External Tensile Load Research Articles

Stress Corrosion Cracking Analysis of The ER70S Wire and SS400 Stell Plate Joints

The susceptibility of weld joints to the stress corrosion cracking(SCC) load alarmed the researchers since pipeline blow-out which were initiated in the area closed to the weld joints. This article is evaluating the SCC resiliences of the ER70S wire filler metal to the SS400 plate. The capacitive discharge welding (CDW) with varied angle of the filler metal as an independent variable is applied, whilst the other parameters were kept constant. The joint, then exposed to the SCC load, i.e., dipped in the 1M HCl solution with varied external tensile load to obtain the dependent variable: time to failure (time to brake). The results show that, generally, a sharper wire tip provides higher SCC resilience accept what was shown by the 30° speciment. With the sharper wire tip, the higher volume of weld nugget is provided which guarentee the enough number of weld metal. However, the impact phenomenon in the CDW process splashed this too much nugget beyond the formed joint which is proven by many spatter in the weld joint. This thrown out nugget substance in turn decreases the intended nugget volume to form the joint. The results show the 60° wire tip angle provide the joint with the highest SCC resiliences, indicated by the longest time to brake when loaded with an equal external load.

Atomic-Scale In Situ Observations of Reversible Phase Transformation Assisted Twinning in a CrCoNi Medium-Entropy Alloy.

Twinning is an important deformation mode of face-centered-cubic (FCC) medium- and high-entropy alloys, especially under extreme loading conditions. However, the twinning mechanism in these alloys that have a low or even negative stacking fault energy remains debated. Here, we report atomic-scale in situ observations of the deformation process of a prototypical CrCoNi medium-entropy alloy under tension. We found that the parent FCC phase first transforms into a hexagonal close-packed (HCP) phase through Shockley partial dislocations slipping on the alternate {111} planes. Subsequently, the HCP phase rapidly changes to an FCC twin band. Such reversible phase transformation assisted twinning is greatly promoted by external tensile loads, as elucidated by geometric phase analysis. These results indicate the previously underestimated role of the metastable HCP phase in nanotwin nucleation and early plastic deformations of CrCoNi alloys and shed light on microstructure regulation of medium-entropy alloys with enhanced mechanical properties.

Effect of Polyoxymethylene Fiber on the Mechanical Properties and Abrasion Resistance of Ultra-High-Performance Concrete.

It is necessary to prepare marine UHPC with synthetic fibers instead of steel fibers, owing to the corrosion risk of steel fibers in marine environments. Currently, the performance of UHPC prepared with different types of fibers has not been comparatively investigated. This work prepared UHPC with steel fiber, polyoxymethylene (POM) fiber, polypropylene (PP) fiber, and polyvinyl alcohol (PVA) fiber. The effects of different fibers on the mechanical properties, impact, and abrasion resistance of UHPC were studied and compared. The results showed that increasing POM fiber can increase the mechanical strength, flexural toughness, impact, and abrasion resistance of UHPC. When its content reaches 2%, the adsorbed-in-fracture energy and abrasion strength of UHPC are 2670 J and 105 h/(kg/m2), respectively. At the same fiber content, POM fiber-reinforced UHPC shows better mechanical strength, toughness, and impact- and abrasion-resistance than the polypropylene (PP)- and polyvinyl alcohol (PVA)-fiber-reinforced UHPCs. Microstructure investigation found that PP fiber has the weakest binding with UHPC paste, which would directly pull out of the matrix under external tensile loading. This weak connection limits the strengthening and toughening effect on the UHPC. PVA fiber has an excellent interfacial connection with the UHPC paste. However, the low tensile strength of PVA fiber limits the strength and toughness of UHPC. POM fiber has a high tensile strength and can absorb tensile loading through debonding, fracture, and tearing. The fracture interface of POM fiber is large, indicating its significant role in strengthening and toughening the UHPC.

Effect of the loading condition on the statistics of crackling noise accompanying the failure of porous rocks.

We test the hypothesis that loading conditions affect the statistical features of crackling noise accompanying the failure of porous rocks by performing discrete element simulations of the tensile failure of model rocks and comparing the results to those of compressive simulations of the same samples. Cylindrical samples are constructed by sedimenting randomly sized spherical particles connected by beam elements representing the cementation of granules. Under a slowly increasing external tensile load, the cohesive contacts between particles break in bursts whose size fluctuates over a broad range. Close to failure breaking avalanches are found to localize on a highly stressed region where the catastrophic avalanche is triggered and the specimen breaks apart along a spanning crack. The fracture plane has a random position and orientation falling most likely close to the centre of the specimen perpendicular to the load direction. In spite of the strongly different strengths, degrees of 'brittleness' and spatial structure of damage of tensile and compressive failure of model rocks, our calculations revealed that the size, energy and duration of avalanches, and the waiting time between consecutive events all obey scale-free statistics with power law exponents which agree within their error bars in the two loading cases.

Exploring the capability of acoustic emission technique in early detecting mode I and mixed mode fractures

Acoustic Emission non-destructive technique was used coupled with Digital Image Correlation to explore its early warning capability in detecting Mode I and mixed Mode fractures in Scots pine samples. The acoustic behaviour of the specimens, being different for tree rings number (high and low) and grain angle (0-20-40-60°), was investigated while undergoing an external tensile load by a Universal Testing Machine. A risk amplitude threshold (51.9 dB) was experimentally computed a posteriori as an early warning indicator for Scots pine samples with mixed Mode fractures. In the case of Mode I fracture, as cracks occur instantaneously, the oncoming fracture could not be predicted.

Modeling Corrosion Product Film Formation and Hydrogen Diffusion at the Crack Tip of Austenitic Stainless Steel.

Corrosion product films (CPFs) have significant effects on hydrogen permeation and the corrosion process at the crack tip. This paper established a two-dimensional calculation model to simulate the formation of CPFs at the crack tip and its effects on the crack tip stress status and hydrogen diffusion. The CPFs were simplified as a single-layer structure composed of Fe2O3, the effective CPFs boundary was modeled by the diffusion of oxygen, and the CPF-induced stress was modeled by hygroscopic expansion. The simulation was conducted with two stages; the first stage was to simulate the formation of CPFs formation and its effects on the crack tip stress status, while the second stage focused on the hydrogen diffusion with and without CPF formation under different external tensile loads. The results indicate that the highest compressive stress induced by the formation of CPFs is located at 50~60° of the crack contour and dramatically weakens the crack tip tensile stress at low-stress status. The CPFs can inhibit the hydrogen permeation into the crack tip, and the hydrostatic pressure effects on the redistribution of the permeated hydrogen are significant under larger external load conditions.

An elastoplastic phase-field study of the precipitation behaviors of Mg17Al12 phase in Mg-Al-based alloys: Part II. Precipitation under various loadings

An elastoplastic phase-field model, developed in Part I, was employed to study stress-assisted diffusional phase transformation, taking plastic deformation into consideration. Different loading conditions were applied to a single crystal of Mg-Al-based alloys during precipitation, aiming at investigating the effects of elastoplastic deformation associated with both phase transformation and external loadings. The simulation results show that even when external loadings are below the materials’ yield limits, plastic deformation may occur due to stress accumulation triggered by the volume expansion of β-Mg17Al12 precipitates and the lattice mismatch between the precipitate and the matrix. Under both axial and shear loading conditions, plasticity plays a significant role in the morphological evolution of β-Mg17Al12 precipitate with Burgers orientation. In contrast to the lath morphology observed in the absence of external loadings, a rhombic-like precipitate is formed when applying an external tensile loading of 30 MPa along [112̅0]α direction, while a mirror-symmetrical-parallelogram-like morphology emerges under a shear loading of + 30 MPa. Additionally, plasticity plays a similar dual role during precipitation under different loading conditions, which would promote the growth of the precipitate at the initial stage but tend to retard it afterward. These findings illustrate that the plastic strain generated under external loadings has a great impact on the precipitate microstructure, which provides guidelines for designing the precipitate microstructure to obtain better mechanical properties.

Investigation of the LME Susceptibility of Dual Phase Steel with Different Zinc Coatings

The application of anti-corrosion coated, high-strength steels in the automotive industry has increased in recent years. In combination with various zinc-based surface coatings, liquid metal embrittlement cracking can be observed in some of these materials. A high-quality, crack-free spot-welded joint is essential to realize the lightweight potential of the materials. In this work, the LME susceptibility of different coatings, which will be determined by the crack length and the occurrence rate, will be investigated using a welding under external load setup. The uncoated specimens did not show any LME. EG, GI and GA showed significantly less LME than ZM coatings. The latter coatings showed much larger crack lengths than the EG, GI and GA coatings. Furthermore, two mechanisms regarding the LME occurrence rate were observed: the occurrence of LME in zinc–magnesium coatings was theorized to be driven by the material properties of the coatings, whereas the occurrence of LME at EG, GI and GA samples was forced mainly by the application of the external tensile load. In the experimental setup of this work, the materials were exposed to unusually high mechanical loads (up to 80% of their yield strength) to evoke LME cracks.

Effect of external tension on the wetting of an elastic sheet

Recent studies of elastocapillary phenomena have triggered interest in a basic variant of the classical Young-Laplace-Dupré (YLD) problem: the capillary interaction between a liquid drop and a thin solid sheet of low bending stiffness. Here we consider a two-dimensional model where the sheet is subjected to an external tensile load and the drop is characterized by a well-defined Young's contact angle θ_{Y}. Using a combination of numerical, variational, and asymptotic techniques, we discuss wetting as a function of the applied tension. We find that, for wettable surfaces with 0<θ_{Y}<π/2, complete wetting is possible below a critical applied tension due to the deformation of the sheet in contrast with rigid substrates requiring θ_{Y}=0. Conversely, for very large applied tensions, the sheet becomes flat and the classical YLD situation of partial wetting is recovered. At intermediate tensions, a vesicle forms in the sheet, which encloses most of the fluid, and we provide an accurate asymptotic description of this wetting state in the limit of small bending stiffness. We show that bending stiffness, however small, affects the entire shape of the vesicle. Rich bifurcation diagrams involving partial wetting and "vesicle" solution are found. For moderately small bending stiffnesses, partial wetting can coexist with both the vesicle solution and complete wetting. Finally, we identify a tension-dependent bendocapillary length, λ_{BC}, and find that the shape of the drop is determined by the ratio A/λ_{BC}^{2}, where A is the area of the drop.

Evaluating the slurry erosion rates of uniaxially stressed stainless steel 304

Erosion enormously affects the chemical processing industry and the oil and gas industry. Particulates in the stream of flow cause material loss to the tune of millions of dollars. Parameters that are known to affect erosion include particle size, impact angle and velocity. However, very few have studied the effects of the stress state of the target on erosion rates. This paper studies the erosion rates of stainless steel 304 under the effects of a uniaxial stress from an external tensile load. Loads up to 70% of yield strength (YS) were applied and erosion rates were determined from the weight loss of the samples. The Taguchi method was used to analyze the influence of each parameter on the erosion rates. Results show that velocity and particle size enormously affect erosion rates followed by angle of impact. Stress state of the target showed no significant effects on erosion rates.

Process Stability and Reproducibility of the Dieless Drawing Process for AZ31 Magnesium Wires

Magnesium (Mg)-based wires are in the focus of interest for numerous applications like micro-forming technologies or medical engineering. Manufacturing thin Mg-based wires is widely realized by applying a conventional multiple pass cold wire drawing process. This requires a complex manufacturing schedule of multiple passes with intermediate heat treatments to overcome work hardening, because of the cold forming process. Especially Mg and its alloys are known for their rather low formability at room temperature associated with the hexagonal close-packed lattice structure. The dieless drawing process uses local heating to initialize a localized plastic zone under an external tensile load to achieve higher reductions in diameter in a single wire drawing pass. It can therefore present a solution for a more efficient warm manufacturing process of Mg-based wires. In this study, the stability of the steady state material flow during a dieless wire drawing process and its reproducibility was investigated. For this purpose, a variation of process parameters was selected and wire manufacturing was carried out using magnesium alloy AZ31. A single and double dieless drawing process was applied. Additionally, a conventional cold wire drawing process including a die with the same forming schedule was executed as a benchmark experiment. The results of this study show, that the dieless drawing process is not only a stable process after reaching the steady state, but it is also a reproducible and accurately adjustable process. Moreover, the dieless drawing process maintains the property profile of the starting material to a large extend.

Fracture Simulation of Ni–YSZ Anode Microstructures of Solid Oxide Fuel Cells Using Phase Field Method

The performance degradation of solid oxide fuel cells (SOFC) is directly related to the damage and fracture of electrode microstructures. In this study, the phase field fracture method is used to simulate the fracture of anode microstructures, and the effects of boundary constraints, thermal load, and Ni phase on the fracture of Ni–YSZ anode microstructures are investigated. Results show that tensile stresses occur in the Ni and YSZ phases whether above or below the reference temperature. The cracks propagate along the direction perpendicular to the first principal stress, showing a brittle fracture characteristic. When the microstructure is cooled, all cracks appear in YSZ phase, and almost all cracks initiate at the lowest point of YSZ–pore concave interface. When the microstructure is heated, the tensile first principal stress induces few cracks at local positions but will not make the cracks propagate continuously. The thermal mismatch between Ni and YSZ is not enough to induce cracks, and the fracture of electrode microstructure is more likely to be caused by external tensile load or the thermal mismatch between anode and electrolyte layers. The presence of Ni increases the stiffness of the microstructure, and solid phase’s disconnection reduces the strength of the microstructure.

Brittle fracture development through sets of preexisting small-scale cracks under quasi-static and dynamic impact loading

Fracture development and its possible relation with wave motion in a brittle rectangular solid material with sets of preexisting small-scale parallel cracks are investigated. Experimental observations using high-speed cameras under external quasi-static tensile or dynamic impact loading conditions indicate that depending on the inclination angle, length and distribution pattern of cracks, fractures evolve considerably differently. Quasi-static load generally produces dynamic or quasi-static primary fracture with ensuing dynamic secondary retrograde fractures that are initiated at distant positions. Fractures can be arrested and jump easily, often resulting in clusters. Impact-related waves can induce primary fracture moving in both prograde and retrograde directions.

Insect antennae: Coupling blood pressure with cuticle deformation to control movement

Insect antennae are hollow, blood-filled fibers with complex shape. Muscles in the two basal segments control antennal movement, but the rest (flagellum) is muscle-free. The insect can controllably flex, twist, and maneuver its antennae laterally. To explain this behavior, we performed a comparative study of structural and tensile properties of the antennae of Periplaneta americana (American cockroach), Manduca sexta (Carolina hawkmoth), and Vanessa cardui (painted lady butterfly). These antennae demonstrate a range of distinguishable tensile properties, responding either as brittle or strain-adaptive fibers that stiffen when stretched. Scanning electron microscopy and high-speed imaging of antennal breakup during stretching revealed complex coupling of blood pressure and cuticle deformation in antennae. A generalized Lamé theory of solid mechanics was developed to include the force-driven deformation of blood-filled antennal tubes. We validated the theory against experiments with artificial antennae with no adjustable parameters. Blood pressure increased when the insect inflated its antennae or decreased below ambient pressure when an external tensile load was applied to the antenna. The pressure–cuticle coupling can be controlled through changes of the blood volume in the antennal lumen. In insects that do not fill the antennal lumen with blood, this blood pressure control is lacking, and the antennae react only by muscular activation. We suggest that the principles we have discovered for insect antennae apply to other appendages that share a leg-derived ancestry. Our work offers promising new applications for multifunctional fiber-based microfluidics that could transport fluids and be manipulated by the same fluid on demand. Statement of significanceInsect antennae are blood-filled, segmented fibers with muscles in the two basal segments. The long terminal segment is muscle-free but can be flexed. To explain this behavior, we examined structure-function relationships of antennae of cockroaches, hawkmoths, and butterflies. Hawkmoth antennae behaved as brittle fibers, but butterfly and cockroach antennae showed strain-adaptive behavior like fibers that stiffen when stretched. Videomicroscopy of antennal breakup during stretching revealed complex coupling of blood pressure and cuticle deformation. Our solid mechanics model explains this behavior. Because antennae are leg-derived appendages, we suggest that the principles we found apply to other appendages of leg-derived ancestry. Our work offers new applications for multifunctional fiber-based microfluidics that could transport fluids and be manipulated by the fluid on demand.

Pretension loss in bolted timber joint under external tensile load

Pretension loss in bolted timber joint under external tensile load

Modeling irradiation-induced intragranular gas bubble in tungsten under external tensile loading

Microstructure damage created by high-energy particle irradiation has an inevitable effect on the performance of material. Helium (He) as the transmutation element in irradiated solid prefers to occupy the vacancy (V) center to form HeV complex, which in turn induces the formation of He bubble. Herein, the external applied stress driven irradiation-induced He bubble formation and evolution in single-crystalline tungsten (W) has been investigated using the phase-field method. Importantly, the trapping and resolution kinetic behavior between He atom and He bubble is described by the diffusion coefficient in terms of rate theory continuum model, and the effect of external stress on the movements of vacancy, self-interstitial and He atom has been implemented into their diffusivities as well. We first concentrate on the intrinsic lattice distortion (stress) patterns of void and bubble to validate the developed model by comparing the reported numerical results. Then, the accelerated growth velocity of bubble along the loading direction is predicted, which agrees well with the previously observed stress pattern around the void/bubble. The evolution behaviors of the stress-assisted single, bi-dispersed and multiple bubbles vary with the direction and magnitude of external loading, indicating a strong correlation between the size and density of bubble and the loading level. It is found that with the contribution of increasing external stress, more bubbles can be generated at the formation stage and visible bubbles tend to reduce at the coarsening stage due to bubble coalescence.

Finite Element Analysis of the Load Factor and New Design Method for Bolted Joints Consisting of Dissimilar Hollow Cylinders Under Tensile Loads

Abstract In designing a bolted joint consisting of dissimilar hollow cylinders, the load factor (the ratio of an increment in axial bolt force to an external tensile load) is important. However, no researches on the characteristics of bolted joints consisting of dissimilar joint members have been conducted. In this paper, the effects of load application positions, the ratio b/a of the outside diameter to the inside diameter of dissimilar hollow cylinders, Young's modulus ratio between the dissimilar hollow cylinders on the load factor, and a load when the interface separation starts are examined using finite element method (FEM) calculations. As a result, it is found that the values of the load factor decrease as the ratio b/a increases, and the load application position approaches the interfaces, while the value of the load factor is independent of the bolt preload. For verification of the FEM calculations, experiments to measure the load factor and a load when the interfaces start to separate were carried out. The FEM results are fairly coincident with the experimental results. It is found that the value of the load factor is less than 0.15 for steel and aluminum joints, it is less than 0.1 for steel and steel joints, and it is less than 0.2 for aluminum and aluminum joints, where the bolt material is steel in this study. Finally, using the obtained load factor, a new design method for bolted joints with dissimilar hollow cylinders is demonstrated for determining the nominal diameter of bolt, the bolt strength grade, a target tightening torque, and a target bolt preload. Additionally, in the design procedure, an issue if a washer should be inserted or not inserted is discussed as well as determination of bolt preload.

Model description of hydrogen-induced damage evolution in high-strength steel weld metal based on results of a novel test method

In this paper, the development of a novel method for testing welded tensile specimens under two-stage external tensile loading is presented. The test method is intended to investigate the susceptibility of submerged arc welded high-strength steel specimens of type S690QL-S3Ni2.5CrMo to hydrogen-induced damage. Multiple cracking events within one specimen prove that the locally prevailing boundary conditions decisively determine the hydrogen-induced damage sequences.By means of SEM and EBSD analyses on specimens after test completion, interrelationships about the microstructural damage behavior are being examined. The crack tip environments are of particular importance here, since complex stress and strain conditions tend to cause hydrogen accumulation and further propagation of inter- and transgranular cracks here. In the vicinity of crack tips, retained austenite is of special importance. This metastable phase might undergo a deformation-induced transformation into crack-sensitive martensite and simultaneously release high local hydrogen contents as a former hydrogen trap. Finally, a model description including various sections of the stress- and hydrogen-induced damage evolution is derived from the empirical-analytical results.

Features of Thermomechanical Stability of Anionic-Cation Exchange Matrix "Polikon AC" on Viscose Non-Woven Materials.

The thermomechanical stability of the anion–cation exchange matrix “Polikon AC” on viscose nonwoven materials is investigated. In this work, a molecular model of a solvation environment for experimentally obtained “Polikon AC” mosaic membranes is refined. Mosaic membranes on a viscose fiber base were fabricated by the method of polycondensation filling. The temperature dependence of deformation was investigated for dry and wet anion and cation exchange membrane components at a constant tensile load of 1.5 N and a heating rate of 8 °C/min. The effect of moisture content on the deformation of anionite and cationite fragments under a constant external tensile load of 1.5 and 3 N in a temperature range up to 100 °C was studied.

Elucidating the specific and combined effects of particle size, impact angle, velocity and stress from an external load on the slurry erosion of mild steel S275JR

Erosion is known to cost the oil and gas industry millions of dollars in maintenance and repairs. While velocity, particle size, angle of impact and material properties such as hardness of particle and target are known to affect erosion rate, little is known about the effects of the stress state of the target itself. This paper studies the individual and combined effects of particle size, impact angle, velocity and stress from an external tensile load on the erosion rates of mild steel S275JR. Loads up to 70% of yield strength (YS) was applied and the erosion rates were determined from the weight loss of the samples. Microscopy analyses, hardness tests, 2D and 3D profilometry studies were also carried out.