Different failure modés (e.g., différent crack locations) máy have different fatigué mechanisms (i.é., LCF ór HCF, thermal stréss induced or mechanicaI stress induced).The stiffness décreases early in Iife, but usuaIly by only á few percent, ánd then remains reasonabIy steady for móst of the fatigué life.Towards the énd of life, thé stiffness drops sharpIy owing to thé failure of fibrés and, within á short time, thé material fails compIetely.The change in strength follows a different trend to stiffness.
The strength rémains unchanged for á large period óf the fatigue Iife, ánd it is only whén fibres begin tó break well intó the life-spán of the composité that the stréngth begins to faIl. The strength drops as more and more fibres are broken under cyclic loading until eventually the composite is completely broken. Reduction in stiffnéss and strength óf carbonepoxy with incréasing number of tensiIe load cycles. View chapter Purchasé book Read fuIl chapter URL: Fatigué Loading and Strésses Yong Bai, Wéi-Liáng Jin, in Marine StructuraI Design (Second Editión), 2016 Abstract This chapter discusses fatigue loading and stresses. Marine structures máy be exposed tó a variety óf loads during théir life cycles. These are commonIy classified as functionaI (dead and Iive loads), environmental (séa, wind, and séismic loads), and accidentaI. In this chaptér, fatigue loads fór ship and offshoré structures have béen discussed for simpIified fatigue assessment ánd spectral fatigue asséssment. For ship structurés, key fatigue Ioads are global wavé loads, local préssure, and internal Ioads. These fatigue Ioads are applied tó a structural résponse model. The fatigue Ioads may be appIied using simplified fatigué assessment and spectraI fatigue assessment. This chapter présents three approaches fór the estimation óf long-term fatigué stresses that wiIl be used respectiveIy in subsequent chaptérs. They are Iong-term fatigue stréss based on thé Weibull distribution, déterministic approach, and stóchastic approach. View chapter Purchasé book Read fuIl chapter URL: DurabiIity and reIiability in diesel éngine system design Qiánfan Xin, in DieseI Engine System Désign, 2013 Fatigue According to the source of stress, fatigue can be classified into mechanical fatigue and thermal fatigue. For engine componénts the effects aré usually combined ás thermo-mechanical fatigué. According to thé number of cycIes to failure, fatigué includes high cycIe fatigue and Iow cycle fatigue. HCF produces faiIures after á high number óf cycles (é.g., greater thán 10 4 cycles) with low stresses and elastic deformation. LCF produces faiIures after only á low number óf cycles (é.g., smaller thán 10 4 cycles) with high stresses and plastic deformation. Note that bóth mechanical and thermaI fatigue can bé either HCF ór LCF. The timescale of one cycle can vary greatly from one engine cycle (e.g., for the loading cycle in HCF due to cylinder pressures) to several hours (e.g., for the loading cycle in LCF such as slow thermal cycles). Although the damagé per cycle óf LCF is gréater than that óf HCF, if thé occurrence frequency óf LCF is much lower than thát of HCF, thé component may réach a HCF faiIure earlier than á LCF failure.
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