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Fatigue crack growth in fiber metal laminates: experiment and modeling
Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fiber Metal Laminates (FML) is a class of materials with highly resistant fatigue behavior, developed primary for the aerospace industry. The laminates are comprised of alternating layers of high strength aluminwn sheet and fiber reinforced polymers. The high fatigue resistance is mainly provided by the fatigue resisting fibers bridging the metal fatigue crack.

Several works to describe and to prediet the fiber bridging phenomena and their effect on crack growth rate of the laminate have been published in the literature. Some of these studies have used a modeling approach, where with the help of geometry and constitutive relations the effect or interaction of the fiber bridging and the metal crack propagation rate has been evaluated. Others have used an experimental approach, where the metal crack propagation rate is measured for different load ranges, or with modified reinforcement, to be compared with the behavior of non-reinforced aluminum sheets, so called monolithic sheets.

In this work, an experimental method has been developed and used with the purpose of increasing the understanding of the stress field around a metal crack in fiber metal laminates. The experimental results and the assumptions in the method have been compared with FE analysis. Knowledge of the stress field around a metal crack for fiber-metal laminates is useful for further development in modeling the fiber bridging phenomena in fiber metal laminates.

In order to prove the validity of an effective stress intensity range model found in the literature, a parametric study of some of the key variables of the mode! has been performed. Crack growth tests have been performed to give crack growth data for the fiber-metal-laminates and for the metal sheet material, used in the fiber metal Jaminates. The idea was to compare the fiber-metal-laminates with the meta! sheet material in respect of the crack growth rate - stress intensity range relation.

A comparison between different residual stress measurement methods on FML has been made. The methods used were X-ray diffraction, neutron diffiaction and strain measurement throughout destructively produced stress release. Good agreement was found between the different methods.

Neutron diffraction residual stress measurements have also been performed on fatigue-damaged material, specifically in the wake of a fatigue-induced metal crack in the laminate.

A 3D FEA of a fatigue crack has been made with different fatigue crack geometries. The results has been compared with experimental data for the two crack fronts (delamination growth and metal crack growth).

In order to magnify the role of the delamination shape on metal crack growth in FML, further crack growth tests have been performed. For different levels of the alternating loading different delamination shapes were developed. By changing the level of the alternating loading for some tests, a comparison ofthe metal crack growth at small delamination damage and larger delamination damage could be made. The experimental crack growth results are compared with 3D FEA and other models found in the literature.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2004. , 40 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 861
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-22794Local ID: 2127ISBN: 91-7373-894-8 (print)OAI: oai:DiVA.org:liu-22794DiVA: diva2:243107
Public defence
2004-02-13, Föreläsningssal C3, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-30
List of papers
1. Parametric study for som variabels, which affects the fatigue crack growth of fiber metal laminates
Open this publication in new window or tab >>Parametric study for som variabels, which affects the fatigue crack growth of fiber metal laminates
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Research has been carried out to investigate the crack growth behavior of glass fiber reinforced aluminum laminates (GLARE®). In order to prove the validity of an effective stress intensity range model found in the literature, a parametric study of some of the key variables of the mode! has been performed. Crack growth tests have been performed to give crack growth data for the fiber-metal-laminates and for the metal sheet material, used in the fiber metal larninates. The idée is to compare fibermetal-laminates with metal sheet material with respect to the crack growth rate - stress intensity range relation. The experimental results show that the model seems to overestimate the stress intensity range for test conditions having a high mean stress in the aluminum layers. For the load range used, a high average stress in the aluminum layers also leads to larger delaminations. Any individual change of the key parameters investigated, cannot shift the calculated effective stress intensity range for the fiber-metal-laminates so that the experimental crack growth data fit the crack growth data of the non-reinforced aluminum.

Even if the model overestimates the effective stress intensity range for some test conditions, the model succeeds to describe the overall crack growth behavior of fiber-metal-laminates.

Keyword
stress intensity factor, fiber-metal-laminate, crack growth, delamination
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88096 (URN)
Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2013-11-28
2. The influence of delamination size on fibre reinforcement in fibre metal laminates
Open this publication in new window or tab >>The influence of delamination size on fibre reinforcement in fibre metal laminates
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Research has been carried out to investigate the influence of delamination size for crack growth behaviour of glass fibre reinforced aluminium laminates (GLARE®). The aim of this work has been to investigate to what degree the restraining fibres in the wake of a metal fatigue crack carry load, and to what extent the size and shape of the delamination will affect the magnitude of the fibre-reinforcement. Tests for different delamination shapes by measuring the stiffness change when restraining fibres are removed has been performed and compared with finite element analysis. The investigation shows that the fibres can be assumed to have a constant stress through the metal crack length, and that a smaller delamination gives a higher restraining effect.

Keyword
glare, fibre, reinforcement, aluminium, delamination
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88097 (URN)
Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2013-11-28
3. Residual stress measurement on fiber-metal-laminates
Open this publication in new window or tab >>Residual stress measurement on fiber-metal-laminates
2003 (English)In: Journal of Neutron Research, ISSN 1023-8166, E-ISSN 1477-2655, Vol. 11, no 4, 215-220 p.Article in journal (Refereed) Published
Abstract [en]

A comparison between different residual stress measurement methods on fibre reinforced metal laminates was made. The methods used were X-ray diffraction, neutron diffraction and strain measurement throughout destructively produced stress release. Good agreement was found between the different methods. For these types of laminates, thermally caused residual stresses arise during manufacture. Stretch operation of the laminate will modify the residual stress state. It is well documented that the residual stress state greatly affects the fatigue properties of these laminates, not only during the fatigue initiation stage but also during fatigue crack propagation [1–3]. Neutron diffraction residual stress measurements have also been performed on fatigue-damaged material, specifically in the wake of a fatigue-induced metal crack in the laminate. Delamination and fibre degeneration occur to some extent in the surroundings of the fatigue-induced metal flaw. This will cause a relaxation of the compressive residual stress, and it will affect further development of the fatigue damage.

Keyword
Neutron, X-ray, Diffraction, Residual stress, Glare, Delamination
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88098 (URN)10.1080/10238160410001726639 (DOI)
Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2017-12-06
4. Experimental observations and numerical analysis of fatigue crack development in fiber metal laminates
Open this publication in new window or tab >>Experimental observations and numerical analysis of fatigue crack development in fiber metal laminates
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Experimental and numerical studies have been carried out in order to reveal and explain the crack growth behavior of glass fiber reinforced aluminum laminates (GLARE®). Fatigue crack growth tests with center crack tension specimen have been performed. Optical crack growth measurements for surface cracks combined with in situ ultrasonic measurements, to determine the delamination size and shape, have been conducted. Complimentary fatigue induced delamination growth tests have also been performed, and the results from the two experiments have been compared. A 3D linear elastic model has been developed. Comparison between model and experimental results are made, and suggestions for further development in modeling are given.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88100 (URN)
Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2013-01-30
5. Delamination size dependence on fatigue crack growth in fiber metal laminates
Open this publication in new window or tab >>Delamination size dependence on fatigue crack growth in fiber metal laminates
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A fatigue crack growth study have been carried out in order to reveal the dependence of the delamination shape and size on metal crack growth in fiber metal laminates (GLARE®). Fatigue crack growth tests with center crack tension specimen (CCT) with loading range shifts have been performed. Optical crack growth measurements for surface cracks combined with ultrasonic measurements, to determine the delamination size and shape, have been conducted. Experiment show that the shape of the delamination tip, in particular, but also the delamination size depends strongly on the loading range. The crack growth rate for a given loading range is dissimilar if the prior loading range was different. This dissirnilarity may remain with further crack growth, or disappear with further crack growth. A strong interaction between the development of the delamination tip and a loading shift exists. It is therefore believed that the crack tip shape is causing the dissimilar crack growth rate.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88101 (URN)
Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2013-01-30

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