共查询到19条相似文献,搜索用时 281 毫秒
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通过断口(宏观)形貌分析、微观组织分析、化学成分检测以及硬度测试等手段对SCM435钢发动机缸盖螺栓的疲劳断裂进行失效分析。结果表明,失效SCM435钢缸盖螺栓的化学成分和显微组织合格,硬度符合技术要求。失效样件1的断裂原因为表面脱碳引起的脆性断裂,螺栓断裂部位的表面脱碳层宽为120μm;失效样件2主要是非金属夹杂物所引起的疲劳断裂,近球状的CaS-CaO-Al2O3-MgO复合型冶金夹杂物造成了沿晶裂纹。对材料的塑韧性、表面脱碳及非金属夹杂物等指标,提出了改善建议。 相似文献
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针对液压起重机缸的活塞杆在使用过程中发生的断裂失效,采用扫描电子显微镜(SEM)、能谱仪和硬度检测仪等方法研究了断口形貌及局部位置的成分进行了分析,确定了裂纹源的位置和形成机理,并对断裂的原因进行了分析。结果表明:钢中的非金属氧化物夹杂、第二相粒子是活塞杆疲劳断裂的的主要裂纹源。活塞杆在交变载荷的作用下,在缺口敏感度较高的螺纹切口处产生疲劳断裂。 相似文献
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对HZW500型轴流泵轴的断裂原因进行了分析。结果表明,泵轴的断裂是低载荷小应力集中下的旋转弯曲疲劳断裂。裂纹源区存在的大量的Si、Al、Ca的氧化物夹杂是引起泵轴失效的主要原因。 相似文献
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装载机累计运行1700 h后,柴油发动机曲轴发生断裂失效。通过化学成分分析、硬度检测、金相检查、断口宏观和微观分析等方法,探究曲轴断裂失效的原因。结果表明:该曲轴的失效模式为高周疲劳断裂失效,裂纹源在曲轴第6连杆颈轴颈内部深度约6 mm区域;轴颈内部未完全闭合的缩孔缺陷和呈带状聚集分布的大颗粒(Ti,Nb,V)(N,C)非金属夹杂物是曲轴断裂失效的主要原因。发动机运转过程中曲轴在服役应力的作用下,缩孔缺陷作为裂纹源在(Ti,Nb,V)(N,C)非金属夹杂物偏聚带发生裂纹扩展长大,形成轴颈内部裂缝,并持续疲劳扩展,最终发生疲劳断裂失效。 相似文献
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为研究钛合金轮盘内部硬α夹杂疲劳裂纹扩展特性,对含预置硬α夹杂钛合金轮盘开展低循环疲劳裂纹扩展试验。结果表明:5229次循环后轮盘破裂;疲劳断口宏观、微观特征显示,预置硬α夹杂为本次疲劳破坏的疲劳源;在裂纹扩展前期,轮盘断口裂纹扩展速率较材料试验数据快;在裂纹扩展中期,断口裂纹扩展速率曲线呈对数线性关系;为了解决疲劳裂纹扩展后期疲劳条带不易识别的问题,使用等效裂纹扩展模型拟合断口裂纹扩展速率曲线,从而可以利用疲劳条带宽度来计算总寿命。同时,利用断口数据,提出和总结了预置硬α夹杂钛合金轮盘裂纹扩展特性仿真研究的方法。仿真研究显示:基于Paris公式建立裂纹扩展模型能较好地预测轮盘裂纹扩展特性;轮盘由于疲劳发生最终断裂破坏时,裂纹前沿的应力强度因子远大于断裂韧性,因此,不宜使用应力强度因子直接作为破裂准则。 相似文献
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目的找到不锈钢泵轴断裂原因。方法通过对断裂的泵轴进行失效分析,利用扫描电镜、金相显微镜、直读光谱仪、显微硬度计等测试方法和手段,对失效泵轴的断口形貌、组织、化学成分、显微硬度等进行分析。结果断口形貌呈明显的脆性疲劳开裂特征,且裂纹源呈现多源特征,有疲劳辉纹和二次裂纹存在。316L泵轴材质成分和组织问题不大,在近表面存在大量夹杂物,同时泵轴表面观察到点蚀和微裂纹存在。结论近表面夹杂物在酸性环境中极易引起点蚀,同时泵轴与联轴器根部结合处存在变截面,形成应力集中。当泵轴受到腐蚀、应力以及电机交变载荷作用时,形成腐蚀疲劳裂纹源,裂纹扩展造成瞬断是此次不锈钢泵轴断裂的主要原因。 相似文献
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S135钻杆钢预腐蚀后的弯曲疲劳性能 总被引:1,自引:1,他引:0
目的:考察有机盐钻井液对S135钻杆材料腐蚀及疲劳性能的影响。方法首先利用高温高压釜模拟有机盐钻井液井筒的工况环境,对疲劳试样进行预腐蚀,通过点蚀仪测定试样表面的腐蚀状况;然后利用旋转弯曲疲劳试验机在不同弯曲应力条件下对预腐蚀试样和未腐蚀试样的疲劳性能进行测试,算得不同存活率下的疲劳强度,并绘制不同存活率下的S-N曲线。用体视显微镜和扫描电镜观察预腐蚀试样和未腐蚀试样的疲劳断口形貌,进而得出S135钻杆材料表面腐蚀对其疲劳寿命的影响程度和影响机制。结果经过腐蚀的试样表面有较多腐蚀坑,腐蚀坑深度在0.4~0.7 mm之间。未腐蚀试样的疲劳强度为553 MPa,其疲劳断口只观察到单个疲劳裂纹源;腐蚀试样的疲劳强度为409 MPa,其疲劳断口观察到多个疲劳裂纹源。 S135钻杆材料腐蚀疲劳开裂敏感性指数为26%。结论经过高温高压有机盐钻井液环境腐蚀后,试样表面点蚀严重,腐蚀坑底部存在应力集中并导致裂纹源的形成,多个裂纹源的同时生长加快了裂纹的扩展,最终降低S135钻杆钢的疲劳强度。 相似文献
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Failure patterns of coated carbide tool were investigated by high-speed face milling of the hardened steel SKD11. Tool failure surface morphology, cutting force and machined surface roughness were also analyzed to reveal the failure mechanisms. The results indicated that the dominant failure pattern of coated carbide tool was breakage. The primary mechanism of tool breakage was fatigue fracture. Under different cutting speeds, the distinctive morphologies of fatigue fracture were presented on the failure surfaces. At low cutting speeds, many fatigue sources were observed on the rake face. The distance between fatigue sources and tool nose was approximately two times of the depth of cut. With the increase of cutting speed, the fatigue striations and riven patterns were observed at the fracture surface. In addition, the fatigue steps and crack deflection were found under high cutting speeds. The main fracture mode was intergranular fracture at lower cutting speeds. However, it was transgranular fracture at higher cutting speeds. Furthermore, the irregular fracture surfaces at low cutting speeds and at high cutting speeds contribute to a larger cutting force increment compared with the medium cutting speeds. The increment of surface roughness in the initial and severe wear stages was lower than that in the steady wear stage, while the deviation of surface roughness was relatively large. 相似文献
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目的分析喷丸对铝合金腐蚀损伤构件疲劳性能的影响,为飞机构件的维修提供有效指导。方法以未喷丸、三面喷丸、三面喷丸腐蚀后再三面喷丸3类不同表面状态的7075铝合金试样为研究对象,改变Na Cl溶液质量分数、时间、温度,获得两种程度不同的腐蚀损伤,通过疲劳寿命、断裂位置、断口形貌,分析表面喷丸状态对铝合金疲劳性能的影响。结果腐蚀损伤较轻时,喷丸试样的疲劳寿命为未喷丸试样的7.84倍,喷丸试样腐蚀后若再喷丸处理,疲劳寿命是不再喷丸试样的1.62倍。未喷丸试样的断裂位置位于截面突变颈部区域,另两类喷丸试样的断裂位置则在夹持段前端。未喷丸试样的裂纹在断口表面的边缘位置形成,喷丸试样的中心区域形成光滑平整的稳态扩展区。腐蚀损伤严重时,喷丸处理仍然会提高铝合金的疲劳寿命,但3类不同表面状态试样的疲劳寿命差距会缩小;从试样断裂位置、断口形貌看,3类试样的差异也会弱化。结论铝合金腐蚀损伤件若腐蚀前进行表面先喷丸处理,疲劳性能会有明显提升;若腐蚀后再喷丸处理,疲劳性能还会进一步提升;喷丸处理还会削弱铝合金外形截面突变处的应力集中,抑制疲劳裂纹在构件表面的萌生及延伸。 相似文献
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Influence of nonmetallic inclusion characteristics on the mechanical properties of rail steel 总被引:1,自引:0,他引:1
S. K. Dhua Amitava Ray S. K. Sen M. S. Prasad K. B. Mishra S. Jha 《Journal of Materials Engineering and Performance》2000,9(6):700-709
An extensive investigation has been carried out on six commercial heats of pearlitic rail steel to study the influence of
nonmetallic inclusion characteristics on the tensile, fatigue, and fracture toughness properties. The steels investigated
were made through the basic oxygen furnace (BOF)-continuous casting route and rolled in the rail and structural mill into
90 kg/mm2 ultimate tensile strength (UTS) grade rails. While tensile properties (yield strength [YS], UTS, and elongation) of the rail
steels investigated were found to be insensitive to inclusion type and volume fraction at their present level (0.23 to 0.45%),
the fracture toughness and high-cycle fatigue properties were found to be inclusion sensitive. The fracture toughness values
of the steels were found to range between 42.33 and 49.88 MPa √m; higher values, in general, were obtained in heats exhibiting
lower volume fractions (0.15 to 0.19%) of sulfide inclusions. The high-cycle fatigue limit, i.e., stress corresponding to 107 cycles, was found to be higher in cleaner steels, particularly in those with lower volume fractions of oxide inclusions.
This phenomenon was corroborated by scanning electron microscopy (SEM) observations of fracture surfaces, where oxide inclusions
in particular were found to be instrumental in crack initiation. Although fatigue life did not show any direct correlation
with the volume fraction of sulfides, elongated MnS inclusions were sometimes observed at crack initiation sites of fatigue-tested
specimens. 相似文献