Mathematical Algorithm to Calculate Crack Opening Loads from Local Strain Records
Bennett, Jonathan Wade
AdvisorNewman Jr., James C.
CommitteeSullivan, Rani Warsi
Lacy Jr., Thomas
Many aircraft are designed using the Damage-Tolerance concept. This concept assumes that a structural component is flawed during the manufacturing process. A central feature in this concept is the fatigue-crack-growth-rate properties of the material used in its construction. ASTM E-647 standard describes how fatigue crack growth tests are to be conducted. In the late 1960’s, Wolf Elber discovered the concept of crack closure. He showed that the crack would close prematurely even while under tensile loading. A central feature in this concept is called the crack opening load. The method in ASTM E-647 used to calculate the crack opening load has been found to be inadequate for high load ratios R (Pmin/Pmax>0.4) tests. Herein, an algorithm implementing the least squares method was developed to determine the crack-opening load for low and high R tests on a variety of materials for fatigue crack growth tests conducted on compact C(T) specimens.