今日更新：International Journal of Solids and Structures 2 篇，Journal of the Mechanics and Physics of Solids 3 篇，Mechanics of Materials 1 篇，Thin-Walled Structures 1 篇International Journal of Solids and StructuresInverse identification of plastic anisotropy through multiple non-conventional mechanical experimentsZhang Y., Yamanaka A., Cooreman S., Kuwabara T., Coppieters S.doi:10.1016/j.ijsolstr.2023.112534 通过多个非常规力学实验反向识别塑性各向异性In theory, a single non-conventional mechanical experiment generating inhomogeneous strain fields enables to inversely identify an anisotropic yield function. However, several studies have shown that it is challenging to design such a sufficiently data-rich experiment, particularly when it must be conducted on a standard uniaxial tensile machine. Instead of relying on a single non-conventional uniaxial tensile experiment, combining multiple non-conventional experiments is proposed to inversely identify an advanced anisotropic yield function. The feasibility of the proposed method is verified through the inverse identification of the Yld2000-2d yield function using synthetically generated Digital Image Correlation (DIC) data. This approach accounts for the metrological aspects of DIC while avoiding potential experimental errors and uncertainties related to the selected material model. It has been demonstrated that when a single unconventional tensile test is combined with a non-conventional biaxial tensile test, the inversely identified anisotropy parameters are in good agreement with those found through the conventional method. This finding is contingent on maintaining an equal contribution of the strain states from each experiment to the cost function. Excluding overlapping data points and assigning proper weights to the trustworthy data based on the strain state and the level of plastic deformation is found to be key. The numerical results are experimentally validated, thereby revealing the crucial role of the adopted anisotropic yield function. Furthermore, the uncertainty associated with the inversely identified parameters based on three repetitions of the same experiment is discussed.从理论上讲，产生不均匀应变场的单一非常规机械实验可以反向确定各向异性屈服函数。然而，多项研究表明，设计这样一个数据量足够丰富的实验具有挑战性，尤其是当实验必须在标准单轴拉伸机上进行时。与依赖单一的非常规单轴拉伸实验不同，我们建议结合多个非常规实验来反向识别先进的各向异性屈服函数。通过使用合成生成的数字图像相关（DIC）数据反向识别 Yld2000-2d 屈服函数，验证了所提方法的可行性。这种方法既考虑到了 DIC 的计量方面，又避免了与所选材料模型相关的潜在实验误差和不确定性。结果表明，当单一非常规拉伸试验与非常规双轴拉伸试验相结合时，反向确定的各向异性参数与通过传统方法发现的参数非常一致。这一发现取决于每次试验的应变状态对成本函数的贡献是否相等。排除重叠数据点，并根据应变状态和塑性变形程度为可信数据分配适当权重是关键所在。实验验证了数值结果，从而揭示了所采用的各向异性屈服函数的关键作用。此外，还讨论了基于三次重复相同实验的反向识别参数的不确定性。A Modified Buckling Analysis of Slender Pretwisted BarsRamaswamy Martin, Stolarska Magdalena A., Stolarski Henryk K.doi:10.1016/j.ijsolstr.2023.112537细长预绞杆的修正屈曲分析Some seventy years ago the so-called “helical fiber model” was proposed to address existing discrepancies between experimental observations and theoretical predictions for pretwisted bars. The discrepancies concerned effects the pretwist had on bending and torsional behavior of such bars, but the same model was later used to show that the previously used theory is also likely to provide unconservative (thus unsafe) estimates of their buckling loads. In spite of the theoretical and practical significance of that finding the “helical fiber model” was deemed too approximate, intuitive and, ultimately, it seems to have been abandoned. As far as buckling is concerned, all publications of the last several decades appear to be based on the original theory that was earlier shown to possibly significantly overestimate the buckling load for pretwisted bars. Thus, in this work the problem of pretwisted bars’ buckling is revisited. As most formulations of the problem, the proposed approach is approximate but, as much as possible, it is justified using established principles of mechanics. In particular, two-field Hellinger-Reissner mixed method is used to define axial and bending stiffness of pretwisted bars, with special attention paid to the definition of the stress field. Although the developments presented in this work follow a different path, the main features of the final model are similar to those of the “helical fiber model” introduced much earlier. However, the proposed formulation affords some additional flexibility in the way it may be used. Numerical examples are presented to illustrate effects of the discussed developments.大约七十年前，人们提出了所谓的 "螺旋纤维模型"，以解决预扭曲钢筋的实验观察和理论预测之间存在的差异。这些差异涉及预扭曲对此类钢筋弯曲和扭转行为的影响，但后来人们使用同一模型表明，以前使用的理论也可能对钢筋的屈曲载荷做出了不保守（因而不安全）的估计。尽管这一发现具有理论和实践意义，但 "螺旋纤维模型 "被认为过于近似和直观，最终似乎被放弃了。就屈曲而言，过去几十年的所有出版物似乎都是基于最初的理论，而该理论早先被证明可能大大高估了预扭钢筋的屈曲载荷。因此，本研究重新探讨了预扭曲钢筋的屈曲问题。与大多数问题的表述一样，所提出的方法是近似的，但尽可能使用既定的力学原理来证明其合理性。特别是采用了两场海灵格-赖斯纳混合法来定义预扭曲杆件的轴向和弯曲刚度，并特别关注了应力场的定义。虽然这项工作的发展遵循不同的路径，但最终模型的主要特征与早先引入的 "螺旋纤维模型 "相似。不过，所提出的模型在使用方式上具有一定的灵活性。本文还列举了一些数值示例，以说明所讨论的发展所产生的影响。Journal of the Mechanics and Physics of SolidsNonlinear anisotropic viscoelasticitySadik Souhayl, Yavari Arashdoi:10.1016/j.jmps.2023.105461非线性各向异性粘弹性In this paper, we revisit the mathematical foundations of nonlinear viscoelasticity. We study the underlying geometry of viscoelastic deformations, and in particular, the intermediate configuration. Starting from the direct multiplicative decomposition of the deformation gradient F=FeFv, into elastic and viscous distortions Fe and Fv, respectively, we point out that Fv can be either a material tensor ( Fe is a two-point tensor) or a two-point tensor ( Fe is a spatial tensor). We show that, based on physical grounds, the second choice is unacceptable. It is assumed that the free energy density is the sum of an equilibrium and a non-equilibrium part. The symmetry transformations and their action on the total, elastic, and viscous deformation gradients are carefully discussed. Following a two-potential approach, the governing equations of nonlinear viscoelasticity are derived using the Lagrange-d’Alembert principle. We discuss the constitutive and kinetic equations for compressible and incompressible isotropic, transversely isotropic, orthotropic, and monoclinic viscoelastic solids. We finally semi-analytically study creep and relaxation in three examples of universal deformations.在本文中，我们重温了非线性粘弹性的数学基础。我们研究了粘弹性变形的基本几何，尤其是中间构型。从变形梯度的直接乘法分解开始F=FeFv, 分别分解为弹性变形和粘性变形Fe和Fv 我们指出Fv可以是材料张量（Fe是两点张量）或两点张量（Fe是空间张量）。我们将证明，根据物理原理，第二种选择是不可接受的。假设自由能密度是平衡和非平衡部分之和。我们仔细讨论了对称变换及其对总变形、弹性变形和粘性变形梯度的作用。按照双势垒方法，利用拉格朗日-达朗贝尔原理推导出非线性粘弹性的支配方程。我们讨论了可压缩和不可压缩各向同性、横向各向同性、正交各向同性和单斜粘弹性固体的构成方程和动力学方程。最后，我们对三个普遍变形实例中的蠕变和松弛进行了半分析研究。How does roughness kill adhesion?Afferrante L., Violano G., Dini D.doi:10.1016/j.jmps.2023.105465粗糙度如何破坏附着力？It is well–known that adhesion is strongly influenced by surface roughness. Nevertheless, the literature currently contains an ongoing debate regarding which roughness scales are primarily responsible for adhesion loss. In this study, we aim to contribute to this debate by conducting numerical simulations on self-affine fractal profiles with varying fractal dimensions. Our results reveal that the long-wavelength portion of the roughness spectrum plays a crucial role in killing adhesion when considering profiles with Hurst exponent H > 0 . 5 . Conversely, for profiles with H < 0 . 5 , results show a different trend, indicating that adhesive stickiness is also influenced by short wavelength roughness. These findings are corroborated by our recent experimental observations. In such case, adhesive hysteresis and pull-off force exhibit a continuous decrease with increasing roughness scales. However, for H > 0 . 5 , the pull-off force converges toward a finite value as the magnification increases.众所周知，附着力受表面粗糙度的影响很大。然而，目前文献中仍在争论哪种粗糙度尺度是造成附着力损失的主要原因。在本研究中，我们对具有不同分形尺寸的自凹凸分形轮廓进行了数值模拟，旨在为这一争论做出贡献。我们的结果表明，在考虑赫斯特指数 H > 0 .5 .相反，对于 H < 0 .5 时，结果显示出不同的趋势，表明粘附性也受到短波长粗糙度的影响。我们最近的实验观察也证实了这些发现。在这种情况下，粘滞性和拉拔力随着粗糙度尺度的增加而持续下降。然而，当 H > 0 .5 时，随着放大倍率的增加，拉脱力会趋近于一个有限值。Crystal plasticity modeling for the strengthening effect of multilayered copper-graphene nanocompositesJeong Juyoung, Voyiadjis George Z.doi:10.1016/j.jmps.2023.105468 多层铜石墨烯纳米复合材料强化效应的晶体塑性模型The paper investigates plastic deformation mechanisms in metal-graphene nanocomposite to demonstrate the strengthening effect of materials using a crystal plasticity finite element (CPFE) model, comparing it with published experimental results. Previous experimental research has identified that the two-dimensional shape of graphene, which effectively controls dislocation motion, can significantly enhance the strength of metals. Given the nature of dislocation motions at submicron length scales, nanopillar compression tests were simulated using a physics-based CP model that incorporates surface nucleation and single-arm source dislocation mechanisms. The crystal plasticity models adopt a configuration of nanolayered composites with layers of copper grains and monolayer graphene sandwiched between them, featuring repeat layer spacings of 200 nm, 125 nm, and 70 nm, respectively. This study quantifies the accumulation of dislocations at the graphene interfaces, contributing to the ultra-high strength of the copper-graphene composite. Furthermore, a Hall-Petch-like correlation is established between yield strength and the number of embedded graphene layers.本文研究了金属-石墨烯纳米复合材料的塑性变形机制，利用晶体塑性有限元（CPFE）模型证明了材料的强化效果，并将其与已发表的实验结果进行了比较。以往的实验研究发现，石墨烯的二维形状可有效控制位错运动，从而显著增强金属的强度。鉴于位错运动在亚微米长度尺度上的性质，我们使用基于物理学的 CP 模型模拟了纳米柱压缩试验，该模型包含了表面成核和单臂源位错机制。晶体塑性模型采用了纳米层状复合材料的结构，铜粒层和单层石墨烯夹在铜粒层和单层石墨烯之间，重复层间距分别为 200 nm、125 nm 和 70 nm。这项研究量化了石墨烯界面上位错的积累，这有助于铜石墨烯复合材料的超高强度。此外，在屈服强度和嵌入石墨烯层的数量之间建立了类似霍尔-佩奇的相关性。Mechanics of MaterialsA two-stage approach for material parameters identification in spark plasma sinteringKumar A., Bernet M., Deillon L., Afrasiabi M., Bambach M.doi:10.1016/j.mechmat.2023.104834 火花等离子烧结材料参数识别的两阶段方法A fully coupled electrical-thermo-mechanical model is essential to an in-depth understanding of the spark plasma sintering (SPS) process, where the mechanical modeling is heavily dependent on the constitutive equations and their material parameters. This paper proposes a two-stage approach that integrates direct experimental measurements with numerical simulations, providing a more comprehensive and reliable basis for identifying the material parameters in SPS. We develop a finite element-based fully coupled process model in COMSOL Multiphysics® and validate it experimentally. The parameter identification procedure achieves an average prediction error below 1.5% when applied to copper and nickel SPS at different heating rates from 25 to 100 K/min. This robust numerical-experimental approach establishes a transferable technique that can be used for other materials commonly used in SPS.要深入了解火花等离子烧结（SPS）过程，必须建立一个完全耦合的电气-热力学模型，而力学模型在很大程度上取决于构成方程及其材料参数。本文提出了一种将直接实验测量与数值模拟相结合的两阶段方法，为确定 SPS 中的材料参数提供了更全面、更可靠的依据。我们在 COMSOL Multiphysics® 中开发了基于有限元的全耦合过程模型，并对其进行了实验验证。当应用于铜和镍 SPS 时，在 25 至 100 K/min 的不同加热速率下，参数识别过程的平均预测误差低于 1.5%。这种稳健的数值-实验方法建立了一种可移植的技术，可用于 SPS 中常用的其他材料。Thin-Walled StructuresProtective performance of hybrid triply periodic minimal surface lattice structureZhang Yong, Chen Yangang, Li Jixiang, Wu Jiacheng, Qian Liang, Tan Yuanqiang, Li Kunyuan, Zeng Guoyaodoi:10.1016/j.tws.2023.111288混合三周期最小表面晶格结构的保护性能A hybrid triply periodic minimal surface (TPMS) method is proposed by the implicit mathematical equation to develop a new TPMS structure. Mechanical properties of the basal TPMS structures and the hybrid TPMS structure subjected to axial crushing load are experimentally and numerically investigated. Results show that the specific energy absorption of hybrid additive and subtractive TPMS structures is up to 97.2% and 82.4% enhancement compared to the basal Schwarz Primitive structure, and the Undulation of load-carrying capacity of hybrid additive and subtractive TPMS structure is 60.1% and 33.3% lower than that of the basal Schoen IWP structure. The effect of topological shape and material distribution on mechanical properties of hybrid TPMS structures are further numerically investigated, and structural factor and wall thickness have significant influence on crashworthiness. Furthermore, the crushing behavior of hybrid additive TPMS and square honeycomb subjected to in-plane and out-of-plane impact loads are investigated, and the hybrid additive TPMS structure shows significant crashworthiness advantage in in-plane crushing condition. Furthermore, the multi-objective optimization is carried out to obtain the optimal crushing performance of the hybrid additive TPMS structure. The hybrid design can provide a good guidance for the research on crashworthiness of the TPMS structures.通过隐式数学方程提出了一种混合三周期最小面（TPMS）方法，以开发一种新的 TPMS 结构。实验和数值研究了基底 TPMS 结构和混合 TPMS 结构在轴向挤压载荷作用下的力学性能。结果表明，与基体 Schwarz Primitive 结构相比，混合加法和减法 TPMS 结构的比能量吸收分别提高了 97.2% 和 82.4%，混合加法和减法 TPMS 结构的承载能力 Undulation 比基体 Schoen IWP 结构分别降低了 60.1% 和 33.3%。进一步数值研究了拓扑形状和材料分布对混合 TPMS 结构力学性能的影响，发现结构因子和壁厚对耐撞性有显著影响。此外，还研究了混合添加剂 TPMS 结构和方形蜂窝结构在平面内和平面外冲击载荷作用下的挤压行为，结果表明混合添加剂 TPMS 结构在平面内挤压条件下具有显著的耐撞性优势。此外，还进行了多目标优化，以获得混合添加剂 TPMS 结构的最佳挤压性能。该混合设计可为 TPMS 结构的耐撞性研究提供良好的指导。来源：复合材料力学仿真Composites FEM
