Fatigue properties on the failure mode of a dental implant in a simulated body environment

This study undertook a fatigue test in a simulated body environment that has reflected the conditions (such as the body fluid conditions, the micro-current of cell membranes, and the chewing force) within a living body. First, the study sought to evaluate the fatigue limit under normal conditions and in a simulated body environment, looking into the governing factors of implant fatigue strength through an observation of the fracture mode. In addition, the crack initiation behavior of a tungsten-carbide-coated abutment screw was examined. The fatigue limit of an implant within the simulated body environment decreased by 19 % compared to the limit noted under normal conditions. Several corrosion pits were observed on the abutment screw after the fatigue test in the simulated body environment. For the model used in this study, the implant fracture was mostly governed by the fatigue failure of the abutment screw; accordingly, the influence by the fixture on the fatigue strength of the implant was noted to be low. For the abutment screw coated with tungsten carbide, several times the normal amount of stress was found to be concentrated on the contact part due to the elastic interaction between the coating material and the base material.     

30CrMnSiA钢制电机固定螺栓断裂原因分析

固定电机的30CrMnSiA钢制螺栓在使用过程中发生断裂,通过载荷分析、螺栓外貌及断口形貌观察、显微组织分析、化学成分及硬度检测,对其断裂原因进行了分析。结果表明:螺栓的失效性质为疲劳断裂,螺纹根部的加工损伤是疲劳裂纹源,而螺栓表面脱碳对疲劳断裂起到了促进作用。     

基于有限元分析的螺钉断裂失效研究

油泵进行可靠性强化振动试验时发现一个螺钉提前断裂。通过宏微观观察和组织、硬度检测手段,对该螺钉的断裂性质和断裂原因进行了分析。结果表明:螺钉为疲劳断裂,主要是由螺帽与螺孔周围的不良接触导致。为进一步分析不良接触现象对螺钉应力分布的影响,进行了有限元分析,计算结果表明:局部集中力能够明显改变螺钉应力分布状态,显著增加了与局部集中力同侧的螺纹底部的最大应力水平。综合分析后可知,不良接触现象中焊点与螺帽之间的不良接触是螺钉断裂的主要原因。     

某无人机螺旋桨联接螺栓断裂失效的多学科分析与改进

某型无人机在试飞试验中螺旋桨的4根30Cr Mn Si A联接螺栓发生早期断裂失效故障。综合材料失效分析、表面完整性分析、断裂强度分析、结构动力学分析、载荷-时间历史分析、螺纹联接设计分析和螺纹加工工艺分析的多学科分析方法,确定了造成接螺栓早期断裂失效的多重因素。结果表明,除4号螺栓外,其余3根螺栓均属于疲劳断裂失效。造成疲劳断裂的主要原因如下:该无人机海运中联接螺栓未进行腐蚀防护,导致螺栓遭受了海洋大气环境腐蚀,加上较大的螺栓预紧力,螺纹根部产生了腐蚀剥落和应力腐蚀损伤,大幅降低了螺栓的抗疲劳性能;试飞时发动机工作转速与螺旋桨的1节径3阶模态固有频率吻合,致使螺旋桨产生了共振,从而使联接螺栓遭受了共振疲劳载荷作用。在此基础上提出抗疲劳建议:在储运和使用中对螺栓进行腐蚀防护;避免发动机长时间工作在共振转速附近;应采用滚压加工螺纹以提高螺栓的疲劳强度;调整螺旋桨盘螺栓孔的位置,降低螺栓工作载荷;将螺钉联接设计改为螺栓联接设计,以避免铝合金内螺纹变形;适当减小螺栓预紧扭矩,以降低疲劳载荷的平均应力水平。     

新氢压缩机缸盖螺栓断裂机理及对策

某企业新氢压缩机组一级缸端盖螺栓发生断裂。结合螺纹加工工艺,对螺栓断口宏观形貌、材料化学成分、显微组织、微观形貌等展开分析。结果表明:螺栓材料内部和螺纹加工面夹杂较多,在冷滚压加工过程中导致螺纹加工表面产生开裂,齿根处微裂纹在交变作用力下引起疲劳裂纹扩展,最终导致整个螺栓断裂。     

植入铸造不锈钢髋关节断裂失效事例分析

利用ＳＥＭ对实际使用时断裂的髋关节的断口和表面进行了分析，认为此关节的断裂为以弯曲应力为主的腐蚀疲劳断裂。疲劳裂纹首先在表面的腐蚀点孕育产生，应力和腐蚀的共同作用使得裂纹得以扩展断裂。     

7B04铝合金及其螺接件的微观腐蚀机制及耐久性研究

目的 以飞机结构用7B04高强铝合金及其螺接件为实验对象,通过室内加速腐蚀试验模拟试样在南海海洋大气环境中的环境损伤,并深入分析其微观腐蚀机制与疲劳性能的内在联系。方法 通过数码相机、3D共聚焦显微镜、扫描电子显微镜等手段,研究模拟南海海洋大气环境下7B04铝合金及其螺接件的宏观/微观腐蚀特征,并借助疲劳测试分析经不同腐蚀周期后铝合金试样及螺接件的疲劳寿命。结果 铝合金及其螺接件经室内加速腐蚀试验后发生的腐蚀行为出现了明显差异,7B04铝合金试样表面发生的腐蚀行为以点蚀为主,而螺接件的腐蚀行为更加复杂。其中,远离螺接区域的暴露区的腐蚀情况与铝合金试样一致,在螺接区域发生了明显的缝隙腐蚀。此外,铝合金试样及螺接件随腐蚀周期变化的劣化规律也有所不同,腐蚀使得试样的疲劳性能均不同程度地下降。7B04铝合金疲劳寿命的递减趋势相对平缓,而螺接件在腐蚀进行到第2周期时其疲劳寿命就已降至原始寿命的一半,在腐蚀进行到第4周期时,螺接件的力学性能基本丧失。结论 经腐蚀后,铝合金试样出现了点蚀,且随着时间的延长出现了均匀腐蚀的趋势,疲劳寿命的递减趋势相对平缓。尽管螺接件的过渡区发生了严重腐蚀,但缝隙区诱发的局部腐蚀导致螺接件的受力面积减小,这是造成其疲劳寿命急剧衰减的首要因素。     

波纹管断裂故障分析

材质为1Cr18Ni9Ti不锈钢波纹管进行300h试验后发生断裂。利用光学显微镜、扫描电镜、能谱分析、腐蚀试验等手段分别对波纹管断口微观形貌、表面状态、化学成分及人为腐蚀后的形态特征等方面进行检验和分析。结果表明：波纹管内外表面存在的晶界腐蚀以及试验中振动应力是导致波纹管产生疲劳断裂的主要原因,建议在超薄结构件中不使用1Cr18Ni9Ti不锈钢。     

Investigation of fatigue failure of a stainless steel orthopedic implant device

An orthopedic implant (rush nail) fractured in a patient at a location that corresponded to the site of a prior fracture of the bone (right femur). The crack propagation in the implant proceeded from both sides of the nail, and the final fracture occurred by ductile shear in the midsection of the nail. Dimple structures and tear ridges between fatigue striation patches were observed on the fractured surface. Moreover, the device fractured within a short period of use. Contrary to post-procedure instructions, the patient placed the body’s full weight on the implanted leg at least once, perhaps twice, causing overload-induced fatigue failure of the implant.     

Development of ultrasonic thread root rolling technology for prolonging the fatigue performance of high strength thread

Fatigue failure commonly occurs at mechanical products, especially the threaded joints with high stress concentration. Even though various high strength alloys are adopted, accidence due to fatigue failure of thread still happens. As a novel method to improve the thread fatigue life, ultrasonic thread root rolling (UTRR) process is developed in this paper. The configuration of the UTRR apparatus together with the principle of the UTRR is first introduced and described. Rolling experiments are then conducted on AerMer100 thread specimens by use of the UTRR process and conventional thread root rolling (CTRR) process respectively. Mechanical characteristics and fatigue properties for these treated specimens and untreated specimens are tested. Compared with CTRR, surface finish of thread root is farther improved from Ra 0.106 to Ra 0.051, and higher residual stress is achieved for UTRR. The depth of microstructure-refined zone induced in UTRR is about 20 μm, while that of CTRR is approximately 12 μm. These further enhanced mechanical properties greatly contribute to the improvement of fatigue performance, and it is well proved by fatigue results that an increase of about 7 times for fatigue life of AerMet100 specimens is achieved after UTRR, while only 3 times is achieved for CTRR. Striations from fracture surface explicitly confirm this result.     

Biocompatible Magnesium Alloys as Absorbable Implant Materials - Adjusted Surface and Subsurface Properties by Machining Processes

Biocompatible magnesium alloys offer great potential as absorbable implant materials. They degrade within a certain time span after surgery and are therefore suitable to temporarily accomplish medical functions, for instance as bone screws or plates. These implants support fractured bones until healing. This paper describes approaches to control the corrosion of the magnesium and hereby the degradation kinetics of the implant in the organism. The degradation kinetics is adjusted via surface (e.g. topography) and subsurface properties (e.g. residual stresses) of the implant determined by the manufacturing process. Consequently, a specific degradation profile adapted to the individual medical application is achievable.     

起落架40CrNi2Si2MoVA钢螺桩断裂分析

起落架40CrNi2Si2MoVA钢螺桩在安装一段时间后发生了断裂。为确定螺桩断裂的原因,对断裂螺桩断口宏微观形貌、断裂螺桩及对比件的氢含量、材料的性能以及表面损伤等因素进行了检查,并对电镀工艺进行了评定。结果表明,裂纹主要起源于第一螺纹根部的机械损伤部位,源区以沿晶断裂特征为主,断裂件含氢量较高。综合分析认为。螺桩断裂性质为氢致延迟断裂,表面机械损伤对氢吸收和扩散的促进作用和40CrNi2Si2MoVA钢材料高强度所致的高氢脆敏感性是导致断裂的主要原因。     

直升机尾桨连杆组件失效分析

直升机在飞行降落时尾桨操纵连杆发生断裂,对断裂的尾桨连杆组件损伤及磨损情况进行外观检查,宏微观观察分析连杆断口,并对连杆的材料成分、金相组织和硬度进行检查。结果表明：连杆的断裂性质为疲劳断裂,疲劳起源于螺纹根部,疲劳区占断口总面积80%以上;连杆端部的球轴承产生了异常的磨损。分析认为：由于连杆端的球轴承产生了异常的磨损,导致其对连杆的限位功能不良,连杆发生轻微偏转使连杆上形成了附加的弯曲应力。该应力与连杆上的工作应力叠加,造成连杆发生了疲劳断裂。此外,对连杆硬度的检测表明连杆的硬度仅为HRC 22.7,说明其强度较低,疲劳抗力较差,也是连杆容易发生疲劳断裂的原因。     

飞机平尾大轴断裂故障分析

某型飞机在试验中平尾大轴发生断裂。通过断口的观察分析、颤裂部位的金相分析、硬度检测,确定了平尾大轴的失效模式,并对其断裂原因进行了分析。结果表明,该平尾大轴的断裂性质为腐蚀疲劳断裂,裂纹均起源于衬套与筒体间的定位焊点处;定位焊点处选用了强度远低于基体的08A钢焊丝,导致焊点强度过低,在工作载荷作用下焊点处过早萌生了裂纹,焊接工艺不当是大轴断裂的主要因素;平尾大轴简体内壁涂敷防锈漆的质量较差,导致筒体内壁出现严重腐蚀。裂纹源区有腐蚀坑,且裂纹扩展过程中均有腐蚀特征,说明防腐蚀措施不当引起的腐蚀对大轴断裂也有重要影响。     

Effect of surface coating on the screw loosening of dental abutment screws

Regardless of the type of performed restoration, in most cases, a screw connection is employed between the abutment and implant. For this reason, implant screw loosening has remained a problem in restorative practices. The purpose of this study was to compare the surface of coated/plated screws with titanium and gold alloy screws and to evaluate the physical properties of coated/plated material after scratch tests via FE-SEM (field emission scanning electron microscopy) investigation. GoldTite, titanium screws provided by 3i (Implant Innovation, USA) and TorqTite, titanium screws by Steri-Oss (Nobel Biocare, USA) and gold screws and titanium screws by AVANA (Osstem Implant, Korea) were selected for this study. The surface, crest, and root of the abutment screws were observed by FE-SEM. A micro-diamond needle was also prepared for the scratch test. Each abutment screw was fixed, and a scratch on the surface of the head region was made at constant load and thereafter the fine trace was observed with FE-SEM. The surface of GoldTite was smoother than that of other screws and it also had abundant ductility and malleability compared with titanium and gold screws. The scratch tests also revealed that teflon particles were exfoliated easily in the screw coated with teflon. The titanium screw had rough surface and low ductility. The clinical use of gold-plated screws is recommended as a means of preventing screw loosening.     

Microporosity effects on cyclic plasticity and fatigue of LENS™-processed steel

Special microstructures of the newly developed Laser Engineered Net Shaping (LENS?)-processed steel induce a new variability in fatigue damage formation and evolution mechanisms. The microporosity and mechanism of fatigue damage formation and growth were invested using X-ray computed tomography and scanning electron microscopy. Systematic observations were made of the variations in the fracture surfaces according to three fatigue damage evolution stages: fatigue crack formation (incubation), microstructurally/physically small cracks, and long cracks. The fatigue crack was formed almost exclusively at the relatively large pores located at or near the specimen surface, with rare cases at incompletely melted power particles on the surface. Distributed cracks from large interior pores coalesced with each other in the microstructurally small crack regime to form the major critical crack that eventually fractured the specimen. This coalescence accelerated the fatigue crack growth, which in turn decreased the fatigue life but not significantly. In the long-crack regime, the fracture surface was rougher, but the overall surface tended to be perpendicular to the loading direction, indicating a Mode I type fracture. Cyclic strain-softening, with reduced strain-hardening, was also observed. The multistage fatigue model of McDowell et al. was used to capture the microstructure effects in the three fatigue damage evolution regimes, and the upper and lower bounds for the strain–life are predicted.     

喷丸对预腐蚀后铝合金疲劳性能的影响

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。     

钻铤内螺纹接头断裂原因分析

采用宏观观察、金相检查、SEM形貌观察、EDS能谱分析等方法,对钻铤内螺纹接头断口及其断口附近螺纹根部的小裂纹进行分析,结果表明:该钻铤主要是由于上扣扭矩过大或在钻井过程中发生二次上扣,从而导致钻铤内螺纹接头在螺纹根部萌生疲劳裂纹;该钻铤接头材料的抗拉强度偏低、硬度值偏低、弯曲强度比BSR值偏低、钻井液中0含量较高等因...     

连杆螺栓断裂失效分析

发动机连杆螺栓发生断裂失效,通过断口宏微观观察、金相组织检查、硬度及拉伸性能测试、螺纹尺寸测量和化学成分分析,对连杆螺栓断裂原因进行了分析。结果表明：螺栓的断裂性质为疲劳断裂;螺栓的金相组织及化学成分未见异常,硬度及拉伸性能符合要求,螺纹尺寸不符合标准要求。综合分析认为：螺栓发生松动是螺栓断裂的根本原因;螺栓松动与装配时预紧力过小和螺纹直径偏小有关。针对断裂原因,提出了预防措施。     

2024高强铝合金腐蚀小裂纹行为研究

本文研究了2024-T62高强铝合金在带有腐蚀预损伤的基础上的腐蚀小裂纹行为。小裂纹试验采用单边缺口拉伸试样（SENT）,在试样半圆形缺口根部预制直径大小为100～300μm的单腐蚀坑,然后在3．5％NaCl溶液中进行疲劳小裂纹试验。采用QUESTAR长焦距显微镜与摄像机相结合的QUESTAR—CCD监测腐蚀小裂纹的萌生及扩展情况。试验结果表明,小裂纹绝大多数萌生在缺口根部腐蚀坑位置,并呈半椭圆形的表面裂纹;该材料在R=0.06恒幅载荷下,小裂纹效应不明显;对应可观测到的最小裂纹长度为6～60μm,裂纹起始寿命约占疲劳寿命的15％～25％。