Fatigue crack propagation characteristics of high‐tensile steel wires for bridge cables

The viability of single edge cracked sheet test method for rapidly determining the crack propagation characteristics of steel wires was investigated. First, fatigue tests under 3 different stress ratios were conducted on the sheet specimens which were manufactured from a kind of widely used cable wires. The test data were analysed, and the crack growth rates of sheet specimens were constructed by Walker model. Then, a series of fatigue tests were performed on notched round‐bar specimens to verify the predictability of Walker model parameters. Moreover, the experimental results obtained in different studies on crack propagation characteristics of steel wires were discussed. The results show that the crack propagation characteristics of sheet specimens behave a certain dependence on depth. The sheet crack growth laws can be well used to predict the fatigue life of notched bar specimens when the mechanical heterogeneity is considered. For bridge cable steels, the rational values for the exponent parameter of Paris law, m, should be close to 3.     

Corrosion fatigue and electrochemical behaviour of steel wires used in bridge cables

In‐service bridge wires often fail prior to the design life subjected to alternating stresses and environmental erosion. In this paper, a novel corrosion fatigue test device, integrating fatigue testing machine and electrochemical accelerated corrosion assemblies, was developed to characterize the corrosion fatigue and electrochemical behaviour of the wires. Using the developed device, corrosion fatigue tests of corroded bridge wires under different corrosion and loading conditions were conducted. Electrochemical characteristics, corrosion fatigue behaviour, failure mechanism, and so forth were investigated according to electrochemical measurements, fracture morphologies and the lifetime of wires. Results evidence the synchronization of corrosion and fatigue and show the accelerated corrosion due to static and fatigue stresses. Additionally, cracking and fracture induced by multiple crack initiation was dominant in corrosion fatigue of corroded wires, and the coexistence of multiple corrosion pits decreased the lifetime significantly.     

Beitrag niedriger Lastamplituden zur Ermüdungsschädigung von 0,15 %C Stahl

Contribution of low load cycles to fatigue damage in 0.15 %C steel The S‐N curve of 0.15 %C steel shows an endurance limit. Two‐step variable amplitude loading experiments serve to investigate the influence of numerous cycles below the endurance limit on fatigue damage. If high stress amplitudes of the loading sequences are more than approx. 15 % above the endurance limit, low load cycles contribute significantly to fatigue damage. Investigations of fatigue crack propagation under two‐step variable amplitude loading show accelerated crack growth caused by low load cycles. If high stress amplitudes of the two‐step sequences are less than 15 % above the endurance limit, beneficial influences of numerous low load cycles are found. Under these conditions, the material can sustain far greater numbers of load cycles than predicted by Miner damage accumulation calculation. Fatigue crack growth studies show that under these conditions for the high load numerous low load cycles lead to stop of the crack propagation.     

Fatigue damage of low amplitude cycles in low carbon steel

The influences of low load cycles on fatigue damage in 0.15% C steel (C15E, No. 1.1141) are investigated in the very high cycle fatigue regime using ultrasonic fatigue testing equipment. Constant amplitude (CA) endurance limits at limiting lifetime of 10⁹ cycles are determined in cyclic tension–compression and cyclic torsion tests. Non-propagating fatigue cracks are found in specimens subjected to cyclic torsion loading at the endurance limit. The endurance limit is considered as maximum stress amplitude where possibly initiated fatigue cracks do not propagate to failure. Two-step variable amplitude (VA) tension–compression endurance tests are performed with repeat sequences consisting of high stress amplitudes above the endurance limit and far greater number of cycles below. The measured lifetimes are compared with linear damage accumulation calculations (Miner calculations). If the high stress amplitude is more than approximately 13% above the CA endurance limit, detrimental influences of low load cycles and failures at low damage sums are found. If the high stress is less than 13% above the CA endurance limit, numerous low load cycles cause prolonged fatigue lifetimes and specimens can sustain large damage sums without failure. Two-step VA fatigue crack growth investigations show that load cycles below the threshold stress intensity accelerate crack growth, if the high stress intensity is 18% or more above the CA threshold stress intensity. In repeat sequences with high stress intensities 14% above threshold stress intensity, low load cycles decelerated and stopped fatigue crack growth. Low load cycles can reduce or prolong fatigue lifetimes of low carbon steel and one reason is the accelerated or retarded fatigue crack growth due to numerous low amplitudes, and the maximum load amplitude of a VA load sequence determines whether detrimental or beneficial effects prevail.     

Influence of Inhibitor Concentration on Corrosion Fatigue Crack Initiation and Propagation

The paper reports the effect of0.01,0.1 and 1%NaNO2, a passive inhibitor, on corrosion fatigue (CF) crack initiation and propagation for a low strength structural steel A537 in 3.5%NaCl aqueous solution. The experimental results show that inhibitor increases the required cycles of CF crack initiation effectively, and this effect increases with increasing inhibitor concentration.However, there is nearly no effect of NaNO2 on CF crack propagation. The same CF crack propagation rate was found in all kinds of solutions. The results also indicate that the passive time in 1%NaNO2 solution during plastic deformation is much longer than cyclic time. NaNO2 passivates the specimen sudece and repairs passive film damaged by cyclic loading during the crack initiation. while the passsive film is not formed fully due to continuous plastic deformation at the crack tip during the CF crack propagation, which is much different from that in the stress corrosion cracking and general corrosion     

Effect of acetic acids on the corrosion crack growth of 3.5NiCrMoV steels in high temperature water: synergistic interaction between stress corrosion and corrosion fatigue

Stress Corrosion Cracking (SCC) tests (pH: 3 ~ 5) and Corrosion Fatigue (CF) tests (R = 0.2, 0.1 Hz) were conducted to evaluate the effect of acetic acid on the corrosion crack growth behavior in high temperature water at 150°C. Acetic acid significantly influenced the corrosion fatigue cracking behavior of turbine disc steels in high temperature water. The CF crack growth rates of turbine disc steels increase until the organic acid concentration reaches a critical saturation value (between pH 4 and pH 3) because of the crack tip sharpening. Below the critical value of pH, the CF crack growth rates decreases because of the crack tip blunting. The corrosion fatigue crack growth rate is accelerated by the interaction of the fatigue and the stress corrosion in the test environment. The synergistic interaction should be accounted for in the realistic prediction of the corrosion fatigue life of turbine steel (3.5NiCrMoV steels) in high temperature water of acetic acid solution. With the high temperature corrosion fatigue data obtained in this study, it is possible to assess the life of turbine components in high temperature and high pressure.     

桥梁高性能钢HPS485W疲劳裂纹扩展速率试验研究

以国产桥梁用高性能钢HPS485W为研究对象,对7.5mm、12.5mm和19.5mm的HPS485W紧凑拉伸试样分别在应力比R=0.1、R=0.5和R=0.8的疲劳荷载下进行疲劳裂纹扩展速率(da/dN)试验,采用七点递增多项式的方法进行局部拟合求得试样的疲劳裂纹扩展速率。与传统桥梁用钢14MnNb相比,该文试验测得高性能钢HPS485W具有更优越的忍受疲劳裂纹扩展能力。试验结果表明:试样厚度是影响疲劳裂纹扩展速率的关键因素;对同一厚度的试样,疲劳裂纹扩展速率随着应力比R的增大而增大。此外,对19.5mm试样在荷载比R=0.1的情况下,进行工程门槛值的试验测定和理论门槛值的数值求解,分析求得19.5mm的HPS485W的理论门槛值为7.22MPa·m1/2。该文试验得到的HPS485W疲劳裂纹扩展曲线,可用于高性能钢桥的抗疲劳、防断裂设计与寿命预测。     

Analysis of Acoustic Emissions from a Steel Bridge Hanger

A steel bridge hanger with three fatigue cracks was monitored for acoustic emission (AE) using combined source location, strain gauge monitoring, and waveform analysis. AE activities from all three cracks were clearly identified and classified as crack growth or noise signals using location, strain magnitude, position on strain cycle, and uniqueness of waveforms as the primary criteria. A vast majority of AE from the cracks was found to be due to crack face rubbing and the crushing of corrosion products between the crack faces while limited crack growth emissions were detected. Results from laboratory tests on A588 compact tension specimens under variable-amplitude tension-tension fatigue loading were used to aid in interpreting AE data from the hanger. Crack growth AEs from these tests were detected only on overload cycles mostly above 92% of the maximum load while AE due to crack face rubbing occurred throughout the load cycle.     

Effect of tensile overloads on fatigue crack growth of high strength steel wires

Fatigue of the tensile armor wires is the main failure mode of flexible risers. Techniques to increase the life of these components are required to improve the processes safety on oil exploration. This work evaluates the crack growth retardation of high strength steel wires used in flexible pipelines. Fracture toughness tests were performed to establish the level of stress intensity factor wherein the wires present significant plastic deformation at the crack tip. The effect of tensile overload on fatigue behavior was assessed by fatigue crack growth testing under constant ΔK control and different overload ratios with two different load ratios. The outcomes show that the application of controlled overloads provides crack retardation and increases the fatigue life of the wires more than 31%. This behavior is also evident at stress ratio of 0.5, in spite of the crack closure effect being minimized by increasing the applied mean stress.     

低温环境下桥梁钢Q345qD疲劳裂纹扩展行为研究

为了明确在寒冷地区服役桥梁钢的疲劳裂纹扩展行为,以16 mm厚桥梁钢Q345qD为研究对象,完成了室温和低温下的夏比冲击韧性试验、疲劳裂纹扩展速率试验和疲劳裂纹扩展门槛值试验。结果表明,夏比冲击功和试样断口剪切断面率随温度的降低而减少;在应力比0.1、0.2和0.5条件下,疲劳裂纹扩展速率均随温度降低而变缓,该桥梁钢的疲劳韧-脆转变温度点在-60℃以下;在室温~-60℃,其裂纹扩展速率均对应力比的变化不敏感;应力比0.1条件下的疲劳裂纹扩展门槛值随温度的降低有略微增大的趋势。该批次桥梁钢表现出了良好的抵抗低温疲劳裂纹扩展性能,防止低温脆性破坏成为疲劳设计的重点;试验数据能为钢结构桥梁的进一步抗低温疲劳和防低温冷脆断裂设计提供参考。     

Static and fatigue investigation of second generation steel-free bridge decks

This paper outlines the static and fatigue behavior of two different cast-in-place second generation steel-free bridge decks. Although cast monolithically, the first bridge deck was divided into three segments. The first segment was reinforced according to conventional design with steel reinforcement. The other two segments were both steel-free designs with internal crack control grids, one comprised of CFRP, and the other with GFRP. The hybrid CFRP/GFRP and steel strap design is called the second generation of the steel-free concrete bridge deck. The hybrid system reduces the development of longitudinal crack width and eliminates corrosion in the deck. All three segments were tested under a 25 ton and 60 ton cyclic load to investigate fatigue behavior. The second bridge deck is comprised of an internal panel and two cantilevers and incorporates a complete civionics system [Klowak C, Mufti A. Implementation of civionics in a second generation steel-free bridge deck. In: Proceedings of the 33rd annual general conference of the Canadian Society for Civil Engineering. Toronto, Ont., June 2–4, 2005]. The static test outlined in this paper is useful in the development of fatigue theory derived from the fatigue testing of the first bridge deck.     

Corrosion fatigue behaviors of steel wires used in coalmine

The corrosion fatigue (CF) behaviors of the mining steel wire in different solutions at different applied polarization potentials were investigated in this paper. The surfaces and fracture morphologies of the steel wire at different applied potentials were observed by scanning electron microscope (SEM). The results showed that the CF life of steel wire in acid solution is the shortest. Moreover, the strong anodic polarization potential greatly reduced the CF life of steel wire, while the strong cathode potential did not reduce the CF life. For the smooth steel wire, the hydrogen impacted mainly on the plastic deformation of the wire surface. There was obvious dimple in the fatigue source zone of the wire when coupled with anode potential, and the area of the dimple increased with the increase of the applied anode potential. Conversely, the fatigue source zone of the fracture was relatively smooth at cathode polarization potential, which indicated that the crack propagation followed the mechanism of hydrogen induced cracking.     

Fatigue strength of self‐piercing riveted joints in lap‐shear specimens of aluminium and steel sheets

The self‐piercing riveting (SPR) process is gaining popularity because of its many advantages. This study investigated the fatigue strength of SPR joints in tensile‐shear specimens with dissimilar Al‐5052 and steel sheets. A structural analysis of the specimen was conducted. For this specimen, the upper steel sheet withstood applied load in a monotonic test and played a major role in the low‐cycle region. In the high‐cycle region, however, the harder surface of the upper steel sheet reduced the fatigue strength by enhancing fretting crack initiation on the opposite softer aluminium surface. Therefore, the fatigue endurance of the specimen was reduced. The fatigue endurance of a SPR joint with the combination of steel and aluminium sheets was found to be governed by the strength of the lower sheet, which is more vulnerable to the applied loading. Thus, it is desirable to use a stronger metal sheet as the lower sheet with regard to the fatigue performance. Scanning acoustic microscopy was effectively used to reveal and prove the formation and growth of subsurface cracks in SPR joints. The structural stress can predict the fatigue lifetimes of the SPR joint specimens within a factor of three.     

Corrosion fatigue of BS 4360:50D structural steel in seawater

Research on through-thickness defects is reported for BS 4360:50D structural steel in air and in seawater; the results of experiments on the propagation of surface-breaking, semi-elliptic flaws under three-point bend loading are also presented. The mechanisms of corrosion fatigue crack growth of through-thickness and semi-elliptic cracks in seawater are considered, and the application of crack growth data to endurance tests on welded cruciform and tubular joints is discussed.     

Effect of interruptions on the kinetics of cracks under low cycle loading in rigid regime

The article presents the tests of crack growth rates in low cycle fatigue tests with interruptions, carried out with specimens of steel 45 with a central notch. It is shown that with holding at the maximum, at the minimum of the load, and with zero load, endurance is substantially reduced after the same crack length has been attained. Longer recovery time leads to a more substantial decrease of endurance.Translated from Problemy Prochnosti, No. 6, pp. 121–123, June, 1990.     

Corrosion fatigue behavior of 7050 aluminum alloys in different tempers

Corrosion fatigue (CF) experiments, including both high-cycle axial fatigue (S–N curve) and fatigue crack growth (FCG), have been performed on 7050 aluminum alloys in a 3.5 wt% NaCl solution as a function of aging treatment. The results of these environmental tests were compared with those obtained in laboratory air to characterize the effect of aging treatment on CF susceptibility. Fatigue resistance in both peak aged (T6) and overaged (T73) tempers was dramatically reduced by the aqueous chloride environment. The FCG rates for T73 condition were lower than the counterparts for T6 condition in both air and saline solution. 7050-T73 alloy exhibited longer fatigue lives in air but shorter ones in the corrosive environment as compared to the T6 temper. This may be attributed to the formation of more extensive and larger corrosion pits acting as crack nuclei to facilitate crack initiation, in the T73 tempered condition. Comparison of CF and stress corrosion cracking (SCC) results reveals that overaging treatments used to improve grain boundary characteristics and increase the intergranular SCC resistance might not guarantee an equivalent improvement in the resistance to transgranular CF cracking.     

AF1410与300M钢的腐蚀冲击疲劳行为

根据舰载飞机起落的服务条件提出了腐蚀冲击概念和试验方法，考察了两种起落架材料在盐水中的腐蚀冲击疲劳行为，包括冲击疲劳寿命，裂纹萌生与扩展速率。尽管两种材料在空气中的冲击疲劳寿命几乎相等。但300M钢在盐水中的冲击疲劳寿命下降幅度较大。在盐水介质中，氢脆加速300M钢冲击疲劳裂纹的萌生和扩展。局部塑性变形区优先腐蚀促使AF1410钢的裂纹萌生，盐水对AF1410钢的裂纹扩展速率没有影响。     

Failure analysis of martensitic stainless steel bridge roller bearings

The paper is aimed at finding the likely failure mechanism of a bridge roller bearing made of high strength martensitic stainless steel. Spectroscopy and finite element stress analysis of the roller indicated that an initial radial surface crack, found at an end face of the roller and close to the contact region, was induced by stress corrosion cracking (SCC). The initial crack subsequently changed shape and increased in size under growth through fatigue and finally formed a quarter-circle radial crack centred on the end face corner of the roller. Numerically computed stress intensity factors for the final crack showed that crack loading was predominantly in Mode II. For a crack size as observed on the fracture surface, the maximum service load, as specified by the manufacturer, enhanced by a certain roller bearing misalignment effect, was sufficient for failure through fracture.     

风、列车作用下斜拉桥索-梁相关振动对拉索疲劳可靠性的影响

以实际大跨度斜拉桥为研究对象,研究了随机风、列车作用下发生的索-梁相关振动对拉索疲劳可靠性的影响。使用编制的动力有限元计算程序,建立了大跨度铁路斜拉桥全桥3维精细有限元模型,计算了斜拉桥全桥在风、列车动力作用下的振动响应,分析了全桥索-梁相关振动的特性。建立了列车交通荷载概率模型,根据桥位处风速统计数据资料建立了桥梁的风荷载概率模型,对拉索的应力谱进行了计算。依据损伤理论,使用Monte-Carlo方法开展了拉索在风、列车动力作用下的疲劳可靠度分析。研究结果表明:在斜拉桥日常运营状态中,风、列车作用下索-梁相关振动不会导致拉索共振,索-梁相关振动是拉索疲劳可靠性下降的主要原因;对于拉索在长期动力荷载下的疲劳失效概率,风场作用占比很小,列车作用占比较大;各个拉索的成桥状态索力影响了列车作用下的拉索应力幅,进一步影响了斜拉桥在长期动力作用下拉索的疲劳可靠性。     

Effect of submillimeter size holes on the fatigue limit of a high strength tool steel

The very high cycle fatigue and small fatigue crack growth behaviour of a generic tool steel material for diesel fuel injector application are described. The small crack growth tests for the tool steel material with and without the hardening heat treatment revealed the mechanisms of crack propagation and threshold behaviour. Based on the small fatigue crack propagation threshold value, an elastic plastic fracture mechanics methodology for the prediction of the endurance limit of specimens with submillimeter holes is proposed. The advantages of the new methodology are discussed in relation to existing methodologies for endurance limit prediction of specimens with small holes.