Showing papers on "Tearing published in 1994"

CTOA and crack-tunneling measurements in thin sheet 2024-T3 aluminum alloy

Abstract: The stable tearing behavior of 2.3-mm thick sheets of 2024-T3 aluminum alloy was experimentally investigated for middle crack tension specimens having initial flaws that were: (a) flat fatigue cracks (low fatigue stress) and (b) 45-deg through-thickness slant cracks (high fatigue stress). The critical CTOA values during stable tearing were measured by two independent methods, optical microscopy and digital-image correlation. Results from the two methods agree well. The CTOA measurements and observations of the fracture surfaces have shown that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness (Δa>B), CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness (Δa>2B), crack tunneling stabilized. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only slightly higher CTOA values during initial crack growth. The amount of tunneling in the high fatigue stress tests was about the same as that in the low fatigue stress tests after the flat-to-slant transition. This study indicates that stress history has an influence on the initial portion of the stable tearing behavior. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack-tip constraint. The measured CTOA reached a constant value of 6 deg for crack growth of about the specimen thickness. This coincided with the onset of 45-deg slant crack growth and a stabilized, slightly tunneled (about 20 percent of the thickness) crack-front shape. For crack growth on the 45-deg slant, the crack front and local field variables are still highly three dimensional.

Stability of tearing modes in tokamak plasmas

Abstract: The stability properties of m≥2 tearing instabilities in tokamak plasmas are analyzed. A boundary layer theory is used to find asymptotic solutions to the ideal external kink equation, which are used to obtain a simple analytic expression for the tearing instability parameter Δ’. This calculation generalizes previous work on this topic by considering more general toroidal equilibria (however, toroidal coupling effects are ignored.) Constructions of Δ’ are obtained for plasmas with finite beta and for islands that have nonzero width. A simple heuristic estimate is given for the value of the saturated island width when the instability criterion is violated. A connection is made between the calculation of the asymptotic matching parameter in the finite beta and island width case to the nonlinear analog of the Glasser effect [Phys. Fluids 18, 875 (1975)].

Mechanistic Role of Yarn and Fabric Structure in Determining Tear Resistance of Woven Cloth: Part II: Modeling Tongue Tear

Abstract: This paper is concerned with formulating and evaluating a model of tongue tear. The modeling approach taken is fairly general, and results recorded to this point have been encouraging. Although predicting tearing behavior from parameters determined prior to weaving is not yet possible, the implications of this work are important. The model accounts for the effects of yam pull-out, jamming, and stretching, as well as statistical variation in yam strength. Simulations are conducted where these effects are parametrically varied in order to assess their relative importance in contributing to tear strength. The effect of pre-loading on yam pull-out and the inclusion of jamming resistance are seen to have considerable influence on tearing strength. Furthermore, the success of the model's predictions based on these two principal components suggests a need for developing the mechanics of their associated, unconventional tests. With an understanding of such mechanisms, one can anticipate a fully predictive model o...

Stability of tearing modes in tokamak plasmas

Abstract: The stability properties of m≥2 tearing instabilities in tokamak plasmas are analyzed. A boundary layer theory is used to find asymptotic solutions to the ideal external kink equation, which are used to obtain a simple analytic expression for the tearing instability parameter Δ’. This calculation generalizes previous work on this topic by considering more general toroidal equilibria (however, toroidal coupling effects are ignored.) Constructions of Δ’ are obtained for plasmas with finite beta and for islands that have nonzero width. A simple heuristic estimate is given for the value of the saturated island width when the instability criterion is violated. A connection is made between the calculation of the asymptotic matching parameter in the finite beta and island width case to the nonlinear analog of the Glasser effect [Phys. Fluids 18, 875 (1975)].

Methods for Tearing Systems of Equations in Object-Oriented Modeling

Abstract: Modeling of continuous systems gives a set of differential and algebraic equations In order to utilize explicit integration routines, the highest order derivatives must be solved for In certain cases there exist algebraic loops, ie, subsets of the equations must be solved simultaneously The dependency structures of such subsets are often sparse In such cases, the solution may be found more efficiently by a technique called tearing (Kron 1963) which reduces the dimensions of subsystems This paper gives an overview of the principles of tearing Algorithms to determine how a set of equations should be torn are, in general, inefficient However, physical insight often suggests how this should be done Methods to specify tearing in the object-oriented modeling program Dymola (Elmqvist 1978, 1994) are discussed In particular it is explained, how tearing can be defined in model libraries This allows Dymola to perform tearing automatically and efficiently without user interaction Examples from electrical and mechanical modeling are given, including a tearing strategy for general multibody systems with kinematic loops which allow the equations of motion to be solved by standard explicit integration algorithms

Viscoelastic effects in cutting and tearing rubber

Abstract: Measurements of cutting resistance have been made for a crosslinked styrene—butadiene copolymer over a wide range of cutting speeds and temperatures. A characteristic fracture energy was determined using the procedure of Lake and Yeoh. A lower limit, about 150 J/m2, was obtained at low cutting speeds. This value is significantly higher than the threshold tear strength, about 30 J/m2, due to roughness of the blade tip. The tear resistance increased dramatically as the test temperature was lowered, by a factor of over 1000X, whereas the cutting resistance remained largely unchanged over a considerable temperature range. Much of the enhanced tear resistance at low temperatures is therefore attributed to increasing roughness of the tear tip, the intrinsic strength remaining approximately constant. As the tear strength followed a WLF temperature dependence closely, roughening of the tear tip is associated with viscoelastic effects. Higher cutting resistance was shown by a sulfur vulcanizate, but carbo...

On the energy principle and ion tearing in the magnetotail

Abstract: We re-examine the use of the energy principle as applied to the tearing instability in the magnetotail. We demonstrate that when a magnetic field component normal to the current sheet is present, electron pitch-angle diffusion (PAD) either by micro-turbulence or by chaotic orbits cannot remove the strong stabilization of the tearing mode caused by electron compressibility. We find that our conclusions are in agreement with those of Pellat et al. (1991), who argued on the basis of canonical P(sub y) conservation that the stabilization of the ion tearing mode cannot be removed by the introduction of PAD. Our results are at variance with those of Kuznetsova and Zelenyi (1991), who argued that the application of the energy principle used by Pellat et al. (1991) is incorrect, and that tearing is in fact unstable in the limit of strong PAD. We show that the disagreement between these two studies can be traced to an incorrect orbit evaluation first introduced by Coroniti (1980) and subnsequently used by Kuznetsova and Zelenyi (1991).

Absorbent product provided in roll form

Abstract: A supply of absorbent panty liner pads formed by a contiguous longitudinal array of pad segments forming a strip. The strip has locally weakened zones to facilitate tearing off segments from the strip without the use of a cutting tool. Each pad segment is shorter than a standard panty liner pad so that approximately three segments are required to form a standard length pad. By tearing off two, three, four, or five segments in one piece, the user can create a panty liner having a short, standard, long or extra long length to suit her needs on any given day. The strip is wrapped upon itself into a roll so that pressure sensitive positioning adhesive strips are placed into contact with release surfaces formed on the strip, thereby protecting the adhesive prior to use without the need for release paper.

Effect of local heating on the m=2 tearing mode in a tokamak

Abstract: The effect of electron temperature perturbation induced by local heating on the tearing mode activity is investigated by simulations based on the reduced set of resistive MHD equations, with the transport equation of electron temperature. The effect of poloidal plasma rotation is also considered in the simulations. It is shown that the local heating can suppress the m=2 tearing mode instability when the O point of the rotating magnetic island is effectively heated. While perpendicular thermal conduction imposes a lower limit on the degree of localization of the achievable heating, the ratio of parallel to perpendicular conduction is shown to determine the heating power necessary for complete stabilization of the tearing mode

Easily tearable film and its production

Abstract: PURPOSE:To obtain a film having practical strengths and high tearability by using a general-purpose thermoplastic resin. CONSTITUTION:At least two thermoplastic resins of different kinds of repeating units, such as a styrene polymer and an olefin polymer, are subjected to the T-die process or the inflation process without stretching to form a film. A disperse phase having an average aspect ratio of 3 or above and a thickness of 1mum or below is dispersed in the form of a layer in the continuous phase of the film. The ratio of the continuous phase to the disperse phase is 35-98:2 (by wt.%). The maximum tearing torque of the film is 60g.cm/mum or below, and the maximum tearing tension is 10g/mum or below, and the film can be torn substantially linearly in at least one direction.

Tear and energy properties of three impression materials.

Abstract: A dental impression material must have sufficient strength to allow removal from a gingival sulcus without tearing; it must also have adequate elastic recovery This study examined the tear energy, the permanent deformation upon extension, the energy absorbed to an estimated point of significant deformation, and the extent of permanent deformation at tear of polysulfide, polyether, and addition-reaction silicone impression materials As expected, polysulfide material had a higher tear energy and strain at tear than either polyether or addition-reaction silicone materials However, the more relevant clinical properties, such as energy absorbed per amount of deformation and tear at a point of minimal permanent deformation, favored the addition-reaction silicone material, followed by the polyether material

Elastoplastic trouser tear testing of sheet materials

Abstract: An elastoplastic analysis of trouser tear testing is presented and differences from the Mai-Cotterell rigid-plastic analysis [1] are highlighted. In particular, the simple linear plot of the latter for tearing force per unit thickness against leg width proves to be a curve with a lower intercept for fracture toughness, since the radius of tearing increases with leg width. Furthermore, the curve passes through a maximum and the tearing force decreases at very large leg widths owing to the effects of elasticity. Experiments on NS4 aluminium alloy and on 64/36 brass sheet (including the effects of anisotropy) confirm these results.

Belt-mounted tape dispenser apparatus

Abstract: A belt-mountable tape dispenser operable with one hand for the retrieval and cutting of a predetermined length of tape from a spool of tape mounted to the dispenser. The tape dispenser includes a frame fabricated from a malleable material to accommodate conforming the frame to the waist of the wearer. Belt clips on each end of the frame releasably mount the frame to the belt. A strut extends downwardly from the frame and rotatably supports a reel upon which the spool of tape can be mounted. A cutter assembly and a cutter shield are removably attached to the strut. The cutter assembly and the cutter shield are adaptable to being mounted to the strut for either a left-hand operation or a right-hand operation. The placement of the reel below the frame prevents the pulling and tearing forces imposed on the tape from dislodging the tape dispenser from the belt.

Tearing resistance of multi-layer plastic films

Abstract: The tear resistance of multi-layered plastic films can be generally predicted from the tear resistance of individual layers by an additive rule. The most notable exception from this additive rule is the case of multi-layered films containing a polyethylene layer. The reason for this specific case is explained by the constraint on the plastic yield zone of polyethylene, which causes a dramatic drop in the tear resistance of the multi-layered film. An extensive plastic zone is generated during the tear fracture of a single layer polyethylene film. This yield zone does not appear when polyethylene is laminated with other polymer films.

Effects of tensile loading on upper shelf fracture toughness

Abstract: Constraint has been an important consideration in fracture mechanics from the earliest work that was done to develop the 1974 version of the ASTM Standard E399. O`Dowd and Shih (1991) have proposed that the difference in crack tip stress fields can be quantified in terms of a field quantity that they have call Q. The Q quantity is a function of J, the crack shape and size, the structural geometry, mode of loading and on the level of deformation and can only be calculated from a high resolution elastic-plastic computational analysis. A similar, simpler, but more controversial approach has been suggested by Betegon and Hancock (1991), who use the non-singular term of the elastic, crack singularity solution, called the T-Stress, as a measure of elastic-plastic crack tip constraint. The objective of this work is to develop some upper shelf, elastic-plastic experimental results to attempt to investigate the applicability of the Q and T stress parameters to the correlation of upper shelf initiation toughness and J resistance curves. The first objective was to obtain upper shelf J resistance curves, J{sub Ic}, and tearing resistance results for a range of applied constraint. The J-Q and J-T stress loci were developed and comparedmore » with the expectations of the O`Dowd and Shih and the Betegon and Hancock analyses. Constraint was varied by changing the crack length and also by changing the mode of loading from bending to predominantly tensile. The principle conclusions of this work are that J{sub Ic} does not appear to be dependent on T stress or Q while the material tearing resistance is dependent on T stress and Q, with the tearing modulus increasing as constraint decreases.« less

Thin film wrapping for cassette case

Abstract: A partly-overlapped portion of a sheath film is meltbonded by heat to provide a seal which a user can tear open with ease. A heat sealing area of the sheath film is halftone printed to reduce the bonding area, thereby decreasing the bonding strength. A tearing portion is provided along the heat seal which is printed so that it has a bonding strength which gradually increases along the tear part until it reaches the bonding strength of the remainder of the heat seal. A curl section having minimal bonding strength relative to the tearing portion of the heat seal is induced to curl up using heat treatment to allow the user to grasp the sheath film at the tear part.

Modeling the tearing of paper

Abstract: A model is presented which predicts the path along which ordinary machine‐made paper will tear. Based on the idea of minimum work being done as the paper tears, this model leads to curve‐generating equations which are solved numerically via a simple basic program. A key feature making this a pedagogically attractive activity is that immediate experimental feedback is possible by printing out the theoretical curves and comparing them to the actual tearing curves produced when the printouts are torn. Typical results obtained when this is done are included.

Elastoplastic convergent and divergent crack paths in tear testing of sheet materials

Abstract: — When an initially-parallel-sided tab of material, cut into an isotropic finite-width sheet, is torn by pulling the outer tabs in one direction, and the center in the opposite, the cracks may follow a parallel path, diverge outwards, or converge inwards depending on the widths of the inner and outer “legs”. At the same time, the untorn portion of the material may rotate relative to the pulling axis. The phenomenon is observed in globally elastic tearing, elastoplastic tearing, and in rigid-plastic tearing. A fracture mechanics model using minimum energy explains the tear paths and rotations. Experiments on NS4 aluminium alloy confirm the analysis. The relationship of leg widths and bend radii with standard trousers tear testing of ductile materials is explained.

Nonlinear coupling of disparate helical tearing modes

Abstract: An analytical model has been developed for the nonlinear interaction of linear tearing modes with different helicities in cylindrical geometry. The linear tearing modes are nonlinearly coupled together by the v×B induced electrical field as soon as they exist. According to the standard scaling of linear tearing mode, the nonlinear coupling is mainly through the convective term in evolution equation of poloidal magnetic flux perturbation at resistive layer. The set of nonlinear equations, therefore, can be derived for the time evolution of the flux perturbations of nonlinear coupling modes by asymptotic matching to eliminate the space variable. The nonlinear coupling effect depends on the relative amplitudes of the tearing modes and the nonlinear coupling parameters {αmn}, which are determined by the relative slopes of equilibrium current density in singular layers. The marginally stable m/n mode could be destabilized by the nonlinear coupling with the other modes only if αmn<0. The flux perturbations incl...

Numerical Modeling of Ductile Tearing Effects on Cleavage Fracture Toughness

Abstract: Experimental studies demonstrate a significant effect of specimen size, a/W ratio and prior ductile tearing on cleavage fracture toughness values (J{sub c}) measured in the ductile-to-brittle transition region of ferritic materials. In the lower-transition region, cleavage fracture often occurs under conditions of large-scale yielding but without prior ductile crack extension. The increased toughness develops when plastic zones formed at the crack tip interact with nearby specimen surfaces which relaxes crack-tip constraint (stress triaxiality). In the mid-to-upper transition region, small amounts of ductile crack extension (often < 1-2 mm) routinely precede termination of the J-{Delta}a curve by brittle fracture. Large-scale yielding, coupled with small amounts of ductile tearing, magnifies the impact of small variations in microscale material properties on the macroscopic fracture toughness which contributes to the large amount scatter observed in measured J{sub c}-values. Previous work by the authors described a micromechanics fracture model to correct measured J{sub c}-values for the mechanistic effects of large-scale yielding. This new work extends the model to also include the influence of ductile crack extension prior to cleavage. The paper explores development of the new model, provides necessary graphs and procedures for its application and demonstrates the effects of the model on fracture datamore » sets for two pressure vessel steels (A533B and A515).« less

Tearing a polymeric film or bag

Abstract: An article such as a bag 10 made from a polymeric film such as polyethylene includes a second polymeric film in the form of a strip 13 adhered to the first polymeric film. The strip 13 may be made from a mono-oriented polymeric film such as mono-oriented polyethylene in which a tear will propagate in a single, known direction. When the two films are coupled together the tear still tends to propagate in the single direction. Instead of using a tape a laminate may be used, one entire or part layer of which is a mono-oriented polymeric film. A cub or notch may define the start point of the tear line.

Wall interaction of tearing modes in configurations with multiple rational surfaces

Abstract: The effects of wall stabilization and differential plasma rotation on resistive tearing modes are discussed for configurations with multiple rational surfaces. Results are presented for purely rigid plasma rotation as well as for the case when two rational surfaces are in differential rotation

Dispenser for toilet paper teared with single hand

Abstract: The utility model relates to a box for toilet paper torn with a single hand, which comprises a box body and a paper supporting shaft, wherein, the bottom of the box body with an opening is provided with a paper loading valve, and the paper supporting shaft which is supported on the wall of the box is positioned in the box body A paper back shaft is arranged at the back upper part of the paper supporting shaft in the box body; both ends of the paper back shaft are supported and fixed on the wall of the box A toilet paper roll is sheathed on the paper feeding end of the paper supporting shaft through the paper back shaft and hangs down naturally when the utility model is used; a single hand tightly grasps the end of the paper when the paper is torn, the paper is pulled out and dragged forcibly while a paper surface pulled out is adpressed with the paper surface of the paper roll, and the paper can be torn out when the paper roll is broke by friction force between two paper surfaces The utility model has the characteristics of simple structure, low cost, long service life, and reliable paper tearing effect, and is not easy to breakdown or damage