Shear Breakage Research Articles

Progressive damage and nonlinear analysis of 3D four-directional braided composites under unidirectional tension

A representative volume cell (RVC) is chosen to analyze the progressive damage behavior of 3D four-directional braided composites with large braid angle subjected to uniaxial tension. An anisotropic damage model is established by Murakami-Ohno damage theory. A new damage evolvement model is proposed, which is controlled by material fracture energy of braided composites constituents and equivalence displacements. According to the different damage modes (yarn transverse tension, compression and shear; yarn longitudinal tension and compression; matrix cracking), the different damage states and progressive damage of the braided composite are obtained. The numerical results show that the main failure modes of the braided composites are transverse tension, shear breakage of yarns and matrix cracking, which are in good agreement with the relevant experimental results in some literatures.

A new analytical model for high-velocity impact of thick composites

A new analytical impact/penetration model has been developed for high-velocity impact of thick composite targets using a spring-mass equivalent energy dissipating finite element/finite difference scheme. The initial basic model includes energy dissipating mechanisms such as punching shear and fiber breakage. The impact/penetration law, which is based on a linear distribution of punching shear force, is represented by a stiffness parameter. The equivalent variable mass of the composite target is built into the model by considering two-dimensional shear wave propagation, and its effective stiffness was initially represented by a nonlinear spring stiffness that is obtained from analyzing an infinite hollow cylinder subjected to internal in-plane shear. The two stiffness parameters are characterized by analyzing the forces between the impactor and the composite target at increasing depths of penetration through a series of quasi-static finite element analyses. Results are used to provide a more accurate prediction if the impactor would perforate or stop, and to obtain an estimate of its exit velocity or the depth of penetration for both blunt-ended and sharp-ended impactors penetrating a thick composite target at high speed. Analyses were performed to demonstrate different high-velocity impact scenarios.

THREE-DIMENSIONAL PROGRESSIVE DAMAGE OF LAMINATED COMPOSITES WITH A HOLE UNDER COMPRESSIVE LOADING

The damage initiation and development of laminated composites can be simulated by progressive damage analysis. A 3D progressive damage model and finite element method are used to analyze the damage process of laminated composites with a hole under compressive load. The matrix-cracking, fiber-matrix shear, delamination, and fiber breakage are all con- sidereal. Based on the software of ANSYS, a parametric modeling program is developed to predict the progressive damage process and ultimate strength of laminated composites with any layer direction angle and layer thickness. The validity of the analysis method and program is proved by the comparison between the predicted result and experimental data available in the literature. The predicted precision of ultimate strength may be improved by the program, which provides technical support for the design and use of laminated composites.

Impact and attrition shear breakage of enzyme granules and placebo particles-application to particle design and formulation

The strength and breakage mechanisms of detergent enzyme granules and typical core materials used for enzyme granules (all of size 500–600 μm) have been investigated under impact and shear stress conditions to simulate the stresses experienced in a detergent factory. In an Impact Tester, single-particle experiments were performed at impact velocities of 8–25 m/s. Multiple (bulk) particle experiments were performed in an Attrition Shear Cell (ASC), where the particles were exposed to shear strains of about 1250 and normal stresses of 1–30 kPa. For coated enzyme granules the results indicate that the primary breakage mechanism after repeated impacts at 10 m/s is chipping associated with local delamination. Damages to the coating layer may expose the underlying enzyme-containing layer or core and lead to the release of enzyme-active dust. Markedly lower enzyme dust release was obtained by incorporating the enzyme into the core of the granule as compared to a layer-structured enzyme distribution. Furthermore, the results indicated that stronger enzyme granule core materials provide a better impact resistance of the final enzyme granule towards the release of enzyme-active dust. Coating layers of inorganic salts and water-soluble polymers are observed to enhance the breakage resistance of the enzyme granules tremendously. The impact and shear resistance of four different placebo enzyme granule core particles were investigated. A transition from chipping to fragmentation as the main breakage mechanism was observed at impact velocities from 8 to 20 m/s. Experiments performed with attrition shearing indicated that the extent of breakage depend on surface friction and particle sphericity as well as intraparticular forces. The results obtained in this work are of importance for the design and formulation of mechanically resistant enzyme granules.

Automated fluid mixing in glass capillaries

A fast method and compact device for mixing sub-microliter fluid samples contained in glass capillaries is presented. The fluid is rapidly moved back and forth by air volume displacement driven by a piezo-ceramic actuator. Rapid mixing of different fluids is achieved via diffusion between the main fluid volume in the capillary and the thin fluid film it deposits on the capillary wall through its motion. Bubbles in the fluid are processed out of the capillary by use of an asymmetric velocity profile. A simple analysis model is used to optimize the design of the device and to elucidate the mechanisms involved in mixing. The mixing time is found to be inversely proportional to the fraction of the fluid volume that is left in the film layer for each cycle, which is determined by the wetting properties and the viscosity. The mixing time is therefore controlled by the dead-air volume of the system, the fluid volume, the capillary size, and the displacement limits of the piezo-ceramic actuator, in addition to the intrinsic properties of the fluid being mixed. The device described can mix two 1 μl water solutions in under 3 s. The possible shear breakage of DNA in solution is investigated, and λ-DNA is found to remain intact at aggressive mixing parameters. No evidence of aerosol contamination in polymerase chain reaction reactions was found to date.

Influence of shear breakage of microbial cells on cross-flow microfiltration flux

In the cross-flow filtration of fermentation broth, cross-flow pumping applies shear stress onto bacterial cells. The resulting shear field leads to breakage of bacterial cells. In this study, the influence of cell breakage due to shear stress on filtration flux was examined. Shear stress broke baker's yeast cells and induced discharge of granulated matter such as glycogen and cell wall fragments. These smaller particles contributed to the increase of the mean specific filtration resistance. In the cross-flow filtration, cell breakage due to shear stress reduced the filtration flux because of the increase of the hydraulic resistance of the particle-packed layer, R c, which was formed on the membrane during filtration. This flux reduction was explained by considering the lift velocities, which back-transported the particles from the membrane surface. The lift velocity was expressed as follows: V L = K· u 1.0· C p −0.5· d p 0.67· η −1.0, where V L, K, u, C p, d p and η are the lift velocity, filtration constant, feed velocity, particle concentration, particle size and viscosity, respectively. In the mixture of differently sized particles such as a shear-broken cell suspension, the steady-state flux was given as a value equivalent to the smallest V L, which was derived from the calculation of the V L values for each particle representing particles grouped according to size, using the above equation.

Shear breakage of nylon membrane microcapsules in a turbine reactor

The breakage of nylon membrane microcapsules is proposed as a new method to study and quantify shear effects in biological systems. A critique of this method shows that a narrower particle size distribution may be an important improvement in the breakage study as well as breakage control in many bioreactor and biotechnological applications. In a turbine reactor, it was shown that the primary process which determines the microcapsule breakage is the shear effect. The breakage kinetics are first order with regard to the microcapsule concentration. The breakage kinetic constant was ob served to be dependent on the temperature and the particle size, and proportional to the average shear rate and the third power of the turbine angular velocity. Decrease of the breakage kinetic constant with temperature can be explained by a decrease of fluid viscosity and a change in nylon membrane properties. An increase in the breakage kinetic constant with the microcapsule diameter can be due to a lowering of internal pressure and a reduction of the membrane resistance with size. Proportionality between the breakage kinetic constant and the shear rate shows that shear is the main process which leads to microcapsule breakage. The additional intervention in the shear rate expression of the turbine angular speed in the form of the turbine and particle velocities, results in the dependence of the breakage kinetic constant on the third power of the angular velocity.

Shear breakage of DNA

Determinations were made of the mean length of fragments produced after shearing long (greater than 100 kb) native Hela DNA in a VirTis homogenizer. (VirTis Co., Inc., Gardiner, N.Y.). The mean length (L) is a function of the speed of rotation of the homogenizer blades (omega), time of shearing (t), water concentration ([H2O]), solvent viscosity (eta), temperature (T), and energy of activation (E*), but not a function of the initial length so long as the starting molecules sustain an average of three or more breaks. The relationship of the parameters is expressed by the equation L = (b/omegat1/2eta1/2[H2O])eE*/2kBT, where kB is the Boltzmann constant and b is a constant of proportionality. The breakage rate constant k was determined to have the relationship k = (omega2L2eta[H2O]2/2b2)e-E*/kBT. These equations are valid throughout large ranges of the parameters, and a simple method is described which chooses a final mean length between at least 0.15 and 36 kb by choosing the appropriate shearing conditions and initial fragment length. The heterogeneity of shearing conditions within the shearing vessel permits use of the equations at all breakage rates tested. Based on the work of others using more homogeneous shearing conditions and initial fragment lengths, more complicated forms of the equations are necessary at low breakage rates but not at high ones. A proposed model of the breakage mechanism suggests that molecules with stress-induced localized denaturations break at a rate different from that for native DNA.

Sedimentation properties of the bacterial chromosome as an isolated nucleoid and as an unfolded DNA fiber: Chromosonal DNA folding measured by rotor speed effects

The sedimentation coefficient of the isolated bacterial nucleoid of Escherichia coli depends on the strength of centrifugal field. Isolated membrane-free and membrane-associated nucleoids increased their sedimentation coefficients in lowered centrifugal fields, while in higher fields their sedimentation coefficients decreased (rotor speed effect). These changes were reversible. Although analogous rotor speed effects have been observed for large, extended DNA molecules, this effect was unexpected for the isolated nucleoids, heretofore considered to be particle-like. The results suggest that during sedimentation the condensed DNA of the chromosome can be reversibly extended into less compact conformations. It is proposed that the rotor speed effect provides a method for studying the restraints on condensed DNA in chromosomes. Procedures were developed for minimizing shear breakage of the unfolded nucleoid DNA. When these methods were applied it was found that the magnitude of the “relative rotor speed effect” depended on how extensively the DNA was unfolded. Changes in relative rotor speed effect were only observed when the DNA was unfolded, while changes were not observed when DNA supercoiling was relaxed. As increasing amounts of nucleoid RNA were hydrolyzed with RNA-ase, the DNA was progressively unfolded and the relative rotor speed effect was enhanced. When all RNA was removed by limit digests, a maximal dependence on rotor speed was observed which was similar to the relative rotor speed dependency theoretically predicted for an intact linear genome equivalent of E. coli DNA ( Zimm, 1974 ). When the nucleoid DNA was deproteinized there was no significant enhancement of the rotor speed effect relative to that observed with the RNA-free DNA. The s0 of the unfolded, deproteinized partially replicated DNA was 320S, compared to the 450S for the RNA-free nucleoid DNA. These and other results suggest that all or nearly all DNA folds in the membranefree nucleoid isolated by the methods used here are stabilized by RNA-DNA interactions.

The size of fibroin messenger RNA and its polyadenylic acid content

The molecular weight of fibroin messenger RNA has been measured by its contour length in the electron microscope and its electrophoretic mobility under conditions of complete denaturation. These methods give values of 5.6 × 10 6 and 6.0 × 10 6 daltons, respectively. The average molecular weight of 5.8 × 10 6 (1.6 × 10 4 base residues) would be expected to code for a protein of 414,000 daltons, a value about 12% larger than the most recently published size for fibroin. When the mRNA is prepared carefully to avoid shear breakage, it is as homogeneous in size as ribosomal RNA. Between 43% and 81% of the mRNA molecules bind to oligo(dT)-cellulose and are presumed to contain a poly(A) sequence. This sequence, isolated after ribonuclease digestion, comprises about 0.6% of the molecule, or an estimated 100 nucleotides. The poly(A) has been localized at the end of the molecule by hybridizing with a small poly (dT:dA) piece and subsequent visualization by electron microscopy. This observation, along with the ability of reverse transcriptase to transcribe fibroin mRNA with an oligo(dT) primer, demonstrates that the poly(A) is at the 3′ end of the mRNA.

Hydrodynamic shear breakage of DNA

AbstractThe rate of breakage of duplex DNA molecules by laminar flow through a capillary has been studied. For λb2b5c DNA (molecular wt., M = 25 × 106) the point at which breakage occurs is normally distributed around the center of the molecule with a standard deviation of 12.5% of the molecular length. At constant shear stress or shear rate, the breakage rate is independent of ionic strength. Thus, shear induced local denaturation is not a rate limiting, preliminary step in breakage. In experiments at constant temperature with varying solvent viscosity (controlled by added sucrose) the breakage rate is a function of shear rate, not of shear stress. The rate of opening of hydrogenbonded circles into linear molecules by hydrodynamic shear is also shown to be a function of shear rate and not of shear stress. The breakage rate at constant shear rate is not greatly dependent on temperature. The shear rate required to achieve breakage is inversely proportional to M1,2. The breakage rate constant, k varies as a very high power of the shear rate; at 25°C, d In k/d In Gm ∼ 15; at 10°C, d In k/d In Gm ∼ 26, where Gm is the maximum shear rate at the capillary wall. The unexpected result that breakage rate is mainly dependent on shear rate, not shear stress, supports a model in which the DNA molecule is distorted with a driving force which depends on the hydrodynamic shear stress, ηG, but the rate limiting step is segment diffusion into a highly extended configuration. The characteristic time to achieve this configuration is proportional to solvent viscosity, η, hence the breakage rate is dependent on ηG/η or G, the shear rate.

Hydrodynamic shear breakage of DNA may produce single-chained terminals

High molecular weight DNA in solution is very shear labile when passed through narrow capillaries. We previously showed that under certain conditions of hydrodynamic shear, single-chained terminals are produced on the DNA fragments. By the use of chromatography on benzoylated-naphthoylated DEAE-cellulose, a single-chain specific exonuclease, and velocity sedimentation we have investigated the physical characteristics of these shear-broken fragments. As the salt concentration is lowered or the temperature of shearing is raised, the number of shear-broken fragments containing single-chained regions is increased. Essentially all single-chained regions are removed by a single-chain specific exonuclease, indicating that these regions are located at the fragment terminals. A variety of conditions of salt and temperature do not affect the limit fragment size produced by a given diameter capillary. For certain applications, the presence of single-chained terminals on DNA fragments in the 2 · 10 6–30 · 10 6 molecular weight range may be desired. The methods detailed in this communication provide means of shearing DNA to produce, or to avoid single-chained terminals.

Shear fragility of human erythrocytes.

Shear breakage of human blood cells in saline solution has been studied under conditions of uniform shear, non-penetrating thickeners having been added merely to facilitate application of a sufficiently high stress using a conventional cone

Denaturation pattern of the DNA of adenovirus type 2 as determined by electron microscopy

The DNA of human adenovirus type 2 has been found in electron microscope studies of DNA-protein monolayers to be a linear molecule which is 10.9 μ long. When partially denatured by heating at low salt concentrations and in the presence of formaldehyde to various temperatures in the range between 52 and 58 °C, denaturation sites can be recognized in the electron microscope, and a map of these regions can be constructed. These sites presumably correspond to segments in the DNA molecule which are rich in adenine thymine base pairs. In the range of 10 to 25% denaturation (55 to 57 °C), a unique melting pattern is found in adenovirus type 2 DNA with three major and one minor denaturation sites. On a unit length scale of the molecule, these sites are located between 0 and 0.15, 0.5 and 0.6, and 0.8 and 1.0; and at 0.4. These findings argue strongly against the possibility that the gene sequence in adenovirus type 2 DNA is circularly permuted. Fragments of adenovirus type 2 DNA generated by shear breakage of the molecule can be separated in Hg(II)-Cs 2SO 4 density gradients. This finding supports the interpretation that adenine-thymine-rich clusters are distributed unequally in adenovirus type 2 DNA.

Breakage by hydrodynamic shear of the bonds between cohered ends of λ‐DNA molecules

AbstractThe rate of breakage by hydrodynamic shear of the cohered ends of λ‐DNA molecules has been observed for the circular monomers, joined half molecules, and joined quarter molecules, in a capillary apparatus with known flow parameters. The rate constant for breakage has been measured as a function of shear stress, temperature, ionic strength, and molecular length. There is a large temperature coefficient, with an activation energy of 120 ± 20 kcal./mole. The values of d ln k/dG, where k is the rate constant for breaking and G is shear gradient, in aqueous solution at 25°C. are about 3.8 ± 0.3 × 10−4 see. The shear stresses needed for breakage of joined quarter molecules and of circular monomers, respectively, are about equal, and about half that needed for breakage of joined half molecules. The rate of breakage at a given shear stress increases with decreasing ionic strength, approximately as [Na+]−1.6. Self‐protection effects are not observed for opening of circular monomers at a DNA concentration of 5 μg./ml. but are observed for breakage of joined half molecules at concentrations down to 0.5 μg./ml. The large temperature coefficient which is approximately equal to that of the thermal dissociation of the cohered ends is interpreted to mean that shear breakage is a mechanically assisted thermal reaction in which the thermal fluctuations provide most of the free energy of activation for breakage. A detailed model for this interpretation is presented. The self‐protection effect implies that those molecules which break are not average molecules but exceptional ones which, due to some fluctuation, are more fully extended in the flow field.

A thermal valve for ultracentrifuge cells

1. A method is described for the transfer, at any time, of a predetermined part of a column of liquid from one compartment to another in an ultracentrifuge cell rotating at constant angular velocity. Small connecting channels between the compartments are blocked with solid n-hexadecane. Melting of these blocks by raising the rotor temperature initiates the transfer of the liquid. 2. A centerpiece in which high-molecular-weight deoxyribonucleic acid may be transferred without shear breakage is described. 3. In the first application of these partition cells a band of high-molecular-weight deoxyribonucleic acid at buoyant equilibrium was divided into two parts with different molecular-weight distributions. 4. More than one thermal valve can be incorporated into one ultracentrifuge centerpiece, and the valves may be opened separately.

The expanding-bolt seam-tester: A theory of tensile breakage

The development of the expanding-bolt seam-tester, and laboratory and field results relating to it, have been described by P. Foote, who interprets the results in terms of shear failure in the coal. A consideration of the forces likely to be acting at the interface between tool and coal suggests that shear breakage, if it took place, would do so at markedly different angles from those observed in practice. A tensile theory of breakage is postulated. It is worked out in terms of a two-dimensional analogue of the actual problem. The treatment is successful in that it predicts accurately the mean characteristic angles of the cones of coal that are pulled out with the bolt. A method of adapting the solution empirically to the practical case is suggested, and is shown to give good agreement with experimental results.

The production of phage chromosome fragments and their capacity for genetic transfer

Molecules of DNA isolated from bacteriophage λ break in half, but no further, when subjected to the appropriate amount of hydrodynamic shear. The half-molecules can be separated from whole molecules by zone sedimentation in a sucrose gradient. The phage particles produced by bacteria exposed to λ DNA and active “helper” phage reveal the genes carried into the bacterium by the DNA. Whole molecules of λ DNA appear to be the entire phage chromosome since they carry genes from all parts of the recombination map: m6, m5, h, s, i and mi. One of the two half-molecules produced by shear breakage of λ DNA is capable of transferring s, i and mi, but not m6, m5 or h. Since this incomplete complement is a continuous segment of the linkage map of λ, it is argued that the sequence of genes on the recombination map is the same as the sequence of the nucleotides or blocks of nucleotides which correspond to each of the genes in a molecule of λ DNA.