Quantitative prediction of fracture toughness (K_Ic) of polymer by fractography using deep neural networks

Fracture surfaces provide various types of information about fracture. The fracture toughness KIc, which represents the resistance to fracture, can be estimated using the three-dimensional (3D) information of a fracture surface, i.e. its roughness. However, this is time-consuming and expensive to obtain the 3D information of a fracture surface; thus, it is desirable to estimate KIc from a two-dimensional (2D) image, which can be easily obtained. In recent years, methods of estimating a 3D structure from its 2D image using deep learning have been rapidly developed. In this study, we propose a framework for fractography that directly estimates KIc from a 2D fracture surface image using deep neural networks (DNNs). Typically, image recognition using a DNN requires a tremendous amount of image data, which is difficult to acquire for fractography owing to the high experimental cost. To compensate for the limited number of data, in this study, we used the transfer learning (TL) method and constructed high-performance prediction models even with a small dataset by transferring machine learning models trained using other large datasets. We found that the regression model obtained using our proposed framework can predict KIc in the range of approximately 1–5 [MPa\sqrtm] with a standard deviation of the estimation error of approximately ±0.37 [MPa\sqrtm]. The present results demonstrate that the DNN trained with TL opens a new route for quantitative fractography by which parameters of fracture process can be estimated from a fracture surface even with a small dataset.