调质42CrMo钢的弯曲微动疲劳实验研究

针对循环软化材料调质42CrMo钢进行了常规弯曲疲劳实验和弯曲微动疲劳实验,分析了常规弯曲疲劳和弯曲微动疲劳之间的差异,并讨论了循环弯曲载荷对疲劳寿命的影响。通过分析不同弯曲载荷下弯曲微动疲劳试样断口的形貌和不同循环次数下微动损伤的情况,揭示调质42CrMo钢弯曲微动疲劳过程中的损伤特性。研究结果表明:同一循环载荷作用下,弯曲微动疲劳的寿命明显低于常规弯曲疲劳的寿命;随着循环弯曲载荷的增大,弯曲微动疲劳的寿命降低更明显;微动引起的局部接触疲劳和局部塑形变形促进了弯曲微动疲劳裂纹的萌生和进一步扩展。     

加载方法对ADB610钢疲劳裂纹扩展的影响

在取样方向、几何尺寸、加工方式和加工精度相同的情况下,分别对板厚20 mm的ADB610钢进行了加载方式、加载载荷和应力比不同的成组多试样疲劳裂纹扩展试验,得到不同情况下的ADB610钢的疲劳裂纹扩展长度a与循环寿命N即a-N试验数据,且并将a-N试验数据与增K法和降K法结合进行试验分析。结果表明,当初始最大加载载荷相同时,两者lg(da/dN)-lg(ΔK)的起始位置相同,当初始最大加载载荷不同时,起始位置不相同。     

掺钽TiO2薄膜的生物活性研究

采用射频磁控溅射技术在表面纳米化316L不锈钢基体上制备掺钽TiO2薄膜,研究了不同掺钽量对表面纳米化316L不锈钢基TiO2薄膜形貌、结构、亲水性和生物活性的影响规律。结果表明掺杂适量的钽能够细化TiO2薄膜颗粒;掺钽能够改善TiO2薄膜的亲水性和生物活性;含钽36%的TiO2薄膜表面自由能比未掺杂时提高了30.1mN/m,在SBF溶液中能促进羟基磷灰石在其表面晶化。     

不同应力集中系数下磁记忆信号影响因素研究

以45CrNiMoVA钢为实验材料,加工不同应力集中系数的试件进行拉拉疲劳实验,采用磁记忆检测仪检测不同载荷及疲劳周次时试件不同位置的磁记忆信号.结果表明:载荷及疲劳周次的增加,均会使磁曲线顺时针转动,且载荷的影响明显强于疲劳周次;不同位置磁记忆信号特征不同.出现疲劳裂纹后,在一定范围内异变峰峰值显著增大.     

Multiaxial fatigue of a railway wheel steel under non-proportional loading

The results of an experimental investigation of the multiaxial fatigue behaviour of the R7T steel are presented. The R7T steel is currently employed in the production of solid high-speed railway wheels. Wheel failures due to rolling contact fatigue may occur and, on some occasions, fatigue cracks nucleate in the sub-surface region under the contact area between wheel and rail. Here, the stress field is multiaxial and the loading path is non-proportional. Specimens extracted from the rim of railway wheels were subjected to combined out-of-phase alternating torsion and pulsating compressive axial loads, a non-proportional stress state which is similar to that observed under the contact area in the wheel rim. The tests results are discussed in the light of some multiaxial fatigue theories, chosen among those based on the critical plane concept and those implementing an integral approach, with the aim of selecting a fatigue criterion suitable for the sub-surface fatigue assessment of railway wheels.     

Numerical analysis of low cycle fatigue for welded joints considering welding residual stress and plastic damage under combined bending and local compressive loads

The numerical analysis of low cycle fatigue of HTS‐A steel welded joints under combined bending and local compressive loads are implemented using the damage mechanics approach. First, a finite element numerical simulation of the welding process is employed to extract the welding residual stresses, which are then imported as initial stresses in the subsequent fatigue analysis. Second, a multiaxial fatigue damage model including damage coupled elasto‐plastic constitutive equations and plastic damage evolution formulation is applied to evaluate the mechanical degradation of the material under biaxial fatigue loads. Further, the fatigue lives of the HTS‐A steel welded joints are computed and compared with the experimental results from literature. A series of predicted load‐life curves clearly illustrates the variation of fatigue lives along with the combined loadings. Finally, the effects of local compression on accumulated plastic strain and fatigue damage are studied in detail. It is revealed that the local compression induces a damage competition between two critical zones.     

CFRP板加固含裂纹受拉钢板的疲劳性能研究

根据线弹性断裂力学理论,采用“三维块体-弹簧-板”有限元模型对裂纹尖端的应力强度因子幅值进行计算,并基于Paris-Erdogan裂纹扩展模型,提出了CFRP板加固含裂纹受拉钢板的疲劳寿命预测方法。然后对4个CFRP板加固含初始疲劳裂纹钢板的受拉疲劳性能进行了试验研究,考察了碳纤维板加固量、单面和双面加固方式对疲劳性能的影响。试验结果表明,CFRP板加固钢板的疲劳寿命比未加固钢板显著提高,疲劳裂纹扩展的试验结果与预测结果符合较好。     

MECHANISMS AND FATIGUE PERFORMANCE OF TWO STEELS IN CYCLIC TORSION WITH AXIAL STATIC TENSION/COMPRESSION

Abstract— Fatigue tests conducted under fully reversed cyclic torsion, with and without superimposed axial static tension/compression loads, were carried out using hour-glass smooth specimens in laboratory air. A high strength spring steel and a 316L stainless steel, were employed to evaluate the effects of mean stress on fatigue performance. Experimental test results show that a biaxial tensile/compressive mean stress had no influence on the cyclic stress-strain response in both materials. However a biaxial tensile mean stress was found to be detrimental to fatigue life of the high strength spring steel but had no effect on the total fatigue life of 316L stainless steel. A compressive mean stress was found to be beneficial to the life of both steels. The fatigue behaviour of the two materials was investigated by experimental observations and the application of theoretical analyses of short crack growth behaviour. Based upon the analysis of surface acetate replicas it has been found that fatigue crack growth is material/stress-state dependent. A biaxial tensile static stress promoted a change in the direction of the Stage I (mode II) crack from the longitudinal direction to a plane normal to the specimen axis in the high strength steel but not in the stainless steel. Consequently a different growth behaviour of Stage I (mode II) cracks was observed for the two materials. The effect of a biaxial mean stress on fatigue crack growth behaviour of the two materials is analysed and described in some detail.     

690合金在去离子水和干态下的微幅冲击磨损行为研究

在小载荷冲击实验台上,通过改造夹具,实现了管/平面接触方式,以模拟蒸汽发生器中传热管与抗震条发生的微幅冲击磨损。以690合金传热管和405不锈钢为试验材料,在不同的冲击载荷和润滑条件(干态与去离子水中)下进行了微幅冲击磨损试验,通过分析磨痕面积、微观形貌、断口形貌和磨损区硬度等,探讨了690合金受微幅冲击磨损和失效机理。研究结果表明:在干态环境下,小载荷时690合金的磨损机制主要为氧化和剥落。随着载荷的增大,其损伤机制为氧化磨损和疲劳磨损;在去离子水环境条件下,小载荷时,损伤轻微;随着载荷的增大,其损伤机制为疲劳磨损。水介质显著的延缓了材料的开裂时间。     

Effect of contact stress on fretting fatigue behaviour of 35CrMoA steel under multiaxial nonproportional paths

Fretting fatigue often occurs in contact couples subjected to both bulk oscillatory loads and normal loads, which accelerates the initiation and propagation of fatigue cracks. This study explores the multiaxial fretting fatigue behaviour of 35CrMoA steel with different contact stresses under diamond and square loading paths by experimental methods. From experimental results, the fracture mechanisms with the increase of contact stress have been summarized by combining the analysis of macrorupture and microrupture surface. The strain response behaviour, characteristics of fretting region and crack propagation direction are also analysed and concluded considering the influence of loading path and contact stress in this paper, which have been rarely mentioned in the previous literature. In addition, debris composition of stick and slip regions is investigated as well.     

Toward consistent fatigue crack initiation criteria for 304L austenitic stainless steel under multi-axial loads

In this paper, a new framework to correlate the experimental data of the 304L stainless steel under multi-axial fatigue loadings using a reference curve identified from the experimental data of standard uni-axial fatigue tests is proposed. A total of 15 available fatigue crack initiation criteria are tested on the experimental data of 225 fatigue tests collected from EDF (formerly known as Electricity of France), its partners and the literature. Based on the computational results, it appears that most of the crack initiation parameters of the 15 available criteria can be used to correlate the experimental fatigue data for the 304L stainless steel under uni-axial loadings. Under bi-axial loadings, most of these parameters appear not to be quite consistent. Two criteria are modified in order to better correlate the experimental fatigue data under bi-axial loads. A simple statistical approach to evaluate the consistency of the crack initiation criteria is also proposed. Based on the limited available experimental fagtigue data and within the new framework in this paper, the computational results show that the equivalent crack initiation parameters of the Varvani-Farahani’s criterion, the modified Lagoda–Macha–Sakane’s criterion and the modified Varvani-Farahani’s criterion can be used to correlate the experimental fatigue data under both uni-axial and bi-axial loadings for the 304L stainless steel. These criteria may be used to predict the fatigue life of the material under different loading and testing conditions by using the experimental data from the standard uni-axial fatigue tests.     

Rost‐ und säurebeständige Stähle unter Komplexbeanspruchung

Rust and acid resistant steels under complex loading With corrosion fatigue investigations under different loadings (R = 0,27, ‐1 and 10) and with inner pressure tests a duplex steel (1.4462) and a super austenitic steel (1.3974) are compared. The investigations were carried out in 10 % HNO₃, artificial seawater according to DIN 50905 and in two very important liquids for application (artificial seawater according to DIN 50905 with H₂S aerated and water with chloride, fluoride, bromide, iodide). For comparison the same tests under only mechanical loads were done in acid free oil. The results show that the super austenitic steel has an significantly higher resistance against corrosion fatigue as the duplex steel under one‐ and three dimensional loads up to 10⁷ cycles. The proportion between the results in the corrosive liquids and the oil can be described by a factor. In artificial seawater factors between 0,67 and 0,92 and in 10 % HNO₃ between 0,67 and 0,83 were determined depending from the loading for the duplex steel. With the super austenitic steel factors between 0,86 and 1 in artificial seawater and between 0,7 and 1,0 in 10 % HNO₃ were received.     

循环荷载作用下钢桥面铺装疲劳损伤失效行为研究

针对钢桥面铺装工程中普遍采用的改性沥青(Stone Matrix Asphalt,SMA)、浇筑式沥青(Guss asphalt,GA)、环氧沥青(Epoxy asphalt,EP)混合料双层铺装结构,进行了循环车载作用下钢桥面与沥青混凝土铺装疲劳损伤特性理论分析与试验研究。基于疲劳损伤度,研究了钢桥面铺装疲劳损伤失效行为和疲劳开裂过程中损伤场、应力和应变场动态演变机制,推导出疲劳失效时的损伤场、应力和应变场计算表达式,并给出钢桥面铺装疲劳寿命理论公式。以三座钢箱梁桥桥面铺装(润扬长江大桥2005,南京长江三桥2005,苏通大桥2008)为例,对不同铺装结构组合方案下的复合梁进行疲劳试验分析和使用寿命理论预测。实例研究结果表明,钢桥面铺装疲劳损伤失效行为预估模型合理可行;相较于改性沥青、浇筑式沥青,环氧沥青混合料具有较强高的强度低变形能力,更适合于大跨径钢桥面铺装抗疲劳的设计要求;由环氧沥青混合料组合而成的“双层环氧沥青混凝土”和“浇注式沥青混凝土(下层)+环氧沥青混凝土(上层)”的抗疲劳性能优于其它沥青混合料铺装结构组合方案,同等厚度组合情况下疲劳使用寿命可延长1倍~2倍以上;“双层环氧沥青混凝土”已应用于润扬长江大桥、南京长江三桥和苏通长江大桥钢桥面工程,并已成功运行10年以上,其跟踪观测结果良好。     

An experimental investigation of the static and fatigue fracture behaviour of hybrid composite/metal joints for a tilting car body

The hybrid composite joint structures considered in this work, for application in a tilting railroad car body, are subjected to shear and bending loads. Two types of the joint specimens were fabricated and tested under both static and fatigue conditions: a hybrid bolted-joint specimen subjected to a shear loads, and a hybrid beam-joint specimen for the bending tests. The fracture behaviours of these specimens under static loads were different from those under cyclic loads. For the hybrid bolted-joint specimens, static shear loads caused a pure shear fracture in the bolt pin body itself. However, cyclic fatigue shear loads brought about an opening-mode fracture at the local site of the bolt which was the valley of the screwed region of the bolt pin and/or the perpendicularly angled region between the bolt head and the pin body. On the other hand, for the hybrid beam-joint specimens, static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviours could arise in other industrial hybrid joints with similar sub-structures, and were used in developing a design parameter to improve a hybrid joint structure.     

Microstructural analysis of failure of a stainless steel bone plate implant

Stainless steel is frequently used for bone fracture fixation in spite of its sensitivity to pitting and cracking in chloride containing environments (such as organic fluids) and its susceptibility to fatigue and corrosion fatigue. A 316L stainless steel plate implant used for fixation of a femoral fracture failed after only 16 days of service and before bone callus formation had occurred. The steel used for the implant met the requirements of ASTM Standard F138 but did contain a silica-alumina inclusion that served as the initiation point for a fatigue/corrosion fatigue fracture. The fracture originated as a consequence of stress intensification at the edge of a screw hole located just above the bone fracture; several fatigue cracks were also observed on the opposite side of the screw hole edge. The crack propagated in a brittle-like fashion after a limited number of cycles under unilateral bending. The bending loads were presumably a consequence of leg oscillation during assisted perambulation.     

利用非线性表面波评价材料疲劳损伤

采用非线性Rayleigh表面波检测方法,实现了不同疲劳阶段下钢试样拉伸和腐蚀疲劳损伤的测试与评价;基于楔块\换能器激发与接收声波方式,搭建非线性Rayleigh波检测系统,测量了不同激励水平下基波幅值平方与二次谐波幅值间的线性关系以及Rayleigh表面波二次谐波的累积效应;分别在拉伸载荷和腐蚀疲劳载荷下,采集非线性时域信号并进行频谱分析,测量声学非线性系数在不同疲劳阶段下变化趋势,并分析不同疲劳载荷对钢试样声学非线性系数的影响。实验结果表明:超声非线性系数与疲劳周期数呈单调递增关系,可以用声学非线性系数来表征材料的表面疲劳损伤程度;相比较周期性拉伸疲劳损伤,腐蚀疲劳试样的声学非线性系数会增大,是由于腐蚀环境会加重实验中钢试样的疲劳损伤程度。研究成果可为疲劳损伤无损检测与评价提供一定的指导意义。     

Evaluation of fatigue life of aluminum alloy wheels under radial loads

This paper is concerned with generation of S–N curve for aluminum alloy (Al) A356.2-T6 and estimation of fatigue life under radial fatigue load. The S–N curve is developed by conducting tests at different stress levels under constant amplitude loading. Tests are conducted on alloy wheels for fatigue life evaluation under radial loads. Finite element analysis (FEA) is carried out by simulating the test conditions to analyze stress distribution and fatigue life of the alloy wheels. It is observed from analysis that the prediction of fatigue life using FEA is found to be in close agreement with the corresponding experimental observations. An attempt has been made by conducting parametric study to suggest a suitable safety factor for reliable fatigue life prediction.     

Stability of the plastic and fatigue properties of steel 1Khl8N9t under longtime static loads in vacuum and in liquid lithium

Stainless steel 1Kh18N9T was held for a long time under static loads in vacuum or in liquid lithium at 650°C, and the effect of this treatment on its ductility and fatigue strength was studied. The results showed that the mechanical properties of this steel are affected by the treatment studied only if the stress applied during this treatment exceeds a certain critical level.     

HIGH TEMPERATURE LOW CYCLE BIAXIAL FATIGUE OF TWO STEELS

Abstract— Biaxial low cycle fatigue tests at various temperatures and strain rates were performed on 1% Cr-Mo-V steel and AISI 316 stainless steel under combined torsional and axial loads. A correlation for fatigue strength has been derived, and it is also shown that if the Gough ellipse quadrant criterion is rephrased in terms of strain amplitudes, it may be used as a safe design rule for ductile metals in both the low and high cycle fatigue regimes.     

Thickness effects on the fatigue strength of welded steel cruciforms

Over 100 fatigue tests were conducted on high strength welded steel (HSLA-80) cruciforms of different thickness. Tests were conducted under both constant and random amplitude axial loads to characterize thickness effects on fatigue strength. Specimens were similar in size, except for the thickness which was varied between four nominal values. Examination of both experimental and analytical results (obtained using linear cumulative damage and Rayleigh approximation) indicates thicker specimens exhibit lower fatigue lives under both constant and random amplitude loadings. These results, when compared with the commonly used ‘fourth root rule' thickness correction formula, indicate the latter to be generally conservative, particularly at low stress levels.