Tube Specimens Research Articles

Creep Buckling of 304 Stainless-Steel Tubes Subjected to External Pressure for Nuclear Power Plant Applications

The creep-buckling behaviors of cylindrical stainless-steel tubes subjected to radial external pressure load at elevated temperatures—800, 900, and 1000 °C—were experimentally investigated. Prior to the creep-buckling tests, the buckling pressure was measured under each temperature condition. Then, in creep-buckling experiments, the creep-buckling failure time was measured by reducing the external pressure load for two different tube specimens—representing the first and second buckling modes—to examine the relationship between the external pressure and the creep-buckling failure time. The measured failure time ranged from <1 min to <4 h under 99–41% loading of the buckling pressure. Additionally, an empirical correlation was developed using the Larson–Miller parameter model to predict the long-term buckling time of the stainless-steel tube column according to the experimental results. Moreover, the creep-buckling processes were recorded by two high-speed cameras. Finally, the characteristics of the creep buckling under radial loading were discussed with regard to the geometrical imperfections of the tubes and the material properties of the stainless steel at the high temperatures.

Axial impact behaviors of stub concrete-filled square steel tubes

Existing research on the widely used concrete-filled steel tubes is mainly focused on static or cyclic loading, and the studies on effects of high strain rate are relatively rare. In this article, seven stub concrete-filled steel tubular columns with square section were tested under both static and impact loads, using a large-capacity drop-weight testing machine. The research parameters were variable height of the drop-weight and different load types. The experimental results show that the failure modes of the concrete-filled steel tube columns from the impact tests are similar with those under static load, characterized by the local buckling of the steel tube. The time history curves of impact force and steel strain were investigated. The results indicate that with increasing impact energy, the concrete-filled steel tube stub columns had a stronger impact-resistant behavior. The dynamic analysis software LS-DYNA was employed to simulate the impact behaviors of the concrete-filled steel tube specimens, and the finite element results were reasonable compared with the test results. The parameter analysis on the impact behavior of concrete-filled steel tube columns was performed using the finite element model as well. A simple method was proposed to calculate the impact strength of square concrete-filled steel tube columns and compared favorably with experimental results.

Effect of Ammonium Sulphate ((NH<sub>4</sub>)<sub>2</sub> SO<sub>4</sub>) on Microstructure and Mechanical Properties of SA-213-Gr.T22 and SA-210-Gr.A1 Steel in the Water Tube Boiler

This paper presents the effect of an Ammonium sulphate (NH4)2 SO4) leak mixed in the boiler feed water system on the microstructure, chemistry, metallurgy and mechanical properties of the water tube boiler. Tube specimens were water tube and super-heated tube materials made from ferritic-pearlitic steel alloy grade SA-210-Gr.A1 and ferritic steel grade SA213-Gr.T22, respectively. Specimens were obtained from different height levels of the boiler and tested. The results from the emission spectrometer revealed that the carbon (C) and sulfur (S) did not concentrate inside the tube during five days of operation. Whereas the operating temperature causes the change in the microstructure and mechanical properties due to a segregation of phase and change of mechanical properties (hardness and tensile) in the used tube.

Experimental investigation of concrete-filled single-skin and double-skin steel oval hollow section stub columns

Both concrete-filled single-skin and double-skin steel tubular stub columns were investigated experimentally in this study. The skin of the composite columns was constructed using steel oval hollow section (OHS) tubes. A series of tests was performed to investigate the effects of the geometric dimension of steel OHS tube and concrete strength on the behaviour and strength of composite columns. The overall width-to-thickness ratio of the OHS tube sections ranged from 15.8 to 62.6. The structural performance of the composite columns was investigated using different nominal concrete cylinder strengths of 40, 70 and 100 MPa. The composite column lengths were chosen so that the length-to-width ratio generally remained at a constant value of 3 to prevent overall column buckling. The concrete-filled OHS tube specimens were subjected to uniform axial compression. The test strengths, load-axial shortening relationship and failure modes of the composite columns were presented in this paper. The test strengths were compared with the design strengths calculated using the American Specification and European Code for composite steel and concrete structures. It was shown that the design strengths do not agree well with the experimental results.

Crushing and energy absorption mechanisms of carbon fiber-epoxy tubes under axial impact

The energy absorption capability of carbon fiber-epoxy tubular specimens having closed circular and open C-shape cross-sections was investigated using experimental tests when focusing on the effect of the layup configuration. Specimens were subjected to a wide range of loading rates ranging from axial quasi-static compression to axial impact loading in order to reveal the deformation mechanism of CFRP samples. Several different combinations of mass and velocity of the striker were selected to study the possible effects on the crushing behavior of composite specimens. C-section specimens were used to investigate the effects of the cross-section shape on the crushing performance of carbon fiber material and to provide a better step-by-step visual understanding of the damage initiation and propagation in each layer due to quasi-static compression. It was observed that, in general, the different stacking sequences and loading conditions had minor effects on the SEA value of full-tube specimens while a significant difference between SEA values of C-section specimens with different layups was found. The calculated SEA value of C-section cross-plied specimens was lower than the SEA value of the full circular tubes having the same stacking sequence while an insignificant difference between the SEA values of C-section and full circular tube specimens of angle-ply layup configuration was observed. It was established experimentally that the removal of the outer layer with fibers oriented along the tube axis has no significant effect on the crushing force value under quasi-static compression. As a sequence, the SEA value increased due to the decrease of the total absorber weight.

Fatigue Life Prediction of Steam Generator Tubes by Tube Specimens with Circular Holes

Heat exchangers manufactured from Inconel 690 tubes are widely used for steam generators in nuclear power plants. Inconel 690 tubes have suffered failures of fatigue fracture due to flow induced vibration. It is difficult to obtain the fatigue life of the tube directly since the conventional fatigue test would potentially cause end fatigue failure due to the stress concentration at the clamp end. In this study, a thin-walled Inconel 690 tube with circular hole is designed to deduce the fatigue life of smooth tube based on the notch fatigue life prediction technology. Firstly, the local stress and strain distributions around the hole based on the finite element analysis are discussed. Local stress-strain is calculated and compared with Neuber’s ruler. Meanwhile, fatigue life tests using tube specimens with circular holes are carried out. Finally, based on the best-fitted fatigue life curve of Inconel 690 alloy, the fatigue life of tube specimen is estimated from the local strain according to Neuber’s ruler. The results show that the local stress and strain estimated by Neuber’s ruler are basically consistent with those obtained by finite element analysis. Compared with the average fatigue life of nickel-based alloy, the new predicted equivalent fatigue life of heat Inconel 690 transfer tube with a hole is higher. The Inconel 690 heat transfer tube has better fatigue performance.

Impact of External Quality Assurance on the Quality of Xpert MTB/RIF Testing in Viet Nam.

Following the endorsement of the Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA, USA) by the World Health Organization (WHO) in 2010, Viet Nam's National Tuberculosis Control Program (NTP) began using GeneXpert instruments in NTP laboratories. In 2013, Viet Nam's NTP implemented an Xpert MTB/RIF external quality assurance (EQA) program in collaboration with the U.S. Centers for Disease Control and Prevention (CDC) and the Foundation for Innovative New Diagnostics (FIND). Proficiency-testing (PT) panels comprising five dried tube specimens (DTS) were sent to participating sites approximately twice a year from October 2013 to July 2016. The number of enrolled laboratories increased from 22 to 39 during the study period. Testing accuracy was assessed by comparing reported and expected results; percentage scores were assigned; and feedback reports were provided to sites. On-site evaluation (OSE) was conducted for underperforming laboratories. The results from the first five rounds demonstrate the positive impact of PT and targeted OSE visits on testing quality. On average, for every additional round of feedback, the odds of achieving PT scores of ≥80% increased 2.04-fold (95% confidence interval, 1.39- to 3.00-fold). Future work will include scaling up PT to all sites and maintaining the performance of participating laboratories while developing local panel production capacity.

Histopathology of Surgically Resected Fallopian Tubes with Special Emphasis on Serous Tubal Intraepithelial Carcinoma

Background: The fallopian tube, though very common surgical specimen is rarely studied. It is affected by a spectrum of lesions ranging from inflammatory to rare neoplasms. Recent studies suggest a precursor lesion for high grade serous carcinoma of the ovary in the fallopian tube mucosa and is known as serous tubal intraepithelial carcinoma. In the present study, we analyzed the histopathology of fallopian tube lesions including serous tubal intraepithelial carcinoma. Methods: All the fallopian tube specimens received were grossed according to protocol and were routinely processed and stained. Atypical proliferative lesions of mucosa were subjected to immunohistochemical markers p53 and ki67. Result: Out of 350, 106 specimens showed a spectrum of lesions, of which hydrosalpinx was the commonest. Rest of the lesions were chronic and acute salpingitis, tuberculous salpingitis and tubal endometriosis. We encountered a single case of primary serous carcinoma of the fallopian tube. Immunohistochemistry on ten cases of atypical mucosal proliferations confirmed a single case each of serous tubal intraepithelial carcinoma and serous tubal intraepithelial lesion. Conclusion: Though fallopian tube is unremarkable in most cases, thorough sampling can detect significant pathological lesions including precursor lesions.

Effects of curvature on ductile fracture initiation in curved compact tension specimens of hydrided irradiated Zr-2.5Nb materials with split circumferential hydrides

The effects of curvature on K, J, plastic zone, near-tip stress and fracture initiation in curved compact tension (CCT) specimens of unhydrided and hydrided irradiated Zr-2.5Nb materials are determined by three-dimensional finite element analyses. Based on a strain-based failure criterion, the fracture initiation load for unhydrided CCT specimens is slightly lower than those for unhydrided compact tension (CT) and pressure tube (PT) specimens. For hydrided specimens, the reductions of fracture initiation loads for CT, CCT and PT specimens are similar. The fractions of fracture initiation loads for hydrided specimens are about 60–70% of those for unhydrided specimens.

Experimental Behaviour of Recycled Aggregate Concrete-Filled Steel Tubes Under Axial Loading

This study experimentally explores the behaviour of recycled aggregate concrete-filled steel tubes (RACFST) subjected to axial compression loading. Twenty-four RACFST specimens were tested to failure. For comparison purpose, tests were also performed on 12 normal concrete-filled steel tube (NCFST) specimens, three steel tubes and one specimen of recycled aggregate concrete. Obtained results showed that the RACFST demonstrates distinct mechanical properties, such as much higher strength, avoiding early buckling of steel and spalling of concrete, in comparison to steel tube and recycled aggregate concrete. This may result from mutually beneficial interaction between the steel tube and concrete. More importantly, in comparison to NCFST, RACFST exhibited marginally lower mechanical properties, similar scatter at peak stress and yet lower degradation after peak stress. Quantitative details of these comparisons are reported in the current paper, providing insightful information on the potential use of RACFST.

Lateral crashworthiness response of bombyx mori fibre/glass–fibre/epoxy hybrid composite cylindrical tubes-experimental

Experimental studies were undertaken to investigate the effect of reinforced fibre hybridization on the crushing characteristics of quasi-static laterally compressed cylindrical composite tubes. Woven glass fibre (GF) and woven bombyx mori fibre (B.mori) were used as reinforcements and industrial epoxy was used as the matrix material to fabricate the reinforced hybrid composite specimen. Three sets of specimen were fabricated, (1) glass fibre/epoxy (2) B.mori fibre/epoxy and (3) GF/B.mori/epoxy hybrid composite, to clearly ascertain the effect of reinforced fibre hybridization. Load-displacement curves and specimen’s deformation histories were used to analyze energy absorption and load carriability. The length of each specimen was 80 mm, three specimens were tested from each set and an average value recorded. Generally, the results showed that the hybrid composite tube specimen performed better when compared with the other tubes.

A notch critical plane approach of multiaxial fatigue life prediction for metallic notched specimens

AbstractAn approach based on the local stress response is proposed to locate the fatigue critical point for metallic blunt notched specimens under multiaxial fatigue loading. According to the stress analysis, both stress gradient and gradient of loading nonproportionality exist at notch root. The plane in the vicinity of the notch that passes through the fatigue critical point and experiences the maximum shear stress amplitude is defined as the critical plane for notch specimens (CPN). Furthermore, the Susmel's fatigue damage parameter is modified to assess fatigue life of notched components by combining CPN and the theory of critical distance (TCD). The multiaxial fatigue test of the thin‐walled round tube specimens made of Ni‐base alloy GH4169 is carried out to verify the above approaches. In addition, test data of two kinds of materials are collected. The results show that the maximum absolute error of the fatigue critical point is 9.6° and the majority of the predicted life falls within the three‐time scatter band.

An advanced experimental design for modified burst testing of nuclear fuel cladding materials during transient loading

An advanced tube-burst test system was designed to test samples of nuclear fuel cladding under conditions relevant to a postulated design-basis reactivity insertion accident (RIA) in light-water reactors. The system is based on the “driver tube” concept and allows for high-speed testing with internal pressure impulses of 10–1000 ms. To measure strain, the system was equipped with an ultra-high-speed video camera with a telecentric lens providing high focal depth, to compensate for specimen shift. A mirror system was developed to provide 360° view of the tube specimen into a single camera. Images taken during the test allow the use of a digital image correlation approach in strain evaluation. Several experiments were conducted to assess the performance of the experimental setup, and results are reported.

Theoretical Bending Collapse of Hat-Section Tubes

This paper presents an attempt to modify an existing theoretical model to predict the bending collapse response of hat-section tubular structures. The analytical collapse model was based on Kim and Reid. Additional hinge lines created during deformation of the tube were examined and integrated with existing model to forming a modified analytical solution. Variation of the hinge moments were solved using limit analysis technique. Procedure for developing the finite element (FE) models of tube specimens was also presented. Moment-rotation characteristics from pure bending simulation were compared with analytical model and good agreement was achieved. The average of differences between simulation and calculation were found to be <5% within plastic region. In conclusion, the modified analytical solution has adequate capability to predict the moment-rotation relationship of hat-section tubes subject to pure bending..

Networks of E-cadherin, β1 integrin, and focal adhesion kinase in the pathogenesis of tubal pregnancy

E-cadherin, β1 integrin, and focal adhesion kinase (FAK) are reported to involved in eutopic implantation by mediating cell adhesion. However, less is documented about their roles in ectopic implantation. This study was undertaken to evaluate the roles and networks of E-cadherin, β1 integrin, and FAK in tubal pregnancy. A total of 31 Fallopian tube specimens were obtained from tubal pregnant women. Immunohistochemistry and western blot were used to analyze the distributions and levels of E-cadherin, β1 integrin and phosphorylated-FAK (Pho-FAK) in the Fallopian tube epithelium. Normal Fallopian tube samples derived from non-pregnant women with benign genital diseases were used for comparison. E-cadherin presented in the cytomembrane of tubal epithelial cells and β1 integrin mainly expressed in the cytoplasm. A lowest-level of E-cadherin was detected in the implantation site (0.63 ± 0.29) when compared with the non-implantation site (0.95 ± 0.37) and the controls (0.89 ± 0.33) (P < 0.05). β1 integrin, as well as Pho-FAK in the implantation site (0.81 ± 0.35; 0.72 ± 0.24), showed a higher-level than that in the non-implantation site (0.59 ± 0.26; 0.48 ± 0.27) or the control group (0.38 ± 0.19; 0.36 ± 0.25) (p < .05). The decreased E-cadherin and increased β1 integrin are implicated in tubal pregnancy. The involvement of β1 integrin maybe depends on β1 integrin/FAK signaling.

Comparative investigation of ductile fracture with 316L austenitic stainless steel in small punch tests: Experiments and simulations

This paper deals with a small punch test and ductile failure prediction of austenitic stainless steel 316L. Comprehensive investigation of fracture surfaces was conducted as well as examination of δ-ferrite and σ-phase present in the material in order to reveal the reason of occurrence of nonstandard type of fracture. Three phenomenological ductile fracture criteria were selected for comparative simulations regarding the prediction of crack initiation and propagation during the SPT. These criteria were calibrated by using the fracture tests of smooth cylindrical specimens, notched cylindrical specimens, notched tube specimens and cylinders with spherical recess. The whole material model including the fracture criteria with von Mises plasticity and element deletion technique for simulation of the crack initiation was implemented by using the user subroutine Vectorised User MATerial into the commercial finite element code of Abaqus. Finally, the simulation results with three ductile fracture criteria are compared and discussed based on the experimental results. Only one of the failure criteria captured the displacement at fracture correctly.

Numerical Modeling of Nanostructured Tube Produced by ECAP

— tailoring material properties to specific application requirements is one of the major challenges in materials engineering. Grain size is a key factor affecting physical and mechanical properties of polycrystals materials. Grain size reduction in the metals and alloys can be achieved using Equal channel angular pressing (ECAP) method. In this work, Nanostructure thin walled copper tube specimens with 1 mm wall thickness and 23mm diameter have been produced successfully with ECAP method using flexible polyurethane rubber pad to prevent the tube walls from collapsing. Furthermore, this paper details the development of a numerical simulation to analyse the fabrication of thin walled tube through ECAP process. A copper tube was pushed through a channel with a series of 90° bends. During each successive bend, the magnitude of plastic strains accumulate in the copper tube. A three dimensional numerical simulation was used to model the process and determine the extent of plastic deformation that takes place during each bend process. The numerical simulation was developed using the finite element (FE) code, ABAQUS V6.13, and analysed using the explicit solver.

Specimen size effects on fracture behaviour of SiC/SiC tubes during circumferential tensile test

SiC fiber-reinforced SiC matrix (SiC/SiC) composites are expected as a high-temperature structural material for the application of aerospace and nuclear energy system due to their high-temperature stability, reduced-activation property, and excellent irradiation resistance. It was investigated the size effects of test specimen on the fracture behaviour and apparent strength of SiC/SiC tubes in order to minimize the size of test specimen, as well as to develop circumferential tensile test method for SiC/SiC fuel cladding of nuclear reactor. The tube specimens with a narrow width (less than 5 mm) represented the stable value of apparent strength. In case of wide width (>5 mm), the apparent strength of test specimen decreased with the increase in specimen width. It was observed that the fracture of the test specimen with wide width was initiated from the sides of test specimen due to the local contact between loading pin and the test specimen. It is required to use the material with high modulus as a loading pin material in order to avoid the stress concentration caused by local contact.

Dysregulated erythropoietin-producing hepatocellular receptor A2 (EphA2) is involved in tubal pregnancy via regulating cell adhesion of the Fallopian tube epithelial cells

BackgroundTyrosine kinase receptor erythropoietin-producing hepatocellular receptor A2 (EphA2) is abundant in the endometrium and plays a role in the establishment of eutopic implantation. A similar molecular mechanism may exist between uterine implantation and tubal implantation, therefore EphA2 involvement in tubal pregnancy is suspected. Due to the limited availability of human Fallopian tube specimens, EphA2 expression in human Fallopian tube epithelium remains largely unknown.MethodsA total of 31 women with tubal pregnancy and 41 non-pregnant women with benign uterine diseases were enrolled in this study. Immunohistochemistry was used to investigate the expression pattern of EphA2 in the Fallopian tube epithelium of non-pregnant women (n = 29) and women with tubal pregnancy (n = 17). The changes of EphA2 and its activated form, phosphorylated-EphA2 (Pho-EphA2), in the Fallopian tube epithelium from non-pregnant women (n = 12) and women with tubal pregnancy (n = 14) were compared by quantitative RT-PCR and western blot assay.ResultsEphA2 was expressed throughout the Fallopian tube epithelium, including the isthmus, the ampulla and the infundibulum. EphA2 concentration remained unchanged throughout the whole menstrual cycle, irrespective of menstrual phases and tubal regions. EphA2 mRNA in the Fallopian tube epithelium did not differ between normal women and women with tubal pregnancy (P > 0.05). With respect to the protein level, a significantly higher ratio of EphA2 over Pho-EphA2 was shown in women with tubal pregnancy (P < 0.05).ConclusionsEphA2 is widely expressed in human Fallopian tube epithelium in a temporospatial-independent manner. Dysregulated EphA2 and its phosphorylation-dependent regulatory mechanism may unexpectedly enhance the cell adhesion activity of the Fallopian tube epithelial cells, leading to a mis-contact between the Fallopian tube epithelium and the embryo.

High-cycle fatigue of rotating cantilever round copper tube under load-controlled condition

A cantilever rotating bending testing machine accepting only rod specimen with a fixed clamping diameter of 9 mm is modified for tube specimens using two developed adapters. One end of a ϕ15 mm copper tube is expanded into ϕ18 mm and forms the tube specimen. Two adapters fitting for ϕ15 mm and ϕ18 mm tube ends respectively are designed and fabricated. The ϕ15 mm adapter is connected to a shaft subject to an applied load and the ϕ18 mm adapter is connected to a motor, respectively through two collets. Both tube ends are adhered to the inner wall of the adapters with superglue to prevent slippery under the rotation. Finite element analysis is used to estimate the maximum applied stress in the tube specimen i.e. adjacent to the transition for a known counter weight. Only one fatigue test result i.e. at 2.2 × 106 cycles for applied stress of 205 MPa is successfully obtained from the experiment. The collets failed to clamp the adapters for applied stress higher or lower than 205 MPa due to the present of oxide powders resulting from the wear of the collect as it is a 15-year-old machine.