Papers by Keyword: Stress-Strain Relationship

Abstract: Cambridge model gets the extensive application, which has advantages of rigorous theoretical derivation and model parameters which can entirely be obtained by triaxial tests, while it has deficiencies of the narrow applicative scope and describing the dilatancy hardly. As the most widely used strength theory, Mohr-Coulomb model can directly represent shear strength of soil material simply, without consideration for compression deformation yet. On account of the critical state of dilatancy defined comprehensively, this paper based on the description of dilatancy combines the advantage of Cambridge model and Mohr-Coulomb strength theory, applying to compression deformation and conciseness of Mohr-coulomb model, reflecting shear deformation and puts forward an elastic-plastic model—Coulomb-Cam model. At last, this constitutive model, proved by the contrast of numerical simulation and GDS triaxial tests is of the priority in representing the dilatancy and work-softening rationally.

Abstract: Strain-rate sensitivities of 55-65vol.% aluminum 2024-T6/TiB₂ composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar. Results showed that 55-65vol.% aluminum 2024-T6/TiB₂ composites exhibited significant strain-rate sensitivities, which were three times higher than that of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with reinforcement content increasing (up to 60%), which agreed with the previous researches. The aluminum 2024-T6/TiB₂ composites showed hybrid fracture characteristics including particle cracking and aluminum alloy softening under dynamic loading. The flow stresses predicted by Johnson-Cook model increased slowly when the reinforcement volume fraction ranged in 10%-40%. While the reinforcement volume fraction was over 40%, the flow stresses of aluminum matrix composites increased obviously and the strains dropped sharply. Keywords: Composite materials; Dynamic compression; Stress-strain relationship

Abstract: the results of deep artificial permafrost 's tri-axial compression test showed that the stress-strain relationship of deep original frozen clay presents a character that is weak and soft From the view point of engineering application , the paper gives a exponential model containing two parameter, Comparative analysis showed that the model not only gives a good description of frozen clay stress-strain relationship before peak stress, but also has the advantages of less model parameters, easy to determine and clear physical meaning. The analysis results showed that the model parameters a linear increase with the decrease of the temperature, and the change rule of parameters is contrary.

Abstract: In this paper results are reported of impact tests performed to study the influence of different fibre types on dynamic compressive properties of fibre reinforced concrete (FRC). FRC specimens are prepared with the same concrete and 1% of fibres of different types. The compressive impact tests are conducted with an instrumented drop weight impact system consisting of a hard steel drop weight, two 180t fast response loadcells, a high speed video camera, and a fast response data acquisition system. In this study, six fibre types with different shapes and material properties are considered. They are synthetic fibres, undulated, cold rolled, flattened, hooked end and a new spiral shape steel fibres. The dynamic stress-strain relationship is obtained by fitting the load history from the bottom loadcell to the average strain history captured by the strain gages. The energy absorption capabilities are defined as the area under the stress-strain curve of FRC specimens. The performance of the new spiral shape steel fibre is discussed by comparing the test results with those obtained from specimens reinforced with other types of fibres. The influence of the fibre shapes on the failure modes, ductility and energy absorbing capacity of FRC is discussed.

Abstract: Study the properties of GFRP confining concrete column through eight groups columns subjected to axial loading, and receive the stress-strain curves; various design parameters, such as amounts of GFRP sheets, width of straps and spacing of straps, have been considered. The results are: The axial compressive strength and ductility of concrete prism wrapped by GFRP sheets or GFRP straps have all increased to a certain degree, the process of destruction of concrete prism wrapped by GFRP become slower than common concrete prism. Based on the test results, deducing and validating the stress-strain relationship model of GFRP confining concrete prism.

Abstract: Based on the superiority avoiding the matrix equation to be morbid for those fitting functions constructed by orthogonal base, the Legendre orthogonal polynomial is adopted to fit the experimental data of concrete uniaxial compression stress-strain curves under the frame of least-square. With the help of FORTRAN programming, 3 series of experimental data is fitted. And the fitting effect is very satisfactory when the item number of orthogonal base is not less than 5. What’s more, compared with those piecewise fitting functions, the Legendre orthogonal polynomial fitting function obtained can be introduced into the nonlinear harden-soften character of concrete constitute law more convenient because of its uniform function form and continuous derived feature. And the fitting idea by orthogonal base function will provide a widely road for studying the constitute law of concrete material.

Abstract: Using the static and dynamic triaxial experimental machine, experimental study of the strength of wet-screened aggregate concrete are carried out under biaxial compression stress ratios, 0.25, 0.5, 0.75 and 1 after 0, 50, 100, 150, 200, 250, 300 cycles of freeze-thaw. The change of surface of wet-screened aggregate concrete specimens after different cycles of freeze-thaw are observed and described. The failure characteristic of specimens and the direction of the cracks are also observed. Based on the test data, the influence of freeze-thaw cycles and compressive stress ratio on the ultimate compressive strength and corresponding stress-strain relationship is analyzed respectively. The relationships between the ultimate compressive strength and freeze-thaw cycles, the stress ratios are given, respectively. On this basis, the unified failure criterion with consideration of the influence of freeze-thaw cycles and stress ratio is proposed. It can serve as a reference for the maintenance, design and the life prediction of ocean structures, hydraulic structures, marine structures and offshore platform in cold regions.

Abstract: High strength and high performance steels used in structural engineering have been developed, but the application is constrained and the design work changes as a result of the different material property. In order to study high strength steel material property features, the production process, steel grade and code limit requirement were reviewed and discussed. Some important mechanical property indexes including the stress-strain relationship, yield-tensile strength ratio (i.e. Y/T ratio), ductility and toughness, were analyzed based on a large amount of tension coupon test data reported in the available literature. The stress-strain relationship model used for finite element analysis was proposed. It is concluded that high strength structural steels have excellent toughness but lager Y/T ratio and lower elongation compared with those of traditional steels, some of which even exceed the code limit values. It is necessary to do deep research on the relationship between the steel mechanical property indexes and structure safety and to make further development of high strength steels. This research work is helpful to comprehend the material property of high strength structural steels and relevant code limit requirements.

Abstract: Laboratory triaxial tests of the soil reinforced with roots of Manilagrass were carried out in order to understand the stress-strain relationship. The change of shear strength indexes of the soil reinforced with roots of Manilagrass was investigated with the quantity of grassroots planted in the soil specimens. The results of laboratory triaxial tests show that the strength and capacity for resisting the deformation of soil reinforced with roots are better than those of unreinforced soil. And under the certain number of grassroots layers, the strength and capacity for resisting the deformation of soil reinforced with roots increase firstly and then reduce with the increasing of Manilagrass roots quantity. In other words, there is an optimal quantity of Manilagrass roots affecting the strength and capacity for resisting the deformation of soil reinforced with roots. The research results are important for understanding the mechanism and use of vegetation protection for slope.

Abstract: Based on bending fiber reinforced concrete beam, through the nonlinear analysis, the paper discuss the constitutive models of concrete and reinforcement, the properties of their element and the models of concrete beams reinforced with FRP bars. Using nonlinear analysis and comparing numerical results with experimental results, the fiber reinforced concrete beam bending terminal numerical model constructed in this paper can simulate the entire process of internal force and deformation of fiber reinforced concrete beams, and describe cracks in the formation and extension and the failure process and failure form, which also can provide enough precision to the practical engineering and scientific research. Meanwhile, the finite element computation model verified by test can provide more reactive information to effective structure computation model.