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31.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献
32.
Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast
(PMC) and semi-solid die cast (SDC) with Al−7%Si−0.35%Mg composition in order to examine the relationship between solidification
structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved
in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance
to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate
tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at
the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries. 相似文献
33.
34.
高温预析出对Al-Zn-Mg系铝合金时效硬化和应力腐蚀的影响 总被引:1,自引:0,他引:1
研究了高温固溶后降温处理工艺对中强可使预析出LC52和7039铝合金的组织、时效硬化和应力腐蚀的影响。金相观察发现,高温预析出可优先在晶界处产生,并提高随后时效状态下晶界析出相的不连续分布程度,温度降低到一定程度晶内和晶界产生大量析出。合金拉伸性能和应力腐蚀结果表明,预析出在保持强度和塑性的同时,可提高抗应力腐蚀性能。而预析出温度降低,合金强度呈下降趋势。 相似文献
35.
讨论影响输油管线结垢和腐蚀的主要因素,从理论上分析了结垢形成,推导计算结垢量的公式。介绍了输油管线防止硫酸钡垢的清防方法。 相似文献
36.
Atmospheric corrosion of reference metals in Antarctic sites 总被引:1,自引:0,他引:1
Manuel Morcillo Beln Chico Daniel de la Fuente Elisabete Almeida Günter Joseph Susana Rivero Blanca Rosales 《Cold Regions Science and Technology》2004,40(3):165-178
This paper presents the results obtained at three Antarctic test sites participating in the “Ibero-American Map of Atmospheric Corrosiveness” (MICAT), a project on atmospheric corrosion carried out during the period 1988–1994 at some 70 sites distributed across 12 countries of the Latin-American region, Spain and Portugal. The three Antarctic sites are located near the coastline.The singular climatic characteristics of Antarctic regions are related with the purity of the air, the absence of rainfall and the formation of ice on the metallic surface during an important part of the exposure time. However, electrochemical activity is possible below ice layers. This situation affects the structure and morphology of corrosion product films and the resulting corrosion rates of metallic surfaces. 相似文献
37.
M.G. Pujar N. Parvathavarthini Sidhartha S. Jena B.V.R. Tata R.K. Dayal H.S. Khatak 《Journal of Materials Engineering and Performance》2008,17(6):793-801
In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl.
Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily
over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R
N) as well as the spectral noise resistance at zero frequency (R
SNo) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths,
extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM).
The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed
that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was
noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed
after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the
unstable pits in 316LN after 7 days exposure. It was observed that R
N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period.
Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of
pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as
large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days
of exposure, an observation that corroborates well with the stable R
N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively
prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas
the unstable pits initiated in 316LN get passivated in the simulated coastal environment. 相似文献
38.
Corrosion monitoring in district heating systems has traditionally been performed by using off-line methods, such as weight loss. The disadvantage is that the method is very slow, especially in low-corrosive environments, and that it only provides information about the past corrosion (accumulated over period of time). The purpose of the work is to test on-line monitoring methods in geothermal hot water in the district heating system in Reykjavik, Iceland. Geothermal water poses certain problems with regards to corrosion monitoring due to low conductivity, high pH and the presence of sulphide. These conditions make the geothermal environment low corrosive. However, a quality control is needed, especially since the sulphide causes the steel pipes to be more vulnerable towards localized corrosion. The methods used in this study were: linear polarization resistance (LPR), harmonic analysis (HA), electrochemical noise (EN) and zero resistance ammetry (ZRA). The Pitting Factor was measured with EN and showed promising results for measuring-localized corrosion on-line. A crevice corrosion cell also gave good results but had a low lifetime. However, the results of a galvanic corrosion cell (Fe/Cu) proved more difficult to interpret since they were dependent both on the dissolved oxygen and the sulphide level. 相似文献
39.
40.