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51.
《International Journal of Hydrogen Energy》2022,47(88):37609-37616
When applied to transportation systems, fuel cell structures are exposed to external mechanical disturbance including shocks and harmonic excitations from operating components. To minimize performance degradation from machine operations, the fuel cell structure needs to be examined via vibration reliability tests. In this study, the reduction in the clamping force of the stack by random vibrations was investigated by experiments. The stack mass and gasket were clamped with bolts for vibration tests. The vibration induced shear movements between clamped stacks. To estimate the vibration input magnitudes, the Dirlik method was used. The reduction in the stack clamping force was estimated using the Basquin's power law. The clamping force decreased by the shear vibration input to the stack structure. The degree of clamping force reduction was larger for the heavier stack. When the stacks were separated by the gasket the reduction became smaller. Through the Dirlik method, the vibration reliability of the stack was evaluated. This information provides severity of the external vibration on the stack functionality. 相似文献
52.
针对胶轮车湿式制动器的碟簧使用中发生的碎裂现象,运用标准GB/T 1972中方法对碟簧进行验算,发现在变负荷作用下的碟簧寿命≤105次,属于有限寿命。在保持制动性能不变情况下,采取增加碟簧厚度的改进方案对碟簧结构进行优化。优化后碟簧的设计循环寿命≥2×106次,达到GB/T 1972标准规定的无限寿命,并与工业制动器JB/T 10917中规定碟簧设计循环寿命一致。 相似文献
53.
54.
This study investigates the effects of display technique (2D, autostereoscopic 3D), ball speed (138, 140 km/h), and operation time (5, 10, 15 min) on the four outcomes of signal detection theory (SDT) (i.e., hit, miss, false alarm, correct rejection), β, d’, receiver operating characteristic (ROC) space, Simulator Sickness Questionnaire (SSQ), and the iGroup Presence Questionnaire (IPQ). The results indicated that the display technique was significant on the hit rate, SSQ, and IPQ, where a higher hit rate, visual fatigue, and IPQ were found in the 3D technique. The results also showed that the ball speed was significant on the miss rate and d’, where a low miss rate and high d’ were found in the higher speed of 138 km/h. The results further demonstrated that the operation time was significant on the false alarm rate, correct rejection rate, d’, SSQ, and IPQ, with a long operation time being associated with a better performance for every variable, except the SSQ.Relevance to industryFrom the results obtained regarding the ROC space, this study found that the possibility of participants’ misjudgements was low, and the accuracy of this research is considered reliable. The results of this study could serve as a reference for N3DS and game manufacturers in designing future products. 相似文献
55.
This paper presents an analytical method to study the effect of inclusions in piezoelectric materials on the creep rate. The driven force for the creep rate of piezoelectric materials with inclusion is from diffusional mass transport along the inclusion interface. The results show that the creep rate of piezoelectric materials containing the rigid inclusion with the shape parameter m = 0.8 appears at the minimum, and the effect of inclusion volume fraction on the creep rate of piezoelectric materials with soft inclusion becomes the smaller and smaller, as the stiffness of soft inclusion decreases. Thus, the effect of inclusion on creep characteristics can be improved by controlling the material property, the sizes, shapes, and volume ratio of inclusions. 相似文献
56.
Xin Bai Peng Zhang Zhen‐jun Zhang Rui Liu Zhe‐feng Zhang 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(10):2340-2353
A new method for determining the P‐S‐N curves is proposed by the probabilistic analysis of the mixed samples that are composed of the testing fatigue lives and equivalent fatigue lives. The equivalent fatigue lives at each level are converted from all the testing data at all the testing levels according to the equivalent fatigue failure probability, where the life distributions are determined by the medians of logarithmic fatigue lives at respective levels and a unified coefficient of variation. Comparison results of the P‐S‐N curves of 2024‐T3 and A356.0‐T6 alloys with the different methods indicate that the new method can determine the high‐precision P‐S‐N curves with different sample sizes of the S‐N testing data, and can save testing time and improve testing efficiency, especially for the situation of large‐scatter S‐N testing data. 相似文献
57.
《中国有色金属学会会刊》2020,30(5):1249-1266
The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31B alloy and AZ31B/1.5vol.%Al2O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 °C and then an open-die forging at 450 °C. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain; however, a degradation was observed in the high applied strain region. Unlike AZ31B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging. 相似文献
58.
Scott J. Robertson Marina B. Ruggles-Wrenn Randall S. Hay Theodore Shillig Ronald Mitchell Brian Kroeger Logan Gumucio 《Journal of the American Ceramic Society》2020,103(2):1358-1371
A facility for testing SiC fiber tows in static fatigue and creep at elevated temperatures in air and steam was developed. Static fatigue of Hi-Nicalon™-S fibers was investigated at 800°C-1100°C at applied stresses between 115 and 1250 MPa in air, in Si(OH)4(g)-saturated steam, and in unsaturated steam. Fibers tested in Si(OH)4(g)-saturated steam and in air had silica scales throughout the test sections, but those tested in unsaturated steam did not develop scales near the steam injection point. Fiber lifetimes in static fatigue were shortest in unsaturated steam, intermediate in Si(OH)4(g)-saturated steam, and longest in air. Failure strains did not exceed 0.3%. Steady-state strain rates and static fatigue lifetimes are modelled empirically by the Monkman-Grant relationship. Failure mechanisms are discussed. 相似文献
59.
为了更加精确地研究压力型锚索的锚固机理,基于锚索预应力与岩土体蠕变的耦合效应推导了锚索预应力方程。在此基础上根据Mindlin问题解,推导了耦合效应作用下锚索砂浆体的压应力和剪应力近似解,并考虑锚索预应力与岩土体蠕变之间的耦合效应进行了案例分析。研究结果表明:锚索预应力和砂浆体受到的应力峰值均按反幂函数随时间逐渐衰减并稳定;承压板的长宽比与压应力峰值之间存在正相关关系,与剪应力峰值之间存在负相关关系;岩土体的泊松比与应力峰值之间存在正相关关系。该成果丰富了压力型锚索锚固机理的理论研究,可为边坡锚固设计提供一定的理论依据。 相似文献
60.