今日更新:Journal of the Mechanics and Physics of Solids 1 篇,International Journal of Plasticity 1 篇,Thin-Walled Structures 3 篇
Twinning in porous elastomers
P.J. Caulfield, P. Ponte Castañeda
doi:10.1016/j.jmps.2024.105896
多孔弹性体中的孪生
It has been known for some time that constitutive models for the large-deformation response of porous elastomers can develop ‘macroscopic’ instabilities as a consequence of loss of strong ellipticity. Indeed, constitutive models obtained by homogenization methods for porous elastomers with periodic and random microstructures can lose strong ellipticity under appropriate loading conditions. For periodic microstructures, it has been shown theoretically, and verified experimentally and numerically, that ‘microscopic’ instabilities consisting in solutions that are periodic on ensembles of unit cells tend to occur before the long-wavelength ‘macroscopic’ instabilities that are captured by the loss of strong ellipticity of the homogenized response. But what about the response of porous elastomers with random microstructures? In this case, microscopic instabilities can be excluded, and the question then arises as to what happens after the onset of a macroscopic instability. Building on earlier work for reinforced elastomers, it is shown here that porous elastomers can undergo twinning after the onset of a macroscopic instability. For this purpose, use is made of a generalized Maxwell-type construction arising from the theory of relaxation and applied to linear comparison variational homogenization estimates for a certain class of two-dimensional porous elastomers consisting of aligned cylindrical pores in a rubber matrix subjected to plane strain loadings. It is shown that such porous elastomers recover Legendre-Hadamard stability by twinning after the onset of a macroscopic instability. Interestingly, the porous elastomers behave like elastic fluids in the twinned region, losing their ability to support shear stresses.
一段时间以来,人们已经知道多孔弹性体大变形响应的本构模型会由于失去强椭圆性而产生“宏观”不稳定性。事实上,均匀化方法得到的具有周期性和随机微观结构的多孔弹性体的本构模型在适当的加载条件下会失去强椭圆性。对于周期性微结构,理论已经证明,实验和数值验证了,在单位细胞的周期性集 合的溶液中组成的“微观”不稳定性往往发生在长波长的“宏观”不稳定性之前,这种不稳定性是由均匀化响应的强椭圆性损失捕获的。但是具有随机微观结构的多孔弹性体的响应如何呢?在这种情况下,微观的不稳定性可以被排除在外,然后问题就出现了,在宏观的不稳定性开始之后会发生什么。基于早期对增强弹性体的研究,本文表明多孔弹性体在宏观不稳定发生后可以发生孪生。为此,使用了由松弛理论产生的广义麦克斯韦型构造,并将其应用于某一类二维多孔弹性体的线性比较变分均匀化估计,这些弹性体由橡胶基体中排列的圆柱形孔隙组成,承受平面应变载荷。结果表明,这种多孔弹性体在宏观失稳发生后通过孪晶恢复了勒让德-阿达玛稳定性。有趣的是,多孔弹性体在孪晶区域表现得像弹性流体,失去了支持剪切应力的能力。
Modified crystal plasticity constitutive model considering tensorial properties of microstructural evolution and creep life prediction model for Ni-based single crystal superalloy with film cooling hole
Ping Wang, Zhixun Wen, Meng Li, Guangxian Lu, Hao Cheng, Pengfei He, Zhufeng Yue
doi:10.1016/j.ijplas.2024.104150
考虑微观组织演化张拉性能的改进晶体塑性本构模型及含膜冷却孔镍基单晶高温合金蠕变寿命预测模型
Accurate assessment of the creep life of film cooling hole structures is critical for long-life design and safe operation of aero engines and gas turbines. Firstly, through the high temperature creep experiment of nickel-based single crystal superalloy with film cooling hole, the microstructure evolution process under multiaxial stress state around film hole is characterized. Then, considering the directional effect of rafting structure and the influence of multiaxial stress, a fourth-order tensor is used to describe the evolution of γ phase width, and the microstructure evolution model accounting for multi-axial stress states is established. The microstructure evolution is coupled into the crystal plasticity constitutive model by Orowan stress. Meanwhile, based on continuous damage mechanics, a new multiaxial damage evolution law is established by introducing a multiaxial ductility factor into the constitutive model. The improved crystal plasticity constitutive model can effectively predict the microstructural evolution under multiaxial stress conditions. Furthermore, the combination of the modified crystal plasticity constitutive model and the critical distance method considering stress gradients is used for life prediction of film cooling hole structures. The prediction results show the effectiveness and necessity of considering the microstructure evolution in the life prediction.
准确评估气膜冷却孔结构的蠕变寿命对航空发动机和燃气轮机的长寿命设计和安全运行至关重要。首先,通过带膜状冷却孔的镍基单晶高温合金的高温蠕变实验,表征了膜状冷却孔周围多轴应力状态下的组织演变过程。然后,考虑漂流结构的定向效应和多轴应力的影响,采用四阶张量描述γ相宽度的演化,建立了考虑多轴应力状态的微观结构演化模型。显微组织演化通过Orowan应力耦合到晶体塑性本构模型中。同时,基于连续损伤力学,在本构模型中引入多轴延性因子,建立了新的多轴损伤演化规律。改进的晶体塑性本构模型可以有效预测多轴应力条件下的微观组织演变。将改进的晶体塑性本构模型与考虑应力梯度的临界距离法相结合,用于膜状冷却孔结构的寿命预测。预测结果表明,在寿命预测中考虑组织演变的有效性和必要性。
The bending of 3D-printed Bio-inspired sandwich panels with wavy cylinder cores
Xindi Yu, Qicheng Zhang, Rodrigo J da Silva, Tulio Halak Panzera, Mark Schenk, Fabrizio Scarpa
doi:10.1016/j.tws.2024.112538
弯曲的3d打印仿生夹心板与波浪圆柱芯
Beetle Elytron Plates (BEPs) represent a new class of biomimetic sandwich cores with excellent mechanical properties inspired by the microstructure of the beetle elytra. The cores have a hexagonal centre-symmetric configuration with through-thickness cylinders in the unit cell. In this work, we describe the behaviour of sandwich panels with novel BEP core configurations possessing wavy cylinders under four-point bending tests. Full-scale simulations are also carried out to validate the experimental data. The results show that all the sandwich panels produced with face skins adhesively bonded have material failure earlier than the adhesive bond failure. BEPs with wavy cylinders have larger peak loads compared to those with straight cylinders, and all BEPs show higher peak loads than those of sandwich panels with classical hexagonal honeycombs. Additionally, all the BEPs exhibit an enhanced ductility compared to honeycomb sandwich panels.
甲虫鞘翅片(BEPs)是一种新型仿生三明治芯,具有优异的机械性能,灵感来自甲虫鞘翅的微观结构。芯具有六角形的中心对称结构,在单元胞中具有贯穿厚度的圆柱体。在这项工作中,我们描述了具有波浪圆柱体的新型BEP芯结构的夹层板在四点弯曲试验中的行为。为了验证实验数据,还进行了全尺寸仿真。结果表明:面皮粘接生产的夹层板材料破坏均早于胶合破坏;波浪柱面夹层板的峰值载荷比直柱面夹层板的峰值载荷要大,且所有夹层板的峰值载荷都高于经典六边形蜂窝夹层板。此外,与蜂窝夹层板相比,所有bep都具有增强的延展性。
An improved modal tracking algorithm for dispersion analysis of arbitrary prestressed plates
Xu Zhang, Lei Chen, Gang Liu, Zehui Zhang, Jiacheng Wang
doi:10.1016/j.tws.2024.112582
一种用于任意预应力板频散分析的改进模态跟踪算法
Determining the dispersion characteristics of prestressed plates is essential for guided wave-based structural health monitoring, which can provide theoretical guidance for optimizing excitation mode and frequency. However, the multi-mode nature of guided waves brings huge challenges for modal tracking. Conventional methods require sufficiently small frequency steps and may encounter tracking errors during mode crossing and overlap. To address these issues, this paper established a multi-step superposition model to obtain the dispersion relation of arbitrary prestressed plates and proposed a novel modal tracking method based on structural similarity (SSIM) image registration for identifying all guided wave modes. Drawing inspiration from the image quality assessment technique, a novel index was introduced to evaluate the consistency between modal eigenvectors quantitatively. Furthermore, an improved algorithm using eigenvector operations was developed to further enhance the efficiency and applicability of the modal tracking process. Subsequently, application examples were conducted to thoroughly evaluate the performance of the proposed methods through comparison with conventional modal tracking methods. The results indicated that the proposed methods have accurate and reliable tracking performance even with larger wavenumber steps, which is unattainable with conventional methods. Notably, the computational efficiency of the improved algorithm is nearly 13 times faster than the SSIM-based image registration method. Finally, an investigation into the dispersion characteristics of aluminum plates under tensile, bending, and shear stress demonstrated the versatility of the improved modal tracking algorithm. This study provides valuable insights into the dispersion behavior of guided waves in prestressed plates.
确定预应力板的频散特性是基于导波的结构健康监测的基础,可以为优化激励方式和频率提供理论指导。然而,导波的多模态特性给模态跟踪带来了巨大的挑战。传统的方法需要足够小的频率步长,并且可能在模式交叉和重叠时遇到跟踪误差。针对这些问题,本文建立了多步叠加模型来获取任意预应力板的频散关系,并提出了一种基于结构相似度(SSIM)图像配准的新型模态跟踪方法来识别所有导波模态。受图像质量评价技术的启发,引入了一种新的模态特征向量一致性定量评价指标。在此基础上,提出了一种基于特征向量运算的改进算法,进一步提高了模态跟踪的效率和适用性。最后,通过与传统模态跟踪方法的对比,对所提方法的性能进行了全面评价。结果表明,该方法在较大的波数步长下仍具有传统方法无法达到的准确可靠的跟踪性能。值得注意的是,改进算法的计算效率比基于ssim的图像配准方法快了近13倍。最后,对铝板在拉伸、弯曲和剪切应力作用下的色散特性进行了研究,证明了改进模态跟踪算法的通用性。本研究对预应力板中导波的频散特性提供了有价值的见解。
Analytical and numerical predictions of elastoplastic buckling behaviors of the subsea lined pipelines with ovality defects under hydrostatic pressure
Qian Zhang, Denglian Yang, Meiling Shen, Zhaochao Li
doi:10.1016/j.tws.2024.112584
静水压力下含椭圆形缺陷海底衬管弹塑性屈曲行为的分析与数值预测
The subsea pipelines may deteriorate and/or be cracked after a long period of service. A cost-effective trenchless rehabilitation technology is to install a thin-walled steel liner inside the pipelines. However, elliptical defects may occur in the liner due to issues such as insufficient inflation, deformation of the host pipelines, and joint misalignment in practical engineering. Thus, this study aims to develop a systematic analytical model and numerical model for the elastic and inelastic buckling behaviors of the thin-walled oval steel liner, respectively. An admissible radial displacement function is introduced to describe the single-lobe deformation of the liner. The governing equations are established to trace the equilibrium paths by applying the theory of thin-walled shells and the principle of minimum potential energy. A two-dimensional finite element model is developed for the elastic and inelastic buckling performance of the liner. The analytical solutions of elastic buckling are in good agreement with other closed-form solutions, numerical results, and respective test results available in the literature. Finally, parametric evaluations are carried out in terms of ovality, non-uniform liner-pipeline gap, internal pressure, and liner yield strength.
海底管道在长期使用后可能会恶化和/或破裂。一种具有成本效益的非开挖修复技术是在管道内安装薄壁钢衬垫。但在实际工程中,由于膨胀不足、主管道变形、接头不对中等原因,可能导致衬管出现椭圆缺陷。因此,本研究旨在分别建立薄壁椭圆形钢衬垫弹性屈曲和非弹性屈曲行为的系统解析模型和数值模型。引入容许径向位移函数来描述衬板的单瓣变形。应用薄壁壳理论和最小势能原理,建立了跟踪平衡路径的控制方程。建立了衬垫弹性屈曲和非弹性屈曲的二维有限元模型。弹性屈曲的解析解与文献中其他闭型解、数值结果和相应的试验结果吻合较好。最后,从椭圆度、非均匀衬管间隙、内压和衬管屈服强度等方面进行参数评价。