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PhD Scholarship Position in Multiscale Segmentation and Modeling of Ncf Material

A fully-funded PhD fellowship in mechanical engineering is available at Chalmers University of Technology. This position is available for five years. Potential candidates should apply before January 06, 2019.

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.

[1] K.M. Jespersen, J. Zangenberg, T. Lowe, P.J. Withers, and L.P. Mikkelsen, "Fatigue damage assessment of uni-directional non-crimp fabric reinforced polyester composite using X-ray computed tomography," Compos. Sci. Technol., vol. 136, pp. 94-103, 2016.

[2] M.J. Emerson, K.M. Jespersen, A.B. Dahl, K. Conradsen, and L.P. Mikkelsen, "Individual fibre segmentation from 3D X-ray computed tomography to study the misalignment in unidirectional composite materials," Compos. Part A Appl. Sci. Manuf., no. Accepted with minor revision, 2016.

[3] B.J. Blinzler, D. Wilhelmsson, L.E. Asp, K.M. Jespersen, L.P. Mikkelsen, "A systematic approach to transforming composite 3D images into meso-scale computational models," in proceedings of the 18th European Conference on Composite Materials (ECCM-18), 2018.

Major responsibilities

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

- Micromechanical modeling of the composite microstructure to be used as a sub model in the multi-scale method

- Multi-scale modeling of the global composite test samples with an iterative link to the microstructure via micromechanical modeling

- Techniques of transfer segmented structures in to a multiscale finite element model of a composite on both the non-crimp fabric (3-D bundle structure) level as well as on the sub-bundle (fibre/matrix) level

Segmentation of damage: In order to quantify the 3-D initiation and evolution of fatigue damage, algorithms and software for segments will be explored.

- Segmentation tool of the micro- and meso-structure on the fibre and bundle level: The fibre architecture inside the bundles as well as the 3D bundle structure of the non-crimp fabric need to be segmented for analysis and quantification and later modeling. Used together with mechanical testing, relevant quantification element will be identified.

- X-ray tomography of polymer-based fibre reinforced polymers, including using in-situ stress rigs in order to improving the visibility of fatigue damage.

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

Qualifications

Residency 18 of the last 36 months must be outside Sweden. (Marie Sklodowska-Curie Project Requirement).

We are looking for a candidate to work on image analysis and development of virtural experimentation methods for polymer matrix composite (PMC) materials. The candidate is expected to have a Master's degree (or equivalent) in Mechanical Engineering, Aerospace Engineering, Civil Engineering or similar, with a strong background in mechanics and structures. Excellent problem-solving skills, team-work skills, presentation skills, and fluency in English (both oral and written) are required. Experience from Python, Abaqus, and other simulation software is meritorious.

You should be a quality conscious individual who is positive and motivated, independently directed with dedication and persistence, and strong collaboration skills. Please exemplify in your application, if possible, situations or circumstances where these personal skills have been evident.

Chalmers offers a cultivating and inspiring working environment in the dynamic city ofGothenburg.

Read more aboutworking at Chalmersand ourbenefitsfor employees.

Application procedure

The application should be marked with Ref 20180640 and written in English.

CV: (Please name the document: CV, Family name, Ref. number)

CV

Other, for example previous employments or leadership qualifications and positions of trust.

Two references that we can contact.

Personal letter: (Please name the document as: Personal letter, Family name, Ref. number)

1-2 pages where you introduce yourself and present your qualifications.

Copies of bachelor and/or master's thesis.

Attested copies and transcripts of completed education, grades and other certificates, eg. TOEFL test results.

Application deadline: 6 January, 2019

Prof. Leif Asp, Department of Industrial and Materials Science

Division of Material and Computational Mechanics

leif.asp@chalmers.se, +46 31 772 15 43

Asst. Prof. Brina Blinzler, Department of Industrial and Materials Science

Division of Material and Computational Mechanics brina.blinzler@chalmers.se, +46 31 772 63 36


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