Function Of Strain Amplitude Research Articles

Biomechanical Modelling of Porcine Kidney.

In this study, the viscoelastic properties of porcine kidney in the upper, middle and lower poles were investigated using oscillatory shear tests. The viscoelastic properties were extracted in the form of the storage modulus and loss modulus in the frequency and time domain. Measurements were taken as a function of frequency from 0.1 Hz to 6.5 Hz at a shear strain amplitude of 0.01 and as function of strain amplitude from 0.001 to 0.1 at a frequency of 1 Hz. Measurements were also taken in the time domain in response to a step shear strain. Both the frequency and time domain data were fitted to a conventional Standard Linear Solid (SLS) model and a semi-fractional Kelvin-Voigt (SFKV) model with a comparable number of parameters. The SFKV model fitted the frequency and time domain data with a correlation coefficient of 0.99. Although the SLS model well fitted the time domain data and the storage modulus data in the frequency domain, it was not able to capture the variation in loss modulus with frequency with a correlation coefficient of 0.53. A five parameter Maxwell-Wiechert model was able to capture the frequency dependence in storage modulus and loss modulus better than the SLS model with a correlation of 0.85.

Role of crystallographic orientation on the deformation behaviour of Ti-6Al-4V alloy during low cycle fatigue

ABSTRACT Low cycle fatigue (LCF) tests were carried out on Ti6Al4V alloy at room temperature for different strain amplitudes ranging from 0.5% to 2%. The microstructure and texture evolutions as a function of strain amplitude have been investigated in the present study. Cyclic softening behaviour was observed at all strain amplitudes, and it was found to increase with increasing the strain amplitude. The fatigue transition life was observed to be at 1.25% strain amplitude. Only type tensile twins were formed during the deformation, and this was found to be significant at higher strain amplitude of 2%. The grains along were appeared to be the twinning parent, and the twinned products were appeared along [0001]. The grains were further found to have substantial cyclic deformation than the other grains, such as and [0001]. The dominant texture was found along during the LCF tests. However, the sample at higher strain amplitude of 2% had also prominent [0001] texture along with texture. Fractographic examination revealed a dimple fracture surface at lower strain amplitude (0.5%), whereas a quasi-cleavage type fracture was observed at higher strain amplitudes (1% & 2%).

Nonlinearity in large amplitude oscillatory shear of drilling fluid: A comparative study on the oil and water base muds behavior

A viscoelastic material exhibits both fluid (viscous) and solid (elastic) like properties simultaneously. The rheological behavior of drilling fluids is customarily measured under the assumption of pure viscous flow, yet they exhibit both viscous and elastic characteristics when subjected to deformation. Some imperative properties of drilling fluids such as gel strength, yield stress, and sag tendency at near-zero shear rate region are categorically under the influence of viscoelastic behavior and have not yet been completely understood due to the lack of appropriate measurement methods. Characterizing the complete rheological profile of material requires measuring linear and nonlinear viscoelastic responses at a wide range of stress/strain levels. The viscoelastic nonlinearity can be characterized under Large Amplitude Oscillatory Shear (LAOS) tests. This study presents a large amplitude oscillatory shear rheology investigation of two water-base (Lignosulfonate and KCl/polymer) and two oil-base (low and high temperature) drilling fluids each in three states; unweighted, weighted, and weighted-contaminated. The viscoelastic nonlinearities of four fluid samples were investigated experimentally as a function of strain amplitude and strain-rate space at different temperatures. The results were described using Lissajous-Bowditch (L-B) plots and local nonlinear viscoelastic dynamic moduli through an oscillatory shear cycle. Structural stability of fluid samples was also studied using the creep-recovery test. The nonlinear viscoelastic behavior of drilling fluids was comprehensively compared and distinguished to understand their nonlinear shear mechanism. As a result of the creep-recovery test at 150 °C, high-temperature oil base mud provided higher thermo-structural stability and zero shear viscosity than those of Lignosulfonate, KCl/polymer, and low-temperature oil-base muds. While the elastic nonlinearity was found to be strain/strain rate softening, the nonlinear viscous character was recorded as shear/shear rate thinning at large strain rates for all drilling fluid systems. Quite a different shear mechanism was detected at low and moderate strain rates. Shear rate thinning was found to be the dominant mechanism for all fluids except Lignosulfonate mud samples that demonstrated shear-thickening behavior at moderate strain rates at 25 °C. At high temperatures (100 °C and 150 °C), shear rate thickening followed by shear rate thinning behavior was governing mechanism under the low and moderate strain rates in all mud samples except KCl/polymer muds. An inverse behavior (shear rate thinning followed by shear rate thickening) was observed through low and moderate strain rates in KCl/polymer muds at 100 °C and 150 °C. Therefore, as revealed from the LAOS test results, shear rate thickening behavior at low to moderate strain rates is in contradiction of the commonly known shear thinning behavior for a drilling fluid undergoing viscous deformation. This finding explains the facts underlying some important properties of drilling fluids such as gel structure formation, hole cleaning ability, and sag tendency.

An Experimental and Theoretical Determination of Oscillatory Shear-Induced Crystallization Processes in Viscoelastic Photonic Crystal Media.

A study is presented of the oscillatory shear-ordering dynamics of viscoelastic photonic crystal media, using an optical shear cell. The hard-sphere/“sticky”-shell design of these polymeric composite particles produces athermal, quasi-solid rubbery media, with a characteristic viscoelastic ensemble response to applied shear. Monotonic crystallization processes, as directly measured by the photonic stopband transmission, are tracked as a function of strain amplitude, oscillation frequency, and temperature. A complementary generic spatio-temporal model is developed of crystallization due to shear-dependent interlayer viscosity, giving propagating crystalline fronts with increasing applied strain, and a gradual transition from interparticle disorder to order. The introduction of a competing shear-induced flow degradation process, dependent on the global shear rate, gives solutions with both amplitude and frequency dependence. The extracted crystallization timescales show parametric trends which are in good qualitative agreement with experimental observations.

Bulk and interfacial properties of milk fat emulsions stabilized by whey protein isolate and whey protein aggregates

Whey protein is widely used in the food industry as an emulsion stabilizer because of its outstanding emulsifying ability. Recent studies have shown that heat-induced whey protein aggregates may also have potential to stabilize emulsions. The interfacial behavior of whey protein and whey protein aggregates adsorbed at the milk fat-water interface has not been well investigated, especially not in the nonlinear regime, which is highly relevant for the preparation of products such as recombined dairy cream.In this study, the interfacial properties of milk fat-water interfaces stabilized by whey protein isolate (WPI) and whey protein aggregates (WPA) at different bulk concentrations (0.1 wt% - 4.0 wt%) were studied by Large Amplitude Oscillatory Dilatation (LAOD). Lissajous plots were used to analyse the nonlinear response of the interfaces as a function of strain amplitude and frequency. The elastic modulus was quantified based on the tangent modulus at zero instantaneous strain in expansion and in compression. Bulk stability of creams stabilized with the mentioned proteins was studied by determining creaming rate, droplet size distribution, ζ-potential and viscosity of the continuous phase.At low concentrations (<2.0 wt%), WPI-stabilized cream had smaller oil droplets than WPA-stabilized cream, indicating that at these concentrations WPI had better emulsifying ability. For concentrations higher than 2.0 wt%, WPA was a better emulsifier in terms of creaming stability because of the higher viscosity of the continuous phase of the emulsions. Both WPI and WPA could prevent coalescence equally well if the concentration was higher than 0.5 wt%. LAOD measurements showed that at a protein concentration of 0.1 wt%, there was little difference between WPI- and WPA-stabilized interfaces. At 4.0 wt%, WPI showed abrupt intra-cycle yielding followed by a predominantly viscous behavior at large expansion. The WPA interfacial layer had a larger maximum linear strain, and showed a more gradual softening in expansion and mild strain hardening in compression. We hypothesize that WPI formed denser and more brittle (quasi-) 2d structures at the interface, while the interfaces formed by WPA might have a thicker and more stretchable 3d structure. The WPA-stabilized emulsion was less resistant to coalescence upon drastic stirring, which can be explained with its different large deformation behavior, and is relevant for applications where the cream is subjected to large deformations (whipping or stirring).

Large Amplitude Oscillatory Shear (LAOS) analysis of gluten-free cake batters: The effect of dietary fiber enrichment

The aim of this study is to investigate the effect of dietary fiber enrichment on non-linear viscoelastic behavior of gluten-free cake batters by using Large Amplitude Oscillatory Shear (LAOS) analysis. Textural properties and specific volume of gluten-free cakes were also determined to investigate the possible correlations with LAOS parameters. Gluten-free cake batters were formulated by replacing buckwheat flour with two different dietary fiber sources, namely orange fiber (OF) and orange pomace powder (OPP) at five different levels (0%, 4%, %8, %12 and 16%). All gluten-free cake batter samples exhibited linear viscoelastic properties at small strain amplitudes but rheological properties enters the non-linear region by increasing strain amplitude. The Lissajous-Bowditch curves revealed that stored energy increased by increasing dietary fiber amount and gluten-free cake batters became more elastic in the non-linear region. The normalized elastic Chebyshev coeffients (e3/e1) indicated the strain hardening behavior of cake batters at small strain amplitudes shifted to strain softening in the non-linear region. The e3/e1 and v3/v1 ratios as a function of strain amplitude indicated that non-linearity is more pronounced in the elastic component compared to the viscous component. The S and T values calculated at 50% strain amplitude showed strong correlation with water retention capacity, hardness and specific volume of gluten-free cakes enriched with OF whereas softer correlations were obtained for the OPP-containing ones due to elastic instability of the batters. Principal component (PCA) and hierarchical cluster analysis (HCA) were performed to provide basic graphical comparison of the differences/similarities between non-linear rheological properties of gluten-free cake batters by considering LAOS parameters. The viscoelastic properties of the cake batters containing 16% OPP were found to be suitable for high gas retention capacity since the highest cake specific volume was obtained.

Wall slip and multi-tier yielding in capillary suspensions

Impact of wall slip on the yield stress measurement is examined for capillary suspensions consisting of cocoa powder as the dispersed phase, vegetable oil as the continuous primary fluid, and water as the secondary fluid using smooth and serrated parallel plates. Using dynamic oscillatory measurements, we investigated the yielding behavior of this ternary solid-fluid-fluid system with varying particle volume fraction, ϕ, from 0.45 to 0.65 and varying water volume fraction, ϕw, from 0.02 to 0.08. Yield stress is defined as the maximum in the elastic stress (G′γ), which is obtained by plotting the product of elastic modulus (G′) and strain amplitude (γ) as a function of applied strain amplitude. With serrated plates, which offer minimal slippage, capillary suspensions with ϕ ≥ 0.45 and a fixed ϕw = 0.06 showed a two-step yielding behavior as indicated by two peaks in the plots of elastic stress as a function of strain amplitude. On the other hand with smooth plates, the capillary suspensions showed strong evidence of wall slip as evident by the presence of three distinct peaks and lowered first yield stresses for all ϕ and ϕw. These results can be interpreted based on the fact that a particle-depleted layer, which is known to be responsible for slip, is present in the vicinity of the smooth surfaces. The slip layer presents itself as an additional “pseudo-microstructure” (characteristic length scale) besides the two microstructures, aqueous bridges and solid particle agglomerates, that may occur in the system. With serrated plates, both the yield stresses (σ1σ2) and storage moduli plateau at lower strain (before the first yield point) and at higher strain (before the second yield point) (G $^{\prime }_{p1}$ , G $^{\prime }_{p2}$ ) were found to increase with ϕ (at a fixed ϕw = 0.06) following power-law dependences. Similarly with increasing ϕw (0.02 – 0.08) at a fixed ϕ = 0.62, the system behaved as a solid-like material in a jammed state with particles strongly held together as manifested by rapidly increasing σ1 and σ2. The usage of smooth surfaces primarily affected σ1 which was reflected by an approximately 70–90% decrement in the measured σ1 for all values of ϕ. By contrast, σ2 and G $^{\prime }_{p2}$ were found to be unaffected as shown by close agreement of values obtained using serrated geometry due to vanishing slip layers at higher strain amplitudes.

Thermo-mechanical coupling analysis of transient temperature and rolling resistance for solid rubber tire: Numerical simulation and experimental verification

The achievement of low rolling resistance and long-term durability of tires on various vehicles is of great challenge. Tire performances heavily depend on rubber properties; however, the thermo-mechanical coupling characteristics of rubber composites are complicated rendering the design of high-performance tires time-consuming and costly. In our research, the transient temperature and rolling resistance of a solid rubber tire were performed based on the thermo-mechanical coupling approach and nonlinear viscoelastic theory by using finite element method. Particular attention was paid to the strain cycles as the tire rolling on the road presents non-sinusoidal deformation. First, a static three dimensional tire-road contact analysis was conducted to obtain the principal strain cycles. Second, the 100th-order Fourier sine series was used to approximate the strain amplitude. Third, the heat generation rate proportional to the product of the loss modulus and the square of strain amplitude was calculated. The loss modulus was updated as a function of strain amplitude, temperature and frequency. Loss modulus softening effect was also considered. A practical method was proposed to compute the rolling resistance and transient temperature distributions by establishing a 2-D axisymmetric model. A rubber rolling tester was used to verify the numerical results. The comparison between numerical data and test data reveals that the proposed analytical method is a reliable approach to predict rolling resistance and transient temperature distribution for rubber tires. At last, the dependence of rolling resistance and heat build-up on thermal conductivity and loss factor were investigated by the parametric numerical experiments.

Magnetorheological response of highly filled magnetoactive elastomers from perspective of mechanical energy density: Fractal aggregates above the nanometer scale?

The dynamic shear modulus of magnetoactive elastomers containing 70 and 80 mass % of carbonyl iron microparticles is measured as a function of strain amplitude via dynamic torsion oscillations in various magnetic fields. The results are presented in terms of the mechanical energy density and considered in the framework of the conventional Kraus model. The form exponent of the Kraus model is further related to a physical model of Huber etal. [Huber et al., J. Phys.: Condens. Matter 8, 409 (1996)10.1088/0953-8984/8/29/003] that uses a realistic representation for the cluster network possessing fractal structure. Two mechanical loading regimes are identified. At small strain amplitudes the exponent β of the Kraus model changes in an externally applied magnetic field due to rearrangement of ferromagnetic-filler particles, while at large strain amplitudes, the exponent β seems to be independent of the magnetic field. The critical mechanical energy characterizing the transition between these two regimes grows with the increasing magnetic field. Similarities between agglomeration and deagglomeration of magnetic filler under simultaneously applied magnetic field and mechanical shear and the concept of jamming transition are discussed. It is proposed that the magnetic field should be considered as an additional parameter to the jamming phase diagram of rubbers filled with magnetic particles.

High amplitude internal friction in monocrystalline germanium‐doped silicon

The internal friction and shear modulus of the monocrystalline Si‐Ge alloys with Ge with 0.5 to 2 at.% content grown by Czochralski technique were studied as functions of strain amplitude at the temperatures of 20 and 600 °C. It is shown that internal friction and shear modulus are characterized by one critical value of strain amplitude at which dislocation segments breakaway from weak point centers begins. Measurements at 600 °C show additional second critical strain amplitude and intensive hysteresis‐type change of the internal friction and shear modulus in high strain amplitude range. First and second critical strain amplitudes reveal the tendency of reduction with Ge content increase in Si‐Ge alloys.

Reduction of filler networking in silica based elastomeric nanocomposites with exfoliated organo-montmorillonite

Montmorillonite with dimethyl di(hydrogenatedtalloyl) ammonium as the compensating cation was added to a silica based elastomeric composite and the hybrid filler system led to reduction of filler networking phenomenon, better stability of elastic modulus with temperature, enhancement of stresses at all elongations, improvement of ultimate properties. This composite was based on a blend of natural rubber, poly(1,4-cis-isoprene) and poly(styrene-co-butadiene) from anionic polymerization and contained 70 parts per hundred rubber (phr) of silica. The organically modified clay (OC) was below the threshold required to establish an hybrid OC-silica filler network. Such threshold (about 7phr) was estimated by preparing silica based nanocomposites containing various amounts of OC and determining shear storage and loss moduli as a function of strain amplitude. This work demonstrates that exfoliated OC favour lower dissipation of energy of silica based elastomeric composites under dynamic mechanical stresses and paves the way for further large scale applications.

Analyzing aging under oscillatory strain field through the soft glassy rheology model.

In this work, we solve the Soft Glassy Rheology (SGR) model under application of oscillatory deformation field with varying magnitudes of strain as well as frequency for different noise temperatures. In the glassy domain, the SGR model undergoes time evolution of elastic modulus. Increase in strain magnitude beyond the linear regime is observed to enhance the rate of aging as manifested by a faster evolution of elastic modulus with increase in strain amplitude due to overaging. However at higher strain magnitudes, the rejuvenation effect starts dominating over the aging, thereby reducing the rate at which elastic modulus evolves. We also plot the aging phase diagram describing an occurrence of the linear, the overaging, and the rejuvenation regimes as a function of strain and frequency for different noise temperatures. The aging phase diagram suggests that while the linear regime remains unaffected by the changes in frequency and noise temperature, the width of the overaging regime increases with increase in frequency and noise temperature. We also study the time evolution of the shapes of relaxation time spectra as a function of strain amplitude, which renders further insight into the overaging and the rejuvenation behavior. While the phenomenon of overaging is observed to be an inherent character of the SGR model, experimentally not all the materials demonstrate overaging. Such a discrepancy suggests that the energy well depths before and after a yielding event may not be completely uncorrelated as assumed in the SGR formalism.

Nonlinear behaviour of glass fibre reinforced composites with delamination

Abstract The aim is to assess the nonlinear behaviour of glass fibre composite having controlled delaminations. The experimental analysis focused on the variation of nonlinear parameters as function of delamination size. Through a set of increasing resonance amplitudes applied on a delaminated glass fibre reinforced composite, the frequency shift and the specific damping coefficient shift were evaluated as a function of strain amplitude. The nonlinear elastic and dissipative parameters related respectively to the frequency and damping, were determined for different bending modes and different delamination lengths. These parameters were compared with the linear vibration parameter. The results show that nonlinear parameters are more sensitive to the presence of delamination in composite.

The analysis of the influence of xanthan gum and apple pectins on egg white protein foams using the large amplitude oscillatory shear method

This research study analysed the rheological properties of fresh food foams based on egg white protein, and with the addition of apple pectins and xanthan gum. The rheological analysis was carried out using the large amplitude oscillatory shear (LAOS) technique. From the obtained results two types of Lissajous figures were constructed, describing the elastic and viscous properties. The obtained figures were subjected to geometrical decomposition, which resulted in the determination of the stress values characteristic of nonlinear purely elastic and purely viscous properties. The Fast Chebyshev Transform allowed for the calculation of the Chebyshev coefficients, and further detailed analysis of rheological behaviour of foams as a function of strain amplitude. The determination of the values of elastic and viscous Chebyshev coefficients allowed for the interpretation, with high resolution, of nonlinear rheological properties of the obtained foams.

Nonlinearity from FT-rheology for liquid crystal 8CB under large amplitude oscillatory shear (LAOS) flow

This study systematically investigated the nonlinear stress behavior of liquid crystal (8CB, 4-4′-n-octyl-cyanobiphenyl) in lamellar smectic A phase under large amplitude oscillatory shear (LAOS) flow. To investigate the nonlinear stress response under LAOS flow, the nonlinearity (I3/1) from Fourier transform-rheology as a function of applied shear time (3600 s) was calculated according to changes in both strain amplitude γ0 and frequency ω. The storage modulus G′(t) and loss modulus G″(t) from the conventional rheometer program under various LAOS flow conditions decreased and reached equilibrium as a function of time. This could be attributed to shear alignment of the lamellar smectic A structure. On the contrary, with G′(t) and G″(t), the nonlinearity I3/1(t) showed three different behaviors depending on the magnitude of strain amplitude: (1) Region I: Increased (increased and reached equilibrium), (2) region II: Increased and decreased (showed maximum value; decreased and reached equilibrium), and (3) region III: Decreased (decreased and reached equilibrium) as a function of time. These three different time-dependent behaviors of nonlinearity (I3/1) were shown to be related with the alignment behavior of the lamellar structure. With stress decomposition method, the viscous and elastic stresses of 3600 s were calculated. Viscous and elastic stresses showed different behavior at region I and region III. With an equilibrium value of 3600 s, the G′, G″, and nonlinearity (I3/1) were plotted as a function of strain amplitude, γ0. Interestingly, I3/1(γ0) increased and then decreased (maximum) even though G′(γ0) and G″(γ0) only decreased with increasing strain amplitude. From these results, it can be concluded that LAOS analysis of nonlinear stress, especially I3/1 from FT-rheology, is more sensitive to microstructure than storage modulus G′ and loss modulus G″.

A viscoelastic damage model for hysteresis in PVC H100 foam under cyclic loading

A phenomenological constitutive model for Divinycell PVC H100 foam undergoing crushing and hysteresis under cyclic compression loading was developed. Cyclic compression tests were done with strain amplitudes from 0.02 to 0.1 and strain rates ranging from 0.0005 s−1 to 5 s−1. Within this test range, the PVC H100 foam exhibited strain rate-dependency, damage, and hysteresis. Damage that occurred in the foam after yielding followed the pattern of Mullins damage, i.e. the damage was essentially fixed at a given strain amplitude, and more damage occurred with increasing the strain amplitude. A constitutive model based on damage initiation and viscoelastic damage evolution of the foam was proposed. A simple damage initiation criterion based on critical compressive strain was proposed to separate undamaged and damaged foam response. A standard model, an elastic spring in parallel with Maxwell element, was used to describe viscoelastic behavior before and after damage. Before damage, spring and damper constants were evaluated from the test data. The rate-dependent undamaged stress–strain response and flow stress were found to be in good agreement with the test results. After damage, the spring and dashpot resistances were found to be the functions of strain amplitude and flow stress, which depended on strain rate. These viscoelastic damage functions were shown to give very good predictions of the hysteresis and strain rate-dependent behavior of the foam after damage.

Fatigue properties of a pseudoelastic NiTi alloy: Strain ratcheting and hysteresis under cyclic tensile loading

Low cycle fatigue properties of a commercial pseudoelastic Ni-rich Nickel–Titanium alloy have been analyzed. In particular, strain controlled pull–pull fatigue tests have been carried out on dog-bone shaped specimens, obtained from commercial NiTi sheets. Large ratcheting strains have been observed from the first mechanical cycles, up to a complete stabilization of the stress–strain response of the material. These mechanisms, mainly attributed to the formation of stabilized martensite and dislocation networks, cause a marked evolution of the functional properties of the alloy in terms of pseudoelastic recovery capabilities. This evolution has been systematically analyzed by identifying some functional damage parameters, involving strain, energy, transformation stress, Young’s modulus and phase transition temperatures. Furthermore, the data on structural fatigue, i.e. cycles to failure as a function of strain amplitude, are illustrated and analyzed according to a modified Coffin–Manson approach.

Mechanical spectral hole burning in polymer solutions: Comparison with large amplitude oscillatory shear fingerprinting

Large amplitude oscillatory shear (LAOS) fingerprinting of the nonlinear response of polymers and other complex soft matter has proven an excellent tool in the characterization of such materials. The major methods of quantitative characterization of nonlinearity using LAOS are the use of Lissajous-Bowditch (LB) curves and Fourier transform rheology (FTR). Another LAOS-based tool, mechanical spectral hole burning (MSHB), has been developed in our labs to investigate the heterogeneous dynamics of polymer melts and solutions and offers the possibility of a complementary method to the LB and FTR analyses for the fingerprinting of the nonlinear response of polymers and other complex fluids. Here, we present results from an investigation of the MSHB, LB loop, and FTR behaviors of polybutadiene and polystyrene solutions. The goal of the study was to examine similarities and differences in how these methods “fingerprint” the nonlinear response of the different polymer solutions. We find that the vertical holes in the MSHB experiments vary in intensity with the square of the sine wave pump magnitude. This is also true for the third harmonics obtained in the FTR, but the origins are possibly different for the two signatures. We have analyzed the fingerprinting categories as a function of strain amplitude and frequency from the LB loops and higher harmonics of FTR and add an additional feature to the fingerprints that are related to MSHB signatures, which are found to complement the other two methods and add new information to the fingerprinting diagrams.

Nonlinear viscoelasticity of polymer nanocomposites under large amplitude oscillatory shear flow

In this study, the nonlinear response of polymer nanocomposites under large amplitude oscillatory shear (LAOS) flow was investigated. We first investigated polycaprolactone (PCL)/multiwall nanotube (MWNT) composites under LAOS flow using different analyzing methods including Lissajous plot analysis, stress decomposition, and Fourier transform rheology (FT-rheology). The nonlinear parameter Q (≡I3/1/γ02) was obtained from the FT-rheology as a function of strain amplitude, and the zero-strain nonlinearity Q0 (≡limγ0→0Q) was also calculated. We compared the linear and nonlinear viscoelastic properties as we increase MWNT concentration (ϕ). It was found that the zero-strain nonlinearity (Q0) was more sensitive to detect the effect of MWNT concentration than the linear viscoelastic properties. We also investigated the effect of particle shape on nonlinear viscoelastic properties of the polymer composites containing particles of different shape, e.g., PCL/MWNT (one-dimensional thread shape), PCL/organomodified ...

Effect of organoclay on non-linear rheological properties of poly(lactic acid)/poly(caprolactone) blends

The nonlinear viscoelastic properties of PLA/PCL blends with and without clay (montmorillonite, MMT) under large amplitude oscillatory shear (LAOS) flow were investigated. The G' and G'' as a function of strain amplitude, Lissajous plots and FT-rheology methods were used to interpret nonlinear behavior of PLA/PCL blends with and without MMT. Additionally, scanning electron microscopy (SEM) images of PLA/PCL with MMT blends were taken to inves- tigate the effects of clay on the internal structure of the PLA/PCL blends. A relationship between morphological changes and linear and nonlinear rheological properties was observed. SEM image analysis revealed that clay acted as a com- patibilizer and then reduced the size of droplets in the PCL domain of the PLA matrix. As a result, nonlinear properties sensitively reflect morphological changes with increasing MMT amount. The nonlinear rheological properties of PLA/ PCL/MMT/metallocene-LLDPE (mLLDPE) were also investigated when mLLDPE was used as an impact modifier to improve mechanical properties, and the nonlinear rheological properties of PLA/PCL/MMT and PLA/PCL/MMT/ mLLDPE were also compared.