Papers by Keyword: Viscoelasticity

Abstract: This article deals with determination of the strain of the beam caused by the creep effect. Instant deflection and simulation of creep function have been examined by SCIA Engineer, ANSYS and Marc software. Creep is a complex phenomenon, which is in every software configured differently. Therefore we would like to compare results of calculations obtained using various finite element method software. With increasing time, the deformation of a beam becomes non-linear analysis. Analysis involved monitoring of deflection in the middle of the beam depending on the time. In SCIA Engineer construction stages were created with the creep factor based on period of load. In the ANSYS software different method was selected and creep curve of concrete had been defined.

Abstract: The specimens (980 MPa-grade dual phase steel sheets) were stretched until the pre-defined strain was obtained. Then the specimens were held at the pre-defined strain and measured the change of stress durng holding. We investigated the effects of strain rate and strain at the starting time of holding and whether the stress change during holding could be described by Krempl model. The following results were obtained. First, the stress drop increased with increase of strain rate and the holding time. On the other hand, the stress drop was not affected by strain change at the starting time of holding. Second, initial stress relaxation rate increased with increase of strain rate. However, this strain rate dependency to stress relaxation rate diminished as the holding time became long enough roughly more than 100 s. Third, the stress change during holding obtained by Krempl model accurately agreed with experimental result. It was found that the stress change during holding could be well described by using Krempl model. This suggests that dislocation moves viscously. In addition, the strain rate dependency on stress change during holding could be described by change of the parameter A.

Abstract: To relax the surface residual stress of fused silica lens or windows irradiated by CO₂ laser, it was proposed to treat it at high temperature above glass strain temperature in the traditional annealing process. However it is a time and energy consuming process, and a distortion will be introduced during the heat treatment. To deal with these problems, annealing temperatures lower than glass strain temperature were applied to the annealing process and a new scheme was designed in this paper. An numerical model was built to simulate the laser induced residual stress and optimize the stress variation in the annealing process. The surface stress of fused silica can be relaxed and deformation induced by heat treating can be ignored.

Abstract: In this paper, a viscoelastic-damage cohesive zone model is formulated and discussed. The interface element constitutive law has two elastic and damage regimes. Viscoelastic behaviour has been assumed for the shear stress in the elastic regime. Three element Voigt model has been used for the formulation of relaxation modulus of the material. Shear Stress has been evaluated in the elastic regime of the interface with integration over the history of the applied strain at the interface. Damage evolution proceeds according to the bilinear cohesive constitutive law up to the complete decohesion. Numerical examples for one element model has been presented to see the effect of parameters on cohesive constitutive law.

Abstract: Microdamage, viscoplastic and viscoelastic strain development in 90-layers of cross-ply laminates subjected to tensile loading is studied on unsymmetrical GF/EP laminates measuring the thermal curvature change. All three phenomena partially compensate for the effect of the thermal mismatch reducing the residual stress (specimen curvature). The viscoplastic strain contribution to curvature change is the largest whereas the effect of transient viscoelasticity is the smallest. Damage is included in the analysis through its effect on the effective transverse modulus of the 90-layer.

Abstract: Bearings of small turbo machines support high speed rotors rotating with the frequency over 1 [kHz]. Such bearings are often supported with O-rings made of soft materials like rubber to attenuate high frequency oscillations. Dynamic properties of rubber supporters have been measured experimentally for individual dimensions, but the universal prediction of dynamic properties for various frequencies is difficult not only because rubbers exhibit nonlinearity against its strain, but because O-ring supporters deform heterogeneously. For the precise prediction, it is necessary to investigate the viscoelasticity of rubber under various deformations and frequencies. Such properties can be measured by the standard shear vibration non-response method of ISO 6721-6 (JIS K 7244-6). However this is applicable only to low frequency range under 100 [Hz] because of the limitation of resonance frequency of the load cell. In this research, based on BERM (Base Excitation Resonant Mass) method, a new method was developed to measure the complex shear modulus at high frequencies up to 1 [kHz] of rubber sheets under homogeneous shear deformations. In the presented method, the force is calculated from the acceleration of the mass instead of the direct measurement by a load cell. Hence accurate measurement became possible even in the range beyond the resonance frequency of a load cell. The measured shear storage modulus G’ and shear loss modulus G” of deformed rubber were presented.

Abstract: The effect of different solvents on the acoustic property and morphology of polystyrene (PS) and the stearic acid (SA) layer was investigated in this study. The acoustic property was analyzed by using impedance analyzer and morphology of SA layer in a quartz microbalance (QCM) sensor have been studied to quantify their effects on viscoelasticity within the sensor. The polystyrene coating on a QCM sensor was created by spin-coating with various solvents, such as chloroform and toluene, which contains a 3% polystyrene solution by mass. Then, the SA coating was deposited onto the polystyrene layer using a low-vacuum evaporation method. The viscoelasticity was measured by an impedance analyzer coated with the SA layer to determine whether the material used as a coating will effectively immobilize a biomolecule and whether the material produces an acoustic load. The experimental results showed that the impedance value in the series resonant frequency was small (i.e., near 10 Ω), indicating that the deposited SA coating is rigid and that the SA coating does not produce a loading effect on the QCM sensor. Therefore, the coating technique used on the QCM sensor surface to produce the SA coating is likely to be an effective biosensor material for QCM immunosensor. Additionally, the study shows that the frequency change (Δf) of the SA layer deposited onto the polystyrene coating created with chloroform is larger than that of the coating created with toluene. This also shows that the SA layer deposited onto the polystyrene coating created with chloroform is thicker than the coating created with toluene. The Δf correlates with the mass change (Δm), according to the Sauerbrey equation, which requires that the material be rigid. The Δf value also correlates with the deposited SA mass change. From the calculation of Δf, the SA coating created with the chloroform solvent was shown to be thicker than that created with the toluene solvent. In addition, the roughness of the SA surface using a test of non-contact topography measurement system TMS TopMap-1200 showed that the SA surface roughness with the chloroform solution was 763 nm compared to that with the toluene solution, which was 424 nm.

Abstract: This paper presents a three-dimensional direct boundary element approach for solving transient problems of linear anisotropic elasticity and viscoelasticity. In order to take advantage of the correspondence principle between viscoelasticity and elasticity the formulation is given in the Laplace domain. Anisotropic viscoelastic fundamental solutions are obtained using the correspondence principle and anisotropic elastic Green’s functions. The standard linear solid model is used to represent the mechanical behavior of viscoelastic material. Solution in time domain is calculated via numerical inversion by modified Durbin’s method. Numerical example is provided to validate the proposed boundary element formulation.

Abstract: Abrasive flow machining is a suitable technique for surface polishing due to its rheological characteristics, however, it's difficult to achieve uniform roughness for polished surfaces as the material removal mechanism is still ambiguous. In this paper the viscoelastic properties of abrasive flow media are incorporated to explore the phenomena of inconsistent material removal in the AFM polishing process, where the material removal near the edges is obviously higher than that in the middle along the flow direction. The rheological parameters of the viscoelastic constitutive model adopted are varied to study the polishing effectiveness under different process conditions. The results of numerical analysis reveal that there exist distinct differences of viscoelastic stress fields between the edges and the middle regions, which leads to the material removal near the edges is higher than that in the middle. It could be concluded that the viscoelastic properties of abrasive media play the dominant role for the inconsistent material removal in abrasive flow machining process.

Abstract: This study proposes an experimental-numeric method to identify the viscoelastic properties of flax fibres reinforced composite laminate (flax/epoxide). The used method consists in identifying the evolutions of both loss factor and stiffness when vibrational frequency changes. In this way, several free-free symmetrically guided beams are excited on a dynamic range of 10 to 4000 Hz with sweep sine excitation focused around the 4-first’s modes. Fractional derivative Zener model is used to identify the on-axis ply complex moduli and describe the laminate dissipative linear behavior with the classical laminate theory. Results obtained on a quasi-isotropic laminate show that this model adequately predicts the vibrational behavior of the tested laminates.