Dynamic effective properties of matrix composite materials with high volume concentrations of particles

A new approach is proposed to investigate the propagation of a plane compressional wave in matrix composite materials with high volume concentrations of particles. The theory of quasicrystalline approximation and Waterman’s T matrix formalism are employed to treat the multiple scattering resulting from the particles in composites. The addition theorem for spherical Bessel functions is used to accomplish the translation between different coordinate systems. The Percus–Yevick correlation function widely applied in the molecular theory of liquids is employed to analyze the interaction of the densely distributed particles. The analytical expression for the Percus–Yevick correlation function is also given. The closed form solution for the effective propagation constant is obtained in the low frequency limit. Only numerical solutions are obtained at higher frequencies. Numerical examples show that the phase velocities in the composite materials with low volume concentration are in good agreement with those in previous literatures. The effects of the incident wave number, the volume fraction and the material properties of the particles and matrix on the phase velocity are also examined.     

Dynamic characterization of poroelastic materials

This paper presents a method, based on measurement of material dynamic-complex stiffness, of determining the coefficients appearing in Biot's equations for poroelastic materials. This method is relatively simple to employ and has several self-checking features. Results are presented and compared with theoretical predictions for material systems based on polyurethane foam, wool felt and sand solid phases with fluid phases of water, air and silicone fluid.     

Dynamic fracture of idealized fiber-reinforced materials

Dynamic plane stress of sheets composed of two orthogonal families of inextensible fibers, with infinitesimal elastic shearing stress response, is considered. The fibers through the tip of a propagating tear or crack carry finite forces. Fracture criteria that can be expressed in terms of these tip forces are discussed. In a particular example it is shown that the maximum energy release rate criterion leads to a circular crack trajectory, while the so-called critical force and critical stress criteria imply that the crack is L-shaped, like cracks or tears in real fibrous materials.     

钢质套筒被动围压下混凝土材料的冲击动态力学性能

为了研究混凝土材料在钢质套筒侧限约束下的动态力学性能参数和破坏规律,采用分离式大直径（75 mm）SHPB实验技术,测试了钢质套筒侧限约束下不同混凝土试件在不同载荷作用下轴向或径向的应力、应变峰值,平均应变率,计算了混凝土材料的损伤值,描述了加载破坏现象,对实验结果进行了分析。结果表明:混凝土材料在被动围压下,延性、抗破坏能力得到加强,具有明显的增强效应。被动围压下SHPB实验中混凝土材料的破坏应变为典型SHPB实验中破坏应变的1.8～2.8倍;破坏应力达到150 MPa以上,为静力学无围压条件下的2～5倍。     

Dynamic effects in materials of complex structure

We suggest a two-component model of a material experiencing structural transformations and use it to study how dynamic and evolution processes affect these transformations. We note that an essential role is played by internal interactions caused by internal forces arising between the components as well as by exchange processes describing variations in the composition of both components. We illustrate the model by specific examples.     

Dynamic compressive behavior of thick composite materials

The effect of strain rate on the compressive behavior of thick carbon/epoxy composite materials was investigated. Falling weight impact and split Hopkinson pressure bar systems were developed for dynamic characterization of composite materials in compression at strain rates up to 2000 s^–1. Strain rates below 10 s^–1 were generated using a servohydraulic testing machine. Strain rates between 10 s^–1 and 500 s^–1 were generated using the drop tower apparatus. Strain rates above 500 s^–1 were generated using the split Hopkinson pressure bar. Unidirectional carbon/epoxy laminates (IM6G/3501-6) loaded in the longitudinal and transverse directions, and cross-ply laminates were characterized. The 90-deg properties, which are governed by the matrix, show an increase in modulus and strength over the static values but no significant change in ultimate strain. The 0-deg and cross-ply laminates show higher strength and ultimte strain values as the strain rate increases, whereas the modulus increnases only slightly over the static value. The increase in strength and ultimate strain observed may be related to the shear behavior of the composite and the change in failure modes. In all cases, the dynamic stress-strain curves stiffen as the strain rate increases. The stiffening is lowest in the longitudinal direction and highest in the transverse direction.     

Anisotropy of elastic properties of materials

Papers dealing with the generalized Hooke’s law for linearly elastic anisotropic media are reviewed. The papers considered are based on Kelvin’s approach disclosing the structure of the generalized Hooke’s law, which is determined by six eigenmoduli of elasticity and six orthogonal eigenstates. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 131–151, November–December, 2008.     

Thermoelastic properties of spatially reinforced materials

Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 27, No. 1, pp. 15–24, January, 1991.     

Mechanical properties of nanostructure of biological materials

Natural biological materials such as bone, teeth and nacre are nanocomposites of protein and mineral with superior strength. It is quite a marvel that nature produces hard and tough materials out of protein as soft as human skin and mineral as brittle as classroom chalk. What are the secrets of nature? Can we learn from this to produce bio-inspired materials in the laboratory? These questions have motivated us to investigate the mechanics of protein-mineral nanocomposite structure. Large aspect ratios and a staggered alignment of mineral platelets are found to be the key factors contributing to the large stiffness of biomaterials. A tension-shear chain (TSC) model of biological nanostructure reveals that the strength of biomaterials hinges upon optimizing the tensile strength of the mineral crystals. As the size of the mineral crystals is reduced to nanoscale, they become insensitive to flaws with strength approaching the theoretical strength of atomic bonds. The optimized tensile strength of mineral crystals thus allows a large amount of fracture energy to be dissipated in protein via shear deformation and consequently enhances the fracture toughness of biocomposites. We derive viscoelastic properties of the protein-mineral nanostructure and show that the toughness of biocomposite can be further enhanced by the viscoelastic properties of protein.     

Identification of mechanical properties of inhomogeneous materials

In the present paper, the stress-strain state of tubes made of inhomogeneous elastic materials is considered. We discuss what causes the onset of inhomogeneity and solve a problem for a tube consisting of an inhomogeneous and a homogeneous layer. It is shown how the variations in the thickness ratio of the homogeneous and inhomogeneous material layers affect the values of the longitudinal and circular deformations on the external surface of the tube under the action of constant internal pressure; it is noted that this effect can be used to monitor the pipeline state and to ensure its safe operation. A method for identifying mechanical properties of deformable inhomogeneous materials is proposed; this method is based on the use of thick-walled tubular specimens in calibration tests, which is especially convenient when analyzing the action of aggressive media or radiation on the properties of deformable materials.