Moulded Chamfering Method Prolongs The Fatigue Limitation Of Round Hole Gap Materials

Though the study of metal fatigue bears a history of160years, the theoryof mechanism is not completed nor improved and it still can not satisfy theactual needs of production in engineering application especially. Now it is still aserious and inevitable fact that the incidents of fatigue failure from partcomponents of mechanic structure, vehicles and the like. In accordance with thestatistics,90%incidents of failure from mechanic structure and part componentscontribute to fatigue failure, which most occurs at the surface of metal partcomponents. Therefore, surface—oriented engineering technology, like surfacemodification shall be a quite significant means for lowering the rate of fatiguefailure from part components.This article first systematically illustrates the current—situation study andinfluencing factors of enhancing the anti—fatigue performance of smoothmaterials and gap materials. According to the smooth sample, it discusses theeffect of enhancing the anti—fatigue performance and the surface modificationtechniques based on the engineering application such as surface chemistryprocessing, physics and electronic processing, machine processing and so on. Italso argues the gap sensitivity of material fatigue limitation, the relationshipbetween fatigue gap coefficient and stress concentration coefficient etc.According to the gap sample, it systematically analyzes and discusses themechanics performance of material’s plastic, the shape of gaps and the influenceon the formation of fatigue crack that surface processing has. It subsequentlyfinds that only by the surface modification means of surface plasticstrengthening and quenching processing can it extend the fatigue limitation ofgap material effectively.Seven groups of fatigue experiment are conducted with the material of25#carbon structural steel and the common round hole being the gap. Itsystematically studies the fatigue limitation of gap materials and the effect ofextending the fatigue limitation by mechanical processing chamfering andplastic deformation chamfering. Outlined—below are main conclusions:(1) Comparing with the smooth sample, it shortens the fatigue limitation down tothe half of the previous one with a central blind hole as a gap.(2) The effect ofextending the fatigue limitation of gap materials by mechanical processingchamfering is rather limited. When the pour angular is C1.0, it has the largestrange of extension with the number15.6%.(3) Plastic deformation chamferingcan apparently extend the fatigue limitation of round hole gap materials whenthe pour angular is C1.0, it can make the fatigue limitation the same as thesmooth materials. It can also eliminate the harm caused by the fact that the gapshortens the material limitation.(4) The primary reason why plastic deformationchamfering can extend the fatigue limitation is that this kind of meansintroduces processing sclerosis to the surroundings of round hole and makes thesurroundings of round hole exposed to the joint action with compressive stress.