Content deleted Content added
NeedsGlasses (talk | contribs) Removed empty section of relationship with G |
NeedsGlasses (talk | contribs) Reorganised. |
||
Line 5:
Under [[fatigue (material)| fatigue]] loading, the range of movement of the crack tip during a loading cycle <math>\Delta\delta_\text{t}</math> can be used for determining the rate of fatigue growth using a [[crack growth equation]]. The crack extension for a cycle <math>da/dN</math>, is typically of the order of <math>\Delta\delta_\text{t}</math>.<ref name="suresh04"/>
== History ==
== Relationship between K and CTOD ==▼
Examination of fractured test specimens led to the observation that the crack faces had moved apart prior to fracture, due to the blunting of an initially sharp crack by plastic deformation. The degree of crack blunting increased in proportion to the toughness of the material.<ref>J C Newman, M A James, U Zerbst, "Engineering Fracture mechanics", Elsevier 2003</ref> This observation led to considering the opening at the crack tip as a measure of fracture toughness. This parameter became known as CTOD. Irwin later postulated that crack-tip plasticity makes the crack behave as if it were slightly longer. Thus, estimation of CTOD can be done by solving for the displacement at the physical crack tip.▼
== Use as a design parameter ==▼
CTOD is a single parameter that accommodates cracktip plasticity. It is easy to measure when compared with techniques such as J integral. It is a fracture parameter that has more physical meaning than the rest.▼
However, the equivalence of CTOD and J integral is proven only for non-linear materials, but not for plastic materials. It is hard to expand the concept of CTOD for large deformations. It is easier to calculate J-integral in case of a design process using [[finite element method]] techniques.▼
== Relation with other crack tip parameters ==
CTOD can be expressed in terms of stress intensity factor <math>K</math> as{{sfn|Anderson|2005|pp=104-105}}
Line 12 ⟶ 21:
where <math>\sigma_\text{y}</math> is the yield strength, <math>E</math> is Young's modulus and <math>m</math>=1 for [[plane stress]] and 2 for [[plane strain]].
==
The relationship between the CTOD and J is given by<ref name="suresh04"/>
Line 26 ⟶ 35:
Early experiments used a flat, paddle-shaped gauge that was inserted into the crack; as the crack opens, the paddle gauge rotates and an electronic signal is sent to an x–y plotter. This method was inaccurate, however, because it was difficult to reach the crack tip with the paddle gauge. Today, the displacement V at the crack mouth is measured and the CTOD is inferred by assuming that the specimen halves are rigid and rotate about a hinge point.<ref>B E Amstutz, M A Sutton, D S Dawicke"An Experimental study of CTOD for mode I/mode II stable crack growth in thin aluminium specimens", ASTM Special 1995</ref>
▲Examination of fractured test specimens led to the observation that the crack faces had moved apart prior to fracture, due to the blunting of an initially sharp crack by plastic deformation. The degree of crack blunting increased in proportion to the toughness of the material.<ref>J C Newman, M A James, U Zerbst, "Engineering Fracture mechanics", Elsevier 2003</ref> This observation led to considering the opening at the crack tip as a measure of fracture toughness. This parameter became known as CTOD. Irwin later postulated that crack-tip plasticity makes the crack behave as if it were slightly longer. Thus, estimation of CTOD can be done by solving for the displacement at the physical crack tip.
▲== Use as a design parameter ==
▲CTOD is a single parameter that accommodates cracktip plasticity. It is easy to measure when compared with techniques such as J integral. It is a fracture parameter that has more physical meaning than the rest.
▲However, the equivalence of CTOD and J integral is proven only for non-linear materials, but not for plastic materials. It is hard to expand the concept of CTOD for large deformations. It is easier to calculate J-integral in case of a design process using [[finite element method]] techniques.
== References ==
<references/>
| |||