A numerical study on the high-velocity impact behavior of pressure pipes

Pressure pipes are widely used in modern industry with some in potentially dangerous situations of explosion and impact. The security problems of these pipes when subjected to impact have attracted a lot of attention. A non-linear numerical model has therefore been developed to investigate the dynamic behavior of pressure pipes subjected to high-velocity impact. A high strain rate effect on the pipe response is considered here and the fluid and pipe interaction is modeled to include the coupling effect between the deformation of the pipe and its internal pressure. Low-velocity and high-velocity impact experimental results are used to verify the numerical model, and a reasonable agreement between the numerical and experimental results has been achieved. The effects on the dynamic behavior of the pipes of the nose shape of the projectile, the diameter of the spherical projectile, and the pipe wall thickness and internal pressure, are investigated quantitatively. During high-velocity impacts, the increase of pressure in the pipes decreases their resistance to perforation. A rise in internal pressure increases the elastic resistance of the pipes toward impacts without crack formation.     

T91钢管在冷轧过程中开裂的原因分析

通过显微组织及工艺分析发现,T91钢管在生产过程中发生开裂的原因与冷轧过程中的中间退火热处理制度、热处理炉的温度均匀性有关.要减少T91钢的开裂,可对冷轧后的钢管进行及时、充分的中间退火处理.     

Elastoplastic pipe-soil interaction analyses of partially-supported jointed water mains

Water distribution networks are essential components of water supply systems. The combination of pipe structural deterioration and mechanics leads to the failure of pipelines. A physical model for estimating the pipe failure must include both the pipe deterioration model and mechanics model. Winkler pipe-soil interaction （WPSI）, an analytical mechanics model developed by Rajani and Tesfamariam （2004）, takes external and internal loads, temperature changes, loss of bedding support, and the elastoplastic effect of soil into consideration. Based on the WPSI model, a method to evaluate the elastic and plastic areas was proposed in the present study. An FEM model based on pipe-soil interaction （PSI） element was used to verify the analytical model. Sensitivity analyses indicate that the soft soil, long pipe and high temperature induced the axial plastic deformation more likely, which, however, may not occur in normal scenarios. The soft soil, pipes in small diameters, long unsupported bedding are prone to form flexural plastic area. The results show that the pipes subjected to the same loads have smaller stresses in the elastoplastic analysis than elastic analysis. The difference, however, is slight.     

Fatigue tests of composite beam by steel fiber reinforced self-stressing concrete in the hogging bending

Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete （SFRSC） as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar’s stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone.     

Stress and Fracture Strength Analysis for Three-Way Pipes

l lgtroductionIt is well known that the safety of pipeline systemsfor transpofting oil or gas is very important in the oil orgas industry, and it will be a catastTophe if an accidentoccurs. Howevef, there are a lot of methods for ensuringthe safety of such pipeline systems, for instance,TopRAM program['] (TransCanada Pipeline RiskAssessment Model), IAP program['] (The integrityAssessment Program), In-line inspection tools for crackdetection in gas and liquid pipeline['l etc. The safety …     

Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials: a unified crack growth criterion

Fully automatic finite element （FE） modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys, is of great significance in assessing structural integrity and presents tremendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model （CZM）. The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology, integrating the developed criterion, the CZM to model the crack, a simple remeshing procedure to accommodate crack propagation, the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials, and a local arc-length solver to the nonlinear equation system, is developed and implemented in an in-house program. Three examples, i.e., a plain concrete beam with a single shear crack, a reinforced concrete （RC） beam with multiple cracks and a compact-tension steel specimen, are simulated. Good agreement between numerical predictions and experimental data is found, which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.     

三通管道的应力与断裂强度分析

Three-way pipes, T and Y pipes, are very important connecting components in pipeline systems, their strength are related to the safety of pipelines. In the case that crack is not detected in the three-way pipe, ANSYS finite element program version 5.6 is applied to study the stress distribution of the three-way pipe and to obtain the optimum fillet radius in the crotch region of the two pipes. The reasonable intersection angle φ of the two pipes is also obtained. In the case that a surface crack is detected in the three-way pipe, the maximum stress intensity factor (SIF) near the front of the surface crack is studied.     

Fatigue crack growth rate test using a frequency sweep method

Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed.     

双裂纹损伤下TBM刀盘结构疲劳寿命分析

基于Paris公式建立TBM刀盘的裂纹扩展模型,利用Workbench模拟裂纹的开裂过程,计算出其循环次数与应力强度因子。并改变双裂纹的初始长度、距离、角度,分析多部位损伤时筋板的裂纹扩展寿命。结果表明,裂纹的初始长度越长构件越容易失效,每增加2.5 mm寿命将减少35%,而双裂纹距离对寿命的影响较小,在10%以内。当裂纹方向和受力方向垂直时,构件容易失效,反之则对寿命的影响越小。该研究可为刀盘设计过程中疲劳寿命领域提供参考。     

埋地曲管流固耦合振动分析的数学建模

输液管道(包括埋地管道)的振动问题是当前学术界的一个研究热点,而数学建模又是解决问题的关键。将土约束简化为均布非线性弹簧、线性弹簧和均布荷载,推导出了埋地管道的振动微分方程。     

60Si2MnA盘条断裂原因分析

通过对断裂样品的化学成分、低倍组织、力学性能及金相组织检查进行分析,并将结果与宝钢产品结果对比,找出了样品冷拔断裂的原因,并提出了相应的改进措施。     

输流管道流固耦合振动分析中的数学建模

输流管道的振动问题是当前学术界研究的一个热点,数学建模是解决问题的关键。当前一些文献中给出的方程错误很多,物理背景也不清楚。文章修正了诸多错误,并按地上线性管道、地上非线性管道和埋地管道重新进行了分类,给出了最常用的管道振动微分方程。     

高寒地区隧道的冻害机理综述

简述衬砌混凝土的冰冻破坏、局部存水冻胀破坏、冻胀性围岩冻胀破坏以及既有裂缝裂隙水的冻胀破坏等因素对高寒地区隧道的冻害机理。     

高寒地区隧道的冻害机理综述

简述衬砌混凝土的冰冻破坏、局部存水冻胀破坏、冻胀性围岩冻胀破坏以及既有裂缝裂隙水的冻胀破坏等因素对高寒地区隧道的冻害机理。     

Young Children's Response Tendencies Toward Yes–No Questions Concerning Actions

Two experiments investigated response tendencies of preschoolers toward yes–no questions about actions. Two hundred 2‐ to 5‐year‐old children were asked questions concerning actions commonly associated with particular objects (e.g., drinking from a cup) and actions not commonly associated with particular objects (e.g., kicking a toothbrush). The impact of delay and comprehension of questions were also investigated. Results revealed a consistent developmental transition: Younger children tended to display a yes bias whereas older children did not display a bias unless they faced incomprehensible questions, in which case they displayed a nay‐saying bias. Delay shifted children's responses in such a way that “no” answers were given more often. These findings hold important implications regarding the use of yes–no questions with children.     

Risk assessment based on fault tree analysis for damaged pipe repair during operation in petrochemical plant

In petrochemical plant, the in-operation repairing is usually a repairing strategy with pressured inoperation repairing for avoiding huge economic losses caused by unplanned shutdown when some slight local leakage happens in pipes. This paper studies the effects of repairing strategies on the failure probability of the pipe systems in process industries based on the time-average fault tree approach, especially the in-operation repairing strategies including pressured in-operation repairing activities. The fault tree model can predict the effect of different repairing plans on the pipe failure probability, which is significant to the optimization of the repairing plans. At first pipes are distinguished into four states in this model, i.e., successive state, flaw state, leakage state and failure state. Then the fault tree approach, which is usually applied in the studies of dynamic equipment, is adopted to model the pipe failure. Moreover, the effect of pressured in-operation repairing is also considered in the model. In addition, this paper proposes a series of time-average parameters of the fault tree model, all of which are used to calculate node parameters of the fault tree model. At last, a practical case is calculated based on the fault tree model in a repairing activity of pipe thinning.     

LZ50车轴钢疲劳裂纹扩展试验研究

完成了连铸和模铸LZ50车轴钢疲劳裂纹扩展试验,得到了两类LZ50车轴钢的疲劳裂纹扩展曲线。采用Paris公式和另一种全范围表达式研究了两种铸造工艺下LZ50车轴钢的疲劳裂纹扩展规律。研究结果表明:Paris公式仅能描述LZ50车轴钢疲劳裂纹稳定扩展阶段的规律;全范围表达式对LZ50车轴钢的全范围疲劳裂纹扩展规律描述较好,且得到的疲劳裂纹扩展门槛值与试验曲线得到的门槛值接近,相对误差小于3%;连铸LZ50车轴钢的疲劳裂纹扩展速率门槛值低于模铸LZ50车轴钢,其疲劳裂纹扩展性能不如模铸LZ50车轴钢。     

不同外边界条件下冻结黏土冻胀力试验研究

在自行研制的一套温度、压力、位移、水分均可控的人工冻土多功能冻胀试验系统上,开展了不同外载荷,单、双向冻结模式,预留一定冻胀量等不同外边界条件下黏土冻胀力试验。得出外荷载对冻胀力发展有明显抑制作用,冻胀力变化曲线由上凸型逐渐向下凹型过渡;冻结模式对冻胀力影响很大,双向冻结模式条件下使冻胀力增长明显,但增幅随冷源温度降低呈二次曲线衰减;同一试样的冻胀力与冻胀量可用二次抛物线来拟合。试验获得了更接近工程现场实际冻结工况下黏土冻胀特性,为多排管冻结设计提供参考。     

Life extending control of helicopter based on dynamic inversion

The purpose of using life extending control for Black Hawk UH-60 helicopter is to make a trade-off between the handling qualities and the service life of critical components. An increase in service life span results in enhanced safety and the reduction in maintenance costs. This paper presents a design methodology of life extending control for structural durability and high performance of mechanical system, which is based on an explicit dynamic inversion control scheme. A real-time nonlinear fatigue crack growth model is built to predict fatigue damage resulting from the impact of cyclic bending stress on rotor shaft, which serves as an indicator of service life. The 4-axis gain- scheduled flight controller, whose gains are adjusted as a function of damage and flight velocity, is designed to regu- late roll attitude, pitch attitude, vertical velocity and yaw rate. The nonlinear system simulation results show that the responses can meet the requirements on ADS-33 Level 1 handling qualities and that the 4-axis decoupling control is realized. As the damage increases, the tracking performance is slightly degraded, which results in smaller transients in bending moment response.