EFFECTS OF TENSILE STRESS AND IMPURITIES ON CREEP ACTIVATION ENERGY OF PLATINUM

The effect of tensile stress and trace amounts of impurities on the creep activation energyof platinum was studied and the creep mechanism was disscussed.

Distribution patterns of rock mass displacement in deeply buried areas induced by active fault creep slip at engineering scale

Active fault creep slip induces deformation of rock mass buried deeply in fault zones that significantly affect the operational safety of long linear projects passing through it.Displacement distribution patterns of rock masses in active fault zones which have been investigated previously are the key design basis for such projects.Therefore,a discrete element numerical model with different fault types,slip time,dip angles,and complex geological features was established,and then the creep slip for normal,reverse,and strike-slip faults were simulated to analyze the displacement distribution in the fault rock mass.A disk rotation test system and the corresponding laboratory test method were developed for simulating rock mass displacement induced by creep slippage of faults.A series of rotation tests for softand hard-layered specimens under combined compression and torsional stress were conducted to verify the numerical results and analyze the factors influencing the displacement distribution.An S-shaped displacement distribution independent of fault dip angle was identified corresponding to reverse,normal,and strike-slip faults.The results indicated that the higher the degree of horizontal extrusion,the softer the rock mass at the fault core,and the higher the degree of displacement concentration in the fault core;about 70%of the creep slip displacement occurs within this zone under 100 years of creep slippage.

Microscopic Indicators of Stick-Slip and Creep-Slip in Deformation Products From the Daqingshan Piedmont Active Fault

Through the collection of oriented samples,consolidation of undisturbed samples,and systematic microscopy of thin sections,the deformation products from the Daqingshan piedmont active fault zone have been studied.The obtained results have been analyzed in combination with those of rock fracture experiments and macroscopic surveys.Based on the above,the present article summarizes the microscopic indicators of stick-slip and creep-slip,which reflect the characteristics of fault movement,and has given some suggestion on relevant problems.

The creep behavior of Mg-9Al-1Si-1SiC composite at elevated temperature

The creep properties of as-cast Mg-9Al-1Si alloy and Mg-9Al-1Si-1SiC composite were compared.The results show that Mg-9A1-lSi-lSiC composite performs a better creep resistance than that of Mg-9Al-1Si alloy at constant temperature and stress(473 K,70MPa).Besides,the creep behavior of Mg-9Al-1 Si-1SiC composite at various temperature from 448 K to 498 K and under stresses of 70-90 MPa were systematically investigated.The Mg-9Al-1 Si-1SiC composite exhibited a stress exponent from 5.5 to 6.9 and the creep activation energy fell within the range of 86-111 kJ/mol.The results showed that the creep mechanism of Mg-9Al-1Si-1SiC composite was mainly attributed to the effects of secondary phase strengthening mechanism and dislocation climb mechanism.

Effect of Zr on behavior of compressive creep in as cast ZA27 alloy

The effect of Zr on the behavior of compressive creep in as cast ZA27 alloy was investigated in the temperature range of 20160 ℃ and under different compressive stresses in the range of 50137.5 MPa with special apparatus. The results show that the primary compressive creep strains and steady creep rates of ZA27 Zr alloy and ZA27 alloy increase with increasing temperature and stress. However, the primary compressive creep strain and steady creep rate of the ZA27 Zr alloy are lower than that of the ZA27 alloy below 100 ℃, but higher at 160 ℃. The compressive creep behaviors in both ZA27 Zr alloy and ZA27 alloy obey an empirical equation ln t=C-n ln σ+ Q/RT , and the exponent stress n is 3.63 for ZA27 Zr alloy and 3.46 for ZA27 alloy, respectively, the activation energy Q is 87.32 kJ/mol for ZA27 Zr alloy and 81.09 kJ/mol for ZA27 alloy. Different material structural constants are associated with different compressive creep behaviors in the alloy. The compressive creep rate in the alloy is controlled by the lattice diffusion of zinc and dislocation limb.

CREEP BEHAVIORS OF Mg MICROALLOYED WROUGHT SUPERALLOYS

By adding small amount of Mg to the wrought superalloys,the steady stage of creep,and es- pecially the tertiary stage of creep are prolonged.Also,the steady creep rate is decreased within the range of low strain rates.At higher strain rates,however,the effect of Mg on creep rate vanishes.This may be attributed to the Mg dissolution in the matrix.A mechanism of the effects of Mg addition on creep behaviors is proposed.

Influence of Pre-Compressive Creep on Internal Friction Stress and Creep Parameters of Nickel-Base Single Crystal Superalloys

By means of pre-compressive creep treatment, the cubic γ′ phase in a nickel base single crystal superalloy is transformed into the P-type rafted structure. And the influence of the pre-compressive creep on the internal friction stress and creep lifetimes of the superalloy are investigated by means of the measurement of the creep curves and microstructure observation. Results show that, compared to the P-type structure alloy, the full heat treated state alloy displays a bigger internal friction stress value of dislocation motion during steady state creep and a longer creep lifetimes. The creep activation energies of the full heat treated and P-type structures alloys are measured to be 462 kJ/mol and 412 kJ/mol, respectively. Thereinto, the P-type rafted γ′ phase in the alloy is transformed into the N-type structure during tensile creep. And the N-type γ′ phase transformed from the P-type structure displays a shorter size in length, this is a main reason of the P-type structure alloy possessing a shorter creep lifetimes due to creep dislocation moving easily over the rafted γ′ phase.

STEADY-STATE CREEP OF UNIDIRECTIONAL C/C COMPOSITE WITH PYROLYTIC CARBON MATRIX

The steady-state creep behavior of unidirectional C/C(1-D-C/C) composite with pyrolytic carbon matrix was investigated at high temperatures up to 2160℃ and under tensile stress from 133.83 to 213.46MPa. Based on the creep experiment of single specimen method, the apparent activation energy and the stress exponent for steadystate creep were determined by the use of a self-made apparatus and an auto-testing system. Value of apparent activation volume is provided and the creep mechanism has also been discussed.

Creep Function Parameter Analysis for Optimum Design with Calcium Carbonate Nanofiller – Polypropylene Composite

This paper is about the use of power law model to fit experimental creep data of PP reinforced with calcium carbonate nanofiller at 10% optimum volume fraction with a view to characterizing the new material (PPC2) parametrically. The creep parameters were evaluated for neat (PPC0) and reinforced PP (PPC2) to establish the influence of reinforcement on the creep variables like creep rate and creep activation energy. The coefficient parameter A estimated within the stress level range 13.08MPa-22.88MPa has the range 0.0165-0.0651 while the exponent parameter n has 0.299-0.370. The creep stress coefficient K and exponent m has the respective values 161.495 and 0.3288 for PPC0 and 1881.4965 and 0.5448 for PPC2. The value of the parameter p similar to Larson-Miller has the value 4014.1871. Two creep function models used found that PPC0 has higher activation energy with value 9.3642E-20 J/mol for the stress 13.08MPa and PPC2 has values for the stresses 13.08MPa, 19.61MPa and 22.88MPa as 5.55998E- 20J/mol,5.4573E-20J/mol and 4.845E-20J/mol respectively. Of the two master curves produced, that following Larson-Miller parameter is recommended as the relationship between lnσ and parameter f(σ) is relatively linear and will give better results than the curve assumed to follow Sherby-Dorn that will give average result.

Flux Creep Determination of Field Dependence of Magnetic J_(c) at Low Temperatures

The effective activation energy of one HgBaCaCuO 1223 superconductor as a function of current density was extracted from the magnetic relaxation measurements below 30K,and found to obey a power law.We also obtained effective activation energy as a function of current density from the magnetic hysteresis loops(M-H).The data sets for the M-H loops at different temperatures overlap each other,and all fall on the smooth U_(eff)(J,0)curve based solely on the magnetization relaxation measurements.This indicates that the field dependence of magnetic critical current density is determined by the flux creep via nonlinear effective activation energy at low temperatures.

The Determination of Slip Mode of Some Major Active Faults in China Through Comparative Study of Geologic and Seismic Dislocations

The comparative study of the geologic and seismic dislocations often major active faults,such as the Aikin fault etc.,on China mainland,has shown that the ratio between the seismic slip rate(Vs)and geologic slip rate(Vg),i.e.,Q=Vs/Vg,for most of the active faults ranges between 0.5-0.8,indicating that most of the active faults are characterized by stick slip movement.According to the magnitude of the Q value,the slip mode of the faults can further be classified into four types:strong stick-slip(Q≥0.75),mainly stick-slip(0.5≤Q【0.75),mainly creep-slip(0.5】0≥0.25),and strong creep-slip(Q【0.25).The authors have also analyzed the constraint of the determination of Q value,as well as the prospect of the application of Q value to the determination of slip mode of major active faults.

The Feature of Segmentation Activity on the Northern Segment of the Anninghe Fault Zone Since Late Pleistocene

Based on fault geometric features,composite pattern,faulting land-forms and seismic data,this paper discussed the activity behavior along the northern segment of the Anninghe fault(from Xichang to Shimian)since the Late Pleistocene.The fault can be divided into three active segments by discrepancies of their activity:the segment from Xichang to Mianning,the segment from Mianning to Zimakua,and the segment from Zimakua to Tianwan.The southern segment has the background of occurrence of great earthquakes,but the middle and the northern segments can generate strong and moderate events respectively.According to the features of quartz from fault gouges by scanning electron microscopy(SEM),this paper discussed the movement features along the fault and indicated the stick-slipping feature on the segment from Xichang to Zimakua,the creeping feature on the segment from Jiziping to Tianwan and the transitional feature on the segment in between.

穿越多断层破碎带隧道自适应结构走滑错动特性研究

在活动断裂构造带地区,断层运动往往是沿断层带发生,自活动盘到破碎带错动位移表现出逐级传递的特征,因此穿越活动断裂带的隧道结构应力、变形特征也受到断层错动形式的影响。依托西部高烈度区某穿越大型活动断裂带的公路隧道工程,通过数值模拟分析穿越多断层隧道结构在断层多级走滑错动下的位移、应力响应规律,得出隧道结构纵向基于多断层蠕滑错动的影响分区;建立基于柔性初支、刚性二衬和节段铰接的穿越蠕滑断层隧道自适应结构,探究在错动区和缓冲区内设置隧道自适应结构的抗错性能。研究表明:隧道围岩性质的差异是影响穿越断层破碎带隧道结构变形和应力的最重要因素,隧道自适应结构在蠕滑错动过程中,柔性初支能够吸收部分围岩传递至隧道结构的变形,柔性接头的剪切变形和衬砌节段的刚性转动能够承担较大的位错,随着隧道衬砌节段长度的减小、接头数量的增加,各个接头的剪切变形角和衬砌节段偏转角都将减小,大幅提升结构的抗错安全性。

Influence of temperature, stress, and grain size on behavior of nano-polycrystalline niobium

Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC) niobium established by using the Voronoi algorithm. The effects of varying temperature, applied stress, and grain size(GS) on creep properties and mechanisms are investigated. Notably, the occurrence of tertiary creep is exclusively observed under conditions where the applied stress exceeds 4.5 GPa and the temperature is higher than 1100 K. This phenomenon can be attributed to the significant acceleration of grain boundary and lattice diffusion, driven by the elevated temperature and stress levels. It is found that the strain rate increases with both temperature and stress increasing. However, an interesting trend is observed in which the strain rate decreases as the grain size increases. The stress and temperature are crucial parameters governing the creep behavior. As these factors intensify, the creep mechanism undergoes a sequential transformation: initially from lattice diffusion under low stress and temperature conditions to a mixed mode combining grain boundaries(GBs) and lattice diffusion at moderate stress and mid temperature levels, and ultimately leading to the failure of power-law controlled creep behavior, inclusive of grain boundary recrystallization under high stress and temperature conditions. This comprehensive analysis provides in more detail an understanding of the intricate creep behavior of nano-polycrystalline niobium and its dependence on various physical parameters.

Improvement of Impact Toughness and Creep Properties in Reduced Activation Ferritic Steels by Consumable Electrode Remelting

The effect of smelting processes on mechanical properties and microstructure of reduced activation ferritic steels was studied.Creep properties and impact toughness of reduced activation ferritic steels were obviously improved by vacuum induction melting followed by consumable electrode remelting process in comparison with the conventional vacuum induction melting process.The difference of impact toughness and creep properties between both steels mainly depended on the aspect ratio and mean size of precipitates.Decreasing the aspect ratio of carbides makes development of a shear band more difficult , which could increase impact energy and creep resistance.

多组分混凝土徐变主动控制试验研究

文章针对超高层建筑施工中存在的形变问题,开展了多组分混凝土徐变主动控制试验研究,研究了水泥净浆-砂浆-混凝土徐变相关性、不同弹性模量的工程纤维对混凝土徐变性能的影响等。通过试验研究,得出可通过改变胶凝材料品种实现徐变主动控制的方法。文章研究结果为工程施工提供了重要参考,为超高层混凝土徐变主动控制技术的研究提供了有益建议,试验研究思路可为类似工程提供参考。

小江活动断裂长期蠕滑变形对区域地应力场影响的初步研究

小江断裂是西南地区一条重要地质界线,对白鹤滩水电站库区工程长期稳定有一定影响,研究该活动断裂长期蠕滑变形的影响特征十分必要。基于小江活动断裂及其邻近地区的大地运动监测结果,考虑断裂的走滑与逆冲运动特征,建立三维数值概化模型,对该断裂带在10 mm/a级长期蠕滑运动下的周边应力场的时空演化特征进行模拟分析。计算显示,随着小江断裂长期蠕滑,周边地应力场呈近似线性、平缓的增长势态。在工程百年寿命期或短暂的地质时间尺度内,并不会对周边地应力场造成明显影响,断裂带附近岩体在200年内的最大主应力增量约0.35~0.55 MPa,1000年内的应力增量约1.1~3.3 MPa。水库蓄水后,库水影响区仅限于河谷周边,对大区域地应力场的直接影响不显著。相关研究成果可为工程长期稳定性评估提供一定参考。

一种采用自抗扰控制算法的蠕行控制策略研究

车辆蠕行状态是指驾驶员未踩下油门、刹车踏板时,车辆以较低的设定车速稳定行驶的状态,在跟车、爬坡工况下应用广泛。目前,汽车蠕行控制方法大概有以下几种:根据车速查整车需求扭矩,该方法简单,但无法适应不同载重及坡度条件;电机恒转速控制,能够适应载重及坡度变化,常常采用PID算法控制转速,参数调节困难,容易产生超调问题。文章提出一种采用自抗扰控制算法的蠕行控制策略,能够提高蠕行时车辆的平顺性和稳定性,适应不同的载重及道路条件,降低调参难度,减少蠕行车速的超调,为实现整车蠕行功能给出了新的方案。

Ti40阻燃钛合金的高温蠕变行为

计算了Ti40合金在不同应力、不同温度下的稳态蠕变速率、应力指数及在460℃～540℃范围内蠕变激活能Q=94.0kJ/mol,并在此基础上研究了其蠕变强化机制。实验结果表明:该合金在此温度范围内的蠕变受位错和扩散双重机制控制,晶界移动对蠕变也有一定的贡献。在目前实验条件下,Ti40合金在620℃蠕变性能较差。

纳米Ag颗粒增强复合钎料蠕变性能的研究

制备纳米Ag颗粒增强的Sn-Cu基复合钎料。研究不同温度载荷下复合钎料钎焊接头的蠕变断裂寿命,并与Sn-0.7Cu基体钎料钎焊接头进行对比。此外,确定纳米Ag颗粒增强的Sn-Cu基复合钎料钎焊接头在不同温度和应力水平下的应力指数和蠕变激活能,建立复合钎料钎焊接头的稳态蠕变本构方程。结果表明,在不同的温度和应力下,与Sn-0.7Cu钎料钎焊接头相比,纳米Ag颗粒增强的Sn-Cu基复合钎料钎焊接头的蠕变断裂寿命均有所提高,且具有更高的蠕变激活能,说明复合钎料钎焊接头具有更优的抗蠕变性能。