Crack-Extension Force for a Part-Through Crack in a Plate

1962 ◽  
Vol 29 (4) ◽  
pp. 651-654 ◽  
Author(s):  
G. R. Irwin
Keyword(s):  
Stress Field ◽  
Crack Extension ◽  
Crack Opening ◽  
Elliptical Crack ◽  
Field Parameter ◽  
Experimental Measurements ◽  
Boundary Points ◽  
Crack Extension Force ◽  
Extension Force

The crack stress-field parameter K and crack-extension force G at boundary points of a flat elliptical crack may be derived from knowledge that normal tension produces an ellipsoidal crack opening. Rough correction procedures can be employed to adapt this result for application to a part-through crack in a plate subjected to tension. Experimental measurements suggest this adapted result has a useful range of accuracy.

A crack extension force correlation for hard materials

2007 ◽  
Vol 148 (2) ◽  
pp. 109-114 ◽  
Author(s):  
W. W. Gerberich ◽  
W. M. Mook ◽  
C. B. Carter ◽  
R. Ballarini
Keyword(s):  
Crack Extension ◽  
Hard Materials ◽  
Crack Extension Force ◽  
Extension Force

Energy balance concepts in the physics of fracture

1991 ◽  
Vol 435 (1893) ◽  
pp. 169-184 ◽  
Keyword(s):  
Energy Balance ◽  
Crack Growth ◽  
Crack Extension ◽  
Driving Forces ◽  
Second Law Of Thermodynamics ◽  
Crack Extension Force ◽  
Fracture Toughening ◽  
Extension Force ◽  
Definition Of ◽  
Energy Balances

It is pointed out that there are a number of incompatible energy balances used in the study of fracture and fracture toughening. The original Griffith theory is based on the second law of thermodynamics and in the framework of this law a cracked body is in unstable equilibrium when the appropriate thermodynamic potential reaches a maximum value. This energy balance allows the identification of both the thermodynamic driving forces for crack extension and the forces resisting crack growth. A second, and widely used, energy balance is based on the first law of thermodynamics which is simply one of energy conservation and can yield no information about crack instability without further assumptions. The two energy balances are considered in relation to the effect of energy dissipating processes on fracture. It is shown that a crack extension force cannot be defined by dividing the sum of all the energy increments arising from all the processes accompanying crack extension by the increment of crack area since this gives rise to paradoxical results. It is concluded that the energy changes brought about by processes such as plastic deformation which accompany crack extension should not be included in the definition of a crack extension force. A local energy balance is used to define a crack extension force which yields results identical to crack shielding calculations in fracture toughening studies. It is shown that the work done by energy dissipating processes per unit area of crack surface does not act to increase the crack resistance or the ‘effective surface energy’. Energy dissipating processes have their effect on fracture by virtue of the fact that they alter the state of stress around the crack tip and thus reduce the thermodynamic driving force for crack growth.

The Growth of Surface Microcracks in Fatigue

1969 ◽  
Vol 91 (4) ◽  
pp. 770-779 ◽  
Author(s):  
P. H. Francis
Keyword(s):  
Crack Extension ◽  
Fatigue Loading ◽  
Test Results ◽  
Small Surface ◽  
Crack Extension Force ◽  
Micro Cracks ◽  
Theoretical Predictions ◽  
Extension Force ◽  
Elastic Fracture ◽  
Surface Microcrack

An analytical theory is proposed for describing the growth of a small surface “microcrack” under uniaxial fatigue loading. The theory is based upon dimensional analysis and uses the stress-intensity factor and crack extension force concepts of elastic fracture mechanics. Experimental measurements were made of the growth of surface micro-cracks, ranging from 0.0005–0.040 in. long, in polished specimens of 4340 steel. Good correlation was achieved in comparing the test results with the theoretical predictions. Finally, an approach is indicated for extending the analytical model to the prediction of fatigue failure.

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