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PhD student position in Multiscale Segmentation & Modeling of NCF Material

Chalmers Tekniska Högskola AB - Göteborg - Publicerad: 2018-12-06 13:16:11


The main competencies at the department of Industrial and Materials Science are found in the areas of: Human-Technology Interaction | Form and Function | Modeling and Simulation | Product Development | Material | Production and in the interaction between these areas. The research develops the industrial process, from need to finished product while creating added value. To combine skills throughout the whole chain distinguishes the department both nationally and internationally. Here we gather internationally prominent researchers, in dynamic and outstanding research environments, as well as in national and international research networks.

http://www.chalmers.se/en/departments/ims/


Information about the research
Due to high specific stiffness and strength, and good fatigue properties, fibre composites are increasingly replacing metals in structural applications. Particularly within the aerospace, automotive, and wind turbine industry, fibre reinforced plastics are commonly used. In the design of wind turbine blades, almost purely uni-directional (UD) fibre composites (all the fibres are aligned in one direction) are used for the main spars which carry the gravitational and aerodynamics loads on the blade. These fibre composites are made from non-crimp fabrics (NCFs) that have a fibre bundle structure and are stitched to a thin supporting off-axis bundles layer in order keep them aligned during manufacturing and handling.  During the 20-30 years of life, a wind turbine blade experiences fatigue loads in the range of 50-500 million cycles because of the continuous rotation in addition to variation in the aerodynamic loading. The three key material parameters designing wind turbine blades are the axial stiffness, the compression strength and the fatigue resistance of the load carrying laminates. In order to improve those properties, detailed knowledge of the architecture of the reinforcement, i.e. the fibre, bundle and non-crimp fabric, as well as damage initiation and subsequent damage evolution is essential. Here, the stiffness and the compression strength are mainly governed by the fibre misalignment of the uni-directional fibres while the fatigue performance of the uniform laminates are controlled by the secondary oriented backing bundles as well as local fibre arrangement in the load carrying bundles. Even though the backing bundles are only introduced for handling and manufacturing reasons, it has been shown [1], that cross-over backing bundles with the load carrying uni-directional bundles are a key initiation point for progressive tensile fatigue failure.

In order to analyze, understand and improve NCF based composites, non-destructive testing methods can be used that rely on X-ray computational tomography. Development of case-specific automatically segmentation tools are required to fully utilize these methods. In [2] a segmentation algorithm for segment the fibre architecture inside the fibre bundles has been developed. In addition, tools for segmenting the three-dimensional bundle structures and the fatigue damage are required to achieve the full potential of the 3-D x-ray tomography data. Tools which are in the progress of been developed by DTU Compute. Based on those tools, a multi-scale finite element model will be developed with the purpose of predicting the mechanical performance of existing as well new suggested non-crimp fabrics. Thereby, it is expected to be able to improve the stiffness, the compression strength as well as the fatigue performance with the end goal of being able to produce lighter or longer wind turbine blades and thereby decrease the cost of energy of wind power.

A multi-scale segmentation of the bundle and fibre structure  will be developed where the fibre segmentation inside the bundle structure will focus on the transverse and axial fibre arrangement as well as the resulting fatigue damage evolution.  Based on the segmentation of the 3-D bundle structures from a large field of view x-ray CT scan and a segmentation of the microstructural fibre/matrix architecture of a zoomed field of view scans inside the bundles, a multi-scale finite element will be built as sketched in reference [3]. The finite element model will be based on x-ray scans performed at several regions in order to confirm their representability of the structure. By analysing volumes at the fibre scale, relevant parameters will be extracted and input into the homogenized bundle structure. During the applied PhD-project, a 3-D finite element model of an x-ray based bundle structure will be developed where the mechanical properties of the bundle material will be based on micromechanical models of the physical fibre/matrix structure. The micromechanical model will be used in order to understand the failure mechanism in addition to making it possible to predict the effect of change of the fibre and bundle architecture on the stiffness, compression strength and fatigue given lifetime.

Major responsibilities
The person filling this position will participate in research as outlined above and will be conducting mainly computational modeling. 

Position summary
Full-time temporary employment. The position is limited to a maximum of five years.

Application procedure:
Application form: http://www.chalmers.se/en/about-chalmers/Working-at-Chalmers/Vacancies/Pages/default.aspx?rmpage=job&rmjob=6911

Application deadline: 6 January, 2019


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