An analytical model for predicting the shear strength of unsaturated soils

The prediction of shear strength for unsaturated soils remains to be a significant challenge due to their complex multi-phase nature. In this paper, a review of prior experimental studies is firstly carried out to present important pieces of evidence, limitations, and some design considerations. Next, an overview of the existing shear strength equations is summarized with a brief discussion. Then, a micromechanical model with stress equilibrium conditions and multi-phase interaction considerations is presented to provide a new equation for predicting the shear strength of unsaturated soils. The validity of the proposed model is examined for several published shear strength data of different soil types. It is observed that the shear strength predicted by the analytical model is in good agreement with the experimental data, and get high performance compared to the existing models. The evaluation of the outcomes with two criteria, using average relative error and the normalized sum of squared error, proved the effectiveness and validity of the proposed equation. Using the proposed equation, the nonlinear relationship between shear strength, saturation degree, volumetric water content, and matric suction are observed.

Inter-Element Crack Propagation with High-Order Stress Equilibrium Element

The present contribution proposes a formulation based on the use of hybrid equilibrium elements (HEEs), for the analysis of inter-element delamination and fracture propagation problems. HEEs are defined in terms of quadratic stress fields, which strongly verify both the homogeneous and inter-element equilibrium equations and they are employed with interfaces, initially exhibiting rigid behavior, embedded at the elements’ sides. The interface model is formulated in terms of the same degrees of freedom of the HEE, without any additional burden. The cohesive zone model (CZM) of the extrinsic interface is rigorously developed in the damage mechanics framework, with perfect adhesion at the pre-failure condition and with linear softening at the post-failure regime. After a brief review, the formulation is computationally tested by simulating the behavior of a double-cantilever-beam with diagonal loads; the obtained numerical results confirm the accuracy and potential of the method.

Evaluation of extremely steep residual stress gradients based on a combined approach using laboratory-scale equipment

Surface treatments characterized by rapid heating and cooling (e.g. laser hardening) can induce very steep residual stress gradients in the direct vicinity of the area being treated. These gradients cannot be characterized with sufficient accuracy by means of the classical sin2Ψ approach applying angle-dispersive X-ray diffraction. This can be mainly attributed to limitations of the material removal method. In order to resolve residual stress gradients in these regions without affecting the residual stress equilibrium, another angle-dispersive approach, i.e. the universal plot method, can be used. A novel combination of the two approaches (sin2Ψ and universal plot) is introduced in the present work. Prevailing limits with respect to profiles as a function of depth can be overcome and, thus, high-resolution surface layer characterization is enabled. The data obtained are discussed comprehensively in comparison with results elaborated by energy-dispersive X-ray diffraction measurements.

Experimental Study on Stress Uniformity and Deformation Behavior of Coals with Different Length-to-Diameter Ratios under Dynamic Compression

In this study, a uniaxial impact compression test was performed on coal samples with length-to-diameter L / D ratios of 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 using a Φ 50 mm split Hopkinson pressure bar (SHPB) test system. This study researched the stress uniformity and deformation behavior of coal samples with different L / D ratios during dynamic compression, defined the stress equilibrium coefficient ξ , proposed a new method for determining whether a sample meets the stress uniformity hypothesis, and obtained the critical L / D ratio of 0.6 and the optimal L / D ratio of 0.3 or 0.4 for coal samples to obtain the stress equilibrium. The experimental results showed that the dynamic stress-strain curve of coal had an elastic stage, a plastic stage, and a failure stage. As the L / D ratio increased, the proportion of the elastic stage to the prepeak curve of the samples declined progressively; with an increase in the L / D ratio, the peak part of the curve also changed from “sharp” to “stagnated,” while an increase in the plasticity led to strain softening. As the L / D ratio of the samples increased, the average strain rate decreased approximately as a power function, and the decreasing trend was gradually reduced from 296.49 s−1 ( L / D =0.3) to 102.85 s−1 ( L / D =1), with a reduction of approximately 65.31%. With an increase in the L / D ratio, the peak strain gradually decreased exponentially. This study concluded that the SHPB test protocol design is of a certain reference value for low-density, low-strength, heterogeneous brittle materials, such as coal.

Strain Field Development of a Rectangular Dislocation Loop in a Semi-Infinite Medium with Verification

This paper considers a rectangular Volterra dislocation loop lying beneath and parallel to a free surface in a semi-infinite material. The paper utilizes the displacement field of an infinitesimal dislocation loop to obtain the strain field and then integrate over a finite rectangular area. For the loop, it can have three non-zero Burgers vector components. The stress field is also obtained from Hooke’s law for isotropic materials. Analytical and numerical verifications of the strain and stress fields are performed. In addition, the effect of the free surface on stresses is displayed versus depth from the surface. Verification includes satisfaction of the zero-traction boundary condition, the stress equilibrium equations and the strain compatibility equations.

A Mathematical Model to Simulate Static Characteristics of T-Beam Bridge with Wide Flange

This study considers various factors, such as shear lag effect and shear deformation, and introduces the self-stress equilibrium for shear lag warping stress conditions to analyze the static characteristics of T-beam bridges accurately. In the mechanical analysis, three generalized displacement functions are applied, and the governing differential equations and natural boundary conditions of the static characteristics of T-beams are established on the basis of the energy variational principle. In the example, the influences of the shear lag effect, different load forms, and span ratio on the mechanical properties of T-beam bridges are analyzed. Therefore, the method of this study enriches and develops the theoretical analysis of T-beams, and it plays a certain guiding role in designing such a structure.

A Machining Program Employing a Slip Line Field Modelling Technique Over Other Constitutive Models

Machining involves complex plastic material flow at the chip separation site which makes it difficult to predict forces and other machining outputs to higher accuracy. Modelling is a common technique which facilitates incorporation of analytical and experimentally derived equations to visualize the process and analyses the mechanism. It saves time and machining factors can be optimized without any trial and error method. In this paper, the significance of slip line field model over other constitutive laws in defining the complex regions in machining are thoroughly reviewed and a slip line field model is chosen which incorporates build up edge (BUE) of a larger size than the other previously defined slip line models for machining. The modified model also incorporate a region of shear zone instead of a shear line, takes into account the chip curl effect and conform to the velocity discontinuity and stress equilibrium. The slip line fields are generated using MATLAB and employing Dewhurst-Collin's matrix technique.

Coupled multiphase flow and geomechanics simulation of hydrate dissociation using FVM-FEM co-located variables arrangement

<p><span>Natural gas hydrates, which are ice like crystalline solids, contain tremendous amount of potential hydrocarbon gas. Gas recovery through hydrate dissociation can be achieved through depressurization, inhibitor injection and thermal stimulation. The hydrate dissociation by depressurization involves significant pressure and temperature gradients as the dissociation process is highly endothermic. The destabilization of solid hydrate into fluid constituents causes loss of cementation which can alter the stress field which in turn changes the porosity and permeability of the hydrate bearing medium causing subsidence. In the present study, a thermo-hydro-mechanical-chemical (THMC) coupled numerical simulator is developed accounting for the hydrate phase change kinetics, non-isothermal multiphase flow and geomechanics. The point centered or node centered finite volume method is used for space discretization of flow and energy equations while the finite element method is used for stress equilibrium equation. This procedure requires the flow and mechanics variables to be co-located. The finite volumes are constructed around the flow variables defined at nodes while the finite element is defined by the corner nodes. The volumetric strain rate term in the flow equations, which couples the flow and geomechanics equations, is evaluated by interpolating the volumetric strains calculated over the finite elements to the finite volumes. Our simulations show that this procedure results in a stable convergence of the solution without the need for any stabilizing terms due to co-located variable arrangement. Our simulations also show that the iterative coupled approach, where the flow and geomechanics equations are solved separately and sequentially, gives stable convergence without any additional split terms due to sequential but iterative solving of the coupled equations.</span></p>

Stress Measurements in Alumina by Optical Fluorescence: Revisited

Stress measurements in single-crystal and polycrystalline alumina are revisited using a recently developed optical fluorescence energy shift method. The method simultaneously utilizes the R1 and R2 Cr-related ruby line shifts in alumina to determine two components of the stress tensor in crystallographic coordinates, independent of the intended or assumed stress state. Measurements from a range of experimental conditions, including high-pressure, shock, quasi-static, and bulk polycrystals containing thermal expansion anisotropy effects, are analyzed. In many cases, the new analysis suggests stress states and stress magnitudes significantly different from those inferred previously, particularly for shock experiments. An implication is that atomistic models relating stress state to fluorescence shift require significant refinement for use in materials-based residual stress distribution analyses. Conversely, the earliest measurements of fluorescence in polycrystalline alumina are shown to be consistent with recent detailed measurements of stress equilibrium and dispersion.