Improved Elastic Compliance Equation and its Inverse Solution for Compact Tension Specimens

2017 
ASTM E1820 is a well-developed fracture test standard and has been used worldwide for fracture toughness testing on ductile materials in terms of the J-integral or J-R curve. This standard recommends the elastic unloading compliance technique for measuring crack length in a single specimen test, and an accurate elastic compliance equation is needed to estimate physical crack length. Compact tension (CT) specimen is one of the most often used standard specimens with crack length ratios of 0.45≤a/W≤0.70 prescribed in E1820 for J-R curve testing. The stress intensity factor K of CT specimens used in E1820 was developed by Srawley (IJF, 1976) and has been commonly accepted as the most accurate solution. The compliance equation of CT specimens was developed by Saxena and Hudak (IJF, 1978) and has been used in ASTM E1820 for decades. However, recent results showed that the load-line displacement (LLD) compliance equation is not consistent with that determined from its K solution, and the maximum error of LLD compliance can be larger than 7% at a/W = 0.32 and ∼ 5% at a/W = 0.45 (E1820 standard crack size). The FEA results confirmed that the K solution in E1820 is indeed very accurate, but its compliance equation is less accurate. Thus, an improved compliance equation with high accuracy is developed from the accurate K solution using the numerical integration technique and shooting method.Copyright © 2017 by ASME
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