Slow Bending Research Articles

Liquid lead resistance and cracking of novel 1Al-Sc-Y ODS Eurofer steel

Novel 1Al-Sc-Y ODS Eurofer steel for use in high temperature heavy metal cooling technologies has been developed by a mechanical alloying of feedstock powders using spark plasma sintering technique and a two-step heat treatment. The 1 wt.% Al has been added to increase the resistance in the environments at high temperatures. This paper reports the microstructure and mechanical properties of the material in the as-manufactured state, and after exposure in liquid lead. Emphasis is placed on the determination of environmental resistance and namely susceptibility to cracking in contact with liquid lead. The material specimens were exposed to static liquid lead with an average concentration of oxygen 1 × 10−6 wt.% at 600 °C for 1000 h and then, tensile, impact, fracture toughness and slow three-point bend testing was performed. After the exposure, some Pb penetrated into a subsurface layer which in fact caused wetting but testing with the remains of liquid lead at the surface of corroded specimens at 350 °C showed that the steel stayed very low susceptible to the cracking.

Influences of preheating parameters on the quality of weld by thermite rail welding

The major goal of this study is to enhance the mechanical and metallurgical characteristics of rail steel grade R260 joined by thermite welding under various preheating conditions, including preheating time and gas pressure. Mainly two conditions, referred to as the Normal Condition and Improved Condition, are carried out for experiments. Prior to welding, the Normal Condition was preheated using liquefied petroleum gas (LPG) and oxygen gas pressures of 1 bar and 4.5 bar for 3 min, and the Improved Condition was preheated using liquefied petroleum gas and oxygen gas pressures of 1.2 bar and 4.5 bar for 6 min and 30 s. To investigate the mechanical and physical properties, micro-Vickers hardness tests, tensile tests and slow bending tests were also carried out. Welded metal in Normal Condition has many defects, including gas holes and shrinkage cavities. When comparing the Normal Condition to the Improved Condition, the Improved Condition demonstrates significantly more bending load and deflection. Specifically, the thermite welded rail sample of Improved Condition demonstrated a remarkable ability to endure bending loads of 108 tonnes and a deflection of 16 mm, and this sample remained unbroken until it exceeded 50% of the standardized deflection limit (10 mm). In addition, the average hardness values for the Improved Condition of the weld metal zone and the heat-affected zone were 331 HV and 289 HV, respectively. The Normal Condition produced an unsatisfactory fracture surface after slow bending test. This was caused by weld defects at the thermite weld due to inappropriate preheating.

Experimental investigation on the fatigue behaviour of rails in the transverse direction

This paper presents an experimental investigation on 60E2 (UIC 60) rails loaded in the transverse direction up to five million load cycles. A resonance testing machine was applied to achieve a test program with different load levels and a loading frequency of 15 Hz. First, the experimental approach, which includes the specimens, the test setup, the test program, the corrosion treatment as well as the additional slow bending tests, is introduced in detail. Subsequently, the rail steel material behaviour, the fracture characteristics of the rails, and the corrosion effects are analysed and summarized; the fatigue strength of the rails is evaluated with the staircase method and compared with the fatigue strength of rails loaded in the vertical direction. In general, the rails show good fatigue resistance in the transverse direction, which is larger than that in the vertical direction and close to the static yield strength. As a result, a new comprehensive Smith-diagram of the UIC 60 rail for five million load cycles is presented. In the end, necessary further investigations are discussed.

Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel.

The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low Alloy Steels (HSLA), and its microstructure consists of equiaxed ferritic and bainitic grains with a low volume fraction of degenerated pearlite islands. The studied X65 steel specimens were extracted from pipes with 19.15 mm wall thickness. The fracture toughness parameters were determined after imposing the fatigue pre-cracked specimens on air, on a specific electrolytic cell under a slow strain rate bending loading (according to ASTM G147-98, BS7448, and ISO12135 standards). Concerning the results of this study, in the first phase the hydrogen cations’ penetration depth, the diffusion coefficient of molecular and atomic hydrogen, and the surficial density of blisters were determined. Next, the characteristic parameters related to fracture toughness (such as J, KQ, CTODel, CTODpl) were calculated by the aid of the Force-Crack Mouth Open Displacement curves and the relevant analytical equations.

Exploring the susceptibility of P110 pipeline steel to stress corrosion cracking in CO2-rich environments

The low carbon P110 steel has been recently considered as a potential pipeline material for shale gas sequestration using CO2-based fracturing technique. The significant problem in such natural gas production and transportation system is a CO2 corrosion, especially the stress corrosion cracking (SCC) of pipelines. Due to the possible operating conditions, the aim of the present work was to investigate the susceptibility of P110 pipeline steel to SCC in CO2-rich environments. It was determined based on the stress corrosion test of U-bended specimens in the technically pure CO2 and wet CO2 (CO2 + H2O), tensile tests of miniaturized samples cut from different regions of U-bended specimens as well as slow strain rate bending tests in the wet CO2 followed by SEM observations. No clearly visible long SCC cracks and microstructural changes after exposure in CO2 and CO2 + H2O were observed. Nevertheless, some corrosion pits with micro-cracks in their vicinity were formed in the stressed/deformed areas of U-bend SCC specimens. Moreover, the results of tensile and slow strain rate tests indicated that P110 pipeline steel is susceptible to SCC in CO2-rich environments. It was manifested by a significant reduction of ductility in the stressed regions of U-bended specimens exposed to CO2 and CO2 + H2O. Besides, small cracks with brittle fracture characteristics were observed for P110 steel bended in the wet CO2 at the strain rate of 2 × 10−6 s−1. All observed phenomena indicated that the susceptibility of P110 steel to SCC in CO2-rich environments is associated with activity of anodic dissolution process and hydrogen involvement.

Harnessing programmed holes in hydrogel bilayers to design soft self-folding machines

We present a physics-based finite element simulation of self folding of a hydrogel bilayer with programmed holes. Introducing holes in a bilayer modifies the topology and boundary of the bilayer. Early state swelling of a hydrogel bilayer forms rolled tubes along the periphery of the bilayer and adds the local rigidity along the boundary. Our numerical simulation shows that formation of rolled edges switches the deformation mode of hydrogel bilayer from slow and gradual bending to fast and sudden buckling or folding. On demand folding is thus possible by tuning the location, size and shape of holes. The uncovered folding mechanism is leveraged to design a number of soft self-folding machines. The results throw light on design and simulation of soft self-folding machines.

Gender outlaws or a slow bending of norms? South African bisexual women’s treatment of gender binaries

A monosexual configuration of sexuality assumes that sexual desire is directed at either men or women. Bisexuality resists a choice between oppositional categories and is often theorised as having a transgressive potential to destabilise binary logic, not only in relation to sexuality but also to gender. There is, however, a lack of empirical work exploring how this potential might be realised in the accounts of bisexual individuals. Drawing on interviews with South African bisexual women, we use a narrative-discursive lens to examine the discursive resources employed by participants to trouble or resist hetero-gendered norms. Our findings demonstrate how resistance to the gender binary hinges on citational politics that are fundamentally gendered and linked to sexuality. Instead of entirely destabilising hetero-gendered norms, participants draw on gendered scripts that simultaneously expand norms to accommodate their sexual difference and, through processes of othering, function to reiterate hetero-gendered norms. While complete subversion of gender binaries is not possible in participants’ discursive contexts, what does occur is a ‘slow bending’ of norms. Theorising bisexuality as transgressing oppositional categories closes off opportunities to interrogate the pervasive influence of gender binaries in contexts that remain marked by pervasive heteronormativity and heterosexism. Significantly, it also obscures more modest improvisations of gender scripts that hold potential for destabilising gender binaries.

Two-dimensional structure-embedded acoustic lenses based on periodic acoustic black holes

Recent studies have introduced a new class of two-dimensional acoustic metamaterials whose dispersion and propagation properties result from the use of geometric inhomogeneities in the form of Acoustic Black Holes (ABH). The ABH is an element able to smoothly bend acoustic rays and slow down elastic bending waves, therefore providing a variety of unconventional dispersion and propagation properties that are typically observed in more complex multi-material and locally resonant designs. Our approach enables full integration of acoustic lenses in thin-walled structural elements while preserving the structural character. The lenses are capable of different high-level functionalities such as focusing, collimation, and negative refraction. Numerical and experimental results show that such structures exhibit broadband operating conditions that span both the metamaterial and the phononic range.

Solvent tunable multi-block ionomer morphology and its relationship to modulus, water swelling, directionally dependent ion transport, and actuator performance

Abstract Sulfonated penta-block ionomer (SBI) solvent cast film's ion domain spatial arrangement transitioned from random into well-connected lamellar/hexagonal structures. This micro-phase separated morphology was tunable and associated solution properties transitioning from nonpolar cyclohexane/heptane (CH) to polar tetrahydrofuran (THF). The observed morphology changes were characterized using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). SAXS revealed that average sulfonated inter-domain spacing increased asymmetrically within the film. For example, solvent cast SBI-H+ film inter-domain spacing changed from 30.8 nm using CH to 43 nm with THF. This lamellar/hexagonal morphology led to a two-fold water uptake increase from 23 wt% to 46 wt%, and an order-of-magnitude proton conductivity improvement from 4.5 mS/cm to 47.8 mS/cm. Ionomeric polymer-metal composite (IPMC) actuation performance was morphology dependent. The film with a random morphology had small actuation displacement with slow bending speed. However, well-connected ion domains enabled rapid and large bending motions.

A Note on Iris Flower Anthesis: Mechanism and Meaning of Sudden Flower Opening

Abstract Experiments with Iris pseudacorus (Yellow Iris) reveal the mechanics of a sudden-release phenomenon in these flowers caused by slow bending of the outer tepals while their top-margins cling together, leading to stored mechanical energy that is released explosively. In this note, I discuss the possible adaptive significance of this flower behavior in terms o f pollinator learning-behavior.

Restraining IPMC Back Relaxation in Large Bending Displacements: Applying Non-Feedback Local Gaussian Disturbance by Patterned Electrodes

Despite advantages and promising features of ionic polymer–metal composite (IPMC), this smart material has some drawbacks that should be eliminated as much as possible for improving the IPMC performance. One of the most important drawbacks is the back relaxation (BR). When a step input voltage is applied to the IPMC, it bends toward the anode. The BR is the unwanted and slow bending of the IPMC back toward the cathode. Several techniques based on using a feedback control loop have been proposed for eliminating the BR effect. However, these techniques are effective only when the bending displacement of the IPMC is small. In this paper, we propose a nonfeedback method for restraining the IPMC BR effect even in large bending displacement. The proposed technique is based on the fast reciprocating motions of free water molecules in Nafion membrane between the anode and the cathode. For this purpose, we have used a local Gaussian disturbance in a specifically patterned IPMC. We have described our idea conceptually and we have validated it by several experimental results.

Environmentally assisted cracking and hydrogen diffusion in traditional and high-strength pipeline steels

Abstract This article deals with the risk of environmentally assisted cracking of steel structures that are kept under cathodic protection (CP). The experimental results collected on both hydrogen diffusion and hydrogen embrittlement (HE) of high-strength low-alloy (HSLA) steels under CP are discussed. Hydrogen diffusion was evaluated by permeation experiments and a scanning photoelectrochemical current technique, as a function of microstructure orientation, on both loaded and unloaded specimens. HE tests were carried out under constant load, slow strain rate (SSR tests), and slow bending conditions. Tests were also carried out on several grades of HSLA steel having different microstructures. The results confirm that HE in artificial seawater under CP can occur in steel with tensile yield strength in the range of 400–660 MPa only in the presence of high cathodic polarization and continuous plastically straining conditions. HE susceptibility increased with increasing applied cathodic polarization and with decreasing strain rate. HE susceptibility of the rolled steels at relatively high strain rate (10-4 to 10-5 s-1) increased with the hydrogen diffusion coefficient. Similar results were observed in terms of the HE contribution to corrosion fatigue crack growth rate. High-temperature-tempered martensitic steels showed a lower HE susceptibility.

An experimental investigation on flash butt welded rails

In this paper, experimental studies performed for flash butt welded rails used in Turkish railways network having 49E1 and 60E1 rail sections are presented. These studies comprise of full-scale laboratory tests such as four point bending fatigue and three-point slow bending tests, as well as related instrumentation of test specimens and data measurement. Fatigue and bending tests are prepared and carried out in accordance with EN 14587-2 standard. The fracture surfaces of the welded samples are examined to identify the associated failure modes. The fatigue test results are superimposed on a S–N diagram derived from earlier results reported as a part of the European Commission steel rails research project. A best fit curve following an exponential function is derived to describe the load deflection behavior of the weld under the slow bend testing conditions. It is shown that a single component of the equation defining the best fit curve is the factor controlling the scattering in the non-linear part of the load deflection curve, and hence control of this parameter can also be used to impart consistency to the welding process.

Fracture of pearlitic ductile cast iron under different loading conditions

ABSTRACTIn this study, fracture surfaces of pearlitic ductile iron generated under impact, bending and fatigue tests were characterised and compared. The fracture mechanisms in each case were identified from the observation of scanning electron microscopy images, and the characteristic topographic features were quantitatively and qualitatively evaluated. Cleavage was the predominant fracture mechanism for impact loading at all test temperatures and for slow bending testing. On the other hand, under fatigue loading, the fracture surfaces showed a mix of cleavage and ductile striation areas. A complex but reliable methodology for the determination of the direction of propagation of the main crack was also proposed, based on a careful analysis of the river patterns along the cleavage planes.

Modeling and simulation of the chemo-electro-mechanical behavior of ionic polymer-metal composites

Ionic polymer-metal composites (IPMCs) consist of a thin ionomer plated with metal electrodes. IPMCs exhibit large bending deformations when a small voltage is applied between its electrodes. This bending process is the result of variations in the cation and solvent distribution inside the IPMC. The bending behavior differs for different types of IPMCs, and so a numerical prediction of the behavior needs to be formulated based on various physical phenomena. The bending for several IMPCs can consist of two phases: (1) a fast bending towards the anode and (2) a slow reverse bending. As the physical reasons for reverse bending, i.e., back relaxation of Nafion-based IPMCs is not completely understood, a comprehensive physics-based model of the bending process is still a demanding task. In this paper a numerical model describing the actuation behavior of an IPMC is formulated based on a multi-field approach considering chemical, electrical, and mechanical field equations. This model is based on the cluster model developed by Nemat-Nasser and Li [J. Appl. Phys. 87(7), 3321–3331 (2000)] and Nemat-Nasser [J. Appl. Phys. 92(5), 2899–2915 (2002)] and the chemo-electro-mechanical model given by Wallmersperger et al. [Mech. Mater. 36(5-6), 411–412 (2004); J. Appl. Phys. 101, 024912 (2007)]. The cluster model is a model being able to describe the bending behavior of different IPMCs with and without back relaxation. In the present research the chemical, electrical, and mechanical field equations are discretized using finite differences and solved by a full coupling using the Newton-Raphson technique. By this nonlinear process a detailed representation of the cation and solvent distribution as well as the resulting forces inside the IPMCs are obtained in space and time. Finally a comparison with experimental data published by Nemat-Nasser and Wu [J. Appl. Phys. 93(9), 5255–5267 (2003)] is given for a Nafion-based IPMC with distinctive back relaxation.

Three cases of laparo-assisted pancreatectomy

Sulfonated penta-block ionomer (SBI) solvent cast film's ion domain spatial arrangement transitioned from random into well-connected lamellar/hexagonal structures. This micro-phase separated morphology was tunable and associated solution properties transitioning from nonpolar cyclohexane/heptane (CH) to polar tetrahydrofuran (THF). The observed morphology changes were characterized using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). SAXS revealed that average sulfonated inter-domain spacing increased asymmetrically within the film. For example, solvent cast SBI-H+ film inter-domain spacing changed from 30.8 nm using CH to 43 nm with THF. This lamellar/hexagonal morphology led to a two-fold water uptake increase from 23 wt% to 46 wt%, and an order-of-magnitude proton conductivity improvement from 4.5 mS/cm to 47.8 mS/cm. Ionomeric polymer-metal composite (IPMC) actuation performance was morphology dependent. The film with a random morphology had small actuation displacement with slow bending speed. However, well-connected ion domains enabled rapid and large bending motions.

Oroclinal bending of the Middle and Late Paleozoic volcanic belts in Kazakhstan: Paleomagnetic evidence and geological implications

Paleomagnetic data on Middle- and Late-Paleozoic rocks from the central part of the Ural-Mongolian Belt in Kazakhstan are considered. The primary remanences in the Permian rocks and secondary magnetization components of the same age in pre-Permian rocks of central and northern Kazakhstan are not rotated relative to the East European Platform. In southern Kazakhstan adjoining the Tien Shan almost all data point to large, up to 90°, counterclockwise rotation of blocks. These rotations, related to the regional wrench fault zone, must be subtracted from older paleomagnetic data to ensure their correct interpretation. The paleomagnetic declinations in Upper Carboniferous rocks coincide more or less over all of Kazakhstan, whereas the Silurian and Early Devonian declinations in the north and south of Kazakhstan differ approximately by 180°. It can be suggested that the Devonian volcanic belt, having a horseshoe outline, was initially an almost rectilinear NW-trending feature. Its oroclinal bending took place in the Devonian and Early Carboniferous and completed by the Late Carboniferous. We compared the model of the Kazakh Orocline based on paleomagnetic data with the geological events in this territory. It turned out that a slow bending of an initially rectilinear subduction zone is consistent with lateral migration of active volcanism and folding inside a developing loop, whereas extension outside the loop was accompanied by subsidence and rifting. In general, the proposed model connects the main tectonic events in Kazakhstan with the movements established from paleomagnetic data.

Hydrogen Embrittlement Behavior of 430 and 445NF Ferritic Stainless Steels

Hydrogen embrittlement behavior of two kinds of commercial ferritic stainless steels (STSs), 430 (UNS S43000) and 445NF (UNS S44536), was investigated by means of a series of cathodical hydrogen charging, slow strain rate tests, bending tests, and thermal desorption spectrometry analyses. The hydrogen concentration in 445NF STS was lower than that of 430 STS under identical hydrogen charging conditions because of the formation of a more passive layer. In addition, 445NF STS exhibited a larger passive range in the potentiodynamic polarization curve. However, resistance to hydrogen embrittlement of 445NF STS was inferior to that of 430 STS because of precipitation of the Laves phase at grain boundaries of the former at annealing temperatures of 873 K to 1123 K (600 °C to 850 °C). Crack propagation was found to occur along the interface between the Laves phase and the matrix. For 445NF STS, dissolution of the Laves phase by solution heat treatment at 1273 K (1000 °C) followed by quenching was effective in terms of suppressing degradation of its mechanical properties and formability, which were related to hydrogen embrittlement.

Tungsten bending under hydrogen irradiation

Bending of a thin tungsten strip, fixed at one of the ends, under hydrogen plasma exposure was studied by the laser deflection technique. Two stages of the bending were observed: a rapid bending of the stripe outwards the plasma and then a slow bending in the opposite direction that is towards the plasma. The first stage has been concluded to be due to creation of stresses in the near-surface layer, and the second one – due to stresses of the opposite sign, possibly provoked/accompanied by generation of blisters on the plasma exposed surface. Calculations of the fluence dependence of the bending curvature based on the models of hydrogen supersaturation in the near-surface layer and contraction of the surface due to blister formation agree with the experimental data.

Bending waves in crumpled sheets

Crumpled paper has recently emerged as a model for disordered media. Here we use wave propagation to probe aluminum foils crumpled into balls made by hand or into cylinders obtained by confinement in a container. Surprisingly, the raw dispersion relations appear to differ from sample to sample. They correspond to bending waves that follow an effective path that is shorter than the distance between the input and output points. This can be interpreted in terms of two modes of propagation: slow bending waves and a fast mode whose possible origin is discussed. In addition, the effective paths behave differently in spheres and in cylinders. These results enable the characterization of the sample structure and point toward the geometric rigidity of the configurations.