Papers by Keyword: Characteristic Length

Abstract: According to the progressive damage analysis based numerical characteristic length scheme presented by Zhang, a progressive damage model established by Liu is adopted here to calculate characteristic lengths for mechanical composite joints. Four groups of specimens with different lay-ups and geometries were designed and fabricated and static tensile experiments were carried out to verify the suitability of the numerical characteristic length model. Good agreements between the predicted ultimate failure loads of the specimens and experimental outcomes are obtained. In addition, the characteristic lengths calculated from the experimental ultimate failure loads are in accordance with that obtained from numerical ultimate failure loads, which give evidence of the feasibility and suitability of the numerical characteristic length model.

Abstract: This paper proposed a finite element formulation to analysis the vibration of couple-stress continuum. A four-node discrete couple-stress element relaxed the requirement of C₁ continuity is developed. This element is modified by a bubble function, based on the classical four-ode Lagrange element. The element includes the internal bending constants and the internal initial moment of rotation. Numerical examples show that the present FE scheme is accurate for the eigenvalue analysis of couple-stress continuum structures, especially for the low order frequency analysis.

Abstract: In order to simulate the rupture process of Cartridge Case, material failure constitutive model is researched. Johnson-Cook plasticity model is given as an analytical function of equivalent plastic strain, strain rate, stress triaxiality. Johnson-Cook plasticity model and Johnson-Cook Damage initiation criterion are used to describe the plastic deformation and fracture of case for the pressure of power gas. Using the implementation of this stress-displacement and characteristic length, problem of the relationship between fracture energy and the characteristic length in finite element model is solved. Finally, the simulated model which includes barrel, case, bolt and locking rigidity spring is built. Comparing the fracture shape and position in simulated test and physical experiment, the results are very similar. It proves that the rupture process of Cartridge Case can be simulated by the constitutive model which is introduced in this paper.

Abstract: The paper is focused on finding reasonable proportions for both cube-shaped and cylinder-shaped silicate-based composite specimens subjected to wedge-splitting tests. The analysis is conducted using finite element method code with an implemented cohesive crack model. The aspect of the material’s brittleness, related to the heterogeneity of the material and described by what is termed as the characteristic length of quasi-brittle material, is accented. The results yield some recommendations for the determination of parameters of nonlinear fracture models for cementitious composites by means of wedge splitting tests of laboratory specimens of the two standard shapes.

Abstract: In order to determine and actively design the vibration characteristics of micro-cantilever in the MEMS devices, it is highly necessary to research on the modal analysis of micro-cantilever which is driven by electrostatic force. This paper analyzes the coupling of mechanical and electrical coupling beam based on the direct coupling method, applies ANSYS software into creating the model of the micro-cantilever to simulation of electromechanical coupling, and establishes the quantitative impact analysis model between natural frequency of vibration and the thickness of a micro-beam with Trans126 transducer element, through directly embedding intrinsic characteristic length of micro-cantilever beam to the scale effect of vibration mode. The main conclusion is that when the thickness of micro-beam is close to the characteristics size of the materials, the natural frequency will show a significant scale effect phenomenon.

Abstract: Numerical simulations related to polar effects in an infinite extended granular layer under shearing movement and constant vertical pressure are presented. The mechanical behavior of cohesionless granular soil is described within the framework of micro-polar (Cosserat) continuum and using an elasto-plastic constitutive relation. The influence of Cosserat rotations and couple stresses are taken into account using the mean grain size as characteristic length. Finite element method in Updated Lagrangian (UL) frame is used to consider large deformations during calculations. The numerical results demonstrate that for large shearing movement, the shear deformations within the granular layer are localized into a narrow zone. The FE-calculations indicate that the polar effects manifest by the appearance of noticeable grain rotations, high void ratios, pronounced volume changes within the localized shear zone.

Abstract: The geometric proportions of cube-shaped specimens subjected to wedge-splitting tests are numerically studied in the paper. The minimal notch length for specimens made of cement based composites varying in characteristic length of the material (a measure of material brittle-ness/heterogeneity) is verified using finite element method code with an implemented cohesive crack model (ATENA). The problem of assigning the crack initiation point (the notch tip vs. the groove corner in the load-imposing area of the specimen) is solved numerically also using both the theory of linear elastic fracture mechanics and the theory of the fracture mechanics of generalized singular stress concentrators in the second part of the two-part paper. Results ob-tained by the different approaches are compared. The minimal notch length is recommended.

Abstract: Micro-polar and second order homogenization procedures for periodic elastic masonry are implemented to include geometric and material length scales in the constitutive equation. By the solution of the RVE equilibrium problems with properly prescribed boundary conditions the orthotropic elastic moduli of the higher order continua are obtained on the basis of an enhanced Hill–Mandel condition. A shear layer problem is analysed and the results from the heterogeneous models are compared with those ones obtained by the homogenization procedures; the second-order homogenization appears to provide better results in comparison to the micro-polar homogenization.

Abstract: As high strength concrete (HSC) is widely used in construction, more and more attention has been paid to crack resistance of it. In order to improve crack resistance of HSC, we study the influence of mineral admixtures (ground slag, silica fume and fly ash) on brittleness and characteristic length as crack resistance’ indexes. Testing researches shows, without admixture, crack resistance of HSC is the lowest; when one of the three mineral admixtures added, crack resistance increases dramatically; when two of the three mineral admixtures are added in the concrete, crack resistance increases a little more and it does not change very much no matter which two are mixed; crack resistance comes out the highest when the three mineral admixtures are added in concrete. Mechanism analysis shows, Adding fine and high active ground slag, silica fume and fly ash into concrete can greatly improve microstructure of transition zone, decrease Ca(OH)2, ettringite and porosity in concrete, increase C-S-H gel and greatly reduce the original micro-cracks in the transition zone.