ASTM E292-18 Conducting Time-for-Rupture Notch Tension Tests of Materials

Scope:

ASTM E292-18 covers the Notch Test. The notch test determines the time it takes for a notched specimen to rupture or break under pressure. It is not used to make any deformation measurement. A notch is a stress concentrator. A stress concentrator is a place on an object where the stress is significantly greater than the surrounding region. The notched specimen determines the strength of materials with stress concentrators under tension. Rupture life of notched specimens indicates the ability of a material to deform locally without cracking under multi-axial stress conditions, thereby redistributing stresses around a stress concentrator.

Test Procedure:

In ASTM E292-18 the specimen has a notch and a reduced section, a place where the specimen is thinner. The dimensions of the specimen are measured. The specimen and the machine are cleaned with acetone. A thermocouple is attached to the specimen to measure temperature. The specimen is positioned in the testing machine, and it is extended gradually until it breaks. 

Specimen size:

If possible, the specimens should be in the form in which they will be used. The specimen should have a notch and a reduced section in the middle of the specimen for the break to occur there. The part of the specimen gripped by the machine can be threaded or button head or tapered for a cylindrical specimen. Flat specimens can be attached through loading yokes and pins or by wedge grips. 

Data:

1. The notch rupture strength is calculated as follows: 

Notch rupture strength = P/A ₀

P = the load applied to the specimen, and 

A ₀= the initial area at the notch cross-section.

2. The percent reduction in area and true strain at the notch cross-section is calculated as follows:

Percent reduction in area =

True fracture strain = ε_N = InA₀/A_f

where A_f is the final area at the notch section