Failure analysis of vessel propeller bolts under fastening stress and cathode protection environment

This paper describes the failure analysis of propeller blade fastening bolts made from martensitic stainless steel 0Cr16Ni5Mo, which was ruptured under service of cathode protection for 5 years. The general crack pattern of the bolts, fractographic features, hydrogen content determination and slow tensile test results are all exhibiting the characteristics of hydrogen embrittlement. Accordingly, hydrogen diffusion driven by hydrogen concentration gradient and stress concentration was identified by experiment and finite element analysis (FEA). The morphology of the crack was intergranular of initiation from bolt cap root surface, and quasi-cleavage of propagation. The hydrogen distribution indicated that the hydrogen concentration in the bolt was in gradient distribution, and the region farther away from the sea water contains less hydrogen content. This revealed that hydrogen entered the bolt top surface through sea water under cathodic protection, and diffused from top to cap. The hydrogen content of the cap where crack initiated was 7.0 ppm, which was much higher than that in bolt shaft with normal content of 1.1 ppm. Results of low tensile test together with fractographic observation showed that the brittleness of the bolt was enhanced by the effect of hydrogen. Stress distribution calculated by FEA analysis indicated that the maximal stress of the bolt was about 1016 MPa, located at cap root surface which was consistent with crack initiation sites. The stress drove hydrogen to accumulate at root surface until cracking occurred. In a sum, the failure was attributed to the hydrogen diffusion, local high stress, and the martensitic microstructure susceptible to hydrogen embrittlement. Remedial measures such as avoiding over protection potential, that increase tempering temperature were suggested. Methods to optimize stress distribution of the bolt were also suggested based on FEA calculation.     

Impact Response Study on Covering Cap of Aircraft Big-Size Integral Fuel Tank

In order to assess various design concepts and choose a kind of covering cap design scheme which can meet the requirements of airworthiness standard and ensure the safety of fuel tank. Using finite element software ANSYS/LS- DYNA, the impact process of covering cap of aircraft fuel tank by projectile were simulated, in which dynamical characteristics of simple single covering cap and gland double-layer covering cap impacted by titanium alloy projectile and rubber projectile were studied, as well as factor effects on simple single covering cap and gland double-layer covering cap under impact region, impact angle and impact energy were also studied. Though the comparison of critical damage velocity and element deleted number of the covering caps, it shows that the external covering cap has a good protection effect on internal covering cap. The regions close to boundary are vulnerable to appear impact damage with titanium alloy projectile while the regions close to center is vulnerable to occur damage with rubber projectile. Equivalent strain in covering cap is very little when impact angle is less than 15°. Element deleted number in covering cap reaches the maximum when impact angle is between 60°and 65°by titanium alloy projectile. While the bigger the impact angle and the more serious damage of the covering cap will be when rubber projectile impact composite covering cap. The energy needed for occurring damage on external covering cap and internal covering cap is less than and higher than that when single covering cap occur damage, respectively. The energy needed for complete breakdown of double-layer covering cap is much higher than that of single covering cap.     

Base stock versus WIP cap in single-stage make-to-stock production–inventory systems

A single-stage production-inventory system produces parts in a make-to-stock mode, and unsatisfied demand is backordered. The system operates under a so-called base stock with WIP cap replenishment policy, which works as follows. Whenever the Work-In-Process (WIP) plus finished goods inventory falls below a specified level, called base stock, a replenishment order for the production of a new part is issued. If the WIP inventory is below a different specified level, called WIP cap, the order goes through and a new part is released for production; otherwise, the order is put on hold until the WIP inventory drops below the WIP cap. First, it is shown that the optimal base stock that minimizes the long-run, average, inventory holding cost for a given minimum customer service level, is a non-increasing function of the WIP cap that reaches a minimum value, called minimum optimal base stock, at a finite WIP cap value, called critical WIP cap. Then, it is shown that the optimal WIP cap is less than or equal to the critical WIP cap and therefore the optima! base stock is greater than or equal to the minimum optimal base stock. More interestingly, however, it is conjectured that the optimal WIP cap is in fact exactly equal to the critical WIP cap and therefore the optimal base stock is exactly equal to the minimum optimal base stock. The minimum optimal base stock is none other than the optimal base slock of the same system operating under a classical base stock policy (with no WIP cap). Finally, the optimal parameters of a system operating under a base stock with WIP cap policy are related to the optimal parameter of the same system operating under a make-to-stock CONWIP policy.     

Prediction of Interfacial Cracking due to Differential Drying Shrinkage of Concrete in Precast Shell Pier Cap

In a precast shell pier cap, cracking at the interface between the precast shell and the cast-in-place concrete may happen due to differences between the drying shrinkage of the inner and the outer concrete. The objective of this study is to establish a prediction method for interfacial cracking that will consider the real mechanism of differential drying shrinkage and creep. The main parameters used in the analysis were determined from experiments for a concrete mix that is applied to the manufacturing of pier caps. The variation of internal relative humidity over time was first calculated based on the nonlinear moisture diffusion; cracking analysis then followed. Prediction of the initiation of interface cracks and the increase of their width over time was performed. It was found that additional reinforcement across the interface is very effective at reducing crack width.     

某火帽发火可靠性的影响因素

为提高火帽发火可靠性,对击发药的吸湿性、装药量、耐压性、壳底厚度、装配工艺等影响因素进行分析和验证。结果表明:击发药装药量小,火帽输出能量降低;击发药、火帽壳、加强帽受潮,对火帽输出能量的降低影响较大;压药压力过低,针刺感度随之下降。同时,通过不同条件下的药盘点火试验,确定了正确判断火帽发火不可靠的条件。击发药装药量为28~32 mg,压药压力为180~310 MPa,药剂与管壳在装配前进行烘干,火帽能实现可靠发火。     

用爆炸声级评估雷管输出的可能性探讨

雷管在空气中爆炸时，空气中冲击波的能量占雷管释放总能量的绝大部分．在一定条件下冲击波衰减成声波，声级的大小直接与爆炸的药量有关．文中分析了这些理论，对比了铅板法试验结果与爆炸声级，指出了用爆炸声级评估雷管输出的可能性．     

不同缓冲层和保护层对NiFe/PtMn双层膜磁性的影响

制备了以Ta和非磁性NiFeCr作为缓冲层和保护层的NiFe/PtMn双层膜,研究了它们的结构和物性,结果表明:用NiFeCr做缓冲层和保护层的NiFe/PtMn双层膜,其交换偏置场比以Ta为缓冲层和保护层的NiFe/PtMn的交换偏置场有了10%的提高;退火处理以后,以NiFeCr为缓冲层和保护层的样品的磁性层NiFe的磁矩降低要小于以Ta为缓冲层和保护层的样品的磁性层NiFe的磁矩降低.同时,XRD测量计算发现,以NiFeCr为缓冲层生长的NiFe/PtMn样品比Ta为缓冲层生长的NiFe/PtMn样品具有更好的织构,更大的平均晶粒尺寸,因而具有更好的热稳定性.NiFeCr比Ta更适合做基于Mn合金为反铁磁层的缓冲层和保护层.     

承台破坏形式判别的研究

给出针对所作研究的承台冲跨比定义。结合试验、有限元研究与相关理论分析,阐述了承台冲跨比是决定承台破坏形式的第一要素,明确了承台内梁、拱作用的对比变化和破坏形式的变化情况,推导出了梁拱作用并存情况下承台破坏形式的判别表达式,分析确认了完整的承台破坏形式的判别条件,推演出目前实际工程中承台发生的往往是冲切破坏。所作的分析与讨论为承台破坏形式的判别提供了解决方法。     

Numerical Generation of Nanotube Caps II. Exact Results Up to (10, 10)

The numerical algorithm for cap generation [1] is further developed. the cap unfolding method proposed in ref. [2] is used. Some aspects of the cap unfolding onto the honeycomb lattice [3] are also considered. Topological invariants of the cap structures are used to eliminate the duplicate structures. the list of all distinct IPR (5, 5) - (10, 10) caps structures is generated.     

基于机器视觉的偏口桶旋压盖一体机应用研究

目的设计一台偏口桶专用旋压盖一体机,以解决偏口桶桶口位置不确定的问题,提高上盖速度和效率。方法采用机器视觉定位系统自动定位桶口位置信息,经坐标转换后,通过TCP通讯将其传递给机器人,利用机器人的快速性及精确性,完成取盖、旋内盖及压外盖操作。结果现场搭载试验系统,对坐标变换进行数值拟合并进行旋压盖操作,定位误差基本控制在0.8 mm以内,寻口准确快速,取盖一次完成,只需对桶口定位一次,即可完成旋盖和压盖2道工序。结论该设备经实际应用,工作可靠,寻口快速,封口效率高。     

多剂量口服溶液开瓶扭矩影响因素的探究

目的研究对口服溶液开瓶扭矩产生影响的因素,作为制订口服溶液灌装、封盖和检验规程的理论基础。方法运用单因素实验、独立样本t检验的研究和统计方法,对口服溶液开瓶扭矩的影响因素,即封盖扭矩、瓶盖内垫是否接触药液和封装完毕后药瓶的正立静置时间进行探究。结果封盖扭矩在136~226 N·cm范围内时,开瓶扭矩随封盖扭矩的增大而增大;瓶盖内垫与药液接触1 h后,开瓶扭矩显著增大;以169 N·cm旋紧瓶盖后,开瓶扭矩随静置时间延长而增大。结论口服溶液的开瓶扭矩受到多因素影响,包括封盖扭矩、瓶盖内垫与药液的接触和封瓶后的静置时间。在口服溶液的封装、检验、运输和储存中,应控制这些因素,使开瓶扭矩保持在合适范围内。除此以外,开瓶扭矩随封盖扭矩和时间变化的趋势可为生产过程的参数设置提供数据支持。     

Effect of radiation-induced charge accumulation on build-up cap on the signal current from an ionisation chamber

The signal current from a thimble ionisation chamber with a build-up cap made of an insulator decreases by about 0.41 % after being irradiated for 17 h at an air kerma rate of 41 Gy h(-1) by a collimated (60)Co gamma-ray beam in air. In contrast, the signal current remains constant when the thimble ionisation chamber is irradiated in a water phantom. During irradiation, positive charge is considered to accumulate near the outer surface of the build-up cap where electron equilibrium is not achieved. Secondary electrons travelling in the build-up cap and the chamber wall toward the ionisation volume are decelerated by the electric field generated by the positive charge. Consequently, the signal current decreases with increasing charge accumulation because some secondary electrons are prevented from entering the ionisation volume. In the water phantom, electron equilibrium is established in and around the ionisation chamber and charge does not accumulate. To confirm this hypothesis, the signal current was measured for an ionisation chamber in air with a build-up cap wrapped with Al foil and covered with PMMA tubes. Electron equilibrium was established over the build-up cap because the tubes were thicker than the secondary electron range. The signal current decreased with increasing positive voltage applied to the Al foil. It was estimated from the results that positive charges equivalent to a voltage of over 6 kV applied to the Al foil accumulated during irradiation. The signal current was also measured for an ionisation chamber with a metal build-up cap and for an ionisation chamber with a wall and build-up cap made of conductive plastic.     

Computation of the maximum torque of a cap liner using a power‐law friction and finite element analysis

In the ‘filled closed’ containers, the cap removal torque and the sealing of the contents are two crucial criteria in the closing quality, and the consumer perceives these two parameters as constituting a guarantee of packaging integrity. This work looks at the experimental study and the finite element analysis of the maximum torque of a metal cap with a liner over a glass bottle. For studying parameters influencing the cap removal torque (twist‐off torque), several experiments and simulations were conducted in order to evaluate the maximum torque of a loose crown cap. A test bench was built to measure the torque required to slide a cap liner on the top of a glass bottle, and the result of the experiment is compared with the predicted torque given by an axisymmetric finite element (FE) analysis. Since the behaviour of the cap liner is hyperelastic, compression and friction tests were conducted to evaluate the elastic properties and the non‐linear static friction behaviour of the elastomer seal. Contact regions, material non‐linear elasticity for the liner and large displacement options are included in the FE model in order to describe the evolution of the contact area and the distribution of contact pressure as a function of the applied force. The predicted maximum torque is then calculated by a numerical integration scheme over the contact surface, using an experimental coefficient of static friction as a function of the normal pressure. The predicted torque shows good agreement with that measured through experiments, thereby making it possible to understand the influence of the liner on the cap removal torque of a glass bottle. Copyright © 2010 John Wiley & Sons, Ltd.     

碳抵消机制下的制造/再制造生产决策优化研究

为研究碳排放权抵消机制对制造/再制造生产决策的影响,分别构建基于配额和基于排放量两种抵消机制的生产决策优化模型。分析抵消上限、再制造品接受度对产量、企业利润、消费者剩余和社会总福利的影响。结果表明,抵消机制会提高新品产量并降低再制造品产量,增加企业利润、消费者剩余和社会总福利,以上变化幅度随抵消上限的提高先增大后减小。再制造品接受度较高时,最优解对抵消上限变化更敏感。政府应将抵消上限设定在低水平且谨慎调整,可通过适度牺牲企业利润提高社会福利。拥有高配额的企业在配额机制下运作更具效益,反之在排放量机制下更优。     

Numerical Generation of Nanotube Caps II. Exact Results Up to (10, 10)

Abstract

The numerical algorithm for cap generation [1] is further developed. the cap unfolding method proposed in ref. [2] is used. Some aspects of the cap unfolding onto the honeycomb lattice [3] are also considered. Topological invariants of the cap structures are used to eliminate the duplicate structures. the list of all distinct IPR (5, 5) - (10, 10) caps structures is generated.     

Design optimization of the bell type blast cap employed in small scale industrial circulating fluidized bed boilers

Blast cap is the key component of air distributor in circulating fluidized bed (CFB) boilers. Its configuration and performance affects the fluidization quality of the bed, as well as the boiler performance. With the advantage of controlling the jet penetration characteristics and the resistance coefficient individually, bell type blast cap has been widely applied in big-scale utility CFB boilers. Moreover, the inner circuitous gas pass of the bell-type blast cap is able to prevent the bed material from flowing backward into the air chamber effectively, and its tube shield is also convenient to be maintained and replaced. Consequently, the bell-type blast cap is also fit for the small scale industrial CFB boilers with lower operation and maintenance levels in spite of higher manufacturing cost. At present, bell type blast cap is mainly applied in the large scale utility CFB boilers, seldom employed in the small scale industrial CFB boilers with lower bed pressure drop. In the study, aim to acquire favorable fluidization quality and reasonable pressure drop of the bed of small scale industrial CFB boiler, the air jet penetration characteristics of the bell type blast cap were investigated in static beds composed of two typical solids in CFB individually, and the impacts of the inner configuration on blast cap’s resistance characteristics were studied via numerical simulation. The detailed design principle and approach of bell type blast cap was proposed finally based on the study results.     

On the bullet sensitivity of commercial explosives and blasting agents

This paper presents the results of experiments conducted to compare the projectile, cap, and bullet sensitivity of a number of commercial explosives and blasting agents. It was found that No. 8 electric blasting caps having either aluminum or copper shells yield essentially equivalent results in cap sensitivity testing. It was also found that the results of projectile impact tests could be correlated with the results of cap sensitivity measurements in the sense that a projectile velocity could be defined that represented the approximate threshold between cap sensitivity and cap insensitivity. The most important finding was that under ordinary conditions of confinement expected in the transport and storage of explosives, materials that were not sensitive to a No. 8 blasting cap were not observed to be sensitive to rifle-fired bullets.     

不平衡弯矩作用下有受拉桩的厚承台梁拱作用机理探讨

进行了不平衡弯矩作用下有受拉桩的厚承台实验与有限元研究,表明该种承台可以因有梁作用而发生弯曲破坏,而受弯曲作用的同时,又因有拱作用而使得空间桁架的传力体系依然存在。梁拱作用并存在厚承台中具有一定的普遍性。     

Failure Analysis of Cap Screws in a Diesel Engine Front Gear Train

Two failures of the front gear train cap screws of a diesel engine in a marine vessel are investigated. Fractured cap screws were present in both failures. The cap screws’ strength was compared to standards. The thread engagement was also analyzed. In one failure, the cap screws used did not comply with the standard properties and in the other failure, improper thread engagement resulted in fast fracture after few load cycles.     

Failure of malleable cast iron sprinkler pipe end cap due to freezing of water within

Failures in end caps of sprinkler firewater systems frequently occur due to the freezing of the water inside the sprinkler systems on cold winter days. In these failures, a flat top of an end cap of a sprinkler system fails and completely separates from the threaded body of the end cap. In this study, metallurgical investigations including fractography, metallography, EDS analysis, and hardness measurement were performed for the failure analysis of the end cap. Finite element analysis was employed to identify both the maximum stress location and the maximum stress magnitude resulting from the freezing of and interaction between the ice and end cap when temperature dropped below the freezing point.Microstructure observations confirmed the ferritic malleable cast iron of the end cap. The hardness of the end cap was significantly below the hardness range specified for standard ferritic malleable cast iron. Small cracks formed during the casting of the end cap and the low strength of the end cap caused the final fracture. Failure stress determined by finite element analysis simulating the freezing of the inside water could accurately predict the failure stress and failure temperature. High tensile stress and poor manufacturing quality caused the crack to propagate in the cleavage mode and at the final stage in the ductile mode.