The yarn/matrix interface in composite materials: fragmentation tests and micro-CT based digital volume correlation
Topic(s) : Special Sessions
Co-authors :
Quentin DROUHET (FRANCE), Fabienne TOUCHARD (FRANCE), Laurence CHOCINSKI-ARNAULT (FRANCE), David MELLIER (FRANCE), Teddy FOURNIERAbstract :
Plant fibre composites compete with glass fibre composites in terms of specific mechanical properties. This is an increasing motivation for industry to consider them in the development of structural or semi-structural products. However, it is important to consider the quality of the yarn/matrix interface because debonding can have important consequences on the mechanical properties of the composite. Moreover, hydrothermal conditions can induce damage at the yarn/matrix interface, especially in the case of natural fibre reinforced polymer [Bhuvaneswari, 2022].
In this study, the hemp/epoxy interface quality is investigated through different scales and different techniques. First, microtomographic acquisitions were performed on woven hemp/epoxy composites at different stages of hydrothermal fatigue ageing, before and after mechanical testing. Image segmentations were made by using an artificial intelligence based Fiji plug-in named Weka Trainable Segmentation 3D. Due to the large amount of data, segmentations were realised by using the supercomputer facilities at the Mesocentre SPIN hosted by the University of Poitiers. The reconstructed volumes allowed to determine the damage rate as a function of the ageing and its influence on the mechanical behaviour. Results showed the predominant role of the yarn/matrix interface.
Then, at a lower scale, the interfacial shear strength (IFSS) values were calculated for different pairs of treated or not hemp yarns/matrices. To do this, fragmentation tests were carried out on single yarn composite samples by using a tensile testing machine. For each test, the crosshead speed was determined to obtain the maximum number of yarn breaks in the gauge length of the sample. This crosshead speed is material-dependent. This study made it possible to classify each yarn/matrix pair from the one with the best quality of adhesion at the interface to the one with the worst. In particular, the plasma treatment realised at the CANOE platform (Pessac, France) produced promising results [Barbière, 2021].
Finally, the internal full-field strains in a single yarn composite during fragmentation test were measured by coupling micro-CT scans with digital volume correlation (DVC). An interrupted fragmentation test was performed on a single hemp yarn composite. DVC calculations were made by using the opensource Matlab code ALDVC [Yang, 2020]. This enabled to follow the full-field strain evolution at the yarn/matrix interface throughout the test and to better understand the stress-strain redistribution which occurs when fibre breaks appear in the yarn [Drouhet, 2023] (Figure 1).
In this study, the hemp/epoxy interface quality is investigated through different scales and different techniques. First, microtomographic acquisitions were performed on woven hemp/epoxy composites at different stages of hydrothermal fatigue ageing, before and after mechanical testing. Image segmentations were made by using an artificial intelligence based Fiji plug-in named Weka Trainable Segmentation 3D. Due to the large amount of data, segmentations were realised by using the supercomputer facilities at the Mesocentre SPIN hosted by the University of Poitiers. The reconstructed volumes allowed to determine the damage rate as a function of the ageing and its influence on the mechanical behaviour. Results showed the predominant role of the yarn/matrix interface.
Then, at a lower scale, the interfacial shear strength (IFSS) values were calculated for different pairs of treated or not hemp yarns/matrices. To do this, fragmentation tests were carried out on single yarn composite samples by using a tensile testing machine. For each test, the crosshead speed was determined to obtain the maximum number of yarn breaks in the gauge length of the sample. This crosshead speed is material-dependent. This study made it possible to classify each yarn/matrix pair from the one with the best quality of adhesion at the interface to the one with the worst. In particular, the plasma treatment realised at the CANOE platform (Pessac, France) produced promising results [Barbière, 2021].
Finally, the internal full-field strains in a single yarn composite during fragmentation test were measured by coupling micro-CT scans with digital volume correlation (DVC). An interrupted fragmentation test was performed on a single hemp yarn composite. DVC calculations were made by using the opensource Matlab code ALDVC [Yang, 2020]. This enabled to follow the full-field strain evolution at the yarn/matrix interface throughout the test and to better understand the stress-strain redistribution which occurs when fibre breaks appear in the yarn [Drouhet, 2023] (Figure 1).