Papers by Keyword: Shear-Lip

Abstract: A stress intensity factor K was used as a fracture parameter to determine the plane strain fracture toughness KIC of AZ61 magnesium alloy using a single edge notch bend (SENB) specimen in accordance to ASTM E399 testing method. Five different specimen thicknesses of 2 to 10 mm were used in the test. A sharp fatigue pre-crack was initiated and propagated to half of specimen width at a constant crack propagation rate of about 1 x 10-8 m/cycle before the specimen was loaded in tension until the fracture stress is reached and then rapid fracture occurred. The fracture toughness KC values obtained for different thicknesses showed that KC value decreased with increasing specimen thickness. The highest KC value obtained was 16.5 MPa√m for 2 mm thickness specimen. The value of KC became relatively constant at about 13 MPa√m when the specimen thickness exceeds 8 mm. This value was then considered as the plane strain fracture toughness KIC of AZ61 magnesium alloy. Calculation of the minimum thickness requirement for plane strain condition and the size of the shear lips of the fracture surface validate the obtained KIC value.

Abstract: Dimple fracture tests are conducted under mode I and mixed mode lading conditions. Dimple fracture zone and shear-lip fracture zone are observed by scanning electron microscope precisely. It is found that crack growth direction is affected largely by the change of loading condition. It is also found that the differences of fracture pattern between mid-plane and at free surface are very large. Void diameter and crack growth direction are measured. Numerical simulation is conducted to simulate fracture tests in three-dimensional field. Gurson’s constitutive equation is used and large deformation analyses are conducted. It is assumed that void nucleation is controlled by both plastic strain and stress. Numerical results are compared with those of experiments. It is found that results of numerical simulation agree well with those of experiment qualitatively.