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《Energy Materials: Materials Science and Engineering for Energy Systems》2013,8(3):1826-1831
AbstractThe present paper presents results about cyclic behaviour and the evolution of the dislocation structure of reduced activation ferritic–martensitic steels and commercial martensitic steels AISI 410 and 420. The variation of the free dislocation density within subgrains and subgrain size was mainly analysed during the cyclic softening of EUROFER 97 steel. From the analysis of the flow stress components, the friction and back stresses, and the information of the evolution of the dislocation structure, it could be concluded that the softening of tempered martensitic steels at 20°C is produced by the contribution of the friction stress and aided later by the back stress. 相似文献
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A special designed experiment was conducted for observing crack initiation and growth in P/M Rene9S superalloy under ten- sion-tension loading by self-made SEM in-situ fatigue loading stag. Several alumina inclusion particles exposed at the specimen surface were observed carefully. During fatigue test inclusions led to cracks initiation. The cracks can be formed by two mechanisms. Generally, the cracks nucleated at the interface between inclusion and matrix. Sometimes, cracks were also formed inside the inclusion. As the in- crease of cycles, some cracks at the interface between inclusion and matrix broadened and propagated along the direction about 45° to the loading axis. On the other hand, the cracks inside the inclusion propagated in the inclusion and towards matrix. 相似文献
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The low cycle fatigue René 80, a Ni-base superalloy, was studied at temperature of 871 °C, R = (min/max) = 0 and strain rate of about 2 × 10−3 s−1. The dislocation structure and failure surface observations were evaluated through TEM and SEM. TEM studies showed that at Δt = 0.8% during the first cycle the dislocations formed a hexagonal network in the γ-phase matrix. When the number of cycles increased, the density of dislocations increased as well. At N = Nf and Δt = 0.8% the cutting of γ′ precipitates took place. SEM studies at Δt = 0.8% and N = Nf showed that fatigue crack initiation generally occurred at the surface, where it is depleted of the γ′ phase as a result of oxidation by the high-temperature exposure. In addition to depleted zones, the grain boundary oxidation and oxide spikes were also considered as further crack initiation sites. 相似文献
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粉末冶金高温合金FGH97的低周疲劳断裂特征 总被引:2,自引:0,他引:2
研究了粉末冶金镍基高温合金FGH97在650℃,30—980 MPa,1 Hz实验条件下的低周疲劳断口的宏观及微观特征,裂纹源的类型及其形貌特征,以及裂纹源的位置、缺陷类型、形状和尺寸对低周疲劳寿命的影响.结果表明,在本次实验条件下该合金的低周疲劳寿命均超过了5000 cyc;统计得出,低周疲劳断口裂纹源在表面的试样占23%,在亚表面的占47%,在试样内部的占30%;裂纹源分平台、粉末颗粒、夹杂物3种类型,其中平台类型约占5%,粉末颗粒间断裂占15%,夹杂物占80%.由统计分析和计算得出,不同类型裂纹源对疲劳寿命的影响程度不同:夹杂物最严重,其次为异常粉末颗粒,再次为局部塑性变形. 相似文献
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In the present investigation the life behaviour of the titanium alloy IMI 834 under loading conditions which are close to real service was considered. Different types of creep–fatigue loadings were applied at 600°C, i.e. balanced and unbalanced cycles with different ramping times into tension and into compression and stress hold Strain Range Partitioning (SRP) cycles. The testing was performed in laboratory air. The results of the creep–fatigue tests showed that life was reduced by the different types of creep–fatigue cycles. In the stress hold tests the mean stresses had a pronounced influence on life. The observed life of the stress hold SRP cycles could be predicted within a factor of ±2 of actual life by frequency-modified approaches. If mean stresses were considered in terms of maximum tensile stress or by a modified Morrow approach, life predictions remained within a factor of ±1.5 of the actual test results. A SRP approach which was frequency modified in the present study led to life predictions which fell within a band of a factor of ±1.35 of the actual test results. 相似文献
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