Numerical Modelling of the Interaction Macro–Multimicrocracks in a Pipe under Tensile Stress

In this paper, the evaluation of the SIFof a macrocrack in interaction with one or several microcracks in a material containing a geometrical defect was investigated. Several configurations were considered in order to apprehend the mechanisms induced by the interaction effect and in particular the effects of reduction and/or amplification of the stress field between macro and single or multiple microcracks. The obtained results show that, macro–microcrack spacing is an important parameter if the microscopic crack is relatively close to the macrocrack-tip. The macrocrack has the tendency to accelerate as it propagates towards the microcrack. When the relative distance characterizing this spacing is higher than 0.3, the interaction effect can be neglected and the SIF remains unchanged for both defect types. When this ratio is lower than 0.3, the interaction between the two defects becomes significant and the stress intensity factor at the macrocrack tip strongly increases.

Cracked tooth diagnosis and treatment: An alternative paradigm

ABSTRACTThis article reviews the diagnosis and treatment of cracked teeth, and explores common clinical examples of cracked teeth, such as cusp fractures, fractures into tooth furcations, and root fractures. This article provides alternative definitions of terms such as cracked teeth, complete and incomplete fractures and crack lines, and explores the scientific rationale for dental terminology commonly used to describe cracked teeth, such as cracked tooth syndrome, structural versus nonstructural cracks, and vertical, horizontal, and oblique fractures. The article explains the advantages of high magnification loupes (×6–8 or greater), or the surgical operating microscope, combined with co-axial or head-mounted illumination, when observing teeth for microscopic crack lines or enamel craze lines. The article explores what biomechanical factors help to facilitate the development of cracks in teeth, and under what circumstances a full coverage crown may be indicated for preventing further propagation of a fracture plane. Articles on cracked tooth phenomena were located via a PubMed search using a variety of keywords, and via selective hand-searching of citations contained within located articles.

Studies on Crack Propagation of Carbon Fiber Reinforced Epoxy Resin Composite

Unidirectional carbon fibre reinforced resin matrix composite (CFRP) with different fibre volume fraction are stretched dynamically under static load in SEM, initiation and propagation mechanism of crack is in-situ observed, and tensile fracture of specimens is also observed. The results show that: Microscopic cracks are mainly originated from fracture of fibre, numerous fibre cracks transfixion each other in form of matrix or interface cracking, and cause failure of CFRP. Microscopic crack propagation path is related to the thickness of matrix layer between fibres. Propagation of single fibre crack at interface accord with description of microscopic crack deflection criterion for fibre reinforced composite, but the crack deflection criterion cannot descript microscopic crack propagation mechanism of unidirectional CFRP effectively, because distribution discreteness of fibre and its strength are not considered.

Application of Multifractal to Characterize Microscopic Crack Propagation in Red Sandstone

Most of existing studies on rock damage are focused on investigating the macroscopic stress-strain relationship, and only limited research is available on analyzing the microscopic crack propagation due to measurement difficulty, cumbersome data reduction procedures, and complexity of damage in micro-level. In this study, a powerful image-processing program is developed to extract the microscopic crack distribution from the digital image of microscopic crack status of red sandstone, and the microscopic crack propagation of red sandstone under single-axial pressure is then evaluated by the technique of multifractal. It demonstrates that the microscopic crack distribution possesses the multifractal character, and the capacity dimension of multifractal singular spectrum can be used to quantitatively characterize the microscopic crack propagation of red sandstone. By comparing the stress-strain relationship with the one of stress-capacity dimension, the capacity dimension is capable of acting as a physical quantity to effectively reflect the damage of red sandstone by the means of characterizing its microscopic crack propagation.