材料力学课堂教学软件（英文版）-范钦珊-chap.9 Fatigue Strength.pptVIP

* * * TSINGHUA UNIVERSITY * TSINGHUA UNIVERSITY HIGHER EDUCATION PRESS BEIJING CHINA Fan’s Studio for Education and Teaching Prof.Fan’s Studio for Education and Teaching Back to main Menu (9) Guide to Solve Problems of Mechanics of Materials * Q.S.Fan Tsinghua University P.R.CHINA The Compendium on Fatigue Strength of Elements in Alternate Stresses Mechanics of Materials Chapter 9 Back to the first page Back to main Menu Problem:As shown in the figure, shaft is fixed at both ends and pulley can axially rotate. Knowing that the constant load FP is applied to the pulley. Determine the stress ratio at point B in the cross section of the shaft. The First Kind of Exercise: The Estimation of Alternate Stresses, the Determination of Stress Ratio Problem 1 Solution： Because the shaft is fixed and FP is a constant load, in other words, its direction and magnitude will not change. So, the stress in point B is not a time-varying stress but a static stress. So, we can write Then, stress ratio is: Back to the first page The First Kind of Exercise: The Estimation of Alternate Stresses, the Determination of Stress Ratio Problem 1 As shown in the figure, the shaft is simply supported at both ends and the pulley is fixed with the shaft. Knowing that the constant load FP is applied to the pulley.The shaft and the pulley will rotate together. Determine the stress ratio at point B in the cross section of the shaft. The First Kind of Exercise: The Estimation of Alternate Stresses, the Determination of Stress Ratio Problem 2 Solution： Although FP is a constant load and its direction and magnitude will not change, because the pulley will rotate with shaft, the position of point B is time-varying. So, the stress at point B is time-varying. When point B is at the bottom, it is subjected to maximal tension force; when point B is at the top, it is subjected to maximal compression force. The values of these two forces are equal. So, we have Then, the stress ratio at