Small Cyclic Strains Research Articles

Training β relaxation to rejuvenate metallic glasses

In the current work, we demonstrated that the rejuvenation of metallic glasses can be achieved through training the β relaxation process. With the increase in the training frequency, a transition from structural relaxation to rejuvenation can be observed. This rejuvenation treatment is unexpected due to it occurs at a relatively small cyclic strain of 0.2%. Rejuvenation is beneficial to increase the relaxation enthalpy and promotes the decoupling of the β relaxation process and α relaxation process. A cluster of β relaxation time curves are formulated to describe any energetic state between ultrastable and ultimately rejuvenated metallic glasses. In addition, rejuvenation expands the distribution of β relaxation process, anelastic and viscoplastic components during the deformation process.

Evaluating the effectiveness of combined hardening models to determine the behavior of a plate with a hole under combined loadings

Geometrical discontinuities in a material such as holes and notches on machine elements are called as critical regions due to the stress concentrations. They are the potential failure initiation locations Therefore, researchers put significant effort on the prediction of the material response in these discontinuities under repetitive loadings. 
 Cyclic plasticity is concerned with the nonlinear material response under cyclic loadings. In this study, numerical cyclic stress – strain response of a plate with a hole was evaluated under the combined loadings which are cyclic bending and tensile loadings. Oxygen Free High Thermal Conductivity (OFHC) Copper alloy was considered as material, and finite element simulations were performed in Marc software. A user defined material subroutine known as Hypela2 was utilized in order to define the material response. The plasticity model used in the present study comprises J2 plasticity along with combined isotropic – kinematic hardening model. Evolution of the backstress was introduced by Armstrong – Frederic type kinematic hardening model. The results were compared with the literature study, and it was seen that presented hardening model provides accurate results in small cyclic strain range.

Cyclic Secant Shear Modulus and Pore Water Pressure Change in Sands at Small Cyclic Strains

AbstractWhen fully saturated sandy soil is subjected to cyclic straining in undrained conditions, pore water pressure increases and effective stress decreases. Therefore, it has been assumed that i...

Heterogeneous role of integrins in fibroblast response to small cyclic mechanical stimulus generated by a nanoporous gold actuator

It is important to understand the effects of mechanical stimulation on cell behaviors for homeostasis. Many studies have been performed on cell responses to mechanical stimuli, but the mechanosensing mechanism is still under debate. In the present study, experiments employing molecular dynamics (MD) simulations concerning the effects of cyclic mechanical stimulus on cell proliferation were performed based on the hypothesis that mechanosensing depends on integrin types. We used a nanoporous gold (NPG) actuator to prevent transfer of a mechanical stimulus via molecules other than integrins. Surprisingly, a small cyclic strain of only 0.5% enhanced the proliferation of fibroblasts. α5β1 and αvβ3 integrins showed high sensitivity to the mechanical stimulus, whereas α1β1 and α2β1 integrins exhibited low mechanosensitivity. The MD simulations showed that different conformational changes of the integrin headpiece induced by binding to the ECM led to a difference in mechanosensitivity between αI and αI-less integrin types. Thus, the present study provides evidence to support the hypothesis and suggests the mechanism for the heterogeneous roles of integrins in mechanosensing.

Cyclic secant shear modulus versus pore water pressure in sands at small cyclic strains

Cyclic strain-controlled behavior of fully saturated sands in undrained condition is analyzed at small cyclic shear strain amplitudes, γc, around the threshold shear strain for cyclic pore water pressure buildup, γtp≈0.01%. The cyclic triaxial and simple shear test results obtained in the past by different researchers and the results of new cyclic simple shear tests reveal that: (i) at very small γc below γtp where there is no buildup of cyclic pore water pressure, ΔuN, with the number of cycles, N, the cyclic secant shear modulus, GSN, initially increases with N for 10–20% of its initial value GS1 and then levels off or just slightly decreases, (ii) at small γc between γtp≈0.01% and 0.10–0.15%, ΔuN continuously increases with N while the modulus GSN first increases for up to 10% of GS1 and then gradually decreases, and (iii) at γc larger than approximately 0.15%, relatively large ΔuN develops with N while the modulus GSN constantly and significantly decreases. This means that at γc between γtp and 0.10–0.15% the sand stiffness initially increases with N in spite of the reduction of effective stresses caused by the cyclic pore water pressures buildup. In this range of γc, the pore water pressure ΔuN can reach up to 40% of the initial effective confining stress before GSN drops below GS1. The microstructural mechanisms believed to be responsible for such a complex behavior are discussed. It is suggested that during cyclic loading the changes at mineral-to-mineral junctions of grain contacts can cause soil stiffening while, at the same time, the buildup of cyclic pore water pressure causes the softening.

Electrocapillary coupling during electrosorption.

The electrocapillary coupling coefficient, ς, measures the response of the electrode potential, E, to tangential elastic strain at the surface of an electrode. Using dynamic electro-chemo-mechanical analysis, we study ς(E) simultaneously with cyclic voltammetry. The study covers extended potential intervals on Au, Pt, and Pd, including the electrosorption of oxygen species and of hydrogen. The magnitude and sign of ς vary during the scans, and quite generally the graphs of ς(E) emphasize details which are less obvious or missing in the cyclic voltammograms (CVs). Capacitive processes on the clean electrode surfaces exhibit ς < 0, whereas capacitive processes on oxygen-covered surfaces are characterized by ς < 0 on Au but ς > 0 on Pt and Pd. The findings of ς < 0 during the initial stages of oxygen species adsorption and ς > 0 for hydrogen electrosorption agree with the trend that tensile strain makes surfaces more binding for adsorbates. However, the large hysteresis of oxygen electrosorption on all electrodes raises the question: is the exchange current associated with that process sufficient for its measurement by potential response during small cyclic strain?

Closure to “Strain-Rate Effects on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Closure to “Strain-Rate Effects on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Discussion of “Strain-Rate Effect on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Discussion of “Strain-Rate Effect on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Closure to “Strain-Rate Effects on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Closure to “Strain-Rate Effects on Soil Secant Shear Modulus at Small Cyclic Strains” by Leo Matesic and Mladen Vucetic

Strain-Rate Effect on Soil Secant Shear Modulus at Small Cyclic Strains

The effects of the shear strain rate γ˙=dγ/dt on the secant shear modulus Gs of three clays and three sands at small cyclic shear strain amplitudes γc under simple shear loading conditions are described. The amplitude γc varied between 0.0003 and 0.02% and γ˙ between 0.0002 and 0.04 %/s. For all six soils Gs increases with γ˙, such that the Gs versus log γ˙ data plot approximately along a straight line. The slope of this line is αG=strain-rate shear modulus parameter, while its normalized value αG/Gs=Nγ˙-G=shear strain-rate modulus factor. For the clays tested αG ranges between 2.5 and 7.5 MPa and Nγ˙-G between 2.0 and 11.5%. For the sandy soils αG ranges between 0.2 and 3.0 MPa and Nγ˙-G between 0.2 and 6.0%. Both αG and Nγ˙-G decrease moderately with increasing γc, i.e., the largest αG and Nγ˙-G were obtained at the smallest γc. For five soils the families of the normalized modulus reduction curves (Gs/Gmax)-log γc were constructed, such that each curve pertains to a constant γ˙. It was found that γ˙ has essenlially no effect on the shape of the constant-γ˙ (Gs/Gmax)-log γc curve. A brief review of previous experimental studies is included.

Fatigue Properties of the Ti-Ni Base Shape Memory Alloy Wire

The effect of the alloy compositions on the cyclic bending fatigue behaviors of the Ti–Ni base shape memory alloy wires was investigated using a rotary bending fatigue tester specially designed for wires. The fatigue test results were discussed in connection with the static tensile properties. The results were summarized as follows. (1) The martensite inducing stress increased with the increasing of the Ni-content. (2) The fatigue life decreased with the increasing of the test temperature and the Ni-content. (3) The fracture pattern resulted from the rotary bending fatigue test has changed from the dimple pattern under the room temperature and small cyclic strain to the quasi-cleavage fracture under the high temperature and large cyclic strain.

Effect of Soil Plasticity on Damping Ratio at Small Cyclic Strains

In soil dynamics, the most common parameter for measuring soil damping is the equivalent viscous damping ratio, which is derived from the theory of a single-degree-of-freedom system with viscous dashpot. The results of a comprehensive literature review on the equivalent viscous damping ratio at small cyclic shear strain amplitudes, yc, between 0.0001% and 0.01% are presented and discussed. On the basis of the published data from different types of laboratory tests two important trends are established. The first is a significant increase of the scatter of the data points as the plasticity index of the soil, PI, decreases. This indicates that damping in low-plasticity clays and sands is more sensitive to factors such as confining stress, overconsolidation ratio and cyclic loading waveform than the damping in high-plasticity clays. The second trend is an increase of the damping ratio with PI. This trend with PI is opposite from the trend at yc > 0.01% established earlier, where damping ratio generally decreases with PI. An explanation is provided that the phenomena responsible for the increase of the damping ratio with PI at small yc are viscous creep and relaxation of the soil.

Characterization of the pseudoelastic damping behavior of shape memory alloy wires using complex modulus

The pseudoelastic stress/strain hysteresis behavior observed in nickel-titanium (Ni-Ti) shape memory alloys (SMAs) above the austenite finish temperature can be exploited to provide passive structural damping in a variety of applications. The present study characterizes the damping behavior of Ni-Ti SMAs using the complex modulus approach, commonly used in structural dynamics for the characterization of damping materials. Results indicate that as excitation frequency increases, the loss modulus (a measure of the damping) undergoes a rapid initial decrease. The value of loss modulus (and available damping) at 6-10 Hz is approximately 50% of that at low frequencies, but does not show significant reduction thereafter. As the cyclic strain amplitude increases, the storage modulus (a measure of the stiffness) initially undergoes a rapid decrease, implying that the material softens with increasing motion amplitude. As the static strain offset increases, the loss modulus decreases, and the storage modulus increases. The loss modulus decreases at temperatures above , while the storage modulus shows a significant increase above associated with the SMA operating outside its ideal pseudoelastic temperature window. The experimental stress/strain hysteresis loops and the idealized loops based on complex modulus characterization compare very well for small cyclic strain amplitudes, but may differ for higher amplitudes. However, the energy dissipation estimates from the idealized and experimental hysteresis loops compare very well over the entire range of cyclic strain amplitudes, indicating that complex modulus characterization is well suited for estimating the damping capability of SMAs.

Fracture toughness characteristics of metals in fatigue. Report no. 2

1. Based on an analysis of the experimental data obtained and the results of fractographic studies of fracture surfaces, we have proposed a model of fatigue crack growth under cyclic loading and the transition to unstable crack growth, based on a consideration of the crack growth rate in a zone damaged during cyclic loading and explaining the above-noted test results. 2. It has been shown that, together with strain-rate sensitivity, characteristics of the cyclic strain of metals may be used as bases for classifying materials according to the degree to which the cyclicity of load application effects a reduction in fracture toughness. The reduction is greatest for materials sensitive to strain rate and steels which do not strain-harden under cyclic loads. There is no such effect for materials not strain-rate sensitive and for steels which strain-harden under cyclic loads, as well as for steels with very small cyclic strains.

Investigation of Small Cyclic Strains By Etch Pits at Dislocation Sites

Investigation of Small Cyclic Strains By Etch Pits at Dislocation Sites

Internal Dissipation in Solids for Small Cyclic Strains

When a solid body vibrates, the alternating strain within it induces a correlated dissipation of energy resembling internal static or rubbing friction. No material is purely elastic. Elasticity must be regarded as having a phase angle which varies little, or not at all, with frequency, and in metals is a small fraction of 1°. This friction introduces losses in acoustic apparatus in amounts depending on design, and also on choice and heat treatment of materials. Taking metals as a class, this dissipation is generally least in light materials like aluminum and duralumin, and greatest in the heaviest substances like lead. They may be varied by a factor of as much as 10 by heat treatment.

Internal Dissipation in Solids for Small Cyclic Strains

This paper presents the results of investigations of dissipation of energy in vibrating solids, mostly metals, by means of longitudinal and torsional vibrations of cylindrical rods. The amplitudes of strain used have been kept between 10−5 cm/cm and 10−8 cm/cm, in which range the dissipation of energy is proportional to the square of the strain. The specific dissipative property of a material is expressed in three different ways: (1) Equivalent viscosity or the ratio of stress to dissipative component of strain rate; (2) hysteretic constant defined as the area in ergs of the cyclic stress-strain diagram; and (3) elastic phase constant defined as the ratio of specific elastic reactance to equivalent viscosity. Within a range of frequencies 100 to 100,000 cycles per second the results show that the hysteretic constant is proportional to some power Δ of the frequency, the numerical value of the exponent Δ varying between the limits − ⅓ and + ½, depending on the kind of material and its internal structural condition. Measurements made with longitudinal and torsional vibration indicate that dissipation is associated with dilatation as well as with pure shear. Preliminary studies are described showing the correlation between internal dissipation in metals and temperature hardness effects of annealing and aging.