What is crack density?
Given this limitation, crack density, defined as the number of cracks per unit volume of rock, is often used to estimate the number of micro-cracks in a rock instead [4], assuming that their proportions are related.
What is matrix cracking?
Matrix cracking is a major pattern of the failure of composite materials. A crack can form in the matrix during manufacturing, or be produced during loading. Erdogan, Gupta, and Ratwani (1974) first considered the interaction between an isolated circular inclusion and a line crack embedded in infinite matrix.
What is crack initiation?
Crack initiation is a process that forms cracks on the surface of a material. The primary reason for the formation of cracks on any surface is fatigue. Fatigue leads to progressive and localized structural damage when any material experiences cyclic loading.
Is the initiation and propagation of cracks in a material due to cyclic loading?
Nucleation and propagation of cracks caused by cyclic loading leads to catastrophic failure at stress much lower than yield strength. In case of ductile welded joint, crack-initiation period is shorter than the crack-propagation period due to the existence of sharp-edged discontinuities in welds.
What is crack porosity?
Crack density parameter – in whose terms the effective elastic or conductive properties are expressed – contains no reference to crack openings and hence to “crack porosity”. It is shown that, under certain conditions, crack density can be estimated from the porosity data.
What is crack coalescence?
Coalescence is produced by the linkage of two flaws by a combination of wing and secondary cracks. When coalescence occurs through wing cracks or a combination of wing and secondary cracks, the process is stable.
What causes crack propagation?
Generally, a crack is propagated through two different methods: the plastic deformation around the crack tip and the shear-stress effect at the planes oriented at 45◦ to the loading direction.
How are cracks formed in materials?
Cracking is a common damage caused by stress in a material that can easily be exaggerated by other factors, including corrosion, fatigue, high pressure, and material of construction.
How do cracks propagate?
A crack is propagating through the structure. The evolution is assumed to be quasi-static: at each time , the structure is in elastic equilibrium with the load at , and this for any admissible crack state at .
What is crack tip singularity?
Stress singularity in elasticity indicates a point at which the stress is infinite. Therefore, the stress field near the crack tip is recognized as stress singularity.
What is crack front?
The crack front is the forward part of the crack. Abaqus uses the crack front to compute the first contour integral using all of the elements inside the crack front and one layer of elements outside the crack front. Abaqus computes the contour integral at each node along the crack line.
What is crack material?
Crack: A place in or on a solid material where there is an absence of solid material, and the linear magnitude of either one or two dimensions of this absence (its length and/or width) greatly exceed the linear magnitude of its third dimension.
What are the physical and chemical properties of crack rocks?
Physical and chemical properties. In purer forms, crack rocks appear as off-white nuggets with jagged edges, with a slightly higher density than candle wax.
What is the difference between crack cocaine and regular cocaine?
Whereas cocaine hydrochloride cannot be smoked (burns with no effect), crack cocaine when smoked allows for quick absorption into the blood stream, and reaches the brain in eight seconds. Crack cocaine can also be injected intravenously with the same effect as powder cocaine.
What are the physiological effects of crack cocaine?
Main physiological effects of crack cocaine. The short-term physiological effects of cocaine include constricted blood vessels, dilated pupils, and increased temperature, heart rate, and blood pressure. Some users of cocaine report feelings of restlessness, irritability, and anxiety.
What are the health risks of smoking crack?
Like other forms of cocaine, smoking crack can increase heart rate and blood pressure, leading to long-term cardiovascular problems. Some research suggests that smoking crack or freebase cocaine has additional health risks compared to other methods of taking cocaine.