Analysis of Biaxial Mechanical Properties and Failure Criterion of Self-Compacting Concrete

Biaxial compression-compression, biaxial tension-compression and compression-shear tests were carried out on self-compacting concrete (SCC) using the rock true triaxial machine and compression-shear hydraulic servo machine to explore the biaxial mechanical properties of SCC. The failure modes and stress-strain curves of SCC under different loading conditions were obtained through experiment. Based on the comparison with the biaxial loading test data of ordinary concrete, the following conclusions are drawn: the failure modes and failure mechanisms under biaxial compression-compression and biaxial tension-compression are similar between SCC and ordinary concrete. Under compression-shear loading, the oblique cracks formed on the lateral surface of the specimen parallel to the shear direction gradually increased and the friction marks on the shear failure section were gradually deepened with the increase of axial compression ratio. The development trend of the stress-strain curve in the principal stress direction was not related to the lateral stress. Under the influence of lateral compressive stress, the principal compressive stress of SCC was increased by 55.78% on average; under biaxial tension-compression, the principal tensile stress of SCC had a maximum reduction of 62.79%; and under the compression-shear action, the shear stress of SCC had a maximum increase of 3.35 times. Compared with the biaxial stress test data of ordinary concrete, it can be seen that the lateral compressive stress had a more significant effect on the principal stress of SCC under biaxial loading. Subsequently, the strength criterion equations of SCC under biaxial loading were proposed based on the principal stress space and octahedral space stress respectively, which have shown good applicability in practice.

Photoelectric properties and stability of the single-layer transition metal dichalcogenides under three stress states

In this paper, the electrical and optical properties of single-layer MoS2 and single-layer WS2 in three strain states: biaxial tension, biaxial compression, biaxial tension and compression are systematically studied. All calculations are based on the first-principle of density functional theory. The results show that after biaxial tension strain, biaxial compression strain, and biaxial tension-compression strain are applied, the atomic structure, energy band structure, and optical absorption coefficient will show disparate changing trends. When the biaxial tension and compression strain intensity is less than 15%, the bond length, bond angle, and light absorption peak will have little fluctuation with the increase of strain intensity. However, compared with the other two strain states, these two crystal structures are the most volatile at this time. In addition, when 15% biaxial tensile strain is applied, the two crystals can still maintain their kinetic stability.

Verifying the Movable Elastoplastic Boundary Method by Using Galin’s Problem

Galin’s solution for the problem of biaxial tension of a plate with a hole completely covered by the plastic region appears to be a pearl recognized by the world scientific community. This solution serves as a test for all sorts of approximate approaches to solving elastoplastic problems, including the semi-analytical iterative method being developed by the author, focused on solving more complex problems such as the Kirsch problem in the elastoplastic formulation. The proposed iterative approach for a semi-analytical solution involves an explicit analytical expression for stresses in the plastic region and an iterative numerical solution in the elastic region with a refined border. The paper shows the convergence of the results based on the iterative procedure for the elastoplastic region boundary approaching its analytical position, which follows from the analytical solution of Galin’s elastoplastic problem. Consideration has also been given to obtaining results on the determination of the boundary between the elastic and plastic regions using a competing approximate perturbation method. The advantage of the proposed method lays in not limited modifications in parameters due to the requirement for small differences while formulating a problem from the axisymmetric case as seen in the perturbation method.

Surface construction for orthrotropic perfectly elastic-plastic Murnaghan material

The problem of constructing a yield surface is described. The magnitude of the stress velocity potential is explained graphically. The parameters of an elastic-plastic process are introduced: a modified R. Schmidt parameter and an analogue of the Lode parameter, the sign of which changes only when the singular point of the plasticity curve passes. The formal work area of the Murnaghan law is calculated, the real area will be much smaller. An effect similar to the Bauschinger effect for the deviator of the stress tensor is assumed to be fair. In the basic experiments of uniaxial and biaxial tension, compression and shear, a piecewise-linear generator with vertices at the corresponding singular points of the plasticity curves is determined. The magnitude of the effect is approximated by a quadratic dependence in the place parameter and piecewise-linear one in the hardening parameter. According to the magnitude of the effect, at the point of the active process there is a singular point of the curve, into which the basic generator moves. The yield surface is constructed by ductility curves drawn through the generator. Determination of the magnitude of the effect under repeated loading after unloading is considered.

Molecular dynamics simulation of plastic deformation in polyethylene under uniaxial and biaxial tension

Plastic deformation of polyethylene in uniaxial and biaxial loading conditions is studied using molecular dynamics simulation. Effects of tensile strain rates from 1 × 105 to 1 × 109 s−1, and mass density in the range of 0.923–0.926 g/cm3 on mechanical behaviour and microstructure evolution are examined. Two biaxial tensile deformation modes are considered. One is through simultaneous stretching in both the x and y directions and the other sequential stretching, firstly in the x-direction and then in the y-direction while strain in the x-direction remains constant. Tangent modulus and yield stress that are determined using the stress–strain curves from the molecular dynamics simulation show a strong dependence on the deformation mode, strain rate and mass density, and all are in good agreement with results from the experimental testing, including fracture behaviour which is ductile at a low strain rate but brittle at a high strain rate. Furthermore, the study suggests that the stress–strain curves under uniaxial tension and simultaneous biaxial tension at a relatively low strain rate contain four distinguishable regions, for elastic, yield, strain softening and strain hardening, respectively, whereas under sequential biaxial tension, stress increases monotonically with the increase of strain, without noticeable yielding, strain softening or strain hardening behaviour. The molecular dynamics simulation also suggests that an increase in the strain rate enhances the possibility of cavitation. Under simultaneous biaxial tension, with the strain rate increasing from 1 × 106 to 1 × 109 s−1, the molecular dynamics simulation shows that polyethylene failure changes from a local to a global phenomenon, accompanied by a decrease of the void size and increase of uniformity in the void distribution. Under sequential biaxial tension, on the other hand, the density of the cavities is clearly reduced.

ASSESSING THE MULTIAXIAL DEFORMATION RESPONSE OF UNIDIRECTIONAL NON-CRIMP FABRICS

In this study, the mixed-mode deformation response of a unidirectional non- crimp fabric (UD-NCF) was investigated. Multiaxial in-plane shear-biaxial tension tests were performed using a new multi-branched fabric specimen on a custom multi-axial loading device. Tests were performed with various ratios of deformation along three loading directions to impose combined tension and shear deformation on the fabric specimens. The different loading cases revealed a strong inter-dependency between shear and tensile deformation modes. Observation and measurement of local deformations provided important quantitative and qualitative information to deeply understand the interaction of typical meso- and macro-scale deformations, which can be leveraged during the forming process of liquid composite molded components to reduce shear-induced defects such as wrinkling.