Synchrotron radiation holotomography for in-situ 3D monitoring of longitudinal debonding around fibre breaks
Topic(s) : Special Sessions
Co-authors :
Thanasis CHATZIATHANASIOU (BELGIUM), Christian BREITE (BELGIUM), Sina AHMADVASHAGHBASH (BELGIUM), Babak FAZLALI , Martin DIEHL (BELGIUM), Mahoor MEHDIKHANI (BELGIUM), Yentl SWOLFS (BELGIUM)Abstract :
A single fibre fragmentation test (SFFT) is one of the most established testing methods to extract interfacial shear properties of fibre-reinforced composites. The test consists of a single fibre composite subjected to longitudinal tension. The applied load is transferred from the matrix into the fibre through interfacial shear stresses. As the tensile load increases, the fibre tends to fracture first into fragments since the failure strain of the fibre is typically lower than that of the matrix. The local fibre stress at the break site becomes zero. Fragmentation proceeds to saturation, where the fibre fragments reach the so-called “ineffective length”.
To extract the interfacial shear strength from SFFT tests, the probabilistic nature of the fibre strength needs to be incorporated into the data reduction via Weibull statistics [1]. The identification of the Weibull parameters requires the consistent tracing of the fibre fragments. Therefore, the tests are typically coupled with optical microscopy. While this setup is relatively easy to implement for a transparent matrix and an opaque fibre, it is not the case for an opaque matrix or a transparent fibre, like glass fibre. Furthermore, when interfacial shear toughness is sought after, the 3D debond volume ideally needs to be monitored, which cannot be achieved using optical microscopy.
Considering these limitations, in-situ fragmentation tests were conducted at the ID16B beamline at the European Synchrotron Radiation Facility (ESRF) [2]. The unique capabilities of ID16B, in terms of (a) variable spatial resolution down to 50 nm voxel size, (b) phase-contrast imaging mode (holotomography), and (c) fast acquisition times, were deemed essential to scrutinise the micromechanical in-situ damage behaviour of the material under study. Two types of fibres were investigated: (a) carbon fibre T700SC and (b) glass fibre Advantex® R25HX14. The fibres were embedded in an SR8500-KTA313 two-component epoxy.
The in-situ fragmentation tests were conducted using an in-house developed miniature loading rig, compatible with the requirements set by the beamline in terms of weight (< 200 g) and dimensions. The rig allowed exerting a tensile load onto the single-fibre specimens at load levels pre-calculated based on the specimen’s expected ultimate tensile stress (UTS). After each desired load step was reached, a holotomography scan was acquired.
Successful tests were conducted for both fibre types, granting 3D insight into the in-situ fibre fragmentation process (Figure 1). For the first time, longitudinal debonding was visualised in 3D, which, through a thorough image analysis procedure, sheds light on aspects such as the in-situ length (volume) of the debond and its uniformity along the radial direction.
To extract the interfacial shear strength from SFFT tests, the probabilistic nature of the fibre strength needs to be incorporated into the data reduction via Weibull statistics [1]. The identification of the Weibull parameters requires the consistent tracing of the fibre fragments. Therefore, the tests are typically coupled with optical microscopy. While this setup is relatively easy to implement for a transparent matrix and an opaque fibre, it is not the case for an opaque matrix or a transparent fibre, like glass fibre. Furthermore, when interfacial shear toughness is sought after, the 3D debond volume ideally needs to be monitored, which cannot be achieved using optical microscopy.
Considering these limitations, in-situ fragmentation tests were conducted at the ID16B beamline at the European Synchrotron Radiation Facility (ESRF) [2]. The unique capabilities of ID16B, in terms of (a) variable spatial resolution down to 50 nm voxel size, (b) phase-contrast imaging mode (holotomography), and (c) fast acquisition times, were deemed essential to scrutinise the micromechanical in-situ damage behaviour of the material under study. Two types of fibres were investigated: (a) carbon fibre T700SC and (b) glass fibre Advantex® R25HX14. The fibres were embedded in an SR8500-KTA313 two-component epoxy.
The in-situ fragmentation tests were conducted using an in-house developed miniature loading rig, compatible with the requirements set by the beamline in terms of weight (< 200 g) and dimensions. The rig allowed exerting a tensile load onto the single-fibre specimens at load levels pre-calculated based on the specimen’s expected ultimate tensile stress (UTS). After each desired load step was reached, a holotomography scan was acquired.
Successful tests were conducted for both fibre types, granting 3D insight into the in-situ fibre fragmentation process (Figure 1). For the first time, longitudinal debonding was visualised in 3D, which, through a thorough image analysis procedure, sheds light on aspects such as the in-situ length (volume) of the debond and its uniformity along the radial direction.