Abstract
Discontinuous carbon fiber-carbon matrix composites dispersed Si/SiC matrix composites have complicated microstructures that consist of four phases (C/C, Si, SiC, and C/SiC). The crack stability significantly depends on their geometrical arrangement. Nondestructive evaluation is needed to maintain the components in their safe condition. Although several nondestructive evaluation methods such as the Eddy current have been developed, any set of them is still inadequate in order to cover all of the scales and aspects that (C/C)/Si/SiC composites comprise. We propose a new method for nondestructive evaluation using vibration/resonance modes and deep learning. The assumed resolution is mm-order (approx. 1–10 mm), which laser vibrometers are generally capable of handling sufficiently. We utilize deep neural networks called convolutional auto-encoders for inferring damaged areas from vibration modes, which is a so-called inverse problem and infeasible to solve numerically in most cases. We solve this inference problem by training convolutional auto-encoders using vibration modes obtained from a non-damaged specimen with various frequencies as the dataset. Experimental results show that the proposed method successfully detects the damaged areas of validation specimens. One of the noteworthy points of this method is that we need only a few specimens for training deep neural networks, which generally require a large amount of data.
Highlights
Discontinuous carbon fiber-carbon matrix (C/C) composites dispersed Si/SiC matrix composites (hereafter denoted as (C/C)/Si/SiC composites) have been expected for applications of light-weight structural components, such as car/motorbike brake disks [1,2], emergency brakes for elevators [3], and high-performance wear components, etc
Mechanical performances of (C/C)/Si/SiC composites have been extensively studied [4], and those reports have shown unique mechanical performances of the composites, which are difficult to obtain for monolithic ceramics and metals
The microstructure of the composites is complicated: the structure consists of four major phases, C/C, Si, SiC, and C/SiC [8], and the crack stability in the composite is affected by the geometrical arrangement of these four major phases [8]
Summary
Discontinuous carbon fiber-carbon matrix (C/C) composites dispersed Si/SiC matrix composites (hereafter denoted as (C/C)/Si/SiC composites) have been expected for applications of light-weight structural components, such as car/motorbike brake disks [1,2], emergency brakes for elevators [3], and high-performance wear components, etc. In application, (C/C)/Si/SiC composites are subjected to various kinds of mechanical damage. Such as damage should be detected at maintenance periods, where it is decided whether the components are continuously used or replaced. Once a composite has a source of some stress concentration where tensile/shear loads are applied, the composite falls into a dangerous situation as a component-bearing load because the fracture strength of the composite becomes ~ √KaIc : ae f f is the effective crack size [7]. The effective crack size, ae f f , means ef f the length scale for possible application of continuum mechanics (at least ten times larger than the microstructural units [7]). Dangerous mm-order damage zones including cracks close to ae f f ~ mm order should be detected with a relatively simple process for safe operation
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