今日更新:Journal of the Mechanics and Physics of Solids 1 篇,Mechanics of Materials 1 篇,International Journal of Plasticity 1 篇,Thin-Walled Structures 1 篇
Is a high-throughput experimental dataset large enough to accurately estimate a statistic?
Yifan Zhou, Sirui Lin, Xuhui Zhang, Hou Wu, Jose Blanchet, Zhigang Suo, Tongqing Lu
doi:10.1016/j.jmps.2023.105521
一个高通量的实验数据集是否足够大,可以准确地估计一个统计量?
In materials science, experimental datasets are commonly used to estimate various statistics of random variables. This paper focuses on a specific random variable: the rupture stretch of a material. Examples of statistics include average, standard deviation, coefficient of variation, and different quantiles. How accurate is the estimate of such a statistic? The answer depends on the statistic, the size of the experimental dataset, and how much the random variable scatters. Here we demonstrate a procedure to generate a large experimental dataset and use the experimental dataset to estimate the accuracy of various statistics of the rupture stretch. We use a high-throughput experiment to measure the rupture stretches of 160 specimens of a silicone rubber. We then use the bootstrap method to determine the 90% confidence intervals of several statistics. We find that the experimental dataset accurately estimates the average, standard deviation, and 50% quantile. However, the experimental dataset does not reliably estimate extremely low or high quantiles. This finding indicates an experimental dataset much larger than 160 specimens is needed to accurately estimate rare-event rupture stretch. We further apply the bootstrap method to an experimental dataset of strengths of 33 specimens of a ceramic. The result indicates that this experimental dataset is too small to accurately estimate the average strength of the ceramic. Our findings demonstrate that the common practice of using small datasets to estimate statistics of material properties is outdated and meaningless. The high-throughput experiment provides a large experimental dataset of rupture stretch, from which the bootstrap method quantifies the accuracy of the estimates of various statistics. The bootstrap method does not require the user to have sophisticated expertise in statistical analysis. Nor does the bootstrap method require the dataset to obey any statistical distribution.
在材料科学中,实验数据集通常用于估计随机变量的各种统计量。本文主要研究一个特定的随机变量:材料的断裂拉伸。统计的例子包括平均值、标准差、变异系数和不同的分位数。这样的统计估计有多准确?答案取决于统计数据、实验数据集的大小以及随机变量的分散程度。在这里,我们演示了一个程序来生成一个大型实验数据集,并使用实验数据集来估计断裂拉伸的各种统计数据的准确性。我们使用高通量实验测量了160个硅橡胶试样的断裂拉伸。然后,我们使用bootstrap方法来确定几个统计量的90%置信区间。我们发现实验数据集准确地估计了平均值、标准差和50%分位数。然而,实验数据集不能可靠地估计极低或极高的分位数。这一发现表明,需要一个比160个样本大得多的实验数据集来准确估计罕见事件的断裂拉伸。我们进一步将自举法应用于33个陶瓷样品强度的实验数据集。结果表明,该实验数据太小,无法准确估计陶瓷的平均强度。我们的研究结果表明,使用小数据集来估计材料性能统计数据的常见做法已经过时且毫无意义。高通量实验提供了一个大的断裂拉伸实验数据集,bootstrap方法从中量化了各种统计估计的准确性。自举方法不需要用户在统计分析方面具有复杂的专业知识。bootstrap方法也不要求数据集服从任何统计分布。
Flexural wave rainbow trapping effect in the periodic non-uniform Euler-Bernoulli beams and its application in energy harvesting
Tian Deng, Luke Zhao, Feng Jin
doi:10.1016/j.mechmat.2023.104892
周期性非均匀欧拉-伯努利光束中的弯曲波彩虹捕获效应及其在能量收集中的应用
The rainbow trapping of elastic wave enables spatial frequency shunting and energy concentration phenomenon, which implies that the broadband vibration will forbid propagating forward and occur energy concentration at different positions of metamaterial structure. This paper proposes a novel metamaterial consisting of the periodic non-uniform Euler-Bernoulli beams with an arbitrary profile section to achieve the rainbow trapping effect of flexural wave and application in piezoelectric energy harvester. Firstly, the differential quadrature method is introduced to solve a partial differential equation with variable coefficients. The convergence of this method is systematically demonstrated, and the correctness of band structures is validated by comparing theoretical results calculated by the differential quadrature method with those from the finite element method for different profiles. Based on band structures analysis, the working mechanism of the flexural wave rainbow trapping effect is attributed to the group velocity modulation; thereby, the constructed periodic array of non-uniform beams achieves integration of specific-band vibration reduction and energy enhancement at specific positions. Secondly, simulations indicate that the resonance rainbow trapping frequencies demonstrate more intense concentration of flexural wave energy compared to the counterpart with initial frequencies. Finally, the resonance rainbow trapping phenomenon demonstrates superiority in vibration energy harvesting. Specifically, when piezoelectric films are pasted on specific-position with enhanced energy density, the maximum output voltage in the independent circuit connection reaches up to 2.30V for the resonance rainbow trapping frequency of 8752Hz and the PVDF film position of x = 670 mm. Furthermore, simulations illustrate that the maximum output voltage and power are up to 4.52V and 1894.12 nW for the Series-A circuit connection, respectively, which is approximately the sum of the individual maximum output electrical energy generated by independent circuit connection at positions A and B. The proposed metamaterial beams can offer new selection guidelines for high-performance vibration energy harvesters.
弹性波的彩虹俘获导致了空间频率分流和能量集中现象,这意味着宽带振动将阻止向前传播,并在超材料结构的不同位置发生能量集中。本文提出了一种由任意截面的周期性非均匀欧拉-伯努利光束组成的新型超材料,以实现弯曲波的彩虹捕获效应,并将其应用于压电能量采集器。首先,引入微分正交法求解变系数偏微分方程。系统地论证了该方法的收敛性,并通过将微分正交法与有限元法在不同剖面下的理论计算结果进行比较,验证了该方法的正确性。基于能带结构分析,认为弯波彩虹捕获效应的工作机制是群速度调制;因此,所构建的非均匀光束周期阵列实现了特定频段减振和特定位置能量增强的一体化。其次,模拟结果表明,共振彩虹捕获频率比初始频率更能集中弯曲波能量。最后,共振彩虹捕获现象证明了在振动能量收集方面的优越性。其中,当压电膜以增强的能量密度粘贴在特定位置时,谐振彩虹捕获频率为8752Hz, PVDF膜位置为x = 670 mm时,独立电路连接的最大输出电压可达2.30V。仿真结果表明,A系列电路连接的最大输出电压为4.52V,最大输出功率为1894.12 nW,近似于A、b两个位置独立电路连接产生的最大输出电能之和。所提出的超材料梁可以为高性能振动能量采集器的选型提供新的指导。
On the strain delocalization mechanism of Cu/Nb nanolayered composites with amorphous interfacial layers
Yaodong Wang, Jianjun Li, Jiejie Li, Shaohua Chen
doi:10.1016/j.ijplas.2023.103856
具有非晶界面层的Cu/Nb纳米复合材料应变离域机制研究
Nanostructured metals and alloys possess ultrahigh strength but suffer from severe shear instability (strain localization). Recent experiments have shown that the strength and strain delocalization capability of some novel nanostructured alloys and nanolayered composites can be enhanced simultaneously by introducing nanoscale amorphous interfacial layers. However, the underlying mechanism is still in the embryonic stage due to the ignorance of the complicated elemental composition of the interfacial layers, especially the compositional gradient along the interface thickness. Here, the atomic mechanisms of the tensile deformation of Cu/Nb nanolayered composites with amorphous interfacial layers are systematically investigated by molecular dynamics simulations. Depending on whether the composition of the interfacial layers is invariable or has a gradient distribution along the interface thickness, these samples are classified as amorphous or gradient samples, respectively. The simulations of normal Cu/Nb nanolayered composites with ordinary incoherent Cu‒Nb interfaces are also included for comparison, the results of which show that strain localization occurs due to the inhomogeneous plastic deformation between soft and hard grains in the Cu and Nb layers. The strain localization is inhibited in the amorphous samples mainly through the activation of deformation twinning in the Cu and Nb layers that produce a co-deformation between grains. Intriguingly, the gradient arrangement of the elemental composition of the amorphous interfacial layers gives a further stronger strain delocalization by further promoting the co-deformation between grains through stimulating more twin boundaries in Cu layers and hindering twin boundary migration in Nb layers, and by producing a much more uniform von Mises strain distribution in the interfacial layers. In addition, a better strain delocalization capability can be obtained when the thickness of interfacial layers is closer to that of the crystalline ones or the range of gradient composition is larger.
纳米结构金属和合金具有超高的强度,但存在严重的剪切不稳定性(应变局部化)。最近的实验表明,引入纳米级非晶界面层可以同时提高一些新型纳米结构合金和纳米层复合材料的强度和应变离域能力。然而,由于对界面层复杂的元素组成,特别是沿界面厚度方向的成分梯度的研究尚处于萌芽阶段。本文采用分子动力学模拟方法,系统研究了Cu/Nb纳米复合材料非晶态界面层拉伸变形的原子机理。根据界面层的组成是不变的还是沿界面厚度呈梯度分布,这些样品分别被分类为非晶或梯度样品。通过对普通Cu - Nb非共格界面的普通Cu/Nb纳米复合材料的模拟进行比较,结果表明,应变局部化是由于Cu和Nb层中软硬晶粒之间的不均匀塑性变形引起的。非晶试样中的应变局部化主要是通过激活Cu和Nb层中的变形孪晶,从而产生晶粒间的共变形来抑制的。有趣的是,非晶态界面层元素组成的梯度排列通过在Cu层中激发更多的孪晶界而在Nb层中阻碍孪晶界迁移,从而进一步促进晶粒之间的共变形,并通过在界面层中产生更均匀的von Mises应变分布,从而进一步增强了应变的离域。此外,界面层厚度越接近晶体层厚度或梯度组成范围越大,可以获得较好的应变离域能力。
On the mechanical behavior of carbon fiber/epoxy laminates exposed in thermal cycling environments
Zhihao Qiu, Dongrun Wu, Yao Zhang, Chang Liu, Yuan Qian, Deng'an Cai
doi:10.1016/j.tws.2023.111481
热循环环境下碳纤维/环氧复合材料的力学性能研究
Carbon fiber reinforced polymer (CFRP) composites are commonly used for reflectors of artificial satellites operating in low earth orbit (LEO). The decay of the modulus of the CFRP composite varies under different thermal cycling environments, which can lead to a reduction in the accuracy of the reflector panels, affecting the transmission of signals. This paper investigates the impact of different thermal cycling conditions on the mechanical behavior of carbon fiber/epoxy laminated composites experimentally. Three kinds of thermal cycling conditions involving continuous temperature changes are employed to explore the influence of temperature range on the residual tensile and in-plane shear moduli of the laminates. Test results indicate that the upper temperature limit and the temperature span of the thermal cycling conditions jointly affect the mechanical properties of CFRP composite laminates, but the responses of the residual tensile and in-plane shear moduli are different under the variation of each temperature parameter alone. The residual tensile and in-plane shear moduli of the laminates under thermal cycling decrease with an expansion of the temperature span having the same upper limit. If the temperature span remains constant, an increase in the upper temperature limit leads to an increase in the residual tensile modulus, but a decrease in the residual in-plane shear modulus. The main damages causing the decay of residual tensile and in-plane shear moduli of unidirectional laminates were investigated by scanning electron microscopy (SEM) technology. Observations of the microscopic fracture of the material show that the post-curing reaction factor predominantly influences the residual tensile modulus of unidirectional laminates, while the fiber/matrix interface damage factor dominates the residual in-plane shear modulus of the unidirectional laminates. Furthermore, an increase in the fiber tensile modulus decreases both residual tensile and residual in-plane shear moduli. Notably, the residual in-plane shear modulus exhibits greater sensitivity to thermal cycling compared to the residual tensile modulus. The findings reported in this paper would provide valuable insights and guidance for the design and application of carbon fiber/epoxy composites subjected to thermal cycling conditions.
碳纤维增强聚合物(CFRP)复合材料是近地轨道人造卫星反射器的常用材料。CFRP复合材料的模量衰减在不同的热循环环境下是不同的,这会导致反射板的精度降低,影响信号的传输。通过实验研究了不同热循环条件对碳纤维/环氧复合材料力学性能的影响。采用三种温度连续变化的热循环工况,探讨温度范围对层合板残余拉伸模量和面内剪切模量的影响。试验结果表明,热循环工况的温度上限和温度跨度共同影响CFRP复合材料层合板的力学性能,但各温度参数单独变化时残余拉伸模量和面内剪切模量的响应不同。热循环作用下层合板的残余拉伸模量和面内剪切模量随着温度跨度的扩大而减小,但温度跨度的上限相同。在温度跨度一定的情况下,温度上限的增加会导致残余拉伸模量的增加,但会导致残余面内剪切模量的减少。采用扫描电镜(SEM)技术研究了引起单向层合板残余拉伸模量和面内剪切模量衰减的主要损伤。对材料微观断裂的观察表明,固化后的反应因子对单向层合板的残余拉伸模量有主要影响,而纤维/基体界面损伤因子对单向层合板的残余面内剪切模量有主要影响。此外,纤维拉伸模量的增加会降低残余拉伸模量和残余面内剪切模量。值得注意的是,与残余拉伸模量相比,残余面内剪切模量对热循环表现出更大的敏感性。本文的研究结果将为热循环条件下碳纤维/环氧复合材料的设计和应用提供有价值的见解和指导。