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基于橡胶试样单轴拉伸试验得到的拉力和变形量等试验数据,利用最小二乘法拟合求得橡胶材料的Mooney-Rivlin模型及Yeoh模型常数。基于有限元方法,用得到的模型常数对试样变形量进行计算并与试验结果对比。结果表明,Mooney-Rivlin模型在小应变和中等应变时可以较好地描述材料的力学行为,Yeoh模型适合模拟大应变时材料的力学行为。利用得到的模型常数计算分析异形密封圈的静态性能,最大变形量计算值与试验值的相对误差为2.74%,表明了所选模型常数的准确性。 相似文献
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通过对油浸式电抗器器身-油箱间阻尼橡胶材料进行轴向压缩滞回性能试验,研究了其阻尼特性;依据实验数据并结合ABAQUS数值模拟结果,校正了适用于油浸式电抗器器身-油箱间阻尼橡胶材料的Mooney-Rivlin和Yeoh本构模型参数。结果表明,相比普通抗振橡胶试件,丁腈橡胶试件的轴向压缩刚度更大,滞回曲线更饱满,耗能能力更强;Mooney-Rivlin模型和Yeoh模型均适用于NBR试件的小变形和大变形行为,其中Mooney-Rivlin模型参数和Yeoh模型参数计算结果最大误差分别为-11.31%和-12.21%。 相似文献
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采用单轴拉伸、等双轴拉伸及平面剪切下橡胶材料试验数据的4种不同组合方式分别对主要用于表述橡胶超弹性的Yeoh模型和Ogden三阶模型进行拟合,并得出两种模型的材料参数。建立单轴拉伸、等双轴拉伸及平面剪切试验的有限元模型,探究1种仅仅借助单轴拉伸试验数据并结合其他2种试验有限元模型预测结果,进行橡胶类本构模型参数拟合的新方法。结果表明:选用Yeoh模型时,利用单轴拉伸和等双轴拉伸组合方式可获得较理想的材料参数;在只具备单轴拉伸试验数据的条件下,利用单轴试验数据和等双轴有限元模型预测数据的组合方式在低应变区用Yeoh模型拟合得到的材料参数较可靠;Ogden三阶模型较Yeoh模型精度高,但计算效率低且不易收敛。 相似文献
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在深冷环境下密封橡胶易发生变脆、丧失高弹性等现象,从而导致密封性能降低。密封橡胶的力学性能是评估密封可靠性的重要参数。选择低苯基硅橡胶及以低苯基硅橡胶为基体分别添加全氟聚醚油和聚酰亚胺粉的改性橡胶为研究对象,考察3种橡胶在超低温下的力学性能,在常温(23℃)和超低温(-196℃)下进行单轴拉伸和压缩永久变形试验,并利用有限元软件Abaqus超弹性材料拟合板块对本构模型进行参数模拟,探讨Mooney-Rivlin模型、Ogden模型和Yeoh模型对超低温下密封橡胶的适用性。结果表明:在超低温下,聚酰亚胺粉改性低苯基硅橡胶的密封性能优于其他两种橡胶材料;在单轴拉伸试验拟合中,Yeoh模型拟合误差较小;在压缩试验拟合中,Mooney-Rivlin模型和Ogden模型能更准确地描述橡胶力学性能。 相似文献
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Herman P. Ruyter 《Fuel》1982,61(12):1182-1187
A series of low-rank materials, ranging from biomass waste to subbituminous coal, were subjected to hydrothermal coalification, i.e. heat treatment in an autoclave with water. The results, together with relevant literature data, cover a wide range of reaction conditions: temperatures from 120° to 390° and residence periods from 1 min to 6 months. Using overall kinetics, the progress of hydrothermal coalification in terms of the evolution of carbon dioxide as a function of the conditions has been expressed in a simple model. Low-rank materials can be described in terms of properties that can be gathered into general relations which hold over wide ranges. Over the range from biomass to subbituminous coal, where coalification mainly implies the evolution of water and carbon dioxide, the conversion model allows the prediction of the enrichment of a material on the basis of feedstock properties and the conditions applied. 相似文献
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Standard variable selection procedures, primarily developed for the construction of outcome prediction models, are routinely applied when assessing exposure effects in observational studies. We argue that this tradition is sub-optimal and prone to yield bias in exposure effect estimators as well as their corresponding uncertainty estimators. We weigh the pros and cons of confounder-selection procedures and propose a procedure directly targeting the quality of the exposure effect estimator. We further demonstrate that certain strategies for inferring causal effects have the desirable features (a) of producing (approximately) valid confidence intervals, even when the confounder-selection process is ignored, and (b) of being robust against certain forms of misspecification of the association of confounders with both exposure and outcome. 相似文献
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模型预测控制算法(MPC)存在设定点控制与区间控制两种策略,区间预测控制较之设定点控制在技术上具有先进性。目前,主流的预测控制软件技术均采用双层结构,即上层稳态优化计算最优设定点,下层动态控制负责动态跟踪最优设定点。从过程稳态的角度出发,分别对区间预测控制和双层结构预测控制进行了机理分析,从定性与定量两个方面比较了这两者的异同点,提出并证明了两者的一致性条件。论述了双层结构预测控制较之单层结构下的区间控制更具先进性。 相似文献
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Determining good parameter estimates in (exponential smooth transition autoregressive) models is known to be difficult. We show that the phenomena of getting strongly biased estimators is a consequence of the so‐called identification problem, the problem of properly distinguishing the transition function in relation to extreme parameter combinations. This happens in particular for either very small or very large values of the error term variance. Furthermore, we introduce a new alternative model – the TSTAR model – which has similar properties as the ESTAR model but reduces the effects of the identification problem. We also derive a linearity and a unit root test for this model. 相似文献
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J. H. Hodgkin 《应用聚合物科学杂志》1976,20(9):2339-2346
Pyromellitic dianhydride was reacted with various substituted aryl amines, under conditions similar to those used for polyimide formation. Yields of model imides have been greatly improved over those found in previous studies. The work has shown that the major impurities formed when the reactions were performed in solutions of N,N-dimethylformamide or N,N-dimethylacetamide were adducts containing chemically bound solvent residues. 相似文献
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The purpose of this article is to develop the likelihood ratio test for the structural change of an AR model to a threshold AR model. It is shown that the log‐likelihood ratio test converges to the maxima of a two‐parameter Gaussian process in distribution. This limiting distribution is novel and we tabulate the critical values. Some simulations are carried out to examine the finite‐sample performance of this test statistic. This article also includes a weak convergence of a two‐parameter marked empirical process, which is of independent interest. 相似文献
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Models fitted to data are used extensively in chemical engineering for a variety of purposes, including simulation, design and control. In any of these contexts it is important to assess the uncertainties in the estimated parameters and in any functions of these parameters, including predictions from the fitted model. Profiling is a likelihood ratio approach to estimating uncertainties in parameters and functions of parameters. A comparison is made between the optimization and reparameterization approaches to determining likelihood intervals for functions of parameters. The merits and limitations of generalized profiling are discussed in relation to the linearization approach commonly used in engineering. The benefits of generalized profiling are illustrated with two examples. A geometric interpretation of profiling is used to elucidate its value, and cases are identified for which the numerical algorithm fails. An alternative approach is suggested for these cases. 相似文献
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耐火材料的本构关系模型是材料对外载荷所作变形响应的一种数学表达,是数值模拟准确性与否的基础。为此,在细观损伤力学模型多尺度特性的基础上,借助商业有限元软件的二次开发功能,通过编制用户子程序接口将其界面细观力学模型的损伤本构关系嵌入到软件中,首先在宏观尺度上对炉衬结构耐火材料进行了拉、压加载数值试验,数值模拟的结果可以与试验结果较好地吻合;之后借助代表体积RVE单元,采用不同灰度代表不同损伤状态,在微观尺度上对损伤进行了直观表征,成功实现了炉衬结构耐火材料的多尺度模拟。 相似文献