The Metal Bar Fatigue Fracture Of The Research And Application

The stress cut-off technology is a method that severs material through putting fatigue load on material to cause fatigue crack initiate on appointed section, and grow quickly to failure. This technology is counter process of safety design according to fracture mechanics principle, and it is a green machining technology, conforming to developing direction of modern precision finishing, having the broad prospects in application. It is insufficient so far if want to make it become to one practical industrial technology. Based on this, barstock was taken as an object, the mechanism involved in stress cut-off process and the choice of main parameters were studied more from theory and experimentation in this article, for promoting the stress cut-off technology translates into productivity.From the factors of affecting barstock brittle failure, the stress and strain condition on the barstock-groove were firstly analyzed in this article, the fatigue crack initial position on barstock-groove and its mechanical model were discussed. Combined the micro-mechanism of fatigue crack growth and the factors of influencing fatigue crack growth speed rate, the macroscopic appearance of barstock fracture face under the different load forms and the fatigue strength at the time of barstock stress cut-off were discussed in this article.On the choice of groove patterns, the groove bottom stress concentration circumstances of 4 kinds of typical groove patterns (U, V, half V and counter-half V ) were analyzed by finite element method. On the choice of groove parameters, the influences of groove parameters (such as groove depth, groove opening angle and groove root radius) on the groove bottom stress concentration extent were analyzed by finite element method. The main conclusions from theory include: the stress concentration degree of V-shaped groove is the biggest, so it is the most favorable groove type for fatigue crack initiation during barstock stress cut-off; to different diameter barstocks, the stress concentration modulus achieves the peak value when the value of relative groove depth is around 0.1; the groove opening angle has little influence to the groove stress concentration modulus, it is suggested that the groove opening angle takes between 60°~90°; the groove root radius has tremendous influence on the groove stress concentration modulus, and so on.On the base of theoretical analysis, two kinds of materials were selected in this article to do experimental verification. Finite element method analysis results were supported well by experimental results.