空心风扇叶片榫头裂纹原因分析

空心风扇叶片振动疲劳试验后在榫头表面出现裂纹。通过外观检查、断口宏微观分析、表面检查、成分分析、组织和硬度检测等试验,对裂纹性质和产生原因进行了分析研究。结果表明:叶片榫头表面裂纹为微动疲劳开裂,叶片与夹具间产生的微动磨损是导致该叶片过早萌生疲劳裂纹的主要原因,而产生微动磨损与叶片榫头的几何特征、夹具与其配合状态及榫头部位未采用表面处理措施有关。     

架桥机大臂钢板开裂分析

架桥机大臂钢板在使用过程中发现表面呈方形开裂,但远未达到设计使用寿命。钢板材料为低合金结构钢Q345,其综合力学性能良好。为了弄清钢板开裂原因,通过宏观观察、扫描电镜及能谱仪分析、光学显微分析等对开裂钢板进行了深入探讨,结果表明:钢板失效属于疲劳断裂,疲劳起源于焊缝夹渣,并沿着方形焊缝路径扩展。焊缝中亦存在马氏体组织,马氏体组织较脆,裂纹遇到这种组织也较容易扩展。因此,在循环使用应力作用下,起源于焊渣的疲劳裂纹沿焊缝不断扩展,最终导致钢板呈方形断裂失效。可通过改善焊接工艺、增加焊接线能量以及焊前预热处理等途径来防止裂纹产生。     

杆端关节轴承失效分析

针对直升机杆端关节轴承杆端体多次出现断裂故障进行失效分析,通过断口宏微观观察、材质检测、能谱分析、裂纹源周围特征观察以及疲劳试验件断口分析等,结合对未装机国产件和进口件杆端体内壁加工表面观察对比,分析出故障件的断裂性质为疲劳断裂,断裂起源于杆端体内壁与轴承外圈的微动磨损处,故障件发生微动磨损的原因与杆端内壁表面加工方式不合理有关。为深入查找原因,对改进工艺后的同一型号国产件通过不同装配方式进行疲劳试验性能分析和疲劳断裂件失效分析,得出采用温差装配改进后的轴承可最大程度的降低发生疲劳断裂的风险。     

连接螺栓的失效分析

某构件进行疲劳性能试验时,连接螺栓发生断裂。通过断口宏微观观察、金相组织检查、硬度及化学成分检测,确定了连接螺栓的断裂性质和原因。结果表明：连接螺栓的断裂性质为微动疲劳;断裂原因是球轴承上由于某种偶然因素形成缺口,导致球轴承上裂纹的萌生和扩展,球轴承裂纹的产生使得连接螺栓与球轴承之间的预紧力减小,局部松动而产生不均匀接触,在径向有规律的往复载荷作用下,导致连接螺栓产生微动磨损,进而发生微动疲劳断裂。     

超细晶纯钛的微动疲劳特性

利用自行设计的微动疲劳实验夹具装置研究超细晶纯钛在柱面-平面接触下的微动疲劳特性,分析循环应力对其微动疲劳寿命的影响,通过观察接触区磨损和断口形貌,分析其微动损伤机制。结果表明,当法向载荷不变时,超细晶纯钛的微动疲劳寿命随着循环应力的增加而减小,比常规疲劳寿命更小。微动疲劳裂纹于接触区边缘萌生,磨损区破裂严重且附着有磨粒,在磨粒磨损作用下加速了试样的疲劳失效。断口同时呈现出疲劳形貌和微动形貌,形貌从平滑转向粗糙直至断裂,裂纹由小变大,裂纹扩展速率也逐渐增加,且在裂纹扩展区存在二次裂纹;由于受力不均在裂纹扩展区与断裂区之间存在山脊状形貌。     

应力幅值对Al-Zn-Mg合金微动疲劳损伤行为的影响(英文)

研究了应力幅值对Al-Zn-Mg合金的疲劳损伤行为的影响。对不同应力幅值下Al-Zn-Mg合金的微动疲劳寿命以及微动疲劳损伤特性进行了研究。采用宏观力学试验与微观分析相结合的方法,对Al-Zn-Mg合金的微动疲劳机理进行了探讨。结果表明,Al-Zn-Mg合金的微动疲劳寿命随应力幅值的增加呈非线性降低;Al-Zn-Mg合金的微动疲劳寿命与位移幅度值具有一定的关系。微动疲劳损伤区存在微动磨损和裂纹萌生及扩展两种破坏机制,随应力幅值的变化而产生竞争关系。微动疲劳裂纹源均形成于微动斑边缘,微动能促使微动疲劳裂纹萌生和加速扩展。     

钛合金自冲铆接头微动磨损机理及疲劳性能

对钛合金同种TA1-TA1（TT）及异种TA1-Al5052（TA）,TA1-H62（TH）自冲铆接头进行疲劳试验,用扫描电子显微镜对断口及微动区进行观测研究其微动磨损机理,并研究下板强度对接头疲劳寿命和失效形式的影响.结果表明,断口裂纹萌生区即为微动磨损区.微动磨损导致微动区亚表面产生微裂纹并逐步扩展为宏观疲劳裂纹导致接头最终失效;微动磨屑在微动磨损过程中主要起减轻磨损作用.总体上TT接头具有最优疲劳性能,疲劳载荷较高时TA接头疲劳性能优异,疲劳载荷较低时TH接头疲劳性能优异.两板强度相当且疲劳载荷较高时失效形式主要为铆钉断裂,疲劳载荷较低时失效形式主要为下板断裂;而下板强度与上板强度相差较大时,疲劳失效形式为下板断裂.     

螺栓底座裂纹分析

本文分析了飞机前襟翼作动筒连接螺栓底座表面裂纹的形成原因。对底座表面裂纹形貌以及渗层组织进行了观察,并且对螺栓的化学成分以及硬度进行了测定。结果表明,螺栓底座的表面裂纹为渗碳层裂纹,该裂纹性质为疲劳裂纹,裂纹起始于微动腐蚀形成的表面点蚀坑。采用显微硬度法检查渗碳层深度为1．2mm,超过了渗碳层深度的设计要求（0．6—1mm）。分析认为,螺栓底座表面裂纹的形成与渗碳层深度超标有关,而微动磨损产生的点蚀坑促进了渗碳层疲劳裂纹的萌生。     

圆形路径载荷下35CrMoA钢的微动疲劳失效特性

通过柱面对柱面的接触方式,研究了35CrMoA钢在圆形路径载荷下的微动疲劳失效特性,采用扫描电子显微镜对微动疲劳试样的微动斑、磨削及微裂纹进行观察。试验结果表明:随着微动摩擦磨损的进行,磨损方式逐渐由粘着磨损转变为磨削磨损;微动斑的粘着区存在着圆形或近圆形的微小斑痕,滑移区上堆积了大量的磨屑;微动疲劳失效部位发生在粘着区与滑移区的交界处,并由于等效应力的不同而失效位置不同;微动疲劳的微裂纹存在于晶界上,并且沿晶界扩展。     

TC4钛合金耳片断裂原因分析

分析了由TC4钛合金材料制造的飞机减速板接头耳片在使用中发生断裂的故障。作动筒通过螺杆与该减速板接头耳片相连接并驱动减速板工作。通过对断裂件进行外观检查,断口宏、微观观察、能谱分析,金相组织检验等手段,确定了减速板接头耳片的断裂性质及失效原因。结果表明:该减速板接头耳片的断裂性质为疲劳断裂,其断裂源是由耳片内孔与连接螺杆之间接触所产生的微动磨损引发的;产生微动磨损的原因是由于耳片与连接作动筒的螺杆之间配合间隙不当和润滑不良所致。     

Fatigue behavior of friction stir spot welded AZ31 Mg alloy sheet joints

The fatigue behavior of friction stir spot welded (FSSW) AZ31 magnesium alloy sheet joints was investigated by tension–compression of fatigue test. The results suggest that all the fatigue failures occur at the stir zone of the FSSW AZ31 sheet joints, and all cracks initiate at the stir zone outer edge between the upper and lower sheet. When the cycle force equals 1 kN, the crack propagates along the interface of heat-affected zone and thermo-mechanical zone, simultaneously across the direction of force; while the cycle force equals 3 kN, the crack propagates along the diameter of stir zone and shear failure occurs finally. Moreover, the transverse microsections indicate that there is a tongue-like region at the outer edge of stir zone between the two AZ31 sheets, and the direction of tongue-like region is toward outside of the stirred zone and all fatigue cracks initiate at the tongue-like region.     

航空发动机高压涡轮盘辐板裂纹分析

航空发动机高压涡轮盘在外场使用后大修时,荧光检查发现后封严臂根部有裂纹显示。裂纹位于涡轮盘辐板与后封严臂转接R处,沿圆周分布,宏观上不连续。为查明涡轮盘产生裂纹的原因,本文对故障件的外观尺寸进行了检查,对开裂涡轮盘的化学成分和力学性能进行了测试,对断口进行了宏观和微观观察,并对涡轮盘裂纹处进行了应力分析和疲劳寿命评估以及实物件模拟试验,实现了故障再现。试验和分析结果表明,涡轮盘辐板与后封严臂转接R处的裂纹性质为低周疲劳裂纹,该位置的应力过大是裂纹形成的主要原因。     

锻压力对铝合金点焊接头疲劳行为的影响

采用试验和有限元分析相结合的方法，考察了锻压力对铝合金电阻点焊接头中残余应力和接头疲劳行为的影响。结果表明，采用锻压力显著降低了熔核边缘外部热影响区中的残余应力，疲劳裂纹不再从热影响区中萌生。而是全部从熔核边缘处开始；残余应力的降低使得疲劳裂纹扩展的驱动力减小，接头的疲劳强度提高。     

海洋柔性立管用钢的疲劳断裂行为

采用GPS100高频疲劳试验机研究了海洋柔性立管用钢在温轧工艺下的疲劳断裂行为。结果表明,海洋柔性立管用钢疲劳寿命随加载应力幅的升高而不断下降;疲劳裂纹产生于试样表面,裂纹源区可见变形带及河流花样,裂纹扩展区存在大量二次裂纹,瞬断区疲劳裂纹呈韧性断裂特征。在疲劳裂纹扩展过程中,裂纹的扩展能力因大角度晶界的铁素体和高强度贝氏体的相互作用而受到限制,同时在晶界处形成的二次裂纹同样可减缓扩展速率,达到提高疲劳寿命的效果。     

低温卷取热轧双相钢的显微组织及疲劳性能

采用扫描电镜、拉-拉疲劳试验机等研究了低温卷取热轧双相钢的显微组织及疲劳性能。结果表明:热轧双相试验钢的疲劳极限约为530 MPa;低温卷取工艺生产的热轧双相试验钢夹杂物平均尺寸多在5 μm以下,晶粒比较细小,马氏体组织较细小且弥散均匀分布,具有良好的综合力学性能。热轧双相试验钢疲劳裂纹源位于样品表面的棱角处,疲劳裂纹扩展区上有大量的韧窝、撕裂棱、疲劳辉纹和二次裂纹,瞬断区以浅韧窝为主,由于铁素体和马氏体发生不同程度的应变,最终二次裂纹在铁素体和马氏体的相界面萌生。二次裂纹虽然萌生但并未扩展,大量二次裂纹分散主裂纹尖端应力集中,可有效降低裂纹扩展的驱动力,降低疲劳裂纹扩散速率,抑制疲劳裂纹扩展,使疲劳强度得到提升。     

TB6钛合金疲劳及裂纹扩展性能研究

本文对TB6钛合金锻件弦向和径向两种取样方向分别进行了室温和200℃下旋转弯曲高周疲劳、轴向低周疲劳和疲劳裂纹扩展性能试验研究。试验结果表明,弦向（C）和径向（R）两种取样方向对该合金锻件的旋转弯曲高周疲劳、轴向低周疲劳性能和疲劳裂纹扩展性能没有影响;温度升高可加速该合金锻件的疲劳裂纹萌生,但在裂纹扩展阶段,该合金高温下的韧性优势与屈服强度降低的劣势平衡的结果使其在室温～200℃温度范围内的疲劳性能基本不受温度的影响;在10—20mm的厚度范围内,厚度对该合金的疲劳裂纹扩展性能没有影响;在3．5％NaCl盐雾环境中。腐蚀介质对TB6钛合金的疲劳裂纹扩展速率在初始阶段有迟滞作用,但在应力强度因子范围大于14MPa m后有加速作用。     

Influence of microarc oxidation and hard anodizing on plain fatigue and fretting fatigue behaviour of Al-Mg-Si alloy

The present study compares the performance of microarc oxidation (MAO) and hard anodizing (HA) treated Al-Mg-Si alloy (AA6063) test samples under cyclic loading in uniaxial tension with a stress ratio of 0.1 (plain fatigue) and fretting fatigue loading. Fatigue test specimens were treated using MAO and HA techniques. MAO coated specimens were ground to reduce the surface roughness comparable with that in HA coated specimens. In that process the porous outer layer was removed. Characterization of coated and uncoated specimens was done with reference to the coating morphology, microhardness, surface roughness and residual stress. The specimens were tested under plain fatigue and fretting fatigue loading at ambient temperature. While the ground MAO coating exhibited relatively less amount of porosity, HA coating had through thickness cracks. MAO coating had compressive residual stress and it was very hard compared with HA coating. Both types of coated samples exhibited slightly higher friction force than that experienced by the uncoated specimens. Fretted region of the HA coated samples was rougher than that of the MAO coated specimens. Plain fatigue lives of both coated samples were inferior to those of the uncoated specimens. The inferior plain fatigue lives of MAO coated specimens compared with those of the substrate may be attributed to the tensile residual stresses supposedly present in the substrate leading to an early crack initiation in the substrate adjacent to the coating. As friction force of MAO coated samples was higher than that experienced by uncoated specimens, the fretting fatigue lives of MAO coated samples were slightly inferior to those of uncoated samples. As the anodized layer had preexisting through thickness cracks and strong adhesion with the substrate, cracks propagated from HA coating through the interface into the substrate easily. This may be the reason for the HA coated samples exhibiting inferior plain fatigue and fretting fatigue lives compared with MAO coated and uncoated samples.     

Fatigue cracks in HVOF thermally sprayed WC-Co coatings

Initiation and early growth of fatigue cracks of a medium carbon steel with HVOF thermally sprayed WC-Co coatings prepared from two types of commercially available powders with similar total chemical composition were investigated under rotating bending conditions. The morphology of the fatigue crack is divided into two type—linear cracks and net-like cracks—depending on the types of powders and the thickness of the coatings. The fatigue cracks in thinner coatings were closer to each other than those for the thick coatings.     

TC4钛合金薄板激光焊接接头的疲劳寿命及断口分析

研究了TC4钛合金薄板激光焊接接头及母材的疲劳性能,并对其疲劳断口进行了观察.结果表明,接头的疲劳寿命在低应力水平时高于母材,在高应力水平时低于母材.母材疲劳裂纹萌生于试样表面;在裂纹扩展区有平行排列的弯曲的二次裂纹和期间更细的疲劳辉纹,瞬断区为细小的等轴韧窝.焊缝疲劳裂纹起源于表面的气孔,源区有笔直且平行排列的二次裂纹;在裂纹扩展区,断口形貌与组织有关,细晶区为韧窝,在细晶与柱状晶交界处为敞口浅韧窝,柱状晶和粗晶区为晶粒大小的刻面,上有大量的微剪切滑移带,断裂机理为滑移带形成及开裂.