Tube Specimens Research Articles

A Stable Dried Tube Specimen for Quality Assurance and Training Programs for HIV Rapid Test for Recent Infection.

The HIV epidemic is still one of the world's most serious public health challenges, affecting about 38 million people worldwide, especially in sub-Saharan African and Southeast Asian countries. In recent years, tests have been developed to discriminate recent from long-term infection in HIV-infected populations, and these tools can help identify new outbreaks and networks of transmission and target prevention and treatment plans. New rapid tests for recent infection are being deployed in point-of-care settings; however, quality assurance programs need to be implemented to ensure consistency and reliability of the results. We have developed a dried tube specimen (DTS) stabilized with disaccharide trehalose as a quality control reagent for rapid recency testing that can be stored unrefrigerated prior to reconstitution at temperatures up to 37°C for up to 12 weeks. Analysis of 10 trehalose-stabilized DTSs showed that they maintained the same recency classification in all of the samples stored at 4°C and 37°C up to 12 weeks and at 56°C for 2 weeks, while the DTSs prepared without trehalose changed their classification from long-term to recent or recent to negative after storage at 37°C for 12 weeks. Development of DTS quality control reagents will facilitate proficiency and training programs, particularly in settings without cold chain capability in field environments. IMPORTANCE Implementation of stabilized dried tube specimens (DTSs) for quality control and training would facilitate HIV recency programs, especially in point-of-care settings without cold chain availability. This study shows that addition of the disaccharide trehalose to DTSs prior to drying the samples increased stability of the samples across a range of temperatures. This finding provides an affordable way to increase the availability of these key reagents for quality control in resource-constrained settings.

Flexural behavior of circular concrete filled steel tubes with partially incorporated demolished concrete lumps

For the past decade, researchers have been experimenting with the use of Demolished Concrete Lumps (DCLs) in structural members, as it has been proven to be a promising method to recycle concrete in different field applications. Although there have been several studies on incorporating DCLs in Concrete Filled Steel Tube (CFST) members, there are no studies that evaluate its effect on the flexural performance of CFST beams. Therefore, this paper focuses on studying the flexural behavior of CFST beams with DCLs, where the DCLs are inserted at the center of the cross-section. In total, fourteen circular CFST and two circular Steel Tube (ST) specimens were tested under bending using a four-point loading setup. The specimens are categorized into two different steel tube sections, where two circular sections of D/t = 55 (C1) and D/t = 45 (C2) were considered. The CFST specimens within each steel tube category differ in DCLs particle sizes and DCLs inner occupation area. CFST beams filled completely with normal concrete were also tested as control specimens. In addition, two CFST specimens from the steel section C2 were left partially hollow at the center to study the contribution of DCLs to the overall flexural performance. The results were very promising as the flexural behavior of DCL CFST specimens was very similar to the control CFST specimens. The DCLs’ particle sizes and the inner occupation area had minimal effect on the ductility, stiffness, yielding capacity, and ultimate capacity of the CFST specimens. The maximum percentage reduction in the flexural capacity between DCL CFST and control specimens were less than 2% for both sections whereas the percentage gain was up to 7%. Furthermore, the obtained flexural capacities were compared with nominal predictions from different design codes and models. All codes underestimated the capacities of all CFST specimens, with Han's model being the most conservative, followed by EC4, BS-5400–5, and AISC-LRFD, respectively.

Static strength of CFRP-strengthened preloaded circular concrete-filled steel tube stub columns, Part I: Experimental test

In the process of strengthening circular concrete-filled steel tube (CFST) stub columns in servicing period with carbon fiber reinforced polymer (CFRP), the CFST stub columns are generally preloaded. This study concerns the efficiency of CFRP in strengthening preloaded CFST stub columns. Thirteen specimens are designed and tested under axial compression, including two un-strengthened CFST specimens, four circular CFRP-strengthened concrete-filled steel tube (CFRP-CFST) specimens without preloading and seven preloaded CFRP-CFST specimens. The failure process, the failure mechanism, and the static strengths of the specimens, including yield strength and ultimate strength, are analyzed based on the experimental results. Improvement of the static strengths of the CFRP-strengthened specimens is discussed. The effect of preloading and CFRP layers on the static strength is investigated. The results show that preloading has certain effect on the yield strength. However, its effect on the ultimate strength is very little and it can be ignored. Increasing CFRP layers can improve the strengths of the preloaded CFST specimens effectively.

Acinetobacter baumannii in suspected bacterial infections: Association between multidrug resistance, virulence genes, & biofilm production.

Acinetobacter baumannii has emerged as a nosocomial pathogen with a tendency of high antibiotic resistance and biofilm production. This study aimed to determine the occurrence of A. baumannii from different clinical specimens of suspected bacterial infections and furthermore to see the association of biofilm production with multidrug resistance and expression of virulence factor genes in A. baumannii. A. baumannii was confirmed in clinical specimens by the detection of the blaOXA-51-like gene. Biofilm production was tested by microtitre plate assay and virulence genes were detected by real-time PCR. A. baumannii was isolated from a total of 307 clinical specimens. The isolate which showed the highest number of A. baumannii was an endotracheal tube specimen (44.95%), then sputum (19.54%), followed by pus (17.26%), urine (7.49%) and blood (5.86%), and <2 per cent from body fluids, catheter-tips and urogenital specimens. A resistance rate of 70-81.43 per cent against all antibiotics tested, except colistin and tigecycline, was noted, and 242 (78.82%) isolates were multidrug-resistant (MDR). Biofilm was detected in 205 (66.78%) with a distribution of 54.1 per cent weak, 10.42 per cent medium and 2.28 per cent strong biofilms. 71.07 per cent of MDR isolates produce biofilm (P<0.05). Amongst virulence factor genes, 281 (91.53%) outer membrane protein A (OmpA) and 98 (31.92%) biofilm-associated protein (Bap) were detected. Amongst 100 carbapenem-resistant A. baumannii, the blaOXA-23-like gene was predominant (96%), the blaOXA-58-like gene (6%) and none harboured the blaOXA-24-like gene. The metallo-β-lactamase genes blaIMP-1 (4%) and blaVIM-1(8%) were detected, and 76 per cent showed the insertion sequence ISAba1. The majority of isolates studied were from lower respiratory tract specimens. The high MDR rate and its positive association with biofilm formation indicate the nosocomial distribution of A. baumannii. The biofilm formation and the presence of Bap were not interrelated, indicating that biofilm formation was not regulated by a single factor. The MDR rate and the presence of OmpA and Bap showed a positive association (P<0.05). The isolates co-harbouring different carbapenem resistance genes were the predominant biofilm producers, which will seriously limit the therapeutic options suggesting the need for strict antimicrobial stewardship and molecular surveillance in hospitals.

Fretting Fatigue Test and Simulation Analysis of Steam Generator Heat Transfer Tube

In a steam generator, the heat transfer tubes are supported by the contact with support plates and anti-vibration bars. The two-phase flow flows over the tubes and causes a vibration when operating. In fatigue analysis, the heat transfer tube is simplified to a beam model, and the contacts with the support plates and the anti-vibration bars are simplified as simple-supported boundary conditions. This linear simplification improves the computational efficiency but cannot simulate the actual situation of the contact area. In consideration of this situation, in the actual analysis, a downwards modified S–N fatigue curve is used to envelop the fretting. For different materials and contact pressure, this modification needs to be obtained through experimental and computational analysis. In this paper, the effect of fretting on fatigue performance of heat transfer tube material 690 alloy is discussed by means of high cycle fretting fatigue test of tube specimen in room temperature air, low cycle fretting fatigue test of sheet specimen in high temperature water environment, and SWT (Smith–Watson–Topper) fretting fatigue predicting simulation, and the conservatism of design fatigue curve is discussed. It is shown that, in range of low cycle and high cycle, the fatigue strength is lower than the mean curve, but it can still be enveloped by the design curve of ASME (the American Society of Mechanical Engineers). However, under the condition of ultra-high cycle, the design curve of ASME can no longer envelop the effect of fretting on fatigue performance, so a further downward modification is necessary to ensure the safety of design.

Expression and T cell regulatory action of the PD-1 immune checkpoint in the ovary and fallopian tube.

Immune cell trafficking and surveillance within the ovary and fallopian tube are thought to impact fertility and also tumorigenesis in those organs. However, little is known of how native cells of the ovary and fallopian tube interact with resident immune cells. Interaction of the Programmed Cell Death Protein-1 (PD-1/PDCD-1/CD279) checkpoint with PD-L1 is associated with downregulated immune response. We have begun to address the question of whether PD-1 ligand or its receptors (PD-L1/-L2) can regulate immune cell function in these tissues of the female reproductive tract. PD-1 and ligand protein expression was evaluated in human ovary and fallopian tube specimens, the latter of which included stages of tubal cell transformation and early tumorigenesis. Ovarian expression analysis included the determination of the proteins in human follicular fluid (HFF) specimens collected during in vitro fertilization procedures. Finally, checkpoint bioactivity of HFF was determined by treatment of separately-isolated human T cells and the measurement of interferon gamma (IFNγ). We show that membrane bound and soluble variants of PD-1 and ligands are expressed by permanent constituent cell types of the human ovary and fallopian tube, including granulosa cells and oocytes. PD-1 and soluble ligands were present in HFF at bioactive levels that control T cell PD-1 activation and IFNγ production; full-length checkpoint proteins were found to be highly enriched in HFF exosome fractions. The detection of PD-1 checkpoint proteins in the human ovary and fallopian tube suggests that the pathway is involved in immunomodulation during folliculogenesis, the window of ovulation, and subsequent egg and embryo immune-privilege. Immunomodulatory action of receptor and ligands in HFF exosomes is suggestive of an acute checkpoint role during ovulation. This is the first study in the role of PD-1 checkpoint proteins in human tubo-ovarian specimens and the first examination of its potential regulatory action in the contexts of normal and assisted reproduction.

A unified method to estimate J-resistance curve of thin-walled metallic tube containing axial cracks

Fracture toughness of thin-walled metallic tubes is an important mechanical property index to ensure their safety in service. Because of the particularity of geometric structure, the fracture toughness test of thin-walled metallic tubes cannot be carried out using traditional standard specimens. In this work, the expressions of load–displacement relationship and J-integral of thin-walled tube specimens containing bilateral axial cracks are proposed based on the energy density equivalence principle, in which the effect of material and specimen geometry has been considered. Through three-dimensional finite element simulation analysis, the relevant parameters of the expression are obtained and validated, and then a fracture toughness test method for thin-walled metallic tubes is established. The method is applicable to the fracture toughness measurement of thin-walled metallic tubes with different sizes and materials. Finally, the fracture toughness tests of two thin-walled alloy tubes were completed by the new method, and the J-resistance curves were obtained.

A correlation-based approach for evaluating mechanical properties of nuclear fuel cladding tubes

The present work offers and evaluates a correlation-based approach to determine the tensile properties of nuclear fuel cladding tubes. A set of model materials with known properties (i.e., austenitic and ferritic steels, fcc- and hcp-alloys) were tested to build a correlation between conventional tensile tests and ring (hoop) and tube (axial) tests. It was shown that close-to-linear relationships exist for the basic mechanical properties (i.e., yield and ultimate stress, uniform and total elongation) between the uniaxial tensile test data and the ring and tube test data. Using the ring and tube specimen geometries, the feasibility of the approach was demonstrated via manufacturing and testing specimens from irradiated Zr and FeCrAl nuclear fuel cladding tubes. Limitations caused by specific deformation mechanisms (e.g., high ductility of 304L steel) were discussed in detail. The approach can be extended to other tubular products with different geometry and dimensions.

Compressive behavior of stiffened steel tubes for wind turbine towers

Steel tubes adopted in wind turbine towers generally sustain the combination of compression, bending, and torsion loads. The study of compressive behavior is crucial for investigating the combined bearing capacity of the tower and proposing the corresponding design method. Local buckling tends to affect compressive behavior due to the large diameter-to-thickness ratios of the tubes. Thus, the authors proposed a new form of tower based on longitudinally stiffened steel tubes, which were experimentally and analytically studied in this paper. A total of six tube specimens (four stiffened ones and two unstiffened ones) were tested under axial compression. The experimental results indicate that the local buckling of the tube can be substantially prevented by stiffeners and the T-type stiffener exhibits a superior effect. Finite element models were built and validated by the test results, and the parametric analysis was conducted, indicating that the diameter-to-thickness ratio of the steel tube, the yield strength of steel, and the proportion of stiffener area are the prime sensitive parameters affecting the ultimate strength. Ultimate compressive strength prediction methods in design specifications were evaluated. A practical method for calculating the ultimate strength of stiffened steel tubes was subsequently developed in this paper.

Thermomechanical fatigue of round tube specimens manufactured by precision directional solidification casting method

AbstractIn the present study, a superalloy round tube specimen prepared by directional precision casting without mechanical turning is experimentally investigated under the thermomechanical fatigue conditions of the in‐phase and out‐of‐phase thermomechanical angels from 500°C to 1000°C. The deformation behavior and damage mechanism of the round tube specimens under TMF load are discussed. It was confirmed that the tension–compression asymmetry under TMF cycling is affected by temperature–load phasing and mechanical strain range. Moreover, the damage to round tube specimens includes creep, fatigue and oxidation. Due to the concentrated stress, the rough surface of the specimen provides suitable locations for crack initiation. A novel life prediction approach that combines the Neu–Sehitoglu model and modified Manson–Coffin model was proposed in response to the traditional life model's insufficient prediction performance. This method may explain the TMF life of precision cast specimens.

Hydriding, Oxidation, and Ductility Evaluation of Cr-Coated Zircaloy-4 Tubing

Accident-tolerant fuel concepts have been developed recently in diverse research programs. Recent research has shown clear advantages of Cr-coated Zr cladding over bare cladding tubes regarding oxidation behavior under the design basis loss-of-coolant accident condition. However, limited data are available about the hydriding behavior of the Cr coating. For that purpose, Cr-coated Zricaloy-4 tubes were tested to investigate the effects of hydriding, oxidation, and postquench ductility behavior on coated Zr cladding. A high-power impulse magnetron sputtering (HiPIMS) process was used to produce a high-density coating on the Zircaloy-4 tube surface. Coated and uncoated Zircaloy-4 tube specimens underwent one-sided hydriding in a tube furnace filled with pure hydrogen gas at 425 °C. The tubing specimen ends were sealed with Swagelok plugs before the hydriding runs. For uncoated specimens, H analysis of the hydrided specimens indicated that the H content increased as the test time and initial pressure increased. However, almost no change was observed for the coated specimens that were hydrided under the same test conditions. After one-sided hydriding, the hydrided coated and uncoated specimens were exposed to steam at high temperatures for two-sided oxidation studies to simulate accident conditions. The coated specimens showed a slower oxidation: oxygen pickup was 50% lower than the uncoated specimens tested under the same conditions. Ring compression testing was performed to evaluate the embrittlement behavior of the Cr-coated specimens after hydriding and oxidation. The results indicated that the HiPIMS coating provides excellent protection from hydriding and oxidation at high temperatures.

Linear and nonlinear electro-elastic/electro-damping effect in ferroelectric ceramics

The linear piezoelectric and nonlinear hysteresis behaviors of ferroelectrics are well-known and have been extensively studied. However, less attention has been paid to the variations of their mechanical properties under electric loading. In this work, using tube and cylinder specimens, three independent elastic coefficients and related internal frictions of PZT-5H ferroelectric ceramics are measured using our proposed modified piezoelectric ultrasonic composite oscillator technique (M-PUCOT) under an electric field E3 along the poling direction. Results show that under low electric fields, the elastic coefficients s11E, s66E and all internal frictions decrease linearly with E3, whereas s44E increases linearly with E3. Based on these linear results, two fifth-order tensors are defined, i.e., linear electro-elastic and linear electro-damping tensor with the reduced symbol of pikl and qikl, among which p311, p366, p344 and q311, q366, q344 are obtained in this work. When the applied electric field exceeds the coercive field (∼500 V/mm), nonlinear electro-elastic/electro-damping effect dominates, resulting in reversed butterfly curves for s11E and s66E and butterfly curves for s44E. As to the internal frictions under large bipolar fields, they seem to be a superposition of the reversed butterfly curves and a peak or valley at the coercive field. The linear electro-elastic effect in ferroelectric ceramics is caused by the reversible domain wall motions while the nonlinear electro-elastic effect is caused by non-180° domain switching and is well reproduced by a statistical model. The linear and nonlinear electro-elastic/electro-damping results obtained in this work offer new insight into the electromechanical coupling behavior of ferroelectric materials.

Concrete-Filled Prefabricated Cementitious Composite Tube (CFPCCT) under Axial Compression: Effect of Tube Wall Thickness.

Research on different prefabricated cementitious composites for constructing composite concrete columns is comparatively more limited than that of concrete filled steel tube columns. The main objective of this study was to observe the axial compressive behavior of concrete-filled prefabricated cementitious composite tube (CFPCCT) specimens. In the CFPCCT composite column, the spiral steel bar is arranged as a hoop reinforcement in the cementitious tube before its prefabrication. Following this, the concrete is poured into the prefabricated cementitious composite tube. The tube is able to provide lateral confinement and can carry the axial load, which is attributed to the strength of CFPCCT composite column. The effect of tube wall thickness on the behavior of CFPCCT is studied in this research. A total of eight short-scale CFPCCT composite columns, with three different tube wall thicknesses (25 mm, 30 mm and 35 mm), are tested under axial compressive load. The cementitious composite tube-confined specimens showed a 24.7% increment in load-carrying capacity compared to unconfined specimens. Increasing the wall-thickness had a positive impact on the strength and ductility properties of the composite column. However, poor failure behavior was observed for thicker tube wall. Therefore, concrete-filled cementitious composite tube columns can be considered as an alternative and effective way to construct prefabricated concrete columns.

Progressive axial crushing behaviour of Al6061-T6 alloy tubes with geometrical modifications under impact loading

Axial crushing of tubes with multiple patterns of cut-outs is studied using numerical analysis. Commercially available finite element ABAQUS/Explicit® package is used to simulate the model under impact loading condition. Split-Hopkinson Pressure Bar (SHPB) is modelled to dynamically test the tube specimens with and without cut-outs. Number, size, and shape of cut-outs are kept constant in all specimens to have a constant weight reduction. In order to improve the crashworthiness characteristics of tubes, cut-outs are arranged on a tube surface along the circumferential and longitudinal direction in multiple rows. Crashworthiness parameters i.e., peak and mean collapse load, crushing efficiency, energy absorption characteristics are studied. The results revealed that a moderate weight reduction of tube can significantly affect the crushing characteristics of tube. In terms of load characteristic values, only 1% of weight reduction in modified tube samples has helped in 4.46% peak load reduction as compared to the normal tube, and crushing efficiency of the modified tube (T2) is found to be 2.17% higher than normal tube (T). In terms of energy absorption characteristic values, 1% of weight reduction in modified tube samples has helped in 1.95% reduction in energy absorption capacity as compared to the normal tube, and energy efficiency of modified tube (T2) is found to be 2.56% higher than the normal tube (T). After arranging the cut-outs in a multiple pattern, the location of cut-out is also seen to be influencing on the tube behaviour. It helps the tube to reduce the initial peak collapse load and optimize the mean collapse load. Further, force–deformation characteristics are also discussed to improve the crashworthiness characteristics of tube under impact load.

Freeze-thaw behaviour of basalt fibre reinforced recycled aggregate concrete filled CFRP tube specimens

This paper is focused on the behaviour of basalt fibre reinforced recycled aggregate concrete (BFRC) short specimens confined by carbon fibre reinforced polymer (CFRP) tubes under freeze–thaw conditions. The main parameters investigated are the replacement rate of recycled coarse aggregate (RCA), the number of freeze–thaw cycle (FTC), the related temperature range, and the shape of short specimen section. The failure mode, dynamic elastic modulus, ultimate bearing capacity and the load–strain response of the specimens are studied. The results show that the failure mode and the load–strain response of CFRP tube confined recycled aggregate concrete (RAC) specimen have insignificant change due to FTCs. However, with the increase of the FTCs, the bearing capacity of the specimen decreases, and the specimen with square cross-section is much more sensitive than that of the circular cross-section counterpart. The smaller the range of freeze–thaw temperature changed, the smaller loss of the dynamic modulus and the smaller decrease range of the ultimate bearing capacity after FTCs.

Improving the quality of HIV rapid testing in Ghana using the dried tube specimen-based proficiency testing program.

BackgroundThe introduction of human immunodeficiency virus (HIV) antibody rapid testing (RT) in resource-limited settings has proven to be a successful intervention to increase access to prevention measures and improve timely linkage to care. However, the quality of testing has not always kept pace with the scale-up of this testing strategy. To monitor the accuracy of HIV RT test results, a national proficiency testing (PT) program was rolled out at selected testing sites in Ghana using the dried tube specimen (DTS) approach.MethodsBetween 2015 and 2018, 635 HIV testing sites, located in five regions and supported by the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR), were enrolled in the HIV PT program of the Ghana Health Service National AIDS/STI Control Programme. These sites offered various services: HIV Testing and Counselling (HTC), prevention of mother-to-child transmission (PMTCT) and Antiretroviral Treatment (ART). The PT panels, composed of six DTS, were prepared by two regional laboratories, using fully characterized plasma obtained from the regional blood banks and distributed to the testing sites. The results were scored by the PT providers according to the predefined acceptable performance criteria which was set at ≥ 95%.ResultsSeven rounds of PT panels were completed successfully over three years. The number of sites enrolled increased from 205 in round 1 (June 2015) to 635 in round 7 (December 2018), with a noticeable increase in Greater Accra and Eastern regions. The average participation rates of enrolled sites ranged from 88.0% to 98.0% across the PT rounds. By round 7, HTC (257/635 (40.5%)) and PMTCT (237/635 (37.3%)) had a larger number of sites that participated in the PT program than laboratory (106/635 (16.7%)) and ART (12/635 (1.9%)) sites. The average testing performance rate improved significantly from 27% in round 1 to 80% in round 7 (p < 0.001). The highest performance rate was observed for ART (100%), HTC (92%), ANC/PMTCT (90%) and Laboratory (89%) in round 5.ConclusionThe DTS PT program showed a significant increase in the participation and performance rates during this period. Sub-optimal performances observed was attributed to non-compliance to the national testing algorithm and testing technique. However, the implementation of review meetings, peer-initiated corrective action, supportive supervisory training, and mentorship proved impactful. The decentralized approach to preparing the PT panels ensured ownership by the region and districts.

Quantification of ovarian lesion and fallopian tube vasculature using optical-resolution photoacoustic microscopy

The heterogeneity in the pathological and clinical manifestations of ovarian cancer is a major hurdle impeding early and accurate diagnosis. A host of imaging modalities, including Doppler ultrasound, MRI, and CT, have been investigated to improve the assessment of ovarian lesions. We hypothesized that pathologic conditions might affect the ovarian vasculature and that these changes might be detectable by optical-resolution photoacoustic microscopy (OR-PAM). In our previous work, we developed a benchtop OR-PAM and demonstrated it on a limited set of ovarian and fallopian tube specimens. In this study, we collected data from over 50 patients, supporting a more robust statistical analysis. We then developed an efficient custom analysis pipeline for characterizing the vascular features of the samples, including the mean vessel diameter, vascular density, global vascular directionality, local vascular definition, and local vascular tortuosity/branchedness. Phantom studies using carbon fibers showed that our algorithm was accurate within an acceptable error range. Between normal ovaries and normal fallopian tubes, we observed significant differences in five of six extracted vascular features. Further, we showed that distinct subsets of vascular features could distinguish normal ovaries from cystic, fibrous, and malignant ovarian lesions. In addition, a statistically significant difference was found in the mean vascular tortuosity/branchedness values of normal and abnormal tubes. The findings support the proposition that OR-PAM can help distinguish the severity of tubal and ovarian pathologies.

Characterization of IASCC crack tips extracted from neutron-irradiated flux thimble tube specimens in view of a probabilistic fracture model

This study reports the properties of irradiation assisted stress corrosion crack tips extracted by means of focused-ion beam from 60 to 80 dpa neutron-irradiated O-ring specimens tested under straining conditions under a pressurized-water reactor environment. Various crack tip morphologies and surrounding deformation features were analyzed as a function of applied stress, surface oxidation state and loading form - constant versus cyclic. All investigated cracks exhibit grain boundary oxidation in front of the crack tip, with the extent of oxidation being proportional to applied stress. These findings clearly demonstrate that, under the subcritical crack propagation regime, the grain boundary oxide grows faster than the crack. On the other hand, crack tips appertaining to specimens with removed oxide layer at the outer surface show comparatively less oxidation at the crack tip, which could indicate towards crack initiation from regions that exemplify lower stress, such as the O-ring inner surface. Cyclic loading is found to have a more pronounced effect on the crack tip microstructure, demonstrating increased deformation twinning and α′-martensitic transformation, which signifies towards an increased susceptibility to intergranular failure. Still, the extent of crack tip grain boundary oxidation in this case agrees well with expected values for maximum stress applied during cyclic loading. All results are interpreted based on the probabilistic subcritical crack propagation mechanism and provide strong support to a stress-driven internal oxidation model.

Processing of in-situ aluminium foam-filled stainless steel tube with foam-tube bonding for enhanced crashworthiness

This work aims to achieve superior mechanical properties in in-situ aluminium foam-filled stainless steel 316L tubes by promoting good bonding between the foam and the tube. Towards this end, the stainless steel tubes (inner surface) were electroplated with copper before in-situ foam-filling. Detailed microstructural studies were conducted at the foam/tube interface. In-situ foam-filled tube specimens were subjected to uniaxial compression and three-point bend testing. The axial compression and bending performance of the in-situ foam-filled tubes were compared with ex-situ foam-filled tubes and in-situ foam-filled tubes produced without copper coating. The deformed samples were sectioned and analysed to understand the deformation modes. The results show that copper coating is very effective in promoting good bonding between the foam and the tube during in-situ foaming, leading to considerable improvement in the mechanical performance of the foam-filled tubes. Ex-situ-heat processed (ex-situ-HP) foam-filled tubes (FFTs) and in-situ-uncoated (in-situ-UC) FFTs were found to display approximately 34 % and 46 % increase in specific energy absorption (SEA) as compared to empty-HP tubes. Electroplating of the inner surface of the steel tube with copper before in-situ foam-filling was found to promote good metallurgical bonding between the foam and the steel tube. Because of the enhanced foam-tube bonding, the in-situ-copper coated (in-situ-CC) FFTs were found to display ~61 % and 10 % higher SEA as compared to the empty-HP and in-situ-UC FFTs, respectively. The deformation mechanisms in foam-filled tubes are discussed in detail.

Experimental Study on Damage Characteristics of Corroded Steel pipe Based on Acoustic Emission Technology

The corrosion damage of steel pipe is mainly characterized by crack initiation and local wrinkling. One of the effective methods to evaluate the damage degree of steel pipe is to find out the law of crack initiation. The research object of this test was Q235 steel pipe specimen with diameter of 700mm, wall thickness of 5mm and height of 260mm. Acoustic emission technology was used to conduct real-time axial compression detection on corroded steel pipe specimens. The relationship between acoustic parameters (cumulative ringing number and amplitude) and the damage degree of steel pipe specimens was established, and the crack propagation law and crack initiation load of steel pipe after corrosion damage were obtained. By analyzing the different characteristics of the relationship between the displacement of loading point and acoustic parameters, the general position of steel pipe damage was detected and the exact value P of crack initiation load was determined. The experimental results provide a basis for further research on the damage mechanism of steel tube specimens. The test results provide a certain basis for further research on the damage mechanism of steel pipe specimens.