Analysis and Subsequent Testing of Cracked Brass Connector Housings

This paper details the examination of brass coaxial cable connectors which exhibited cracks in their outer housings. Failure analysis indicated a brittle failure due to stress corrosion cracking. Two common stress corrosion cracking tests for copper materials were conducted on new connectors from the same manufacturing lot. Failure of these connectors confirmed the observed fracture mode. This paper shows that failure analysis can involve testing to duplicate and confirm failure mode in addition to the requisite examination of failed components. This additional testing can be especially helpful in corrosion-related failures.     

Fatigue fracture of embedded copper conductors in multifunctional composite structures

The fatigue failure mechanisms of copper strips embedded into glass/epoxy were investigated. This combination of materials composes a multifunctional electrical-composite load bearing structure that is essential for systems such as large antennas integrated into aircraft skins. In smart structures applications, bulky and heavy wiring harnesses associated with densely deployed sensors, actuators, and devices can be avoided by using embedded electrical interconnects in a manner analogous to printed circuit boards. Since metals generally exhibit lower fatigue life relative to composites, understanding the failure mechanisms associated with embedded metal conductors is necessary for improving operational life. Specimens having 0.127 mm thick embedded copper strips were used to measure fatigue life as a function of copper strain amplitude. Fracture of the conductor was observed for loading below 75% of the composite ultimate strength, without failure of the composite. The fracture surface morphology was composed of a combination of fatigue crack growth and ductile fracture, with a higher percentage of the latter existing for greater load amplitude. Crack growth in the copper was found to be strongly coupled with debonding between the copper and composite. Prevention of debonding directly influences the fatigue life of the embedded copper strip, much in the same way as composite patches retard crack growth in repaired metal structures.     

Creep fracture phenomena in iron embrittled by liquid copper

Tensile creep studies of the embrittlement of notched iron by liquid copper in the range 1100 to 1130° C have shown the embrittlement to be of the delayed failure type, from diffusion-controlled, grain boundary penetration by copper with accompanying extended surface notching. Linking of surface cracks and internal cavities along copper-penetrated grain boundaries was the final failure mode. Crack growth was determined by the rate and amount of copper diffusion ahead of a crack and not by the feed of liquid to the crack tip.     

Empirical investigation of factors affecting the stability of cable-in-conduit superconductors

Experiments investigating the stability of cable-in-conduit superconductors were performed using test conductors composed of small, quadruplex cables enclosed in steel tubes. To examine the effects of a variation in stabilizer resistivity, all test conductors contained two strands of identical NbTi/Cu composite superconductor and two strands of solid copper. The grade of copper was varied for each test conductor so that a different net stabilizer resistivity existed for each conductor. When these conductors were operated outside the range of multiple stability, tests showed that their stability was negligibly affected by stabilizer resistivity; conversely, the range of operating currents for which multiple stability occurs was affected. However, the surprising result of this study is that stability is apparently affected when a large fraction of the copper stabilizer is segregated into separate cable strands. These observations are compared with other data in the literature.     

Fracture mechanisms in a series of locomotive axle failures

This article describes the investigation of failures in a series of diesel locomotive axles. It was found that embrittlement of the axle material occurred by liquid babbitt metal embrittlement following intermittent lubrication breakdown. The embrittlement led to the formation of surface cracks that eventually propagated by fatigue until final failure occurred. The microstructure and fractographic analyses are discussed in some detail, the failure mechanisms observed differing in some aspects from those quoted in the literature in other detailed studies.     

多跨输电线路脱冰动力响应研究

提出了输电线路脱冰动力响应有限元分析方法,采用3自由度等参抛物线索单元模拟导线及覆冰,空间杆单元模拟绝缘子串,建立了多跨覆冰输电线路有限元模型.使用生死单元技术杀死覆冰单元来模拟脱冰瞬间,使动力分析时间范围包含由覆冰至脱冰的荷载突变过程,采用考虑几何非线性的隐式时间积分算法,利用自适应时间步技术克服收敛困难,对线路脱冰...     

基于铜线夹与ACSR电缆线束的异种材料磁脉冲压接接头分析

目的 探究磁脉冲技术在铜线夹与钢芯铝绞线(ACSR)电缆线束压接接头中的应用,以及放电能量对电缆接头性能的影响.方法 利用磁脉冲放电设备在40 kJ和45 kJ放电能量下压接Cu-ACSR电缆接头,观察接头宏观形貌,进行接头拉伸试验,观察接头失效情况并评价接头性能.结果 压接的位置越靠近末端,压接区直径的变形量越大.4...     

Current test on a flexible superconducting core for a 2 GVA ac cable

A 5 m long prototype co-axial flexible superconducting cable core has been made and tested at currents up to 30kA. The inner and outer tubular conductors were both formed from helically-laid strips, and the dielectric between was lapped polyethylene tape. The dielectric was tested in separate experiments. The conductor strips contained layers of nobium, niobium-zirconium and high conductivity copper. The axial contraction of the cable core was restrained by titanium tie-rods and the lay angles of the conductor strips were chosen so that the core tightened radially on cooldown. Lead-filled termination cylinders between the ends of the cable and the current leads inhibited the formation and propagation of normal regions at high currents. Local and average ac loss measurements were made from 4.7 to 10.2 K and at current densities between 10 and 200 A mm^? with very satisfactory results.     

Failure Characteristic of Laser Cladding Samples on Repeated Impact

Using self-made impact fatigue test instruments and related analytic devices, the mechanical components with laser cladding layer have been attempted. It is found that, on repeated impact force, several failure modes of the components include the surface cracks, surface plastic deformation, corrosive pitting and coat collapse, etc. The paper reported the test method and initial analysis conclusions about the unique failure characteristics of the mechanical components on repeated impact load.     

Effect of high mean tensile stress on the fretting fatigue life of an Ibis steel reinforced aluminium conductor

The aim of this work is to evaluate the effect of a high mean tensile pre-load on the fatigue life of an Ibis type of steel reinforced aluminium conductor (ACSR) mounted on a monoarticulated cast aluminium suspension clamp. To carry out the tests a new and enhanced version of a fretting fatigue rig for overhead conductors was built. Based on the obtained S–N curves for this assembly it was shown that an increase of the Everyday stress (EDS) from 20% to 30% of the cable rated tensile strength (RTS) caused an average reduction of 50% in life. Failure analysis revealed that cracks always initiated at contact interfaces within the cable/clamp assembly, at the fretting marks.     

磨煤机电机轴断裂原因分析

利用光学金相显微镜、化学分析、硬度测试等实验手段,对35号钢电机轴在使用过程中发生的断裂原因进行分析。结果表明,电机轴表面的焊接热加工使得电机轴变径台肩处的次表面部位产生高硬度马氏体组织,造成该处的严重应力集中。在长期交变载荷的作用下,电机轴的变径台肩处产生微裂纹,构成多处裂纹源。随着这些裂纹长大并不断扩展,最终造成电机轴的疲劳断裂。     

On the direct use of recovered scrap copper and saving copper with aluminum in the Chinese cable industry

The copper consumption by the Chinese Cable Industry amounted to 3.54 million tons in 2006, taking over 70% of the total copper consumption in China in that year. At present, making copper rod directly from recovered scrap copper and saving copper with aluminium have become topics of general interests in the Chinese Cable Industry. The quality of the copper conductors in the Industry is declining, resulting in sharp decrease in the rate of qualified wire and cable products. More and more copper wires are drawn from the rods made directly from scrap copper. The manufacturers know well some of the wires or rods are unqualified products though, they continue to use or produce products not complying with standards in order to make profits. Now the consumption of copper-clad-aluminum and copper-clad-steel is growing gradually. In 2006, the consumption of copper-clad-aluminum in China amounted to ca. 50 000 tons. But in some applications, neither the common understanding between buyer and supplier nor the results of feasibility study are achieved in the product orientation and technical/economic feasibility in terms of saving copper with aluminium. This paper presents the status-quo, problems arisen and suggestions in terms of making copper rod directly from recovered scrap copper and saving copper with aluminium, in a view to promote these two topics of general interests to go toward a virtuous circle.     

A flexible super conducting ac cable: radial thermal contraction and the x-ray examination of a sample length of cold core

The temperature reduction which a superconducting cable core will have to undergo following its manufacture and installation is nearly 300 K before it can be used. The satisfactory accommodation of the corresponding significant amount of thermal contraction of its component parts is therefore of major importance.This paper is concerned with such thermal contraction upon cooling of a flexible superconducting ac cable core comprising helically laid strip conductors of niobium clad copper and a polyethylene tape dielectric with electrostatic screens and bedding layers.A method is described of designing, for a controlled amount of radial contraction, a core held at near constant length. A report is also given of the x-ray examination of a sample core used for voltage tests. The relevance of the results to some other designs of core is discussed.     

Fatigue crack growth simulation in a first stage of compressor blade

A first-stage rotary compressor blade of a Model GE-F6 gas turbine failed due to vibration in early March 2008. Initial investigations showed that pitting on the pressure side of the blade caused micro cracks, leading to larger cracks due to high cycle fatigue. To assess this failure, a series of experimental, numerical, and analytical analyses were conducted. Fractography of the fractured surface of the blade indicated that two semi-elliptical cracks incorporated and formed a single crack. In this study, static and dynamic stress analyses were performed in Abaqus software. Moreover, fracture mechanics criterion was accomplished to simulate fatigue crack growth. This was carried out using a fracture analysis code for 3-dimensional problems (Franc3D) in two states. Firstly, stress intensity factors (SIFs) for one semi-elliptical surface crack and then SIFs for two semi-elliptical surface cracks were taken into account. Finally, the Paris and Forman–Newman–De Koning models were used to predict fatigue life. Since stress level and crack shape in both conditions are the same and the SIF at the crack tip reaches the fracture toughness of the blade, SIFs results indicate that insertion of a second crack has no effect on the final SIF, however, the second crack facilitates the process of reaching the critical length. So, fatigue life in two-crack condition is less than in the one-crack state.     

Failure analysis of a lead-free brass tap used in potable water

In this case study, the failure cause of a lead-free brass tap was investigated. The features of cracks were carefully studied by macroscopic inspection, chemical analysis, optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The analysis results showed that the micro segregation of bismuth in the failed lead-free brass tap was considered as an important reason for crack formation. Further examination indicated that coarse bismuth rich phases were distributed mainly along grain boundaries. The cracks were found to be a typical intergranular failure, which revealed brittle fracture for the failed lead-free brass tap. It is expected that this work may help reduce the incidences of failures during the productive process of the lead-free brass taps.     

Phases analysis and impact of phases on fracture mechanism of AZ61‐SiC composite

Phase composition of AZ61‐SiC composite with 5 wt.% of nanosized silicon carbide reinforcement was analysed and failure mechanism by in situ tensile test in scanning electron microscope was observed. Microstructure of the experimental materials was heterogeneous with grain size of 15 μm. Based on the quantitative analysis of composite, besides, silicon carbide strengthened particles added externally into the matrix magnesium silicide, magnesium oxide, and aluminium/manganese particles formed in situ were found in the matrix. In situ tensile test in scanning electron microscope has shown that reinforcing particles substantially influenced failure mechanism. Large, brittle magnesium silicide particles (size of 40 μm–50 μm) cracked during tensile deformation and at the same time, as a result of different physical properties, decohesion of the matrix and smaller aluminium/manganese, silicon carbide and magnesium oxide particles (size of 5 μm–10 μm, 10 μm and 50 nm respectively) occurred. Reinforcing particles and brittle secondary phases driven micro voids and their coalescence was found as a major cause of large cracks formation. Subsequently the increase of stress caused the cracks propagation by the coalescence of fractured particles and decohesively release smaller dispersed particles. The fracture propagated at approximately 90° angle to the direction of the tensile load direction. Fracture surface had feature of transcrystalline and intercrystalline failure.     

Fracture behavior of a corroded structural component under bending load

In order to clarify the significance of corrosion damage for risk assessment, bend tests were carried out on a roughened corroded annular plate prepared from an oil storage tank. It was found that a marked decrease of load carrying capacity occurred in the high deflection region depending upon the degree of corrosion damage. The reason for extensive loss of load carrying capacity was successfully explained from successive observation of crack growth behavior on the corroded surface of the annular plate. Photographic evidence showed that multiple cracks, initiated around individual pits, grew rapidly not only by crack growth, but also by coalescence with other neighboring cracks under the influence of plastic constraint derived from the welded joint. The linking up of multiple cracks leading to a catastrophic failure was considered to be a characteristic event of the roughened corroded component, and was expected to occur depending upon the degree of corrosion damage under a complex stress state.     

A study on the surface flashover characteristics for a HTS cable termination

Terminal technology is important component to a HTS cable as well as a conventional cable. HTS cable terminations are required when the insulated shield HTS cables connect with other conductors such as a bus or a overhead lines. HTS cable terminations must span a temperature range from 77 K to 300 K. The termination is insulated with insulating oil or air, cryogenic gaseous nitrogen and liquid nitrogen. Particularly, difficult conditions for high voltage insulation had to be overcome with HTS cable. And, several environments can substantially raise the flashover possibility at the HTS cable termination. Therefore, in order to insulating design of HTS cable termination, this paper will report on experimental investigations of the surface flashover characteristics under various surface length and GFRP thickness in the atmospheric air, transformer oil, LN₂ at atmospheric pressure and complex condition.     

微交联聚乙烯应力-光氧老化开裂行为的研究

为了提高桥梁缆索护套耐老化性能,通过制备微交联的聚乙烯材料研究不同交联度聚乙烯材料的应力-光氧老化开裂行为.采用剥离一段缆索护套并测定收缩率来计算聚乙烯护套在实际中的内应力,利用表面形貌观察、形变量测定、红外光谱分析、差式量热扫描法、凝胶含量测定等表征手段研究样品老化过程中的老化开裂行为.研究表明：随着交联度的增加,聚乙烯材料发生断裂的时间先增加后减少,表面裂纹发展的速度先增加后减小,裂纹发展速度及抗老化开裂性能最佳的交联度约为10%;聚乙烯材料的氧化速率与断裂时间呈正相关;表面裂纹出现后,材料被完全氧化;老化过程中,聚乙烯凝胶含量和结晶度均不断上升.     

Failure analysis of a cableway rope

This study is focused on the failure analysis of a cable way rope composed by different wires in which the magnetoscopic analysis has pointed out a significant and abnormal number of failure indications after a relatively short time of service. Such a phenomenon has taken place in one of the longest worldwide cableway plant and it is interesting that the performed microstructural analysis has clearly indicated that the applied steel seems featured by a good soundness of the very fine perlite micro-structure that has not been interested in any way by the decarburation phenomena. Moreover, the realized micro-hardness tests indicate a reliable homogeneity of the strength properties featuring the steel along the wire section. On the other hand, the fractographic analysis clearly indicates that the source of the failure mechanism is the initiation of the cracks in the surface of the z-shaped wire of the outer wire layer in contact with the wires of the inner layer. The coupling of the different results seems to indicate that the most probable cause of the failure mechanism has to be found in the excessive pressure applied on the rope and to the consequent sliding between the external wire layer and the inner adjacent one that produces debris and the nucleation of the crack.