The Study Of Crack Height Error By Phased Array Ultrasonic Testing Based On AATT Method

Cracks are common defects of welding parts and components. Because of a sharp edge, cracks’risk is great. The defect size on height direction directly decides the fatigue strength and service life of the work piece, which should be strictly controlled by priority. Given crack height precision is crucial to ensure the safety of the component reliability, the testing results of conventional ultrasonic testing is not intuitive and its detection efficiency is low, therefore, phased array ultrasonic testing technology began to widely used in the defect quantitative detection by its unique focus deflection ability, multiple view and fast scan to all the product.Combined with the relevant references, with the aid of experiment and simulation, this paper makes a preliminary research and optimization on the important factors which affect crack height quantitative result.Using one-dimensional linear phased array probe, based on AATT (Absolutely Arrival Time Technique), the paper analyzes the influence of the probe parameters, the parameters of the wedge and testing condition on the test results. The main results are as follow:(1) Using sector scan combined with original signal to test the bottom opening crack defect, the results show the crack and cutting-edge imaging. Based on the character of sector scan, this paper selects the AATT as the quantitative method.(2) By 3.5 MHz linear array probe, select different height of bottom vertical cuttings of the 55.0 mm thickness carbon steel block instead of floor crack as the research object. The paper makes a research on parameter optimization for wedge velocity, the wedge angle, the first chip height deviation, and gets the following conclusion.Under the same focus depth, the more arrays, the smaller quantitative deviation error is, and for the same array elements, the closer focus depth, the more accurate quantitative resultsUsing transverse wave detection, by controlling the wedge block velocity deviation in ±100 m/s, the crack height deviation can be controlled at ±0.25 mm. For the longitudinal wave detection, by controlling the longitudinal wave detection in ±100 m/s, the height deviation can be controlled at ±0.20 mm.By controlling the wedge Angle range in ±1° , we can limit the height deviation to ±0.2 mm.The first chip height deviation is controlled at ±2.0 mm, which can limit the crack height deviation in ±0.15 mm. (3) Simultaneously, the study analyzed the influence between the testing body sound velocity and the height of crack quantitative results. For transverse wave, the material velocity deviation is controlled at ±100m/s, the height of the crack deviation will be limited within ±0.3mm. In comparison, the longitudinal wave velocity error affect the result of the height quantitative results turn out to be smaller, about ±0.13 mm.(4) Researching about the influence coming from the system calculation precision and the testing state, it was inferred that the smaller angle resolution is more conducive to depth and height quantitative. For a long spread path,we need to adopt more sampling points. At the same test conditions, height quantitative is no difference in the view of symmetrical detection. The consequences respectively getting from near the defect side OD (outside defect) and far away from the defect side ID (inside defect) exist a difference that OD’results will be smaller and ID’results will be larger.