Effect Of Creep Strain Research Articles

Behavior of stiffened deck plates under hydrocarbon fire

Hydrocarbon fire accidents in offshore deck structures are of serious concern due to the confined environment of offshore oil drilling and production platforms, which limits the escape routes. One of the major structural components that are highly affected during fire accidents is the deck plates. The deck plates are usually designed as stiffened plates with high strength steel. The increase in temperature during fire changes the mechanical properties of steel significantly, which may result in strength and geometric instability of the structure. The present study aims to investigate the behavior of a stiffened steel deck plate under different hydrocarbon fire scenarios using sequential thermal and structural analyses using Ansys. The stress distribution and deformation of the plate in time scale are presented, discussing the highly affected region concerning the source of the fire. The fire rating for the steel deck under hydrocarbon fire is also suggested for different fire scenarios considered in the study. It was observed that the deformation of the deck plate varies to the area of deck plate in direct contact with fire, boundary conditions of the plate, and the area of steel plate with elevated temperature beyond which the mechanical properties of steel are highly affected. Also, the numerical investigations of the deck plate under the combined action of mechanical load and hydrocarbon fire had shown an increased deformation in the deck plates, which in turn reduces the fire rating of the plate under all fire scenarios. The effect of creep strain at high temperature on the response of the steel deck plate is also studied for the different fire loading cases.

Creep analysis of a rotating functionally graded simple blade: steady state analysis

Initial thermo-elastic and steady state creep deformation of a rotating functionally graded simple blade is studied using first-order shear deformation theory. A variable thickness model for cantilever beam has been considered. The blade geometry and loading are defined as functions of length so that one can define his own blade profile and loading using any arbitrary function. The blade is subjected to a transverse distributed load, an inertia body force due to rotation and a distributed temperature field due to a thermal gradient between the tip and the root. All mechanical and thermal properties except Poisson's ratio are assumed to be longitudinally variable based on the volume fraction of reinforcement. The creep behaviour is modelled by Norton's law. Considering creep strains in stress strain relation, Prandtl-Reuss relations, Norton' law and effective stress relation differential equation in term of effective creep strain is established. This differential equation is solved numerically. By effective creep strain, steady state stresses and deflections are obtained. It is concluded that reinforcement particle size and form of distribution of reinforcement has significant effect on the steady state creep behavior of the blade.

Effect of creep strain on mechanical behaviour of ultra-high strength (Grade 1200) steel subject to cooling phase of a fire

This paper evaluates the mechanical behaviour of Grade 1200 ultra-high strength steel (UHSS) tube under a multi-phase loading scenario including fire and creep. To achieve this, two sets of experiments are performed on standard dog-bone specimens taken from UHSS tubes. In the first set of experiments, termed Creep-Heat-up tests, the specimens are axially loaded to a specific stress level, fs. Whilst the axial load is maintained, the samples are heated to elevated temperatures of up to 700°C and a tensile test is performed on them at elevated temperature. The second set of experiments, which are the main focus of this study, are termed Creep-Cooling tests and are similar to the first set except that the specimens are tested to failure after being cooled to room temperature. The axial load in this set of tests is maintained during both heat-up and cooling phases of a fire. The stress-strain curves, the creep strain the specimens experience due to the sustained axial load during fire, and the residual strength of the test specimens are discussed. In order to investigate the effect of steel grade, Grade 800 high strength steel (HSS) and Grade 350 mild steel (MS) specimens are also tested and the results are compared. Finally, the microstructural origin of accelerated softening in UHSS due to creep strain is discussed.

CONSTITUVE MODELLING FOR CREEP OF DRAWN COPPER WIRE

The high-temperature creep behaviour of drawn copper wire was studied by different constant stresses 98,108 and 118 MPa and under the temperatures of 250, 290 and 340°C. This study deals with the creep based prediction modelling of an industrial copper wire. The proposed unified creep damage constitutive equations were determined using experimental data achieved for materials at applied stress. The comparison of experimental and predicted effective creep strain curves is carried out for all applied stresses applied on the drawn copper wire. The evaluated stress exponent n = 9.21, 10 and 14 and the activation energy Q = 22.25, 31.75 and 50.75 indicated that the creep deformation of the drawn copper wire is controlled by the dislocation creep. The evaluated of the mean relative error from 5.18 % to 10.11 confirmed the creep strain predicted by the proposed model well agree with experimental data.

Effect of particle content, size and temperature on magneto-thermo-mechanical creep behavior of composite cylinders

The effects of particle content, particle size, operating temperature and magnetic field on steady-state creep behavior of thick-walled rotating cylinders made of Al-SiC composites have been investigated. Loading is composed of a uniform magnetic field in axial direction, steady-state heat conduction in radial direction and an inertia body force due to rotation. The composite creep constitutive equation has been described by Norton’s law in which the creep parameters are functions of particle size, temperature and particle content. The composite properties are radial dependent based on volume fraction of SiC reinforcement. It has been found that the minimum effective creep strain rate belongs to a composite identified by 25% SiC at the inner and 5% at the outer surfaces. Therefore this composite has been selected for the design of the cylinder. It has been concluded that increasing particle size and operating temperature significantly increases the effective creep strain rates. It has also been illustrated that magnetic field decreases the stresses and the effective creep strain rates.

Semi-analytical solution for electromagnetothermoelastic creep response of functionally graded piezoelectric rotating disk

Time-dependent electromagnetothermoelastic creep response of rotating disk made of functionally graded piezoelectric materials (FGPM) is studied. The disk is placed in a uniform magnetic and a distributed temperature field and is subjected to an induced electric potential and a centrifugal body force. The material thermal, mechanical, magnetic and electric properties are represented by power-law distributions in radial direction. The creep constitutive model is Norton's law in which the creep parameters are also power functions of radius. Using equations of equilibrium, strain-displacement and stress–strain relations in conjunction with the potential-displacement equation a non-homogeneous differential equation containing time-dependent creep strains for displacement is derived. A semi-analytical solution followed by a numerical procedure has been developed to obtain history of stresses, strains, electric potential and creep-strain rates by using Prandtl–Reuss relations. History of electric potential, Radial, circumferential and effective stresses and strains as well as the creep stress rates and effective creep strain rate histories are presented. It has been found that tensile radial stress distribution decreases during the life of the FGPM rotating disk which is associated with major electric potential redistributions which can be used as a sensor for condition monitoring of the FGPM rotating disk.

Time-dependent magnetothermoelastic creep modeling of FGM spheres using method of successive elastic solution

Magnetothermoelastic creep behavior of thick-walled spheres made of functionally graded materials (FGM) placed in uniform magnetic and distributed temperature fields and subjected to an internal pressure is investigated using method of successive elastic solution. The material creep, magnetic and mechanical properties through the radial graded direction are assumed to obey the simple power law variation. Using equations of equilibrium, stress–strain and strain–displacement a differential equation, containing creep strains, for displacement is obtained. A semi-analytical method in conjunction with the Mendelson’s method of successive elastic solution has been developed to obtain history of stresses and strains. History of stresses, strains and effective creep strain rate from their initial elastic distribution at zero time up to 55 years are presented in this paper. Stresses, strains and effective creep strain rate are changing in time with a decreasing rate so that after almost 50 years the time-dependent solution approaches the steady state condition when there is no distinction between stresses and strains at 50 and 55 years.

Tensile Creep Behavior of Medium-Density Polyethylene

This research investigated the effect of stress and temperature on the viscous behavior of medium-density polyethylene (MDPE). The creep properties of pure MDPE using film specimens were studied under the static loading range 15—55 MPa by a thermomechanical analyzer at room temperature and elevated temperature (30°C, 60°C, and 90°C). Viscoelastic properties were derived from experimentally measured creep data, including isochronous stress—strain diagram, creep modulus, and creep rate charts with the influence of stress and temperature. In addition, the effect of creep strain and viscous flow on MDPE structure was investigated by a thermogravimetry analyzer. The results of this study showed that the linear viscoelastic behavior of MDPE changes with stress and temperature, and any reduction of polymer chains and structure revolution under the tensile creep test were not shown.

Investigation of Effect of Creep Strain on Low-Cycle Fatigue of Lead-Free Solder by Cyclic Loading Using Stepped Ramp Waves

The fatigue life of a material varies with the strain rate if it has time-dependent deformation. An interesting phenomenon related to the effect of the strain rate on the fatigue life can be observed when a cyclic tension-compression loading of which strain rate in the tensile region is different from that in the compressive region is employed for the fatigue test. Different fatigue lives due to different strain rates in the tensile and compression regions originate from the difference of development behaviors of creep strain generated in the cyclic loading. This paper investigates the effects of creep strain on the difference of fatigue life due to the different strain rate in the tensile and compression regions. The creep strain of the lead-free solder Sn–3.0Ag–0.5Cu subjected to a cyclic loading was investigated using stepped ramp wave loading. The experimental results reveal that the creep strain develops differently in the tensile and compression regions. A new parameter is proposed for estimating fatigue life when the strain rate varies in the loading direction.

Experiments for the long-term prediction of creep strain of expanded polystyrene under compressive stress

Expanded polystyrene (EPS) slabs were tested to determine their strength and the effects of creep strain under compressive stress. The results were statistically analysed based on long-term experiments between 65 and 2034 days. The analysis shows that it is possible to predict creep strain development for a lead time of 50 years on the basis of the data obtained in experiments shorter than 608 days, as specified in Standard EN 13163. Sufficiently accurate point-wise prediction of creep strain of EPS slabs under a compressive stress σ c of (0.25 and 0.35) σ 10% for a lead time of 50 years is possible by extrapolating the creep described via a power equation (Findley W.N.) and using data from the 65-day direct experiment.

Effect of creep strain on the optomechanical properties and some structural properties of terylene fibers

AbstractThis article sheds light on the effect of creep strain [ϵ(t); %] on the optomechanical properties and some structure properties of terylene fibers at several constant applied loads. Automated multiple‐beam Fizeau fringes in transmission were used with a mechanical creep device attached to a wedge interferometer where the fiber was subjected to a constant load. This technique was used to determine the mean refractive indices and the mean birefringence values of terylene fibers under different conditions of ϵ(t). The obtained optical results were used to evaluate the optical orientation function, optical stress coefficient, density, crystallinity, and mean‐square density fluctuation with ϵ(t). The obtained results show that, under a constant load, the terylene fibers extended with time, the rate of which decreased with time. An empirical formula is suggested to represent the variation of ϵ(t) of terylene fibers with time, and the constants of this formula were determined. A mechanical model is proposed to represent ϵ(t) of terylene fibers, which consists of two Kelvin elements combined in series, which were used to provide an accurate fit to the experimental creep curve. The stress–strain curve via creep was studied to determine some mechanical parameters of the investigated fibers: Young's modulus, yield stress, and yield strain. Illustrations with microinterferograms, graphs, and tables are given. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Electrical property of cement-based composites filled with carbon black under long-term wet and loading condition

Cement-based composite filled with 120 nm carbon black (CBCC) in the amount of 15% by weight of cement was a promising strain sensor material candidate, of which the resistance was sensitive to strain. This paper showed that the initial resistance of CBCC not only increased with water content, but also increased with the measurement time. These two phenomena were mainly attributed to a polarization effect which strengthened with water content. A waterproof measurement, i.e. a specimen encapsulated by epoxy resin, was developed to insulate the composite from ambient moisture. The effects of full water absorbing capacity of epoxy, creep behavior of CBCC and environmental temperature on the waterproof efficiency were studied. The results indicated that the effects of creep strain and temperature on resistance could be compensated and an epoxy with full water absorbing capacity less than 1.83% could meet the waterproof requirement of CBCC that guaranteed the accuracy of the resistance measurement.

Creep rupture of copper and aluminium alloy under combined loadings—experiments and their various descriptions

Creep tests are carried out under tension, pure torsion, and combined tension and torsion at an elevated temperature of 523 K for pure copper and 423 K for an aluminium alloy. Different creep and rupture properties of the materials are observed throughout the deformation process under the different stress states. The effects of stress states on primary creep, secondary creep, the failure and lifetime of the materials are analysed. A new set of multiaxial mechanisms-based creep damage constitutive equations has been formulated on the basis of analysis of previous creep models. The proposed unified creep damage constitutive equations are determined using experimental data achieved for both materials at three effective stress levels. Creep tests for each stress level were carried out for three stress states. The comparison of experimental and computed effective creep strain curves is carried out for all the stress states and stress levels tested for both materials. In addition, it has been verified that the determined multi-stress-state creep damage constitutive equations can be used to predict the isochronous surfaces of the materials very precisely. To compare with conventional constitutive descriptions, a set of multiaxial constitutive equations is also determined for the experimental data of the two materials using the same optimisation techniques. The quality of the fittings is compared and further discussion is carried out for the stress-state variable α .

建築構造用鋼材(SN490B)を用いた柱材の高温時の座屈強度

An experimental study was performed to obtain the data about the buckling strength of the columns using structural steel(SN490B) at high temperature. Two kinds of experiments under the centrally compressive load with rectangular cross-sections of thickness 10mm X width 26mm, (1)tests at constant high temperature, and (2), tests at increasingly higher temperature under a constant axial load. By the tests(1), the buckling loads of column models which were enforced axial edge compression at a constant-high temperature were examined. And, by the tests(2), the collapse temperatures of the column models at increasingly higher temperature under a constant load were examined. The results of these tests were compared on a chart of buckling curves, and the effect of creep strain on the buckling strength of the column models was investigated. Furthermore, numerical simulations of the tests were performed. And the results of the calculations clearly show that numerical analysis can be used to provide accurate predictions of the buckling characteristics of columns at high temperatures, when an appropriate mechanical model and data of steel materials at high temperature are used. Comparing the results of tests and analyses, the effects of creep strain (time effect) on the buckling characteristics of steel columns at high temperature are shown.

Effect of creep strain on microstructural stability and creep resistance of a TiAi/Ti3ai lamellar alloy

Creep of a TiAl/Ti3Al alloy with a lamellar microstructure causes progressive spheroidization of the lamellar microstructure. Microstructural observations reveal that deformation-induced spheroidization (DIS) occurs by deformation and fragmentation of lamellae in localized shear zones at interpacket boundaries and within lamellar packets. Deformation-induced spheroidization substantially increases the interphase interfacial area per unit volume, demonstrating that DIS is not a coarsening process driven by reduction of interfacial energy per unit volume. Creep experiments reveal that DIS increases the minimum creep rate (emin) during creep at constant stress and temperature; the activation energy (Q c ) and stress exponent (n) for creep are both reduced as a result of DIS. Values ofn andQ c for the lamellar microstructure are typical of a dislocation creep mechanism, while estimated values ofn andQ c for the completely spheroidized microstructure are characteristic of a diffusional creep mechanism. The increase in (emin) associated with DIS is thus attributed primarily to a change of creep mechanism resulting from microstructural refinement.

Modeling Creep in Thermoplastic Composites

A creep model for unidirectionally reinforced fiber composites was devel oped based on a one-parameter potential function. The same potential function was used to describe plastic flow and time-dependent creep deformation. The material constants in the model were determined by using the uniaxial tension test of off-axis coupon specimens. In terms of effective stress and effective creep strain, the anisotropic creep behavior can be given by a stress-dependent master creep curve irrespective of loading direction relative to fiber orientation. DuPont's AS4/PEKK thermoplastic composites were used in the creep experiment. Results for both unidirectional and laminated composites were presented.

Effects of complex loadings on plastic deformation of stainless steel (SUS 304) at high temperature

The plastic deformation for complex loadings are experimentally investigated under various high temperature conditions. The experiments are conducted by subjecting thin wall tubular specimens to combined axial load and torsion. The stress-strain curves after plastic prestraining are obtained by subsequent loading along the stress path with corners. The subsequent loadings are given at a different temperature from that of the prestrained temperature. The effects of plastic prestraining as well as temperature history on the stress-strain curves are examined under variable temperature conditions. The stress-strain curves after creep straining are determined by subsequent loading at constant temperature. The effects of creep strain on plastic hardening are observed by comparison with the stress-strain curves without creep straining. The stress-strain curves for cyclic loading are obtained under various temperature conditions. The cyclic loadings are performed between fixed strain limits. The effects of cyclic loadings on the saturation properties of cyclic hardening are examined at constant and variable temperatures.

Modeling Creep Behavior of Fiber Composites

A micromechanical model for the creep behavior of fiber composites is de veloped based on a typical cell consisting of a fiber and the surrounding matrix. The fiber is assumed to be linearly elastic and the matrix nonlinearly viscous. The creep strain rate in the matrix is assumed to be a function of stress. The nominal stress-strain relations are derived in the form of differential equations which are solved numerically for off-axis specimens under uniaxial loading. A potential function and the associated effective stress and effective creep strain rates are introduced to simplify the orthotropic relations.

The effect of creep strain on grain boundary sliding during diffusion creep

Abstract A now theoretical approach is used to determinc the contribution that grain boundary sliding makes to the overall creep strain during diffusion creep. The approach has the advantages that it is generally applicable to three dimensional grain shapes and that the effect of creep strain can be treated exactly. Furthermore, since the basic approach is to determine the sliding and diffusional displacements on individual grain boundaries those can do used to predict parameters connected with the crept microstructure. The approach is applied to the creep of initially equiaxed grains and shows that grain boundary sliding makes a decreasing contribution to the overall creep strain with increasing creep strain. Further parameters connected with the microstructure and which are experimentally verifiable are predicted. Finally, data aro presented on the sliding and diffusional displacements between grains in terms of the boundary orientation in order to give a graphical representation of, the boundary displacements and their variation with creep strain.

低炭素2 1/4 Cr-1Mo鋼溶着金属のフェライト粗粒化におよぼすクリープ歪みの影響

低炭素2 1/4 Cr-1Mo鋼溶着金属のフェライト粗粒化におよぼすクリープ歪みの影響