Creep Measurements Research Articles

Experimental study on ultra-early tensile creep of cement paste

Tensile creep releases the internal tensile stress caused by the restriction of internal deformation in cement-based structure at ultra-early age (from initial setting to final setting) and thus reduces the risk of cracking under tension. However, the tensile creep measurement at that age is challenging due to insufficient strength of specimens. Therefore, a test device for measuring the tensile creep of ultra-early age cement paste was designed in this study, which applied multilevel incremental tensile load on the ultra-early age cement paste in a tailored molud. The effect of water-cement ratio and loading age on the ultra-early was studied using that device. The results revealed that the specific creep of ultra-early cement paste decreases exponentially with the increase of loading age, while increases with the increase of water-cement ratio. The ultra-early tensile creep of cement paste was characterized by variable viscosity dashpot element. Moreover, the increase rate of viscosity with time under external force was found equal to the creep modulus of cement paste, and in the logarithmic coordinate system, there is a linear relationship between the initial viscosity of cement paste and the loading age.

Effect of the interaction between wood constituents and swelling liquid on the creep properties of wood during drying

Abstract This study aimed to clarify the effect of the interactions between the swelling liquid and wood constituents on the creep behavior during drying. Creep tests were conducted during drying of four sample groups (untreated, acetylated, delignified, and hemicellulose-extracted samples) that were swollen using water, one organic liquid, or water-organic mixtures. The largest creep deformation was measured for the hemicellulose-extracted samples, followed by delignified, untreated, and acetylated samples. Apart from the acetylated samples, all treated samples tended to have large creep deformation in water-organic mixtures. For the acetylated samples, the creep deformation was small, except in case of acetone. These differences in the creep deformation behavior are mainly due to the differences in the glass-transition temperature of lignin as a result of the interaction between the wood constituents and the swelling liquid. The considerable increase in creep deformation due to hemicellulose-extraction suggests that hemicellulose, which interacts with lignin and cellulose, reduces the fluidity of the wood due to liquid desorption during creep measurements.

Dislocation theory of steady and transient creep of crystalline solids: Predictions for olivine

In applications critical to the geological, materials, and engineering sciences, deformation occurs at strain rates too small to be accessible experimentally. Instead, extrapolations of empirical relationships are used, leading to epistemic uncertainties in predictions. To address these problems, we construct a theory of the fundamental processes affecting dislocations: storage and recovery. We then validate our theory for olivine deformation. This model explains the empirical relationships among strain rate, applied stress, and dislocation density in disparate laboratory regimes. It predicts the previously unexplained dependence of dislocation density on applied stress in olivine. The predictions of our model for Earth conditions differ from extrapolated empirical relationships. For example, it predicts rapid, transient deformation in the upper mantle, consistent with recent measurements of postseismic creep.

CAE Prediction for Compression Behavior in Multi-Stacked Packages with an EPS-Based Cushioning System: Modeling of Compression and Compressive Creep Behavior

The compression and compressive creep behavior of target shipping containers, which are material properties based on finite element analysis, and the lifetime and load-sharing rate, were analyzed in this study to develop a computer-aided engineering prediction technology for predicting the multi-stage compression behavior of three target packages with different logistics conditions. In the experiment performed in the study, the relative humidity levels were 50%, 70%, and 90%, with creep measurements performed for 12 h for a combination of three levels of applied load and relative humidity. Using the nonlinear model of the stress–strain and creep behavior of the target shipping container, the lifetime was analyzed by estimating the average creep rate of the target shipping container. The load-sharing rate for each logistics situation of the target packages was also analyzed. The reduction rate of the compression strength of the container with respect to the increase in relative humidity was greater in the ‘horizontal long’ container than in the ‘vertical long’ container. As the applied load increased, the rate of increase in the average creep rate increased, i.e., the higher the applied load, the larger the difference in the average creep rate with respect to the relative humidity. The lifetime estimated from the failure strain and average creep rate of the container gradually decreased as the applied load increased at all relative humidity levels. However, as the applied load increased, the difference with respect to the relative humidity tended to decrease. In the target packages used in this study, the ratio of the load-sharing rate between the shipping container and an expanded polystyrene cushioning material was determined to be 2%:98%, with most of the stacking load applied to the product through the cushioning material.

Long-Term Performance of Semimetallic Gaskets

Abstract Flexible graphite-based gaskets are used extensively in high-temperature applications as a replacement for asbestos-based gaskets. The effects of aging and temperature exposure on flexible graphite sheet gaskets were the subject of a previous work (Derenne et al., 1997, “Elevated Temperature Characterization of Flexible Graphite Sheet Materials for Bolted Flanged Joints,” Welding Research Council Bulletin, Issue 419, pp. 1–87.). In this paper, the effects of aging on flexible graphite under a confined-gasket configuration will be examined as they are yet unknown. This study outlines the performance evaluation of the elevated temperature behavior of flexible graphite-based gaskets under a confined configuration and long-term exposure employing a high-temperature aged leakage relaxation (HALR) fixture. This aged relaxation leakage adhesion test (ARLA)-like fixture retains the mechanical features of the aged tensile relaxation screening (ATRS)/high-temperature aged tensile relaxation (HATR) while enabling cold leakage rate and weight loss measurements. Four distinct semimetallic gaskets with different graphite-confined configurations, namely, corrugated metal, spiral wound, kammprofile, and double jacketed, were evaluated within a temperature range of 800–1200 °F (430–650 °C) for an exposure time of 2500 h. Graphite weight loss, gasket thickness change, leakage and tightness parameters, and creep and relaxation measurements were taken at regular intervals for each gasket style. To better assess the aging process, these critical mechanical and leakage properties were scrutinized; the influence of the degradation process, related mainly to graphite oxidation, was emphasized.

Viscoelastic behavior of softwood based on a multiscale computational homogenization

In the present study, a numerical multiscale model is made to show how the hierarchical structure of softwood affect its macroscopic viscoelastic properties. The performance of the model is demonstrated for two softwood species — Norway spruce and Japanese cypress, whose creep behavior has been characterized experimentally. The results show that by using the same transversely isotropic viscous properties of the cell wall for both species, it is possible to predict creep deformation relatively close to experimental creep measurements for both species. Assuming that the variability is larger on the microstructural level (density, cell-wall geometry, microfibril angle, composition of wood tissues) than on the cell-wall level, it is possible to predict the macroscopic creep behavior based on the microstructural parameters alone. Such predictions can potentially save cost and time, since creep characterization in all material directions is demanding.

Mechanical Properties of Structural Components in Hastelloy X Joints Brazed with Ni-Pd-Cr-B-Si Alloy.

The brazing of structural high-temperature-resistant nickel alloys is a predominant method in manufacturing jet engines in the aircraft industry. Ni-Cr-base brazing filler metals (BFMs) containing B and Si as the melting point depressants are used for this purpose. The presence of the latter can lead to the formation of brittle constituents in the joints, decreasing their strength, toughness and creep resistance. The structures of Hastelloy X nickel superalloy joints brazed with Palnicro 36M BFM are presented in this paper along with the mechanical properties of their particular phases as a function of brazing time. Indentation hardness, Martens hardness, reduced modulus and creep coefficient were measured using the instrumented indentation method. The elastic part of the indentation work was also calculated. Pd forms an unlimited solution with Ni, but its high content in BFM does not fundamentally change the general joint structure known from other Ni-superalloy-Ni-BFM systems. However, new Pd-containing phases are emerging. The hardest components were Ni-B and Cr-B boride phases and Pd-Ni-Si phase in MZ and the boundary of DAZ and BM. MZ reduces the plasticity of a joint to the highest extent. The hardness of particular parts in the joints and the elastic portion of the indentation work decreased with the increase in brazing time, while the reduced modulus of the indentation contact and indentation creep increased. The results of indentation creep measurements indicate that all structural components of the joints were less susceptible to creep than the parent material at room temperature.

Correlations between Microscale Indentation Creep and Macroscale Tensile Creep of Polymers.

We compared the results of various microscale indentation creep (microcreep) measurements with macroscale tensile creep (macrocreep) measurements of three common polymers: high-density polyethylene (PE), polypropylene (PP), and polystyrene (PS). The main objective was to verify if the short-term microcreep experiments could predict long-term macrocreep behavior of the selected polymers, whose properties ranged from very soft and ductile (PE) to very hard and brittle (PS). The second objective was to compare several creep predictive schemes: the empirical power law model (PL) and several types of phenomenological elasto-visco-plastic models (EVP). In order to facilitate this task, we developed a universal program package named MCREEP, which fits PL and EVP models to both tensile and indentation creep data. All experimental results and theoretical predictions documented that: (i) regardless of the creep experiment type, both micro- and macrocreep resistance increased in the following order: PE < PP < PS, (ii) the short-term microcreep experiments could be used to predict qualitatively the long-term macrocreep behavior, and (iii) the simple empirical power law model yielded better predictions of long-term creep behavior than the more sophisticated elasto-visco-plastic models.

Creep in wood studied via continuous naation ranging from nano- to macro-scale

The paper presents the results of creep measurement in common pine wood at different scales ranging from nano to macro by means of continuous naation. It is shown that wood structure elements pertaining to different scale levels make different contribution to steady creep rate. Keywords: naation, wood, creep.

Ползучесть древесины, исследованная методами непрерывного наноиндентирования от нано- до макромасштаба

The paper presents the results of creep measurement in common pine wood at different scales ranging from nano to macro by means of continuous nanoindentation. It is shown that wood structure elements pertaining to different scale levels make different contribution to steady creep rate.

Melt State Reinforcement of Polyisoprene by Silica Nanoparticles Grafted with Polyisoprene.

We systematically vary the nanoparticle (NP) dispersion state in composites formed by mixing polyisoprene homopolymers with polyisoprene grafted silica particles, and demonstrate how creep measurements allow us to overcome the limitations of small amplitude oscillatory shear (SAOS) experiments. This allows us to access nearly 13 orders in time in the mechanical response of the resulting composites. We find that a specific NP morphology, a percolating particle network achieved at intermediate graft densities, significantly reinforces the system and has a lower NP percolation loading threshold relative to other morphologies. These important effects of morphology only become apparent when we combine creep measurements with SAOS re-emphasizing the role of synergistically combining methods to access the mechanical properties of polymer nanocomposites over broad frequency ranges.

In-situ irradiation creep behavior of dilute Al-Sc alloys: Using a thin film bulge test method

• In situ thin film bulge test on nc-AlSc is effective method for irradiation induced creep. • Preexisting Al 3 Sc precipitates suppress irradiation induced creep deformation. • Transition regime of AlSc binary system is located between room temperature and 75 °C. In-situ irradiation induced creep(IIC) measurements on a nanocrystalline AlSc 1.1 binary alloy were performed using a thin-film bulge test technique. A thin film bulge technique was employed since any substrate effect can be excluded, and hence is beneficial to analyze the intrinsic properties of specimen. Here, an as-deposited film and a pre-annealed film, both underwent heavy ion irradition with 1.8 MeV Kr ions. Al 3 Sc precipitates in the pre-annealed samples appear to reduce the irradiation creep compliance. Dissolution of these precipitates during irradiation led to increased irradiation creep rates. Microstructural evolution during irradiation was investigated by transmission electron microscopy and high resolution transmission electron microscopy.

Nonlinear creep of early-age cement mortar assessed by minutes-long flexural test

Nonlinear creep normally defined as the time-dependent deformation of materials under high stress condition, is highly coupled with the damage condition. The microstructure evolution of early-age cementitious materials due to the cement hydration influences the accurate measurement of nonlinear creep. Besides, the commonly-used assumption in the uniaxial creep test that the shrinkage of the loaded concrete is the same as that of the unloaded concrete is questionable for the high stress case. To reduce the influence of cement hydration and shrinkage on the measured results, a minutes-long flexural test was designed in this study to investigate the nonlinear creep of cement mortar with w/c ratio of 0.45 at the ages of 7 and 28 days under drying condition with relative humidity of 70 %. The maximum stress applied to the mortar beam was set as 30 %, 40 %, 70 %, 85 %, and 90 % of the flexural strength. The results show that cement mortar subjected to less than 40 % of the flexural strength exhibits a linear creep property, while a significant nonlinear creep is observed when the stress level is greater than 70 %. The influence of curing time on the creep rupture time seems more significant than that of the stress level. The nonlinear creep coefficient of early-age cement mortar decreases gradually and tends to converge to a constant if it is not ruptured during the minutes-long creep test, which cannot be characterized by the existing models where the nonlinear creep coefficient depends only on the stress level. A new model is proposed in this study with the function form of η(t)=η0+ke-xt, which is capable of capturing the evolution of the nonlinear creep coefficient of early-age cement mortar with good accuracy.

Effect of multi‐walled carbon nanotubes on rheological behavior and electrical conductivity of poly(ethylene‐co‐vinyl acetate)/acrylonitrile‐butadiene rubber/multi‐walled carbon nanotubes nanocomposites

AbstractIn this work, the effect of multi‐walled carbon nanotubes (MWCNTs) on electrical conductivity and rheological behavior of poly(ethylene‐co‐vinyl acetate) (EVA)/acrylonitrile‐butadiene rubber (NBR) blends containing 0 to 7 wt% MWCNTs are investigated. The theoretical calculations according to the interfacial free energy of the components revealed that the nanofillers had a tendency to locate in NBR domains. However, the rheological, electrical, and morphological studies indicated that the majority of the MWCNTs remained in the EVA phase. Shear creep measurements of the molten materials showed that the creep stability improved steadily with the increase in MWCNTs content. The creep behaviors of the materials, except EVA, were analogous to the Burgers model prediction and all four parameters of the model increased in value with the increase in the nanofillers content in comparison with those of the unfilled blend. The rheological studies indicated that the damping factor (tanδ) for the materials containing small amounts of the nanofillers reached a maximum and subsequently decreased with rising temperature. However, for the materials having 1 wt% MWCNTs and higher, the tanδ values were smaller at the highest temperature (200°C) than those of the lowest temperature (100°C) investigated in this work. The electrical percolation threshold was also found to take place at about 2.80 wt% MWCNTs loading.

Nociceptive pain in adult patients with 5q-spinal muscular atrophy type 3: a cross-sectional clinical study

BackgroundSpinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by mutations in the SMN gene, leading to progressive muscular weakness, atrophy and so far neglected musculoskeletal pain. This study is the first to characterize nociceptive pain in patients living with SMA type 3 by assessing whether muscle pain is associated with alterations in muscle strength, function, stiffness, frequency, decrement, relaxation, or creep.MethodsWe performed a cross-sectional pilot study on 20 SMA3 patients. We evaluated motor function and muscle strength (dynamometry, quick motor function test and 6-min-walk test), nociceptive pain (pressure algometer evaluating muscular pressure pain threshold (PPT)) and non-invasive measurement of muscle stiffness, frequency, decrement, relaxation, or creep (myotonometry with the MyotonPro®). For statistical analysis, we used t tests, Mann–Whitney U tests and linear regression.ResultsSignificantly more women than men reported musculoskeletal pain (p = 0.003). A lower score in dynamometry was associated with lower scores in PPT in all extremities reflecting a higher sensitivity of these muscles to pressure. We did not find significant correlations between the PPT values and the MyotonPro values in the corresponding muscles. Assessments of PPT before and after the 6-min walk test did not show clinical meaningful changes. Besides nociceptive pain, fatigue was prevalent in 50% and pain in 55% of the patients.ConclusionsMuscle pain in SMA3 is associated with muscular weakness in the arms and legs, but not with changes in muscular stiffness, frequency, decrement, relaxation, or creep. This shows that muscle pain in SMA3 is mainly caused by changes in the dysbalanced musculoskeletal system due to muscle weakness.

Permafrost geomorphology

Abstract Permafrost geomorphology came of age in 1965–2000, evolving from a field-based subdiscipline largely based on qualitative observation to one of detailed process measurement, field experimentation, and analytical modelling. In this, the development of permafrost geomorphology exemplified the change in geomorphology as a whole. Fundamental advances were made in understanding the development of ice wedges and ice-wedge polygons and the genesis and growth of closed-system pingos, especially by J. Ross Mackay working in the continuous permafrost terrain of the western Canadian Arctic coastlands. Mackay also investigated moisture movement in relation to the ground thermal regime, which led to seminal insights regarding ground freezing, frost heave, near-surface ground ice development, and hummocky micro-relief. Others used these ideas to examine frost shattering of rocks and the development of sorted circles, as most well known from Svalbard. In the second half of the period, measurements of permafrost creep and deformation of hillslopes and rock glaciers were presented, complementing antecedent measurements of solifluction in the active layer. Significant investigations of thermokarst development foreshadowed the preoccupation with permafrost thaw that now gathers so much attention.

Creep behavior and life prediction of P91 heat-resistant steel using modified Wilshire model

The reliable prediction of long-term creep life is of great importance in order to ensure the service safety of high-temperature components. In this work, the novel Wilshire-Cano-Stewart (WCS) relationships were introduced to model the creep behavior and predict the long-term creep life of P91 steel based on the short-term creep data. The accelerated creep experiments were firstly carried out at the temperature range of 580–620 °C, while the stresses varied from 135 to 200 MPa. According to the analyses of normalized-mean-squared error (NMSE) and mean logarithmic error (MLE), it demonstrated that the WCS model can express all the obtained creep data very well due to the average relative errors lower than 10%. Meanwhile, these values are much lower than those of traditional Time-Temperature-Parameter (TTP) models. In addition, the WCS model can provide the reasonable estimates of 200,000 h creep life with accelerated creep measurements lasting up to only 2000 h.

The Synergistic Effects among Crystal Orientations, Creep Parameters, Local Strain, Macro–Microdeformation, and Polycrystals’ Hardness of Boron Alloyed P91 Steels

This article induces proficient microstructure––creep reciprocity by electron backscatter diffraction (EBSD) and impression creep measurements (ICM). The article has further contributed to understanding the synergistic effects of boron in extenuating microstructural degradation. Herein, 22 and 100 ppm boron alloyed P91 steels (P91 and P91B steels, respectively) are subjected to ICM, assessing stress exponent (n), threshold stress (σTh), effective activation volume (Veff), and activation energy. Base metal and narrowed crept realm of each steel are measured by employing EBSD. ICM results are correlated with crystal orientations and 1) strain accumulation, 2) macroscopic and 3) microscopic deformation resistance, and 4) hardness of grain in polycrystals by calculating kernel average misorientation (KAM), elastic stiffness, grain reference orientation deviation (GROD), and Taylor factor (M) within microstructure before and after ICM. Measurements of P91B steel show a small value of n and Veff and a high value of σTh and activation energy as regards P91 steel. Lower KAM and stiffness before and after creep, higher GROD in base metal, and lower GROD in the crept realm in P91B steel as regards P91 steel corroborate microstructural homogeneity. M indicates both steels are hard before creep, while ICM moderates hardness. Finally, this study reveals synergistic effects of crystal orientations, KAM, stiffness, GROD, M, and creep.

Measurement and modeling of creep property of high-strength concrete considering stress relaxation effect

Measurement of concrete creep under constant sustained stress conditions is usually a long process. The external load applied on the specimen may relax gradually during this long process due to the time-dependent properties of concrete and test set-up, which would lead to an improper assessment of concrete creep without considering the stress relaxation effect. This study developed a theoretical method based on the linear superposition principle to derive the specific creep of concrete from the compressive creep test results where a certain amount of stress has relaxed. Three types of high-strength concretes were cast for the creep tests. In addition, the workability, mechanical properties, and shrinkage of the three concretes were measured. Then the application of the existing models including the ACI model, CEB-FIP model, GL2000 model, and B4 model to predict the creep and shrinkage of high-strength concrete was discussed. The results reveal that the specific creep of concrete used in this study without considering the stress relaxation effect decreases by 4.3%∼11.0% when 6.7%∼13.1% of the applied stresses relax during the creep tests. Both creep and shrinkage of high-strength concrete exposed to drying decrease with increasing curing age. It is found that the CEB-FIP model can predict the shrinkage of high-strength concrete well and the B4 model can give a predicted result relatively close to the measured creep of high-strength concrete.

Experimental Study of Mechanical Properties of Polypropylene Random Copolymer and Rice-Husk-Based Biocomposite by Using Nanoindentation.

Nanoindentation is widely used to investigate the surface-mechanical properties of biocomposites. In this study, polypropylene random copolymer (PPRC) and biowaste rice husk (BRH) were used as the main raw materials, and glass-fiber-reinforced polypropylene and talc were also used with BRH to enhance the mechanical characterization of the biocomposites. The interfacial bonding between the polymer and the rice husk was increased by treating them with maleic anhydride and NaOH, respectively. The results obtained from the nanoindentation indicated that the plastic behavior of the biocomposites was prominent when untreated BRH was used and vice versa. The modulus and hardness of the biocomposite improved by 44.8% and 54.8% due to the neat PPRC, respectively. The tribological properties were studied based on the hardness-to-modulus ratio and it was found that BRH- and talc-based biocomposites were better than other samples in terms of low friction and wear rate. The creep measurements showed that untreated rice husk biocomposite exhibited high resistance to load deformation.