper aims to provide an overview of the body of knowledge with respect to Single Point Incremental Forming. Without claiming to be exhaustive, each section aims for an up-to-date state-of-the-art review with corresponding conclusions on scientific progress and outlook on expected further developments.
We conduct an incisive investigation of the existence of a one-to-one correspondence between a material's elastoplastic properties and its indentation responses, with particular emphasis on the residual imprint. We first unravel a so-called "mystical material" pair reported by Chen et al. (2007) by examining the specimens' post-indentation morphologies, despite using a single self-similar indenter. Next, using Metric Multidimensional Scaling (MDS), we mitigate the mystical material issue for materials hardening according to the popular Hollomon's power law equation. In contrast, the same exact protocol reveals the absence of a one-to-one correspondence between the single indentation response and Voce hardening parameters. To alleviate this, we propose a multi-depth indentation strategy.
A general approach to the mechanical behaviour of woven fabrics at the scale of individual fibers is proposed in this paper. In order to simulate the behaviour of samples of woven fabrics, all fibers constituting these samples are taken into account in the model, and particular attention is paid to detecting and modeling of contact-friction interactions occuring within the assembly of fibers. The global problem is set within a large deformation framework, and is solved using an implicit algorithm. The developed methods are first employed to compute the unknown initial configuration of woven structures by reproducing the arrangement of yarns generated by the weaving process. Various loading cases can then be applied in order to identify the mechanical properties of such materials. Numerical results about samples made of nearly 400 fibers are given to show the ability of the method to handle representative examples. Very useful informations at the scale of individual fibers are obtained from these simulations and should help to understand the mechanisms at microscopic scale governing the complex nonlinear behaviour of woven fabrics.
In this study, a model based on a strain localization level to overcome the shortcomings of the well-established Forming Limit Diagram (FLD) in predicting the physical phenomenon of necking is introduced. An optical measurement system was used to capture the strain history of the Nakazima experiment until rupture occurred. In order to measure the fracture strain more accurately, a further method is introduced, which is based on the microscopic measurements of ruptured regions. This model is validated using a 3-point bending test. The results show the ability of the method to predict failure under bending conditions as well. Additionally, failure is investigated based on the pressure sensitivity and the Lode dependency. The results show that the triaxiality at the failure point is independent of the loading path.
CVD diamond-coated carbide tools could provide an economical alternative for trimming CFRPs components compared to their PCD tools counterpart. Nevertheless, there are still some technical issues to understand related to wear resistance and surface quality. In this work, a CVD tool with six straight flutes was used to investigate the relationship between surface roughness, surface damage, tool wear, cutting force and cutting parameters during the high speed trimming of CFRPs. Statistical techniques for identifying and selecting the best cutting conditions for CVD tool are developed. In terms of tool wear, results show that the best operational condition to minimize the tool wear is achieved at lower feed rates and higher cutting speeds. Experimental results show also that a 0° ply orientation represents the worst case and produces the maximum tool wear. Furthermore, a strong correlation between the feed force and the tool wear was observed. It was found that the surface roughness decreases as a reciprocal function of cutting length. This decrease was due to the matrix burning/sticking and the thermal damage related to the low thermal conductivity of CFRP. In such situation, Ra becomes inappropriate indicator for roughness evaluation. On the other hand, it wasn’t seen any type of delamination or fiber pull-out on the trimmed surface of all coupons for the three tool life tests. Accordingly, delamination can be avoided using high fixture rigidity, high quality of CFRP laminates, a suitable cutting tool and stable operational conditions.
In recent times a growing interest has arose on the development of data-driven techniques to avoid the employ of phenomenological constitutive models. While it is true that, in general, data do not fit perfectly to existing models, and present deviations from the most popular ones, we believe that this does not justify (or, at least, not always) to abandon completely all the acquired knowledge on the constitutive characterization of materials. Instead, what we propose here is, by means of machine learning techniques, to develop correction to those popular models so as to minimize the errors in constitutive modeling.
The use of composite materials reinforced by flax fibres has been increasing steadily over the last 20 years. These fibres show attractive mechanical properties but also some particularities (naturally limited length, presence of a lumen, fibres grouped in bundles in the plant, complex surface properties and composition). An analysis of the available literature indicates that the quality of the composite materials studied is not always optimal (high porosity, incomplete impregnation, heterogeneous microstructure, variable fibre orientation). This paper reviews published data on the specific nature of flax fibres with respect to manufacturing of biocomposites (defined here as polymers reinforced by natural fibres). All the important steps in the process which influence final properties are analyzed, including the plant development, retting, fibre extraction, fibre treatment, preform preparation, available manufacturing processes, the impregnation step, fibre cell wall changes during processing and fibre/matrix adhesion.