On a numerical strategy to simulate nanotube‐reinforced composite materials

The application of carbon nanotubes as the reinforcing phase in composite materials is considered. A literature review in regards to the simulation approaches that have been done in order to study the behavior of nanotube‐reinforced composites from several aspects is provided. After that, a new approach for investigating the mechanical properties of the composites reinforced with randomly oriented fibers using the finite element method is proposed. The main idea is to create regular shaped islands around the distributed fibers and to connect these islands to each other and to the representative volume element. Two application examples show the flexibility and the reliability of the proposed method. It has been shown that this approach can handle both aligned and arbitrary distributions of the nanotubes.     

Charakterisierung von Randentkohlungsvorgängen bei der Austenitisierung des Wälzlagerstahls 100Cr6. Teil 2: Modellierung des Kohlenstoff‐Tiefenverlaufs mit Hilfe der Methode der Finiten Elemente

Characterization of Decarburisation Processes During Austenitising of the Rolling Bearing Steel 100Cr6. Part 2: Modelling of the Carbon Concentration Profile by Means of the Finite Element Method The quantitative measurement of carbon concentration‐distance curves serves as fundamental prerequisite for the evaluation of rim zone properties connected with decarburisation processes in material science. This was shown in part 1 of the present work with two samples from through‐hardenable rolling bearing steel 100Cr6 (SAE 52100) austenitised in different oxidising atmospheres by position dependent determination of hardness, residual stresses, and X‐ray line broadening ({211} α’‐Fe diffraction line). In practice, it is important to predict carbon concentration‐distance curves under prevailing heat treatment conditions or to conclude conversely from profile measurements. Based on a refined kinetics model of a diffusion‐controlled process, part 2 therefore presents a simulation tool developed by means of the finite element method (FEM). Apart from the concentration dependence of the diffusion coefficient, it also considers the decarburisation induced austenite‐ferrite phase transformation, the time dependent influence of scaling, and variable atmosphere conditions. The interpretation of the carbon concentration‐distance curves, measured very accurately in the rim zone of both 100Cr6 samples by secondary ion mass spectrometry (SIMS), confirms the possibilities of application of the new numerical tool.     

Perspective Measurement of the Out‐of‐plane Displacement and Normal Strain Field Distributions Inside Glass Fibre‐reinforced Resin Matrix Composite

A depth‐resolved wavenumber‐scanning interferometer (DRWSI) was built up to measure the out‐of‐plane displacement and normal strain field distributions on the front surface, rear surface and internal glass fibres of a glass fibre‐reinforced resin matrix composite before and after loading. Series of the fringe patterns were recorded, while the wavenumber of the laser, monitored online by an optical wedge, was scanned by tuning the temperature. Random sampling Fourier transform is used to overcome the non‐linearity of the wavenumber series. In the end, the distributions of the out‐of‐plane displacements and normal strain field are presented as the applied loads were 10 µm, 20 µm and 30 µm, respectively. In conclusion, DRWSI is a suitable method to measure the mechanical properties inside resin composite non‐destructively.     

The investigation of effect of adherend thickness on scarf lap joints

In this paper, the mechanical behavior of the Scarf Lap Joints (SLJs) bonded with adhesive under a tensile load was analyzed. The effects of adherend thickness at the interface stress‐strain distributions of SLJs were examined. The stress‐strain analyses were performed by Finite Element Method (3D‐FEM). The 3D‐FEM code was employed with Ansys (Ver.12.0.1). Experimental results were compared with the 3D‐FEM results and were found quite reasonable. It was concluded that both experimental and 3D‐FEM failure loads were increased with increased adherend thickness. The results indicated that the maximum failure loads were determined at t=8 mm in all joints. The analysis of the SLJs under tensile load showed that the stress and strain concentrations occurred around the edges of the joints.     

Investigation of Residual Stress in 2D Plane Weave Aramid Fibre Composite Plates Using Moiré Interferometry and Hole‐Drilling Technique

Residual stress (RS) is crucial to the fabrications of woven composite plates and difficult to measure experimentally because of the complex structures of these plates. This study aims to investigate the RS in 2D plane weave aramid fiber composite plates using hole‐drilling technique coupled with moiré interferometry. A two‐step drilling method is proposed to solve the problems caused by the ‘peel up’ phenomenon, which facilitates the analyses of the obtained moiré patterns. The holes are deliberately selected at the intersection points of the symmetry axes of warp and weft yarns to obtain symmetrically released displacement fields. Moreover, finite element method calibration is conducted to measure RS using a model created based on the real structure of the woven composite. Based on the error analysis in numerical simulations, the less sensitive points are proposed for the RS calculation. The results show that the RS components of each specimen are compressive along the aramid yarns and tensile perpendicular to them. In addition, investigating of the influence of drilling depths on RS shows that RS decreases along the hole‐depth direction. Findings of this study are helpful for the manufacture and quality evaluation of woven aramid fibre composites.     

Querschnittseinfluss beim Zugversuch von siliziertem kohlenstoffkurzfaserverstärktem Kohlenstoff (C/C‐SiC)

On the influence of cross section in tensile tests of siliconized short carbon fibre reinforced carbon (C/C‐SiC) This study deals with the mechanical testing of a carbon short fibre reinforced ceramic. For this material group, which has already been successfully used in several applications, no valid testing specifications are existing at present. This is one of the reasons why manufacturers and research institutes often make use of test standards for monolithic or composite materials. In these tests, sample cross sections and testing volumes are choosen freely or on the basis of a standard and are accordingly adapted by an appropriate factor. This approach can lead to misinterpretations. Because of the broad variety in the different kinds of fibre reinforced ceramics, this study examines the influence of cross sections in tensile tests in an examplary study on a siliconized short carbon fibre reinforced carbon of the Schunk Kohlenstofftechnik GmbH labeled FU2952/1P77. In order to verify the test results, the fracture surfaces will be examined by means of incident light photography and scanning electron microscopy (SEM).