Composites trend to failure in their defects, which are randomly distribuited. This causes that the tensile strength decreases when the volumen of material tested increases. This fenomenon is known as size effect or volume effect. Knowing the value of the Weibull parameters is key for modeling and the correct design of large components. In this work, one tensile test are proposed, named the fragmentation test to obtain the shape and scale Weibull parameters that are validated with the scaled test. Carbon/glass hybrid composites can exhibit pseudo-ductile response in the stress-strain curves by having a part with small slope or plateau. The specimen design promotes fragmentation or gradual fracture of carbon layer and suppresses unstable delamination at the plateau. The facture events have been identified by video and accoustic emission monitoring in 11 specimens. The data of fracture strain has been adjusted to the Weibull distribution following the proposed iterative process. The process has been validated using previous results of Finite Elements. The volumen effect has been validated with the results of series of tensile tests, with dimensions scaled by factors of 2,4 and 8 in each direction. Another important advantage of hybridization is the suppression of the stress concentration in the carbon layer, which makes simple end-tab free specimens feasible. The results of two tests have been compared, obtaining very close values.
Abstract
Composites trend to failure in their defects, which are randomly distribuited. This causes that the tensile strength decreases when the volumen of material tested increases. This fenomenon is known as size effect or volume effect. Knowing the value of the Weibull parameters is [...]
Air jet weaving, where the weft yarn is transported through the machine using air as propelling medium, is a popular weaving method due to its superior productivity, however at the cost of a high energy demand. The interactions between the weft yarn and the air jets are complex and not yet fully understood. Moreover, state-of-the-art techniques to simulate these interactions, are far from mature since the yarn is often simplified as a smooth and solid cylinder. Therefore, a novel multi-scale and multi-physics approach is proposed to simulate the interaction between weft yarns and air jets. Starting from microcomputed tomography (µCT) scans of a yarn used in air jet weaving, a high-fidelity microscale geometrical model is constructed, representing the yarn by its fibers. This geometrical model is used as input for microstructural simulations and will be used for flow simulations on microscale, where the aim is to extract local coefficients and as such characterize the yarn. These coefficients are then used as input for computationally cheap macroscale models, where the yarn is represented by its centerline containing the microscale properties. In a final stage, the macroscale structural and flow models will be coupled as to obtain a full FSI simulation of a weft insertion in an air jet loom. Current paper highlights the microscale geometry extraction of a fine wool fiber yarn of 28.8 tex. Consecutively, a computational framework is proposed to simulate the tensile behavior of this yarn, using the previously obtained microscale geometrical model. The resulting stress-strain curve of the yarn is compared to experiments and shows good correspondence.
Abstract
Air jet weaving, where the weft yarn is transported through the machine using air as propelling medium, is a popular weaving method due to its superior productivity, however at the cost of a high energy demand. The interactions between the weft yarn and the air jets are complex [...]