Elastic Stress Levels Research Articles

The Use of X-Ray Diffraction Peaks Profile Analysis to Define the Structural Condition of Elastically Stressed 09G2S Steel

By using X-ray diffractometry, it was determined how short-term stresses, being within the limits of the offset yield strength σs, influence changes in the diffraction line profile characteristics resulting from static tension in plate specimens of 09G2S (09Г2С) structural steel. Microstructural changes in the surface of 09G2S steel specimens considered in this work were studied at different levels of elastic stress. The special aspects of changes in the diffraction line profile characteristics are presented and discussed, specifically, a broadening of the profile maximum half-width (B), as a response to the external mechanical impact on the surface layers.

Effect of Elastic Stresses on Pitting Behavior of Stainless Steel 304

Stress/deformation-induced accelerated corrosion has been reported for many alloys used in structural and functional applications. To understand the effect of applied elastic stresses on corrosion behavior of alloys, samples of stainless steel (SS) 304 were subjected to different levels of elastic tensile stresses and their corrosion behavior was studied. The applied elastic stress is believed to alter materials’ pitting behavior in chloride-containing environments. Results from this study show that applied tensile stresses hinder pitting resistance of SS304. Stress and stress concentration around pit vicinity accelerate salt-film repair, thereby impeding repassivation. Through this mechanism, pit growth is stabilized. Results from electrochemical tests on samples at different elastic stress levels are discussed in this paper.

A study on time-variant corrosion model for immersed steel plate elements considering the effect of mechanical stress

In this study, the effect of low levels of elastic stress on corrosion behavior of Q235B steel in an aerated 3.5% NaCl solution was investigated through measurements of linear polarization resistance (LPR), potentiodynamic polarization characteristics and electrochemical impedance spectra (EIS). Through theoretical analysis and experimental results, new corrosion models which can distinguish the effect of mechanical stress on the corrosion process of actual marine structures have been respectively proposed on the basis of three representative existing corrosion models. The effect of corrosion models on lifetime assessment was studied by employing a steel plate element subjected to the combined effects of corrosion and mechanical stress. Analytical expressions have been obtained for the structure's lifetime, which is identified with the time when the stress reaches the yield level. An example was presented to demonstrate the combined effects of corrosion and elastic stress on the lifetime assessment of marine structures.

A study on effects of elastic stress on protective properties of marine coatings on mild steel in artificial seawater

Abstract The effects of macro-elastic stress on protective properties of two marine coating systems applied on mild steel plates in artificial seawater at room temperature were investigated through the measurement of electrochemical impedance spectroscopy (EIS). One coating system contained zinc-rich epoxy primer, micaceous iron oxide anchor coat and aliphatic polyurethane top coat and the other was composed of zinc-rich epoxy primer, micaceous iron oxide anchor coat and acrylic polyurethane top coat. Two different elastic stress levels (tensile and compressed modes) were applied on coated substrates by using bent samples and non-bent coated samples were used as references. The obtained results indicated that elastic stress could have a significant influence on coating resistance, water absorption and diffusion coefficient, and meanwhile the extent of this influence depends on both the magnitude and direction of elastic stress. Furthermore, the disparity in the evolution of water uptake and diffusion coefficient with elastic stress was discussed, and a thermodynamic approach was employed to evaluate the enthalpic and entropic contributions of the water diffusion coefficient under various elastic stress levels.

Hydrogen embrittlement susceptibility of welded 2¼Cr–1Mo steel under elastic stress

In this work, the influence of simultaneous hydrogen charging and elastic loading in hydrogen embrittlement of 2¼Cr–1Mo ferritic steel and its weldments was studied. A steel plate was welded by gas tungsten arc welding, GTAW and weldment microstructures characterized by SEM; tensile specimens were submitted to hydrogen cathodic charging under constant levels of elastic stress. Uniaxial tensile tests were performed right after hydrogenation and analyzed by scanning electron microscopy, SEM. The results of tensile tests showed that unloaded samples of base material, cathodically charged with hydrogen, underwent 28% of ductility loss, as compared to the same material without hydrogen charging. Hydrogen charging was performed when the specimens were subjected to 50% of the original yield strength (0.5Ys), these samples did not exhibit any ductile deformation at all; they even failed under a tensile stress lower than their Ys. Moreover, the degradation was largely permanent, very slight recovering in mechanical properties was observed after heat treatment at 450 °C for 4 h for degassing. The level of loss of ductility induced, solely by hydrogen charging, in welded samples was similar to the one observed in base material samples. When tensile load was applied along with hydrogen charging, ductility loss showed to be related with the availability of trapping sites within the welded samples, larger HAZ resulted in higher levels of ductility loss. Furthermore, rupture location on tensile tests consistently shifted from base material to HAZ, when 0.5Ys of elastic stress was applied under hydrogen cathodic charging.

Strain localization at dislocation channel–grain boundary intersections in irradiated stainless steel

The interaction of dislocation channels with grain boundaries in irradiated stainless steel was observed on multiple length scales using scanning electron microscopy (SEM) digital image correlation (DIC) and confocal microscopy (micro-scale), in situ straining and transmission electron microscopy (TEM) (nano-scale), and atomistic modeling (atomic scale). Interactions were divided into three classifications; slip transmission, discontinuous slip, and discontinuous slip that induced grain boundary slip. DIC and confocal microscopy were used to quantify the plastic strain at dislocation channel–GB intersections. In situ TEM was used to image dislocations inside of channels as they interacted with the grain boundary. Slip in the dislocation channels, as observed by TEM, was found to involve cross slip between different slip planes, as well as the possibility of different slip systems activated on parallel slip planes. Atomistic simulations agreed well with experiments on the nature of channel-grain boundary interactions and also showed elevated levels of elastic stress at DC–GB intersections where slip was discontinuous with no slip transmission. The two distinct classifications of discontinuous slip are significant, suggesting two possible cracking mechanisms that both lead to the rupture of the oxide over the grain boundary.

Stainless steel pitting and early-stage stress corrosion cracking under ultra-low elastic load

Pitting and crack nucleation at the early stages of stress corrosion cracking (SCC) under ultra-low elastic load were studied. Pits initiated on the sample surface and grew faster in the thickness direction rather than other directions. This corresponds with the stress and strain concentrations calculated using the finite element analysis. At the ultra-low elastic stress levels it is essential for the stress corrosion cracks to emanate from the pits/defects on the sample surface. Furthermore, the preferential SCC initiation sites are at the shoulders, rather than at the bottoms of the surface pits/defects.

Application of the Monkman–Grant law to the creep fracture of nodular cast irons with various matrix compositions and structures

Creep behaviour of nodular cast irons with three different matrix compositions and microstructures has been investigated up to fracture in the elastic regime for temperatures between 650 °C and 900 °C. The elastic stress levels were chosen taking into account the non-linear dependence between elastic stresses and corresponding strains. Results show that austenitic cast irons are more creep resistant than ferritic ones. However, all materials obey to a single Monkman–Grant law. Fracture of samples with short life times is dominated by the plastic straining of the matrix independently of their metallurgical state. Creep fracture of long life time samples is controlled by diffusion mechanisms like cavity nucleation on the grain boundaries. It is shown that the damage growth in secondary and tertiary creep regimes can be represented by a single parameter whatever the creep mechanisms and the metallurgical properties of nodular cast irons.

Evaluation of the high-density pulse current effect on the plastic strain rate in metals

A direct (nonthermal) high-density pulse current effect on the plastic strain rate in the metal under loading and on the relaxation of elastic stresses in it is evaluated. The evaluation is based on existing notions of electronic conductivity and thermally activated dislocation motion-controlled plastic strain mechanisms in metals. The effect of pulse current on the plastic strain rate is shown to become more and more pronounced with current density, elastic stress levels, and temperature; at low current densities and applied loads its effect is inessential.

Assessing residual stress development and stress relaxation in restrained concrete ring specimens

Abstract Recently, the American Association of State Highway and Transportation Officials implemented a provisional standard that uses the `ring test' to help quantify a materials' propensity for cracking. While this test may provide qualitative information that enables different mixtures to be compared, it does not provide quantitative information to describe how close a specimen is to failure. This paper will describe how the ring test may be used to provide quantitative information about stress development that may be used to assess the potential for cracking in concrete. An analytical stress formulation is presented to compute the actual residual stress level in the concrete using only the measured strain from the steel ring. The theoretical elastic stress is computed using the free shrinkage, ring deformation, and elastic modulus of the concrete. A comparison of the residual and theoretical elastic stress levels provides information about the extent of stress relaxation in a material. Continuously monitoring the strain that develops in the steel ring from the time of casting enables the effects of autogenous shrinkage to be determined as well as the effects of drying shrinkage.

Limit loads for knuckle-encroaching nozzles in torispherical heads: Experimental verification of finite element predictions

The manufacturing and testing procedures for two experimental pressure vessels with large nozzles encroaching into the knuckle region of the vessel head are described. Experimental linear elastic stress levels and plastic loads for pressure and combined axial and in-plane bending nozzle loads are compared with predicted values determined using non-linear finite element analysis. The quality of the results are considered to justify the procedures developed by the authors to conduct a parametric study of the individual limit loads and their interaction for these complex structures.

Moment loads on branch-pipe junctions: The effect of run-pipe fixing on elastic stress levels and its implications on plastic limit loads

Experimental stress analysis results on a series of eight branch-pipe intersections, and finite element results on a series of four branch junctions, have been used to assess the effect on elastic stress levels, arising from branch moment loading, of varying the run-pipe boundary conditions. It is shown that for branch/run-pipe diameter ratios of 0·5 or less boundary condition effects are not significant. Conversely, for junctions with larger diameter ratios, there are significant differences, depending on whether one or both run-pipe limbs are clamped. The implications of the results on plastic limit loads for branch-pipe junctions are discussed.

Formulae and graphs of elastic stresses for design and analysis of U-shaped bellows

This paper presents equations describing the meridional and circumferential elastic stress levels at the root and crown due to external pressure and axial deflection of U-shaped bellows. The derivation is based on a statistical analysis of selected bellows configurations. The mathematical formulations and various graphical representations are proposed as aids to bellows design and analysis.

A comparison of fracture toughness parameters for titanium alloys

High strength titanium alloys in thick sections are of interest for use in complex structures such as deep-diving vehicles, hydrofoils, and aircraft. Successful application of these materials in such structures requires a knowledge of the notch fracture toughness of these alloys to preclude the possibility of catastrophic fracturing. Experience has shown that no single test method presently exists that can provide reliable fracture toughness information for the whole spectrum of titanium alloys. A previously established relationship between drop-weight tear test energy and explosion tear test performance provides reliable fracture toughness information on those alloys characterized by a toughness level requiring gross plastic deformation to propagate fractures. This analysis has not been extended to the ultra high strength alloys in which fractures can propagate catastrophically at elastic stress levels. For these alloys, analytical methods of linear elastic fracture mechanics provide the required elastic stress level and flaw size relations for fracture. This paper deals with a 'marriage' of the two approaches — the engineering and the analytical — by correlative techniques. A direct correlation has been found for titanium alloys between the drop-weight tear test (DWTT) energy for fracture and the corresponding stress intensity factor, K IC . The relationship appears to be valid up to a DWTT value of 1200ft-lb and may likewise be expressed in terms ofβ IC-DWTT or ℷ IC-DWTT. There is also a correspondence betweenβ IC and a fracture appearance as determined by the percentage of shear lip on the single-edge notch specimen. On the other hand, the Charpy-V notch test proved to be relatively insensitive to change in fracture toughness and could not be correlated with K IC . The practical implication of this study is that reasonable estimates of plane strain fracture stress-intensity K IC , should be possible from results obtained with other reliable engineering methods for measuring fracture toughness.