Influence of microfluidic flow rates on the propagation of nano/microcracks in liquid core

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Liquid core and hollow fibers were produced using a melt-spinning process. The internal micro channels of the fibers were employed as a new media for microflow, developing a bundling technique and attaching the fiber bundles to a microfluidic pump. The microflow and leakage behavior of the hollow fibers and LCFs were investigated by means of microfluidic tests and the fracture mechanisms were identified via SEM images of the fractured surfaces. Microfluidic tests indicated that most of the cracks appear in the early stages (low flow rates) of the microfluidic studies. Moreover, LCFs showed a lower number of leakages compared to the hollow fibers. The strengthening and toughening of the LCFs is a result of the thicker sheath walls and the damping properties of the core liquid already present in the fiber. From the SEM images, the main mechanism of crack propagation involves the type I (opening mode) initiated by the mechanical loads during operation in addition to residual stresses, where the cracks are formed preferentially in the axial direction. Optimization of the fiber spinning process can certainly lead to a significant reduction of the already very low proportion of cracks appearing in these fibers. Future work will include a parametric study to analyze the relation between fiber spinning parameters and crack formation, where the insights gained on nano/microcrack formation and propagation will allow to perform an optimization of fiber spinning parameters.

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