Prediction of mode I fracture toughness of rock using linear multiple regression and gene expression programming

Prediction of mode I fracture toughness(KIC) of rock is of significant importance in rock engineering analyses. In this study, linear multiple regression(LMR) and gene expression programming(GEP)methods were used to provide a reliable relationship to determine mode I fracture toughness of rock. The presented model was developed based on 60 datasets taken from the previous literature. To predict fracture parameters, three mechanical parameters of rock mass including uniaxial compressive strength(UCS), Brazilian tensile strength(BTS), and elastic modulus(E) have been selected as the input parameters. A cluster of data was collected and divided into two random groups of training and testing datasets.Then, different statistical linear and artificial intelligence based nonlinear analyses were conducted on the training data to provide a reliable prediction model of KIC. These two predictive methods were then evaluated based on the testing data. To evaluate the efficiency of the proposed models for predicting the mode I fracture toughness of rock, various statistical indices including coefficient of determination(R2),root mean square error(RMSE), and mean absolute error(MAE) were utilized herein. In the case of testing datasets, the values of R2, RMSE, and MAE for the GEP model were 0.87, 0.188, and 0.156,respectively, while they were 0.74, 0.473, and 0.223, respectively, for the LMR model. The results indicated that the selected GEP model delivered superior performance with a higher R2value and lower errors.

Investigation of stress corrosion cracking behavior and mechanism analysis of a 1900 MPa-grade ultra-high-strength stainless steel

The stress corrosion cracking(SCC)behavior of a 1900 MPa-grade ultra-high-strength stainless steel in 3.5 wt.% NaCl solution was investigated by X-ray diffractometer,scanning electron microscopy,electron back-scattered diffraction,X-ray photoelectron spectroscopy,and potentiodynamic polarization curves.The results showed that USS122G stel has good SCC resistance,and the critical stress intensiy factor(K_(iscc))of USS122G steel was about 68.906 MPa m^(1/2) and Kiscc/K_(ic)=0.76(K_(ic) is plane strain fracture toughness).The existence of film-like austenite along the lath martensite boundary and the protective effect of thecc passivation flm were the main factors for its high Kiscc.Among them,the main components of the passivation film on the surface of USS122G steel were Cr_(2)O_(3),Cr(OH)_(3),FeOOH,and Ni(OH)_(2).The fracture morphology of SCC zone was intergranular and transgranular.Through the slow and fast scanning rate polarization curve test results,it can be concluded that SCC mechanism of USS122G steel in 3.5 wt.%NaCl solution at the open-circuit potential was a mixed mechanism involving hydrogen embritlement and anodic dissolution.