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P. S. Leevers - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the effect of residual stresses and interfacial adhesion on Rapid Crack Propagation in bilayered polypropylene polyethylene pp pe100 pipes
Polymer Engineering and Science, 2017Co-Authors: Andrea Guevaramorales, P. S. LeeversAbstract:Rapid Crack Propagation (RCP) resistance of bilayered pipes consisting of a polyethylene core and a polypropylene skin was investigated using the ISO 13477 Small Scale Steady State “S4” test. It was found that bilayered pipes met all the RCP requirements, but the addition of a thin (0.4–1.5 mm) skin slightly increased the S4 critical temperature. This embrittlement effect is attributed to increased constraint, which is mainly influenced by the elastic moduli of the skin and core and the adhesion between them. Because the elastic moduli of the skins were very similar, the investigation focused on the effect of adhesion and residual stresses. It was found that higher adhesion leads to higher constraint and higher S4 critical temperature. However, when both adhesion and residual stresses were modified during annealing, the effect of residual stress relaxation was more significant on RCP performance than that of increasing adhesion. Annealed pipes in which residual stresses had relaxed by ∼40%, showed better RCP resistance even though adhesion was almost doubled. It was found that in some cases, bilayered pipes may even present better RCP resistance than monolayered ones when the adhesion falls below a threshold at which the skin no longer constrains the pipe. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers
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Rapid Crack Propagation failures in hdpe pipes structure property investigations
Polymer Engineering and Science, 2006Co-Authors: Rajendra K. Krishnaswamy, Mark J. Lamborn, Ashish M. Sukhadia, D.f. Register, Pamela L. Maeger, P. S. LeeversAbstract:The influence of molecular architecture on the Rapid Crack Propagation (RCP) resistance of a wide variety of high-density polyethylene pipes was investigated. It was concluded that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important architectural attributes for RCP resistance. The ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the RCP resistance of the resultant pipes. POLYM. ENG. SCI., 46:1358–1362, 2006. © 2006 Society of Plastics Engineers
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Correlation between full scale and small scale steady state (S4) tests for Rapid Crack Propagation in plastic gas pipe
Plastics Rubber and Composites, 1999Co-Authors: C J Greenshields, P. S. LeeversAbstract:The full scale and small scale, steady state (S4) tests are the principal methods for measuring the critical pressure above which Rapid Crack Propagation can occur in a gas pressurised plastic pipe. The full scale test delivers a critical pressure which directly reflects service performance. The S4 test is less costly, but produces a critical pressure which is significantly lower than that of the full scale test. The discrepancy in critical pressures is due largely to differences in gas dynamics of the two tests. A well known gas dynamics analysis, which has previously been incorrectly applied, is used in the present work to derive a correlation function, which compares well with limited experimental data. Further experiments and analysis illustrate some other factors that influence the correlation and suggest that the application of a more precise correlation function is impractical.
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Impact and Rapid Crack Propagation Measurement Techniques
Polymer Science and Technology Series, 1999Co-Authors: P. S. LeeversAbstract:Some plastics which show outstanding ductility under slowly-applied loads can fail in a brittle manner under impact. This tendency is enhanced by low temperatures and by the presence of a sharp notch, and it is of particular concern for the tough crystalline thermoplastics which have earned most respect as engineering materials. For this and other reasons (including their speed and ease of use), impact tests are accorded a status comparable to tensile tests in specification data for plastics.
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Brittle-tough transition of Rapid Crack Propagation in polyethylene
Polymer, 1998Co-Authors: S.j.k. Ritchie, Paul Davis, P. S. LeeversAbstract:Abstract The brittle–tough transition of Rapid Crack Propagation in pressurised polyethylene pipes is examined. The transition is correlated with the presence of shear lips. Two new tests are described and then used to examine the mechanism of shear lip formation. The mechanism is found to be largely governed by the post-yield drawing behaviour of the polyethylene and is sensitive to both rate and temperature. The degree of drawing before failure is discussed from a micro-structural viewpoint and is shown to depend, at least in part, on lamella size and hence processing conditions.
Patrick S. Leevers - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of the effect of residual stresses and interfacial adhesion on Rapid Crack Propagation in bilayered polypropylene/polyethylene (PP/PE100) pipes
Polymer Engineering & Science, 2016Co-Authors: Andrea Guevara-morales, Patrick S. LeeversAbstract:Rapid Crack Propagation (RCP) resistance of bilayered pipes consisting of a polyethylene core and a polypropylene skin was investigated using the ISO 13477 Small Scale Steady State “S4” test. It was found that bilayered pipes met all the RCP requirements, but the addition of a thin (0.4–1.5 mm) skin slightly increased the S4 critical temperature. This embrittlement effect is attributed to increased constraint, which is mainly influenced by the elastic moduli of the skin and core and the adhesion between them. Because the elastic moduli of the skins were very similar, the investigation focused on the effect of adhesion and residual stresses. It was found that higher adhesion leads to higher constraint and higher S4 critical temperature. However, when both adhesion and residual stresses were modified during annealing, the effect of residual stress relaxation was more significant on RCP performance than that of increasing adhesion. Annealed pipes in which residual stresses had relaxed by ∼40%, showed better RCP resistance even though adhesion was almost doubled. It was found that in some cases, bilayered pipes may even present better RCP resistance than monolayered ones when the adhesion falls below a threshold at which the skin no longer constrains the pipe. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers
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Experimental investigation of the effect of residual stresses on Rapid Crack Propagation in polyethylene (PE100) pipes
Polymer Engineering & Science, 2012Co-Authors: Andrea Guevara-morales, Patrick S. LeeversAbstract:Pipe extruded from polyethylene of strength class PE100 was tested using the ISO 13477 Small Scale Steady State ‘‘S4’’ method, to investigate the effect of frozen-in stress on Rapid Crack Propagation (RCP). It was found that the lower the residual stress, the lower the S4 critical temperature TcS4 for RCP. Different experimental thermal treatments were used to independently modify residual stresses and crystallinity, to study the separate effects on RCP. It was found that the effect of crystallinity was less significant than that of residual stresses. It has previously been suggested that the residual stress influence on TcS4 is determined by the balance of two mechanisms: additional stored strain energy prior to fracture helps to drive the Crack, while the closing moment after fracture helps to close the flaring pipe wall. Tests on annealed specimens suggested that the first effect dominates, especially soon after Crack initiation. However, the observed effect seems too large to be explained by this mechanism, and we suggest that the observed benefit from annealing may be better explained by a change in Crack front shape. POLYM. ENG. SCI., 00:000–000, 2012. a 2012 Society of Plastics Engineers
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An engineering model for Rapid Crack Propagation along fluid pressurized plastic pipe
Engineering Fracture Mechanics, 2012Co-Authors: Patrick S. LeeversAbstract:Abstract The appearance of new pipe materials has revived interest in the modelling of Rapid Crack Propagation (RCP) along fluid-pressurized plastic pipelines. The correlation of results from two International Standard RCP test methods—one full-scale and partially simulating installation and service conditions, the other lab-scale—remains imperfectly understood. There is no standard method for measuring the dynamic fracture toughness of the pipe material, and models relating toughness to pipe fracture pressure have not gained widespread use. This paper demonstrates an adaptable, extendable, analytically transparent model which accounts for all major influences including residual stress in the pipe wall, constraint from surrounding backfill and partial substitution of the pressurizing gas by water.
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Rapid Crack Propagation in loosely fitted PE liner pipe
Plastics Rubber and Composites, 2007Co-Authors: Patrick S. Leevers, A Henderson, R. PereiraAbstract: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 PESO polyethylene in which RCP is normally possible at 0°C, 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 ∼50% 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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Rapid Crack Propagation failures in HDPE pipes: Structure–property investigations
Polymer Engineering & Science, 2006Co-Authors: Rajendra K. Krishnaswamy, Mark J. Lamborn, Ashish M. Sukhadia, D.f. Register, Pamela L. Maeger, Patrick S. LeeversAbstract:The influence of molecular architecture on the Rapid Crack Propagation (RCP) resistance of a wide variety of high-density polyethylene pipes was investigated. It was concluded that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important architectural attributes for RCP resistance. The ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the RCP resistance of the resultant pipes. POLYM. ENG. SCI., 46:1358–1362, 2006. © 2006 Society of Plastics Engineers
P. Yayla - One of the best experts on this subject based on the ideXlab platform.
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Rapid Crack Propagation in pressurised plastic pipe ii critical pressures for polyethylene pipe
Engineering Fracture Mechanics, 1992Co-Authors: P. Yayla, P. S. LeeversAbstract:Abstract A new small-scale test method has been developed for generating steady-state Rapid Crack Propagation in plastic pipe. Using this method, a series of exploratory tests are used to investigate the variation in critical pressure (i.e. the threshold of Crack self-arrest) with parameters which are seen to influence it in full-scale tests: temperature, pipe wall thickness, decompression properties of the pressurising medium, and external constraint. Scaling rules relating small- and full-scale results for different diameters are discussed using British Gas full-scale test data, and in the light of thickness effects measured in small-scale tests.
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Rapid Crack Propagation in pressurised plastic pipe i full scale and small scale rcp testing
Engineering Fracture Mechanics, 1992Co-Authors: J. M. Greig, P. S. Leevers, P. YaylaAbstract:Abstract Rapid Crack Propagation can occur along pressurised pipelines of polyethylene, if a well-defined (but as yet unpredictable) critical pressure is exceeded. The standard for type-testing of pipe to meet exacting service conditions is currently set by full-scale tests. Results from the British Gas full-scale test method are presented and the effects of material, pipe diameter and wall thickness, extrusion process, pressurising fluid and temperature on the critical pressure are reviewed in the light of the Irwin-Corten “strain energy” analysis. These observations have guided the development of a new, complementary small-scale method. It is demonstrated that a small-scale technique designed to promote a steady state can, like the full-scale test, locate a precise transition in Crack behaviour from prompt arrest to steady-state Propagation, but that the effect of reducing the test size is to reduce the critical pressure at which this transition occurs. A correlation between the techniques is therefore necessary.
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CHARPY AND DYNAMIC FRACTURE TESTING FOR Rapid Crack-Propagation IN POLYETHYLENE PIPE
Plastics Rubber and Composites Processing and Applications, 1992Co-Authors: Patrick S. Leevers, P. Yayla, M. A. WheelAbstract:Ductile pipe grade polyethylenes can, under severe conditions, fail by Rapid Crack Propagation (RCP). Critical pressures (below which RCP always arrests) of medium density and modified high density polyethylene pipe, measured using a small-scale pressure test, identify temperature and thickness mediated brittle-ductile transitions which effectively characterise their performance in full-scale tests
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Rapid Crack Propagation in pressurised plastic pipe—II. Critical pressures for polyethylene pipe
Engineering Fracture Mechanics, 1992Co-Authors: P. Yayla, Patrick S. LeeversAbstract:Abstract A new small-scale test method has been developed for generating steady-state Rapid Crack Propagation in plastic pipe. Using this method, a series of exploratory tests are used to investigate the variation in critical pressure (i.e. the threshold of Crack self-arrest) with parameters which are seen to influence it in full-scale tests: temperature, pipe wall thickness, decompression properties of the pressurising medium, and external constraint. Scaling rules relating small- and full-scale results for different diameters are discussed using British Gas full-scale test data, and in the light of thickness effects measured in small-scale tests.
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Rapid Crack Propagation in pressurised plastic pipe—I. Full-scale and small-scale RCP testing
Engineering Fracture Mechanics, 1992Co-Authors: J. M. Greig, Patrick S. Leevers, P. YaylaAbstract:Abstract Rapid Crack Propagation can occur along pressurised pipelines of polyethylene, if a well-defined (but as yet unpredictable) critical pressure is exceeded. The standard for type-testing of pipe to meet exacting service conditions is currently set by full-scale tests. Results from the British Gas full-scale test method are presented and the effects of material, pipe diameter and wall thickness, extrusion process, pressurising fluid and temperature on the critical pressure are reviewed in the light of the Irwin-Corten “strain energy” analysis. These observations have guided the development of a new, complementary small-scale method. It is demonstrated that a small-scale technique designed to promote a steady state can, like the full-scale test, locate a precise transition in Crack behaviour from prompt arrest to steady-state Propagation, but that the effect of reducing the test size is to reduce the critical pressure at which this transition occurs. A correlation between the techniques is therefore necessary.
C J Greenshields - One of the best experts on this subject based on the ideXlab platform.
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Correlation between full scale and small scale steady state (S4) tests for Rapid Crack Propagation in plastic gas pipe
Plastics Rubber and Composites, 1999Co-Authors: C J Greenshields, P. S. LeeversAbstract:The full scale and small scale, steady state (S4) tests are the principal methods for measuring the critical pressure above which Rapid Crack Propagation can occur in a gas pressurised plastic pipe. The full scale test delivers a critical pressure which directly reflects service performance. The S4 test is less costly, but produces a critical pressure which is significantly lower than that of the full scale test. The discrepancy in critical pressures is due largely to differences in gas dynamics of the two tests. A well known gas dynamics analysis, which has previously been incorrectly applied, is used in the present work to derive a correlation function, which compares well with limited experimental data. Further experiments and analysis illustrate some other factors that influence the correlation and suggest that the application of a more precise correlation function is impractical.
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Rapid Crack Propagation in plastic water pipes measurement of dynamic fracture resistance
International Journal of Fracture, 1996Co-Authors: C J Greenshields, P. S. LeeversAbstract:A classical analysis of Irwin and Corten relates the minimum pressure to sustain Crack Propagation along a pipeline to the dimensions, elastic modulus and fracture resistance of the pipe wall. Although the model is inapplicable to gas pressurisation, it is here modified to become sufficiently accurate for water pressurised thickwalled pipe to provide the basis of a dynamic fracture resistance test. Results for three commonly used water pipe grade polymers agree well with the predictions of the ‘Thermal Decohesion’ model, and with other experimental data where available. Rapid Crack Propagation behaviour, in both test and service pipeline configurations, is dominated by the ratio of Crack speed to fluid decompression wave speed. This ratio can be adjusted in a controlled test environment.
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The effect of air pockets on Rapid Crack Propagation in PVC and polyethylene water pipe
Plastics Rubber and Composites Processing and Applications, 1995Co-Authors: C J Greenshields, P. S. LeeversAbstract:Rapid Crack Propagation in gas-pressurised plastic pipe has been under research for several years, more recently using the S4 small scale test. This paper describes tests using a modified S4 method in which water - with or without a controlled volume fraction of air ― is used as the pressurising medium. The results show that air volume fractions representative of those trapped in water distribution pipelines can significantly reduce the critical pressure, which is otherwise much higher than for air pressurisation. Two materials widely used for cold water and sewerage systems, medium density PE and unplasticised PVC, are compared. Polyethylene pipe, although rated for a lower pressure, showed greater resistance to both initiation and Propagation of impact Cracks.
Sunwoong Choi - One of the best experts on this subject based on the ideXlab platform.
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Decompression wave speed and Crack velocity measurements during S4 test in water pressurized plastic pipes: Part 2. Criteria for onset of Rapid Crack Propagation
Polymer Testing, 2017Co-Authors: Vipin Vijayan, Tom Marti, Sunwoong ChoiAbstract:Abstract The Rapid Crack Propagation behavior in pressurized plastic pipes was investigated to establish the criteria for onset of Rapid Crack Propagation in terms of the relationship between decompression wave speed and Crack velocity. The study was performed by using an instrumented S4 test apparatus, the methodology for which is described in Part 1 of this paper. To establish the criteria for the onset of Rapid Crack Propagation in water-filled plastic pipes, PVC pipes of 440 mm outside diameter having dimensional ratios of 14, 18 and 25 were tested following the procedure described in ISO 13477. From the measurements made on decompression wave speed and Crack velocity, it was determined that, for Rapid Crack Propagation to occur in the S4 test, two conditions were required. The decompression wave speed, Cw,S4, needs to be lower than the Rapid Crack velocity, a ˙ . Also, the Crack velocity must be equal to or above the critical Crack velocity, a ˙ c r i t . That is, C w , S 4 ≤ a ˙ a ˙ ≥ a ˙ crit It was shown that this critical Crack velocity is always greater than the theoretical decompression wave speed in water filled pipes. Until now, the criterion for Rapid Crack Propagation in S4 was understood to only involve the former condition in water pipes. With this and the latter condition proposed, more complete criteria for Rapid Crack Propagation in water filled plastic pipes using the S4 method is now established.
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Decompression wave speed and Crack velocity measurements during S4 test in water pressurized plastic pipes: Part 1. Experimental methods
Polymer Testing, 2016Co-Authors: Vipin Vijayan, Tom Marti, Sunwoong ChoiAbstract:Abstract In a Small Scale Steady State (S4) test apparatus of ISO 13477, instrumentations were designed and successfully adapted to determine decompression wave speed and Crack velocity during Rapid Crack Propagation event in water-filled plastic pipes. The basic design for decompression wave speed measurement involved the use of high-frequency dynamic pressure transmitters, located external to the water-filled pipe and connected to pressure measurement positions inside the pipe, by means of stainless steel tubes. For the Crack velocity measurements, timing wire system with the required circuitry capable of giving the precise temporal indication of the propagating Crack was designed and employed. In this paper, detailed design of instrumentations adapted to the S4 test apparatus and the assessment techniques used to obtain decompression wave speed and Crack velocity are described. It was also demonstrated that the methods developed were viable for these measurements which are known to affect the Rapid Crack Propagation behavior in water-filled plastic pipes.
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Measurement of Rapid Crack Propagation in pressure pipes: A static S4 approach
Polymer Testing, 2012Co-Authors: Sooho Pyo, Jungho Woo, Jaeheun Park, Myung-ho Kim, Sunwoong ChoiAbstract:Abstract A method for creating Rapid Crack Propagation in pressurized pipes under slow static loading using modified S4 apparatus is described. In the development of the method a complexity involved with dynamic loading in the S4 test (ISO 13477) is eliminated by the use of a displacement controlled static loading machine. The experimental system consisted of an universal testing machine, a low compliance wedge loading device, notch tip quenching apparatus and a pipe specimen where a through thickness hole is drilled to accommodate the wedge loading device. The pipe specimen is made in such a way that a section containing a hole is free from the internal pressure, while the rest of the specimen is made to carry the internal pressure which would eventually drive the unstable Crack along the pipe axis. The idea of such Rapid Crack initiation under static loading was derived from the concept of time-temperature equivalence, where impact loading may in part be simulated by lowering the temperature at the site of Rapid Crack initiation. The details of the method for Rapid Crack Propagation under static loading are described and the correlation of the results to Rapid Crack Propagation obtained by ISO 13477 is illustrated. The two methods were shown to compare quite well in terms of critical pressure determination and the details regarding normalized Rapid Crack length versus the internal pressure curve as well as the Crack Propagation pattern.