今日更新:International Journal of Solids and Structures 1 篇,Journal of the Mechanics and Physics of Solids 1 篇,Mechanics of Materials 1 篇,International Journal of Plasticity 1 篇,Thin-Walled Structures 2 篇
Numerical and Analytical Analyses of the formability and fracture of AA7075-O aluminum sheets in hemispherical punch tests
Shahzamanian M.M., Parsazadeh M., Wu P.D.
doi:10.1016/j.ijsolstr.2023.112558
在半球冲压试验中对 AA7075-O 铝板的成形性和断裂进行数值和分析
In this study, numerical simulations and experimental validations of the simulation of hemispherical punch tests for AA7075-O aluminum sheets with various sample widths are presented. It is convincingly believed in literature that a finite element (FE) based forming limit diagram (FLD) can be predicted very well using various time-dependent criteria. This matter has been investigated and securitized deeply and the FE-based FLD was predicted using three time-dependent criteria and compared with the experimental FLD. Results show that two of the three criteria could predict the relatively appropriate shape of the FLD while one of them has failed to match. Aside from using FE simulation to predict the FLD, an analytical method, namely, Marciniak-Kuczynski (M-K) was also used to make a better evaluation about the capability of the FEM to predict FLD. Among the FE-based FLDs, the one predicted using the Martinez-Donaire et al., 2014 (Martínez-Donaire et al., 2014) was found to be close to the one predicted using the M-K method. Although, the main objective of this paper is to investigate the capability of the FEM to predict an FLD for AA7075-O aluminum sheets, the fracture behavior for each case was predicted using a unified fracture model. Several computer runs were executed to perform the tests and reproduce the experimental results. The aim of this study was to discuss the simulation of hemispherical punch tests and analyze the numerical results and compare them with the experimental and analytical methods. It was observed that the experimental FLD can be reproduced using various time-dependent criteria in a relatively appropriate manner but with limitations especially at the equibiaxial stress state. These limitations were scrutinized and discussed in detail by comparing the results with experimental and analytical calculations.
本研究介绍了对不同试样宽度的 AA7075-O 铝板进行半球冲压试验模拟的数值模拟和实验验证。有文献令人信服地认为,基于有限元(FE)的成形极限图(FLD)可以利用各种随时间变化的准则进行很好的预测。我们对这一问题进行了深入研究和论证,并使用三种随时间变化的标准对基于有限元的 FLD 进行了预测,并与实验 FLD 进行了比较。结果表明,三个标准中的两个可以预测出相对合适的 FLD 形状,而其中一个则无法匹配。除了使用 FE 仿真预测 FLD 外,还使用了一种分析方法,即 Marciniak-Kuczynski (M-K),以更好地评估 FEM 预测 FLD 的能力。在基于有限元的 FLD 中,使用 Martinez-Donaire 等人,2014(Martínez-Donaire et al.虽然本文的主要目的是研究有限元预测 AA7075-O 铝板 FLD 的能力,但每种情况下的断裂行为都是使用统一的断裂模型预测的。为了进行测试并重现实验结果,执行了多次计算机运行。本研究旨在讨论半球冲压试验的模拟,分析数值结果,并将其与实验和分析方法进行比较。研究发现,使用各种随时间变化的标准可以以相对适当的方式再现实验的 FLD,但存在局限性,尤其是在等轴应力状态下。通过将结果与实验和分析计算结果进行比较,对这些局限性进行了详细的研究和讨论。
Deformation and failure mechanisms in spider silk fibers
Olive Renata, Cohen Noy
doi:10.1016/j.jmps.2023.105480
蜘蛛丝纤维的变形和破坏机制
Spider silk fibers are protein materials that exhibit high strength and toughness thanks to a unique microstructure. In this work, a microscopically motivated model that sheds light on the underlying mechanisms behind the mechanical response of silk fibers is developed. The governing deformation mechanisms are as follows: initial stretching is enabled by the distortion of intermolecular hydrogen bonds that restrict the mobility of polypeptide chains. Once a sufficient force is applied, these bonds dissociate and the external load is transferred to the chains. Next, intramolecular β-sheets in the chains and/or the crystalline domains dissociate to provide additional chain length, thereby resulting in a macroscopic softening. Further deformation is enabled by the entropic elasticity of the chains, which stiffen with stretch. Based on the model, an algorithm to determine the overall constitutive response of silk fibers as a function of the initial distribution of chains and their composition is introduced. Experiments have shown that these two quantities can be controlled by supercontracting and dehydrating fibers under load. The model is validated through a comparison to various experimental findings at different alignment parameters. The merit of the model is three-fold: (1) it captures the microstructural evolution of the network as the fiber experiences stretch and reveals the role of key microstructural quantities such as chain-density, chain alignment, and chain composition, (2) it enables to compare between the microstructures of silk fibers produced by different spider species, and (3) it provides a platform for the microstructural design of biomimetic synthetic fibers with tunable properties.
蜘蛛丝纤维是一种蛋白质材料,由于其独特的微观结构而具有高强度和韧性。这项研究建立了一个微观模型,揭示了蛛丝纤维机械响应背后的基本机制。其变形机制如下:最初的拉伸是通过限制多肽链流动性的分子间氢键的变形实现的。一旦施加了足够的力,这些氢键就会解离,外部负载就会转移到多肽链上。接下来,分子内β-表层和/或结晶结构域解离,以提供额外的链长,从而导致宏观软化。链的熵弹性使其进一步变形,并随着拉伸而变硬。在该模型的基础上,引入了一种算法来确定丝纤维的整体构成响应,它是链的初始分布及其组成的函数。实验表明,这两个量可以通过纤维在负载下的超收缩和脱水来控制。通过与不同排列参数下的各种实验结果进行比较,验证了该模型。该模型有三方面的优点:(1)它捕捉到了纤维经历拉伸时网络的微观结构演变,并揭示了链密度、链排列和链组成等关键微观结构量的作用;(2)它能够比较不同种类蜘蛛生产的丝纤维的微观结构;(3)它为具有可调特性的仿生物合成纤维的微观结构设计提供了一个平台。
Modeling the thermo-responsive behaviors of polydomain and monodomain nematic liquid crystal elastomers
Chen Baihong, Liu Changyue, Xu Zengting, Wang Zhijian, Xiao Rui
doi:10.1016/j.mechmat.2023.104838
多域和单域向列液晶弹性体的热响应行为建模
Liquid crystal elastomers (LCEs) are polymeric materials that combine liquid crystal orientation and rubber elasticity. The mechanical responses of LCEs strongly depend on the nematic order and temperature. Developing a thermo-order-mechanical coupling model is important for the engineering applications of LCEs. In this work, we first synthesize both polydomain and monodomain LCEs. The shape change with temperature under a certain stress level is further characterized. In the theoretical part, the Landau-de Gennes model and neo-classical model is combined to construct the free energy density of LCEs. A linear term accounting for the effect of interior stress on nematic-isotropic transition is incorporated into the Landau-de Gennes free energy density, while a macro-order parameter is defined to describe the polydomain-monodomain transition for polydomain LCEs induced by the external force. Comparison between the model predictions and experimental results shows acceptably consistency for both polydomain and monodomain LCEs. Therefore, this work provides an efficient approach to predict the shape change of LCEs in various scenarios.
液晶弹性体(LCE)是一种结合了液晶取向和橡胶弹性的聚合物材料。液晶弹性体的机械响应在很大程度上取决于向列阶数和温度。开发一种热阶-机械耦合模型对于 LCE 的工程应用非常重要。在这项工作中,我们首先合成了多域和单域 LCE。并进一步研究了在一定应力水平下形状随温度变化的特征。在理论部分,我们结合朗道-德-吉尼斯模型和新古典模型构建了 LCE 的自由能密度。Landau-de Gennes 自由能密度中包含了一个线性项,用于解释内部应力对向列-各向同性转变的影响,同时定义了一个宏阶参数,用于描述外力诱导的多域 LCE 的多域-单域转变。模型预测与实验结果之间的比较显示,多域和单域 LCE 都具有可接受的一致性。因此,这项工作为预测 LCE 在各种情况下的形状变化提供了一种有效的方法。
Microstructural insights into fatigue short crack propagation resistance and rate fluctuation in a Ni-based superalloy manufactured by Laser powder bed fusion
Li Jianghua, Huang Qinghui, Wang Zhiyang, Zhang Ningyu, Chen Gang, Qian Guian
doi:10.1016/j.ijplas.2023.103800
通过激光粉末床熔融技术制造的镍基超级合金抗疲劳短裂纹扩展能力和速率波动的微观结构启示
The microstructural sensitivity of fatigue short crack path and its propagation rate in a Ni-based superalloy GH4169 manufactured by laser powder bed fusion (LPBF) was investigated at room temperature. In-situ digital image correlation (DIC) observation and post-mortem microstructural analysis around the crack path were performed. The results show that the intragranular cracks developed in the shear cracking mode are closely aligned along the activated slip bands in the γ-matrix grains with the crystallographic characteristics of parallel to the γ-{111} slip planes. Multiple slip was also activated, causing the crack retardation or deflection. Low-angle grain boundaries and subgrain boundaries can affect intragranular cracking, while high-angle grain boundaries significantly arrest the short crack propagation. Moreover, the resistance of grain boundaries to short cracking was assessed using combined metrics including the crystallographic parameter of twist angle, the Schmid factor and the geometrical compatibility factor. These site-specific microstructural analyses around the crack path provide insights into the microstructural origins of resistance to the short crack propagation as well as an interpretation of the observed significant fluctuations in the crack propagation rate.
研究了室温下通过激光粉末床熔融(LPBF)制造的镍基超合金 GH4169 中疲劳短裂纹路径的微观结构敏感性及其传播速度。对裂纹路径周围进行了原位数字图像相关(DIC)观察和死后微观结构分析。结果表明,在剪切开裂模式下产生的粒内裂纹沿着γ基质晶粒中被激活的滑移带紧密排列,其晶体学特征是平行于γ-{111}滑移面。多重滑移也被激活,导致裂纹延缓或偏转。低角度晶界和亚晶界会影响晶内开裂,而高角度晶界则会显著阻止短裂纹的扩展。此外,晶界对短裂纹的阻力是通过包括扭转角晶体学参数、Schmid 因子和几何相容性因子在内的综合指标来评估的。这些围绕裂纹路径的特定部位微观结构分析有助于深入了解短裂纹扩展阻力的微观结构起源,并解释所观察到的裂纹扩展速率的显著波动。
Experimental and analytical studies on a novel double-stage coupling damper
Sun Tongfei, Liu Ye, Dai Kaoshan, Camara Alfredo, Lu Yujie, Wang Lijie
doi:10.1016/j.tws.2023.111324
新型双级耦合阻尼器的实验和分析研究
A series of experimental and numerical studies on the novel double-stage coupling damper (DSCD) are presented in this paper. The effects of the damper configuration, friction-yield ratio (Rfy), and loading protocol on the hysteresis performance of the DSCD are investigated via quasi-static tests on seven specimens, and the variation in the failure mode, compression-strength adjustment factor, energy dissipation capacity, and equivalent viscous damping ratio of the DSCD is discussed. The test results demonstrate that the arrangement of ribs in the DSCD increased the average energy dissipation per loading cycle, compared to the device without these elements. The damper exhibits double-stage energy dissipation characteristics for several friction-yield ratios, however, relatively low values of this parameter (Rfy =0.5) leads to reduced energy dissipation capacity, due to significant variations in the friction force associated with creep, ploughing, and preload effect. Furthermore, a detailed finite element model of the DSCD is conducted based on the experimental data, focusing on exploring the effectiveness of the device. Numerical analysis revealed that the cumulative energy dissipation and peak force of the DSCD reduced with increasing the length of the friction mechanism (Lf). A large clearance between the yield segment and the restraining system (Cb) reduces the stability of the equivalent viscous damping ratio of the damper under compression, but Cb has no effect in the cumulation energy dissipation of the damper, which has important implications in the design of these devices for the seismic control of structures. Based on these results design recommendations for the DSCD are provided.
本文对新型双级耦合阻尼器(DSCD)进行了一系列实验和数值研究。通过对七个试样进行准静态试验,研究了阻尼器配置、摩擦屈服比(Rfy)和加载协议对 DSCD 滞后性能的影响,并讨论了 DSCD 失效模式、压缩强度调整系数、耗能能力和等效粘性阻尼比的变化。试验结果表明,与没有这些元件的装置相比,DSCD 中肋条的布置增加了每个加载周期的平均耗能。阻尼器在多个摩擦屈服比下表现出双级消能特性,然而,由于蠕变、犁地和预载效应导致摩擦力发生显著变化,该参数值相对较低(Rfy =0.5),导致消能能力降低。此外,还根据实验数据对 DSCD 进行了详细的有限元建模,重点探讨了该装置的有效性。数值分析表明,随着摩擦机构长度(Lf)的增加,DSCD 的累积能量耗散和峰值力减小。屈服段与约束系统之间的较大间隙(Cb)会降低阻尼器在压缩下的等效粘滞阻尼比的稳定性,但 Cb 对阻尼器的累积耗能没有影响,这对设计这些用于结构抗震控制的装置具有重要意义。基于这些结果,我们提出了 DSCD 的设计建议。
Improvement of Ni-CFRP Interfacial Properties using Compound Coupling Agent Treatment
Chen Yizhe, Xiang Wenfeng, Zhang Qingsong, Wang Hui, Hua Lin
doi:10.1016/j.tws.2023.111334
使用复合偶联剂处理改善 Ni-CFRP 的界面性能
When nickel and carbon fiber-reinforced plastics (CFRP) are combined, poor surface wettability of nickel makes it difficult to obtain ideal interfacial properties, which limits its extensive application in the aerospace field. In this paper, the surface of the nickel plate was modified by sandblasting, coupling agent treatment, and compound coupling agent treatment, the results showed that the bonding strength of CFRP/Ni joints was increased by 19.6%, 30.2%, and 49.7%, respectively, compared with the untreated joint. From the aspects of microstructure, surface wetting, and chemical bonding, the mechanism of strengthening nickel and CFRP bonding with the above surface modification methods were researched. Sandblasting treatment could form irregular pits on the surface of the nickel plate. These irregular pits effectively improved the surface roughness of nickel plate, but had little effect on the surface wettability. Coupling agent treatment has little effect on the surface roughness of the nickel plate, but greatly improvement on wettability with grafting the coupling agent molecule. Compound coupling agent treatment introduces -OH and -NH2 groups through plasma treatment to improve the grafting rate of coupling agent molecules on the surface of the nickel plate, achieving the purpose of strengthening the bonding of CFRP/Ni. This research is expected to provide research ideas for the connection of Ni and CFRP and other heterogeneous materials.
镍与碳纤维增强塑料(CFRP)结合时,镍的表面润湿性较差,难以获得理想的界面性能,限制了其在航空航天领域的广泛应用。本文通过喷砂、偶联剂处理和复合偶联剂处理对镍板表面进行了改性,结果表明,与未处理的接头相比,CFRP/镍接头的粘接强度分别提高了 19.6%、30.2% 和 49.7%。从微观结构、表面润湿和化学键合等方面,研究了上述表面改性方法强化镍与 CFRP 键合的机理。喷砂处理可在镍板表面形成不规则凹坑。这些不规则凹坑有效改善了镍板的表面粗糙度,但对表面润湿性影响不大。偶联剂处理对镍板的表面粗糙度影响不大,但接枝偶联剂分子后,润湿性会大大改善。复合偶联剂处理通过等离子处理引入 -OH 和 -NH2 基团,提高偶联剂分子在镍板表面的接枝率,达到增强 CFRP/Ni 粘接的目的。该研究有望为镍与 CFRP 及其他异质材料的连接提供研究思路。