Tham khảo tài liệu 'advanced mechanics of materials (1993-john willey) episode 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 642 16 FATIGUE ỡmax - min 2va and ơmax ơm ơa. Hence ơm Ơa 1L Substituting this value of ơm and values of ơam and ơu in Eq. we obtain ơa 289 MPa. Thus Tmax 315 MPa and ơmin 263 MPa. This result indicates that a smooth fatigue specimen cycled between these stress levels would not fracture before 107 cycles. Since ơmax is less than y failure would be by fatigue and not general yielding. The load p on member ACB in Fig. can be cycled from Pmax SF to Pmin SF through 107 cycles before fracture by fatigue. The reactions at A and B when Pmax SF is applied are equal to Pmax SF 2 . The reaction produces a moment and torque of equal magnitude at the critical section at c. Thus M T 720Pmax The bending stress Ơ due to M and shear stress T due to T at c are Me 720Pmax 10 4 __ T maxl. 7 I 7t 10 4 max 2c 720P 10 2 J 7l 10 4 The magnitude of Pmax is obtained by means of Eq. when ơmax 315 MPa is substituted for Y. Thus A 2 2 o I vs-r-sv max I 1 1 max I 4 V 315 315 7 Pmax 260N and Pmin -216N b For ơmin ỡmax 2 we obtain ơm ơa 3. Substitution of this value of ơm along with values for Y and ơu into Eq. gives ơa 282 MPa and ơmax 376 MPa. Since ơmax is greater than y failure of the member occurs by general yielding and not fatigue. Substitution of values of ơ T and y into Eqs. gives PmaJ 285 N and Pmin -142 N. EFFECTIVE STRESS CONCENTRATION FACTORS REPEATED LOADS The value of the stress concentration factor Sce for a notched member subjected to completely reversed repeated loads fatigue is obtained by comparison of data taken from two sets of test specimens. One set of specimens 5 to 10 specimens is notch-free the other set notched. The significant stress in the notch-free specimens is the nominal stress as computed with an elementary stress formula. For the notched specimens the nominal stress is again computed with the same elementary stress formula as for the notch-free specimens. Both sets of .
