Fully non-linear wave models in fiber-reinforced anisotropic incompressible hyperelastic solids

Many composite materials, including biological tissues, are modeled as non-linear elastic materials reinforced with elastic fibers. In the current paper, the full set of dynamic equations for finite deformations of incompressible hyperelastic solids containing a single fiber family are considered. Finite-amplitude wave propagation ansätze compatible with the incompressibility condition are employed for a generic fiber family orientation. Corresponding non-linear and linear wave equations are derived. It is shown that for a certain class of constitutive relations, the fiber contribution vanishes when the displacement is independent of the fiber direction.Point symmetries of the derived wave models are classified with respect to the material parameters and the angle between the fibers and the wave propagation direction. For planar shear waves in materials with a strong fiber contribution, a special wave propagation direction is found for which the non-linear wave equations admit an additional symmetry group. Examples of exact time-dependent solutions are provided in several physical situations, including the evolution of pre-strained configurations and traveling waves.     

Implicit frictional-contact model for soft particle systems

We introduce a novel numerical approach for the simulation of soft particles interacting via frictional contacts. This approach is based on an implicit formulation of the Material Point Method, allowing for large particle deformations, combined with the Contact Dynamics method for the treatment of unilateral frictional contacts between particles. This approach is both precise due to the treatment of contacts with no regularization and artificial damping parameters, and robust due to implicit time integration of both bulk degrees of freedom and relative contact velocities at the nodes representing the contact points. By construction, our algorithm is capable of handling arbitrary particle shapes and deformations. We illustrate this approach by two simple 2D examples: a Hertz contact and a rolling particle on an inclined plane. We also investigate the compaction of a packing of circular particles up to a solid fraction well above the jamming limit of hard particles. We find that, for the same level of deformation, the solid fraction in a packing of frictional particles is above that of a packing of frictionless particles as a result of larger particle shape change.     

Morphology and dynamics of a crack front propagating in a model disordered material

We present an experiment on the morphology and dynamics of a crack front propagating at the interface between an elastomer and a glass slide patterned with a prescribed distribution of defects. Regimes of high and low pinning strength are explored by changing the fracture energy contrast of the defects. We first analyze the roughness of crack fronts by measuring their typical amplitude in real and Fourier space. Irrespective of the pinning regime, no well defined self-affine behavior is found which may be explained by the emergence of an intermediate lengthscale between the defect size and the sample size. Then, we show that the dynamics at high fracture energy contrast results in rapid jumps alternating with periods of arrest. The distributions of speeds, displacements and waiting times are found to have an exponential decay which is directly related to the distribution of distances between defects along the direction of propagation.     

Mathematical characterization and identification of remodeling,growth, aging and morphogenesis

A clear demarcation between various processes of material evolution is established and the implications of the symmetry type on our ability to distinguish between them are investigated. The general features of the various types of material evolution are emphasized by establishing a spatio-temporal analogy between material uniformity and processes of material evolution.     

Wave propagation in graded rings with rectangular cross-sections

In this paper, a double orthogonal polynomial series method is proposed to investigate the guided wave propagation in a two-dimensional (2-D) structure, namely, a FGM ring with a rectangular cross-section. Two kinds of graded rings are considered: material gradient directions being in the radial direction and in the axial direction respectively. Numerical comparison with available reference results for a straightly homogeneous rectangular bar illustrates the validity of the proposed method. The dispersion curves and displacement distributions of various FGM rings, which have different radius to thickness ratios, different material gradient directions and different thickness to height ratios, are calculated to reveal the guided wave characteristics.     

Assessment of Digital Image Correlation as a method of obtaining deformations of a structure under fluid load

Digital Image Correlation (DIC) is employed for the measurement of full-field deformation during fluid–structure interaction experiments in a wind tunnel. The methodology developed for the wind tunnel environment is quantitatively assessed. The static deformation error of the system is shown to be less than 0.8% when applied to a curved aerofoil specimen moved through known displacements using a micrometre. Enclosed camera fairings were shown to be required to minimise error due to wind induced camera vibration under aerodynamic loading. The methodology was demonstrated using a high performance curved foil, from a NACRA F20 sailing catamaran, tested within the University of Southampton RJ Mitchell, 3.5 mx2.4 m, wind tunnel. The aerodynamic forces induced in the wind tunnel are relatively small, compared with typical hydrodynamic loading, resulting in small deformations. The coupled deflection and blade twist is evaluated over the tip region (80–100% Span, measured from the root) for a range of wind speeds and angles of attack. Steady deformations at low angles of attack were shown to be well captured however unsteady deformations at higher angles of attack were observed as an increase in variability due to hardware limitations in the current DIC system. It is concluded that higher DIC sample rates are required to assess unsteady deformations in the future. The full field deformation data reveals limited blade twist for low angles of attack, below the stall angle. For larger angles, however, there is a tendency to reduce the effective angle of attack at the tip of the structure, combined with an unsteady structural response. This capability highlights the benefits of the presented methodology over fixed-point measurements as the three dimensional foil deflections can be assessed over a large tip region. In addition, the methodology demonstrates that very small deformations and twist angles can be resolved.     

基于离散元法的干湿颗粒系统仿真

介绍了基于离散元法的干湿颗粒系统仿真软件DEMSIM。对于干颗粒系统,DEMSIM可以分析二维和三维颗粒系统的弹性和塑性接触碰撞过程;对于湿颗粒系统,DEMSIM采用传统的液桥模型;对于颗粒-流体系统,DEMSIM采用CFD-DEM细观耦合模型模拟。一系列典型算例的模拟分析,验证了干湿颗粒系统仿真软件DEMSIM的精度和有效性。     

聚离子液体功能材料研究进展

聚离子液体(PILs)材料兼具离子液体和聚合物的性质, 近年来已经在高分子化学、材料科学及能源科学等领域得到初步应用, 并引起了人们广泛关注. 本论文介绍了聚离子液体的合成, 综述其在(准)固态电解质、燃料电池聚电解质膜、刺激响应性功能材料, 以及碳材料等相关领域的研究与应用.     

水醇溶性小分子卟啉衍生物的合成及其在聚合物太阳电池中的应用

设计合成了Por-N, Por-NBr, Por-Cu-N和Por-Cu-NBr四种水醇溶性小分子卟啉衍生物. 对这类卟啉小分子衍生物的紫外可见吸收光谱研究表明, 基于金属铜配位的卟啉小分子衍生物较未配位化合物有微弱的蓝移. 循环伏安法对这类小分子卟啉衍生物的研究表明, 基于金属铜配合物的卟啉衍生物的最高占有分子轨道能级均没有明显变化. 采用空间电荷限制电流方法对小分子卟啉衍生物的研究表明, 基于金属铜配位的卟啉小分子衍生物的电子迁移率得到明显提高. 以聚合物PCE10为给体材料, 富勒烯衍生物PC₇₁BM为受体材料, 以及合成的小分子卟啉衍生物为阴极界面层制备了结构为ITO/PEDOT:PSS/PCE10:PC₇₁BM/卟啉小分子衍生物/Al的聚合物太阳电池器件. 器件研究结果表明, 化合物Por-NBr, Por-Cu-N与Por-Cu-NBr作为电子传输层的器件的光电转换效率达到9%以上, 其中以Por-Cu-N作为阴极界面层的器件达到的最高效率为9.12%, 相应器件的短路电流密度, 开路电压以及填充因子分别为16.91 mA· cm^-2, 0.79 V和68.1%. 表明这类水醇溶性小分子卟啉衍生物作为聚合物太阳电池的阴极界面层有着广阔的应用前景.