黄铜应力腐蚀敏感性及其与脱Zn层拉应力的对应性

测量了不同极化电位下,Ｈ６２黄铜在氨水溶液腐蚀过程中表面脱Ｚｎ蔬松层引起的拉应力,并用单边缺口试样测量的不同极化电位下的应力腐蚀敏感性,结果表明：黄铜在氨水中自然腐蚀时,在脱Ｚｎ层界面会产生 大的拉应力,整个试样的平均应力为σ＝１８．１ＭＰａ;阳极极化使表面拉应力略有下降,阴极极化则使疏松层引起的拉应力急剧下降乃至为零,阴极极化在表层产生镀Ｃｕ层后出现尖力;应力腐蚀敏感性随外加电位的变化规律和疏松     

7075铝合金在液体金属Ga中的脆断行为

用WOL恒位移试样研究了7075铝合金在液体金属Ga中的脆断行为金相跟踪观察表明,Ga吸附后首先促进局部塑性变形,在缺口前方形成四下的塑性区,然后脆性激裂纹形核．液体金属脆断的临界应力强度因子．反向加载（位移V＜0）时,液体金属脆性激裂纹在远离缺口顶端的拉应力区中形核,微裂纹向拉应力区扩展而中止于压应力区反向加载时,试作断裂的名义应力强度因子为．所有断裂试样均为沿晶断口．     

Mo-Si-B三元系中T2相合金制备及其室温力学性能

通过放电等离子烧结(SPS)制备T2(Mo5SiB2)相合金,并采用SEM、XRD及压痕、压缩和三点弯曲等实验对合金的微观组织和室温力学性能进行表征。结果表明:SPS法以独特的等离子活化烧结方式制备出纯度高、致密且晶粒细小的T2相合金。该合金在室温压缩下几乎没有塑性变形,抗压强度为2907MPa;维氏硬度为17.86GPa,压痕法测得的断裂韧性为3.23MPa·m1/2,与三点弯曲法测得的3.34MPa·m1/2接近,沿{001}面发生解理断裂。共价键交替排列,是T2相室温脆性、高强度、高硬度的根本原因。     

高强钢螺桩应力腐蚀断裂研究

对超高强钢螺桩的大批量断裂事故进行了断日分析,确认是水介质或БФ—2~(**)胶中的应力腐蚀断裂。测量了几种高强钢在不同热处理条件下的K_(ISCC)和da/dt(平台值)。应用断裂力学对带裂纹螺桩断裂的可能性进行了定量分析, 测量了缺口形成应力腐蚀裂纹的临界应力场强度因子K_(ISCC)。利用不同曲率的缺口试样详细研究了缺口形成应力腐蚀裂纹的规律。由此也可估算无预裂纹的螺桩产生应力腐蚀断裂的力学条件。     

钝化膜应力导致不锈钢应力腐蚀

用恒位移载台，在透射电镜（TEM）中原位观察应力前后裂前方位错组态的变化以及微裂纹的形核和扩展，结果有明，310不锈钢在沸腾的25％MgCl2水溶液中应力腐蚀时腐蚀过程能促进位错发射，增殖和运动，当腐蚀促进的位错发射和运动达到临界状态时，应力腐蚀裂纹形核和扩展，测量表明，304不锈钢在沸腾MgCl2中自然腐蚀时表面钝化膜会产生一个附加拉应力，它可能是腐蚀促进位错发射和运动的原因。     

Fracture morphology and toughening mechanism of Al2O3/ZrO2 eutectic ceramic prepared by the combustion synthesis under ultra-high temperature

Al₂O₃/ZrO₂ (ZrO₂:47.37 mol%) eutectic ceramic with fine and uniform microstructure was fabricated by combustion synthesis under ultra-high temperature. The fracture toughness and Vickers Hardness reached 10.6 ± 0.49 MPa·m^1/2 and 17.8 ± 0.61 GPa, respectively. The fracture morphology and toughening mechanism are investigated. When cracks meet rod-like ZrO₂, the expansion path would deflect along the interface with a slip for a certain distance, while part of the rod-like ZrO₂ will be pulled out. The effect of rod-like ZrO₂ toughening, residual compressive stress toughening and t-ZrO₂ phase transformation toughening is discussed. The toughening mechanism of rod-like ZrO₂ includes crack deflection and fiber pull-out. The relevant calculated results show that the pull-out of rod-like ZrO₂ makes the largest contribution to toughness, while the residual stress toughening makes the smallest contribution. For t-m transformation toughening, the size of transformation is estimated by XRD method. The calculated value of fracture toughness is 10.25 MPa·m^1/2. Compared with the measured value of toughness, there is an error of 0.35 MPa·m^1/2.     

受力的LY12和LC4铝合金在中国西部盐湖大气环境中的腐蚀行为

通过现场大气暴露实验,利用金相显微镜和SEM等手段分析试样表面和截面形貌,研究了U弯受力状态下包铝与无包铝的LY12和LC4两种铝合金在我国西部盐湖大气环境中的腐蚀行为。结果表明,包铝的两种铝合金的腐蚀主要发生在包铝层,以点蚀为主,未观察到包铝层被穿透现象。无包铝的铝合金试样都发生了明显的沿晶应力腐蚀开裂,其中LY12铝合金在拉应力和压应力下都有较多的应力腐蚀裂纹,LC4铝合金只在拉应力下观察到了裂纹;两种铝合金在压应力下都发生了剥层腐蚀,拉应力下剥层腐蚀受到抑制。     

On the stress vs. Barkhausen noise relation in a duplex stainless steel

Various parameters of a Barkhausen noise burst were measured under applied stress in prestrained duplex stainless steel specimens. After quenching, the root mean square value of the Barkhausen noise amplitude was low because of the compressive macroscopic and interphase macrostresses in the ferrite phase. Prestraining increased the amplitude of the Barkhausen noise in all measuring directions due to reduction of macroscopic compressive residual stress and introduction of tensile interphase microstresses in the ferrite phase. Under applied stress, Barkhausen noise measured in the loading direction behaved similarly to ferritic steels: Barkhausen noise increased under tensile stress and decreased under compressive stress. In the direction transverse to the loading axis, the Barkhausen noise response was anomalous: Barkhausen noise increased or remained unchanged under macroscopic compressive strain in the transverse direction and decreased under tensile strain in the transverse direction. In unstrained specimens in the loading direction, applied stress vs. Barkhausen noise showed a linear relation under the applied stress range from −200 to 250 MPa. The stress sensitivity of the Barkhausen noise was, however, low. In the prestrained specimens, the stress sensitivity was higher than in the unstrained specimens, especially under applied compressive stress.     

Damage and fracture mechanism of 6063 aluminum alloy under three kinds of stress states

To study the damage and fracture mechanism of 6063 aluminum alloy under different stress states,three kinds of representative triaxial stress states have been adopted,namely smooth tensile,notch tensile,and pure shear.The results of the study indicate the following.During the notch tensile test,a relatively higher stress triaxiality appears in the root of the notch.With the applied loading increasing,the volume fraction of microvoids in the root of the notch increases continuously.When it reaches the critical volume fraction of microvoids,the specimen fractures.During the pure shear test,the stress triaxiality almost equals to zero,and there is almost no microvoids but a shear band at the center of the butterfly specimen.The shear band results from nonuniform deformation constantly under the shear stress.With stress concentration,cracks are produced within the shear band and are later coalesced.When the equivalent plastic strain reaches the critical value（equivalent plastic fracture strain）,the butterfly specimen fractures.During the smooth tensile test,the stress triaxiality in the gauge of the specimen remains constant at 0.33.Thus,the volume of microvoids of the smooth tensile test is less than that of the notch tensile test and the smooth specimen fractures due to shearing between microvoids.The G-T-N damage model and Johnson-Cook model are used to simulate the notch tensile and shear test,respectively.The simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well.In addition,the empirical damage evolution equation for the notch specimen is obtained from the experimental data and FEM simulations.     

Factors influencing fatigue crack propagation behavior of austenitic steels

In the present study, the fatigue crack propagation (FCP) behaviors of austenitic single phase steels, including STS304, Fe18Mn and Fe22Mn with different grain sizes ranging from 12 μm to 98 μm were investigated. The FCP tests were conducted in air at an R ratio of 0.1 using compact tension specimens and the crack paths and fracture surfaces were documented by using an SEM. The highest ΔK_th value of 9.9MPa·m^1/2 was observed for the Fe18Mn specimen, followed by 5.2MPa·m^1/2 for the Fe22Mn specimen and 4.6MPa·m^1/2 for the STS304 specimen, showing a substantial difference in the near-threshold FCP resistance for each microstructure. The crack path and fractographic analyses suggested that the near-threshold FCP behavior of these austenitic steels was largely influenced by the degree of slip planarity, as determined by stacking fault energy and grain size, rather than the tensile properties. In the Paris’ regime, the slip planarity still played an important role while the tensile properties began to affect the FCP. The FCP behavior of austenitic steels with different microstructural features are discussed based on detailed fractographic and micrographic observations.     

DUCTILE FRACTURE OF FERRITE NODULAR GRAPHITE CAST IRON UNDER MULTIAXIAL TENSILE STRESS

为研究多轴应力下铁素体球铁延性断裂机制,采用三种不同曲率半径(ρ=2,4,10mm)的缺口圆柱试样进行拉伸试验,并用大弹塑性变形有限元分析法计算试样缺口部位的应力、应变分布。在中断拉伸试样上进行金相观察,跟踪石墨球与基体界面处微空洞的形核和长大。研究结果表明,当石墨球与基体界面处的应力到达650MPa时,微空洞形核,空洞长大和聚合导致延性断裂。     

INFLUENCE OF TOP TEMPERATURE OF THERMAL CYCLE ON THERMAL STRESS/STRAIN AND THERMAL FATIGUE BEHAVIOR OF PURE IRON

１．ＩｎｔｒｏｄｕｃｔｉｏｎＦｉｇ．１　ＴｈｅｒｍａｌｆａｔｉｇｕｅｔｅｓｔｍａｃｈｉｎｅｗｉｔｈＯｕｔｅｒｃｉｎｓｔｒａｉｎｔＴｈｅｄａｍａｇｅｃａｕｓｅｄｂｙｔｈｅｒｍａｌｆａｔｉｇｕｅｉｓｏｎｅｏｆｔｈｅｍａｉｎｆａｉｌｕｒｅｆｏｒｍｓｏｆｍｅｔａｌｗｏｒｋｉｎｇｐｉｅｃｅｓｕｎｄｅｒｔｈｅｔｅｍｐｅｒａｔｕｒｅｖａｒｉａｔｉｏｎｃｏｎｄｉｔｉｏｎｓ．Ａｌｏｔｏｆｔｈｅｒｍａｌｆａｔｉｇｕｅｔｅｓｔｓｃｏｎｃｅｒｎｉｎｇｔｈｅｆａｉｌｕｒｅｗｅｒｅｃｏｎｄｕｃｔｅｄｏｎｔｈｅｖａｒｉｏｕ…     

Stress corrosion cracking behaviour of Al‐Li alloy 8090‐T8171 plate exposed to various synthetic environments

The stress corrosion cracking (SCC) behaviour of 8090‐T8171 plate material was investigated in short transverse direction performing constant load tests and constant extension rate tests under permanent immersion conditions. At an applied stress of 100 MPa, smooth round tensile specimens were exposed to synthetic environments containing chlorides and various nonhalide anions. Environment‐induced cracking was not observed in aqueous solutions of 0.6 M NaCl, LiCl, NH₄Cl, or MgCl₂. In 0.6 M NaCl solutions containing 0.06 M Na₂SO₄ or Na₃PO₄, the SCC behaviour of 8090‐T8171 plate was similar to that observed in pure 0.6 M NaCl solution. Sodium chloride solutions with additions of nitrate, hydrogen carbonate, or carbonate promoted stress corrosion cracking. Threshold stresses below 100 MPa were obtained from constant load tests using the latter environments. When sodium sulfite or sodium hydrogen phosphate was added, values being 100 MPa or slightly higher were determined. Lithium and ammonium present as cations in mixed salt electrolytes accelerated SCC failure. Lithium chloride solutions containing nitrate, hydrogen carbonate, carbonate, or sulfite were highly conducive to stress corrosion cracking. Very low SCC resistance was found for alloy 8090‐T8171 exposed to synthetic environments with additions of ammonium salts. Constant extension rate tests were carried out using notched tensile specimens. Displacement rates were in the range 2 × 10^?6 ? 2 × 10^?5 mms^?1. Aqueous 0.6 M NaCl solutions with additions of 0.06 M NH₄HCO₃, (NH₄)₂SO₄, or Li₂CO₃ promoted environment‐induced cracking with 8090‐T8171 plate, as indicated by severe degradation of notch strength. The constant extension rate testing technique did not indicate SCC susceptibility using sodium chloride solutions containing sodium sulfate or lithium sulfate. For specimens exposed to substitute ocean water a slight degradation of notch strength was found at the lowest displacement rate applied.     

5CrNiMoV钢马氏体相变塑性和应力对其相变动力学的影响

利用DIL-805ADT动态相变膨胀仪测定了5CrNiMoV钢在低于奥氏体屈服强度的应力下的马氏体相变膨胀曲线,根据膨胀曲线分析并计算出了不同应力下Greenwood-Johnson相变塑性机制中的相变塑性系数k值和Koistinen-Marburger马氏体相变动力学模型中α和Ms的值,并且将Greenwood-Johnson模型和Leblond模型计算结果与实际试验值对比。结果显示:k值随应力的变化有所波动,但趋近于一个定值;通过对比,Leblond模型更符合试验结果;Ms点随着应力的增大呈现微小的上升趋势,说明小于或等于80 MPa 的应力对Ms点的影响不显著;拉应力下α值普遍大于无应力下的α值,压应力下α值普遍小于无应力下的α值,说明拉应力对相变有一定的促进作用,压应力对相变有一定的阻碍作用。     

隐伏溶洞对隧道围岩稳定性的数值模拟研究

为分析隐伏溶洞对隧道围岩稳定性的影响,本文以辽宁某在建隧道为工程背景,采用MIDAS/GTS NX有限元数值模拟方法对不同溶洞跨度、不同隧道与溶洞之间距离进行数值模拟研究,分析了不同工况下隧道的拱顶、拱底、边墙的位移变化情况,并对隧道周围岩体的拉压应力分布进行了分析.结果表明:隧道拱顶沉降位移、拱底隆起位移、左边墙收敛...     

Notch effect of surface compression and the toughening of graded Al2O3/TiC/Ni materials

The fracture behavior of graded Al₂O₃/TiC/Ni materials with a symmetric structure was investigated using single-edge notch-bend (SENB) specimens with surface compression. The fracture toughness of the graded materials was determined according to ASTM Standard E399. The results show that the effective fracture toughness increases with an increase in notch depth in the compressive stress zone, and reaches the maximum of 39.2 MPa m^1/2 at the interface of compressive/tensile stress zones. Finite element analysis reveals that the surface compression will be intensified at the notch root once the specimen is edge-notched because of the stress concentration, and the degree of the compressive stress intensification increases with an increase in notch depth. The dependence of the effective fracture toughness of the graded materials on the notch depth shows a behavior similar to the R-curve that is usually associated with microstructural toughening mechanisms. This toughening behavior is caused by the intensification of the compressive stress concentration with the increase of the notch depth. A theoretical analysis based on fracture mechanics verifies that the mechanical reliability of brittle ceramics can be improved effectively by tailoring and controlling the internal stresses.     

The role of residual stress in neutral pH stress corrosion cracking of pipeline steels. Part I: Pitting and cracking occurrence

In this investigation, tensile test specimens were fabricated with increasing levels of compressive and tensile residual stress on the surface and through the thickness of the specimen. These residual stresses were then measured by neutron diffraction at multiple points along the length and through the depth of the specimens. The specimens were then exposed to a neutral pH aqueous soil environment in combination with an applied cyclic stress for various lengths of time in order to initiate and propagate stress corrosion cracking (SCC). The formation of micro-pitting was found to occur preferentially in areas where the tensile residual stresses were the highest (approximately 300 MPa), while SCC initiation occurred with a 71% normalized frequency in areas where the surface residual stress was in the range 150–200 MPa. The difference between residual stress levels occurring at SCC locations versus pitting locations resulted from both the change of residual stress during cyclic stress application during SCC testing and the residual stress gradient in the depth direction.     

The role of residual stress in neutral pH stress corrosion cracking of pipeline steels – Part II: Crack dormancy

This investigation provides a quantitative analysis of the effect of Type I residual stresses on the occurrence of pitting and stress corrosion cracking (SCC) formation in pipeline steel exposed to neutral pH aqueous environments. It has been shown that SCC generated in neutral pH environments can be readily blunted due to plastic deformation (room temperature creep) and/or extensive anodic dissolution. As a result, a high positive tensile residual stress gradient is necessary for continued growth of SCC in pipeline steels exposed to this neutral pH environment. The tensile residual stress represents a large mechanical driving force for crack nucleation and short crack growth. Active cracks may become dormant as the near-surface residual stress gradient changes, due to self-equilibration, from highly tensile to a lower tensile state or to a compressive state. The change in residual stress level can occur within 1 mm of the surface, resulting in a large proportion of dormant SCC.     

Ⅱ型试样的氢致开裂和应力腐蚀

用有限元法计算了Ⅱ型缺口前端的应力场和应力场强度因子KⅡ。结果表明,最大正应力和最大三向应力所在位置(θ=-110°)和最大剪应力位置(θ=80°)并不重合;最大正应力的指向和缺口延长线成α=10°。 实验表明超高强度钢Ⅱ型缺口试样能产生氢致滞后开裂,在水溶液中也能发生应力腐蚀。氢致裂纹和应力腐蚀裂纹都在最大三向应力所在位置形核,但裂纹的取向并不和该处的最大正应力垂直,而是指向该处的剪应力方向。如果没有氢,则裂纹在最大剪应力所在位置处形核,并沿最大剪应力方向扩展,即开裂角α=5°。 无论是氢致滞后开裂,还是应力腐蚀,Ⅱ型试样的规一化门槛应力强度因子均比Ⅰ型试样的相应值要高,断口形貌则和Ⅰ型试样的基本相同。     

不锈钢Ⅱ型试样的应力腐蚀和氢致开裂

研究了奥氏体不锈钢(1Cr18Ni9Ti)Ⅱ型试样的应力腐蚀和氢致开裂。实验表明,该试样在沸腾MgCl_2溶液中能产生应力腐蚀,裂纹形核门槛值为K_(ⅡSCC)/K_(ⅢX)=0.16。但裂纹并不在缺口面的最大剪应力处(θ=80°)形核,而是在最大正应力处(θ=-110°)形核,并指向正应力的法线方向。该试样动态充氢时能发生氢致开裂,其门槛值K_(ⅡH)/K_(ⅡX)=0.59,远比应力腐蚀的值要高,当K_Ⅱ较高时,氢致裂纹在最大剪应力处形核。当K_Ⅱ较低时,则在最大三向应力处(θ=-110°)形核。应力腐蚀是解理断口,且与K_Ⅱ无关。而氢致开裂断口则与K_Ⅱ有关,K_Ⅱ较高时是分布有二次裂纹的剪切韧窝断口,K_Ⅱ较低时则是准解理断口。