The Use of the S_(pb) Parameter to Estimate the Crack Length in 6061T6 Aluminum Fracture Specimens

摘要

The variable separability property is the theoretical base for J determination and the incremental methodology used to obtain J-R and J_M-R curves. The separability parameter S_(ij) is used to study the separability property with blunt notched specimen. It reach a constant value when this property is evident for a set of material, geometry, constrain, etc. Under this condition, the separability parameter become independent from material deformation properties as it was proposed by Sharobeam y Landes for blunt notched specimen with S_(ij) parameter and for precracked specimens with S_(pb) parameter. This property and the S_(pb) parameter was used in this work to estimate continuous crack length from pre-cracked fracture mechanics specimen test record A set of pre-cracked three point bending ASTNS E(B) specimen was prepared from AA6061T6 aluminum alloy. Specimens with different side groove ratio were included to the testing matrix in order to studied the thickness influence on the crack length estimation. For each specimen initial and filial crack length were measured on the surface crack. Intermediate crack length was determined by mean of standard elastic unloading and using the S_(pb) parameter from the load displacement record. An statistical analysis was conducted to evaluated the intermediate crack length estimations. The results were compared against to those obtaining using the unloading compliance methodology show a good agreement between them. The S_(pb) crack lengths were very close to those estimated using the standard elastic unloading and difference between them was less than 15% Δa. The initial, final and crack extension were compared with those measure on the crack surfaces and the difference observed was less than those suggested in ASTME1820-96 for alternative methods of measuring crack extension.