Experimental and Numerical Analysis of Ratcheting Behavior of SS 316 L Thin-Walled Pipes Subjected to Cyclic Internal Pressure

This paper investigates ratcheting behavior of SS316 L thin-walled steel pipes subjected to cyclic internal pressure experimentally and numerically. Numerical simulations were performed using abaqus software, and nonlinear isotropic/kinematic hardening model. According to experimentations, it was found that the ratcheting strain is only significant in the hoop direction of a pipe subjected to cyclic internal pressure. The effects of pressure amplitude and mean pressure on ratcheting behavior of thin walled pipe in hoop direction were studied experimentally and numerically, and it was observed that increasing the pressure amplitude and mean pressure increased the percentage of ratcheting strain. Another important point about the results was the dominance of pressure amplitude on mean pressure. The results showed that at higher mean pressures the effect of pressure amplitude on increasing the percentage of ratcheting strain was greater. Finally, the experimental and numerical results were in good agreement.

Effect of fiber angles on hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns under monotonic axial compression

Hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns are a novel form of hollow columns that combine two traditional construction materials (i.e. concrete and steel) with fiber-reinforced polymer composites. Hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns consist of an inner tube made of steel, an outer tube made of fiber-reinforced polymer, and a concrete layer between the two tubes. Existing studies, however, are focused on hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns with fibers of the fiber-reinforced polymer tube oriented in the hoop direction or close to the hoop direction. In order to investigate the effect of fiber angles (i.e. the fiber angle between the fiber orientation and the longitudinal axis of the fiber-reinforced polymer tube), monotonic axial compression tests were conducted on hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns with an fiber-reinforced polymer tube of ±45°, ±60°, or ±80° fiber angles. There were two types of steel tubes adopted for these hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns. The fiber-reinforced polymer tube thickness was also investigated as an important parameter. Experimental results showed that the confinement effect of the fiber-reinforced polymer tube increased with the increase of the absolute value of fiber angles, whereas the ultimate axial strain of hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns decreased with the increase of the absolute value of fiber angles. An existing stress–strain model, which was developed on the basis of hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns with an fiber-reinforced polymer tube of ±90° fiber angles, is verified using the test results of this study. For the compressive strength of the confined concrete in hybrid fiber-reinforced polymer–concrete–steel double-skin tubular columns, the existing model provides conservative predictions for specimens with a ±80° fiber-reinforced polymer tube, overestimated predictions for specimens with a ±60° fiber-reinforced polymer tube, and close predictions for specimens with a ±45° fiber-reinforced polymer tube.

The influence of coupling on the whole process of construction simulation of chord dome structure

：Chord dome structure is a new type of hybrid prestressed spatial steel structure system, which is often used in large-span structures. During the construction of the structure, it is necessary to apply prestress to the ring cable. Taking the chord dome roof of Hebei North University gymnasium as an example, the whole process of prestressed cable construction is simulated and analyzed by using the finite element software ANSYS. The hoop cable of the dome roof can slide freely in the hoop direction, and the attribute of free sliding in the ANSYS interface is "coupling". In this paper, two kinds of simulation models, coupling and uncoupling, are established to compare, and then to explore the influence of coupling on the construction process of string dome structure.

Effect of Fiber Angles on Hybrid Double-Tube Concrete Columns under Monotonic Axial Compression

Hybrid double-tube concrete columns (hybrid DTCCs) are a novel form of hybrid columns that combine fiber-reinforced polymer (FRP) composites with two traditional construction materials (i.e., concrete and steel). Hybrid DTCCs consist of an outer FRP tube and an inner steel tube aligned concentrically, with the space between the two tubes and inside of the steel tube filled with concrete. The three materials (i.e., FRP, concrete, and steel) in hybrid DTCCs are combined optimally to deliver excellent performances, such as excellent ductility and remarkable corrosion resistance. Recently, hybrid DTCCs have received increasing research attention on their compressive behavior. Existing studies, however, are focused on hybrid DTCCs with fibers of the FRP tube oriented in the hoop direction or close to the hoop direction. Against this background, this paper presents a series of monotonic axial compression tests on hybrid DTCCs with a particular focus on the effect of fiber angles (i.e., the angle of the fiber orientations to the longitudinal axis of the FRP tube). Three types of fiber angles (i.e., ±45°, ±60°, or ±80°) and two FRP tube thicknesses (i.e., 4 mm and 8 mm) were employed in the present study. Experimental results show that the concrete in hybrid DTCCs is well confined by both the FRP tube and the steel tube, leading to excellent ductility; the confinement effect of the FRP tube increases with the increase of the absolute value of fiber angles, whereas the ultimate axial strain decreases with the increase of the absolute value of fiber angles. An existing analysis-oriented model, which considers the different confining states of the concrete between the two tubes and that inside of the steel tube, is verified using the present test results. The model is capable of providing accurate predictions for hybrid DTCCs with a ±80° FRP tube. For hybrid DTCCs with a ±45° or ±60° FRP tube, the model yields reasonable accurate predictions for the peak axial load but underestimates the ultimate axial strain consistently.

Inflation and rupture of vaginal tissue

Around 80% of women experience vaginal tears during labour when the diameter of the vagina must increase to allow the passage of a full-term baby. Current techniques for evaluating vaginal tears are qualitative and often lead to an incorrect diagnosis and inadequate treatment, severely compromising the quality of life of women. In order to characterize the failure properties of the vaginal tissue, whole vaginal tracts from rats ( n = 18) were subjected to free-extension inflation tests until rupture using a custom-built experimental set-up. The resulting deformations were measured using the digital image correlation technique. Overall, the strain and changes in curvature in the hoop direction were significantly larger relative to the axial direction. At a failure pressure of 110 ± 23 kPa (mean ± s.d.), the hoop and axial stresses were computed to be 970 ± 340 kPa and 490 ± 170 kPa, respectively. Moreover, at such pressure, the hoop and axial strains were found to be 12.8 ± 4.4 % and 6.4 ± 3.7 % , respectively. Rupture of the vaginal specimens always occurred in the hoop direction by tearing along the axial direction. This knowledge about the rupture properties of the vaginal tissue will be crucial for the development of clinical approaches for preventing and mitigating vaginal tearing and the associated short- and long-term traumatic conditions.

Efficiency of Carbon Fibre Buckle Arrestors for Subsea Pipelines

This paper experimentally investigates the feasibility and efficiency of using Carbon Fiber Reinforced Polymer (CFRP) buckle arrestors in controlling the buckle propagation failure of subsea pipelines. Hyperbaric chamber tests are conducted on 1.6m Steel pipe with D/t = 28 and using CFRP buckle arrestors with different thickness, fiber orientation and spacing. Using an external pressure gauge and a high-pressure camera inserted inside the hyperbaric chamber, the pressure magnitude, rate and shape of collapse and its propagation in the vicinity of the arrestors are measured. The dynamics of buckle propagation and efficiency of different arrestor configurations are reported. It is observed that in the vicinity of the CFRP arrestors wrapped in the hoop direction, the well-known dog-bone buckle shape changes into a U-shape and the pressure level upsurges significantly. The optimum results were obtained with CFRP as thick as the pipeline wall-thickness and wrapped in the hoop direction of the pipeline. The results show that at similar arrestor efficiency, the CFRP arrestors can be much thinner than the existing steel slip-on arrestors. Also, the spacing between the CFRP arrestor can be larger than that of the steel slip-on arrestor.

Biaxial-EDC Test Attempts With Pre-Cracked Zircaloy-4 Cladding Tubes

When the pellet-cladding mechanical interaction (PCMI) occurs in a reactivity-initiated accident (RIA), the states of stress and strain in the fuel cladding varies in a range depending on the friction and degree of bonding between cladding and pellet. Japan Atomic Energy Agency has developed the improved Expansion-due-to-compression (EDC) test apparatus to investigate the PCMI failure criterion of high-burnup fuel under such conditions. In this study, the failure behavior of cladding tube was investigated by using the improved EDC test apparatus. Cold-worked, stress-relieved and recrystallized Zircaloy-4 tubes with a pre-crack were used as test specimens: this pre-crack simulated the crack which is considered to form in the hydride rim of high-burnup fuel cladding at the beginning of PCMI failure. In the EDC test, a tensile stress in axial direction was applied and displacement-controlled loading was performed to keep the strain ratio of axial/hoop as a constant. The data of cladding deformation had been achieved in the range of strain ratio of 0, 0.25, 0.5 and 0.75 and pre-crack depth of 41–87 micrometers. Failures in hoop direction were observed in all the tested samples, and a general trend that higher strain ratio and deeper crack depth lead to lower failure limit in hoop direction could be seen. Different crack propagation mode was observed between recrystallized and stress relieved and cold worked samples, which might be due to the difference in microstructure caused by the final heat treatment at the fabrication of cladding.