Characterization by micromechanical approaches of fiber/matrix interfacial properties in C fiber and polymer matrix composites
Topic(s) : Experimental techniques
Co-authors :
Milena TOSTI UMEMURA (FRANCE), Florent DALMAS (FRANCE), Pascal REYNAUD (FRANCE), Jérôme BIKARD , Didier LONG , Gilbert FANTOZZIAbstract :
Long fiber-reinforced polymers are increasingly used as high-performance composite materials, for a large diversity of applications. In this context, carbon fiber (CF) reinforced poly ether ether ketone (PEEK) composites are one of the most promising thermoplastic matrix composites, due to excellent thermal and chemical stability and elevated mechanical properties. However, failure properties of composite materials remain a subject of research, as better comprehension requires multi-scale experiments and modelling. The fiber/matrix interface determines the quality of the load transfer from the matrix to the fiber and its properties are key for the mechanical and damage tolerance of composites [1]. Interface quality is influenced by a diversity of physico-chemical factors, such as the chemical composition of fiber and matrix, fiber surface roughness, adhesion, and processing. Debonding modelling remains a hurdle, especially in thermoplastic composites, as PEEK, reinforced with continuous CF, needing to consider non-linear fracture mechanics with plasticity both at interface and matrix level. Different techniques were developed for the characterization of the interface’s quality, being micromechanical tests with single fiber samples widely used, even though the representativeness of mechanical properties obtained by it on the final commercial composite is still questionable.
In this study, the interfacial properties between two carbon fiber, with different surface roughness, and PEEK were compared. Single carbon fiber embedded in PEEK samples were submitted to transverse tensile tests and analyzed in situ by scanning electron microscopy (SEM). A refined speckle of Au nanoparticles deposited on the surface of the sample (Figure 1) allows Digital Image Correlation (DIC) aiming in the determination of the strain field formed in the polymeric zone neighboring the fiber, as well as fracture initiation and propagation. However, debonding is believed to be a 3D phenomenon, and properties obtained in the extreme surface are not fully representative [2]. Hence, transverse tensile tests and fragmentation tests with in situ tomography monitoring were performed in single fiber samples in order to be compared with SEM observation. The same tests in model unidirectional composites with higher fiber volume fraction evidences the effects of neighboring fibers in the fracture properties of composite materials, and are expected to enlighten the link between mechanical properties obtained at the microscale to those of unidirectional composites at the macroscale.
In this study, the interfacial properties between two carbon fiber, with different surface roughness, and PEEK were compared. Single carbon fiber embedded in PEEK samples were submitted to transverse tensile tests and analyzed in situ by scanning electron microscopy (SEM). A refined speckle of Au nanoparticles deposited on the surface of the sample (Figure 1) allows Digital Image Correlation (DIC) aiming in the determination of the strain field formed in the polymeric zone neighboring the fiber, as well as fracture initiation and propagation. However, debonding is believed to be a 3D phenomenon, and properties obtained in the extreme surface are not fully representative [2]. Hence, transverse tensile tests and fragmentation tests with in situ tomography monitoring were performed in single fiber samples in order to be compared with SEM observation. The same tests in model unidirectional composites with higher fiber volume fraction evidences the effects of neighboring fibers in the fracture properties of composite materials, and are expected to enlighten the link between mechanical properties obtained at the microscale to those of unidirectional composites at the macroscale.