| Small punch test has a good development potential that can assess the material degradation of in-service equipments in the petrochemical industry with micro-damage sampling. As the conventional small punch specimens have no groove or pre-crack, the fracture toughness of material is evaluated difficultly by small punch test. The circular type pre-crack of notched specimens are in conformity with fracture patterns and crack constraint degree is higher than other types of cracks. The axisymmetric structure of specimen is conducive to research material fracture toughness. In this paper, the circular type pre-crack specimens were designed by finite element simulation, the effect of different crack error factors on the test were studied and the feasibility of processing methods was discussed. Different pre-crack depth of specimens were analyzed by small punch test and finite element anslysis, the main research resultsof this paper are as follows:(1) Finite element analysis method has determined that the optimal diameter of the annular crack at small punch specimen was φ2mm.(2) Accuracy of crack in small punch specimen was proposed:crack tip radius p is less than 5μm; error of 0.5mm depth h1 is less than±2%; the gap width l0 is less than 200∴m.(3) Feasible processing method of circular type pre-crack in the specimens was determined. Locating, alignment and depth control method in the process of crack were proposed. Processing error of cracks was in the allowable error range.(4) Crack propagation of pre-cracks at different depths was observed. Crack initiation point at different depths of the samples was obtained.0.5mm deep notched specimen as the main research object, specimen failure mode and the proportion of different crack types was determined. The J-integral of crack initiation point in the speciemens obtained by SPT and 3D elasto-plastic numerical analysis was calculated. |
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