Failure Criteria and Constitutive Relationship of Lightweight Aggregate Concrete under Triaxial Compression

This paper investigates the compression behavior and failure criteria of lightweight aggregate concrete (LAC) under triaxial loading. A total of 156 specimens were tested for three parameters: concrete strength, lateral confining pressure and aggregate immersion time, and their effects on the failure mode of LAC and the triaxial stress-strain relationship of LAC is studied. The research indicated that, as the lateral constraint of the specimen increases, the failure patterns change from vertical splitting failure to oblique shearing failure and then to indistinct traces of damage. The stress-strain curve of LAC specimens has an obvious stress plateau, and the curve no longer appears downward when the confining pressure exceeds 12 MPa. According to the experimental phenomenon and test data, the failure criterion was examined on the Mohr–Coulomb theory, octahedral shear stress theory and Rendulic plane stress theory, which well reflects the behavior of LAC under triaxial compression. For the convenience of analysis and application, the stress-strain constitutive models of LAC under triaxial compression are recommended, and these models correlate well with the test results.

Disentangling Between-Person and Reciprocal Within-Person Relations Among Perceived Leadership and Employee Wellbeing

Based on transactional stress theory and theoretical propositions regarding affective perceptions and reactions, we develop and test a model of reciprocal within-person relations between perceptions of directive and empowering leadership and employee emotional engagement and fatigue. A sample of n = 1,610 employees participated in a study with a three-wave fully crossed and lagged panel design across 6 months. We used a random intercepts cross-lagged panel model (RI-CLPM) to separate within- from between-person sources of variance in leadership perceptions and employee wellbeing. Consistent with previous research, at the between-person level of analysis, we found that directive leadership was positively related to both engagement and fatigue, whereas empowering leadership was positively related to engagement and negatively related to fatigue. Interestingly, at the within-person level, we found that some of these relations occur reciprocally, in that directive leadership predicts engagement and, simultaneously, engagement positively predicts perceptions of both directive and empowering leadership. These findings challenge existing assumptions about the directionality of the association between perceived leadership and employee wellbeing and contribute to an enhanced understanding of the role of employee wellbeing for the development of leadership perceptions over time.

A Perturbation Approach for Lateral Excited Vibrations of a Beam-like Viscoelastic Microstructure Using the Nonlocal Theory

In this paper, we investigate the lateral vibration of fully clamped beam-like microstructures subjected to an external transverse harmonic excitation. Eringen’s nonlocal theory is applied, and the viscoelasticity of materials is considered. Hence, the small-scale effect and viscoelastic properties are adopted in the higher-order mathematical model. The classical stress and classical bending moments in mechanics of materials are unavailable when modeling a microstructure, and, accordingly, they are substituted for the corresponding effective nonlocal quantities proposed in the nonlocal stress theory. Owing to an axial elongation, the nonlinear partial differential equation that governs the lateral motion of beam-like viscoelastic microstructures is derived using a geometric, kinematical, and dynamic analysis. In the next step, the ordinary differential equations are obtained, and the time-dependent lateral displacement is determined via a perturbation method. The effects of external excitation amplitude on excited vibration are presented, and the relations between the nonlocal parameter, viscoelastic damping, detuning parameter, and the forced amplitude are discussed. Some dynamic phenomena in the excited vibration are revealed, and these have reference significance to the dynamic design and optimization of beam-like viscoelastic microstructures.

Deformation and stress theory of surrounding rock of shallow circular tunnel based on complex variable function method

After reviewing many literature foundations, the thesis combines the basic methods of elastic mechanics with mathematical knowledge, sets the bipotential stress potential complex function and analyses the relationship between stress component, strain component and stress potential function, and applies the complex variable function. The expression of the relevant stress component is derived, and the displacement boundary conditions of the surrounding rock of shallow circular tunnel are obtained. Furthermore, the paper applies the basic theory of complex variable function to solve the boundary condition complex variable function for common tunnel sections, and obtains the analytical expression of the surrounding rock stress of shallow circular tunnel. The simulation is carried out by finite element method. The establishment of complex variable function has a good application value in solving the stress of surrounding rock of shallow tunnel.

Groundwater Lowering for Construction of the Kilsby Tunnel – Geological and Geotechnical Interpretation

The Kilsby Tunnel, constructed in the 1830s, faced severe problems when a section of the tunnel, almost 400 m long, encountered unstable ‘quicksand’ conditions. The engineer for the project, Robert Stephenson, developed an extensive groundwater lowering scheme, unique for the time, using steam engines pumping from multiple shafts, to overcome the quicksand. Modern geological information indicates most of the tunnel was in Middle Lias bedrock, but the ‘quicksand’ section passed through a buried channel of water-bearing sand of glacial origin. In the early 19th century the impact of glacial processes on British geology was not widely accepted and, based on contemporary geological knowledge, Stephenson’s problems appear to be genuine unforeseen ground conditions, not predicted by his experienced advisers. It seems just random chance that trial borings missed the buried channel of sand. The work at Kilsby was two decades before Darcy’s law established the theoretical understanding for groundwater flow, and 90 years before Terzaghi’s effective stress theory described how reducing pore water pressures changed ‘quicksand’ into a stable and workable material. Despite the lack of existing theories, Stephenson used careful observations and interpretation of groundwater flow in the ‘quicksand’ to navigate the tunnel project to a successful conclusion.

Supercomplex organization of the electron transfer system in marine bivalves, a model of extreme longevity

The mitochondrial oxidative stress theory of aging (MOSTA) suggests that the organelle’s decay contributes to the aging phenotype via exacerbated oxidative stress, loss of organ coordination and energetics, cellular integrity and activity of the mitochondrial electron transfer system (ETS). Recent advances in understanding the structure of the ETS show that the enzymatic complexes responsible for oxidative phosphorylation are arranged in supramolecular structures called supercomplexes that lose organization during aging. Their exact role and universality among organisms are still under debate. Here, we take advantage of marine bivalves as an aging model to compare the structure of the ETS among species ranging from 28 to 507 years in maximal lifespan. Our results show that regardless of lifespan, the bivalve ETS is arrayed as a set of supercomplexes. However, bivalve species display varying degrees ETS supramolecular organization with the highest supercomplex structures found in A. islandica, the longest-lived of the bivalve species under study. We discuss this comparative model in light of differences in the nature and stoichiometry of these complexes, and highlight the potential link between the complexity of these superstructures and longer lifespans.

2D and 3D numerical simulation of fatigue crack growth path and life predictions of a linear elastic

This paper describes implementation of the finite element method (FEM) to investigate crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental and numerical data. The approach involved using two different software to compute stress intensity factors (SIFs), the crack propagation trajectory, and fatigue life estimation in two and three dimensions. According to the software, crack modeling might be run in various ways. The first is a developed source code program written in the Visual Fortran language, while the second is the widely used ANSYS Mechanical APDL 19.2 software. The fatigue crack propagation trajectory and the corresponding SIFs were predicted using these two software programs. The crack direction was investigated using the maximum circumferential stress theory, and the finite element (FE) analysis for fatigue crack growth was done for both software based on Paris's law. The predicted results in both software demonstrated the influence of holes on the crack growth trajectory and all associated stresses and strains. The study's findings agree with other experimental and numerical crack propagation studies presented in the literature that reveal similar crack propagation trajectory observations.