Adaptive remeshing for ductile fracture prediction in metal formingRemaillage adaptatif pour la prévision de la rupture ductile en mise en forme

The analysis of mechanical structures using the Finite Element Method in the framework of large elastoplastic strain, needs frequent remeshing of the deformed domain during computation. Indeed, the remeshing is due to the large geometrical distortion of finite elements and the adaptation to the physical behavior of the solution. This paper gives the necessary steps to remesh a mechanical structure during large elastoplastic deformations with damage. An important part of this process is constituted by geometrical and physical error estimates. The proposed method is integrated in a computational environment using the ABAQUS/Explicit solver and the BL2D-V2 adaptive mesher. To cite this article: H. Borouchaki et al., C. R. Mecanique 330 (2002) 709–716.     

Discrete element simulation of effects of multicontact loading on single particle crushing

Particle crushing commonly occurs in granular materials and affects their structures and mechanical properties. Unlike idealized particles in experimental single particle crushing tests with two loading points, natural particles are crushed under multicontact loading. To date, the criteria and patterns of particle crushing under multicontact conditions are not fully understood. By using the three-dimensional discrete element method, this report explores the effect of multicontact loading on the crushing criterion of a single particle, the crushing pattern, and the relationship between the particle crushing strength and loading distribution. The particles are modelled as aggregates of glued Voronoi polyhedra. The numerical results indicate that the logarithm of the mean principal stress has a good linear correlation with the coordination number. For a specific coordination number, the number of child particles presents a significant normal distribution. For a specific number of child particles, the volumes of child particles can be statistically described as normal or gamma distribution. Three typical models are proposed to qualitatively analyse the relationship between the loading distribution and crushing strength. The relevant conclusions can be helpful in engineering practice and in further studies on crushable granular materials via the discrete element method.     

泡沫铝夹芯双圆管结构的准静态轴向压缩性能研究

对泡沫铝夹芯双圆管结构的准静态轴压性能进行了实验研究,发现该新型结构的比质量吸能效率远远高于传统的泡沫铝夹芯单管,并接近甚至超过相应的空管结构;其内外管变形模式均与空管不同且受内外管组合的影响.本文讨论了它的变形机理,分析了外管壁厚对其压缩行为的影响,发现增大外管壁厚有利于增大结构的行程利用率,提高结构的比质量能量吸收...     

偏心率效应对金属圆柱管轴压性能的影响

用含有偏心率因子的直链塑性铰叠缩模型来分析金属圆柱管轴向压缩能量吸收，根据能量原理推导了瞬时载荷，从而获得压缩过程的载荷-位移曲线．讨论了偏心率对平均压缩载荷和载荷-位移曲线形貌的影响．实验结果与模型分析符合得很好．     

分层递变梯度蜂窝材料的面内冲击性能

提出了一种分层递变梯度蜂窝材料模型,以期控制蜂窝材料的能量动态吸收性能.此模型通过改变胞元的半径来改变蜂窝材料的面内特征参数,以实现蜂窝材料面内动力响应特性的多目标优化设计.计算结果表明,此模型可以在减小初始峰值应力水平的前提下,同时实现材料能量吸收过程的控制,并可以有效控制进入被保护结构的应力水平.此模型可为蜂窝材料...     

丹参超微粉碎前后丹参酮ⅡA的溶出行为比较

采用高效液相色谱法测定丹参超微粉体和常规粉体中丹参酮ⅡA体外溶出量和溶出速率.丹参超微粉体和常规粉体中丹参酮ⅡA体外溶出量无显著性差异,超微粉体的溶出速率较常规粉体明显增加.实验表明超微粉碎可明显提高丹参酮ⅡA溶出速率.     

Neutron emission from fracturing of granite blocks: An experimental revisitation

A series of experimental tests, such as those of Carpinteri et al. (2013), have been performed. The aim was to check the emission of neutrons in the fracture of Luserna granite blocks under mechanical loading, as reported by the above mentioned authors. No neutrons have been detected and some doubts have emerged on the soundness of the previous measurements.     

混合式陶瓷球轴承在液氮中的摩擦学性能研究

研究了由ＳｉａｌｏｎＳｉ３Ｎ４陶瓷球,９Ｃｒ１８内外环以及由ＰＴＦＥ和玻璃纤维制成的保持架组合成的混合式陶瓷球轴承在液氮气氛和重负荷条件下的摩擦磨损性能,结果表明,通过９０ｍｉｎ的－１９６℃超低温台架试验后,混合式陶瓷球轴承仍可以正常工作,对试验后的陶瓷球进行显微镜观察未发现大面积的接触疲劳破坏,但在内外环滚道表面有轻微疲坑,混合式陶瓷球轴承的摩擦功耗明显低于钢制球轴承。     

Dynamic crushing of aluminum foams: Part II – Analysis

Part II of this study uses micromechanically accurate foam models to simulate and study the dynamic crushing of open-cell foams. The model starts as random soap froth generated using the Surface Evolver software to mimic the microstructure of the foams tested. The linear edges of the cellular microstructure are “dressed” with appropriate distributions of solid to match those of ligaments in the actual foams and their relative density. The ligaments are modeled as shear-deformable beams with variable cross sections discretized with beam elements in LS-DYNA, while the Al-alloy is modeled as a finitely deforming elastic–plastic material. The numerical contact algorithm of the code is used to model ligament contact and limit localized cell crushing. The quasi-static and all dynamic crushing experiments in Part I are simulated numerically. The models are shown to reproduce all aspects of the crushing behavior including the formation and evolution of nearly planar shocks, the force acting at the two ends, the shock front velocity, the strain in the crushed material behind the shock, and the energy absorbed.     

带有圆弧形凹槽金属薄壁圆管抗撞性优化设计

在金属薄壁圆管的基础上,引入圆弧形凹槽诱导结构并以其为研究对象,建立以凹槽数量及其半径为优化参数,以比吸能和压溃力效率为评价指标的多目标优化模型。分析研究均布设置诱导凹槽对结构吸能、最大峰值压溃力及压溃力曲线平稳性的影响。采用有限元软件LS-DYNA得到不同几何参数模型的碰撞响应,结合径向基函数法构造近似函数,并采用理想点法进行优化设计,得出使结构最优时的凹槽数量和半径,从而得到了理想的诱导凹槽优化结构。