Papers by Keyword: Constitutive Relation

Abstract: Split Hopkinson bar technique was often used to measure the dynamic mechanical properties of engineering materials. In this paper, the dynamic tensile and compression mechanical properties of polymer explosive bonded (PBX) under different strain rates were obtained by using split Hopkinson pressure/tension bar. The thickness of the specimen and the shape of the incident wave are designed to ensure the rationality of the experimental results. By comparing the experimental results, it was found that the PBX had different dynamic tensile and compression properties. The PBXs have been tested and shown tensile and compressive strengths ratios that range between 5 and 7. A constitutive relation is developed for modeling the dynamic mechanical response of PBX-I by using the Boltzmann superposition principle with a Prony series representation. The parameters of the PBX-I were fitted by using least square method. A finite element model was used to simulate the dynamic compressive and tensile behavior of PBX-I, and the numerical simulation results were in good agreement with the experimental results, which proved that the linear viscoelastic constitutive relation can be applied to the PBX-I.

Abstract: The self-similar isotropic hardening model developed by Deshpande and Fleck has been widely used. An important issue in this model is to determine the value of ellipticity. The ellipticity was treated as a constant in the subsequent yield, but different values were suggested in the literature. In this paper a cell-based finite element model based on the 3D Voronoi technique is used to verify the Deshpande-Fleck foam model. It is found that the ellipticity determined from uniaxial and hydrostatic compressions varies with the equivalent plastic strain.

Abstract: The conventional characterization of work-hardening is to approximate the stress-strain diagram using the empirical curve-fitting of Hollomon or Voce. The new method uses the Taylor slip analyses to derive a functional form which is optimally fitted to the data. This constitutive relations analysis (CRA) duplicates the data using at least two fit loci. The fit parameters relate to the slip motion within the microstructure and hence its interpretation reveals the possible dynamic shape-change reactions. The fit-process defines a new yield stress which separates the yielding from the deformation mechanisms at large strains that breaks up into two regions separated by intersection parameters. The applications of CRA to nanovoid formation and growth leading to ductile failure, plane stress yield locus prediction using tensile tests and decoding the stress-strain diagram for age-hardened aluminum alloys have been successful. Using super-pure aluminum, this study confirms that CRA is based on crystal plasticity principles and that CRA can predict the correlation of the obstacle strength factor, α, with work-hardening, hence permitting conversion of flow stress at given strains to obstacle density. The derived results show that the inherent annihilation process and the changing strength factor are coordinated to result in a self-consistent constitutive relation.

Abstract: The corrosion of concrete structures is serious in sulfuric acid environments. Corrosion damage of reinforcements caused sulfuric acid corrosion is very serious. The rapid experiments of sulfuric acid corrosion steel bars were carried out, and the apparent morphology and mechanical properties of sulfuric acid corrosion steel bars were studied. The results show that the corrosion of steel bars is uniform corrosion. With the increase of corrosion rate, the yield platforms and the yield strengths and ultimate strengths are reduced. Based on the experimental datas, the relationship models between yield strengths and ultimate strengths and corrosion rates were obtained. The constitutive models of corrosion steel bars were established. The stress - strain relationship model is in good agreement with the experimental data.

Abstract: Isothermal constant strain rate compression testing of a new as-cast high-temperature titanium alloy Ti-6.5Al-11.5(Sn,Zr)-2.5(Mo,W,Nb)-0.25Si-0.1Er was carried out at the deformation temperatures range from 900°C to 1100°C, strain rate range from 0.001 to 1 s^-1 and 60% of engineering strain. The deformation behavior of this high-temperature titanium alloy was analyzed based on the stress-strain result, and the constitutive equation based on the hyperbolic sine model and the parameters of Zener–Hollomon was established, showing a close accordance with the experimental value. The hot processing maps based on the dynamic material model and the Prasad’s instability criterion were constructed at strains of 0.3 and 0.6. The maps exhibit two stable deformation domains in the temperature range of 940~960°C and strain rate range of 0.001~0.002s^-1, and in the temperature range of 1030~1070°C and strain rate range of 0.02~0.06s^-1 with the power dissipation efficiency of 58.5% and 54.5%, respectively.

Abstract: Carbon nanotubes are a promising candidate for the next generation high performance structural and multi-functional composite material due to extremely high aspect ratios and ultra-high strength. It is evident from contemporary researches that utilization of carbon nanotubes in reinforcing cement-based composite materials has a great potential. Industrial carbon nanotubes paste was used for pro-dispersion by ultrasonic and dispersant (PVP) in this study. The mechanical properties of concrete reinforced by carbon nanotubes with different weight percent (0, 0.05, 0.1, 0.15, 0.2, and 0.25 wt. %) were studied in this paper. Test results indicated that the optimal dosage of carbon nanotubes was about 0.22wt. %. Cubic compressive strength and splitting tensile strength were found to be increased by 30.8% and 46.0% in comparison with normal concrete, respectively, while the change of elastic modulus was immaterial. For further analysis, the scanning electron microscope was employed to observe the dispersion of carbon nanotubes in concrete.

Abstract: Steel fiber reinforced polymer high strength structural concrete (SPHSC) is a new composite material which is used in long-span bridge structures invented by this research team. Based on the new composite material, the experiments of stress-strain full curves under uniaxial compression were carried out. The stress-strain full curves were achieved from the simple improved method. By the method of theoretical derivation and experimental data fitting, the constitutive equation of SPHSC which contains only two undetermined parameters of compressive strength and parameter of steel fiber was obtained. The study is the theoretic basis of the new material which was widely use in civil engineering.

Abstract: This chapter proposes an efficient approach to thermomechanical constitutive modeling for shape memory alloys using a novel separation of a martensite internal variable. This approach assumes that the martensitic internal variable has two components corresponding to two contrary martensite ensembles, which are separated by their opposite signs of contributions to a quantity of transformation strain. The constitutive models, based on a new separating concept, are presented in this chapter for uniaxial and three-dimensional proportional loading. The kinetic relations of these models are constructed using the Brinson model ideas concerning the interphase transformation processes in shape memory alloys. A number of illustrative numerical examples are presented here for one-dimensional modeling. The new separation of the internal variable has prospects for the description of material behavior in cases when mechanical loading may change sign and the phenomena are caused by martensitic reorientation. The conceptual and methodological solutions stated in the present work may be useful for subsequent modeling.

Abstract: This paper introduces the process of the nonlinear finite element model which is established by using ABAQUS software, and introduces the characteristics of ABAQUS software, meanwhile, lists the constitutive relation of steel pipe, steel and concrete, finally introduces some experimental model.

Abstract: From the feature of rock micro-unit failure obeys Poisson random distribution, the damage softening statistical constitutive of was established under true triaxial confinement based on D-P criterion, so the impact of the intermediate principal stress on rock deformation and failure was considered in theory, and the actual engineering rock complex stress path evolution was reflected more realistically. Furthermore, according to the geometrical conditions of stress-strain relationship, the theoretical relationship between constitutive model parameters and the stress-strain curve characteristic parameters during the process of rock softening and deforming, which enhance the adaptability of the model. Finally, the rationality of the model verified by the measured data.