Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

Zhang, Lijun; Zhao, Shengdun; Wang, Zhenwei

doi:10.1155/2014/861465

Cited by 3 publications

(3 citation statements)

References 5 publications

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“…The method is a promising low-stress blanking. In course of cropping, the machine skillfully utilizes the fatigue radial-forging action to make the crack propagate along the prefabricated V-shaped notch in metal bar for shearing bar, and it is also a fast and energy-saving cropping system because of stress concentration effect of V-shaped notch and vibration action [3].…”

Section: Introductionmentioning

confidence: 99%

Research on Radial Motion Characteristic of the Cropping Hammer in Radial-Forging Cropping Method

Zhang

Zhao

Wang

2015

Advances in Materials Science and Engineering

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The radial loading form applied to the bar is very important for reducing or avoiding the impact and vibration of the radial-forging cropping system and obtaining the high-quality cross section. A new radial stroke loading curve of the cropping hammer based on the cycloid form is proposed and the dynamic model of radial stroke loading mechanism is built. With the aim of obtaining the equivalent stiffness of the bar with V-shaped notch, which is a key parameter affecting the dynamic characteristic of radial stroke loading mechanism, the analytic model of the bar is built and the simulation experiments are designed by means of the orthogonal test method. The analytical results show that the diameter of the bar has the significant influence on the equivalent stiffness of the bar. Furthermore, the equivalent stiffness of the bar with V-shaped notch can be directly calculated according to the equivalent stiffness of smooth bar whenh/d<0.05andr>0.15. By using the cycloid stroke curve, the cropping experimental results for 45 steel bars and 20 steel bars show that the radial impact and vibration of the cropping system are decreased and the bar cross-section qualities have been significantly improved.

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Section: Introductionmentioning

confidence: 99%

Research on Radial Motion Characteristic of the Cropping Hammer in Radial-Forging Cropping Method

Zhang

Zhao

Wang

2015

Advances in Materials Science and Engineering

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“…When the crack expands to sufficient depth, the bar will fracture instantly because it cannot bear the external loading force. 28,29 As all signals obtained by AE are waveform, AE parameters need to be analyzed to obtain the crack initiation time t 0 after the whole acquisition process. And the crack initiation force is calculated according to the strain value obtained at this time.…”

Section: Experimental Study On the Measurement Of Crack Initiation Forcementioning

confidence: 99%

Influence of the reasonable crack initiation force obtained by coupling AE parameters and stress-strain on low-stress cropping quality

Zhang

Zhou

et al. 2022

Proceedings of the Institution of Mechanical Engineers, Part C:

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In view of the problem that it is difficult to accurately obtain the crack initiation force required for the metal bar with V-shaped notch in the low-stress precision cropping, a new method for synchronous measurement of coupling AE parameters and stress-strain is proposed, and a corresponding test platform is also established. By analyzing the ringing count and RMS parameters of AE, it is found that the crack at the tip of V-shaped notch begins to appear at the boundary between the crack accumulation area and the plastic failure area. At the moment, the reasonable crack initiation force for metal bar with V-shaped notch can also be determined by coupling the value of strain. Based on it, a new constant loading curve based on the FR is built. The results show that by means of the constant loading curve, the crack initiation time and the area of bar transient breaking zone are reduced by 63.6% and 51.2% respectively compared with ones of the traditional linear loading methods. Further research based on XFEM shows that the initial crack depth is between 0.25mm and 0.4mm, and the cracking angle and the crack offset distance can also meet the precision cropping requirement, which provides a technical guarantee for truly improving the cropping quality.

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“…First, artificially prefabricate a ring-like approximate crack on the bar surface. And then, exert a certain force to the bar with the circumferential surface crack to separate it in the form of low-stress brittle fracture [1]. Since V-notch crack initiation and propagation is a complicated process, in order to get the best cropping effect, it is necessary to establish a crack model at the V-notch tip; investigate its crack initiation and propagation; determine the bar V-notch tip stress field during the cropping process; and, finally, obtain V-notch tip crack initiation conditions.…”

Section: Introductionmentioning

confidence: 99%

Research on the Crack Initiation in Precision Cropping Based on Energy Release Rate Theory

Zhang¹,

Zhang²,

Chen³

et al. 2018

dteees

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In the low-stress precision technology, the initiation of crack at the V-shaped notch tip is a complicated process. It is of great significance to improve the quality of the bar cross-section through obtaining the conditions that influence the initiation angle and the critical loading force of the bar. Due to the complexity of the force at V-shaped notch tip, the parameter model of the V-shaped notch tip is established and the stress field of the composite crack is analyzed, thus obtaining the stress component formula of the V-notch tip. The energy release rate theory is used to calculate the crack initiation angle and the critical loading force in the low-stress cropping. The formula for calculating the energy release rate at the maximum initiation angle is established. The calculated results show that when the critical loading force is 1500N, the micro-cracks at the V-shaped notch tip first occur at the initiation angle of 20.28°, and the corresponding energy release rate is 7.539×10 4 Pa.m 2 . The radial blanking fatigue experiments also prove that when the critical loading force was 1500N, the bifurcate micro-cracks are generated at the tip of V-shaped notch.

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Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

Cited by 3 publications

References 5 publications

Research on Radial Motion Characteristic of the Cropping Hammer in Radial-Forging Cropping Method

Research on Radial Motion Characteristic of the Cropping Hammer in Radial-Forging Cropping Method

Influence of the reasonable crack initiation force obtained by coupling AE parameters and stress-strain on low-stress cropping quality

Research on the Crack Initiation in Precision Cropping Based on Energy Release Rate Theory

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