High speed double torsion tests on tough polymers. I: Linear elastic steady state and dynamic analysis

Wheel, M. A.; Leevers, P. S.

doi:10.1007/bf00012396

Cited by 9 publications

(12 citation statements)

References 24 publications

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“…Clearly, assumption (iii) is difficult to justify for a pipe in a gas tight containment. Assumption (iv) is, in fact, very difficult to justify for any polyethylene pipe material, or indeed for most thermoplastics; it is known that the resistance of polyethylene to cracks running at speeds lower than several tens of m s 21 is very high indeed, so that fracture test methods cannot drive such a crack 1 and an arresting crack in a pipe appears to stop almost instantaneously. 9 If assumption (iv) is invalid, the backflow analysis cannot fully explain the magnitude of observed p cFS /p cS4 ratios (typically 5 or greater).…”

Section: Discussionmentioning

confidence: 99%

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Rapid crack propagation in loosely fitted PE liner pipe

Leevers¹,

Henderson²,

Pereira³

2007

Plastics, Rubber and Composites

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Laboratory scale tests have been used to assess whether a loosely fitted PE liner within a rigid host pipe could, at any realistic working pressure, fail by rapid crack propagation (RCP). The standard 'S4' test method for RCP was modified, the usual cage of containment rings being replaced by a rigid, closed sleeve maintaining a predefined radial clearance from the unpressurised pipe. Pipe specimens of 125 mm diameter with wall thicknesses of 11?4 and 7?1 mm, made from a PE80 polyethylene in which RCP is normally possible at 0uC, were tested with three different clearances as well as with the usual S4 cage. For pipe having an unpressurised clearance down to 2% or so of the diameter, the RCP critical pressure was increased by y50% for both thicknesses; for smaller clearances, by progressively more. These results reinforce suspicions that pipe installation conditions may affect full scale RCP resistance.

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Section: Discussionmentioning

confidence: 99%

“…The total crack driving force is resisted by the fracture resistance G D of the pipe material, itself a difficult material property to evaluate. 1 During steady RCP, G5G D . Solution of this equation would provide a prediction for the critical pressure p c , above which RCP can be sustained.…”

Section: Introductionmentioning

confidence: 99%

Rapid crack propagation in loosely fitted PE liner pipe

Leevers¹,

Henderson²,

Pereira³

2007

Plastics, Rubber and Composites

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“…29 of Ref. [1]) according to which a higher striker speed at a given crack velocity provided more external work, a proportion of which provided a higher driving force at the crack tip. According to the nonlinear model, the reduced modulus resulting from a higher crack speed both limits the input of external work and, by reducing the torsional wave speed, prevents much of it from reaching the crack tip.…”

Section: Nonlinear Elastic Dynamic Model Of the Hsdt Testmentioning

confidence: 99%

“…In the first part of this paper [1], the usefulness of the High Speed Double Torsion (HSDT) test for studying Rapid Crack Propagation (RCP) in tough structural polymers was investigated using pipe grade polyethylenes, in which it provides an effective simulation of plane-strain RCP along pressurised pipelines. The test imposes fast four-point displacement at one end of a rectangular plane, twisting it apart by symmetrical torsion around the long axis.…”

Section: Introductionmentioning

confidence: 99%

High speed double torsion tests on tough polymers. II: Nonlinear elastic dynamic analysis

Wheel

Leevers

1993

Int J Fract

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Although the High Speed Double Torsion (HSDT) test readily generates steady rapid crack propagation in tough structural polymers, computation of the dynamic fracture resistance from displacement data using a transient dynamic torsional beam-on-elastic-foundation model leaves considerable scatter in the results. Much of this scatter is here traced to the use of a single high-rate, small strain elastic modulus to model these highly nonlinear materials for generation mode analysis. The use of nonlinear, large-strain dynamic shear stress-strain data, from a test which measures the impedance to HSDT displacement loading of a previously cracked specimen, increases the consistency of fracture resistance data for pipe-grade polyethylenes. For crack velocities approaching the torsional wave speed, consistency is further improved by accounting for energy transmitted to the crack front by axial stresses set up by differential warping. The corrected data show fracture resistance to be almost constant for crack velocities exceeding some critical minimum.

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Rapid crack propagation in tough polymers; A note on the crack tip temperature field

Wheel

Leevers

1993

Int J Fract

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The High Speed Double Torsion (HSDT) test has recently been used to determine the dynamic fracture resistance, Gt,, of tough pipe grade polyethylenes and other engineering thermoplastics [1]. These materials, which exhibit very high resistance to slow tearing, tend to become relatively brittle at high crack speeds. Fracture resistance is not normally measured directly, it is inferred from the crack driving force or energy release rate provided by the structure. However, extracting consistent Gt, data for non-linear elastic materials requires careful energy accounting when deriving the crack driving force [2]. The problems involved in this approach could be avoided if a method of measuring the energy consumed locally at the crack tip were available.Previous research on brittle polymers has shown that much of the energy consumed by the irreversible processes occuring close to the crack tip is converted to heat. Fuller et al. [3] reported that the heat generated in polymethylmethacrylate (PMMA) increased with crack speed in a similar manner to that in which GD was thought to vary. DUll [4] compared the amount of heat generated in PMMA to the dynamic energy release rate determined from the remotely applied stress. He concluded that approximately 60 percent of the energy released was converted to thermal energy. He also reported that as the molecular weight of the PMMA increased more heat was produced at a given crack velocity. Zimmermann et al. [5] determined the dynamic energy release rate from the response of strain gauges placed close to the crack path in PMMA samples and concluded that all of the energy released appeared as heat. These observations on amorphous polymers suggest that the transition to brittle rapid crack propagation in tough semi crystalline polymers may be caused by breakdown of the reinforcing crystalline phase, due to the heat generated adiabatically within the process zone. Direct measurements of heat generated near a fast running crack tip could therefore serve two objectives. Firstly, it could provide a direct, straightforward measurement of the intrinsic fracture resistance of the material, unaffected by any uncertainties about bulk elastic properties that affect the crack driving force. Secondly, it could provide an insight into the mechanism by which increasing crack speed adversely influences the separation process, and may suggest material development strategies to counteract this influence.

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High speed double torsion tests on tough polymers. I: Linear elastic steady state and dynamic analysis

Cited by 9 publications

References 24 publications

Rapid crack propagation in loosely fitted PE liner pipe

Rapid crack propagation in loosely fitted PE liner pipe

High speed double torsion tests on tough polymers. II: Nonlinear elastic dynamic analysis

Rapid crack propagation in tough polymers; A note on the crack tip temperature field

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