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疲劳是涡轮叶片的一种主要失效模式.本文开展了DD11单晶合金在650℃中温条件下2种应力集中系数(K_t=1(光滑状态)、K_t=3(缺口状态))的旋转弯曲疲劳性能研究,对比了2种应力集中系数下的疲劳强度,并开展了相关断口分析.结果表明:应力集中系数由K_t=1增大到K_t=3时,疲劳极限由446 MPa降低为311 MPa,说明DD11单晶合金疲劳性能存在应力集中敏感性;疲劳寿命由10~5提高到10~7时,光滑状态由600 MPa降低为420 MPa,疲劳强度降低幅度为180 MPa,而缺口状态由370 MPa降低为290 MPa,降低幅度为80 MPa,说明应力集中条件下DD11单晶合金的疲劳寿命对于外载变化较敏感.断口分析表明,光滑试样断口(应力500 MPa/疲劳寿命9.7×10~5)由几个相交的光滑晶体学平面组成,疲劳源萌生在距表面100μm左右的铸造孔洞;缺口试样断口(应力340 MPa/疲劳寿命8.1×10~5试样)呈平面状,与应力轴垂直,为多源疲劳模式,疲劳源观察到小刻面,在加工刀痕不连续位置萌生. 相似文献
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喷丸强度对不同粗糙度表面超高强度钢疲劳性能的影响 总被引:1,自引:0,他引:1
不同方式加工的高强度钢零件具有不同的表面状态,对其采用相同的喷丸工艺是否合理尚不明确。对不同表面粗糙度23Co14Ni12Cr3Mo E超高强度钢作不同强度的喷丸强化。采用扫描电镜及白光干涉仪观察了喷丸试样的表面形貌,采用金相显微镜观察喷丸试样的表面组织,采用旋弯疲劳试验机测试了喷丸试样的疲劳性能,采用X射线衍射残余应力测试仪测试喷丸试样的残余应力。研究了喷丸强度对不同表面粗糙度超高强度钢的表面组织、形貌、残余应力场及疲劳性能的影响。结果表明:喷丸过程可以细化表面组织,引入残余压应力场,改变表面形貌特征,从而引起表面应力集中状况的改变,其改善效果与原始表面状态有关;对于初始表面粗糙度Ra≤0.4μm的表面,喷丸强化过程能有效提高材料的疲劳寿命,促使疲劳裂纹源内移;随表面粗糙度的提高,当应力集中状况过于严重时,表面组织细化和残余压应力对疲劳性能的提升作用会被抑制,喷丸工艺对疲劳寿命的提升效果大幅下降,疲劳裂纹源均位于表面。 相似文献
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以直接时效态(DA)GH4169合金为研究对象,通过旋转弯曲疲劳实验,分别研究该合金在650℃和室温大气状态下,应力集中系数分别为K_t=1,K_t=3,K_t=4时的疲劳极限。结果表明,直接时效态GH4169合金在高温650℃和室温状态下,均具有很强的应力集中敏感性,650℃时的疲劳极限,K_t=4较K_t=1下降了68%;室温时的疲劳极限,K_t=4较K_t=1下降了66%。同时,直接时效态GH4169合金在室温条件下,疲劳极限较650℃显著降低,室温较650℃时的疲劳极限在K_t=1时下降了32%,K_t=3时下降了30%,K_t=4时下降了28%。 相似文献
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为提高异种高强度铝合金焊接接头在复杂交变载荷作用下的服役可靠性,采用疲劳极限测量、疲劳断口形貌分析、金相分析和显微硬度测试等方法,研究了6 mm厚的6082-T6/7075-T6异种铝合金搅拌摩擦焊接接头疲劳性能及疲劳断裂的影响因素.结果 表明,1200 r/min、80 mm/min条件下,焊接接头疲劳极限为107.5 MPa.110 MPa疲劳载荷下,疲劳裂纹起源于前进侧(6082-T6)的焊核区与热机械影响区(TMAZ)交界位置的试样棱边尖角附近.这是由于焊接热循环导致β"相转变为β'相并粗化形成软化区、试样表面存在脆性第二相、2种材料在焊核区与热机械影响区交界处混合不均匀引起的应力集中,以及试样棱边尖角引起的应力集中等几种因素共同叠加作用所致. 相似文献
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基于郑公式,从应力比和应力集中系数与疲劳寿命之间的关系出发,得到了TC11钛合金高周疲劳性能归一化模型的数学表达式。结果表明:公式Nf=Sf(Sa-Sac)-2可以有效地拟合TC11钛合金在不同应力集中系数和应力比条件下的疲劳试验数据;而使用公式Nf=Sf[Segv-(Segv)c]-2能有效地归一化处理TC11钛合金的疲劳试验数据,获得的归一化数学模型表达式为:Nf=4.14×109(Segv-424.58)-2。 相似文献
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《理化检验(物理分册)》2016,(8)
采用不同的碳当量,对某发动机用灰铸铁材料的化学成分进行了优化改进,改进前硅碳含量比cSi/cC=0.63,改进后硅碳含量比cSi/cC=0.7左右,对改进前后附铸试棒的静力学性能和疲劳性能进行了检测。结果表明:当碳当量cCE=3.80%(质量分数)、硅碳含量比cSi/cC=0.7左右时,灰铸铁材料的各项性能均处于较好状态;硅碳含量比cSi/cC高的材料,其弹性模量也高,而抗拉强度和规定总延伸强度又均随弹性模量的提高而提高;相同疲劳环境下,弹性模量高的材料,其疲劳循环周次也高;经改进后,试验灰铸铁材料的抗拉强度在330~350 MPa、弹性模量在185 000~195 000 MPa,拉拉疲劳极限在47.5~51 MPa。 相似文献
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A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling. 相似文献
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Liebert A Wabnitz H Grosenick D Möller M Macdonald R Rinneberg H 《Applied optics》2003,42(28):5785-5792
A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue. 相似文献
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An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a
rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate
agreement is demonstrated between the derived relations and experimental data. 相似文献
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Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995. 相似文献
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由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。 相似文献
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M. M. Gadenin 《Inorganic Materials》2013,49(15):1352-1356
It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle. 相似文献
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V. T. Kornienko 《Strength of Materials》1991,23(7):760-765
The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991. 相似文献
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水三相点是开尔文热力学温度的唯一基准点,也是ITS-90国际温标重要的定义固定点。因此,水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来,中国计量科学研究院研制出一系列高质量的水三相点容器,加强了水三相点的研究,为不确定度的分析提供了更为可靠的实验依据。同时,不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此,根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明,其扩展不确定度为0.16mK(k=2.69,P=0.99)。 相似文献