共查询到20条相似文献，搜索用时 15 毫秒
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Cun-jian MIAO Jin-yang ZHENG Xiao-zhe GAO Ze HUANG A-bin GUO Du-yi YE Li MA 《浙江大学学报(A卷英文版)》2013,14(1):31-37
Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301(equivalents include UNS S30400 and AISI 304) in solution-annealed(SA) and cold-stretched conditions(9% strain level) and the response of fatigue properties to cold stretching(CS),low-cycle fatigue(LCF) tests were performed at room temperature,with total strain amplitudes ranging from -.4% to -.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1?03 to 2?04 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels. 相似文献
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对调质42CrMo钢进行室温下各种应力循环和对称应变循环的低周疲劳实验,揭示材料的循环软化特性,棘轮变形和低周疲劳特性以及棘轮-疲劳交互作用。结果表明,调质42CrMo钢体现出明显的循环软化;在应力幅值或平均应力较高时,试样的棘轮变形较大,其破坏形式为延性破坏,而在应力水平较低时,材料的破坏由疲劳裂纹扩展所致的脆性断裂引起;材料在应力循环下的低周疲劳寿命由于有棘轮变形的产生而受到平均应力、应力幅值、最大应力和应变比等多种因素的影响。 相似文献
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Zhu Huiyuan Yan Shaochun Wu Jingshuo Zhang Zhong Li Xiaolin Liu Zheng Ma Xing Zhou Lina Zhang Lin Feng Mingming Geng Yiwei Zhang Aixin Janciauskiene Sabina Xu Aiguo 《Journal of Zhejiang University. Science. B》2021,22(6):512-520
Background: Previous studies have shown that macrophage migration inhibitory factor(MIF) is involved in the pathogenesis of asthma. This study aimed to investigate whether serum MIF reflects a therapeutic response in allergic asthma.Methods: We enrolled 30 asthmatic patients with mild-to-moderate exacerbations and 20 healthy controls, analyzing the parameter levels of serum MIF, serum total immunoglobulin E(tIgE), peripheral blood eosinophil percentage(EOS%), and fractional exhaled nitric oxide(FeNO). Lung function indices were used to identify disease severity and therapeutic response.Results: Our study showed that all measured parameters in patients were at higher levels than those of controls. After one week of treatment, most parameter levels decreased significantly except for serum tIgE. Furthermore, we found that serum MIF positively correlated with EOS% as well as FeNO, but negatively correlated with lung function indices. Receiver operator characteristic(ROC) curve analysis indicated that among the parameters, serum MIF exhibited a higher capacity to evaluate therapeutic response. The area under the curve(AUC) of MIF was 0.931, with a sensitivity of 0.967 and a specificity of 0.800.Conclusions: Our results suggested that serum MIF may serve as a potential biomarker for evaluating therapeutic response in allergic asthma with mild-to-moderate exacerbations. 相似文献
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系统介绍了MTS材料试验机在评价油井管抗应力腐蚀开裂性能领域中的应用。通过实测双悬臂梁试样(DCB)加载-卸载柔度闭环曲线可以建立卸载柔度系数与裂纹长度的对应关系,实现了在疲劳预裂时对DCB试样裂纹扩展的有效测控。此外,对硫化物应力腐蚀试验(SSC)后的DCB试样进行加载-楔劈移除-卸载控制与二次疲劳裂纹扩展,可获得楔劈加载的平衡载荷与SSC诱导裂纹扩展量,从而准确测定材料的K1SSC指标。 相似文献
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刘宁 《实验室研究与探索》2007,(11)
研究了316L和316LN不锈钢在常温下的低循环特性并对其组织结构的变化进行了观察.结果显示,材料在循环变形过程中呈现不同程度的硬化、软化现象。组织结构的演变与循环应力特性曲线的变化规律相呼应。 相似文献
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A constitutive model for methane hydrate-bearing sediment(MHBS)is essential for the analysis of mechanical response of MHBS to the change of hydrate saturation caused by gas extraction. A new elasto-plastic constitutive model is built in order to simulate the mechanical behavior of MHBS in this paper. This model represents more significant mechanical properties of MHBS such as bonding, higher stiffness, softening and stress-strain nonlinear relationship. The bonding behavior can be described by use of a parameter related to mechanical hydrate saturation. Higher stiffness can be modeled by the introduction of hydrate saturation into traditional expression of soil stiffness. Softening can be controlled by a function describing the relationship between cohesion and bonding structure factor. Dilatancy can be estimated by establishing the relationship between the lateral strain and axial strain. Meanwhile, the hypothesis of isotropic expanding is applied to the calculation of the volumetric strain. The stress-strain curves under different hydrate saturation conditions predicted by the proposed model are in good agreement with the test data. All the coefficients can be easily obtained by the triaxial test of MHBS. 相似文献
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To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the con-crete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex. 相似文献
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To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex. 相似文献
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为了降低高性能聚乙烯醇(polyvinyl alcohol,PVA)纤维增强水泥基复合材料ECC(engineered cemen-titious composites)的成本,用国产PVA纤维和其他本地原材料如粉煤灰、水泥和细砂等研制了高延性ECC材料.采用四点弯曲试验和光学显微镜研究了ECC的弯曲变形能力、裂缝宽度及裂缝自愈合现象,并对其进行了经济性分析.实验结果表明:利用国产原料制备的ECC均表现出大变形能力,平均裂缝宽度能控制在60μm左右;开裂的试件经过干湿循环养护之后,裂缝中出现了自愈合现象;经济性分析表明利用国产PVA纤维可以极大地降低ECC成本.利用国产PVA纤维等材料制备高性价比的ECC是可行的. 相似文献
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Considering the effects of particle crushing and intermediate principal stress on material yielding strength, the spatial mobilization plane(SMP) yielding criterion and state parameter model including a general critical state line are selected in the analysis of cylindrical cavity expansion.Meanwhile, combining Rowe's flow rule and Bolton's simplification to stress-dilatancy relationship to reflect soil shear dilatancy and softening behavior, this paper analyzes the problem of cylindrical cavity expansion i... 相似文献
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Sheng-mei Zhu Yong-min Liu Er-dan An Qing-lian Chen 《Journal of Zhejiang University. Science. B》2009,10(8):625-630
Postherpetic neuralgia (PHN) is a severe sequela of herpes zoster (HZ). Until now, only age and pain severity were considered
predisposing factors for the development of PHN. We evaluated 49 patients with acute phase HZ, 10 of whom developed PHN (Group
A) and 39 of whom did not develop PHN (Group B). Twenty-five healthy volunteers similar in age and gender distribution to
the study group were recruited as controls (Group C). Numbers of serum CD3+ (pan-T lymphocytes), CD4+ (helper/inducer), and CD8+ (suppressor/cytotoxic) lymphocytes were decreased significantly in Groups A and B relative to the control group, but there
were no statistical differences between Groups A and B. Interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, IL-8, and
IL-10 were significantly elevated in Groups A and B relative to Group C. IL-6 was significantly higher in Group A than in
Group B, and was significantly positively correlated with pain severity scored on a visual analog scale. Therefore, we suggest
that the inflammatory response, especially that of IL-6, in the acute phase of HZ may be associated with hyperalgesia and
the development of PHN.
Project (No. 2008ZYC07) supported by the Zhejiang Medical Bureau of China 相似文献
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Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks
In this paper, numerical method is used to study the strain rate effect on masonry materials. A typical unit of masonry is selected to serve as a representative volume element (RVE). Numerical model of RVE is established with detailed distinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor (DIF) of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results. 相似文献
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用行波变换方法和分叉理论研究里非线性薛定谔方程的定常解和定常解的稳定性.计算结果表明:非线性薛定谔方程存在两类定常解,静态解和平面波解.对于具有正阻尼和软特性的非线性薛定谔方程,稳定的平面解存在于正常色散媒质中;而对于具有正阻尼和硬特性的非线性薛定谔方程,稳态平面波解只存在于反常色散媒质中.此外,非线性薛定谔方程在行波变换下的派生系统在处发生Hopf分叉. 相似文献
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Don M. Cregier 《College Teaching》2013,61(4):215-217
This study examined the statistical effect of changing from a 10-point to a 5-point response scale on students' evaluation of instruction. Participants were 5,616 students enrolled in classes offered by the College of Social Sciences and Public Affairs at a large Western university, who completed both the old evaluation (10-point response) and the new evaluation (5-point response). On average, students used a greater range of points on the scale for the 5-point scale (32 percent) than on the 10-point scale (19 percent). The effects of changing the response scale are discussed. 相似文献
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基于柔度测试方法,提出了J积分增量算式;对CT试样,提出了裂纹嘴张开位移V0和加载线裂纹张开位移VLL之间的V0~VLL转换算式,裂纹长度a与弹性模量E计算的简化算式。基于适合同时测试V0和VLL的CT试样设计,对45#钢CT试样进行了多级加-卸载,对CT试样的V0~VLL转换算式进行了试验验证。计算与试验结果表明,新公式具有良好精度。 相似文献
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集体教学是幼儿园课程的重要实施途径,幼儿园教师应当具备设计与实施、观察与评价集体教学活动的能力。本研究基于关键事件技术,采用德尔菲法和观察评定法,建构了幼儿园教师教学行为观察评价指标体系。该体系包含3个一级指标,即预设性事件、生成性事件、管理事件;10个二级指标,即材料投放、环节组织、提问、总结、个别指导、理答、评价、应变、规则与期望、纠正不当行为;20个三级指标,即材料充足、材料种类多样、材料适宜、环节形式、环节次序、开放性问题、提问对象、发展概念、迁移经验、个别指导、回应幼儿需求、候答、纠正补充、追问、高级语言、有意义的评价、意料外的回答、与预设不同的做法、规则与期望、纠正不当行为,并对不同专业水平的教师在各指标上的教学行为表现进行了描述。该指标体系可用于评价和改进幼儿园教师的集体教学行为。 相似文献
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张莉莉 《荆门职业技术学院学报》2007,22(3):52-55
研究了C.F.Lo定义的广义多模压缩态(Phys.Rev.A 47 733-735)在N=3时的三模压缩态与介观约瑟夫森结超导环相互作用时超导电流期望值随时间演化的情况。在三模量子化光场的模与模之间的压缩参数不相同的情况下,探究了超导电流时间演化的量子坍塌复苏现象与压缩参数的关系。 相似文献
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Attempting to deepen the understanding of factors that explain student performance, this study seeks to identify and characterize profiles of Chilean students based on academic performance in mathematics. As analytical method, statistical techniques known as random forest (RF) and classification and regression tree (CART) were used to identify groups of eighth-grade elementary students according to their performance in 2011 test, using features related to individual and family behavior. The analysis was performed with a database provided by the Education Quality Measurement System of Chile. Results show that “parents’ educational expectations” (42.7%) is key factor to obtain the best children's performances. Additionally, the analysis showed that the “type of school” (26.6%) and the “index of mathematical abilities” (26.1%) influence good performance. 相似文献