摘要:

The mechanical behavior of composite gels consisting of spherical deformable filler particles (Sephadex beads) embedded in a gelatin gel matrix has been investigated. The shear modulus of composite gels is dependent on the shear modulus of the matrix, the deformability of the particles, and their volume fraction. Under uniaxial compression, at high strains, the importance of the filler‐matrix interface in influencing the strength of the composites was demonstrated. Failure properties of the composite were shown to be controlled by altering the chemical affinity between filler and matrix. Studies with a composite food starch gel showed similar dependence on the previously identified parameters.

ISSN:0148-6055    

DOI:10.1122/1.549941

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

Volume‐filling flocculated dispersions respond elastically to small deformations. We have modelled such systems as disordered elastic networks with statistically homogeneous structures. The disorder of the actual network is represented by a partially filled f.c.c. lattice and the elastic moduli calculated through an effective medium approximation. In this paper we present results for triangular networks in two dimensions with arbitrary combinations of central and bond bending forces for bond as well as site percolation. The moduli increase from zero above an apparent threshold value dependent on the type of percolation and the force law. However, these results are bounded by the isotropic and central force cases, both of which are known for three dimensions. Hence qualitative results for three‐dimensional networks can be obtained without further computations. The theory explains experimental results qualitatively but further refinement is needed to predict the moduli as well as the conductivity of the dispersions accurately.

ISSN:0148-6055    

DOI:10.1122/1.549954

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The evolution of linear viscoelasticity during cross‐linking of a stoichiometrically imbalanced polydimethylsiloxane (PDMS) was measured by small amplitude oscillatory shear. At the gel point (GP), stress relaxation was found to follow a power law,St−n,as described by the previously suggestedgel equation. However, while stoichiometrically balanced gels (PDMS, polyurethanes) gave the specific exponent value ofn=1/2,a higher exponent value,1/2

ISSN:0148-6055    

DOI:10.1122/1.549955

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

Three techniques for measuring yield stresses are compared by performing parallel experiments on five model oil‐in‐water emulsions. The emulsions displayed yield stresses of50–550 dynes/cm2.The three techniques involved: (1) measurements of rotation rate and stress in a concentric‐cylinder geometry, (2) measurement of torque and apparent shear rate in a parallel disk geometry at two different gap heights, and (3) measurement of rotation under constant applied stress in a vane geometry previously described by Boger. Emulsions are prone to slip at solid boundaries; therefore, methods to assess wall slip contributions for techniques (1) and (2) are developed. The vane device eliminates the possibility of slip. The measurements give comparable results. The techniques are compared with respect to: precision, ease of implementation, information obtained, and sample requirements.

ISSN:0148-6055    

DOI:10.1122/1.549956

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The dynamic viscoelastic properties of 30 wt% solutions of styrene (S)‐butadiene (B) radial (star) block copolymers were measured to investigate the effect of deformation history. The block structure for SBH1 examined was(S‐B‐)mand that for BSH1(B‐S‐)n,wheremandnare about 5. The solvents used were chlorinated diphenyl (KC4) and dibutylphthalate (DBP); the former is a good solvent for both polystyrene (PS) block and polybutadiene (PB) block, and the latter is a good solvent for PS block and a poor solvent for PB block. Both storage modulusG′and loss modulusG″vary little with maximum strain amplitude(γ0)for the solutions in KC4, or for those in DBP at 80°C. On the other hand,G′,andG″depend significantly onγ0for solutions in DBP at temperatures lower than 60°C, implying that the former systems are homogeneous solutions and the latter contain microdomain structure.G′andG″of DBP solutions of SBH1 are independent ofγ0forγ0⩽0.03,G′decreases andG″increases in the range0.04<γ00.1.This increment inG″with increasingγ0is attributed to a domain structure existing in the solution which will be broken down gradually; correspondingly the relaxation time will be shortened. Reformation of the micro‐domain structure takes about 40 min at 60°C.

ISSN:0148-6055    

DOI:10.1122/1.549943

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549944

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The one‐dimensional equations describing Newtonian fiber flow have been derived previously using lubrication scaling of the axisymmetric equations of motion. Here, we present an extension of that analysis using a generalized convected Maxwell model. We find that the non‐Newtonian behavior of the fluid must be severely limited for the one‐dimensional equations to be determinate. In this sense, the primary effect of viscoelastic behavior is to make the flow more two dimensional. Limiting cases based on previous one‐dimensional models are shown to violate the axisymmetric equations of motion. In addition, questions are raised about the validity of elongational viscosity measurements of highly elastic fluids.

ISSN:0148-6055    

DOI:10.1122/1.549957

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The properties of a set of even‐order tensors, used to describe the probability distribution function of fiber orientation in suspensions and composites containing short rigid fibers, are reviewed. These tensors are related to the coefficients of a Fourier series expansion of the probability distribution function. If ann‐th‐order tensor property of a composite can be found from a linear average of a transversely isotropic tensor over the distribution function, then predicting that property only requires knowledge of then‐th‐order orientation tensor. Equations of change for the second‐ and fourth‐order tensors are derived; these can be used to predict the orientation of fibers by flow during processing. A closure approximation is required in the equations of change. A hybrid closure approximation, combining previous linear and quadratic forms, performs best in the equations of change for planar orientation. The accuracy of closure approximations is also explored by calculating the mechanical properties of solid composites with three‐dimensional fiber orientation. Again the hybrid closure works best over the full range of orientation states. Tensors offer considerable advantage for numerical computation because they are a compact description of the fiber orientation state.

ISSN:0148-6055    

DOI:10.1122/1.549945

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

A discussion of mathematical aspects of general stress‐strain problems involving viscoelastic materials is given. Constitutive equations are presented in a general differential form. These equations generalize the Boltzmann constitutive relations and provide a convenient way to solve stress‐strain problems. A stable and efficient finite‐difference scheme is constructed and applied to the calculation of the residual stress distribution in a laminar viscoelastic‐elastic composite plate cooled by convection from both sides. In the appendices general relations among relaxation functions are discussed. The results can be used to determine the shift in average relaxation times depending on geometry of relaxation experiment.

ISSN:0148-6055    

DOI:10.1122/1.549958

出版商:The Society of Rheology    

年代:1987

数据来源: AIP

摘要:

The onset of extrudate distortion (sharkskin) in linear low‐density polyethylene is shown to coincide with the failure of adhesion at the polymer/metal interface. The transition to slip‐stick melt fracture is characterized by a catastrophic failure of adhesion, with periodic nearly complete slip over a capillary residence time alternating with adhesion. The onset of sharkskin is in agreement with a calculation based on a stability theory of Pearson and Petrie.

ISSN:0148-6055    

DOI:10.1122/1.549942

出版商:The Society of Rheology    

年代:1987

数据来源: AIP