Showing papers on "Pure shear published in 1980"

Shear‐Induced Structure in a Concentrated Suspension of Solid Spheres

Abstract: Two novel phenomena were observed in steady and transient shear measurements which were made in a Couette device of a R‐17 Weissenberg Rheogoniometer with suspensions of polystyrene spheres, 40–50 μm in diameter, suspended in a mixture of silicone oils at volume fractions 0⩽φ0.55. When φ⩾0.3, the steady‐shear viscosity at a given shear rate was found to drift for many hours to an asymptotic value which, in contrast to the scatter of the initial measurements, was very reproducible. Again, when φ⩾0.3, the shear stress showed a memory for the direction of previous shearing when the shear was stopped for a while and then restarted with either the same or the opposite sign. Moreover, during oscillatory shear experiments, these suspensions exhibited a nonlinear response which in fact could be predicted from their response to a sudden reversal of the direction of steady shear. It would appear, therefore, that such concentrated two‐phase systems cannot be modeled as isotropic fluids having a scalar effective viscosity unless the solids concentration is low.

Shear band inclination and shear modulus of sand in biaxial tests

Abstract: The spontaneous shear band formation in the biaxial test on dry sand samples with constant cell pressure is treated as a bifurcation problem. The constitutive response of sand is described in terms of mobilized friction and dilatancy. Dilatancy is looked upon as an internal constraint and the hardening rule is expressed in terms of an adequate dimensionless stress measure. Owing to fail of normality in sand, localization always occurs in the hardening regime. The theoretical solution of the shear band inclination is a geometrical mean of the classical Coulomb and Roscoe solutions and is in good agreement with the experimental data. The incipient shear modulus is proportional to the stress level and can be estimated to be also proportional to these cant modulus.

Relation between steady shear flow and dynamic rheology

Abstract: The relationships between steady shear flow and dynamic rheology are investigated at relatively high shear rates and frequencies A useful empirical relationship in this region predicts that the magnitude of the complex dynamic viscosity |η*| should be compared with the shear viscosityη at equal values of frequency and shear rate (Cox-Merz-rule) Polystyrenes (PS) and Polyacrylamides (PAAm) have been investigated over a wide range of concentration and molecular weight Only in case of PAAm/H2O solutions we have found that the results do not coincide with Cox-Merz-rule As far as we know this is the first time that deviations from Cox-Merz-rule were observed in a homogeneous system A molecular interpretation is given

Determination of the impact response of PMMA using combined compression and shear loading

Abstract: Large amplitude one‐dimensional compression and shear wave measurements have been made in polymethyl methacrylate (PMMA). Measurements of shear and longitudinal wave velocities were used to determine the shear modulus, bulk modulus, and the mean stress‐volume relations under impact loading. The mean stress‐volume relation determined from impact data is considerably stiffer than the static hydrostat often used to interpret shock data and leads to a lower strength in shock wave data. Unlike the quasi‐static‐uniaxial strain results, the shock data show strength reduction at higher stresses. Measurement of shear wave amplitudes, at different compressive stresses, independently support the strength loss determined from wave velocity analysis. Measurement of shear particle velocity at the impact surface shows that the dynamic friction behavior of PMMA depends on the inelastic material response near the surface.

Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands

Abstract: Experiments were conducted to determine the shear strains and strain rates in adiabatic shear bands in a Ni-Cr steel. An explosively driven punch was used to shear plugs from steel plates and, thereby, create adiabatic shear bands for investigation. There were originally planes of chemical inhomogeneity (reference bands) in the plane of the steel samples. The slopes of the reference bands were altered by the plastic shear, and they were, therefore, a measure of the plastic shear strain. From measurements of the slopes of the reference bands, it was found that the plastic shear was approximately an exponential function of distance through an adiabatic shear band. Shear strains of at least 572 developed after the onset of adiabatic shear, and with measured rates of punching, it was estimated that shear strain rates as great as 9.4 x 107 sec−1 were attained within the adiabatic shear bands. The results suggest how heating occurs within the shear bands and that there is a plastic instability due to carbide and lath morphology changes and, possibly, a magnetic transformation associated with the deformation and heating.

Further Development of a Computational Shear Band Model.

Abstract: : Experimental and analytical work was performed to improve the computational model for adiabatic shear band nucleation and growth (SNAG) A series of contained fragmenting cylinder experiments were performed with 4340 steel treated to hardness of R sub c 40, R sub c 52, and R sub c 21 The resulting damage ranged from homogeneous plastic deformation to extensive shear banding and resulting fragmentation The results showed strong positive correlation between shear banding damage and material hardness for identical loading conditions A simplified method of damage quantification was used to obtain shear band density, size and orientation distributions for all of the R sub c 40 experiments Preliminary computer simulations were performed to determine plastic shear strain rate histories in the direction of the predominant shear banding orientation mode, and the computations were compared with experimental data to yield first estimates for the values of the nucleation and growth parameters A shear band nucleation criterion based on measurable material properties was proposed and tested against the experimental data; the criterion was seen to be promising although not yet conclusive Several experimental techniques for characterizing the shear banding resistance of materials were evaluated and compared The contained fragmenting cylinder experiment was concluded to be the best single technique, although the dynamic punch test has special value for armor penetration applications

A Sandwich-Type Creep Rheometer for the measurement of rheological properties of polymer melts at low shear stresses*)

Abstract: A new Sandwich-Typ Creep Rheometer (SCR) is described which is suited for measuring the zero shear viscosityη 0 and the steady-state shear complianceJ e 0 of polymer melts. The range of shear stresses extends from 2 N/m2 to 5000 N/m2. Measurements down to shear rates of 10−5 s−1 and less are possible on high viscosity melts. The agreement between the SCR data and results from a modified Weissenberg rheogoniometer is shown for the viscosities as well as the compliances. Relations are presented which allow to take into account the non negligible influence of the surface tension of the sample on the measurements. From the reverse shear rate of the unloaded sample after total recoil the magnitude of the surface tension can be determined.

Rheology of the lecithin-water system in its lamellar phase

Abstract: Though there exists already some knowledge about the rheological properties of the water-lecithin system in its lamellar phase we have resumed a more comprehensive study in this field. For this purpose, dispersions of hen-egg lecithin with a water content ranging from 5 to 42.5% were examined by means of a Weissenberg Rheogoniometer. Each sample was previously sheared at a low shear rate (0.229 s−1) to produce a steady state. The stresses arising from various mechanical deformations always applied according to the same protocol have been analysed. The deformations were induced by steady rates of shear or by a steady rate of shear partly modulated at various frequencies or by pure oscillatory rates of shear. These are the main results: (i) When subjected to steady rates of shear, the dispersions show a plastic flow behaviour with a stress varying only a little as the rate of shear decreases to zero. (ii) When a steady rate of shear is brought abruptly to zero a part of the stress relaxes immediately and the other part much more slowly. (iii) When submitted to a modulated rate of shear these dispersions show the behaviour of a quasi-Newtonian liquid. (iv) When submitted to pure oscillatory rates of shear they give rise to stresses in a non-linear relationship with deformations. — In this last case, the variation of the stresses may be divided into a steep and a smooth one. The former is related to a solid-like behaviour whereas the latter is related to that of a non-Newtonian liquid. However when the amplitude of the oscillatory shear rate is very small these dispersions have only a solid-like behaviour. To get a deeper insight of the rheological behaviour of these dispersions, we have studied the effect of the surface roughness of the platens and the effect of the sample thickness. The stresses are the higher, the rougher the surfaces and the thinner the samples. These results have led us to propose a model for the sample under shear composed of a liquid sheet lying at each plate and a viscoelastic body with a high viscosity between them. In addition we have shown that the rheological properties of the lecithin water system may vary quantitatively in an abrupt manner for small variations in the water content of the system.

Note: Mechanical Characterization of an Adhesive Layer in situ under Combined Load

Abstract: The mechanical behavior of an adhesive layer was characterized by a specially designed torsion-tension device which yields the shear moment displacement relationship at different levels of axial load. The derived failure envelope shows an increase in shear strength with increasing axial compression, and the opposite under tension. Small changes of the shear modulus were also observed.

Natural Frequency of Timoshenko Beam on Flexible Base

Abstract: The influence of base rotational and horizontal springs has been investigated for Euler and Timoshenko beams. The results were presented in terms of convenient dimensionless parameters so that the influence can be easily evaluated. The parameters were varied to cover the behavior of beams ranging from pure bending to pure shear. An example, demonstrating the use of the results to a multistory shear building, is included.

Ice adhesion tests on coatings subjected to rain erosion

Abstract: : Screening tests to select ice phobic coatings displaying low ice release forces, both before and after exposure to rain erosion in a whirling arm simulator, were performed on approximately 60 commercial materials. A unique linear ball-slide shear test apparatus was designed to provide pure shear forces. No coating survived the erosion test to give an interfacial shear strength as low as 15 psi (103 kPa), an arbitrarily established goal. Several coatings showed shear strengths between 30 and 45 psi (207 and 310 kPa) after rain erosion.

Dispersion in Laminar Flows

Abstract: The dispersion of clusters of small spherical particles (20–400 m) suspended in a liquid has been studied by subjecting them to linear two-dimensional flow fields which include pure shear as one limit pure rotation as the other with simple shear as an intermediate case. If the liquid used to form the suspension is the same as the bulk medium, dispersion proceeds in a well-defined fashion depending upon: the amount of vorticity in and the strength of the undisturbed flow, the initial radius of the cluster, the radius and volume fraction of particles. It was Found that a model based upon the assumption that the rate at which the particles leave the surface of the cluster is proportional to its surface area adequately describes the dispersion process.

Shear strength of some semisintered oxides at high pressure

Abstract: The shear strength of semisintered MgO, ZrO2, Al2O3, and Fe2O3 has been measured up to 30 kbar using an opposed anvil shear device. The shear strength of each oxide increases quite linearly with increasing pressure.

Visco-elasticity under large, uniform deformations of rubber-like polymers in the transition range

Abstract: The relaxation moduli of crosslinked polymers as a function of the main elongation ratios have been calculated on the basis of a non-Gaussian sub-chains model. The effect of a mobility reduction of the sub-chains as a result of elongation has been examined on freely jointed chain models and those having a weak correlation in orientationally adjacent chain units. The movements are thought to be instant rotations by 180° of an adjacent chain unit pair. The effect of a chain rigidity increase in the case of the freely jointed chain model in fully compensated by a reduction in movement as regards the relaxation time, while the existence of a correlation reduces the latter. A reduction of the sub-chain movements due to elongation makes stronger the dependence of the relaxation functions only on the elongation ratio. The simple elongations, uniform expansion, pure shear at constant rate of natural deformations, and also pure shear at constant rate, were examined for constant relaxation times. The finite extensibility of the chains results in a typical increase of the viscous stress in the network and the appearance of normal viscous stresses in simple shear.

Testing for evaluation of stress-strain behavior of clays

Abstract: A technique to predict the stress-strain behavior of clays along various stress paths is presented. The experimental results of stress-controlled triaxial pure shear and consolidation tests conducted on normally consolidated and lightly overconsolidated samples are given, and a method to evaluate the parameters required for prediction by the proposed technique is discussed. Comparison between experimental and predicted stress-strain behavior of normally consolidated and lightly overconsolidated samples along stress paths shows that the technique predicts the behavior quite well. (Author)

Test methods for in-plane shear modulus g12 and transverse shear moduli g13 and g23

Abstract: This paper mainly presents two experimental methods to determine the shear moduli of laminated composites which may be regarded as orthotropic. 1 A new method to determine the in-plane shear modulus, G12, of a laminated specimen, called the “pure bending shear test of 45° off-axis laminates ”is reported. Result of this test is in agreement with the modulus, determined by tensile shear test of 45° off-axis laminates widely used in material testing laboratories. 2 Because of the very low values of the transverse shear moduli, G13 and G23 of laminated composite plates, their contribution to ttan-sverse deflections can not be neglected under many circumstances. A “simplified five-point loading test ”method is developed to determine in the same test not only the transverse shear modulus G13 (or G23), but also the value of fexural rigidity, E11I (or E22I). Results of this paper show that the magnitude of transverse shear moduli G13and G23 may be one order of magnitude lower than G12 and two orders lower than Young's modulus E.

The Shear Strain to Fracture Characteristics of a Titanium Alloy and an Ultrahigh Molecular Weight Polyethylene Under Complex Loading Conditions

Abstract: Thin-walled tubular specimens of titanium alloy and an ultrahigh molecular weight polyethylene are twisted at various strain rates up to approximately 100/s with the simultaneous application of an axial tensile load or compressive load. The strain to fracture of the titanium alloy, that is, the point of instability, is calculated and shown to decrease with an increase in the strain rate. It is also shown to decrease with increasing tensile load and increase with increasing compressive load at all the strain rates. The polyethylene also shows a decrease in strain to fracture with an increase in the strain rate but appears to be independent of axial load.