Showing papers on "Tearing published in 2000"

Two-phase modeling of mushy zone parameters associated with hot tearing

Abstract: A two-phase continuum model for an isotropic mushy zone is presented. The model is based upon the general volume-averaged conservation equations, and quantities associated with hot tearing are included, i.e., after-feeding of the liquid melt due to solidification shrinkage is taken into account as well as thermally induced deformation of the solid phase. The model is implemented numerically for a one-dimensional model problem with some similarities to the aluminium direct chill (DC) casting process. The variation of some key parameters that are known to influence the hot-tearing tendency is then studied. The results indicate that both liquid pressure drop due to feeding difficulties and tensile stress caused by thermal contraction of the solid phase are necessary for the formation of hot tears. Based upon results from the one-dimensional model, it is furthermore concluded that none of the hot-tearing criteria suggested in the literature are able to predict the variation in hot-tearing susceptibility resulting from a variation in all of the following parameters: solidification interval, cooling contraction of the solid phase, casting speed, and liquid fraction at coherency.

Nonlinear evolution of double tearing modes

Abstract: The linear and nonlinear behaviors of the tearing mode is systematically studied for nonmonotonic q-profiles on the basis of the reduced magnetohydrodynamics (MHD) equations in cylindrical geometry, and some new features about the double tearing mode are revealed. The linear eigenmode scales as a resistive internal mode for a small distance between two rational surfaces with the same q-value, Δrs, and as the tearing one for large Δrs. New nonlinear phenomena appear in the tearing mode regime and for shorter Δrs. The linear eigenfunction shows sharply localized fluid motion at both resonant surfaces and small but global convective motion between the resonant surfaces; consequently the mode goes through a Rutherford-type regime. When the islands have grown enough, the mode shows explosive growth. This results from the nonlinear coupling among the higher harmonics, so that the inner and outer magnetic islands interact with each other leading to an internal disruption.

Cloth-like polymeric films

Abstract: A polymeric film having a plurality of perforations is described. The polymeric film provides a strong, high-tensile strength material that permits hand tearing of the film along one or two axes. In specific implementations, the polymeric film is incorporated into a multi-layer film having cloth-like properties of strength and tear propagation, and is suitable for use various adhesive tape applications. Methods of making the polymeric film are also disclosed.

Nonlinear evolution of double tearing modes in tokamaks

Abstract: The Δ′ formalism with neoclassical modifications has proven to be a useful tool in the study of tearing modes in high β, collisionless plasmas In this paper the formalism developed for the inclusion of neoclassical effects on tearing modes in monotonic q-profile plasmas is extended to plasmas with hollow current profiles and double rational surfaces First, the classical formalism of tearing modes in the Rutherford regime in low beta plasmas is extended to q profiles with two rational surfaces and it is shown that this formalism is readily extended to include neoclassical effects The evolution of a double tearing mode on the Tokamak Fusion Test Reactor is then simulated Reasonable agreement is found for the outer island, but the stabilizing effect of the neoclassical term is overly large for the inner island

Fracture energies and tensile strength of an EPDM/PP thermoplastic elastomer

Abstract: Measurements of the tear strength of EPDM/PP thermoplastic elastomers (EPDM/PP TPEs, Santoprene 201-87) were carried out at various rates and temperatures. In addition, a cutting technique developed recently was adopted to measure the fracture energy in a process where a well-controlled geometry of the crack tip was obtained. Results show that the EPDM/PP TPEs possess a relatively high tear strength of 10.40 ± 0.94 kJ/m2 at room temperature. Furthermore, good tear strength is still preserved, about 1.87 ± 0.38 kJ/m2, at 150°C, where some PP crystals are melted and start to flow. In contrast, the intrinsic strength of EPDM/PP TPEs determined from a cutting test is varied slightly, 700–1000 J/m2, over a wide range of temperatures and rates. A comparison of the fracture energy measured by tearing and cutting tests is provided and discussed. The energy density per unit volume of EPDM/PP TPEs determined from the cutting test is 9.7 GJ/m3, which is about twice larger than that for the rupture of CC bonds at room temperature. It is suggested that plastic yielding is a more effective process to enhance the toughness than is simply viscoelastic motion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1033–1044, 2000

3D reconnection due to oblique modes: a simulation of Harris current sheets

Abstract: . Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

Tamper evident resealable extended text label

Abstract: A label includes a bottom panel and a top panel overlying the bottom panel. A tear line is formed in the top panel. A hole is formed in at least one of the top and bottom panels. An exposed adhesive is disposed in the hole. The label may be opened by tearing along the tear line and the label may be resealed using the exposed adhesive.

A Novel Approach to Assessing the Hot Tearing Susceptibility of Aluminium Alloys

Abstract: Previous work has shown that hot tearing is the result of differential contraction between the solid and liquid phases during the solidification of the ingot. Most of these studies have been on hot tearing problems in the bulk metal. However, it remains to be demonstrated how the shell region affects the occurrence of hot tearing during solidification of a DC ingot. This work examines that particular area of a DC cast ingot and it addresses aspects of the surface stresses and strains, and the unique microstructural features of the shell region.

Effect of Hydrostatic Testing on Ductile Tearing of X-65 Line Pipe Steel with Stress Corrosion Cracks

Abstract: Hydrostatic testing is one method to confirm the integrity of pipelines containing colonies of stress corrosion cracks. Although this technique is widely used, a concern of the pipeline industry is the potential for ductile tearing damage of subcritical flaws. Objectives of the current study were to evaluate the influence of hydrostatic testing on the crack tip morphology and to determine the amount of ductile tearing that may occur for different hydrostatic testing conditions. Stress corrosion cracks were grown in compact tension specimens of X-65 line pipe steel in a near-neutral-pH stress corrosion cracking (SCC) environment. Simulated hydrostatic tests were performed at loads that corresponded to hoop stresses at and above the specified minimum yield strength (SMYS), resulting in applied J-integral values near to and above the J(Q) fracture toughness value of the material. Some specimens ruptured; some did not fail. Crack tip blunting occurred and the tearing extent was small and proportional...

Kinetic simulations of the coupling between current instabilities and reconnection in thin current sheets

Abstract: . We investigate the coupling between current and tearing instability modes of a thin current sheet using the particle code GISMO. We identify pure tearing modes (kx≠ 0), instabilities in the current flow direction (ky≠ 0) and general 3D reconnection modes (kx≠ 0 and ky≠ 0). Our results give evidence that the coupling between tearing modes and current instabilities plays an important role for spontaneous magnetic reconnection. These modes give a substantial contribution to magnetic reconnection, additional to the well known 2D tearing mode. When allowing reconnection to occur in three spatial dimensions, a configuration, which was initially invariant in the current How direction, develops into a configuration with no invariant direction.

Pressure die-casting process of magnesium alloys

Abstract: A method for die-casting a magnesium alloy comprises the step of casting a die cast product free of any hot tearing, shrinkage tearing and shrinkage cavity starting from a magnesium alloy comprising i) 1 to 10% by weight of aluminum; ii) at least one member selected from the group consisting of 0.2 to 5% by weight of a rare earth metal, 0.02 to 5% by weight of calcium and 0.2 to 10% by weight of silicon; and iii) not more than 1.5% by weight of manganese, and the balance of magnesium and inevitable impurities, using a cold chamber type die-casting machine, wherein a) the temperature of the molten magnesium alloy is maintained at 650 to 750°C; b) the charging velocity of the molten metal is set at 1/100 to 10/100 second; and c) the intensified pressure after the charging is set at a level of not less than 200 kgf/cm2. Thus, a die cast product free of any hot tearing, shrinkage tearing and shrinkage cavity can be produced by appropriately specifying injection conditions, mold conditions, conditions for melting a magnesium alloy and mold plan in the cold chamber type die-casting machine, or by appropriately controlling the temperature of the molten metal from the molten metal-accommodating pot to the gate portion of the machine.

The rheological properties and hot tearing behaviour of an Al-Cu alloy

Abstract: An experimental device was constructed for the present research. The strain of Al-4.5Cu alloy during loading and unloading was measured in the solidification temperature range. Based on these experiments and analyses, a five-component elastic-visco-plastic rheological model of the alloy is proposed, the creep equation is obtained, and the rheological property parameter is defined. Based on this investigation, the shrinkage stress of a casting can be measured, which enables the determination of critical values of strain for the formation of hot tearing.

Controlled directional tear laminates

Abstract: The present invention relates to multilayer laminates having controlled directional tearing in both the machine direction (MD) and the transverse direction (TD). It is desirable to have controlled tearing for use in connection with pouches or other packages having a reclose device. The laminate is made up of a biaxially oriented inner layer containing linear low density polyethylene (LLDPE) and having a tensile elongation to break of less than 200% in the MD and less than 150% in the TD, an outer layer having a heat distortion temperature of at least 10° C. higher than the inner layer and a tensile longation to break of less than 200% in the MD and less than 150% in the TD, and an adhesive layer containing an adhesive polymer sandwiched between the inner and outer layers and adhering the two layers to each other.

Simulating 2D tearing phenomena for interactive medical surgery simulators

Abstract: This paper introduces a methodology to simulate a particular kind of the fracture phenomenon : the tearing one. The objective of the method is to provide realistic tearing simulations, occuring on 2D deformable objects, and working in real-time. This method can find applications in surgery simulators, where tearing human tissue is an important feature to provide. It can also be applied, in a more general scope, in virtual environment applications. The central idea in this scheme is to "separate" the physical simulation elements, instead of destroying or dividing them. This avoids the increase of physical elements that need to be simulated (which occurs when they are divided) and gives a more accurate simulation than when they are destroyed.

Stiffness Identification and Tearing Analysis for Coated Membranes under Biaxial Loads

Abstract: In the first part of this paper, we have developed a mixed numerical and experimental method for the evaluation of the in-plane stiffness matrix of coated fabrics used in tensile architecture and submitted to biaxial loading. The evaluation of the stress distribution on cross-shaped samples is conducted with a finite element analysis soft ware.In the second part, we have observed and analysed failure mechanisms of previously ripped samples, particularly by the evaluation of the influence of the crack length and direction on its propagation with uniaxial and biaxial tests.

Hot tearing in 319 alloy

Abstract: To study the effect of strontium on hot tearing in 319 alloy, a special cast iron mould was made to produce a casting with “built-in” restraints that act to create tensile stresses along the length...

Some Insights Into The Mechanism Of TheDeformation And Tearing Of Thin Plates At HighStrain Rates Incorporating TemperatureDependent Material Properties

Abstract: The response of structural components subjected to blast loads result in deformation strain rates in the range of 10^ s"^ to 10* s"\ Hitherto the effects of temperature dependent material properties for such situations have been excluded in both the experimental and numerical predictions. This phenomenon is extremely difficult to measure for the experimental tests and has only recently been included in the analysis. This paper describes a series of tests in which circular steel plates are subjected to a central localised blast load. The numerical predictions indicate that failure occurs as a result of a thermo-mechanical instability and localised shear banding. Hitherto, the failure criterion for the tearing mechanism has been considered to be one of either a stress based criterion, a strain based criterion, or an energy based criterion. These localised shear bands provide new insights into the subsequent failure and tearing mechanism through the thickness of the plate.

Application of the two-parameter J-A2 description to ductile crack growth

Abstract: Typical ASTM fracture testing determines the J-integral resistance (J-R) curve or fracture toughness (J 1 C ) based on specimens with high-constraint geometry such as those specified in ASTM E 1737-96. A three-term asymptotic solution with two parameters, J and A 2 (a constraint parameter), has been developed for characterizing the constraint effect of various geometries. The present paper extends the J-A 2 characterization of a stationary crack tip to the regime of stable crack growth. Similar to the concept of J-controlled crack growth, the J-A 2 description can be approximately used to characterize ductile crack growth under certain amount of crack extension. The region of J-A 2 controlled crack growth is much larger than that controlled by the J-integral alone. From the relationships between A 2 and the test data, J I C , and tearing modulus, T R , the coefficients used to define a J-R curve can be determined. For non-standard specimens or actual structures, once the constraint parameter A 2 is determined, the J-R curves appropriate for these geometries can then be obtained. A procedure of transferring J-R curves determined from the standard ASTM procedure to non-standard specimens or flawed structures is outlined in the paper.

Stamping of continuous fiber thermoplastic composites

Abstract: Despite demonstrated success in low volume aerospace and defense applications, structural composites remain at the periphery of high volume industries such as construction, automotive, and consumer goods because of long cycle times. Stamping provides a means of making composite sheet products at rates ten to a hundred times faster than any existing continuous fiber processes. However, to make composites stamping a viable process, one must understand how the combination of fabric architecture, tool design, and process conditions interact to produce a part free of wrinkling and tearing. In this paper, the effect of temperature, stamping rate, and boundary constraints on the material deformation is presented. The focus of this study is a co-mingled glass/polypropylene fabric, in the form of a layer of unidirectional yarns held together by stitches. The results show that temperature variations have the greatest effect on deformation. In addition, a finite element model of parallel strips with linear constraints was shown to successfully simulate the sliding deformation or draw-in of the stitched unidirectional material.

Rapid design of corner restraining force in deep drawn rectangular parts

Abstract: With the development of finite element method and computer technology, the complete modeling of the forming of a 3D sheet metal part is becoming realistic. However, an accurate 3D simulation is usually too time-consuming to be used in the early stage of design. One solution is to model the straight side of a 3D part as a plane strain problem and the corner section as an axisymmetric problem. Unfortunately, the axisymmetric solution often over-predicts the severity of the deformation at the corner and leads to a very conservative design. In this study, a modified axisymmetric model with a center offset is proposed to predict tearing failure in the corner sections of 3D parts. The proposed offset is found to be a function of the center strains, failure height, and tooling/process parameters, including tooling geometry, material properties, friction coefficient, and restraining force provided by the binder. Finite element analyses of both 3D and 2D axisymmetric models for square and rectangular cup forming are utilized to verify the proposed concept and to define the function. Excellent predictions of the failure heights are obtained. The proposed model enables engineers to rapidly specify the right amount of the restraining force in the corner section based on the desired center strains and forming depth. A detailed design algorithm is provided.

Easily tearable film

Abstract: PROBLEM TO BE SOLVED: To provide a film excellent in low-temperature heat-sealability, heat seal strength, impact strength, tensile strength and elongation, nerve, opening nature, etc., and capable of being torn in any desired direction. SOLUTION: An easily tearable film having a tearing strength of 30 gf/(g/m2) or below as measured according to the Elemendorf tearing strength test is molded from a resin composition comprising 40-95 wt.% ethylene/α-olefin copolymer having an MFR of 0.1-50 g/10 min, a density of 0.88-0.935 g/cm3, a TREP integrated eluate amount of at least 90 % at 90 deg.C or above, and an average thickness of an amorphous region (la) of 100 Å or below and 5-60 wt.% amorphous resin.