交实应 2.脉动循环: max r=-mIn=0 max O=0 max min O 2 3.静循环: max min min O=0 五、稳定交变应力:循环特征及周期不变。 O min
t 2.脉动循环： 0 max min = = r 2 max = a = m 3.静循环： 1 max min = = r a =0 m = max 五、稳定交变应力：循环特征及周期不变。 min max a t m m min max = min o o
ALTERNATING STRESS Example 1 A bolt connected the connecting with rod in a generator is subjected to the maximum tensile force in work Pmax =583kN, the minimum tensile force is Pmin =558KN. Inside diameter of the whorl is d=11. 5mm, try to determineσn、on,andr Solution P4×58300 00Ax×0.0115 561MPa P4x55800 n 537.2MPa min A×0.0115 max min 561-537 =12MPa 2 2 R to max min 561+537 O537 =549MPa min 0957 2 2 56 max
561MPa 0.0115 4 58300 2 max max = = = A P 537.2MPa 0.0115 4 55800 2 min min = = = A P 12MPa 2 561 537 2 max min = − = − = a 549MPa 2 561 537 2 max min = + = + = m 0.957 561 537 max min = = = r Example 1 A bolt connected the connecting with rod in a generator is subjected to the maximum tensile force in work Pmax =58.3kN，the minimum tensile force is Pmin =55.8kN. Inside diameter of the whorl is d=11.5mm，try to determine a、m and r. Solution：
交实应力 例1]发动机连杆大头螺钉工作时最大拉力Pnax=583kN,最小 拉力Pmn=558kN,螺纹内径为=115mm,试求an、amn和r 解: P4×58300 A丌×0.0115 6=56IMPa P4×55800 min =5372MPa mnAx×0.0115 561-537 max min 12MPa 2 2 0+O, 561+537 O537 max min =549MPa min -0.957 2 2 O 561 max
561MPa 0.0115 4 58300 2 max max = = = A P 537.2MPa 0.0115 4 55800 2 min min = = = A P 12MPa 2 561 537 2 max min = − = − = a 549MPa 2 561 537 2 max min = + = + = m 0.957 561 537 max min = = = r [例1] 发动机连杆大头螺钉工作时最大拉力Pmax =58.3kN，最小 拉力Pmin =55.8kN ，螺纹内径为 d=11.5mm，试求 a 、m 和 r。 解：
ALTERNATING STRESS 8 14-3 ENDURANCE LIMIT OF A MATERIAL AND ITS TEST I\ Endurance limit (fatigue limit)of a materials: As long as the maximum stress of the cycle stress does not exceed a the maximum limit,', a material may be subjected to millions of times cycling without fatigue. This maximum stress is called the fatigue limit. It is designated by o 20-N curve Stress-life curve) O--Nominal endurance limit N 0-cycle base Or ----5 N(cycling o,Endurance limit of materials numbers) N No
§14–3 ENDURANCE LIMIT OF A MATERIAL AND ITS TEST 1、Endurance limit (fatigue limit)of a materials： As long as the maximum stress of the cycle stress does not exceed a“the maximum limit”, a material may be subjected to millions of times cycling without fatigue. This maximum stress is called the “fatigue limit”. It is designated by r . 2、 —N curve（Stress—life curve）： N0—cycle base r—Endurance limit of materials A—Nominal endurance limit N(cycling numbers) NA A r N0 o
交实应 §143材料持久限及其测定 一、材料持久限(疲劳极限): 循环应力中的最大只要不超过某个“最大限度”,构件就可 以经历无数次循环而不发生疲劳破坏,这个限度值称为“疲劳 极限”,用σ表示。 二、σ-N曲线(应力一寿命曲线): σ名义持久限。 N—循环基数 N循环 ----5 σ材料持久限。 次数 N No
§14–3 材料持久限及其测定 一、材料持久限(疲劳极限)： 循环应力中的最大只要不超过某个“最大限度”,构件就可 以经历无数次循环而不发生疲劳破坏，这个限度值称为“疲劳 极限”，用r 表示。 二、 —N 曲线（应力—寿命曲线）： N0—循环基数。 r—材料持久限。 A—名义持久限。 N(循环 次数) NA A r N0 o