Development of a macro-element model for rockfall steel wires using

This paper aims to present a few aspects of the development of a plastic-hardening macro-element model for steel wires in flexible protection systems. First, the material behaviour is obtained using uniaxial tensile tests. Successively, the evolution of the elastic and plastic domain is obtained using a combination of physical tests, analytical models, and numerical simulations. Finally, the results obtained with the macro-element model are compared to those obtained using other approaches found in literature.

A constitutive model for gassy clay

Fine-grained marine sediments often contain gas bubbles that can cause many geotechnical problems. This soil has a composite structure with gas bubbles fitting within the saturated soil matrix. The gas cavity has a detrimental effect on the soil stiffness and strength when they are filled with undissolved gas only. The gas cavity can be filled with gas and pore water due to ‘bubble flooding’. Bubble flooding has a beneficial effect on the soil stiffness and undrained shear strength because it makes the saturated soil matrix partially drained under a globally undrained condition. A critical state constitutive model for gassy clay is presented which accounts for the composite structure of the soil and bubble flooding. The gas cavity is assumed to have a detrimental effect on the plastic hardening of the saturated soil matrix. Some of the bubbles can be flooded by pore water from the saturated soil matrix which leads to higher mean effective stress of the saturated soil matrix. Consequently, both soil stiffness and strength increase. Only one new parameter is introduced to model the detrimental effect of gas bubbles on plastic hardening. The model has been validated by the results of three gassy clays.

Study on the Mechanical Properties of Red Clay under Drying-Wetting Cycles

To study the mechanical properties of red clay under repeated dry and wet cycle test conditions, in this paper, the disturbed red clay in an engineering area in Liuzhou, Guangxi Province, was taken as the research object. By artificially controlling different dry and wet cycles in the laboratory, a direct shear test and triaxial consolidation drainage test were carried out on the red clay samples after different dry and wet cycles. The stress-strain curve and change rule of corresponding c and φ values were obtained. The results showed that, in both the direct shear test and the triaxial test, the shear strength parameters of red clay decreased with an increase in the number of dry and wet cycles and the attenuation was most obvious during the first cycle. With an increase in the number of dry and wet cycles, the attenuation gradually decreased. The constitutive model of the deviatoric stress and strain curve of red clay under dry and wet cycles was a plastic-hardening type. By analyzing the variation in parameters in the P-H model, the relationship between c, φ, and the number of dry and wet cycles n was obtained. The results showed that the parameters had different degrees of attenuation with the action of dry and wet cycles. To explain the above rules, some samples under different drying-wetting cycles were selected for environmental electron microscope scanning, and appropriate assumptions were made based on the microstructure.

Improved analysis method for structural members subjected to blast loads considering strain hardening and softening effects

In analysis and design of structures subjected to blast loading, equivalent Single-Degree-of-Freedom (SDOF) method is commonly recommended in design guides. In this paper, improved analysis method based on SDOF models is proposed. Both flexural and direct shear behaviors of structures subjected to blast load are studied using equivalent SDOF systems. Methods of deriving flexural and direct shear resistance functions are introduced, of which strain hardening and softening effects are considered. To collocate with the improved SDOF models, the improved design charts accounting for strain hardening and softening are developed through systematical analysis of SDOF systems. To demonstrate the effectiveness of the proposed analysis method, a model validation is made through comparing the predictions with laboratory shock tube testing results on reinforced concrete (RC) columns. It is found that compared to the conventional approach with elastic and elastic-perfectly-plastic model, the elastic-plastic-hardening model provides more accurate predictions. Additional non-dimensional design charts considering various levels of elastic-plastic-hardening/softening resistance functions are developed to supplement those available in the design guides with elastic-perfectly-plastic resistance function only, which provide engineers with options to choose more appropriate resistance functions in design analysis.

A non-associative macro-element model for vertical plate anchors in clay

This work proposes a new plastic hardening, non-associative macro-element model to predict the behaviour of anchors in clay for floating offshore structures during keying and up to the peak load. Building on available models for anchors, a non-associated plastic potential is introduced to improve prediction of anchor trajectory and loss of embedment at peak conditions for a large range of padeye offsets and different pull-out directions. The proposed model also includes a displacement-hardening rule to simulate the force and displacement mobilisation at the early stages of the keying process. The model is challenged and validated against different sets of numerical and centrifuge data. This extensive validation process revealed that two of the four newly introduced model parameters assume a constant value for the range of simulated cases. This suggests that only two of the newly introduced parameters may need to be calibrated for the use of the proposed macro-element model in practice.

The effect of surface plastic hardening technology, residual stresses and boundary conditions on the buckling of a beam

The complex influence of the surface plastic hardening technology, residual stresses, and boundary conditions on the bending of a hardened beam of EP742 alloy was performed. A phenomenological method of restoring the fields of residual stress and plastic deformations performed by its experimental verification in the particular case of ultrasonic hardening is given. The correspondence of the calculated and experimental data for the residual stresses is observed. For assess the influence of the formed residual stresses on convex cylinders, the calculation methods are used for initial strains based on using analogies between the initial (residual) plastic strains and temperature strains in an inhomogeneous temperature field. This allowed us to reduce the consideration of the problem to the problem of thermoelasticity, which was further solved by numerical methods. The effect of four types of boundary conditions for fixing the ends of the beams (rigid fastening and articulation of the ends and ribs in various combinations, cantilever) on the shape and size of the bending of the beam 10×10×100 mm after ultrasonic hardening is studied in detail. It was found that the minimum deflection is observed with a hard seal of both ends of the beam. The effect of the thickness of the beam, which varied from 2 to 10 mm, on their buckling under the same distribution of residual stresses in the hardened layer was studied, and the nonlinear nature of the increase in the deflection boom with decreasing thickness for all types of boundary conditions was established. It is shown that under all boundary conditions, the curvature along the length of the beam practically does not change, therefore it can be considered constant. The consequence of this is the preservation of the hypothesis of flat sections after the hardening procedure, which is confirmed by the calculated profile of the beam section in plane symmetry, close to a straight line. The influence of the anisotropy of surface plastic hardening on the buckling of the beam was found to be significant, which can serve as the basis for choosing the optimal hardening procedure. The performed parametric analysis of the task is presented in the form of graphical and tabular information on the results of the calculations.

Development of a Novel Plastic Hardening Model Based on Random Tree Growth Method

The flow functions for plastic deformation have been developed to describe the plastic behavior of sheet metals. In order to explain the plastic behavior of material in metal forming processes via finite element analyses, two basic input functions should be applied. One is the yield function that determines the yielding behavior. The other is flow function to describe the hardening property of sheet metal. To describe the hardening properties of sheet materials under quasi-static tension condition in a wide range of plastic straining, various different equations are known such as classical Swift, Voce, Holloman, combined Swift-Voce, and recently proposed Kim-Tuan equations, etc. Those hardening equations are based on metallurgical or phenomenological investigations, and however the application of each equation has some limitation. In this study, the random growth of the binary tree method is introduced to develop the reliable hardening equations of various sheet metals (i.e. DP980, Pure Ti, AA5052-O, STS304, Ti-Gr2, and Mg-AZ31B) with no knowledge of existing hardening equation types. To evaluate the proposed method, the proposed equations developed by new approach are compared with the Voce, Swift, and Kim-Tuan hardening equations for stress-strain curve and the plastic instability point. Consequently, the proposed approach was proven to be very efficient to find the reliable and accurate hardening equation for any kind of materials.