今日更新：Journal of the Mechanics and Physics of Solids 2 篇，Mechanics of Materials 1 篇，International Journal of Plasticity 1 篇，Thin-Walled Structures 1 篇
Journal of the Mechanics and Physics of Solids
Combined influence of shallowness and geometric imperfection on the buckling of clamped spherical shells
Kanghyun Ki, Jeongrak Lee, Anna Lee
doi:10.1016/j.jmps.2024.105554
浅度和几何缺陷对夹紧球壳屈曲的综合影响
We investigate the combined influence of shallowness and geometric imperfection on the pressure-induced buckling behavior of clamped spherical shells. The buckling phenomenon in spherical shells has gained significant interest in diverse fields, such as soft robotics and biomechanics, due to its distinct and drastic shape morphing characteristics. However, a notable discrepancy between analytic solutions and experimental results persists, necessitating further research to comprehend the buckling behavior of spherical shells with varying shallowness and geometric imperfection. To address this gap, we experimentally investigate the buckling of clamped spherical shells under uniform pressure while controlling the shell shallowness over a wide range. The experimental results validate finite element simulations, enabling analysis of the variation in buckling pressure and behaviors by manipulating the shell shallowness and geometric imperfection. Our analysis reveals decaying oscillatory variations in the buckling strength versus the shallowness curves, eventually converging to stable buckling strength for sufficiently deep shells. Moreover, these curves exhibit changes in level and shape with varying geometric imperfection. We also observe non-axisymmetric buckling modes in shells with small geometric imperfection and specific shallowness ranges. Through parametric studies, we identify the geometric conditions influencing the buckling behavior, particularly the non-snap-through criteria and non-axisymmetric buckling modes. This comprehensive investigation sheds light on the interplay between shallowness and geometric imperfection affecting the buckling behavior of clamped spherical shells. The findings contribute to a deeper understanding of shell buckling phenomena and have implications for various shell design applications.
A machine learning perspective on the inverse indentation problem: uniqueness, surrogate modeling, and learning elasto-plastic properties from pile-up
Quan Jiao, Yongchao Chen, Jong-hyoung Kim, Chang-Fu Han, Chia-Hua Chang, Joost J. Vlassak
doi:10.1016/j.jmps.2024.105557
反缩进问题的机器学习视角:唯一性、代理模型和从堆积中学习弹塑性特性
The inverse analysis of indentation curves, aimed at extracting the stress-strain curve of a material, has been under intense development for decades, with progress relying mainly on the use of analytical expressions derived from small data sets. Here, we take a fresh, data-driven perspective to this classic problem, leveraging machine learning techniques to advance indentation technology. Using a neural network (NN), we efficiently assess uniqueness and identify materials that have indistinguishable indentation responses without the need for complex, domain knowledge-based algorithms. We then demonstrate that inclusion of the residual imprint information resolves the non-uniqueness problem. We show that the elasto-plastic properties of a material can be learned directly from indentation pile-up. Notably, an accurate stress-strain curve can be derived using solely the applied indentation load and pile-up information, thereby eliminating the need for depth-sensing. We also present a systematic analysis of the machine learning model, covering important aspects such as prediction performance, sensitivity, feature selection, and permutation importance, providing insight for model development and evaluation. This study introduces and provides the groundwork of a machine-learning-based profilometry-informed indentation inversion (PI3) technique. It showcases the potential of machine learning as a transformative alternative when analytical solutions are difficult or impossible to obtain.
On the flat punch hole expansion test of sheet metals: Mechanics of deformation and evaluation of anisotropic plasticity models
A. Abedini, A. Narayanan, C. Butcher
doi:10.1016/j.mechmat.2024.104931
板料平冲孔膨胀试验:变形力学及各向异性塑性模型的评价
The conventional approach to calibrating anisotropic yield functions relies upon uniaxial and biaxial tension data. Consequently, the stress state in which plane strain conditions arise is allowed to occur anywhere between uniaxial and equal-biaxial states despite growing experimental evidence suggesting that it is close to the theoretical stress state predicted by pressure-independent plasticity for steel and aluminum alloys. The objective of the study was to investigate the role of the plane strain stress state on yield surface calibration and its influence upon the mechanics of the flat punch hole expansion test. First, a parametric study was performed to determine how the plane strain stress state affects the predicted strain field in flat punch hole expansion simulations of an AA6022-T4 sheet. It is shown that the flat punch hole expansion deformation can be described as being under stress-controlled boundary conditions. The predicted location behind the hole edge where zero minor strain occurs was observed to be directly related to the yield function calibration and its accuracy evaluated from optical strain measurements. It was shown that the thinning strain distributions away from the edge could be well predicted by coupling the major strain gradient near the hole edge (geometry effect) with the normal vectors of the yield function from uniaxial-to-plane strain tension (yield function effect). The resulting best practices for plasticity characterization were then applied to a 3rd Gen 1180 steel. The global and local responses of the 3rd Gen 1180 flat punch hole expansion tests were accurately predicted by simulations using calibrations of the Yld2000 and Yld2004 anisotropic yield functions that enforced the plane strain constraint.
Characterization and unified modelling of creep and viscoplasticity deformation of titanium alloy at elevated temperature
Yong Li, Haosheng Chen, Lihua Du, Feng Yang, Ying Zhang, Dongsheng Li
doi:10.1016/j.ijplas.2024.103892
钛合金高温蠕变与粘塑性变形表征及统一建模
A unified model to characterize the mechanism transitions in a wide range of strain rates at elevated temperatures of titanium alloys has been developed and validated in this study. Models of microstructure-based backstress and strain rate dependent stress sensitivity covering both creep and viscoplasticity domains have been proposed, so as to predict different deformation behaviors concurrently for hot forming. Systematical experiments, including hot tensile, creep, stress-relaxation, and corresponding loading-unloading tests have been designed and performed, to get the different deformation behaviors, as well as the evolution of backstresses of titanium alloys at elevated temperatures. Microstructural observations, such as electron backscatter diffraction (EBSD), have also been performed to assist the mechanisms characterization. Based on the microstructural and macro properties results, the developed unified model has been calibrated and further implemented for typical cases of hot stamping - stress-relaxation forming (HS-SRF). The developed model achieved an excellent accuracy for all the tensile, creep, and stress-relaxation behaviors concurrently, with an error of only about 4.9%, and a comparative 71.8% ∼ 90.8% reduction in springback prediction error has been reported for hot forming of typical thin-walled titanium alloy components when compared with the conventional modelling strategy where a single deformation mechanism is considered. The potential of the proposed model for process design and optimizations has also been discussed.
Stainless steel has advantages such as corrosion resistance, durability and aesthetic appearance, with extensive application prospects in the field of construction engineering. In order to investigate the mechanical properties of duplex stainless steel S22053 at elevated temperature and after fire, 58 standard coupons were fabricated, with 4 coupons for tensile tests at ambient temperature, 18 coupons for steady-state tests at elevated temperatures, and 36 coupons for tensile tests after fire. The temperatures were set at 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C and 900 °C, in total of 9 temperature levels. Two cooling methods, water cooling and air cooling, were employed for the postfire coupons. Based on the test results, the expressions of stress-strain relations for duplex stainless steel S22053 under two fire conditions were proposed, and comparisons were made with existing models. The reduction formulas for 6 major mechanical parameters (E0, σ0.05, σ0.2, σ1.0, σ2.0 and σu) of duplex stainless steel S22053 under two fire conditions were obtained through data fitting. Reliability analysis was performed on the mechanical property parameters, and corresponding standard values were proposed.
