CTOD Evaluation Using ASTM 1820 and BS 7448

Crack Tip Opening Displacement ( CTOD or δ ) is used as a fracture toughness parameter in ASTM 1820 and BS 7448. The critical CTOD is estimated in these standards through distinct concepts and also resulting in varied magnitudes. Here, the comparison between CTOD estimation standards ASTM 1820 and BS 7448 is carried out for AA2050-T84 alloy. Firstly, the CTOD as per ASTM 1820 is estimated for Compact Tension (CT), Disc-Shaped Compact Tension (DCT), and Single Edge Notch Bend (SENB) by varying yield stress to ultimate stress ( S yt /S ut ) and crack length to width of the specimen ( a/W ). The constraint parameter ( m ) equations used to relate J -integral ( J ) and CTOD were modified to first order polynomials. The error of less than 1% between third order (recommended in ASTM 1820) and first order polynomial equations ensured the accuracy of the newly proposed equations. Further, the CTOD were estimated by both ASTM 1820 and BS 7448 for various S yt /S ut using experimental results of AA2050-T84 alloy made CT specimen. The CTOD estimated from BS 7448 were almost four times higher compared to ASTM 1820. Finally, author recommends the necessity of reliable J - CTOD relationship among the standards, to popularize the CTOD as a fracture toughness parameter.