Papers by Keyword: Size Effect

Abstract: The purpose of this study is to investigate the influence of specimen size and shape on compressive strength of concrete. Concrete cubes, cylinders and prisms with their size ranging from 150mm to 450mm were tested in unaxial compression. Failure patterns and the effect of specimen shape and size on compressive strength of concrete were investigated. In addition, theoretical size effect models, such as the MSEL and MFSL were used to analyze the size effect of concrete strength. It is shown that for specimens tested in this study, the two models are both applicable to predicting the compressive strength of specimens in various sizes with a reasonably good accuracy.

Abstract: A number of methods for assessing wind-induced vibration of structures are available ranging from simplified procedure using quasi-static methods to the detailed procedure using statistical methods. The appropriate procedure should be selected in accordance with wind sensitivity of structures. However, it still remains unresolved concerning how to provide a universal criterion with physically meaningful and convenient for the concept of the wind sensitivity until now. In order to solve the previous problem of how to distinguish between those structures for which the wind effects can be treated by simplified procedure, and those for which the wind effects must be treated by detailed procedure, a concept of sensitivity for wind-resistance is presented in this paper. The essential idea of this theory is to provide a general expression of wind sensitivity of structures by synthesizing three factors between wind load and the structure, including the size-effect factor, frequency-effect factor and mode-effect factor, which are based on the analytical derivation and take duly into account the influence of all the significant parameters for the response. Based on that, two case studies of cantilevered roof and single-layer reticulated shell structures under wind actions are demonstrated as illustrative examples.

Abstract: Based on the constrained variational principle, the mixed multi-variable natural neighbor Galerkin method for couple-stress elasticity is proposed for three-dimensional problems. The displacements and micro-rotations are taken to be independent nodal degrees of freedom, and the geometrical constraints between them are enforced through Lagrange multipliers. The C⁰-continuous non-Sibsonain interpolation is used to obtain the discrete equations. The proposed method is tested by the numerical example and the results show that strong size effects are observed when the length of deformation field and the characteristic length of the material are comparable.

Abstract: This paper presents methodologies for fracture analysis and fatigue remaining life prediction of concrete structural components with and without accounting for tension softening and size effects. Stress intensity factor (SIF) is computed by conducting finite element analysis (FEA) and compared with that obtained by using analytical approach. The domain integral method has been used to calculate the strain energy release rate (SERR) and SIF by post-processing the FEA results. Nonlinear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Details of size effect in the computation of SIF and remaining life prediction have been presented. Size effect has been accounted for by modifying the Paris law, leading to size adjusted Paris law. Numerical studies have been conducted for fracture analysis, crack growth studies and remaining life prediction. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature.

Abstract: This paper deals with an analysis of a crack-tip field of particulate-reinforced composites which can describe the evolution of debonding damage, matrix plasticity and particle size effect on deformation and damage. Numerical analyses were carried out on a crack-tip field in elastic-plastic matrix composites reinforced with elastic particles by using a finite element method developed based on an incremental damage theory. The particle size effect on damage is described by a critical energy criterion for particle-matrix interfacial debonding. The effect of debonding damage on a crack-tip field is discussed based on numerical results. The debonding damage initiates and progresses ahead of a crack-tip. The stress distribution shifts downward in the debonding damage area. It is concluded that a crack-tip field is strongly affected by debonding damage.

Abstract: The bearing capacity decreases continuously along with the deterioration of material property under the action of external effects. It is important to evaluate the damage of concrete, and the damage parameter plays an important role in this process. An experimentation method has been designed, which can simulate the initial damage by mixed initiator into concrete. Using the elastic modulus of axial compression experimentation, the initial damage D0 and damage threshold value Df have been gained. The Size effect of concrete compress damage parameters is verified.

Abstract: A comprehensive numerical study of tensile deformation on electro-deposited Cu with nano-scale growth twins is presented using a conventional theory of mechanism-based strain gradient plasticity (CMSG). Systematic research on the size effects of growth twins in Cu polycrystalline is carried out. The roles of many material parameters which affect the size effects, such as grain sizes, Young’s modulus, twin/matrix lamellar structures aspect ratio and volume fraction, as well as the plastic strain hardening exponent, are presented.

Abstract: A progressive forming process for micro-components was developed to circumvent the issue of handling of small micro-parts while keeping in mind the need for high manufacturing through-put. The mechanical properties and microstructure of the material have been found to play a significant role in the forming of micro-components. In this work, the effect of mechanical property on the forming of copper micro-pins by the progressive forming process is highlighted. Empirical results show that the forming load decreases for forming micro-pin with 0.3mm diameter after annealing but the pin height obtainable decreases as well compared to that prior to the heat treatment.

Abstract: Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.

Abstract: The description of different effects observed in nature by only one general equation is the “Holy Grail” for all physicists. This goal has been achieved for characteristic temperatures through a top-down approach (studying size effects from macroscopic laws) and is presented in this chapter. Here, we show the general equation based on the surface area to volume ratio of nanostructures and statistics (Fermi-Dirac or Bose-Einstein) followed by the particles involved in the investigated phenomena. From the distinction between fermions and bosons, so-called particles which follow a Fermi-Dirac or a Bose-Einstein statistics respectively, this equation indicates the universal behaviour of size and shape effects on different material properties like melting, ferromagnetism, vibration and superconduction. The same shape parameter used in this universal equation can be used to determine the melting enthalpy, the phase diagrams of alloys, the energy bandgap and also the creep behavior of nanomaterials. Theoretical predictions show satisfactory agreement with experimental data taken from literature.