What is crack initiation and propagation?
Crack initiation and propagation occur in a fractured structure under dynamic loading, resulting in structure failure or crack arrest. The condition of these processes is called a criterion.
What are the main steps of the crack propagation?
Basically, fatigue crack propagation can be divided into three stages: stage I (short cracks), stage II (long cracks) and stage III (final fracture). Stage I: Once initiated, a fatigue crack propagates along high shear stress planes (45 degrees), as schematically represented in Figure 1.
How dislocations initiate crack propagation?
(a) Dislocation behaviour [19] is a key mechanism at crack initiation. This effect is widely accepted [19]. This effect causes the slip planes to extrude or intrude, which results in stress concentration at the surface and then leads to crack nucleation.
Is the initiation and propagation of cracks in a material due to cyclic loading?
Fatigue failure is the formation and propagation of cracks due to a repetitive or cyclic load. Most fatigue failures are caused by cyclic loads significantly below the loads that would result in yielding of the material.
What initiates the crack in fatigue?
Dislocations play a major role in the fatigue crack initiation phase. It has been observed in laboratory testing that after a large number of loading cycles dislocations pile up and form structures called persistent slip bands (PSB).
How many modes are there for crack propagation?
Explanation: opening, sliding and tearing are the 3 modes.
What is crack propagation in concrete?
It is a measure of the resistance of a material to the propagation of an existing crack and is sometimes called the fracture toughness. The energy release rate G may be related to the elastic stress and displacement fields near the tip of a crack in a homogeneous material.
What is the final stage of crack propagation?
fatigue life prediction methods in metallic components consider three stages: crack initiation (consisting of two phases: crack nucleation and small crack growth, respectively), long crack propagation and final fracture.
What is crack propagation in metals?
Fatigue-crack propagation in ductile metallic materials In simplified concept, it is the accumulation of damage from the cyclic plastic deformation in the plastic zone at the crack tip that accounts for the intrinsic mechanism of fatigue crack growth at K levels below Kc.
Crack initiation and propagation occur in a fractured structure under dynamic loading, resulting in structure failure or crack arrest. Crack initiation models based on physical modeling principles are now well understood and can be used to account for deviations from standard operating conditions.
What is the condition of crack propagation called?
Crack initiation and propagation occur in a fractured structure under dynamic loading, resulting in structure failure or crack arrest. The condition of these processes is called a criterion. The condition of these processes is called a criterion.
What is the Rankine criterion for crack initiation?
Crack initiation follows the Rankine criterion, in which crack is introduced once the maximum principal stress in the tip element exceeds the tensile strength, and the normal direction of the crack is consistent with that of the maximum principal stress. From: Seismic Safety Evaluation of Concrete Dams, 2013
Why measure crack initiation and growth in EAC testing?
The measurement of crack initiation and growth is of crucial importance in rising displacement EAC testing. The crack initiation is to be detected, and the actual length is recorded, together with the applied force, the key parameter for calculating the stress intensity factor.