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Cyclic material tests were done on Divinycell PVC H100 foam to obtain out-of-plane and in-plane compression and shear material properties after foam yielding. The compression and shear stress-strain behaviors were very similar to each other except that a plateau (flow) stress occurred after yielding in compression, while the foam underwent mild strain hardening after shear yielding. The ratio of out-of-plane to in-plane stiffness and yield strength for the PVC H100 was found to be approximately 3/2 in both the compression and shear modes. After viscoplastic yielding, the foam underwent permanent damage and exhibited hysteresis, mainly in the form of viscoelasticity. Damage that occurred in the foam after it yields 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. Hysteresis was much more pronounced as the damage grew, suggesting that viscoelastic properties of the foam could be changing with the amount of damage. [ABSTRACT FROM AUTHOR]

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide-cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30-42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow-Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2-5 particle diameters. [ABSTRACT FROM AUTHOR]

Small amounts of organoclays in different sizes and concentrations were added into thermotropic liquid crystalline polymer (TLCP) by a combination method of ultrasonication, centrifugation, and solution casting (and shear-induced phase separation). Four kinds of organoclay-modified TLCP composites were obtained. TC3 UP was a kind of organoclay which displayed a marked shear-induced phase separation phenomenon at 190 °C and higher temperatures. TC3 UP could be separated into a TLCP-rich part, TC3 white, and an organoclay-rich part, TC3 dark. TC3 white was an organoclay-modified TLCP with fully exfoliated organoclay of a uniform size of 15–25 nm well dispersed in the TLCP. TC3 dark had a typical intercalated model structure with some TLCP molecules confined in organoclay galleries. TC3 FS was an organoclay-modified TLCP with organoclay of comparable size to that of the fully extended TLCP molecule, i.e., 85 nm. The organoclay layers dispersed into the polymeric matrix as a few randomly organized organoclay layers or stacks of layers in the quiescent condition in organoclay-modified TLCPs. The larger organoclay size or higher concentration of organoclay in the composites (such as, TC3 UP and TC3 dark) caused a greater proportion of the layers or stacks be hydro-dynamically impeded in the quiescent state, resulting in the filler–filler interaction becoming important and in fact dominating the long-term viscoelasticity of the composites. Additionally, the ease with which the organoclay structure could be altered by flow was considerably enhanced, primarily because of filler–filler interactions. Organoclay size has primary effect on the liquid crystallinity of TLCP. Small or comparable organoclay size with the fully extended TLCP molecule in TC3 white and TC3 FS has weak or negligible negative influence on the liquid crystallinity of TLCP, while larger organoclay size totally damages the liquid crystallinity of TLCP. The morphologies, liquid crystallinity as well as the linear and non-linear viscoelastic behaviors of organoclay-modified TLCPs have been characterized in detail. [ABSTRACT FROM AUTHOR]

One of the successful approaches to model the time-dependent behaviour of elastomers is proposed by Bergström and Boyce (JMPS 46:931–954, 1998). The model is micromechanically inspired from the relaxation of a single entangled chain in a polymer gel matrix. Although the theory of inelasticity based on multiplicative decomposition of the deformation gradient is well established, the complexity of the nonlinear evolution law as well as the nonlinear equilibrium and non-equilibrium material response necessitates a precise description of the algorithmic setting. This contribution presents for the first time a novel numerical implementation of the Bergström–Boyce model in the context of finite element analysis and elaborates theoretical aspects of the model. The thermodynamical consistency of the evolution law is proven and a parameter study with respect to the material parameters has been carried out. The agreement of the model with the recent experimental data is investigated. [ABSTRACT FROM AUTHOR]

Viscoelastic behavior has been examined for polypropylene and polyvinylidene fluoride monofilaments for making reticular endoprostheses. The deformation behavior corresponds to linear viscoelasticity. The parameters have been determined for monofilament creep. A method is proposed for describing the creep, and the strains calculated from it in creep at various stresses agree with the experimental ones. These results serve as basis for forecasting the viability of implants made from these monofilaments. [ABSTRACT FROM AUTHOR]

This paper presents a finite element study of cohesive crack growth in a thin infinite viscoelastic strip to investigate the effects of viscoelastic properties, strip height, and cohesive model parameters on the crack growth resistance. The results of the study show that the dependence of the fracture energy on the viscoelastic properties for the strip problem is similar to that obtained for the infinite body problem even when the cohesive zone length is large compared to the height of the strip. The fracture energy also depends on the crack speed v through the dimensionless parameter v τ/ L ∞ where L ∞ is the characteristic length of the cohesive zone and τ is the characteristic relaxation time of the bulk material. This relationship confirms that at least two properties of the fracture process must be prescribed accurately to model viscoelastic crack growth. In contrast, the fracture energy and crack speed are insensitive to the strip height even in situations where the growth of the dissipation zone is severely constrained by the strip boundaries. We observe that at high speeds, where the fracture energy asymptotically approaches the maximum value, the material surrounding the cohesive zone is in the rubbery (equilibrium) state and not the glassy state. [ABSTRACT FROM AUTHOR]

A mechanical model is presented, in which viscoelastic response is described by the action of time-dependent latch elements. The model represents viscoelastic changes occurring through incremental jumps as opposed to continuous motion. This is supported by the observation that polymeric creep, recovery and stress relaxation can be correlated with stretched exponential functions, i.e. Weibull and Kohlrausch-Williams-Watts, since (i) the former is also used in reliability engineering to represent the failure of discrete elements and (ii) there is evidence of the latter being an approximation to the Eyring potential energy barrier relationship, which describes motion in terms of molecular jumps. [ABSTRACT FROM AUTHOR]

The photoelastic behavior of a linearly viscoelastic orthotropic plate containing a crack is described by using the well-known Netrebko-Vasyl'chenko equations of photoelasticity for linearly viscoelastic bodies. Relations for the stress intensity factors near the crack are deduced according to the data of polarization optical measurements. It is shown that the behavior of the stress intensity factors as functions of time depends on the angle between the direction of tension and the crack. [ABSTRACT FROM AUTHOR]

An epoxy-functionalized hyperbranched polymer (HBP) was used to toughen a conventional epoxy resin, diglycidyl ether of bisphenol A (DGEBA) cured with diethyltoluene-2,6-diamine (DETDA). There was little change in gel time as a result of addition of HBP, even though the HBP reacts at a slower rate with amine hardeners compared to DGEBA alone. Phase separation was investigated for various HBP contents and as a function of cure conditions as well. The thermal and dynamic viscoelastic behavior of the modified matrices have been examined and compared to the DGEBA epoxy matrix. It appears that the HBP which phase separates does not react as fully as when it is reacted with the amine alone. Nonetheless, good improvement in impact strength as a result of incorporation of HBP were observed and explained in terms of morphological behavior for a DGEBA matrix modified with various amounts of HBP. [ABSTRACT FROM AUTHOR]

In this paper the results of the experimental determination of the viscoelastic tensile and shear properties of the eutectic 62 wt% Sn–36 wt% Pb–2 wt% Ag solder alloy in the temperature range between −20 and 100 °C are presented. The dynamic tensile and shear moduli and the viscous damping coefficients were measured using a phase-sensitive resonance technique. The results show that the temperature dependence of the dynamic Young's and shear moduli can be approximated by linear functions and a quadratic polynomial can be used to define a lower bound of the temperature dependence of the viscous damping coefficients of the material. For a temperature rise from 20 to 65 °C the dynamic Young's and shear moduli decrease by approximately 6% and the damping coefficient increases by approximately 80%. [ABSTRACT FROM AUTHOR]

Studies the complete contact indentations of viscoelastic materials. Consideration of a rigid frictionless axisymmetric indenter with a polynomial profile and the axis of revolution; Measurement of the viscoelastic properties of thin films; Measurement of the material's creep function.