Eccentric Compressive Behavior of Round-Ended Rectangular Concrete-Filled Steel Tubes with Different Central Angles

The application of round-ended rectangular concrete-filled steel tubes (RRCFSTs) in high-rise buildings or bridge structures is increasing, improving structural performance and meeting aesthetic requirements. Researching this novel steel–concrete composite helps to fully utilize the properties of the materials. In this study, 15 specimens were tested for analysis of the behaviors of RRCFSTs with different central angles under eccentric compression. Influences of central angles of round ends (θ), aspect ratios of rectangular parts (κ), steel strength and the eccentric ratio on failure modes, material utilization, confinement effect and eccentric bearing capacity are studied. Besides, the mechanism of confinement effects of steel tubes with different θ values was evaluated with the finite element method (FEM). The results show that local bulking usually occurs at the compression zone. When θ gradually changes from 0° to 180°, the local bulking position of straight steel plate changes from mid-length to both ends of the columns. Additionally, the interfacial stress between steel tube and concrete at round ends rises, but that at the corner, it decreases continuously, which results in an improved overall confinement effect and increased material utilization. In contrast, a larger κ leads to lower material efficiency because of the reduced overall confinement effect. The increases in both θ and κ enlarge the cross-sectional area and the eccentric ultimate bearing capacity, whereas θ has a better influence on the ductility than κ. A feasible simplified calculating approach for the eccentric ultimate bearing capacity of RRCFSTs is presented and validated.

Theoretical background for simulation of physical processes in the interfacial layer “solid-liquid”

The paper shows a modification of the quasi-thermodynamic approach to simulation of the interfacial layer from conditions of its mechanical equilibrium. The anisotropy of the interfacial stress tensor is represented as the sum of the ball and deviator parts, where the ball part defines the pressure in the medium and the deviator part forms the components responsible for the liquid surface tension. Obtaining a closed system of equilibrium equations was possible taking into account evaporation from free surface of liquid. The result is a simple expression for determining the thickness of the interfacial layer.

Roof deformation and collapse of stamps with isolated grooves: a contact mechanics approach

This paper has revisited the roof deformation and collapse of stamps with isolated grooves based on a contact mechanics approach, with emphasis on establishing the non-adhesive and adhesive contact solutions for surfaces containing a shallow rectangular groove with the effects of applied load and interfacial adhesion taken into account. By solving singular integral equations and using the energy release rate approach, closed-form solutions are derived analytically for the deformed groove shapes, interfacial stress distributions and equilibrium relations between load and contact size, which reduce to the previously proposed solutions without adhesion or without applied load. Finite element analysis is performed to validate the non-adhesion solutions, while experiment results of stamp collapse reported in the literature are adopted to examine the adhesion solutions. By introducing the Johnson parameter a to represent a competition between surface energy and elastic strain energy of the groove, four kinds of contact behaviors of the groove roof can be characterized appropriately: non-adhesion, weak adhesion, intermediate adhesion and strong adhesion. Hysteresis loop and energy loss due to distinct load/unloading paths are revealed in the cases of intermediate and strong adhesion. We also provided the critical applied pressure to achieve roof collapse and the corresponding equilibrium contact size for full range of a.

A novel thermal-mechanical model and the characteristics of interfacial stress in the laminated structure for flexible electronics

Flexible electronics have attracted rapidly growing interest owing to their great potential utility in numerous fundamental and emerging fields. However, there are urgent issues that remain as pending challenges in the interfacial stress and resulting failures of flexible electronics, especially for heterogeneous laminates of hard films adhered to soft polymer substrates under thermal and mechanical loads. This study focuses on the interfacial stress of a representative laminated structure, that is, the Si film is adhesively bonded to soft polydimethylsiloxane with a plastic polyethylene terephthalate substrate. An novel thermal-mechanical coupling model for this flexible structure is established in this paper, which presents the essential characteristics of interfacial shear stress. In addition, under thermal and mechanical loads, a typical case is investigated by combining an analytical solution with numerical results using the differential quadrature method. Furthermore, thermal and mechanical loads, material and geometry parameters are quantitatively explored for their influences on the interfacial shear stress. Targeted strategies for decreasing stress are also suggested. In conclusion, the thermal-mechanical model and application case analyses contribute to enhancing the design of interfacial reliability for flexible laminated structures.

Comparison of polymerization stresses of dental resin composites evaluated by two indentation fracture methods

BACKGROUND: Polymerization stress is a major problem in dental resin composite restorations. Two indentation fracture methods can be applied to evaluate the stress, however, they often calculate different values. OBJECTIVE: To compare polymerization stresses of dental composites determined by the two methods. METHODS: Glass disks with a central hole were used. Two indentation fracture methods (Methods 1 and 2) were employed to determine the polymerization stresses of low-shrinkage and bulk-fill composites. Method 1: Cracks were made in the glass surface at 300 μm from the hole. The hole was filled with the composite. Polymerization stresses at 30 min after filling were calculated from the lengths of crack extension. Method 2: The hole was filled with the composite. Cracks were introduced in the glass at 1,000 μm from the hole at 30 min after the polymerization and the stresses were calculated from the crack lengths. Stresses at composite-glass bonded interface were calculated from the stress values obtained by the two methods. RESULTS: The bulk-fill composite generated the smallest interfacial stress, and Method 1 revealed lower values than Method 2. CONCLUSIONS: The composites yielded relatively small stresses. Method 1 calculated smaller stress values, possibly affected by the lower threshold stress intensity factor.