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Relaxation Tests (relaxation + test)
Selected AbstractsDerivation of Recovery Kinetics From Stress Relaxation Tests,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Sheila Bhaumik The recovery behavior of a commercial aluminum alloy 3103 was investigated by the means of two alternative experimental methods: stress relaxation (SR) and double tension tests (DT). In case of SR, the stress,time evolution after deformation was recorded, and for DT the yield stress after several recovery times were measured. The DT tests were further sub-divided into tests with and without external load during recovery. The results revealed that the recovery kinetics is clearly accelerated by the external stress during the SR. However, the difference between the DT and SR stresses is much larger. It is caused by continued dislocation glide after the deformation, which causes continued plastic elongation of the specimens. This is demonstrated quantitatively by appropriate evaluation models for both experiments. In contrast to DT, the SR evaluation accounts for the elastic SR due to plastic elongation, but the recovery parameters are the same ones as for DT. This makes it possible to replace DT by SR experiments, which are materially less laborious. [source] Determination of Activation Volume in Nanocrystalline Cu Using the Shear Punch Test,ADVANCED ENGINEERING MATERIALS, Issue 10 2007K. Guduru Stress relaxation test (SRT) is very useful to study the dislocation dynamics and thus the deformation behavior. It becomes quite difficult to use conventional testing methods when the material availability is limited. In such instances, miniaturized specimen testing procedures such as shear punch test (SPT) becomes significantly useful for studying the mechanical behavior of materials. Current research deals with a novel SRT method employed on nanocrystalline Cu using SPT to study the deformation mechanism. [source] PREDICTING TEXTURE ATTRIBUTES FROM MICROSTRUCTURAL, RHEOLOGICAL AND THERMAL PROPERTIES OF HAZELNUT SPREADSJOURNAL OF TEXTURE STUDIES, Issue 5 2008ROSSELLA DI MONACO ABSTRACT Eight trained assessors evaluated one visual, eight texture and four gustative attributes of 15 commercial spreads. In addition, 100 consumers evaluated the acceptability of the spreads. Rheological behavior of the samples was evaluated in transient (stress,relaxation test) and dynamic (strain and frequency sweep test) shear mode. Thermal measurements were also performed. Finally, the microstructure of the samples was analyzed by scanning electron microscopy. Partial least squares regression was used to predict acceptability from sensory attributes and texture from instrumental data. Scanning electron micrographs indicated that spreads differed in morphology, size and distribution of hazelnut particles. Overall liking of the spreads was found to be related to hazelnut flavor and texture attributes. Prediction of the most important texture properties from instrumental measurements was quite successful, especially for spreadability which was found negatively related to the consistency and flow indices and, secondly, for meltability which was found to be strongly dependent on measured thermal parameters. PRACTICAL APPLICATIONS This study contributes to knowledge development in the research area of acceptability, sensory and instrumental correlation for semi-solid foods. The results confirm that texture properties of spreadable foods play a most important role in consumer acceptability. The research also allows better understanding as to why no single measurement is able to predict all texture attributes adequately and why more appropriate tests need to be developed for an accurate prediction of some sensory attributes as perceived by the human senses. [source] Viscoelastic Properties of Clay-Containing Nanocomposites of Thermotropic Liquid-Crystal PolymerMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2009Jayita Bandyopadhyay Abstract The nanocomposites of liquid-crystal polymer (LCP) with two different weight per cents of clay were prepared via the melt extrusion method. To investigate the properties of the materials in the linear and non-linear viscoelastic regions, both oscillatory and rotational tests were carried out. The results showed that the nanocomposite with higher clay content exhibited an almost defectless partially cross-linked structure compared to the nanocomposite with lower clay content or the pure LCP. The linear stress relaxation measurements revealed that the pure LCP relaxed faster than nanocomposites after imposition of a constant strain for a specific time. During the step rate relaxation test, high shear rate modified the defects in the pure LCP very quickly and probably attained almost an equilibrium position while the nanocomposite samples showed strong shear thinning behaviour. [source] Texture Changes During the Ripening of Port Salut Argentino Cheese in 2 Sampling ZonesJOURNAL OF FOOD SCIENCE, Issue 5 2002R.A. Verdini ABSTRACT: Texture changes during ripening of Port Salut Argentino cheese for different sampling zones were studied. Compression relaxation tests were performed and results were analyzed using both Maxwellian and Peleg's models. Elastic equilibrium modulus obtained from the Maxwellian model decreased from 1.22 to 0.11 104Pa during ripening. The constants derived from Peleg's model, k1 and k2, diminished with ripening time from 1.18 to 0.71 min and from 1.27 to 1.12, respectively. Asymptotic equilibrium modulus from Peleg's model decreased from 0.95 to 0.07 104Pa during ripening. Rate parameters derived from a 1st order kinetics applied to both equilibrium moduli showed that the decrease was faster in the external zone (0.0846 d,1) than in the central zone (0.0368 d,1). The correlation between equilibrium moduli, salt concentration, moisture content, and maturation indexes was obtained with a determination coefficient of 0.76. [source] Effect of viscoelastic properties of resilient denture liners on pressures under denturesJOURNAL OF ORAL REHABILITATION, Issue 11 2001N. Taguchi In order to evaluate the influence of viscoelastic properties of resilient denture liners on the pressures under dentures, a series of creep and stress relaxation tests were carried out using a simplified mandibular edentulous model and denture model. Two diaphragm pressure sensors were attached to the edentulous model so that they contacted the residual ridge and the buccal slope. The results may be summarized as follows: (i) The use of resilient denture liners is effective for stress relief under dentures. (ii) The thickness increase of each denture liners causes the effect of stress relaxation. (iii) The material exhibited viscoelastic behaviour after applying the stress and has the ability to distribute stress or stress relaxation. It is important to understand the viscoelastic behaviours of each resilient denture liner and choose the material according to the clinical situation. The information obtained should be useful to clinicians when they select materials for their patients. [source] PREDICTING SENSORY COHESIVENESS, HARDNESS AND SPRINGINESS OF SOLID FOODS FROM INSTRUMENTAL MEASUREMENTSJOURNAL OF TEXTURE STUDIES, Issue 2 2008R. DI MONACO ABSTRACT The sensory evaluation of cohesiveness, hardness and springiness of 15 solid food samples was performed by eight trained assessors. The rheologic response of the 15 samples was estimated by performing cyclic compression tests and stress,relaxation tests. From the force,deformation curves of the first two cycles of the compression test, texture profile analysis parameters related to cohesiveness, hardness and springiness were calculated. Young's modulus (E), strain (di) and stress (si) at peak as well as irrecoverable strain (ri) and irrecoverable work (Li) were monitored during the first five cycles. From the stress,relaxation response, Peleg's linearization model parameters, K1 and K2, were estimated by best-fit regression. These parameters were used for predicting sensory attributes. Hardness and springiness were both accurately predicted by rheologic properties, while cohesiveness prediction was less representative. PRACTICAL APPLICATIONS This study contributes to enhance the knowledge in the research area of sensory instrumental correlation. Also, the research allows to better understanding that no single instrument is able to measure all texture attributes adequately. In fact, the results demonstrate that both stress,relaxation and cyclic compression tests need to be performed for the correct prediction of sensory responses. [source] COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENINGJOURNAL OF TEXTURE STUDIES, Issue 6 2002W. K. SOLOMON ABSTRACT The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R2= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes. [source] QUANTIFYING TEXTURE CHANGES IN CORN TORTILLAS DUE TO STALINGJOURNAL OF TEXTURE STUDIES, Issue 1 2002B. LIMANOND ABSTRACT The change in texture of corn tortillas due to staling is described using stress relaxation methods. Tortilla strips (70 × 35 mm) were subject to stress relaxation under tension at 3% strain. Force versus distance values were transformed into the textural indicator of stiffness. Fresh corn tortilla had significantly lower stiffness values than the stale tortilla (up to 10 days old). Stiffness decreased with increasing storage temperature from 6C up to 35C. The stiffness value from stress relaxation tests may be used as an objective indicator of tortilla texture. [source] The effect of annealing on the nonlinear viscoelastic response of isotactic polypropylenePOLYMER ENGINEERING & SCIENCE, Issue 4 2003Aleksey D. Drozdov Three series of tensile relaxation tests are performed on isotactic polypropylene at room temperature in the vicinity of the yield point. In the first series of experiments, injection-molded samples are used without thermal pre-treatment. In the second and third series, the specimens are annealed at 130°C for 4 and 24 hours, respectively. Constitutive equations are derived for the time-dependent response of semicrystalline polymers at isothermal loading with small strains. A polymer is treated as an equivalent temporary network of macromolecules bridged by junctions (physical cross-links, entanglements and crystalline lamellae). Under loading, junctions slide with respect to their positions in the bulk material (which reflects the viscoplastic behavior), whereas active strands separate from their junctions and dangling strands merge with the network at random times (which reflects the viscoelastic response). The network is thought of as an ensemble of meso-regions (MRs) with various activation energies for detachment of chains from temporary nodes. Adjustable parameters in the stress-strain relations are found by fitting the observations. The experimental data demonstrate that the relaxation spectrum (characterized by the distribution of MRs with various potential energies) is independent of mechanical factors, but is altered at annealing. For specimens not subjected to thermal treatment, the growth of longitudinal strain does not affect the volume fraction of active MRs and the attempt rate for detachment of chains from their junctions. For annealed samples, the concentration of active MRs increases and the attempt rate decreases with strain. These changes in the time-dependent response are attributed to broadening of the distribution of strengths of lamellae at annealing. [source] Cellular rubber: Dependency between relaxation time and pretreatmentPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Nadine Koprowski In this contribution we investigate experimentally a porous carbon-filled rubber. The main focus is on the dependency of the mechanical behaviour using different pretreatments. Therfore, cyclic tests and relaxation tests with different pretreatment are performed. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||