The Damage Analasis Of Medium Carbon In Low Cycle Fatigue

The essence of crack-technique is, using the stress concentration effect or notch effect on precut notch, to make crack growth near the cut-tip and to realize continuous interface quickly and regularly separated of solid materials in sensitive stress produced by means of proper preloading. From preventing fracture to designing crack, that named fracture design, that is a new branch of crack-theory in the regular and controllable directionThe rotational bending baiting, utilized the notch effect and bending fatigue effect in order to implement the brittle failure and achieve a blank with vertical and smooth fracture surface without geometric distortion, is a kind of method in crack-technique;and it has other merits, such as the short time, low consumed energy, without other effects to the material, the primary material saving;it is especially applicable for cutting plastic material. So the study of it's mechanism is one of the important parts to improve the principle of crack technique and the structure of cutting machine.This paper, from the fracture mechanism under rotational bending, takes 45 steel with precut V-notch as the subject investigated, by controlling the amplitude value of strain during the process of loading, studies the notch effect to fatigue life of round bar, and applies the theoretical knowledge of the life prediction on ductile materials in low cycle fatigue, proposes the amended Manson equation and algorithm of the estimating-life model;furthermore, and compares the life according to classical Manson-Coffin equation and the life according to the corrected Manson equation with the test results. By those compared results, it is very obvious that the life errors of classical Manson-Coffin equation are far more excessive for amended Manson-Coffin equation's, so proves the accuracy of the amended Manson model;in a word, the model proposed also reduce greatly the difficulty of the calculation process. At last, the reasons of life errors in amended model are discussed and analysed. All those conclusions have some value in engineer application.From the perspective of damage mechanics, use the character of damage variable which is process variable, apply it to simulate the process of crack growth, and propose a new estimation life model. Based on the test data, by least square method, the damage-life model in different notch depth of the specimens is obtained, and the curves of the damage-life in the different constraint of specimens also are presented. Finally, the conclusions gained show correct throughout comparing with many studies.At last,utilizing macroscope fractography, obtain some new features of the fracture surface under rotational bending fatigue and find out some differences between the fracture surface under rotational bending fatigue and the fracture surface under tension and compression fatigue.The conclusions of this paper have a high value in the field of engineering application. At the same time, they also improve the basic theory of crack-technique, and provide theory basis for the further development of cracking machine in rotational bending conditions.