Critical Strain Limit Research Articles

Study on Critical Drawdown Pressure of Sanding for Wellbore of Underground Gas Storage in a Depleted Gas Reservoir

Accurately predicting the critical differential pressure (CDP) of sand production contributes to improving the peak-shaving capacity and ensuring safe operation of underground gas storage (UGS). The CDP of sanding production in the target wells of the UGS was predicted coupling laboratory tests, inversed analysis with well logging data and numerical simulations. The in-situ mechanical properties of rock were estimated by coupling the laboratory test results and well-logging data. The in-situ stress field of the target formation was then deduced through inversed analysis coupled finite element method (FEM) and genetic algorithm (GA), based on the existing known stress data and the seismic data of the measured points. Using the critical strain limit (CSL) of 5‰ as the sanding criterion of the wellbore, the CDPs of the gas production in the UGS were predicted, which was 5.59 MPa, 3.98 MPa, and 4.01 MPa for well #1, well #2 and well #3, when the pressure of the gas storage was 30 MPa, respectively. The simulation results showed good agreements with the field-measured benchmark data of well #2 and well #3. The effects of moisture contents (ranging from 10 to ~40%), and cycling times of gas injection and withdrawal (ranging from 40 to ~200 cycling times) on the critical differential pressure were simulated and analyzed. The results indicated that the CDP decreased with an increase of the moisture content and the cycling times. This study provides a reliable tool for the sanding prediction of the wellbore in the UGS.

Enhanced critical axial tensile strain limit of CORC® wires: FEM and analytical modeling

Conductor on Round Core (CORC®) cables and wires are composed of spiraled high-temperature superconducting (HTS) rare-earth barium copper oxide (REBCO) tapes, wound in multiple layers, and can carry very high currents in background magnetic fields of more than 20 T. They combine isotropic flexibility and high resilience to electromagnetic and thermal loads. The brittle nature of HTS tapes limits the maximum allowable axial tensile strain in superconducting cables. An intrinsic tensile strain above about 0.45% will introduce cracks in the REBCO layer of straight HTS tapes resulting in irreversible damage. The helical fashion at which the REBCO tapes are wound around the central core allows tapes to experience only a fraction of the total axial tensile strain applied to the CORC® wire. As a result, the critical strain limit of CORC® wires can be increased by a factor of more than 10 that of REBCO tapes. Finite element (FE) and analytical models are developed to predict the performance of CORC® wires under axial tensile strain. A parametric analysis is carried out by varying the winding angle, the Poisson’s ratio of the CORC® wire core, the core diameter, and the tape width. The results show that a small variation in winding angle can have a significant impact on the cable’s axial tensile strain tolerance. While the radial contraction of the helically wound tapes in a CORC® wire under axial tensile strain depends on its winding angle, it is mostly driven by the Poisson’s ratio of the central core, affecting the tape strain state and thus its performance. Contact pressure from multiple layers within the CORC® wire also affects the CORC® wire performance. The FE model can be used to optimize the cable design for specific application conditions, resulting in an irreversible strain limit of CORC® cables and wires as high as 7%.

Utilization of hot deformation to trigger strain induced boundary migration (SIBM) in Ni-base superalloys

The effect of strain on the resultant microstructure of an experimental low stacking fault energy Nickel based superalloy containing 24 wt. pct. Co was investigated. Billets subjected to a preliminary heat treatment at 1110 °C were compressed to strain limits of 0.15 and 0.5 at strain rates ranging from 0.1/s to 0.01/s and temperatures at 1020 °C and 1060 °C. The as-deformed microstructures were assessed and characterized using electron backscatter diffraction, as were microstructures corresponding to a super-solvus anneal heat treatment at 1160 °C for one hour. This study sought to identify a critical strain limit at which conditions indicative of Strain induced boundary migration (SIBM) could be effectively triggered for the experimental Ni-based superalloy over a set range of thermal-mechanical parameters. Microstructures corresponding to SIBM were then compared to more extensively deformed billets which contained notable fractions of dynamically recrystallized grains to quantify differences in the length fraction and density of ∑3 twin boundaries of the respective microstructures. Though billet samples deformed to both 0.15 and 0.5 contained notable magnitudes of stored strain energy, microstructures deformed to 0.15 were noted as having maintained larger length fractions of ∑3 twins due to a predominant absence of dynamic recrystallization. Annealed samples originally deformed to 0.15 yielded annealing twin length fractions as high as 59% when compared a sample deformed to the 0.5 strain limit under equivalent thermal-mechanical conditions that resulted in a twin length fraction of 50%. Although samples deformed to the lower strain limit exhibited higher length fractions of annealing twins, samples deformed to the higher strain limit of 0.5 were noted to yield ∑3 densities as high as 0.65 μm−1, whereas the annealed sample deformed under equivalent thermal-mechanical parameters to the 0.15 strain limit produced ∑3 densities as low as 0.32 μm−1.

Helium permeation as a fast quality indicator for barrier properties of solar cell encapsulates

AbstractThe advent of flexible electronic devices and flexible thin‐film photovoltaic modules increases the need for transparent and flexible high‐barrier films. Conventional methods for measuring the barrier properties of such films are costly and time consuming. In our work, we present a method where we correlate water vapor and helium transmission rate measurements on strained barrier films with thin‐film solar module performance. We show that the detected properties correlate well with the performance of a CIGS mini module exposed to damp‐heat environment. The critical strain limit for a substantial decrease in barrier properties was identified for an ETFE‐based barrier film incorporating an inorganic barrier layer. It was found that the detection of the helium transmission rate provides a fast and reliable way to identify damage to barrier films and is therefore suitable as means for quality control or incoming goods inspection.

Characteristic Irreversible Critical Strain Limit of GdBCO Coated Conductor Tapes under Various Temperature and Magnetic Field Conditions

Superior mechanical and electromechanical properties of the coated conductor (CC) tapes made them a viable option for coil and magnet applications. In this study, investigation on the characteristics of I c under different B, T, and e conditions were conducted. Tensile load was applied using the Katagiri type test rig under different high magnetic field and low-temperature conditions wherein irreversible strain, e irr was determined. The I c behavior with magnetic field of both reactive co-evaporation by deposition and reaction (RCE-DR) and metal organic chemical vapor deposition (MOCVD) processed CC tapes at different T and B were obtained. The critical irreversible strain limit e irr of Cu-stabilized REBCO CC tape increased with decreasing temperature from 65 K down to 20 K. This behavior was resulted from the increased yield strength of the CC tape due to thermal hardening effect.

Ratcheting behavior of bearing support structures during windmilling in aero engines*

Abstract A major safety concern in commercial civil aviation is losing a fan blade from jet engine during its normal operation either due to bird strike or limited fatigue. The assessment of fatigue strength of the support structures like bearing and intermediate connection in aero engine during windmilling has become an essential requirement for safe-fly-home situation. Windmilling is the rotation of a non-operating engine due to the airflow induced forces on the blades caused by the forward motion of the aircraft. The imbalanced rotation during windmilling post fan blade off (FBO) creates unavoidable vibratory loads in transient nature which leads to shorter fatigue life of the support structures. Since the repeated imbalance loads beyond elastic limit of the structure can cause the accumulation of plastic deformation, which exceeds the critical strain limit of the structure. This article deals with the ratcheting behavior (low cycle fatigue) of bearing support structures during windmilling post FBO in aero engine. When the accumulated plastic strain exceeds the critical strain limit of the bearing structure, then it experiences ratcheting fatigue failure.

Ruga mechanics of creasing: from instantaneous to setback creases

We present mechanics of surface creasing caused by lateral compression of a nonlinear neo-Hookean solid surface, with its elastic stiffness decaying exponentially with depth. Nonlinear bifurcation stability analysis reveals that neo-Hookean solid surfaces can develop instantaneous surface creasing under compressive strains greater than 0.272 but less than 0.456. It is found that instantaneous creasing is set off when the compressive strain is large enough, and the longest-admissible perturbation wavelength relative to the decay length of the elastic modulus is shorter than a critical value. A compressive strain smaller than 0.272 can only trigger bifurcation of a stable wrinkle that can prompt a setback crease upon further compression. The minimum compressive strain required to develop setback creasing is found to be 0.174. If the relative longest-admissible perturbation wavelength is long enough, then the wrinkle can fold before it creases, and the specimen can be compressed further beyond the Biot critical strain limit of 0.456. Various bifurcation branches on a plane of normalized longest-admissible wavelength versus compressive strain delineate different phases of corrugated surface configurations to form a ruga phase diagram. The phase diagram will be useful for understating surface crease, as well as for controlling ruga structures for various applications, such as designing stretchable electronics.

The shear rheology of bread dough: Analysis of local flow behaviour using CFD

The local shear flow behaviour of bread dough has been studied using computational fluid dynamics (CFD). A simulated power-law model together with a wall slip boundary condition agreed satisfactorily with experimental observations for tube flow geometry. Lower shear strain rates were shown to promote greater damage to the dough's microstructure. Predictions revealed that dough remained fairly undamaged near the centreline of the flow field, as the critical strain limit for failure (γ∼20) was not achieved, suggesting a process model should include an element of viscoelasticity. Flow behaviour through a sudden contraction suggested that shearing plays a significant role in the orientation of the gluten network within dough. Further, extremely high shear strain rates were predicted within the geometry which highlighted the usefulness of CFD in identifying unstable process regions and the need for a model that includes such conditions. The results demonstrate the potential of CFD to allow development of a model that links process variables and the microstructure of dough for application for process control and the modernisation of the bread-making process.

Impact Response Analysis of Wire Ring Net System Using the Concept of Particle Method

In Japan, there are many steep mountainous areas and we have local severe rain in the season, thus rock-fall accidents occur in mountain regions year after year. In order to protect an arterial road and the urban areas from the rock-fall accidents, various protective structures had been already constructed. However most of them are made of reinforced concrete and they require huge construction cost. Hence a new economical protective structure has been expected for a long time. From these needs, several high-energy absorption rock-fall nets have been developed. Some of them have specialized shock absorbing device or specialized column which has plastic rotation capacity. On the one hand, wire frame structure (called the wire ring net system) that is composed of interconnected many wire rings of about 30 cm in diameter are predominant in Europe. Because these structures can absorb large kinetic energy of a falling rock due to their deformation capacity, they are introduced from Europe as the highly-effective structures. The wire ring net system is composed of many parts (wire ring, wire rope, supporting post, etc), and it does not require large bases due to its light weight. However, there is no analysis method that can calculate their impact response (dynamic behaviour and energy absorbing capacity), and it has been only confirmed by the full-scale falling weight tests. Although, there are several cases that evaluate the performance by same tests in Japan, the test condition is limited by restriction of test station and its cost. Therefore, this study aims at simulating the impact response of wire ring net system by using the concept of particle method. The following conclusions are obtained from this study. 1) The proposed method can simulate the impact response of the wire ring net system. 2) Fracture of the wire ring net is predicted applying critical strain limit for the material.

Comparison of different caster designs based on bulging, bending and misalignment strains in solidifying strand

If the strain level in the solidifying strand is more than the critical strain limit, cracking occurs. This strain depends strongly on the caster design and the process parameters. In the present work, an attempt has been made to show the effect of various caster designs and process parameters on the bulging and bending strain in the continuously solidifying strand. For simplicity an analytical tool is chosen for the strain prediction. As the solidifying front is the most critical, strain is calculated on the solidifying front and therefore, the use of the hard box approach near the edges is not considered. Three different caster designs are considered for the comparison and the effects of casting speed, radius of the machine and roll pitch on the strains are studied. It is found that the misalignment strain is quite significant. The strong dependence of strain level on the rolls not in contact with the solidifying strand and the misalignment has highlighted the importance of good machine maintenance. A comparison between the prediction from the soft and the hard box approaches for bending/unbending strain is carried out and it is found that the soft box approach is more conservative for strain prediction.

The Influence of Microstructural Features and Mechanical Properties on the Cold Formability of Ferritic Steel Sheets

In the present study, the formability of cold rolled and annealed steel sheets having carbon equivalent values in the range of 0.028 to 0.098 wt% were investigated. The steel sheet having the lowest carbon equivalent was a titanium-stabilized interstitial free steel, which established the highest strain hardening exponent, anisotropy coefficient and higher Forming Limit Diagram (FLD). Since plain strain intercept (FLD 0 ) is the most critical strain limit on the FLD, the empirical equations were derived between FLD 0 and microstructural features and mechanical properties. As a microstructural feature grain size and as a mechanical property anisotropy coefficient gave the most reliable correlations.

Comparison of structural and optical properties in strained GaInAsP MQW structures grown by MOVPE and MOMBE

The growth parameter dependence of the transition from 2D to 3D growth of GaInAsP multiple quantum well (MQW) structures up to ε B=0.5% tensile-strained barriers was examined. Identical MQW structures with ε W=1% compressively strained wells were grown by metal organic vapor-phase epitaxy (MOVPE) and metal organic molecular beam epitaxy (MOMBE) and characterized by photoluminescence (PL), X-ray diffraction and transmission electron microscopy. Increasing the tensile barrier strain resulted in deteriorated optical and crystalline properties beyond a critical strain limit, which depends on growth temperature. The deterioration originates from lateral layer thickness and strain modulations. Their density, amplitude and thus their effect on the optical MQW properties are different for both growth methods. High-quality MOMBE-grown MQW structures up to ε W=2% compressive well strain and ε B=0.5–1% tensile barrier strain could be achieved by inserting thin intermediate layers at each internal interface. The composition of these intermediate layers has a significant effect on MQW material properties.

Evaluation of Mechanical Loading of a Trileaflet Polyurethane Blood Pump Valve by Finite Element Analysis

The mechanical loading of the leaflets of a polyurethane blood pump valve at closing pressure (max 300 mmHg) and during the opening phase can be numerically calculated by the finite element method. Geometrical and physical non-linearities, supporting forces by neighbouring leaflets and manufacturing-related thickness distribution are taken into account. The valve housing is assumed to be rigid. Volume forces are neglected. The calculations showed that the critical strain limit of 4.5% (long-term failure limit) was exceeded at closing pressure and during valve opening. During valve operation the connection between leaflet and valve housing and the central leaflet region seem to be the critical areas.

Grain growth and secondary recrystallization in iron

The effect of impurities and of slight deformations as factors modifying the kinetics of normal grain growth after primary recrystallization in pure iron is investigated. Samples of pure iron and Armco iron, each with or without a content of precipitated oxides, were examined. Inclusions inhibit grain growth up to high temperatures, whilst the influence of strain depends on its amount: very low deformations (∼2%) generally block grain growth; for deformations around 5%, secondary recrystallization takes place; higher deformations (∼10%) accelerate the early stages of growth, leading to not very large final grain dimensions. 2.0% elongation has been found to be, in our conditions, the critical strain limit for secondary recrystallization.