应变硬化和应变速率敏感材料在单向拉伸状态的塑性分析

对于即具有应变速率敏感,又具有应变强化效应的材料在单向应力拉伸的塑性流动及失稳分析,本文证明了Hart的分析的基础相同于Hutchinson等基于流动方程b＝Kε{sup}nε{sup}m的分析。然后,以Hart的分析为出发点,对Hart提出的流动稳定性及其判据（及JHC判据）给予讨论。表明Hart的流动稳定性判据适用于力学缺陷,并主要地依赖于应变硬化指数。在Hart的分析基础上,考虑到初始几何缺陷2（0）,对失稳过程给予增量分析和积分分析。增量分析给出了m和δ之间的（及n≠0的）简明关系：δ＝（1/α （0））{sup}m－1,δ＝（1/α （0））{sup}me{sup}n－1,积分分析得到了和Hutchinson等及Ghosh的“非线性长波分析”得到的积分关系在n＝0的情况下相同的结果。将这些关系和实验结果比较,吻合是好的。此外,对载荷的分析给出了恒定十字头速度L及恒定应变速度ε的载荷表达式。     

铸态奥氏体-贝氏体球墨铸铁的研究

本文较系统地研究了在不同模数下,合金加入量对铸态奥氏体-贝氏体球墨铸铁的组织和性能的影响。研究结果表明,通过合金化获得铸态奥-贝球铁是可行的。它的抗拉强度可达9×10{sup}8N/m{sup}2以上,延伸率可达3%以上。并且它具有较高的低温冲击韧性,在-40℃时,冲击韧性（V型缺口）达4.6J。常温断裂韧性可达5.4×10{sup}7N/m{sup}(3/2),经325℃回火后可再提高20%,研究表明,残余奥氏体对于机械性能有良好的作用。     

圆管进口段层流一湍流边界层发展区的流动阻力

本文提供了一种计算模型,可以根据前文[1][13]所提供的圆管进口段边界层单纯层流和单纯湍流时的近似分析解作为基础,计算3×10{sup}3≤ReD≤1×10{sup}5时进口平滑的圆管进口段内边界层先层流、然后过渡为湍流的任何区段不可压缩流体的流动阻力和壁面摩擦阻力。计算的流动阻力为文献[6]所报导的实验原始资料所验证。     

直-横控制式浇注系统模化特性的研究

从理论上证明了一组几何相似的直-横控制式浇注系统模型是动力相似的,这组浇注系统的E u＝F（R e）特性曲线和进入第二自动模化区的临界雷诺数R{sup}L e是相同的（具有唯一性）。利用水力模拟试验和实际浇注金属液给予了证明。进而得出结论：R e≥R{sup}L e是直-横控制式浇注系统模型和原型进入第二自动模化的唯一条件。     

外差干涉比相技术在纳米测量中的应用

利用塞曼激光和光波比相技术的结合实现了一种高精度激光外差干涉测量系统。它也可以用来直接测量空气折射率n。多次实验证实,dn/n的重复性为5×10{sup}-8。     

电磁振动设备动力学参数分析与研究

根据简化的某型号电磁振动设备的物理模型,对电磁振动运行装置的激振系统进行动力学的分析和研究。经实验测试,得出了理论与实验相吻合的槽体振幅—输入电流关系公式。在槽体的振幅不大（〈2mm）时,理论计算与实验相吻合;但随着振幅加大,理论值与实验值将出现偏离,在测量的限度范围内,最大相对误差为3．7％。文章为进一步研究电磁振动设备,为参数化和优化电磁振动设备的设计过程提供理论依据和实验参考。     

激光处理对Cr—Mo—Cu合金铸铁气蚀腐蚀的影响

用Ｍａｇｎｅｔｏｓｔｒｉｃｔｉｏｎ仪研究ＣＯ２连续激光波处理Ｃｒ－Ｍｏ－Ｃｕ合金铸铁（内燃机气缸套材料）试样的气蚀特性表明，经激光处理的Ｃｏ５０合金涂敷层显示出优良的抗气蚀腐蚀性能。本文还研究了各种微观组织的气蚀腐蚀主要机理。     

外界压力消除铸件析出性气孔的测定

金属凝固时,由于气体的析出,会使铸件得到析出性气孔和增大缩孔体积（在此文中为简化叙述起见,把这两种由于析出性气体而引起的铸件内孔洞的增加统称为析出性气孔）。采用在凝固的铸件上施加压力的方法（如压力结晶、反压铸造,液压金属冲压等工艺）,可有效地消除铸件中的分散性显微孔洞。但外界压力除了可减少铸件中的因析出性气体而引起的孔洞外,还可同时减少铸件中因金属本身收缩所引起的缩孔,所以一直到现在,还没有设计出一种能单独地测定外界压力消除铸件中析出性气孔的效果的方法。本工作通过理论推导,提出一种能单独地测定外界应力消除析出性气孔效果的实验方法;还建议根据试验结果的数据,计算这种效果的参数方式;并利用了专门的装置,浇注了A1-1.5%Cu合金的试样,根据所指出的方法和参数公式,测得当铸件凝固时外界气体应力由0增至4公斤/厘米{sup}2时,可使因液体金属含氢量由0.187厘米{sup}3/100克增至0.365厘米{sup}3/100克时所引起的析出性气孔消除68%。     

机床动力学(三)

2.固有频率和主振型多自由度系统的固有频率和主振型是从求解系统的无阻尼自由振动方程得到,设方程的解为{X}={A}e~(iwnt),则有=i~2ω_n~2{A}e~(iωnt),将它们代入公式(50),消去因子e~(iωnt)后得 ([K]-ω_n~2[M]){A}={O} (55)求解方程(55)就能得固有频率。由于振幅向量{A}的系数行列式等于零,即Δ(ω_n~2)=det([K]-ω_n~2[M])=0 (56)公式(56)称为特征方程或频率方程,将其展开后可得一个ω_n~2的n次代数方程ω_n~(2n)+a_1ω_n~(2(n-1))+a_2ω_n~(2(n-2))+……+a_(n-1)ω_n~2+ a_n=O解此方程,可得n个根:ω_(n1)~2,w_(2n)~2……ω_(nn)~2,称为特征值,将其开方即可得n个固有频率,按大小顺序排     

基于轴向振动配粉技术的药物微量配粉

针对轴向振动配粉技术在植入式可降解缓释给药系统微量配粉中的应用,搭建了轴向振动配粉实验台。采用毛细玻璃漏斗和圆锥状塑料吸头作为配粉管,研究两者稳定流动的振动幅值区间,讨论了振动频率对稳定出粉起始幅值、振动幅值对出粉流量及出粉流量稳定性的影响。结果表明：采用圆锥状塑料吸头作为配粉管的配粉过程更稳定,并且具有良好的抗堵性能;振动频率越大,实现配粉需要的起始激振幅度越小;在固定激振频率下,出粉流量随振幅先增大后减小,且管体中粉体处于充分流动状态;在激振频率为50 Hz,150 Hz,振幅为200~300 μm和35~50 μm时,可以得到最大且不随振幅改变的稳定出粉流量。实验论证了轴向振动配粉技术可以实现微量粉体的稳定、精确配给。     

Comparison of cavitation erosion test results from venturi and vibratory facilities

A detailed comparison of cavitation erosion performance in tap water for five alloys in a vibratory (no-flow) system and a Venturi (flow) system was made. The effects of temperature variation (80 – 200 °F), Venturi throat velocity (34 – 49 m s^?1) and vibratory horn double amplitude were studied. Correlations between maximum erosion rate (maximum mean depth of penetration rate (MDPR_max)) and incubation period IP, and the material mechanical properties Brinell hardness and ultimate resilience $\text{UR =}\text{UTS}{}^2\text{2E}$. (where UTS is the ultimate tensile strength and E is the elastic modulus), were examined. Only moderate success was achieved in correlations between “erosion resistance” MDPR_max^?1 and IP and these mechanical properties. However, a good correlation was found between MDPR_max and IP, pertinent to both facilities, of the form MDPR_max^?1 = aIPⁿ, where n is near unity (0.94). The cavitation intensity, as measured by MDPR_max, was found to be 10–20 times greater in the vibratory system, depending on horn amplitude and material. This ratio varies between 5 and 30 if individual materials are considered separately, being greatest for 1018 carbon steel and least for 316 stainless steel. This indicates the important differences in form between these cavitating regimes and the imprecision of material comparisons made in both regimes.     

Cavitation damage prediction

New results from cavitating venturi water tests were used to reinforce the concept of cavitation erosion efficiency previously developed from tests in a vibratory facility with both water and sodium. The concept emerges from a technique which allows a priori prediction of eventual cavitation erosion rates in flow machines. Bubble collapse pulse height spectra obtained from submerged microprobes are correlated with measured erosion rates in given laboratory and/or field devices to allow this prediction. Preliminary results from such correlations are presented together with other measurements of the effects of gas content, velocity and cavitation condition upon the mechanical cavitation intensity as measured by the pulse height spectra.New results from vibratory facility tests in tap water and synthetic seawater upon three materials of variable corrodability (304 stainless steel, 1018 carbon steel and 1100-0 aluminum) are presented. The ratio between maximum erosion rates for the saltwater and freshwater tests were found to increase toward unity as the mechanical cavitation intensity is increased, i.e. increased mean depth to penetration (MDPR), as expected on theoretical grounds.The relation between the incubation period and MDPR_max was examined from the vibratory test results, and was found to depend upon the material properties as well as the fluid flow conditions.     

Cavitation erosion incubation period

To evaluate the “incubation period” (IP) stage of cavitation erosion, short-duration vibratory horn tests in tap water were made on soft aluminum alloy (aluminum alloy 1100-O) and also on a much more resistant alloy (316 stainless steel). Curves of weight loss versus time, and corresponding scanning electron microscopy photomicrographs taken during the IP, are presented and discussed. The effects of horn amplitude and temperature are investigated for “open-beaker” tests. The IP for 316 stainless steel is found to be about 500 times that for aluminum alloy 1100-O for the same amplitude and temperature. This ratio can be predicted almost exactly by applying an assumed relation between MDPR_max and IP, i.e. MDPR_max^?1 = k(IP)ⁿ.Fatigue cracks and individual-blow craters were found for 316 stainless steel but only individual craters were found for aluminum alloy 1100-O, although their ductilities are approximately equal. It is found that the IP based on the eroded area only, IP_erod, is much less than the conventional IP (based on the total specimen area) if IP is based on the attainment of a given mean depth of erosion MDP.Relations between the eventual erosion rate MDPR_max and the IP are considered. It is found that IP data can often be used to predict eventual MDPR_max values according to the relation MDPR_max^?1 ∝ (IP)ⁿ where n ≈ 0.93 and n ≈ 0.95 for our vibratory and Venturi data respectively. However, different values for n have been reported in the literature. By assuming a “characteristic” erosion-time curve the time of occurrence of MDPR_max can also be estimated.It is verified that only bubble collapse stresses are important in the vibratory horn test, although specimens are vibrated under very high accelerations.     

A study of cavitation bubble collapse pressures and erosion part 3: the results in a venturi facility

Cavitation erosion generated in a venturi facility was studied by comparing the erosion loss with the distributions of cavitation bubble collapse pressures (impact loads). The erosion process in the venturi tests is similar to that in the vibratory tests, although its progression is very slow. That is, the surface first deforms and fractures as a result of fatigue with repeated bubble collapse pressures below the threshold pressure needed to form a pit impulsively. By comparing the distributions of impact loads measured using our method with the hypothetical stress-number of cycles curves for fatigue, it is found that the incubation period and the volume loss rate during the stable period follow Miner's law regardless of the venturi, vibratory and cavitation conditions and materials. Therefore we found that we are able to estimate cavitation damage in a flowing system in the same way as damage in the vibratory tests from Miner's law although the distributions of cavitation bubble collapse pressures are markedly different.     

Unified empirical relations for cavitation and liquid impingement erosion processes

Several attempts have been made in the past to predict erosion due to cavitation and liquid impingement. Most of the models and formulations suffer certain deficiencies so that they do not adequately predict the magnitude of erosion, particularly during the acceleration period and for long-term exposure. This report presents a power-law relationship between average erosion rate and cumulative erosion during the acceleration and deceleration zones of erosion for copper, brass and stainless steel specimens examined in a rotating disk device. Data analyses from other types of erosion devices, including venturi, magnetostriction and liquid jet impingement, conform to the present unified relation. This agreement is indicative of the similar nature of erosion in the acceleration and deceleration zones. Attempts are made to understand the relationship between the coefficients in the power-law relation and the material properties.     

Deformation and Fracture of Single-Crystal and Sintered Polycrystalline Silicon Carbide Produced by Cavitation

An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25°C using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 μm. The results of the investigation indicate that the SiC {0001} surface could be deformed, in a plastic manner during cavitation. Dislocation etch pits ware formed when the surface was chemically etched. The number of defects, including dislocations in the SiC {0001} surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated during cavitation. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.     

1100-0铝和1018碳钢文氏管空蚀试验的流速指数和空化数

本研究的目的是要估价一下文氏管喉部流速在空化数不变时对试件空化侵蚀的影响。此处的空化数是根据文氏管的出口条件算出的。最近在密执安大学高速空蚀试验装置中曾用27℃的自来水对1018碳钢和1100－0铝进行了试验。目前的试验结果与密执安大学过去所得的结果很符合,表明对于流速范围为10～49米/秒的情况,流速破坏指数在±1～5的范围内变动。     

Mechanisms of Formation of Spheroids Produced by Cavitation Erosion

The prediction, control, and prevention of unscheduled downtime due to wear of industrial equipment is an important engineering problem. The characterization of wear particles and the study of the mechanism of their formation will aid in preventive maintenance. Of particular interest is the mechanism of formation of spherical particles during wear and erosion. It has been suggested that cavitation erosion is a mechanism of formation for these spherical particles. Using both a vibratory apparatus and a jet erosion facility, spherical particles were produced on various materials including aluminum and 52100 steel. Special techniques for isolating and mounting the eroded particles were developed. Spheroids ranging from 0·5 μ (microns) to 30 μ in diameter were observed in the vibratory cavitation method both in distilled water and in SAE 10W nondetergent oil. Much larger spheroids up to 150μ in diameter were observed in clusters with the jet erosion method. Scanning electron microscope studies revealed craters, plastic flow, overflowing lips, and splashing stems. Based on these observations, it is theorized that the high strain rate indentation of the cavitation bubbles leads to the splash of metal into the surrounding liquid where surface tension produces spherical particles. Supporting experimental evidence and calculations are also presented.     

Vibratory cavitation erosion in aqueous solutions

Vibratory cavitation erosion tests on AISI-SAE 1018 carbon steel in tap water and in mild (0.1 M) aqueous solutions of CaCO₃, CaO, NaHCO₃ and NaOH were conducted at a temperature of 80 °F (27 °C), a double amplitude of 1.38 × 10^?3 in (35.1 μm) and a pressure of 1 atm. For the maximum (150 min) test duration the weight loss in tap water (no additive) is the smallest. However, this is not the case for shorter test times. The biggest difference between weight losses among the various solutions is about 10% – 30%, which is somewhat beyond natural data scatter for such vibratory tests. Released gases and also particles may play an important role in the results.There are three easily distinguishable damage regions for all cavitated surfaces, i.e. generally undamaged rim, central heavily damaged region and transition region, as for most vibratory tests. The relative areas of the three regions are about 53.5%, 0.13% and 46.4% respectively for the present tests.The erosion rate and extent of the damaged regions do not depend substantially on the solute tested. The very small area of the heavily damaged central region is presumably due to the relatively low horn amplitude used in these tests. The increase in damage rate with respect to tap water is about 50% for the maximum test duration.Surface photographs and scanning electron microscopy photomicrographs (for a test duration of 150 min) are presented. Cracks, intercrystalline fractures and single-blow craters are most concentrated in the central region, as would be expected.