Abstract
The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar.
Highlights
In recent years the precision cropping of metal bar in the manufacturing has been paid more and more attention
Taking 45 steel bars as a sample to calculate the crack initiation life of V-shaped notch in the low stress cropping, the chemical compositions and mechanical parameters of 45 steel bar material are shown in Tables 1 and 2, respectively
It showed that the crack initiation life of V-shaped notch tip is more than 80% of the total cropping time for every segment of metal bar
Summary
In recent years the precision cropping of metal bar in the manufacturing has been paid more and more attention. To obtain the high-quality cropping cross-section, the initiation direction of the crack in tip of Vshaped notch should be perpendicular to the axial cord of the metal bar along the V-shaped notch section. It is very important to study the relationship between the stress state of V-shaped notch tip and the crack initiation location and the crack initiation direction in detail, which is very helpful to improve the cropping cross-section quality. The theoretical and experimental studies presented in this paper aim to analyze the influences of main factors on the crack initiation location, the crack initiation direction, and the crack initiation time in order to get the desired methods of improving the cropping cross-section quality and calculating the crack initiation life
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