接触疲劳伤损

• 接触疲劳伤损的�Ş成大致可分三个阶�D�：�W�一阶段是钢轨踏面外形的变化�Q�如钢轨�t�面出现不��^��，焊缝处出现鞍形磨损，�q�些不��^��将增大车轮寚w��轨的冲击作用�Q�第二阶�D�|��轨头表面金属的破坏，�׃��轨头�t�面金属的冷作硬化，使轨头工作面的硬度不断增长，通过总质�?50~200Mt�Ӟ�����度可达HB360�Q�此后，���化层不再发生变化，对碳素钢轨来��_��通过总质�?00~250Mt�Ӟ��在轨头表层�Ş成微裂纹。对于弹性非均等的线路当车轮及钢轨有明显不��^��时�Q�轨�剙��所受之拉压力几乎相�{�，若存在微型纹�Q�同时挠曲应力与�D�余应力同号�Q�会极大的降低钢轨强度。第三阶�D��ؓ轨头接触疲劳的�Ş成，�׃��金属接触疲劳强度不��和重载�R轮的多次作用�Q�当最大剪应力作用点超�q�剪切屈服极限时�Q�会使该�Ҏ��为塑性区域，车轮每次通过必将产生金属�U�维�l�织的滑�U�，通过一�D�|��间的�q�营�Q�这�U�滑�U�M�生积累和聚集�Q�最�l�导致疲劌����U�的形成。随着轴蝲的提高、大�q�量的运输条件、钢轨材质及轨型的不适应�Q�将加速接触疲劌����U�的萌生和发展�?/p>The formation of contact fatigue damage can be divided into three stages: the first stage is the change of rail tread shape, such as the rail surface irregularity, saddle wear at the welding joint, the irregularity will increase the impact of rail wheels; the second stage is the railhead surface metal damage, because the rail head tread metal the cold hardening, the hardness of the working surface of the rail head is constantly increasing, the total mass of 150~200Mt, the hardness is up to HB360; then, the hardening layer do not change, on the carbon steel rail, the total mass of 200~250Mt, into a tiny crack in the rail head surface shape. For elastic non equal line when the wheel and rail have obvious irregularities, rail top the tensile stress is almost equal, if the existence of micro lines, at the same time bending stress and residual stress of the same number, will greatly reduce the strength of the rails. The third stage is the rail contact fatigue formation, due to repeated action of metal contact fatigue strength is insufficient and the heavy wheel, when the maximum shear stress point over shear yielding limit, will make this point become plastic zone, wheel slip each produce metal fiber tissue by will, through a period of operation, the slip accumulation and accumulation, eventually leading to the formation of fatigue crack. With the increase of axle load does not adapt, large capacity transport conditions, the rail material and rail type contact, will accelerate the initiation and development of fatigue crack.

• 轨头工作边上圆角附近的剥���M��要是�׃��下三个原因引��L���Q�由�Ҏ��物或接触剪应力引��L��向疲劌����U�而导致剥���；导向轮在曲线外轨引�v剪应力交变��@环促使外轨轨头疲劻I����D��剥离�Q��R轮及轨道�l�修不良加速剥��ȝ��发展。通常剥离会造成�~�口区的应力集中�q�媄响行车的�q�顺性，增大动力冲击作用�Q�又促�ɾ~�口区域裂纹的��生和发展。缺口区的存在，�q�会�ȝ��金属塑性变形的发展�Q���钢轨塑性指标降低�?/p>Rail head on the edge of the stripping work near the fillet is mainly caused by the following three reasons: by inclusions or contact shear stress caused by the longitudinal fatigue crack caused in the curve stripping; guide wheel outer rail caused by shear stress alternating cycle makes the outer rail railhead fatigue, resulting in debonding; wheel and rail repair bad development accelerated stripping. Usually peeling will cause the gap region of stress concentration and influence the driving comfort, increase power of impact, but also promote the emergence and development of gap area crack. Gap area, but also hinder the metal plastic deformation, to make Rail plastic index decrease.

• 轨头�怼�是最危险的一�U�伤损�Ş式，会在列�R作用下突然断裂，严重影响行�R安全。轨头核伤��生的主要原因是轨头内部存在微���裂�UҎ���~�陷�Q�如非金属夹杂物及白点等�Q�，在重复动�?载作用下�Q�在钢轨走行面以下的轨头内部出现极�ؓ复杂的应力组合，使其不裂�U�先是成核，然后向轨头四周发展，直到�怼�周围的钢料不���以提供���_��的抵抗，钢轨在毫元预兆的情况下猝然折断。所以钢轨内部材质的�~�陷是�Ş成核伤的内因�Q�而外部荷载的作用是外因，促���怼�的发展。核伤的发展与运量、��u重及行�R速度、线路��^面状态有兟뀂�ؓ���保行�R的安全，寚w��轨要定期探伤�?/p>Head injury is one of the nuclear damage the most dangerous, will suddenly fracture in train loads, serious impact on traffic safety. The main reason of rail head injury is the existence of nuclear generated micro cracks or defects in the rail head internal (such as non metallic inclusions and white spots, etc.) in repeated dynamic load function, in the rail walking surface below the rail head internal appear extremely complex stress combination, so it does not crack first nucleation, and then to the development of rail head around, until around the nuclear injury steel material is not enough to provide enough resistance, no element warning rail in case suddenly broken. So the defect of internal rail material is the formation of nuclear weapon injury, while the external load is external, promoted the development of nuclear injury. The development of nuclear injury associated with traffic, axle load and vehicle speed, line plane state. In order to ensure the safety of driving, on the rail to regular inspection.

• 减缓钢轨接触疲劳伤损的措施有�Q�净化轨钢，控制杂物的�Ş态；采用淬火钢轨�Q�发展优质重轨，改进轨钢力学性质�Q�改革旧轨再用制度，合理使用钢轨�Q�钢轨打���；按轨钢材质分�c�铺轨等�?/p>Mitigation of rail contact fatigue measures: purification of rail steel, control of debris morphology; using the quenched rail, the development of high quality heavy rail, improve the mechanical properties of rail steel; reform the old rail reuse system, the rational use of rails; rail grinding; according to the rail steel material classification laying etc.