Creep Analysis Research Articles

Creep behavior of Nickel–Titanium shape-memory alloys under static and dynamic loadings: an FEM approach

The shape-memory effect and superelasticity properties of NiTinol alloys make them a versatile candidate for various engineering and biomedical applications. The use of these alloys as biomedical implants necessitates the study of any long-term creep failure possibility. The present study utilizes the finite element method to investigate this creep behavior of NiTinol alloys under static and dynamic loading conditions over a long period. The Maxwell creep model has been implemented, as well as validated with the polypropylene and low-density polyethylene. Further, the same model has been utilized for the creep analysis of NiTinol with suitable material properties and assumptions, for a time of 10,000 h. The results demonstrated the application of sinusoidal varying loads, the creep strain observed was lower as compared to other loading conditions, and in the case of static load, higher creep strain values were experienced than that of the dynamic smooth step loading case.

FTMP-based Hierarchical Modeling and Creep Analyses of Lath Martensite Structure for High Cr Steels

FTMP-based Hierarchical Modeling and Creep Analyses of Lath Martensite Structure for High Cr Steels

REFINED ANALYSIS OF STEADY STATE CREEP OF A ROTATING DISK AND A PLATE WITH A CENTRAL HOLE UNDER UNIFORM TENSILE LOAD BY THE QUAZILINEARIZATION METHOD

Refined analysis of the steady state creep of a rotating disk and a plate with a central hole under uniformtensile load by the quasilinearization method is presented. It is shown that the high values of the creepexponent in power law constitutive equations require more iterations in the framework of the quasilinearizationmethod in each problem. The approximation solution of the problem for an infinite plate with the circularhole under creep regime is obtained by the quazilinearization method. Four approximations of the solution ofthe nonlinear problems are found. It is shown that with increasing the number of approximations the solutionconverges to the limit numerical solution. It is worth to note that the tangential stress reaches its maximumvalue not at the circular hole but at the internal point of the plate. It is also shown that quazilinearizationmethod is an effective method for nonlinear problems.

Comparative study on the effect of adding two transition-metal-substituted polyoxometalates on the mechanical properties of the (Bi,Pb)-2223 superconducting phase

This comparative study sheds light on the optimum addition x of K5[SiFe(OH2)W11O39]·14H2O ({FeSiW11}) and K6[(H2O)MnSiW11O39]·21H2O ({MnSiW11}) (x = 0.02, 0.04, 0.08, 0.12, 0.16 and 0.20 wt%) nanoparticles to produce the desired mechanical characteristics of the (Bi,Pb)-2223 superconducting phase using a Vickers microhardness (HV) tester. HV measurement was performed at room temperature for different applied loads (0.245–9.8 N) and times (10–60 s). From the HV measurements, all the prepared samples had a normal ‘indentation size effect’ behaviour. It was found that 0.04 wt% {FeSiW11} nanoparticles and 0.08 wt% {MnSiW11} nanoparticles were the optimal addition to increase the microhardness of the (Bi,Pb)-2223 phase. Accordingly, other mechanical parameters for potential applications, such as the elastic modulus, yield strength and fracture toughness of the samples studied, were extracted from HV as a function of nanoparticle addition. The measured HV data were theoretically analysed with use of different models. The modified proportional sample resistance model was identified as the best theoretical model to describe the true HV values for both phases. Indentation creep analysis was also performed using time-dependent microhardness to indicate the enhancement of new cavity formation in the measured samples.

The Creep and Fracture Properties of Additively Manufactured Inconel 625

High temperature creep tests of additively manufactured (AM) nickel-based superalloy 625 (IN625) and wrought IN625 were conducted at 650 ˚C and 800. Thermal treatments were conducted for both AM and wrought IN625 samples prior to creep testing: either solution heat-treated or hot isostatically pressed and, additionally, long-term cyclic heat-treatments (LHT) at 650 ˚C for 6 months and 1 year. AM IN625 showed equal or even higher creep strength than wrought IN625 for all heat treatments. However, AM IN625 exhibited poor ductility compared to wrought IN625 under all creep testing conditions, and the ductility decreased after the LHT. Both AM and wrought IN625 obtained some additional strength after the LHT. The amount of extra strength in the alloys was generally proportional to the matrix volume fraction of γ’’ phase (650 ˚C) and δ phase (800 ˚C). The creep analysis suggests that dislocation climb is the rate controlling mechanism for creep. Atomic probe tomography revealed that oxygen content at the grain boundaries of creep-deformed AM IN625 was too small to cause any embrittlement. Nano-secondary ion mass spectrometer analysis found strong sulfur segregation at Al2O3 /matrix interfaces. Fracture is intergranular where alumina (that forms as a result of oxygen absorption by the powder particles before additive manufacturing) is sometimes located. Cracking can occur from these interfaces and repeated sulfur diffusion to the crack tip was the foremost possibility to explain the poor ductility of AM IN625 within the temperature range tested.

Model assessment of the lifetime of a composite overwrapped pressure vessel under creep conditions

An approach has been developed to estimate the lifetime of a composite overwrapped pressure vessel under creep conditions. Creep tests of unidirectional composite material based on T1000 carbon fibers and epoxy resin were conducted at high temperatures. Experimental creep curves were obtained and the creep rate for each specimen was determined. A numerical analysis of creep of a composite overwrapped pressure vessel subjected to a constant pressure was carried out. Time-strain curves are obtained for each characteristic point in the composite shell. The strains range up to 12.5%. The curves of relaxation of tensile stress in a composite overwrapped pressure vessel are obtained. The stress gradually decreases from 926 to 564 MPa. The structure of the vessel considered remains stable without critical strains and stresses after 50 years of exploitation. Using the proposed modeling approach of a composite overwrapped pressure vessel, taking into account the effect of creep in the composite shell, it is possible to evaluate the lifetime of the structure.

Analysis and modeling of uniaxial compressive creep of MMA-modified unsaturated polyester polymer concrete

Creep and shrinkage are the major time-dependent phenomena occurring in concrete. Because they significantly affect the long-term dimensional changes and relaxation of restrained stresses in concrete, it is of great importance to accurately consider these characteristics in the structural analysis and design process. In this study, laboratory experiments were conducted to examine the creep under uniaxial compression and linear setting shrinkage of unsaturated polyester (UP) polymer concrete modified with three different levels of methyl methacrylic (MMA) monomer (i.e., 10, 20, and 30 wt.%). The creep of UP-MMA polymer concrete was measured as per ASTM C512 under a sustained compressive stress of 20% of the compressive strength for 90 days, while the linear setting shrinkage was monitored based on the JSCE method for 7 days. Results indicated that as the MMA content increased, the 90-day creep increased although the differences were non-significant. On the contrary, the linear setting shrinkage tended to decrease with an increase in MMA content. The compressive strength was found to decrease by 7.2% as the MMA content increased from 10 wt.% to 30 wt.%. Additionally, the present study compared the measured creep coefficients with those estimated by ACI 209 and CEB-FIP Model Code 1990. It was revealed that the current creep models for Portland cement concrete are inappropriate in predicting the creep of UP-MMA concrete. A new predictive model for creep applicable to the UP-MMA concrete is proposed.

Probabilistic Finite Element Analysis of Cooled High-Pressure Turbine Blades—Part B: Probabilistic Analysis

Abstract Modern high-pressure turbine (HPT) blade design stands out due to high complexity comprising three-dimensional blade features, multipassage cooling system (MPCS), and film cooling to allow for progressive thermodynamic process parameters. During the last decade, probabilistic design approaches have become increasingly important in turbomachinery to incorporate uncertainties such as geometric variations caused by manufacturing scatter. In Part B of this two-part article, real geometry effects are considered within a probabilistic finite element (FE) analysis that aims at sensitivity evaluation. The knowledge about the geometric variability is derived based on a blade population of more than 400 individuals by means of parametric models that are introduced in Part A. The HPT blade population is statistically assessed, which allows for reliable sensitivity analysis and robustness evaluation taking the variability of the airfoil, profiled endwalls (PEWs) at hub and shroud, wedge surfaces (WSFs), and the MPCS into account. The probabilistic method—Monte Carlo simulation (MCS) using an extended Latin hypercube sampling (eLHS) technique—is presented subsequently. Afterward, the FE model that involves thermal, linear-elastic stress, and creep analysis is described briefly. Based on this, the fully automated process chain involving computer-aided design (CAD) model creation, FE mesh morphing, FE analysis, and postprocessing is executed. Here, the mesh morphing process is presented involving a discussion of the mesh quality. The process robustness is assessed and quantified referring to the impact on input parameter correlation. Finally, the result quantities of the probabilistic FE simulation are evaluated in terms of sensitivities. For this purpose, regions of interest are determined, wherein the statistical analysis is conducted to achieve the sensitivity ranking. A significant influence of the considered geometric uncertainties onto mechanical output quantities is observed, which motivates to incorporate these in modern design strategies or robust optimization.

Potato creep analysis during storage using experimental measurement and finite element method (FEM)

AbstractAnalysis of static forces has an important role in bulk storage of agricultural products. The forces exerted on individual fruits, vegetables, or grains cause mechanical damage to them and lead to their permanent deformation. By analyzing the forces involved, we can manage them with proper methods and prevent the creation of waste. In this research, by conducting experiments, the required parameters for potato samples were obtained and simulated through the finite element method under load. Creep and tension tests were conducted on a cylindrical potato sample with the diameter and height of 25 mm. Apparent shear modulus had been extracted over time and imported to the Abaqus 2016. Simulation results showed that the maximum tension of 0.061 MPa occurred in layers near the pressure plate. Tension concentration caused the maximum tension of 0.07 MPa in the center of the potato. In accordance with the created tension, maximum displacement of 0.35 mm occurred in contact layer with the pressure plate and by moving away from this plate, displacement decreased linearly and reached to zero at bottom layer. The results showed that measuring the forces in storage and knowing the forces applied to the product can be effective in controlling the storage quality of agricultural products and reducing waste.Practical ApplicationsAnalysis of static forces has important role in bulk storage of agricultural products. By analyzing the involving forces, they can be managed with proper methods and prevent the creation of waste. This paper found that maximum stress and damage occur at force inserted areas and in areas of tubers are in contact with external material like transporting and storage boxes. Then, it should be tried to fabricate new flexible and viscoelastic materials such as polymers which acts like tubers in contact areas to decrease tubers’ stress to minimum value at contact points. Also more attention should be paid to stress concentration that may occur inside tubers which can lead to crush and destroy the product. Stacking more tubers on storage which can increase inserted stress beyond the value that leads to stress concentration should be avoided.

Long-Term Creep Behavior of a CoCrFeNiMn High-Entropy Alloy

The potential of high-entropy alloys (HEAs) to meet or exceed austenitic stainless steel performance with the additional benefit of improved hot corrosion/oxidation resistance makes FCC HEAs attractive for use in energy applications. While shorter-term creep tests have been reported in the literature on HEAs, not all methodologies utilize repeatable techniques. This manuscript reports on over 23,500 accumulated hours of tensile creep testing with adherence to ASTM standards on a melt-solidified ingot of CoCrFeNiMn HEA converted to wrought plate using conventional thermo-mechanical processing techniques. The typical standard creep analyses are reported, i.e., Larson–Miller parameter, Monkman–Grant relationship, activation energy for creep, and creep stress exponents were calculated and compared to previously reported short-term creep tests. Additionally, characteristics of creep fracture and microstructural evolution are reported with cursory dislocation mechanisms investigated.

Impression creep behaviour of ultrasonically processed in-situ Al3Zr-Al alloy composite in as-cast condition

Impression creep behaviour of Al3Zr/Al composites with varying amounts of Al3Zr particles was studied at different temperatures (543, 573 and 603 K) and stresses (113, 141 and 170 MPa). The uniform distribution of Al3Zr particles throughout the matrix was achieved by ultrasonication during casting. The microstructure of the composites was refined by the homogeneously distributed insitu formed Al3Zr particles. From the creep analysis, it was found that the stress exponent and activation energy values of the Al3Zr/Al composites were higher than that of the base alloy making them more creep resistant. Uniform dispersion of the in-situ Al3Zr particles in the matrix and the clean interface between them played an important role in the improvement of the creep properties of the composites. It was also observed that the creep property of the composites was improved with the increased amount of Al3Zr particles. The calculated activation energy and stress exponent values suggest that the creep mechanism is dislocation climb controlled by lattice diffusion.

Tridimensional Long-Term Finite Element Analysis of Reinforced Concrete Structures with Rate-Type Creep Approach

This paper presents a general procedure for a rate-type creep analysis (based on the use of the continuous retardation spectrum) which avoids the need of recalculating the Kelvin chain stiffness elements at each time step. In this procedure are incorporated three different creep constitutive relations, two recommended by national codes such as the ACI (North-American) and EC2 (European) building codes and one by the RILEM research association. The approximate expressions of the different creep functions with the corresponding Dirichlet series are generated using the continuous retardation spectrum approach based on the Post–Widder formula. The proposed rate-type formulation is implemented into a 3D finite element code and applied to study the long-term deflections of a prestressed concrete bridge built in Romania, which crosses a wide artificial channel that connects the Danube river to the port of Constanta in the Black Sea.

Creep behaviour of elastomeric nanocomposites by flat punch indentation: Influence of graphene modification and content

Creep can be understood as the resistance of a material to a continuous stress and represents an important property for engineering design. The creep behaviour of a series of nanocomposites with electromechanical applications based on a thermoplastic elastomer, poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), and small amounts of graphene has been explored using cylindrical flat punch depth-sensing indentation. Special attention is paid to the influence of the nature of the polymer brushes (polyethylene or polystyrene) attached to the graphene surface. Common methodologies for indentation creep analysis are critically examined and brought together to provide a comprehensive picture of creep deformation. It is found that graphene significantly reduces the creep rate and this is most significant under viscoplastic deformation than in the linear viscoelastic regime. Most interesting, polyethylene branches reduce visco-elastic-plastic flow in a more effective manner and this is attributed to the selective interaction of the filler with the matrix chains.

Analysis and Selection of Creep Models for Concrete Structures in Tropical Regions

There are a number of models for predicting concrete creep behaviour such as models proposed in RILEM - B3, EN 19921-1-:2004, SABS 0100-1; MC -10… The existence of these different models for concrete creep analysis is resulted from the dependence of creep characteristics on many factors, including internal factors and external factors. Each model is therefore suitable for a specific condition. This study aims to analyse the creep models of concrete given in some concrete standards. Characteristics and scope of application of each model were clarified. These models were then applied to calculate concrete creep based experimental results on long-term deformation of reinforced concrete column sample in Viet Nam. A method of determining concrete creep coefficients was also established in this study. Compare the concrete creep coefficient calculated from the above methods and the results of the experiment to select the expected model. The results show that models ACI 209-2008 and EN 1992-2004 were the most suitable ones for applying in Vietnamese conditions. We recommend using these models for creep analysis of concrete in Viet Nam and in tropical climate.

Creep analysis of E‐glass/vinyl‐ester laminated composites for underground vault structures

AbstractCreep is eminent in fiber reinforced polymer matrix composite materials given the susceptibility of polymers to constant loading. The response of polymer matrix composites used in retrofitting vital infrastructure to long‐term flexural loadings is investigated to elucidate the effect of creep. The experimental approach consisted of first establishing a benchmark of the quasi‐statically tested flexural properties. A fresh set of samples were then flexural tested for an extended period. Failure was determined to be strain‐driven in both quasi‐static and long‐term testing conditions. The mechanical properties were found to be insensitive to the strain rate (in the low strain regime), while being mildly sensitive to creep loading. The flexural response also showed dependence on the historic creep loading. The creep strain was successfully fitted into Baily‐Norton power law, which allowed for forecasting the creep life based on the critical strain failure criteria. The overall results explicate the interrelation between long‐term loading and fidelity of composites‐based infrastructures.

Effect of pelletization pressure on the physical and mechanical properties of (Bi, Pb)-2223 superconductors

Conventional solid-state reaction technique was used to prepare bulk samples with nominal composition of (Bi, Pb)2Sr2Ca2Cu3O10+δ superconductors. The prepared powder was pelletized at different pressure (P = 0.3, 0.7, 1.0, 1.4 and 1.9 GPa) before the calcination process. Structural parameters and phase purity were evaluated using x-ray diffraction (XRD). The formation of the tetragonal major phase is improved with increasing the pelletization pressure up to 1.4 GPa. The morphology and elemental compositions were performed by using scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX), respectively. The results showed the enhancement of the grain alignment at an optimum pelletization pressure of 1.4 GPa with a decrease in the porosity percentages. Superconducting transition temperature (Tc) and the critical current density (Jc) were obtained by means of DC electrical resistivity and the voltage-current characteristic, respectively. Both Tc and Jc are improved with increase the pelletization pressure up to 1.4 GPa. Room temperature Vickers microhardness Hv measurement was performed at different applied loads (0.245–9.8 N) and times (10–60 s). As a result of the Hv measurements, all the prepared samples have a normal indentation size effect behaviour. It was found that P = 1.4 GPa was the optimal pressure to improve the microhardness in the (Bi, Pb)-2223 phase. The measured Hv data were theoretically analysed using Meyer’s law, the Hays-Kendall approach, the elastic plastic deformation model and the proportional sample resistance. The last model was recognized to be the best theoretical one describing the true Hv values for the considered phase. Room temperature indentation creep analysis was also performed using time-dependent microhardness to identify the operative creep mechanisms in the measured samples.

Developing a micro-macromechanical approach for evaluating long-term creep in composite cylinders

Abstract In most industries, composite materials have dominated the market compared with traditional materials and structures, due to their unique properties. Composite structures are usually subjected to long-term loading and experience creep phenomenon. In this study, an integrated modeling for evaluating long-term creep in cylindrical composite structures under constant loading is developed. The modeling procedure is performed at two levels of micro and macro comprising four distinct stages as modeling stress analysis at macro level, long-term creep analysis in pure resin, stress analysis at micro level for extending creep behavior of resin to lamina and updating constitutive relations of each layer. The modeling is in need of short-term creep tests on pure resin as input data and the long-term creep of the composite structure is evaluated for a period of 10,000 h as the output of the modeling. The developed modeling is validated on the basis of a long-term empirical study on a composite pipe subjected to compressive transverse loading. The very good agreement between experimental data and theoretical modeling is observed.

Application of various creep analysis methods for estimating the time-dependent behavior of cracked concrete beams

A structural model is developed to predict the time-dependent behavior of cracked reinforced and partially prestressed concrete beams. The model considers creep, shrinkage, cracking, prestress relaxation and temperature. Three different methods to model the effect of creep are presented and compared, which include the effective modulus method, integral-type and rate-type formulations. The effect of temperature on both the creep and shrinkage is considered. A smeared cracking model is adopted and an iterative procedure is implemented at each time step to determine the cracked rigidities which vary through the length of the beam. The governing equations are solved using the multiple-shooting method at each time step. The validity of the proposed model is demonstrated through comparison to experimental data available in the literature. It was found that all three analysis methods provide equally reasonable prediction of the long-term behavior. A numerical study is also presented to demonstrate the capability of the model in simulating the time variation of stresses and strains in cracked concrete beams.

Hygrothermal Creep and Stress Redistribution Analysis of Temperature and Moisture Dependent Magneto-Electro-Elastic Hollow Sphere

In this article, the time-dependent stress redistribution analysis of magneto-electro-elastic (MEE) thick-walled sphere subjected to mechanical, electrical, magnetic and uniform temperature gradient as well as moisture concentration gradient is presented. Combining constitutive equations of MEE with stress-strain relations as well as strain-displacement relations results in obtaining a differential equation in which there are the creep strains. At the first step, discounting creep strains in the mentioned equation, an analytical solution for the hygro-thermo-magneto-electro-elastic behavior is achieved at the initial state. After that, the creep stress rates can be achieved by keeping only the creep strains in the differential equation for the steady-state condition. The analysis is done by applying the Prandtl-Reuss equations as well as Norton’s law in creep behavior modeling. Finally, the history of stresses, displacement as well as magnetic and potential field, at any time, is achieved using an iterative method. Results show that the increase in tensile hoop stress resulted from creep progress must be considered in design progress. Also, the effect of hygrothermal loading is more extensive after creep evolution.

Improved MPS model for concrete creep under variable humidity and temperature

The creep of concrete is significantly affected by ambient temperature and humidity. In design codes, the influence of ambient temperature and humidity on concrete creep is approximately considered by correction coefficient terms. However, this method is not suitable for creep analysis of specific structure under complex temperature and humidity environments. At present, the Microprestress-Solidification (MPS) theory is widely adopted to analyze the complex influence of temperature and humidity on concrete creep. However, the MPS theory still has some shortcomings (The MPS theory fails to reflect the size effect in drying creep. Besides, the humidity dependence of transient thermal creep cannot be correctly modeled.). On the basis of MPS theory, this paper makes some appropriate corrections and modifications: firstly, the evolution equation of micro-prestress S is reasonably updated by redefining the relationship between the long-term creep viscosity and micro-prestress S. Meanwhile, based on the thermodynamics, the influence of temperature and humidity variation on the evolution of micro-prestress S is reformulated and the transient thermal creep effect is modified to be humidity-dependent. In order to verify the improved MPS model, experiment data in literatures are adopted to make verifications. Results prove the correctness of the modifications and the practicability of the improved model.