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Fracture stress for a brittle material having a crack lenght of 1μm is 200 MPa. Fracture stress for the same material having a crack lenght of 4 μm is
According to the fracture theory of the material, the critical value of the crack extension force, which makes the crack propagate to the fracture is called the fracture toughness of the material.
A brittle material is mechanically tested in medium P in which it has surface energy γs = 0.9 J m-2. This material has a fracture strength of 300 MPa for a given flaw size. The same solid containing the same flaws is then tested in medium Q in which γs = 0.1 J m-2. The fracture strength (in MPa) in medium Q based on Griffith's theory is
The young’s modulus of the steel is 600 MPa, and the plastic stress required to extend the crack is 50*10-9, and the initial crack length is 2 microns. Find the fracture stress required to crack the material?
Consider the following statements regarding crack : 1. Crack is more likely to occur in the regions of discontinuity such as oil holes. 2. Crack is more likely to occur in the regions of irregularities in machining operations such as stamp mark. 3. Crack is more likely to occur in the internal cracks due to defects in materials like blow holes. Which of the above statements are correct ? 
In a brittle material, the maximum internal crack is 8 μm. If Young's modulus is 400 GPa and surface energy is 3.14 J/m2, the estimated theoretical fracture strenght (in MPa) is
According to Griffith theory, which of the following are true for the fracture stress in a brittle material?
P. Increases with increasing surface energy
Q. Decreases with increasing elastic modulus
R. Decreases with increasing length of pre-existing crack
S. Decreases with increasing number of pre-existing cracks of same size
The fracture stress according to Orowan’s theory of brittle fracture is __________ (where E is Yong’s modulus, ϒp is the plastic work required to extend the crack wall of the length 2
In the case of plane stress, the relationship between the fracture toughness and crack extension force is given as _______ (where K is the fracture toughness, δ is the crack extension force, and E is the young’s modulus).
In the case of plane strain, the relationship between the fracture toughness and crack extension force is given as _______ (where K is the fracture toughness, δ is the crack extension force, ν is the poison’s ratio, and E is the young’s modulus).