Effects of Applied Stresses on Martensite Transformation in AISI4340 Steel

This study aims at the experimental analysis of the transformation induced plasticity （TRIP） phenomenon. Experiments are conducted in which martensite is allowed to grow under the influence of a series of externally applied stresses. The magnitude of the applied stresses is less than 67% of the yield strength of austenite σγ （Ts）. Since there is no obvious difference between the transformation plasticity under tension and the compression for the lower applied stresses, only compressive stresses are applied. The results confirm that the transformation plasticity is proportional to the applied stress if the latter does not exceed 67 % of σγ （Ts）. The TRiP-strain, the kinetics, and their dependence on the applied stresses are studied. The comparison between calculated results and experimental results shows that the model accurately describes the phenomenon.

Degration of Partially Stabilized Zirconia Ceramics underan Applied Stress

Partially stabilized zirconia ceramics were sintered using fine powder of ZrO 2 3mol%Y 2O 3 prepared by the chemical co precipitation method.The tetragonal to monoclinic phase transformation in ZrO 2 ceramics during the aging in boiling water and the effect of an applied stress of 100MPa were mainly investigated.The degradation of ZrO 2 ceramics is considered to be caused by the reaction between Y 2O 3 and H 2O,which leads to a decreasing in the stability of tetragonal phase of ZrO 2.It is found that the tensile stress improves the driving force of the phase transformation and accelerates the degradation while the compressive stress has no obvious effect on the degradation.

Inverse approach to determine piston profile from impact stress waveform on given non-uniform rod

An essential problem in the design of mechanical impact systems is the impact of a piston on a rod. The impact of a semi finite cylindrical piston on a non uniform rod was studied. Based on wave mechanics and characteristic line theory, an inverse numerical approach to determine the piston profile was proposed, by means of which the geometry of an impact piston may be determined from the given stress waveform for a given rod profile. Numerical results show that the given stress waveform may be produced by means of the alternatives of design of piston and rod. There is good agreement between the experimental results and numerical results. [

Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

The penetration of CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings(APS TBCs).The direct penetration of CMAS changes the thermal/mechanical properties of the top coat(TC)layer,which affects the thermal mismatch stress behavior and the growth of thermally grown oxide(TGO)at the TC/bond coat(BC)interface,thereby resulting in a more complicated interface stress state.In the present study,a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior.Subsequently,a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth.The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs,which consequently causes the stress behavior to vary along the interface.Furthermore,the CMAS pen-etration depth imposes a significant effect on the TC/TGO interface stress behavior,whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration.This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.

Experimental Research on Damage Parameter of Concrete in Non-Uniform Stress Field

The damage variables of describing the material damage state should be chosen first when the research of concrete structures by use of theory of damage theory. The method of calculation of damage parameter by the measure of the change of the elastic modulus of concrete specimens is effectively. In this paper, the wedge splitting tests with double bearing of three groups of different initial crack lengths of concrete specimens were conducted, and the stress and the strain of the points with different distance from the initial crack tip measured and calculated, and the damage value with peak stress of the various points were calculated based on the stress-strain curves. From the results of the test, the damage parameter can be confirmed under the non-uniform stress field, and the initial crack length has some influence on the damage parameter, and the longer the initial crack length and the greater the damage parameter.

含聚合物防水膜的隧道衬砌界面剪切-滑移力学特性试验研究

为研究隧道衬砌结构中密贴型防水层界面的力学特性,根据隧道喷膜防水衬砌结构的特点,采用粘结强度试验和压剪试验探讨聚合物防水膜复合试件的界面剪切-滑移力学行为和特性。通过粘结强度试验绘制3种类型防水膜的拉伸应力-位移曲线,通过压剪试验绘制界面剪切应力-位移曲线,基于试验结果曲线计算得到防水层的界面参数,包括剪切强度、残余剪切强度、剪切模量、剪切滑移能量和剪切失效位移,并讨论防水材料性能和法向压应力对这些参数的影响。结果表明,防水层界面的剪切-滑移特性主要受防水材料特性和法向压应力的影响,防水材料特性对界面剪切强度和剪切模量的影响较大,而残余剪切强度、剪切滑移能量和剪切失效位移则受到法向压应力的影响更多。

Influence of stress on the stray field signals of ferromagnetic materials

To investigate the influence of stress alone on the stray field signals of ferromagnetic materials,the static tensile tests of 0.45%C steel and 45CrNiMoVA steel flat-shaped specimens were performed on an MTS810 hydraulic testing machine. Hp（y） signals,the normal component of spontaneous stray field,were measured during the testing process by an EMS-2003 metal magnetic memory diagnostic apparatus cooperated with a non-magnetic electric control displacement instrument. Fracture and microstructure were observed by a scanning electronic microscope and a transmission electron microscope,respectively. The relationships between axial applied stress or residual stress measured by X-ray diffraction method and Hp（y） were analyzed. The results indicate that some regular pattern of the magnetic curve is displayed only between applied stress and stray field signals. The magnetic ordering process stops due to dislocation pinning magnetic domain structure,and Hp（y） value unvaried nearly with applied load increasing in the plastic deformation stage.

STRAIN-GRADIENT STRESS ANALYSIS IN SAINT-VENANT BENDING

Light beam deflections caused by stress or strain gradients are inves- tigated analytically and experimentally in homogeneous beam specimens which are subjected to a particular case of flexure with shear. This study is a generalization of the prior an alytical-experimental examination of strain-gradient light deflections produced in stressed plates, which had concentrated on the simplest case where in- formation of interest is collected along a line of symmetry of the stress field. Main purpose of the present investigation is to document the efficacy of the strain-gradient method in analysis of the general case of stress state. The most interesting stress state is that in a beam subjected to the Saint-Venant bending, where the transversal and the longitudinal axes of the beam are in pure shear. The obtained results are compared with the predictions of the developed analytical models and with the pre- dictions of Filon's stress function. The procedures of evaluating the photoelastic and material coefficients using strain-gradient techniques were tested positively.

A NEW NON-UNIFORM YIELD PHENOMENON AND ITS MECHANISM

A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite transformation. It is essentially different from non-uniform yield that is related to dislocation obstacles. The experimental results show that ξph and ξL increase with increaslng strain rate, and ξph, increases but ξL decreases with increasing prestmin.Tronsformation enengy of strain-induced martensite keeps a constant, 3.85×106J/m3, with increasing strain at the stages of both elasto-plastic instability and stress plateau.

Localized corrosion of LY12CZ under stress in chloride media

Electrochemical methods were applied to investigate the corrosion behaviour of LY12CZ under applied stress in 3% sodium chloride aqueous solution. The experimental results indicate that LY12CZ shows two breakdown potentials on its polarization curve: one is related to the dissolution of the intermetallic particles and the other is related to the cracking of oxidation film and the dissolution of the matrix. When the stress is applied, it varies both breakdown potentials and makes the intermetallic particles and matrix dissolute at lower potentials. The relationship between the variation of the two breakdown potentials and applied stress was summarized. At the same time the influence of stress on the pitting and intergranular corrosion sensitivity of LY12CZ was also investigated. From the results it can be concluded that the stress can significantly affect the localized corrosion behaviour of LY12CZ in 3% NaCl solution.

外加电位对X80管线钢模拟海岸土壤腐蚀的影响

为探究双相X80管线钢在沿海土壤模拟溶液环境中的腐蚀机理,采用极化曲线、慢应变速率拉伸试验(SSRT)和交流阻抗(EIS)法对不同外加电位(-750,-900和-1050 mV vs.饱和甘汞电极(SCE))下双相X80管线钢的应力腐蚀和电化学腐蚀行为进行研究。结果表明,双相X80管线钢在-1050 mV电位下对应力腐蚀(SCC)最为敏感。慢应变拉伸呈现为脆性断裂,断口可见铁素体区域圆形或椭圆形的凹坑,这是由于过度阴极反应产生的氢原子扩散进入到钢中在铁素体晶界聚集,氢气析出产生的较高氢压超过材料的强度产生圆形孔洞,在拉伸应力作用下变为椭圆形。在此电位下EIS模拟电阻最小,耐腐蚀性最差。-750 mV的外加电位可起到一定的电化学保护作用,但不足以防止X80管线钢应力腐蚀的发生。-900 mV的外加电位可有效抑制X80管线钢的阳极溶解,SSRT的强度和延展性均高于0 mV电位试样,表现出韧性断裂特征,EIS模拟电阻最高,因此双相X80管线钢在模拟海岸土壤环境下最佳的阴极保护电位约为-900 mV vs.SCE。双相X80管线钢在沿海土壤模拟环境中的应力腐蚀行为的研究可对其在实际使用过程中的安全服役提供一定理论依据,同时为腐蚀抑制与防护工作提供参考。

Effects of Surface State and Applied Stress on Stress Corrosion Cracking of Alloy 690TT in Lead-containing Caustic Solution

The effects of surface state and applied stress on the stress corrosion cracking （SCC） behaviors of thermally treated （TT） Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit （ground）, shot-peened （SP） and electro-polished （EP） and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.

Numerical Analysis of Residual Strength in the Perforated Casing of Ultra Deep Wells

A three-dimensional model for the numerical simulation of casing-cement behavior is used to investigate residual strength in the perforated casing of ultra deep wells.The influence of the hole diameter,hole density and phase angle on the residual strength of the casing under non-uniform stress and fracturing conditions is revealed through the consideration of different perforation parameters.It is shown that the residual strength of the casing increases with the hole diameter and periodically changes with the hole density;the phase angle is the main factor that affects the residual strength of the perforated casing,and the perforation should be avoided in the direction of the minimum principal stress to reduce stress concentration at the perforation hole.Moreover,as shown by a companion orthogonal experiment,the descending order of influence of the different influential parameters is:phase angle,hole diameter,hole density and the thickness of casing.

外加应力及预变形对700L回火碳化物析出行为的影响

回火是残余应力调控的重要手段。采用Gleeble热模拟实验、非等温双回火实验及SEM、TEM组织分析等实验方法,研究了不同预变形及外加应力条件下700L回火碳化物的析出行为。结果表明,在回火过程中,外加应力可以促进碳化物的形核析出。当外加载荷为零时,碳化物主要分布于晶界,且尺寸偏大,为13.9 nm。在50、100 MPa应力回火后,组织中的碳化物数量明显增多,尺寸分别为11.4、11.6 nm,且碳化物的析出位置也由以晶界为主变为晶内弥散分布。在本文研究的应力范围内,回火前增加预变形有效提高了析出物的形核率,并减小了析出物的平均直径。在0MPa下,未变形回火试样的碳化物尺寸为13.9 nm,而5%、10%预变形回火试样的碳化物尺寸为12.9、11.5 nm,较未变形试样分别减小了7.2%和17.2%。经定量统计可知,不同回火工艺下析出物的体积分数几乎保持不变。

Phase-feld Study for Texture Evolution in Polycrystalline Materials under Applied Stress

The formation and evolution of deformation texture in polycrystalline materials are studied by phase-field dynamic model. In addition, the driving force of texture evolution is also discussed. In this model, grains with different orientation are defined by a set of continuous non-conserved order parameter fields. Simulation results show that grains with preferred orientation grow at the expense of those with unfavorable orientations. It is more important that, elastic potentia evolution of texture whether the polycrystalline system rather than elastic energy plays a crucial role in the s subjected to uniaxial stress or shear stress.

冷涂型非固化橡胶沥青防水涂料的性能研究

通过环氧树脂反应来制备冷涂型非固化橡胶沥青防水涂料,分别探讨了相容剂添加量、养护时间及环氧树脂与固化剂添加量对涂料相容性、耐热性、延伸性及应力松弛等的影响。结果表明,分子链结构由脂肪族环氧化合物和多元醇组成的相容剂可以改善环氧树脂与沥青的相容性,最佳添加量为2~4份;涂料的耐热性与养护时间存在正相关关系;随着A:B比值的增加,涂料的延伸性及应力松弛均呈现先增大后减小的趋势,当A:B=1:1时,涂料的延伸性和应力松弛均可满足JC/T 2428—2017要求,且长期蠕变性能优异。

基于光干涉法的光学玻璃应力测量方法研究

以平板理论为基础,利用牛顿环应力变形导致干涉图样的微小变化,提出一种基于光干涉法测量玻璃体应力的无损测量方法。理论推导出牛顿环曲率半径与应力之间的变换关系,利用自行设计的可安装在牛顿环仪上的施压装置,实验研究了施加应力与干涉图样的变换关系,通过理论分析与实验比较,证明了用牛顿环干涉法测量应力的可行性。利用该装置及方法对光学玻璃试样的应力进行测量,测量结果与实际施加的应力进行比较,误差最小为0.8%。

外力对常温氧化膜开裂和剥落行为的影响

对外力下常温氧化膜开裂和剥落行为的影响作出了研究.从理论上推导出计算氧化膜临界开裂外力的公式,并通过A3钢发蓝膜和LY12CZ铝合金化学转化膜在扫描电镜下的动态拉伸实验证明氧化膜临界开裂外力的存在,同时还比较了两种不同氧化膜开裂行为的异同.另外,进行了氧化膜在3%NaCl溶液中开裂和剥落行为的电化学研究,通过两种材料在介质中拉伸时的自腐蚀电位变化情况,根据电位转折点的存在进一步验证了临界开裂外力的存在,最后进行了有无裂纹氧化膜的阻抗谱测量,说明氧化膜开裂将会加速电化学腐蚀.

力学化学效应对LY12CZ铝合金点蚀行为的影响

利用电化学测量技术研究了加载弹性载荷对LY12CZ铝合金在3%NaCl溶液中的自腐蚀电位、点蚀电位和保护电位的影响规律,同时利用小孔发展速率(PPR)—电位曲线法和电位扫描技术及显微测量技术研究了载荷对预选电位下的真实小孔发展速率的影响,根据点蚀电流密度随应力变化情况来研究力学化学作用对LY12CZ点蚀敏感性的影响,结果表明在加载应力时,LY12CZ铝合金的自腐蚀电位、保护电位和破裂电位都有不同程度的负移,负移的量取决于应力的大小。在加载应力时点蚀电流密度随应力增加也出现增大的现象,研究结果表明力学化学效应对LY12CZ铝合金的点蚀行为有显著影响。

应力释放构造煤煤层气开发理论与关键技术研究进展

构造煤煤层气高效开发是我国煤层气资源禀赋的选择,构造煤储层与煤层气赋存特征决定了疏水降压煤层气开发理论技术不再适合构造煤储层,应力释放(原位)煤层气开发理论技术是新的技术方向,有望将构造煤煤储层从煤层气开发禁区变为新领域,同时也有望成为煤矿煤与瓦斯突出治理、煤矿区甲烷温室气体减排的治本之策。依托国家重大科研仪器研制项目,以应力释放构造煤煤层气开发关键实验平台和工程装备原理机为基本定位,以开发理论创新、技术原理探索为先导,以装置、装备及其工艺技术为研究核心,应力释放构造煤煤层气开发理论技术研究取得重要和实质性进展。探索构建了应力释放煤层气开发理论技术基础,阐明了水平井造洞穴应力释放构造煤原位煤层气开发的工程原理。水平井造洞穴应力释放构造煤原位煤层气开发模拟试验系统已完成设计进入加工阶段,系列配套基础实验取得了重要数据;探索建立了构造煤储层应力释放与煤层气解吸扩散关系模型;揭示了应力释放构造煤煤层气开发煤储层渗透率变化规律。研发形成了构造煤储层大口径水平井双向往复式钻进+多级扩孔+复杂循环钻井液成井、水平井泵注+喷射诱导控制造洞穴应力释放与储层激励、气/水/高浓度煤粉混合物直井射流泵+配套井底装置组合高效举升、产出物地面高效重力分离+回收+水循环、煤层气应力释放开发装置(装备)数据采集和控制系统等应力释放构造煤煤层气开发关键技术。