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 5 篇
Journal of the Mechanics and Physics of Solids
Quantized plastic deformation
N. Perchikov, L. Truskinovsky
doi:10.1016/j.jmps.2024.105704
量子化塑性变形
In engineering crystal plasticity inelastic mechanisms correspond to tensorial zero-energy valleys in the space of macroscopic strains. The flat nature of such valleys is in contradiction with the fact that plastic slips, mimicking lattice-invariant shears, are inherently discrete. A reconciliation has recently been achieved in the mesoscopic tensorial model (MTM) of crystal plasticity, which introduces periodically modulated energy valleys while also capturing in a geometrically exact way the crystallographically-specific aspects of plastic slips. In this paper, we extend the MTM framework, which in its original form had the appearance of a discretized nonlinear elasticity theory, by explicitly introducing the concept of plastic deformation. The ensuing model contains a novel matrix-valued spin variable, representing the quantized plastic distortion, whose rate-independent evolution can be described by a discrete (quasi-)automaton. The proposed reformulation of the MTM leads to a considerable computational speedup associated with the use of a robust and efficient hybrid Gauss–Newton–Cauchy energy minimization algorithm. To illustrate the effectiveness of the new approach, we present a detailed case-study focusing on the aspects of crystal plasticity that are beyond reach for the classical continuum theory. Thus, we provide compelling evidence that the re-formulated MTM is fully adequate to deal with the intermittency of plastic response under quasi-static loading. In particular, our numerical experiments show that the statistics of dislocational avalanches, associated with plastic yield in 2D square crystals, exhibits a power-law tail with a critical exponent matching the value predicted by general theoretical considerations and also independently observed in discrete-dislocation-dynamics (DDD) simulations.
The creep behaviors of laser powder bed fusion (LPBF) additively manufactured (AM) 316L stainless steel (SS) and its recrystallized (Re) counterpart were investigated via uniaxial constant-load creep tests at 600 °C with nominal stress levels ranging from 235 to 360 MPa. Anisotropic creep behavior was observed in AM 316L SS, with superior creep resistance but inferior creep ductility in the horizontal sample (loaded perpendicular to the build direction (BD)) compared to the vertical sample (loaded parallel to the BD). This superior creep resistance was likely resulted from shorter dislocation slip distance and the inferior creep ductility was due to faster propagation of cracks along the columnar grain boundaries. Compared with both the Re counterpart and conventional 316L SS, AM 316L SS in this study exhibited an extraordinary creep resistance at various stress levels, with the minimum creep rate being two to three orders of magnitude lower and much longer creep life. This exceptional creep resistance of AM 316L SS was attributed to the presence of dislocation cells that impeded the deformation-induced dislocations. This led to a remarkably low rate of creep deformation and delayed the creep crack initiation, ultimately resulting in a long creep life. The gradual development of the precipitate films enriched with Mo, Si and Cr along high-angle grain boundaries, following prolonged exposure to high temperatures, was found to restrict the creep ductility in AM 316L under low stress conditions. Nevertheless, the study demonstrates that the stable dislocation cells are beneficial in enhancing the high-temperature creep resistance of AM 316L SS.
Structural characteristics of irrational Type-II Twin interfaces
Ahmed Sameer Khan Mohammed, Huseyin Sehitoglu
doi:10.1016/j.ijplas.2024.104016
不合理ii型孪晶界面的结构特征
The Type-II Twin Boundary (TB) is a critical interface in functional materials whose irrational Miller-index identity has recently drawn significant research interest. This study establishes general structural characteristics of the Type-II twin interface, utilizing TBs in Shape Memory Alloys (SMAs) - TiPd, TiPt, and AuCd - as study targets. It is shown how the irrational identity of each TB is explained by the Terrace-Disconnection (T-D) structural topology. It is proposed that the terrace is the rational-plane nearest to the irrational TB in the reciprocal space, having integral Miller-indices of least magnitude. Crystallographic-registry on this terrace requires non-trivial coherence-strains. A novel kinematic-origin of the coherence-strain is proposed, coming directly from a transformation of the classical twinning deformation-gradient. This transformation revealed that the classical twinning-shear partitions into the coherence-strain and a new metric termed the “terrace-shear”. It is shown that the magnitude of shear relating the twin-structure to the matrix is the terrace-shear and not the twinning-shear, contrary to classical understanding. Furthermore, the Burgers vector of the twinning disconnection is shown to be related directly to the terrace-shear. The energy of each Type-II interface is determined from ab initio Density Functional Theory (DFT) calculations. It is shown that the energy-minimal atomic-structure on the terrace requires determination of a “lattice-offset” that is non-trivial and unknown apriori. In summary, this study expounds on T-D topological structure of Type-II twin interfaces, establishing methods to identify rational terraces, coherence strains, ab initio planar TB energies and revealing a unique partitioning of the twinning-shear exhibited by this class of interfaces.
Critical Size and Internal Force Analysis of Tendril-inspired Spontaneous Helicalization Mechanism
Zeyi Zhang, Changguo Wang
doi:10.1016/j.tws.2024.112036
卷须自发螺旋化机构的临界尺寸及内力分析
Tendrils initially exhibit straight morphologies before gradually transforming into helical conformations during longitudinal growth. Tendril-inspired helical structures possess advantageous physical properties and functions including versatile morphologies, adaptability, enhanced strength, and scalability. With advancements in nanoscience and nanotechnology, helical architectures across various length scales have been discovered or artificially synthesized. However, the fundamental mechanisms underlying the formation and evolution of helical structures remain elusive. This lack of mechanistic insight has impeded the controlled design and fabrication of helical structures, especially three-dimensional functional devices with integrated helical motifs. Here a mechanical model is systematically proposed for the spontaneous formation of the helical structures, based on the hypothesis of decoupled curling and warping phases. Applying nonlinear elasticity theory, a detailed analysis of the energetics and thermodynamics is presented, accounting for the large deformation that may emerge during planar curling. Additionally, differential relations between internal forces and associated displacements induced by bending and twisting of a slender curved beam under out-of-plane loading are derived, obtaining solutions via Laplace and inverse transforms. The theoretical solutions closely match ex- perimental evidence from shape memory polymers. Furthermore, the theoretical model is utilized to guide the fabrication of the smart helical antenna proposed in our previous work, and discuss the influence of configuration changes on the electromagnetic properties. Elucidating these fundamental mechanisms will facilitate the development of next-generation technologies exploiting helical architectures for diverse applications including flexible electronics, optics, and soft robotics.
Effects of differential hardening on energy absorption prediction of AA6061-T6 thin-walled rectangular tube
Songchen Wang, Hongchun Shang, Can Zhou, Miao Han, Yanshan Lou
doi:10.1016/j.tws.2024.112050
差异硬化对AA6061-T6薄壁矩形管能量吸收预测的影响
In this study, the energy absorption characteristics and deformation modes of AA6061-T6 thin-walled rectangular tube are investigated experimentally and numerically under different crushing conditions, including axial crushing, three-point bending and oblique crushing. Mechanical tests are carried out on four specimens of uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions for AA6061-T6. Besides, the effect of differential hardening behavior on the energy absorption prediction of AA6061-T6 rectangular tubes is illustrated by comparing Lou2022, von Mises and SY2009 functions. The mechanical experiment results indicate that AA6061-T6 shows obvious anisotropy, differential hardening behavior and tension-compression asymmetry, and its plastic evolution is accurately characterized by the Lou2022 model. The axial crushing properties show that the AA6061-T6 thin-walled rectangular tube undergoes the progressive symmetrical folding deformation mode. The introduction of geometric discontinuity can obviously reduce the peak force and improve the crashworthiness performances under the axial load. The main crushing mode is bending with a small amount of indentation for three-point bending. Moreover, the three-point bending simulation shows that the Lou2022 function considering differential hardening behavior has the highest simulation accuracy. Three different oblique crushing simulations of 10°, 20° and 30° illustrate that the AA6061-T6 rectangular tube at 10° mainly occurs progressive folding deformation. while the other two oblique crushing angles undergo global buckling deformation. The total energy absorption at 10° is 1.87 and 2.43 times of that at 20° and 30°, respectively. The crushing force efficiency of 20° and 30° is 41.28% and 31.8% lower than that of 10°, respectively. A comprehensive understanding of the energy absorption performance of AA6061-T6 thin-walled rectangular tube under different crushing conditions is helpful to determine its position and shape as a vehicle safety structure, and to exert its optimal plastic deformation potential to dissipate the collision energy and ensure passenger safety.
Optimizing dimension selection for rain flow counting in fatigue assessment of large-scale lattice wind turbine support structures: a comprehensive study and design guidance
Chuannan Xiong, Kaoshan Dai, Yuxiao Luo, Jianze Wang
doi:10.1016/j.tws.2024.112051
大型格子式风力机支撑结构疲劳评估中雨流计数尺寸优化选择:综合研究与设计指导
The selection of dimension (d) for the rain flow counting matrix significantly influences the reliable prediction of fatigue life in wind turbine support structures. However, there are limited public reports on the impact of dimensions on the fatigue assessment of wind turbine structures. This study explores the influence of dimensions on the fatigue assessment process and outcomes, focusing on a large-scale ultra-high lattice wind turbine support structure from an engineering project. Through integrated load simulation, fatigue load time series for different design load cases (DLCs) are obtained for the overall structure. The rain flow counting method is utilized to derive the overall rain flow counting matrix (Markov_n) with varying dimensions. Subsequently, employing a multi-scale fatigue assessment method, the damage matrix (Markov_D), cumulative fatigue damage (D), and fatigue life are computed. A detailed exploration examines the impact of rain flow counting matrix dimensions on Markov_n, Markov_D, D, fatigue life, and calculation time (t). Furthermore, guidance is provided for selecting the optimal dimension for engineering design. The findings indicate that selecting dimensions that are too small results in the loss and merging of smaller mean and amplitude load values, thereby failing to accurately represent the load history. Moreover, a small dimension yields an excessively cautious estimation of cumulative fatigue damage (D) and underestimates the fatigue life, consequently inflating construction expenses.
Studies on post-global flexural–torsional buckling strength and global-global interaction between flexural–torsional and flexural buckling modes in cold-formed steel equal-lipped angle columns have been reported in the literature. Similar global-global interaction involving the first two modes of flexural–torsional buckling in unequal-lipped angles has not yet been explored. In this study, a total of 11 cold-formed unequal lipped angle specimens having two different ranges of ratios of elastic flexural–torsional buckling loads (Pcrft2/Pcrft1 < 3, and Pcrft2/Pcrft1 > 24), indicating high and low interaction of flexural–torsional buckling modes, were tested under axial compression. Additionally, test results from the literature for specimens having 5 < Pcrft2/Pcrft1 < 9 are also used. This is the first study reported in the literature that demonstrates interaction of flexural–torsional modes in cold-formed unequal lipped angle members. All possible interaction between different buckling modes is then systematically studied using the ultimate strength database generated using nonlinear finite element analysis. An interaction equation is proposed based on 36 experimental and 719 numerical data.
In the past few decades, the development of aircraft engines has targeted high bypass ratios and lightweight construction. The use of lighter and larger fan blades can facilitate the technical requirements of engine weight reduction with an increased bypass ratio, achieving improved engine operating efficiency and performance. The current literature has established that resin matrix composite fan blades (RMCFBs), as an alternative to traditional lightweight metal fan blades, exhibit high energy absorption efficiency and a stable response curve. This review assesses the latest research progress in the development and application of RMCFBs for aircraft engines. Firstly, the characteristics of different manufacturing processes are established with a classification of RMCFBs. Current application status of RMCFBs is discussed, evaluating the progress that has been made in specific systems. The pertinent experimental tests and numerical simulations applied to mechanical performance of RMCFBs at different levels are reviewed in detail, taking account of the defects in RMCFBs with consideration of non-destructive testing and the on-line monitoring technologies that have been employed. Finally, the current key research issues are identified, and future directions are proposed. This review can serve as a valuable reference that establishes current state-of-the-art in the design and development of RMCFBs for aircraft engine.