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Durability of high-performance Thin-Ply composites
Citation Link: https://doi.org/10.15480/882.3949
Publikationstyp
Doctoral Thesis
Date Issued
2021
Sprache
English
Author(s)
Advisor
Referee
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2021-09-30
TORE-DOI
First published in
Number in series
40
Citation
Technisch-wissenschaftliche Schriftenreihe / TUHH Polymer Composites (40) : (2021)
To decrease the weight of composite structures further, it is essential to develop a method to exploit the full potential of carbon fibres. One approach is to reduce the layer thickness. As a result, the degree of freedom in design and the tensile and compressive strength increases. However, the use of thinner layer thicknesses leads to a higher notch sensitivity and premature failure in areas of high stress concentrations. Unfortunately, concerning structural applications, a compromise has to be made.
Therefore, this thesis examines the research hypothesis:
Thin-Ply composites improve the lightweight potential of primary structures
Four limitations regarding the use of Thin-Ply composites in primary structures were identified, and working assumptions were formulated, which were investigated experimentally:
1. Local steel hybridisation of Thin-Ply laminates reduces the impact of stress concentrations and strength degradation
2. Local steel hybridisation of Thin-Ply laminates improves load-bearing capacity
3. Reducing the layer thickness improves the durability under fatigue loading
4. Reducing the layer thickness improves the fatigue behaviour of structures with impact damage
To reduce the impact of stress concentrations and improve the bearing strength 90° CFRP layers are substitute locally by stainless steel foils. The open hole tensile strength increases significantly with increasing steel content. Even if the strength is related to the density, the specific strength increases by up to 36 % and the notch sensitivity decreases. The bearing strength increases by 54.6 % due to the buckling support of the steel foils.
Fatigue tests were carried out with and without impact damage under different load ratios. Reducing the layer thickness and improving long-term behaviour can be achieved independent of the load ratio. The results of the impacted samples show that the layer thickness, the shape of the delaminations and the thickness and structure of the sub-laminates are decisive for the long-term behaviour. Computed tomography images show that the damaged areas of Thin-Ply samples do not increase during fatigue loading. In contrast, the damage of Thick-Ply samples growths progressively throughout the whole sample with increasing numbers of cycles until final failure.
In summary, the research hypothesis can be verified, and Thin-Ply composites improve the lightweight potential of primary structures.
Therefore, this thesis examines the research hypothesis:
Thin-Ply composites improve the lightweight potential of primary structures
Four limitations regarding the use of Thin-Ply composites in primary structures were identified, and working assumptions were formulated, which were investigated experimentally:
1. Local steel hybridisation of Thin-Ply laminates reduces the impact of stress concentrations and strength degradation
2. Local steel hybridisation of Thin-Ply laminates improves load-bearing capacity
3. Reducing the layer thickness improves the durability under fatigue loading
4. Reducing the layer thickness improves the fatigue behaviour of structures with impact damage
To reduce the impact of stress concentrations and improve the bearing strength 90° CFRP layers are substitute locally by stainless steel foils. The open hole tensile strength increases significantly with increasing steel content. Even if the strength is related to the density, the specific strength increases by up to 36 % and the notch sensitivity decreases. The bearing strength increases by 54.6 % due to the buckling support of the steel foils.
Fatigue tests were carried out with and without impact damage under different load ratios. Reducing the layer thickness and improving long-term behaviour can be achieved independent of the load ratio. The results of the impacted samples show that the layer thickness, the shape of the delaminations and the thickness and structure of the sub-laminates are decisive for the long-term behaviour. Computed tomography images show that the damaged areas of Thin-Ply samples do not increase during fatigue loading. In contrast, the damage of Thick-Ply samples growths progressively throughout the whole sample with increasing numbers of cycles until final failure.
In summary, the research hypothesis can be verified, and Thin-Ply composites improve the lightweight potential of primary structures.
Subjects
Thin-Ply
Fatigue
CFRP
Hybrid material
impact
DDC Class
620: Ingenieurwissenschaften
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