What are the conditions of Lefm?
LEFM implies r−1/2 stress and strain singularities at the crack tip, whereas real materials are damaged or yield plastically so that the stresses cannot exceed a certain limit, σc. Damaged and plastic zones perturb the LEFM solutions near the crack tip.
What is Lefm and Epfm?
LEFM is used for material conditions which are predominantly linear elastic during the fatigue process. • For crack growth or fracture conditions that violate this basic. assumption, elastic-plastic fracture mechanics (EPFM) approaches are used to describe the fatigue and fracture process.
What is Epfm?
Elastic plastic fracture mechanics (EPFM) arose from the desire to use fracture mechanics in situations of greater plasticity, where the crack-tip plastic zone is comparable in size to the crack length or specimen dimensions, including the extreme case where the crack is growing in a completely plastic strain field.
What is critical crack length?
The critical crack length is a term used to describe the defects in materials. It is the length of the crack that grows after the fracture occurs rapidly at the same stress.
What is critical stress intensity factor?
The critical stress intensity factor is used to calculate the fracture strength of a material containing a crack. Unlike some other material properties such as elastic modulus, the critical stress intensity factor of a ductile material is not a constant property but changes with the thickness of the material.
What is the central assumption of linear elastic fracture mechanics?
One basic assumption in Irwin’s linear elastic fracture mechanics is small scale yielding, the condition that the size of the plastic zone is small compared to the crack length.
What causes a brittle fracture?
Brittle fracture is often caused by low temperatures. If the steel temperature is at or below its ductile-to-brittle transition temperature (DBTT), then it will be susceptible to brittle fracture.
What is stress intensity factor in fracture mechanics?
The stress intensity factor (K) is used in the field of fracture mechanics. It predicts stress intensity near the tip of a crack caused by a remote load or residual stresses. The magnitude of K depends on: Sample geometry. Size and location of the crack.
Why CTOD test is required?
CTOD test is one of test methods to determine fracture toughness (fracture resistance) of a material with a crack, and a test to determine crack tip opening displacement to generate unstable fracture (limit CTOD value).
What is Griffith criterion?
Definition. The Griffith theory states that a crack will propagate when the reduction in potential energy that occurs due to crack growth is greater than or equal to the increase in surface energy due to the creation of new free surfaces. This theory is applicable to elastic materials that fracture in a brittle fashion …
What is Griffith equation?
σcr2 = 2 Γ E / [π(1 – ν2) a] where ν is the Poisson ratio. According to the Griffith equation, the breaking stress of a homogeneous plate, having a sufficiently long straight crack normal to the applied stress, is inversely proportional to the square root of the crack length.
What is the difference between stress concentration factor and stress intensity factor?
Stress concentration factor is dependent on the geometrical changes of cross section, such as a hole, notch or fillet in the component. This can be designed for as it only depends on the geometry and not on load condition. Stress intensity factor is dependent on geometry and load.