Fiber element modeling of circular double-skin concrete-filled stainless-carbon steel tubular columns under axial load and bending

Circular concrete-filled double-skin steel tubular (CFDST) columns with external stainless-steel are high-performance composite columns that have potential applications in civil construction including the construction of offshore structures, bridge piers, and transmission towers. Reflecting the limited research performed on investigating their mechanical performance, this study develops a computationally efficient fiber model to simulate the responses of short and slender beam-columns accounting for the influences of material and geometric nonlinearities. Accurate material laws of stainless steel, carbon steel, and confined concrete are implemented in the mathematical modeling scheme developed. A new solution algorithm based on the Regula-Falsi method is developed to maintain the equilibrium condition. The independent test results of short and slender CFDST beam-column are utilized to validate the accuracy of the theoretical solutions. The influences of various column parameters are studied on the load-axial strain [Formula: see text] curves, load-lateral deflection [Formula: see text] curves, column strength curves, and interaction curves of CFDST columns. Design formulas are suggested for designing short and beam-columns and validated against the numerical results. The computational model is found to be capable of simulating the responses of CFDST short and slender columns reasonably well. Parametric studies show that the consideration of the concrete confinement is important for the accuracy of the prediction of their mechanical responses. Furthermore, high-strength concrete can be utilized to enhance their load-carrying capacity particularly for short and intermediate slender beam-columns. The strengths of CFDST columns computed by the suggested design model are in good agreement with the test and numerical results.

Rapid Prototypable Biomimetic Peristalsis Bioreactor Capable of Concurrent Shear and Multi-axial Strain

Peristalsis is a nuanced mechanical stimulus comprised of multi-axial strain (radial and axial strain) and shear stress. Forces associated with peristalsis regulate diverse biological functions including digestion, reproductive function, and urine dynamics. Given the central role peristalsis plays in physiology and pathophysiology, we were motivated to design a bioreactor capable of holistically mimicking peristalsis. We engineered a novel rotating screw-drive based design combined with a peristaltic pump, in order to deliver multiaxial strain and concurrent shear stress to a biocompatible polydimethylsiloxane (PDMS) membrane “wall”. Radial indentation and rotation of the screw drive against the wall demonstrated multi-axial strain evaluated via finite element modeling. Experimental measurements of strain using piezoelectric strain resistors were in close alignment of model-predicted values (15.9 ± 4.2% vs. 15.2% predicted). Modeling of shear stress on the ‘wall’ indicated a uniform velocity profile and a moderate shear stress of 0.4 Pa. Human mesenchymal stem cells (hMSCs) seeded on the PDMS ‘wall’ and stimulated with peristalsis demonstrated dramatic changes in actin filament alignment, proliferation, and nuclear morphology compared to static controls, perfusion or strain, indicating that hMSCs sensed and responded to peristalsis uniquely. Lastly, significant differences were observed in gene expression patterns of Calponin, Caldesmon, Smooth Muscle Actin, and Transgelin, corroborating the propensity of hMSCs toward myogenic differentiation in response to peristalsis. Collectively, our data suggests that the peristalsis bioreactor is capable of generating concurrent multi-axial strain and shear stress on a ‘wall’. hMSCs experience peristalsis differently than perfusion or strain, resulting in changes in proliferation, actin fiber organization, smooth muscle actin expression, and genetic markers of differentiation. The peristalsis bioreactor device has broad utility in the study of development and disease in several organ systems.

Undrained Deformation Characteristics of Soft Marine Clay Subjected to One-Way Cyclic Loading with Variable Confining Pressure

To gain a better understanding of the undrained deformation characteristic of saturated marine clay soil subjected to vehicle cyclic traffic load, a sophisticated dynamic triaxial was used to conduct a variety of undrained one-way compression cyclic experiments with variable confining pressure (VCP) as well as constant confining pressure (CCP). The results indicate that, compared to CCP test results, VCP is helpful to raise the axial resilient modulus (Mr) and restrain the permanent plastic strain ( ε a p ) development of the specimens. By normalization analysis of the measured data of Mr and ε a p , the virtually unique correlation between normalized average resilient modulus, normalized permanent axial strain after 1,000 loading cycles, and normalized mean normal stress is established, respectively, regardless of the values of CSR. Additionally, the VCP influence on ε a p is quantified and fitted by a power law function, which can be used for subsoil deformation prediction and provides new insights into the mechanics of strain accumulation under undrained cyclic loading conditions.

Deformation Behavior and Damage-Induced Permeability Evolution of Sandy Mudstone Under Triaxial Stress

The permeability and mechanical behavior in sandy mudstone are crucial to the hazard prevention and safety mining. In this study, to investigate the evolution and characteristic of permeability and mechanical properties of mudstone during the in-site loading process, triaxial compression-seepage experiments were performed. The increase of permeability and decrease of mechanical strength gradually evaluated to the decrease of permeability and increase of mechanical strength subjected to the increase of confining stress from 5 to 15 MPa, which corresponds to the transformation from brittleness to ductility of mudstone, and the transformation threshold of 10 MPa confining stress was determined. The shear fractures across the sample at brittle regime, while shear fracture does not cross the sample or even be not generated at semibrittle and ductile state. The dynamic decrease, slight decrease, and residual response were determined in axial strain, and the divided zone increases with the increase of confining stress. The relatively higher permeability corresponds to the higher pore pressure as the increase of confining stress. The volumetric strain increases as the increase of confining stress, compared to that decrease correspond to the increase of the pore pressure, and the higher volumetric strain and the lower permeability. In addition, an improved permeability model was developed to describe the loading-based permeability behavior considering the Klinkenberg effect.

Effect of Reinforcement on Properties of Silty Sand

The variation of the stress-strain behavior and shear -parameters of reinforced silty sand is studied. The geotextiles were provided at different heights in the sample and tested in unconsolidated undrained condition. Two types of geotextiles, woven and nonwoven were used as reinforcement and the experiment was conducted at three water contents. Tests were performed on samples prepared at OMC, dry of OMC and wet of OMC in order to study the effect of water content. The results demonstrated that geotextile inclusion increases the peak strength, axial strain at failure. The sample was found to fail due to bulging between the layers. Keywords: Optimum Moisture Content, Maximum Dry Density, Unconsolidated Undrained, Deviator Stress, Normal Stress

Quasi-static compression behavior and microstructure changes in low-cost AA6061 composites

The workability study of the composites enhances the understanding of the degree of plastic deformation that can be employed on it. The current research work highlights the response of the low-cost aluminum composites reinforced with exhausted alkaline battery powders under quasi-static compression. The effect of reinforcements and aspect ratio against the strain hardening exponent and strength coefficients were investigated. The microstructural changes after quasi-static compression were studied and related to the changes in the property of the composites. The composite with 6 wt.% of reinforcement showed the least amount of porosity as 1.2%. In most of the cases, the maximum value of average strain hardening exponent with respect to axial strain was noted in the composites with 6 wt. % of reinforcement. The lowest aspect ratio of 0.5 showed the maximum workability in the composites. The average strength coefficient was found to be maximum (308.58 MPa) in the composite with 2 wt.% reinforcement. The elongated grains and slip bands were observed in the microstructure of the compressed specimens.

Magnetic State Switching in FeGa Microstructures

This work demonstrates that magnetoelectric composite heterostructures can be designed at the length scale of 10 microns that can be switched from a magnetized state to a vortex state, effectively switching the magnetization off, using electric field induced strain. This was accomplished using thin film magnetoelectric heterostructures of Fe81.4Ga18.6 on a single crystal (011) [Pb(Mg1/3Nb2/3)O3]0.68-[PbTiO3]0.32 (PMN-32PT) ferroelectric substrate. The heterostructures were tripped from a multi-domain magnetized state to a flux closure vortex state using voltage induced strain in a piezoelectric substrate. FeGa heterostructures were deposited on a Si-substrate for SQUID magnetometry characterization of the magnetic properties. The magnetoelectric coupling of a FeGa continuous film on PMN-32PT was characterized using a MOKE magnetometer with bi-axial strain gauges, and magnetic multi-domain heterostructures were imaged using X-Ray Magnetic Circular Dichroism – Photoemission Electron Microscopy (XMCD-PEEM) during the transition to the vortex state. The domain structures were modelled using MuMax3, a micromagnetics code, and compared with observations. The results provide considerable insight into designing magnetoelectric heterostructures that can be switched from an “on” state to an “off” state using electric field induced strain.

Modelling of Auxetic Woven Structures for Composite Reinforcement

The current research is focused on the design and development of auxetic woven structures. Finite element analysis based on computational modeling and prediction of axial strain as well as Poisson’s ratio was carried out. Further, an analytical model was used to calculate the same parameters by a foldable zig-zag geometry. In the analytical model, Poisson’s ratio is based on the crimp percentage, bending modulus, yarn spacing, and coefficient of friction. In this yarn, properties and fabric parameters were also considered. Experimental samples were evaluated for the actual performance of the defined auxetic material. Auxetic fabric was developed with foldable strips created in a zig-zag way in the vertical (warp) direction. It is based on the principle that when the fabric is stretched, the unfolding of the folds takes place, leading to an increase in transverse dimensions. Both the analytical and computational models gave close predictions to the experimental results. The fabric with foldable strips created in a zig-zag way in the vertical (warp) direction produced negative Poisson’s ratio (NPR), up to 8.7% of axial strain, and a maximum Poisson’s ratio of −0.41 produced at an axial strain of around 1%. The error percentage in the analytical model was 37.14% for the experimental results. The computational results also predict the Poisson’s ratio with an error percentage of 22.26%. Such predictions are useful for estimating the performance of auxetic woven structures in composite reinforcement. The auxetic structure exhibits remarkable stress-strain behavior in the longitudinal as well as transverse directions. This performance is useful for energy absorption in composite reinforcement.

Reinforced Soft Soil by CSV with/without Polypropylene fibres: Experimental and Numerical analysis.

Columns of mixed soil-sand-cement (CSV), is one of the most unknown used methods for soft soil stabilization that has not been studied before. To this end, in this paper, consolidated drained (CD) triaxial compression tests after have been cured for 28 days, were carried out to investigate the effectiveness of CSV, which is mainly used to reinforce soft soil. Then, the influence of soft soil content (25%, 50%, 75%) on materials of CSV with/without polypropylene (PP) fibers is established. The percentages of soft soils (50%, 75%) are experimentally doable and the remaining percentage (25%) was not successfully experimented; for this exact reason, an empirical formula is established based on the design of experiments (DOE) for calculating the soft soil’s characteristics. Then a numerical study using PLAXIS 3D is developed for studying the embankment building on soil which is reinforced by CSV. It is found that the efficacy of the reinforcement of the soft soil by CSV with/without PP fibers provides with satisfying results. Moreover, the less amount of soft soil on CSV materials the better for deviatoric stress, axial strain, the effective cohesion, the effective friction angle and modulus of elasticity E50. Additionally, when PP fibers is added to CSV material, experimental results were strongly affected. As far as the numerical study, the embankment building on the soil that is reinforced by the CSV shows an improvement in the level of displacement in the three directions, the total displacement and security factor. The variation of materials of CSV content with/without PP fibers, a diverse combination with a relatively lower effect can be easily remarked on the achieved results.