ASTM E1820-21 Standard test method for measurement of fracture toughness

ASTM E1820-21 Standard test method for measurement of fracture toughness Scope:

ASTM E1820-21 gives procedure and guidelines to determine the fracture toughness using K, J, and CTOD (d) parameters. Toughness is measured in the R-curve format or as a point value.

Test Procedure:

The Overall objective of this method is to develop a force-displacement record to evaluate J, K, and CTOD. Two procedures are used here, first, is a Basic procedure used to determine the K, J, and CTOD without using a crack extension measurement device. The second one is the complete procedure to evaluate the fracture toughness resistance curve using crack extension measurement equipment. This also includes the evaluation of single-point toughness values. The basic procedure utilizes a force versus displacement plot and is directed toward obtaining a single fracture toughness value such as K_Ic, J_c, or δ_c. Optical crack measurements are utilized to obtain both the initial and final physical crack sizes in this procedure. Multiple specimens can be used to evaluate J at the initiation of ductile cracking, JIC, or δIc.

The resistance curve procedure utilizes an elastic unloading procedure or equivalent procedure to obtain a J or CTOD-based resistance curve from a single specimen. Crack size is measured from compliance in this procedure and verified by post-test optical crack size measurements. The overall procedure for this method is initially to prepare a sample/specimen. The specimen dimension is then measured and the temperature is kept stable. Then the alignment is done for bend testing and compact testing. Then the Basic procedure involves loading a specimen to be selected displacement level and determining the amount of crack extension that occurred during loading. After unloading crack size is measured and the resistance curve is plotted. Figures 1,2 show the specimen requirements.

Test Specimen:

Figure 1: Fatigue Crack Starter Notch Configurations

Figure 2: Recommended Single Edge Bend [SE(B)] Specimen

The two side planes and the two edge planes shall be parallel and perpendicular as applicable to within 0.5°. The machined notch shall be perpendicular to specimen length and thickness to within 62°.

Data:

Special requirements for testing single edge bend specimen

Calculation of K for the bend specimen at a force P(i), calculate K as follows,

Where,

Calculation of J:

For the single edge bend specimen, calculate J as follows:

Where,

J_el = elastic component of J, and

J_pl = plastic component of J.

Conclusion:

Hence, ASTM E1820-21 gives procedures and guidelines to determine the fracture toughness of metallic materials using various parameters.