ASTM E1304 Test for Plane-Strain (Chevron-Notch) Fracture Toughness of Metals

Scope:

ASTM E1304 method is used to determine the plane strain fracture toughness of metals. Fracture toughness is a quantitative way of expressing a material’s resistance to crack propagation. In this test, the fracture toughness is relative to a slowly advancing steady-state crack in a neutral environment under severe tensile constraints. When tested, some metals might show a sporadic crack growth in which the crack front remains nearly stationary until a critical load is reached. The crack then becomes unstable and suddenly advances at high speed to the next arrest point. For these materials, plane-strain fracture toughness, K_Ivj or K_IvM, is determined relative to the crack at the points of instability. This test method is used to infer the effects of metallurgical variables such as composition or heat treatment on fracture toughness. It can also be used to establish specifications of acceptance and quality control. 

Test Procedure:

In ASTM E1304 method, a load is applied to the mouth of a chevron-notched specimen to induce an opening displacement. The load versus mouth opening displacement is recorded autographically. The slopes of periodic unloading-reloading cycles are used to calculate the crack length. These crack lengths are expressed indirectly as slope ratios. The characteristics of the force versus mouth opening displacement trace depend on the geometry of the specimen, the specimen plasticity during the test, any residual stresses in the specimen, and the crack growth characteristics of the material being tested.

There are two types of force versus displacement:  (1) smooth behavior and (2) crack jump behavior. 

K_Iv is the crack extension resistance to a slowly advancing steady-state crack. K_ivj is the crack extension resistance to a sporadically advancing crack. 

Video 01: Method to measure fracture toughness

Specimen size:

The specimen size required for the ASTM E1304 testing increases with the square of the ratio of fracture toughness to yield strength of the material. Therefore, proportional specimen configurations are provided.

Data:

The stress intensity factor (fracture toughness) is reported.

Conclusion:

ASTM E1304 method is used to determine the plane strain fracture toughness of metals. Fracture toughness is a quantitative way of expressing a material’s resistance to crack propagation.