Experimental Investigation into Cyclic Shear Behaviors in the Interface Between Steel and Crushed Mudstone Particles

In the waterway construction projects of the upper streams of the Yangtze River, crushed mudstone particles are widely used to backfill the foundations of the rock-socketed concrete-filled steel tube (RSCFST) pile. The mudstone particles are prone to being crushed, which influences the mechanical properties of the soil and the interface between the soil and the steel cased on the RSCFST pile. The crushing of the particles will be aggravated by reciprocating shear of the interface when the pile experiences repeating lateral loads. The reciprocating shear of the interface may, therefore, weaken the bearing capacity of the pile. In this study, we develop a new apparatus to study the mechanical properties of the steel–soil interface under a reciprocating shear condition. With this apparatus, a set of large-scale direct shear experiments are carried out with two different boundary conditions, that is, a constant stress boundary and a constant stiffness boundary, respectively. Comparative experiments and parallel experiments are carried out to study the physical properties of steel–mudstone particle interface and the stability of the apparatus. Parallel experiments show that the instrument has good stability. The comparative experiment results also reveal the differences of the shear behaviors of the interface under two conditions. Analysis of the experiment results shows that the normal stiffness condition is closer to the real boundary condition when the soil–steel interface is cyclically sheared. The particle crushing and the attenuation of normal stress is the main reason causing the degrading of the interface.

FAILURE PERFORMANCE OF BEND-FREE VARIABLE STIFFNESS COMPOSITE PRESSURE VESSELS

Pressure vessels are designed to store liquids and gases and have various applications spanning from chemical plants to automotive and aerospace industries. Currently, lightweight composite pressure vessels are desirable, especially in transportation industry applications because of their subsequent benefits in fuel consumption, cost and environmental issues. Using composite materials for pressure vessels along with advanced manufacturing technologies such as automated fiber placement provides excellent scope to tailor stiffness through the structural surface using fiber steering to achieve desirable structural performance. Recently, variable angle tow (VAT) technology has been used to suppress bending in super ellipsoids of revolution composite pressure vessels, resulting in minimizing the inefficient bending stresses and deformations and increasing their load-carrying capacity. It is worth noting that such geometries can provide excellent packing efficiency. These advantages make the bend-free super ellipsoids of revolution composite pressure vessels potential candidates for the next generation of pressure vessels. Therefore, their failure performance as the most important design factor should be studied carefully due to safety reasons. In this study, the maximum allowable internal pressure for VAT bend-free ellipsoidal pressure vessels, using the first-ply failure based on both Tsai-Wu and three-dimensional invariant-based failure criteria is determined. Subsequently, VAT bend-free pressure vessels’ failure performance is compared against that obtained for conventional constant stiffness composite vessels. Among structures considered, the VAT bend-free composite vessel has the best failure performance. Moreover, the predicted failure load using the three-dimensional invariant-based failure criterion for the VAT bend-free design is 34% lower than the failure load predicted by the Tsai- Wu. Finally, the effect of various material properties on the difference in predicted failure load using these criteria is assessed. Results provide physical insight useful for designers in materials selection.

A Buckling Analysis and Optimization Method for a Variable Stiffness Cylindrical Pressure Shell of AUV

The composite cylindrical shell pressure structure is widely used for autonomous underwater vehicle (AUV). To analyze the critical buckling problem of variable stiffness (VS) composite pressure structure of AUV, a discrete finite element (DFE) method based on the curve fiber path function is developed in this work. A design and optimization method based on the radial basis function surrogate method is proposed to optimize the critical buckling pressure for a VS composite cylindrical shell. Both the DFE and surrogate methods are verified to be valid by comparison with the experimental data from the listed references. The effects of the geometric parameter and fiber angle on the critical buckling pressure are studied for different cylindrical shell cases. The results indicate that the proposed simulation model and optimization method are accurate and efficient for the buckling analysis and optimization of a VS composite cylindrical shell. Optimization result shows that the optimum critical buckling pressure for the VS cylindrical shell is improved and is 21.1% larger than that of the constant stiffness cylindrical shell under the same geometric and boundary condition.

Thermal and Thermo-Mechanical Properties of Poly(L-Lactic Acid) Biocomposites Containing β-Cyclodextrin/d-Limonene Inclusion Complex

Bio-based composites made of poly(L-lactic acid) (PLLA) and β-cyclodextrin/d-limonene inclusion complex (CD-Lim) were prepared by melt extrusion. Encapsulation of volatile d-limonene molecules within β-cyclodextrin cages was proven to be a successful strategy to prevent evaporation during high-temperature processing. However, small amounts of limonene were released upon processing, resulting in the plasticization of the polymeric matrix. Morphological analysis revealed good dispersion of the filler, which acted as a nucleating agent, favoring the growth of PLLA crystals. The composites′ lowered glass transition temperature upon the addition of CD-Lim was also proved by thermomechanical analysis (DMA). Moreover, DMA revealed constant stiffness of modified materials at room temperature, which is crucial in PLLA-based formulations.

ENHANCING STRUCTURAL RESPONSE USING INERTER DAMPERS

This paper deals with one kind of dampers which is inerter damper, Inerter is a new mechanical element proposed by Professor Malcolm C. Smith from Cambridge University, which is defined as a mechanical two-terminal, one-port device with the property that the equal and opposite force applied at the terminals is proportional to the relative acceleration between the terminals the principle work of inerter damper is how to convert the linear motion into rotational motion to mitigation the external excitation. Theoretical analysis was presented first part is the analytical study which made modeling for the damping structure proposed and get the equation of motion for the inerter behavior, secondly numerical analysis where the program (ANSYS WORK-Bench 18.2) was adopted, and study the parameters which effected on the damping behavior of inerter structure proposed that is (stiffness, coefficient of friction and mass of flywheel). Where it was found that when the stiffness of the springs increased gradually from (0.2, 0.3, 0.4, 0.6 and 0.8) Kn/mm the amplitude reduced from (25.791, 17.194, 12.896, 8.5974 to 6.4482) mm respectively for each stiffness reading, also the mass of inerter when increased gradually (200,400,600,800 and 1000) g with a constant coefficient of friction and constant stiffness 0.4, 0.6 Kn/mm respectively, the amplitude decrease from 6.3525 to 4.036290. Finally, to study the effect inerter mass on the structures, the mass of inerter increased from (200,400,600,800 to 1000) g gradually to the constant cantilever mass structure equal to 130g. The ratio of the inerter mass to the threshold mass is approximately 1.5 to 7.5 As results obtained from the previous study, the amplitude obtained for each mass (1.0778, 1.069, 1.0509, 0.9514 to 0.872) respectively

Influence of Rotational Stiffness Modeling on the Joint Behavior of Quasi-Rectangular Shield Tunnel Linings

A beam-spring model with constant rotational stiffness is a practical tool for the prediction of the general deformations and bending moments in circular tunnel linings. However, in reality, the rotational stiffness of a segmental joint is not constant, due to nonlinear deformations and local yielding in the vicinity of the joint. These are a result of the specific geometry at the joint, which is related to water-tightness measures and buildability issues. For quasi-rectangular tunnels this nonlinearity should not be neglected, as the bending component in the lining is significantly larger compared to circular linings. To date, there are only few studies that have investigated a calculation method for consideration of the joint’s nonlinear moment-axial force and shear-axial force interaction behavior and its consequences on the calculated lining behavior. In this paper, an iterative incremental method is proposed to tackle this issue, based on rotational stiffness curves derived from 3D nonlinear finite element modelling of the joints, and substantiated by testing. The significance of the variable rotational stiffness is highlighted through a comparison with results based on a constant stiffness assumption. Further, using the proposed calculation method, the effects of the circumferential joints, the bending moment transmission and several other parameters on the full-ring behavior of quasi-rectangular tunnels are discussed for a wide interval of design parameters. The results provide some new insights into the behavior of this non-traditional tunnel type. Although the presented results are related to specific overall and local geometries, the presented method is considered to be useful for the design of other special tunnel geometries.

Development and Evaluation of PVA-H 3D Printed Blood Vessel Biomodels With Several Stiffness

Biomodels, which are models of tissues such as blood vessels, have recently come into high demand for surgical training or medical device assessment use. Since the stiffness of blood vessels is not uniform, reproducing this nonuniformity would be advantageous to producing more realistic models, and to do this, we used a poly (vinyl alcohol) hydrogel (PVA-H) 3D printer. As a material, recently PVA-H has received increasing attention. This printing technique may be suitable for fabricating models composed of parts exhibiting different levels of stiffness (multipart models). However, the PVA-H 3D printer uses outer molds as supports. Outer mold removal as a post-process might affect the mechanical properties of the models or other post-processes such as ethanol substitution, and this requires investigation. Quality checks on the mechanical properties of the final product are also necessary. In this study, the effect of outer molds on the efficiency of ethanol substitution was estimated by measuring specimen weights. Additionally, the effect of the heat generated when molds were removed with an ultrasonic cleaner on the Young’s modulus of models was tested using tensile tests. Moreover, multipart pieces were fabricated, and their mechanical properties were measured. The findings were that ethanol substitution was able to be completed by conventional methods. Furthermore, the heat generation did not change the Young’s modulus of the models. Also, it was possible to fabricate multipart PVA-H models, and their level of stiffness followed the theoretical equation that assumes constant stiffness and independency of each part. The PVA-H 3D printer, therefore, has the potential to fabricate multipart models that will enable better surgical training and device assessments.