Showing papers on "Stress–strain curve published in 2010"

Nanoporous Au-Pt Alloys As Large Strain Electrochemical Actuators

Abstract: Nanoporous Au−Pt alloys with pore- and ligament size down to few nanometers were fabricated by dealloying Ag−Au−Pt. Owing to the small structure size and large specific surface area, the surface stress and its variation give rise to significant stress and strain in the bulk of these materials. In fact, dilatometry experiments find electrochemical actuation with large reversible strain amplitude. The linear strain reaches ∼1.3% and strain energy density is up to 6.0 MJ/m3. The associated stresses may approach the elastic limit of the alloy.

Unidirectional Alignment of Lamellar Bilayer in Hydrogel: One‐Dimensional Swelling, Anisotropic Modulus, and Stress/Strain Tunable Structural Color

Abstract: [∗] Dr. T. Kurokawa , Prof. J. P. Gong Faculty of Advanced Life Science Graduate School of Science Hokkaido University Sapporo, 060–0810 (Japan) E-mail: gong@sci.hokudai.ac.jp Dr. T. Kurokawa Creative Research Initiative Sousei Hokkaido University Sapporo, 001–0021 (Japan) M. A. Haque , G. Kamita Division of Biological Sciences Graduate School of Science Hokkaido University Sapporo, 060–0810 (Japan) Prof. K. Tsujii , Nanotechnology Research Center Research Institute for Electronic Science Hokkaido University (Retired) Sapporo, 001–0021 (Japan)

Comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials

Abstract: This paper presents the results of a comprehensive study of the effects of rolling resistance on the stress–strain and strain localization behavior of granular materials using the discrete element method. The study used the Particle Flow Code (PFC) to simulate biaxial compression tests in granular materials. To study the effects of rolling resistance, a user-defined rolling resistance model was implemented in PFC. A series of parametric studies was performed to investigate the effects of different levels of rolling resistance on the stress–strain response and the emergence and development of shear bands in granular materials. The PFC models were also tested under a range of macro-mechanical parameters and boundary conditions. It is shown that rolling resistance affects the elastic, shear strength and dilation response of granular materials, and new relationships between rolling resistance and macroscopic elasticity, shear strength and dilation parameters are presented. It is also concluded that the rolling resistance has significant effects on the orientation, thickness and the timing of the occurrence of shear bands. The results reinforce prior conclusions by Oda et al. (Mech Mater 1:269–283, 1982) on the importance of rolling resistance in promoting shear band formation in granular materials. It is shown that increased rolling resistance results in the development of columns of particles in granular materials during strain hardening process. The buckling of these columns of particles in narrow zones then leads to the development of shear bands. High gradients of particle rotation and large voids are produced within the shear band as a result of the buckling of the columns.

Differences between stress and strain control in the non-linear behavior of complex fluids

Abstract: Various techniques have been proposed to characterize the behavior in the non-linear regime. A new theoretical framework, as proposed recently by Ewoldt et al. (J Rheol 52(6):1427–1458, 2008), provides a quantitative analysis of Lissajous figures during large-amplitude oscillatory shear (LAOS). Intra- and intercycle non-linearities, strain stiffening and softening, and shear thinning and thickening are described and can be distinguished. The new LAOS framework from Ewoldt et al. has been extended to a sinusoidal stress input. Measurements on two different samples reveal significant different results for sinusoidal strain or sinusoidal stress input. For both sinusoidal inputs, the results have been verified by cyclic stress and strain loading tests. The sinusoidal input tests are analyzed as an oscillatory test by the rheometer software and firmware, whereas the cyclic loading tests are purely rotational tests. Since both types of testing give the same results, any instrumental artifacts can be excluded. This implies that complex fluids can behave differently whether periodic stress or strain input functions outside the linear visco-elastic range are applied. All tests in controlled strain and stress in rotational and oscillatory modes have been performed with the same rheometer based on an air bearing-supported electrically commutated synchronous motor.

Dynamic Characterization of Orthogneiss Rock Subjected to Intermediate and High Strain Rates in Tension

Abstract: The dynamic characterization of rocks under intermediate and high strain rates is fundamental to understand the material behavior in case of heavy earthquakes and dynamic events. The implementation of material constitutive laws is of capital importance for the numerical simulation of the dynamic processes as those caused by earthquakes. These data are necessary and require experimental techniques able to induce on the rock materials state of loading reproducing the actual dynamic condition. The dynamic characterization has been carried out by means of two special apparatus: the split Hopkinson tension bar and the hydro-pneumatic machine. These equipments are briefly described with a discussion on the results of dynamic tension tests at three different strain rates (0.1, 10, 100 strain/s) on Onsernone Orthogneiss for loading directions 0°, 45° and 90° with respect to the schistosity. Results of the tests show a significant strain rate sensitive behavior, exhibiting dynamic tensile strength increasing with strain rate, up to about two times with respect to the quasi-static conditions in the case of 0° and 45° orientation and more than three times in the case of 90° at high strain rates. Dynamic increase factors versus strain rate curves for tensile strength were also evaluated and discussed.

Stress–strain behaviour and abrupt loss of stiffness of geopolymer at elevated temperatures

Abstract: This paper reports stress versus strain curves of geopolymer tested while the specimens were kept at elevated temperatures, with the aim to study the fire resistance of geopolymer. Tests were performed at temperatures from 23 to 680 °C and after cooling. Hot strengths of geopolymer increased when the temperature increased from 290 to 520 °C, reaching the highest strength at 520 °C, which is almost double that of its initial strength at room temperature. However, glass transition behaviour was observed to occur between 520 and 575 °C, which was characterised by abrupt loss of stiffness and significant viscoelastic behaviour. The glass transition temperature is determined to be 560 °C. Further, the strength reductions occurred during cooling to room temperature. This is attributed to the damage due to brittle nature of the material making it difficult to accommodate thermal strain differentials during cooling phase.

XRD investigation of the strain/stress state of ion-irradiated crystals

Abstract: In this work, it is demonstrated that XRD is a powerful technique for the study of ion-irradiated materials. For this purpose, XRD experiments have been performed under different configurations on a 〈1 0 0〉-oriented yttria-stabilized zirconia single crystal implanted with 300 keV caesium-ions at 3 × 1014 cm−2. Initially, it is demonstrated that the depth strain profile can be determined from the refinement of a symmetric θ–2θ scan. Moreover, in order to explore the whole XRD data, a model that describes the strain/stress state of the damaged layer is proposed. This model takes into account the elastic response of the bulk material (substrate) underneath the irradiated layer. The measured elastic strain is then the sum of a free strain due to the formation of radiation-induced defects and of an additional strain arising from the substrate elastic reaction. Application of this model allowed the calculation of the different strain contributions and the stress experienced by the irradiated layer. It is shown that these parameters may reach large values (respectively 0.7% and −1.9 GPa) despite the low radiation damage level.

Mechanical properties of proton-conducting sulfonated aromatic polymer membranes: Stress-strain tests and dynamical analysis

Abstract: The mechanical properties of sulfonated aromatic polymers (SAPs: SPEEK and SPPSU) are studied by tensile stress-strain tests and dynamic mechanical analysis (DMA). The elastic moduli are generally above 1 GPa with tensile strength between 25 and 80 MPa and elongation at rupture between 7 and 50%. These properties are consistent with polymers below their glass transition temperature. The glass transition and elastic moduli are strongly increased by thermal treatments of the SAP membranes, due to formation of cross-links between macromolecules. The cross-linking is observed "in situ" during DMA experiments on thermally untreated SPPSU. These data show that previously neglected SAPs might become very interesting PEM fuel cell membranes, if previously thermally treated.

Crystal plasticity modeling of cyclic deformation for a polycrystalline nickel-based superalloy at high temperature

Abstract: Cyclic deformation at elevated temperature has been modeled for a polycrystalline nickel-based superalloy using the crystal-plasticity constitutive formulations. Finite element analyses were carried out for a representative volume element (RVE), consisting of randomly oriented grains and subjected to periodic boundary constraints. Model parameters were determined by fitting the strain-controlled cyclic test data at 650 °C for three different loading rates. Simulated results are in good agreement with the experimental data for both stress–strain loops and cyclic hardening behavior. The model was utilized to predict the stress relaxation behavior during the hold periods at the maximum and minimum strain levels, and the prediction compares well with the experimental results. Localized stress and strain concentrations were observed due to the heterogeneous nature of grain microstructure and the mismatch of the mechanical properties of individual grains.

Soil testing of dynamic deformation processes of arable soils

Abstract: Soil compaction is an ongoing issue of concern in agricultural land use. Measuring and modeling stress–strain relationships for various loading conditions and field traffic intensities is therefore important for assessing and predicting soil deformation and estimating related changes in soil functions such as aeration and hydraulic conductivity. A well-known and widely used parameter that quantifies soil stability is the pre-compression stress (Pc). Pre-compression stress values are determined from compression curves measured in confined compression tests under static loading conditions. It reflects the stress history of the soil and separates the re-compression stress range (below the pre-compression stress), where soil deformation is assumed to be fully elastic, from the virgin compression stress range (above the pre-compression stress), where soil deformation is considered plastic. Particularly, in agricultural land use, however, soil deformation is caused by dynamic rather than static loading processes where in situ stress paths diverge from the conditions applied during standard static soil testing. While the pre-compression stress is a useful indicator for the soil's bearing capacity it neglects plastic soil responses in the re-compression stress range which may become important, especially concerning subsoil compaction, when long-term intensive field traffic inducing multiple reloading events is considered. On the other hand if volume deformation is estimated from compressibility indices derived under static loading conditions it may potentially overestimate the true compression since loading times are much shorter during real wheeling events than during consolidation tests. We developed a new programmable pneumatic multistep oedometer (PMO) in order to quantify soil deformation under dynamic loading conditions. The oedometer allows defining virtually any stress path and hence provides a flexible method for dynamic soil testing. To demonstrate the potential applications of dynamic soil testing accounting for typical loading conditions on arable soils we conducted confined compression tests under various stress paths. Examples from cyclic loading tests (100 loading cycles) and the simulation of stress paths measured in situ with stress-state transducers (SST) during a wheeling experiment are shown. Results suggest that dynamic soil loading leads to cumulative soil deformation with significant effects on soil functions shown by a reduction of air conductivity coefficients. Soil compaction studies concerning agricultural field traffic should account for the time-dependency and non-static nature of load application to obtain more realistic predictions of possible changes in soil functions.

Fatigue behavior of sisal fiber reinforced cement composites

Abstract: The tensile fatigue behavior of long aligned sisal fiber reinforced cement composites was investigated. The fatigue behavior was examined in terms of the stress versus cycles and stress–strain hysteresis behavior of the composites. Composites were tested at stress levels ranging between 4 and 9.8 MPa which represent approximately 30–80% of the monotonic ultimate tensile strength. The composites did not fail in fatigue below a maximum fatigue level of 6 MPa up to 106 cycles. Monotonic tensile testing was performed for composites that survived 106 tests to determine the residual strength. Crack spacing was measured by image analysis technique. There was no observed loss in strength, but a decrease in Young's modulus and an increase in first crack strength was observed with increasing fatigue stress. Fluorescent optical microscopy was used to investigate the micro-crack formation in composites subject to fatigue loading.

Influences of principal stress direction and intermediate principal stress on the stress–strain–strength behaviour of completely decomposed granite

Abstract: The measurement and study of the stress–strain–strength behaviour of soils in general stress states involving the change of magnitudes and direction of the principal stresses are necessary and impo...

Deformation characteristics of Al-4043 alloy

Abstract: Al–Si alloy is one of the most important and popular materials for lightweight automotive components production. This paper reports on structure and tensile properties of Al-4043 alloy. The results showed that the microstructure of Al-4043alloy is characterized by the presence of spherically shaped Si particles ( e ? ) ranged from 5.4 × 10 -5 to 1.2 × 10 -3 s -1 in the temperature range 300–573 K. This study revealed that upon increasing e ? , the yield stress s y0.2 , the fracture stress s f and work hardening coefficient ? p were increased according to the Norton power law s = C e ? m , while the total strain ? T was decreased. On the other hand, increasing the deformation temperature T gave the reverse of the above results. The mean value of the energy, Q , activating the deformation process and the strain rate sensitivity index m were determined to clarify the deformation mechanism. Attention has been paid to the role of other phases such as Fe, Cu and Ti on the structure and tensile behavior of Al-4043 alloy.