Modelling of material cutting with a material microstructure-level (MML) model

In this research work a material microstructure-level cutting model (MML cutting model) is presented. The crystal plasticity theory is adopted for modeling the cutting of the titanium alloy Ti–6Al–4V in orthogonal case. In this model, the grains of the studied material are explicitly presented, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the cutting material. To obtain the material degradation process, the continuum self-consistent intragranular damage model and discrete cohesive zone inter-granular damage model, were developed, wherein the zero thickness cohesive element is implemented to simulate the bond between grain interfaces. This model was validated by a comparison with compression tests from literature. Results demonstrate the possibility to capture the influence of the microstructure on the material removal in terms of chip formation. Particularly, it is demonstrated that the grain orientation angle plays an important role for the chip segmentation and its periodicity during the cutting process

Modelling of aluminium sheet material at elevated temperatures

The formability of Al–Mg sheet can be improved considerably, by increasing the temperature.\ud At elevated temperatures, the mechanical response of the material becomes strain rate dependent. To accurately\ud simulate warm forming of aluminium sheet, a material model is required that incorporates the temperature\ud and strain-rate dependency. In this paper hardening is described succesfully with a physically based material\ud model for temperatures up to 200 ◦C. At higher temperatures and very low strain rates, the flow curve deviates\ud significantly from the model. Strain rate jumps still pose a serious problem to the model

Fire analysis of steel frames with the use of artificial neural networks

The paper presents an alternative approach to the modelling of the mechanical behaviour of steel frame material when exposed to the high temperatures expected in fires. Based on a series of stress-strain curves obtained experimentally for various temperature levels, an artificial neural network (ANN) is employed in the material modelling of steel. Geometrically and materially, a non-linear analysis of plane frame structures subjected to fire is performed by FEM. The numerical results of a simply supported beam are compared with our measurements, and show a good agreement, although the temperature-displacement curves exhibit rather irregular shapes. It can be concluded that ANN is an efficient tool for modelling the material properties of steel frames in fire engineering design studies. (c) 2007 Elsevier Ltd. All rights reserved

The effect of material cyclic deformation properties on residual stress generation by laser shock processing

Laser shock processing (LSP) is a mechanical surface treatment to induce a compressive residual stress state into the near surface region of a metallic component. The effect of the cyclic deformation properties of ductile materials on the final residual stress fields obtained by LSP is analysed. Conventional modelling approaches either use simple tensile yield criteria, or isotropic hardening models if cyclic straining response is considered for the material during the peen processing. In LSP, the material is likely to be subject to cyclic loading because of reverse yielding after the initial plastic deformation. The combination of experiment and modelling shows that the incorporation of experimentally-determined cyclic stress-strain data, including mechanical hysteresis, into material deformation models is required to correctly reflect the cyclic deformation processes during LSP treatment and obtain accurate predictions of the induced residual stresses.</p

From dry yarns to complex 3D woven fabrics: a unified simulation methodology for deformation mechanics of textiles in tension, shear and draping

Common methods of modelling the behaviour of fibrous materials, such as yarns and (woven) fabrics, is to treat them as continuous solids. The fibrous behaviour is then taken into account by appropriate constitutive laws. However, the development of such constitutive laws is very complex and requires several specificities (large deformations, orthotropic material behaviour, local crushing, …). Furthermore, by treating the material as a solid material important information about the micromechanics is “lost”. This presentation will show a more viable modelling methodology to simulate the deformation mechanics of fibrous materials and it is based on the use of virtual fibres. This recently developed method effectively takes the fibrous behaviour into account by modelling a yarn as a bundle of virtual fibres, see Figure 1. Each virtual fibre is modelled as a chain of truss elements in Abaqus\Explicit. The virtual fibres can realign themselves and slide relative to each other resembling the mechanics in a real yarn. The advantages of this method will be illustrated by applying it to some very complex problems such as the mechanical behaviour of 3D woven fabrics, draping behaviour of fabrics and stitching of sandwich panels

Numerical modelling of in-plane behaviour of adobe walls

Some tests for material characterization of adobe blocks and adobe masonry have been carried out in universities and laboratories around the world. However, the number of tests is quite limited in comparison with those carried out with other structural materials, such as masonry or reinforced concrete, and even those tests just refers to elastic properties. The results of adobe tests (i.e. compression strength, elasticity modulus, shear strength, etc.), as well as the results of cyclic and dynamic tests on adobe masonry components and small buildings show that the mechanical properties of adobe masonry and the seismic performance of adobe constructions highly depend on the type of soil used for the production of units and mortar. Basic properties, such as elasticity modulus, can have significant variation from one soil type to another. The state-of-the-art for the numerical modelling of unreinforced masonry point to three main approaches: macro-modelling, simplified micro-modelling and detailed micro-modelling. In all three approaches, the use of elastic and inelastic parameters is required. For adobe masonry, the lack of knowledge concerning some of the material properties makes numerical modelling more difficult. In the proposed work, the mechanical properties of the typical adobe masonry in Peru have been calibrated based on a cyclic in-plane test carried out on an adobe wall at the Catholic University of Peru (PUCP). The mechanical parameters calibration and the modelling results of the in-plane behaviour of the adobe wall are presented. Macro-modelling and simplified micro-modelling strategies are used in finite element software with an implicit solution strategy. The results of this work represent the first step for the numerical modelling of the seismic behaviour of adobe constructions