16 Oct Hygrothermal effeccts on CFRP: testing, analysis and structural optimization
Last November 13th, the AMADE’s researcher Lorena Marín got her PhD in Technology for the research work titled:
Hygrothermal effeccts on CFRP: testing, analysis and structural optimization
Advisor: Dr. Daniel Trias
Structural aircraft components are expected to be exposed to a wide range of changes in the environmental conditions during their service. In the common design and certification process, a large number of experimental tests, going from simple small specimens to the full structure, are performed. In these tests, all the environmental conditions, especially temperature and humidity, which the structural component will be submitted are considered. This multiplies the number of tests to be performed. With the aim of reducing the economic cost and the time needed for the design and the certification of components, numerical tools that allow a reduction of experimental tests and help in the analysis of results, are developed. In this framework, the present doctoral thesis tackles the topic of hygrothermal effects in composite materials in both fields: experimental tests and numerical tools. Specifically, the thesis focuses its attention on two analysis levels which are seldom present in the scientific literature: the optimization of structural components considering environmental changes and the experimental characterization of the translaminar failure of the material under different environmental conditions.
With respect to the structural components, an optimization methodology for stiffened panels is presented. This methodology is based on genetic algorithms and uses a neural network as a metamodel. The proposed methodology is able to find the optimal panel geometry, for a set of different environmental changes together with mechanical loads, in a short time.
On the other hand, the experimental characterization with hygrothermal effects is considered for the translaminar toughness. A test campaign is performed using the Double Edge Notched Tensile specimen. The broken specimens are observed by means of Scanning Electron Microscopy in order to analyse how temperature and moisture effects influence the failure mechanisms. The general conclusion is that the quality of the fibre/matrix interface plays a key role in the translaminar toughness since it is linked to failure mechanisms such as constituent debonding and fiber pull-out. With moisture, a slight weakening of the fiber/matrix interface and small fiber pull-out are produced but humidity reduces the friction coefficient between constituents, which reduces the amount of energy needed to produce slippage between fiber and matrix and, consequently, the material toughness. Conversely, elevated temperature and humidity cause a weakening in the interface in a way that in the failure process a large number of long fiber pull outs are produced, which dissipate an important amount of energy. In this way, translaminar fracture toughness is slightly reduced because of humidity but its value grows under high humidity and temperature conditions.
Members of the panel
- Dr. Ever Barbero, West Virginia University (President)
- Dr. Faustino Mújika, Euskal Herriko Unibersitatea (Vocal)
- Dr. Euskal Herriko Unibersitatea, Universitat de Girona (Secretario)
- L. Marín, D. Trias, P. Badalló, G. Rus, J. A. Mayugo. Optimization of composite stiffened panels under mechanical and hygrothermal loads using neural networks and genetic algorithms. Composites Structures 2012; 94(11):3321-6. (doi:10.1016/j.compstruct.2012.04.024:10.1016/j.compstruct.2012.04.024)