Internal Friction Stress Research Articles

Anisotropic behaviors of calcareous sand dependent on loading direction and initial shear stress

Calcareous sand has been a suitable unbound granular filler in island reef engineering. Given its unique microstructure and the complex loading situation in practical engineering, anisotropy is a crucial factor that cannot be ignored. In light of this, we conducted a set of hollow cylindrical shear tests to explore how the loading direction and initial shear affect the anisotropic behaviors of calcareous sand, with Silica sand as the control material. A remarkable finding is that calcareous sand is more anisotropic than silica sand due to its irregular particles, as evidenced by a greater variation in internal friction angle(φf) and stress ratio at failure(Mf) with influencing factors. To accurately represent these variations caused by anisotropy, a parameter for quantifying anisotropy was found. The dependence of the two influencing factors on Mf was formulated based on the parameter. The formulated Mf was then applied to the UH model, and the predicted and experimental results of the shear response were compared to evaluate the model performance.

Theoretical analysis of stress intensity factor for two unequal collinear cracks subjected to internal pressure and compressive stress

Abstract In this paper, a new solution of the stress intensity factors (SIFs) for two unequal collinear cracks is developed considering internal pressure, friction and compressive stress. The complex stress function and elliptic integral function are used to obtain the analytical solution of the SIFs, and it shows a good agreement with the previous researchers’ solutions and numerical results. The theoretical results show that the difference and interaction of the SIFs at cracks’ tips are caused by crack geometry parameters, and they also indicate that the internal pressure leads to the SIFs of a mode I crack and affects the SIFs of a mode II crack because of friction.

Dislocation anelasticity in Al–Si/Ge alloys obtained by directed solidification

Young’s modulus defect, internal friction (logarithmic decrement), and flow stress at a constant anelastic strain measured at frequency about100 kHz at variable silicon or germanium content near the eutectic points in Al–Si and Al–Ge alloys are considered. Different behavior of anelastic characteristics induced by component contents are observed in these alloys. It is supposed that the important role in the anelasticity is determined by the influence of Guinier-Preston zones on dislocation vibration motion in solid solution of silicon or germanium in aluminum.

Three-Dimensional Mathematical Model of the Liquid Film Downflow on a Vertical Surface

Film downflow from captured liquid without wave formation and its destruction is one of the most important aspects in the development of separation equipment. Consequently, it is necessary to create well-organized liquid draining in areas of captured liquid. Thus, the proposed 3D mathematical model of film downflow allows for the determination of the hydrodynamic parameters of the liquid film flow and the interfacial surface. As a result, it was discovered that the interfacial surface depends on the proposed dimensionless criterion, which includes internal friction stress, channel length, and fluid density. Additionally, equations for determining the averaged film thickness, the averaged velocity vectors over the film thickness, the longitudinal and vertical velocity components, and the initial angle of streamline deviation from the vertical axis were analytically obtained.

Solution of Minor Principal Stress for Generalized Hoek–Brown Rock Material in Two Dimension Using Newton–Raphson Method

Two dimensional generalized Hoek et al. (2002) criteria is very popular for determining the strength of rock materials worldwide. While using this criterion, it is usually required to determine the minor principal stress first. Since, GHB criteria is a nonlinear function of minor principal stress, its solution is not very straightforward and simple. Few analytical and numerical solution to find out the value of minor principal stress already exist. Some solutions are unable to give acceptable value of minor principal stress for whole range of geological strength index (GSI) values of rocks. In the present paper, a solution strategy based on Newton–Raphson method to determine the value of minor principal stress from GHB criteria in two dimensions is presented. The obtained solution of minor principal stress for few problems are compared with the solutions from existing literature. The proposed solution strategy can determine the value of minor principal stress for whole range of GSI (0–100) very accurately with very less computational effort. Finally, the variation of various rock strength parameters such as angle of internal friction, cohesion and shear stress are investigated for different values of GSI and disturbance factor (D).

Attenuation and dispersion of SH-waves in a loosely bonded sandwiched fluid saturated porous layer

The present paper deals with SH-wave propagation in an upper heterogeneous fiber-reinforced layer overlying a loosely bonded heterogeneous porous layer and an initially stressed viscoelastic half-space. Dispersion relations are derived when the ratio of heterogeneity parameter associated with rigidity to that of density of the sandwiched layer is equal to zero, one and greater than one. The real and imaginary part of the dispersion equation correspond to the dispersion and attenuation curves respectively. The effect of presence and absence of heterogeneity, loose bonding, internal friction, width ratio and initial stress on the dispersion curve as well as attenuation curve is studied extensively. The effect of heterogeneity associated to the sandwiched fluid saturated porous layer on the propagation of SH-wave is among the major highlights of the study.

On the mechanical behavior of rubber springs for high speed rail vehicles

There are many engineering design problems that call for rubber components as the best solution. Vulcanized rubber has found its way into all sorts of devices, from the universal automobile pneumatic tire to the ubiquitous compliant bushing. Some high-speed rail vehicle suspensions make use of rubber, not only in the air spring itself, but also in the auxiliary spring. The mechanical characteristics of this component influence vehicle dynamics and, therefore, accurate spring models with which to conduct dynamic analysis would make for powerful design tools. Nevertheless, the mechanical behavior of rubber defies simple modeling on account of stress relaxation, creep, set, viscosity, internal friction, and nonlinear stress–strain relations. Despite the advances in the micromechanical understanding of these phenomena, as well as in the macroscopic modeling of rubber spring behavior, there is ample room for refinement, and this is precisely the goal of this paper. The mechanical behavior of a particular rubber spring for high speed rail vehicles has been characterized. The results reveal the necessary components of the model, and suggest the appropriate procedure for parameter extraction. Our model proposal consists of three elements in parallel: a nonlinear elastic spring; a “soft friction” element; and a Maxwell viscous component. The characterization procedure takes into account both stress relaxation and nonlinear elasticity. The proposed model accurately reproduces experimental results and may then be used with confidence in any type of numerical simulation. Nevertheless, for this statement to be true, the problem of “numerical softening” potentially induced by soft friction models should be resolved. The paper will show that a trailing moving average filter, seamlessly tied to the model, wipes out the softening effect.

Predicting the settlement behaviour of open-ended pipe piles with a large diameter

Axially loaded open-ended pipe piles can collapse in two fundamentally different ways, with or without plug formation. The factors that determine plug formation are generally not yet very well understood or described. A new model is developed to predict the settlement behaviour of large-diameter open-ended pipe piles (diameter 60–300 cm) and a new transfer function is developed for the pile tip resistance and for internal friction stress. A first application was the settlement evaluation of the Second Scheldt bridge in Temse.

Microstructure evolution and its effect on creep behavior of single crystal Ni-based superalloys with various orientations

By means of microstructure observation, internal friction stress (IFS) and creep property measurements, the microstructure evolution and its effect on creep behavior of the [001]-, [011]-, and [111]-oriented single crystal Ni-based superalloys are investigated. Results show that the IFSes of the alloys with various orientations during steady-state creep decrease in turn according to the sequence of σi[001], σi[111] and σi[011], which results in the creep lifetimes of the alloys at 1040°C/137MPa being the [001]-oriented alloy > the [111]-oriented alloy > the [011]-oriented alloy. It is determined according to the Schmid factors that the activated slipping systems in the [001]-, [011]- and [111]-oriented alloys during creep are 8, 4 and 6, respecrively. After crept for 50h at 1040°C/137MPa, the γ′ phase in the [001]-oriented alloy is transformed into the N-type rafted structure, the bigger IFS and better creep resistance of the alloy is attributed to the superimposing action of the strain hardening and N-type rafted γ′ phase for hindering dislocations motions. During creep, the γ′ phase in the [011]-oriented alloy is transformed into the stripe-like rafts along [001] direction, the γr(010) roof and γg(100) gable channels retained in the one result in a weaker effect on hindering the slipping of dislocations. The lower IFS and weaker creep resistance of the alloy are attributed to the superimposing effect of little strain hardening and stripe-like γ′ rafted structure. During creep, the γ′ phase in the [111]-oriented alloy is transformed into the mesh-like rafted structure along (010) plane, and a few activated slipping systems cause only weaker strain hardening effect, which has little effect on hindering the dislocations movement. But the smaller Schmid factors of slipping systems provides only weaker driving force to promote the slipping of the dislocations. The combined action of the two aspects results in the IFS and creep strength of the [111]-oriented alloy located in between the [001]- and [011]-oriented alloys.

Determination of soil properties for plane strain condition from the triaxial tests results

SummarySignificant difference in stress–strain behavior of dense cohesionless soil has been observed between plane strain and triaxial test conditions. At present, majority of geotechnical laboratories have no plane strain testing facility. Therefore, geotechnical professionals are more dependent on the conventional triaxial test for soil properties, whereas many geotechnical structures prevail close to plane strain condition. A method has been proposed to determine soil properties for plane strain condition from the conventional triaxial tests. This method can especially be used to determine the internal friction angle and stress–strain relationship for plane strain condition from triaxial tests results. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of chromium on elastic and plastic deformation of Fe3Al intermetallics

In order to evaluate the effect of chromium concentration on the mechanical properties of single phase iron aluminum intermetallics, specifically those containing 26 at.% Al, a nano-indentation technique was used. The grain orientations of samples were revealed with the aid of Electron Backscatter Diffraction (EBSD) technique. Additionally, the surface roughness of each sample was checked after electropolishing with the aid of Atomic Force Microscopy (AFM). Finally, all nano- and micro-indents were performed within the (001) orientated grains, where the surface roughness was less than 1.06 nm on average, in all samples. The Oliver–Pharr method, with correction for pile up, was used to calculate the Young's modulus and nano-hardness for Fe3Al–xCr alloys. Additionally, the effect of Cr on the shear stress needed for homogeneous dislocation nucleation, internal friction stress of dislocation motion (Peierls–Nabarro stress) and flow stress was studied.

Elasto-plastic properties of Cu-Nb nanolaminate

The Young’s modulus, internal friction, and microplastic flow stress in Cu-Nb nanolaminate has been determined by an acoustic technique. The influence of high hydrostatic compression (1 GPa) on these elasto-plastic properties of the nanolaminate has been studied.

Creep behaviors and effect factors of single crystal nickel-base superalloys

The creep behaviors and effect factors of the single crystal nickel-base superalloys during creep are investigated by means of the measurement of the internal friction stress, creep curve and microstructure observation. Results show that the internal friction stress of dislocations motion during steady state creep are enhanced with the increase of the refractory elements and the Ta concentration. The element Ta displays a better effect for stabilizing the volume fraction of γ′ phase than the element Ti during elevated temperature creep, and the element W possesses a better effect of the solution strengthening than the element Mo. The internal friction stress of superalloy may be obviously enhanced with the elements W and Ta concentration. Significant amount of the finer γ′ phase are precipitated in the γ matrix channels of the alloy during creep, which may effectively hinder the dislocations moving in the matrix channel to decrease the strain rate. In the later period of creep, the deformation feature of alloy 1 is 〈1 1 0〉 screw and edge super dislocations shearing into the rafted γ′ phase, but the ones of alloy 4 are 〈1 1 0〉 super dislocations and (1/2)〈1 1 0〉 partial activated in γ′ phase. The different deformation mechanisms during creep are one of the reasons for resulting in the different creep lifetimes of alloys.

Effect Factors of Internal Stress and Deformation Mechanism for Single Crystal Nickel-Base Superalloys during Creep

By means of the measurement of internal friction stress of dislocation movement during steady state creep stage, and observation of microstructure, an investigation has been made into the effect factors of the internal friction stress of single crystal nickel-base superalloys during creep. Results show that the values of internal friction stress of superalloys are enhanced with the increase of the elements Ta and W concentration. The super-dislocations shearing into the y' phase are supposed to be the deformation mechanism of the superalloy 4 in the period of creep later. The fact that the coarsening y' rafted phase and the finer cubic y' phase are precipitated in the y matrix phase may effectively block the movement of dislocations, and enhance the creep resistance of the alloy, this is a main reason for resulting in the superalloy possessing a longer rupture lifetimes.

Features and effect factors of creep of single-crystal nickel-base superalloys

The creep behavior of two single-crystal nickel-base superalloys with [001] orientation has been studied by measuring the creep curves, internal friction stress of dislocation motion, transmission electron microscopy (TEM) observation and energy-dispersive X-ray analysis (EDAX) composition analysis. The results show that over the stress and temperature range, there are different creep activation energies, time exponents, and effective stress exponents in two alloys at different creep stages. The size and volume fraction of the γ′ phase in the tantalum-free alloy is obviously decreased with the elevated temperature. This results in the decrease of the internal friction stress during steady-state creep. Higher levels of tungsten in the alloy result in a smaller strain value and lower directional-coarsening rate during primary creep. During steady-state creep, the primary reason for the better creep resistance of the other alloy is that it contains more Al and also Ta, which maintains a high volume fraction of γ′ phase. The dislocation climb over the γ′ rafts is the major deformation mechanisms during steady-state tensile creep. The fact that the strain rate is decreased with the increase of the size and volume fraction of the γ′ rafts may be described by a modified constitutive equation that is based on a model of the rate of dislocation motion.

The Contribution of Dislocation - Impurities Interaction to Kinetics of Martensitic Transformation of Quenched f.c.c. Fe-Ni-Mo Alloys

The kinetics of martensitic transformation in austenitic Fe-Ni-Mo alloys depends on the carbon content. Analysis of carbon redistribution between f.c.c. solid solution and dislocation has been carried out with the help of internal friction (amplitude and temperature effects) study and stress relaxation tests. The martensitic transformation was proved by magnetic induction and thermal differential analyses. The increase of carbon content in quenched austenitic alloys leads to the saturation of dislocation atmospheres and to the supersaturation of f.c.c. solid solution. The type of martensitic transformation (athermal or isothermal) kinetics depends on different relaxation resistance of austenite which is controlled by different dislocation pinning degree. The strong correlation between the degree of dislocation pinning, the type of martensitic transformation and the: stress relaxation effect allows to make the conclusion that the dislocation mobility plays an important role in the nucleation and formation of the low temperature structure of Fe-Ni-Mo alloys.

Effect of Core Impurity on Kink Soliton Motion in Dislocation Line

Modified Sine-Gordon equation is established to investigate the kink soliton motion affected by core impurities. The dragging force that the core impurities exert on the moving kink soliton is determined by computer simulation of diffusing of solute atoms in dislocation core .The soliton motion can be dissolves into two kinds of movement : the changing of soliton position and soliton shape. These two kinds of movements correspond to the longitude core diffusion(LCD) and transverse core diffusion(TCD) of solute atoms respectively . We solve the equation of these motions numerically, temperature internal friction peak and stress amplitude internal friction peak are discussed. The results are compared with the anomalous internal friction peaks in Al-Mg,Al-Cu alloy.

A numerical force and stress analysis on a thin twin layer in TiAl

Abstract Distributions of forces and stresses along a thin twin layer in TiAl that was qualitatively described in a related paper were analysed using the experimentally measured locations of twinning dislocations in the thin twin layer. The results show that both the forward stress and the back stress are very large at the twin tip and they drop quickly as the distance from the twin tip increases. The forward stress and the back stress are equal to 1140 MPa and 1200 MPa respectively on the first twinning dislocation and 275 MPa and 300 MPa respectively on the sixteenth twinning dislocation. The external stress is found to be the residual stress in the matrix and it is uniformly distributed along the thin twin layer. The magnitude of residual stress is about 50 MPa. The internal friction stress on the first twinning dislocation is very large, near 765 MPa, but the internal friction stress on the second twinning dislocation is lower than on any twinning dislocations behind it. The high internal friction str...

On the carbon distribution at structural imperfections in manganese austenite

Segregation effects which appear because of interstitial element interaction with austenite structural imperfections have a significant influence on the austenite crystal lattice energy. It has been shown that, for FCC-crystals which show a tendency to split perfect dislocations into partial dislocations, the thermochemical nature is typical for interaction between planar defects and interstitial atoms in spite of the relatively low interaction energy (about 0.1 eV). Electron microscope investigations of stacking fault (SF) aging done at relative later aging stage when dispersive carbide particles have formed at these imperfections. But the internal friction and austenite yield stress measurements have shown changes in solid solution state and dislocation pinning by interstitial solute atoms at 200--400 C. As regards the interstitial atom atmosphere formation at room temperature, there are no publications in the literature on this subject. The carbon atom distribution at different imperfections in manganese austenite was studied in this work by means of analytical electron microscopy (AEM).

The Temperature Dependences of Internal Friction and Yield Stress in Al Alloys

The Temperature Dependences of Internal Friction and Yield Stress in Al Alloys