Non-tip failure of smooth fissure in 3D printed specimens

Abstract

Non-tip cracking for kinked fissures has been investigated in our previous study. This paper reveals that non-tip cracking also occurs for smooth fissures without kinks. 3D printed photosensitive resin specimens with a smooth S-shape fissure are tested under uniaxial compression. The influence of geometry and orientation of the S-shape fissure on the specimen deformation and strength behaviour, especially the non-tip-cracking failure is investigated. Results show that two cracking patterns, tip-cracking and non-tip cracking, occurs in a similar trend with that observed for kinked fissures. The non-tip cracking is sensitive to the inclination angle β and the ratio between the amplitude and ratio of the amplitude to the half length of the S-shape fissure, i.e., the effective curvature A/a, as it only occurs when β equals to 30°, 45°, 60° and the A/a is equal to or greater than 2/7.5. A simplified piecewise linear crack model is proposed to predict the occurrence of the non-tip cracking failure. The S-shape fissure is approximated by three straight segments and the three failure models A, B and C corresponding to their equivalent straight segments are identified based on the maximum circumferential stress criterion. The cracking pattern of the S-shape fissure is governed by model A and C failure and the predicted cracking patterns match well with the respective experimental ones. The results from the present research complement the traditional fracture mechanics by extending the understanding about non-tip cracking failure.