Residual Shear Stress Research Articles

Effect of residual stresses on the stability of bct-5 silicon

This paper investigates the effect of residual stresses on the stability of the bct-5 silicon phase induced by nano-scratching using a diamond cutting tip. The molecular dynamics method was used to simulate the scratching process and stress analysis. The Tersoff potential was employed to describe the interaction of silicon atoms and the Morse potential was used for the interaction of silicon and carbon atoms of the cutting tip. It was found that scratching the {100} surface of silicon along the 〈110〉 direction can initiate the phase transformation of silicon from its diamond structure to bct-5 in the subsurface. The study concluded that the hydrostatic stress component under the cutting tip plays an important role in the initiation and development of the bct-5 phase during nano-scratching, but a residual octahedral shear stress of 6–8GPa is required to make the bct-5 silicon stable after the nano-scratching.

Tunable metallic silicon nanowires and quantum dots with tailored dimensions and spacing

Metallic silicon nanowire and quantum dots are promising low dimensional materials for a great range of applications. A critical issue is their quality-controlled, cost-effective fabrication. This paper presents a simple method for making seamlessly integrated tunable metallic silicon nanowires and quantum dots in the subsurface of mono-crystalline silicon by mechanical scratching. The study predicted, with the aid of the molecular dynamics analysis, that arrays of stable metallic bct-5 silicon nanowires and conductive quantum dots could be produced in the subsurface of silicon by scratching the {001} surface along a ⟨110⟩ direction. The dimension and spacing of the nanowires and quantum dots can easily be controlled by adjusting the distance between scratching tips, the size of the tips, and their depth-of-cut. It was also shown that the metallic bct-5 silicon is stable under a residual octahedral shear stress of 5 to 8 GPa.

Isolation of residual shear stress effects in slitting measurement of residual normal stress in laminated composites

The conventional strain gauge slitting method is usually used to determine the residual stress component normal to the slit plane. Therefore, it is assumed that residual shear stresses released in the slit plane have no effect on the released strains measured by strain gauge. This assumption is valid when measuring released strains by back surface strain gauges. However, in the top surface measurements, it is not true and neglecting residual shear stresses could create a biased estimation of residual normal stresses. In this research, a method based on the use of two symmetrically-placed strain gauges is proposed to separate the measured strains due to residual shear stresses from those due to residual normal stresses in the slitting method. In order to validate the proposed method, two series of slitting experiments were carried out on angle-ply carbon/epoxy laminated composites. The near-surface residual normal stresses were measured using the proposed method. These stresses were also determined using strain data obtained from the back surface strain gauge. Results of both experiments showed good agreement and thus verified the validity of the proposed method for the elimination of residual shear stresses effects in the slitting method.

Energy potential of a tidal fence deployed near a coastal headland

Enhanced tidal streams close to coastal headlands appear to present ideal locations for the deployment of tidal energy devices. In this paper, the power potential of tidal streams near an idealized coastal headland with a sloping seabed is investigated using a near-field approximation to represent a tidal fence, i.e. a row of tidal devices, in a two-dimensional depth-averaged numerical model. Simulations indicate that the power extracted by the tidal fence is limited because the flow will bypass the fence, predominantly on the ocean side, as the thrust applied by the devices increases. For the dynamic conditions, fence placements and headland aspect ratios considered, the maximum power extracted at the fence is not related in any obvious way to the local undisturbed kinetic flux or the natural rate of energy dissipation due to bed friction (although both of these have been used in the past to predict the amount of power that may be extracted). The available power (equal to the extracted power net of vertical mixing losses in the immediate wake of devices) is optimized for devices with large area and small centre-to-centre spacing within the fence. The influence of energy extraction on the natural flow field is assessed relative to changes in the M2 component of elevation and velocity, and residual bed shear stress and tidal dispersion.

Novel flexible electrically conductive adhesives from functional epoxy, flexibilizers, micro-silver flakes and nano-silver spheres for electronic packaging

In this study, five different flexibilizers were added into a matrix resin to improve the flexibility of electrically conductive adhesives (ECAs). The flexible ECAs were fabricated from the matrix resin and electrically conductive fillers. Their curing was fixed at 150 °C for 30 min. Of the five flexibilizers, 1,3-propanediol bis(4-aminobenzoate) (PBA) had the best effect on the electrical, mechanical and thermal properties of the ECAs. During curing, PBA reacted with the functional epoxy in the matrix resin. The soft ether segments in PBA were grafted into the crosslinked epoxy network to form an orderly spaced mesh structure. This led to high-temperature stability, with the pyrolysis temperature being above 350 °C. Flexible ECAs with a 10% weight ratio of PBA in the matrix resin had the best properties. Their viscosity and bulk resistivity were the lowest. Their flexibility and electrical conductivity were the highest. They also had low storage modulus which could effectively dissipate or reduce the residual shear stress generated by the mismatch of thermal expansion coefficient between chip and substrate. Their impact strength was the lowest, and the toughening effect was so significant that the improvement was about 48% compared to ECAs. © 2013 Society of Chemical Industry

Advanced FeCrAl ODS steels for high-temperature structural applications in energy generation systems

Technologies and means for developing biomass plant with higher energy conversion efficiencies are essential in order to implement the commitment to renewable biomass energy generation. Advanced, indirect Combined Cycle Gas Turbine (CCGT) systems offer overall biomass energy conversion efficiencies of 45 % and above, compared with the 35 % efficiency of conventional biomass steam plant. However to attain this efficiency in CCGT operation it will be necessary to develop a heat exchanger capable of gas operating temperatures and pressures of around 1100 °C and 15-30 bar, respectively, for entry heating the gas turbine working fluid. ODS ferritic steels is the kind of advance material to deal with this challenge, however work to optimize the coarse grain microstructure to improve creep hoop strength needs to be done. In this sense, this paper reports the recrystallisation behaviour of PM 2000 oxide dispersion strengthened ferritic alloy which was cold deformed after hot-rolling and extrusion. The results can be interpreted if it is assumed that anything which makes the microstructure heterogeneous, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The combination of these results with finite element modeling are used to interpret the role of residual shear stresses on the development of recrystallized grain structure.

Combined cohesive-bridging zone model for prediction of the debonding between the FRP and concrete beam interface with effect of adherend shear deformations

In this paper, a new analytical method is developed to simulate the debonding procedure between the FRP and concrete interface. The debonding initiation and growth at the interface is modeled by cohesive zone model with a particle interlocking zone modeled by a bridging zone model. Due to the particle interlocking and friction, a residual shear stress exists in this zone, but it is reduced to zero with slip. In all zones of the debonding processes, the adherend shear deformations have been included by assuming a parabolic shear stress through the thickness of the adherends which cheeked the cubic variation of longitudinal displacements function, while all existing solutions neglect this effect. Next, solutions of the FRP plate force and interface shear stress are obtained for different zones of the debonding processes by using the proposed stress–slip law. Obtained results of the interfacial shear stress distribution and pull force are compared to other results given by the literature. Parametric studies are carried out to demonstrate the effect of the mechanical properties and thickness variations of FRP, concrete and adhesive, on the interface debonding. Indeed, limits of elastic, softening, bridging and debonding zones are reached after those computed by other models which neglect adherent shear deformations. Moreover, pull force in the four zones is more important than that calculated without the shear lag model; with considered the thickness effect. Therefore we can say that, by the use of the high order function of shear deformation, interfacial shear stresses and pull forces are suitably approximated and our reinforced concrete beam becomes stiffer.

Experimental characterization of interlaminar shear failure in sandwich structures under three-point bending

We applied an improved six-step phase-shifting method in digital photoelasticity to an adhesively bonded aluminum/epoxy/aluminum sandwich structure in order to study interlaminar shear failure behavior. Before and after three-point bending, a self-balanced thermal residual shear stress appeared on the interface because of the difference in thermal expansion coefficients between aluminum faces and epoxy core interlayer. At the beginning of loading, the shear stress in the core layer distributes continuously and forms shear bands tilting at a 45° direction. It then joins with the upper and bottom aluminum faces in order to realize the shear load transfer. As the bending load increases, the maximum interface shear stress occurs near the supports and a partially debonded region appears at the interface. The interfacial shear stress in the partially debonded region decreases rapidly until a shear failure occurs. A load–flexibility curve of the vibration-damping–type sandwich structure agrees well with the theoretical prediction of a laminated beam.

A Particle Tracking Velocimetric Study of Stress Relaxation Behavior of Entangled Polystyrene Solutions after Stepwise Shear

rheology 1−4 there have been numerous experimental studies performed to validate the model. The most well-known agreement between the theory and experiment in the nonlinear regime involves the stress relaxation behavior after stepwise shear. The tube model anticipates two-step relaxation dynamics for well-entangled polymers after a large step strain. Specifically, there would be a kink in the time dependence of the relaxing stress. 5 The sharp stress drop would occur quiescently around the Rouse relaxation time τR due to the chain retraction, which is assumed in the tube model to take place in a barrier-free manner. This ansatz of the tube model has the consequence that the chain orientation would relax on the time scale of reptation, decoupled from the fast dynamics associated with chain stretching. Thus, the structure of the tube model automatically insures that there would be time-strain separability, i.e., the relaxing stress would have the same time dependence beyond the Rouse time τR, independent of the magnitude of the applied step strain. In particular, the strain softening would take place, due to the assumed barrier-free chain retraction. In other words, the residual shear stress arises entirely from the surviving chain orientation σγ γ γ

The origin of persistent shear stress in supercooled liquids

The persistence of shear stress fluctuations in viscous liquids is a direct consequence of the non-zero shear stress of the local potential minima which couples stress relaxation to transitions between inherent structures. In simulations of 2D and 3D glass forming mixtures, we calculate the distribution of this inherent shear stress and demonstrate that the variance is independent of temperature and obeys a power law in density. The inherent stress is shown to involve only long wavelength fluctuations, evidence of the central role of the static boundary conditions in determining the residual stress left after the minimization of the potential energy. A temperature T(η) is defined to characterise the crossover from stress relaxation governed by binary collisions at high temperatures to low temperature relaxation dominated by the relaxation of the inherent stress. T(η) is found to coincide with the breakdown of the Stokes-Einstein scaling of diffusion and viscosity.

Critical compressive stress for continuous fiber unidirectional composites

Dow and Rosen’s work in 1965 formed an intellectual framework for compressive strength of unidirectional composites. Compressive strength was explained in terms of micro-buckling, in which filaments are beams on an elastic foundation. While groundbreaking, the discrepancy between model predictions and observed compressive strength is well known. This study builds on Dow and Rosen’s model specifically with respect to the dominant shear mode instability. A new method that accounts for matrix thermal residual strain, matrix compressive and shear stresses, with associated reductions in tangent modulus due to matrix non-linearity, is proposed. The method is validated using a specific test case, which is conducted to precisely account for microscopic fiber alignment and matrix non-linearity. Accordingly, a method of measuring and accounting for a continuum of fiber misalignment is developed. Predictions are compared to literature values, with variations in fiber modulus, matrix modulus, and volume fraction. Good agreement is shown, both in terms of trend and magnitude. The approach successfully preserves initial in-plane shear stiffness, while showing that in-plane shear stiffness decreases significantly as compressive stress increases.

Flexural effects of sandwich beam with a plate insert under in-plane bending

The local stress concentrations in sandwich beam with a plate insert under in-plane bending are concerned in the study. An improved six-step phase shifting method in digital photoelasticity is employed to calculate the whole-field shear stress.The shear load transfer is realized by shear bands which connect the top and bottom sheet faces through adhesively-bonded interfaces. The plate insert plays a role in load transfer in the sandwich structure, and the fact that debonding might occur at more sites of the interfaces may also leads to the failure of the structure. The local stress concentrations at the insert end change with the load under three-point bending loads, while they remain as the initial residual shear stress under four-point bending loads. The local stress concentration effects generated by the plate insert is essentially caused by the mismatch of elastic properties of the core materials and the irrational geometry of the insert.

Effect of Residual Shear Stresses on Released Strains in Isotopic and Orthotropic Materials Measured by the Slitting Method

This paper investigates the effect of shear stresses on the determination of residual stresses in isotropic and orthotropic materials by the slitting method. A great deal of research effort is focused on the estimation of the residual stress component normal to the slit face using strain data measured by strain gauges installed on the top or the back surface of the stressed specimens. However, the slitting process will also release two in-plane and out-of-plane shear stress components, which may influence the measured strains. For the two specimens of carbon/epoxy and glass/epoxy laminated composites as well as a steel specimen, the distribution of released strains on the top and the back surfaces due to the shear stresses is calculated using finite element method and compared with those due to the residual normal stress. The results show that on the back surface, the shear stresses have a very small effect on the measured strains. However, on the top surface, strains due to the residual shear stresses are significant compared with those due to the residual normal stress and cannot be ignored. A method using two top surface strain gauges in both sides of the slit is presented to separate the effects of normal and shear stresses from each other. Also, strains due to the in-plane and the out-of-plane shear stresses could be isolated from each other. If these separations could be carried out successfully, the residual shear stress can be calculated by the proposed formulation.

Investigation about Thermal Shock Property of Plasma-Spraying Sm<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> Thermal Barrier Coatings with Different Substrate Condictions

Effect of substrate conditions, including material type, thickness and radius of substrate, on thermal-shocking stresses of plasma spraying Sm2Zr2O7/ NiCrCoAlY TBCs was analyzed through finite element method. Results show that radial stresses decrease with time increasing, and they decrease with the increasing of distance from center to edge along radius. However, axial residual stresses increse abruptly at the edge of specimen. All residual stresses increse with incresing of thermal expansion coefficient of substrate. Radial stresses increase with substrate thickness increasing, however, they are not effectd by substrate thickness if it is great than 20mm.and axial residual stresses and shear stresses are not effected by the substrate thickness. The maximum values of axial stresses and shear stresses were not effected by sustrate radius. and values of radial stresses remian invariable when substrate radius is over 18mm.

Effect of Substrate Conditions on Residual Stresses of Plasma-Spraying YSZ / Sm<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> Thermal Barrier Coatings

Effect of substrate conditions, including material type, thickness and radius of substrate, on residual stresses of plasma spraying YSZ / Sm2Zr2O7TBCs was analyzed through finite element method in this paper. Results show that all residual stresses increse with incresing of thermal expansion coefficient of substrate.Substrate thickness has slight effect on radial residual stress, and it has no effect on axial residual stress and shear stress. Effect of substrate radius on radial stresses can be almost neglected when it is over 18mm. Effect of substrate radius on axial stresses can also be ignored.

3D Simulations of M 7 Earthquakes on the Wasatch Fault, Utah, Part I: Long-Period (0-1 Hz) Ground Motion

Abstract We predict ground motions in the Salt Lake basin (SLB) during M 7 earthquakes on the Salt Lake City segment of the Wasatch fault (WFSLC). First we generate a suite of realistic source representations by simulating the spontaneous rupture process on a planar, vertical fault with the staggered-grid split-node finite-difference (FD) method. The initial distribution of shear stress is the sum of both a regional depth-dependent shear stress appropriate for a dipping, normal fault and a stochastically generated residual shear stress field associated with previous ruptures. The slip-rate histories from the spontaneous rupture scenarios are projected onto a detailed 3D model geometry of the WFSLC that we developed based on geological observations. Next, we simulate 0- to 1-Hz wave propagation from six source models with a 3DFD code, using the most recent version of the Wasatch Front Community Velocity model. Horizontal spectral accelerations at two seconds (2-s SAs) reveal strong along-strike rupture direction effects for unilateral ruptures, as well as significant amplifications by the low-velocity sediments on the hanging-wall side of the fault. For ruptures nucleating near the southern end of the segment, we obtain 2-s SAs of up to 1.4 g near downtown SLC, caused by a combination of rupture-direction and basin-edge effects. Average 3-s SAs and 2-s SAs from the six scenarios are generally consistent with values predicted by four next-generation attenuation models.

Effect of Substrate Condictions on Thermal Shock Property of Plasma-Spraying Sm2Zr2O7 /YSZ Thermal Barrier Coatings

Effect of substrate conditions, including material type, thickness and radius of substrate, on thermal-shocking stresses of plasma spraying Sm2Zr2O7/YSZ TBCs was analyzed through finite element method. Results show that radial stresses decrease with time increasing, and they decrease with the increasing of distance from center to edge along radius. However, axial residual stresses increse abruptly at the edge of specimen. All residual stresses increse with incresing of thermal expansion coefficient of substrate. Radial stresses increase with substrate thickness increasing, however, they are not effectd by substrate thickness if it is great than 25mm.and axial residual stresses and shear stresses are not effected by the substrate thickness. The maximum values of axial stresses and shear stresses were not effected by sustrate radius. and values of radial stresses remian invariable when substrate radius is over 18mm.

Invsetigation about Residual Stresses of Plasma-Spraying Sm<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub>/YSZ Thermal Barrier Coatings of Different Substrate Conditions

Effect of substrate conditions, including material type, thickness and radius of substrate, on residual thermal stresses of plasma spraying Sm2Zr2O7/YSZ TBCs was analyzed through finite element method in this paper. The radial and shear stresses of the coating decrease with increasing of distance from the center to edge, and they decrease abruptly at the edge of the specimen, while the axial residal stress increase abruptly at the edge of substrate. All residual stresses increase with increasing of thermal expansion coefficient of substrate. The thickness of substrate has slight effect on the radial residual stress, axial residual stress and shear stress are almost uneffected by substrate thickness. The optimum thickness of substrate is 10mm. Radius of substrate have no effect on radial stress when it is greater than 28mm.

Effect of fibre transverse isotropy on micro-residual stresses in polymeric composites

In this paper, the influence of transversely isotropic behaviour of the fibre on micro-residual stress fields is investigated. For this purpose, the energy method is utilized to predict the micro-structural stresses in polymer matrix composites under uniform thermal loads. The representative volume element (RVE) considered here includes a transversely isotropic fibre embedded in an isotropic polymer matrix. Based on the energy method, a three-dimensional closed-form solution for micro-residual stresses is obtained. The analytical results are evaluated with a finite element solution. The analysis shows that the transversely isotropic behaviour of the fibre greatly increases the fibre and matrix axial residual stresses in comparison with the isotropic fibre assumption. Fibre anisotropy has a significant effect on the interfacial shear stress distribution, in contrast with the interfacial radial stress field. Both the finite element solution and analytical method result in a similar behaviour for micro-residual stresses distribution along the fibre length. However, the finite element method cannot satisfy the stress-free condition for the residual shear stress at the fibre end due to the stress singularity.

Effect of Substrate Conditions on Residual Stress of Plasma-Spraying Sm2Zr2O7 Thermal Barrier Coatings

Effect ofsubstrateconditions, including material type, thickness and radius of substrate, on residual thermal stresses of plasma spraying Sm2Zr2O7TBCs was analyzed though finite element method in this paper. The radial and shear stresses of Sm2Zr2O7decrease with increasing of distance from the center to edge along radius of specimen, and they decrease abruptly at the edge of the specimen, while the axial residal stress increase abruptly at the edge of substrate. All residual stresses increase with increasing of thermal expansion coefficient of substrate. The thickness of substrate has slight effect on the radial residual stress, and axial residual stress and shear stress are almost uneffected by thickness of substrate. The optimum thickness of substrate is 10mm. Radius of substrate have no effect on radial stress when it is greater than 28mm, and radius of substrate has no effect on axial stress and shear stress of Sm2Zr2O7TBCs.