Li moe key laboratory for strength and vibration, department of engineering mechanics, xian jiaotong university, xian 710049, china. Culver explored the fatigue crack propagation influenced by test frequency, amplitude as well as stress intensity factor and established an empirical model to simulate the fcg rate of hdpe. Fatigue crack propagation testing helps to determine if a material is resistant to crack formation, and to compare different formulations of materials. Fatiguepropagation du melange polymere polystyrene.
Fatigue crack propagation testing in uhmwpe kozak, a. Pdf degradation and failure of some polymers polyethylene. Logarithmic scales are used because fatigue crack growth rates can vary from millions of cycles to advance a crack by one millimeter to only tens of cycles to grow the same distance just before failure. So, a straightline segment will result when logdadn versus log k data are plotted. Tail phenomenon and fatigue crack propagation of pcabs alloy qinzhi fang, t. The effects of annealing on fatigue crack propagation in polyethylene. Studies of field failure indicate that polyethylene fuel pipe fails by brittle crack propagation. Fatigue crack propagation resistance of highly crosslinked. By the use of fracture mechanics principles it is possible to predict the number of cycles spent growing a crack to some specified length or to final failure. Peak stress intensity factor governs crack propagation. The fatigue crack propagation behavior of injectionmolded specimens of pure ps as well as of 955, 8515 and 7030 pshdpe blends and of 950.
To reproduce this type of failure in accelerated laboratory testing requires a similarity criterion. Critical pressures, below which rcp always arrests, have been measured for grades of mediumdensity mdpe and modified highdensity polyethylene hdpe. The fatigue fracture surface features of specimens of pure ps as well as of ps hdpe and pssebs hdpe blends were analyzed in detail in order to interpret their fatigue crack propagation behavior. The reduced fatigue strength of highly crosslinked ultrahigh molecular weight polyethylene could lead to.
Simulation study of fatigue lifetime in pe100 pipes iieta. Fatigue crack propagation fcp rates are studied in 6 mm thick specimens of high density polyethylene hdpe containing razor notches, centrally. The fcp results showed that increasing the hdpe content caused a progressive reduction of the fatigue crack growth rates, especially when a styreneethylene butylenestyrene sebs terpolymer was added as a compatibilizer. The predicted fatigue crack propagation rates are compared with experimental data for different metallic materials, and the results show that the. Pehd fatigue damage accumulation under variable loading based. Comparative crack layer analysis of fatigue and creep crack.
Volume i1 treats exclusively the subject of damage tolerance evaluation of airframes 14. The fatigue crack propagation resistance of unirradiated uhmwpe was insignificantly higher than that of unirradiated but melted uhmwpe p 0. Resistance to rapid crack propagation impact damage, fatigue or joint failure in metal or thermoplastic pipes under certain operating conditions can lead to long, running cracks that will propagate through fused joints and can travel hundreds of feet. Pdf fracture surface analysis in hdpe pipe material. The median rank, the maximum likelihood and the kolmogorovsmirnov fitting are compared for. The fracture toughness, crack propagation rate in fatigue and crack growth speed for pe100 hdpe were determined. The fatigue crack propagation behavior of injectionmolded specimens of pure ps as well as of 955, 8515 and 7030 ps hdpe blends and of 950. The use of crack layer theory to predict the lifetime of the fatigue crack growth of high density polyethylene byoungho choi, werner balika, alexander chudnovsky, gerald pinter, reinhold w. Hdpe pipe has superior resistance to rcp resulting in less maintenance and repair costs.
Fracture propagation is a phenomenon in which a long brittle crack runs along the pipeline at high speeds of approximately 350 ms. While on the subject of dislocations, it is appropriate to briefly discuss fatigue. Description of region i once initiated, the fatigue crack propagates along high shear stress planes 45 degrees. Rapid crack propagation rcp is a rapidly traveling longitudinal crack that can pass through fused joints and destroy a pipeline in seconds. Jan 18, 2011 the crack advances behind the craze until it reaches a critical length, upon which it cannot be supported and results in complete fracture and failure of the pipe. Various thermal histories were used to generate samples with the same crystallinity and supermolecular structure for three different molecular weight hdpes. This cracking is referred to as rapid crack propagation rcp. Early 1960s research showed that it was necessary to take account of the longterm failure mode of pe to ensure the safe operation of distribution networks for gas and water. Numerical results show that the branch point where the declined crack path originates can effectively hinder crack propagation, and that the rate limiting step in fatigue is crack propagation along a small segment of the declined crack. Fatiguepropagation du melange polymere polystyrenepolyethylene. Fatigue material in materials science, fatigue is the weakening of a material caused by cyclic loading that results in progressive and localized structural damage and the growth of cracks.
We determined the radiation dose dependence and decoupled the effects of postirradiation melting on the crystallinity, mechanical properties and fatigue crack propagation resistance of room temperature irradiated uhmwpe from those of irradiation alone. Description astm e647 describes the general protocol for fatigue crack propagation testing in materials using a prenotched. In the injection molding process, minor phase coarsening was attributed to shear coalescence. Simulation of fatigue crack growth of hdpe using crack layer. Features and benefits of hdpe water pipe heat fused leakfree joints small minimum bending radius impact resistant resistant to fatigue from repetitive surge events immune to corrosion resistant to rapid crack propagation highly resistant to scale build up that can reduce flow capacities. Slow crack propagation in polyethylene under fatigue at controlled. Department of macromolecular science, case western reserve. Irradiation and subsequent melting reduce the strength and fatigue resistance of the polymer. Temperature and loading frequency effects on fatigue crack. Unfortunately, the large majority of hdpe fatigue studies concerns the crack propagation, which assumes that stress concentration and crack already exists. Ultra high molecular weight polyethylene uhmwpe has been. Tail phenomenon and fatigue crack propagation of pcabs alloy. Subject terms dmmge tolerance, fracture mechanics, crack initiation, toughness, stress.
Part of the problem for fatigue and fatigue crack propagation is that these behaviors are influenced by a wide range of parameters that include cyclic stress. Fatigue crack propagation tests have been conducted at body temperature 37 c and in physiologically relevant fluid environments 22,23. Fatigue tests were performed on circumferentially notched bars cnb of high density polyethylene in order to analyse the kinetics and mechanisms of crack. Characterization of postuse polyethylene and polypropylene recyclate. The use of crack layer theory to predict the lifetime of. This fatigue life is estimated by integrating the paris law. Experimental analysis the main experimental means were. Dislocations play a major role in the fatigue crack initiation phase. Sep 29, 2004 fatigue crack propagation fcp of injectionmoulded polystyrene ps and 955, 8515 and 7030 pshighdensity polyethylene hdpe blends at loading frequencies of 2 and 20 hz was studied. In this case, fatigue produces accumulated material damage. Stress crack resistance sometimes referred to as slow crack growth resistance. Simulation study of fatigue lifetime in pe100 pipes journal. This study aims to compare different statistical methods and distributions, in order to give convenient modeling of tensile and fatigue test results of commercially available. The nature of polyethylene pipe failure plasticstoday.
Fatigue crack propagation in short and long glass fiber. Part of the problem for fatigue and fatiguecrack propagation is that these behaviors are influenced by a wide range of parameters that include cyclic stress. A stressbased model for fatigue life prediction of high. Fatigue lifetime of hdpe structures such as pipes is recognized to show a large scatter. Usually, fatigue crack propagation can divided into 3 stages 1. The majority of the fatigue life may be taken up in the propagation of a crack. Technical note pp838tn preventing rapid crack propagation. Moet department of macromolecular science, case western reserve university, cleveland, ohio 44106, usa and a. Dislocations play a major role in the fatigue crack. Fatigue crack growth in polyethylene bucknall 1985. Mechanisms of fatiguecrack propagation in ductile and brittle solids 57 figure 2.
Sep 16, 2019 the fatigue lifetime predictions for semicrystalline polymer, high density of polyethylene hdpe cases, is a new research problem, this work is focused on a simulation of the fatigue lifetime in pe100 pipes under internal pressure taking into account the influence of dimension parameters and internal pressures using the afgrow software. Modeling of axisymmetric slow crack growth of highdensity. Minimum required strength mrs this provides longterm strength and creep resistance. The creep crack growth ccg and the fatigue crack growth fcg behaviour of a. Slow crack growth model of hdpe for a circular notched bar specimen is. Comparative crack layer analysis of fatigue and creep crack propagation in high density polyethylene m. Rcp can be initiated by impact, improper tapping, faulty fusion, fatigue, or other forms of failure. The use of crack layer theory to predict the lifetime of the fatigue crack growth of high density polyethylene. Abstract an investigation of the influence of crystalline microstructure on fatigue crack propagation fcp in high. Pressurized pipelines of extruded ductile polyethylenes can, under severe conditions, fail by brittle rapid crack propagation rcp. Ckm where c and m are material parameters one of the first 1962 and most widely used fatigue crack propagation criteria oalgorithmo 1. The goal of this study was to determine the effect of gamma radiation induced crosslinking and postirradiation thermal processing on the fcp resistance of uhmwpe. Effect of residual stress on crack propagation in mdpe pipes. Peak stress intensity factor governs crack propagation velocity in.
Crack layer analysis of nonmonotonic fatigue crack. Simulation of fatigue crack growth of hdpe using crack. Comparative crack layer analysis of fatigue and creep. Fatigue crack growth measurements are made on two grades of hdpe, of density 940 and 958 kg m minus 3, and relationships between crack growth rate dadn and stress intensity factor k are examined. Microscopic observations reveal a single crazelike active zone preceding the crack during the initial crack acceleration. The effects of annealing on fatigue crack propagation in.
Fatigue crack propagation fcp of injectionmoulded polystyrene ps and 955, 8515 and 7030 ps highdensity polyethylene hdpe blends at loading frequencies of 2 and 20 hz was studied. Simulation of fatigue crack growth of hdpe using crack layer theory. Working pressure rating and fatigue life pp402 in addition to pressure ratings, fatigue lift is a critical issue to consider when selecting pipe. It represents the early development of a fatigue crack and the crack growth rate. Schematic illustration of mutual competition between intrinsic mechanisms of damage crack advance and extrinsic mechanisms of crack tip shielding involved in crack growth.
The rate of fatigue crack propagation fcp in high density polyethylene hdpe is a nonmonotonic function of the energy release rate, a phenomenon previously noted for other semicrystalline polymers. More stringent operating and test pressures of larger diameter polyethylene gas pipes have had to be introduced nationally. Modeling of fatigue crack propagation during sliding wear. It is proven that in fretting fatigue failure scenario after nucleating crack at contact interface, in early stage of crack propagation its behavior is governed by frictional shear stress at the contact interface. The relationship between slow crack propagation in creep and fatigue in a medium density polyethylene pipe material was studied by increasing the rratio defined as the ratio of minimum to. Various fracture criteria and crack growth rules are studied. Fatigue propagation behaviour of polystyrenepolyethylene. Quantitative fractographic analysis of field failure in mdpe pipe suggests that the number of. By studying the fatigue crack for hdpe specimens containing razor notches, bucknall and dumpleton found that the required cycles for crack initiation. One of the main design criteria for limiting the operational pressures of polyethylene pe gas pipes is its resistance to rapid crack propagation rcp. Fatigue propagation behaviour of polystyrenepolyethylene blends.
The empirical paris law for crack growth is verified, offering a means for estimating the total life of a pressurized hdpe pipeline. Hdpe pipes contain additives which protect the pipe from the oxidizing effects of disinfectants. This theory considers the interaction between crack. Fatigue crack propagation fcp in unfilled and short sgf and long glass fiber lgf reinforced injectionmolded polypropylene pp composites was studied on notched compact tension ct specimens in tensiontension mode. The life of a fatigue crack has two parts, initiation and propagation. Technical report by polymer engineering and science. Antec 2016 proceedings of the annual technical conference and exhibition of the society of plastics engineers. Ram extruded 1050 gur ticona, bayport, tx was used. It is now reasonably clear that fatigue accelerates ductile crack propagation in hdpe by accelerating the dominant damage mechanism in that kinetic region. The fcp results showed that increasing the hdpe content caused a progressive reduction of the fatigue crack growth rates, especially when a styreneethylene butylenestyrene sebs terpolymer. The fcp results showed that increasing the hdpe content caused a progressive reduction of the fatigue crack growth rates, especially when a styreneethylene butylenestyrene sebs terpolymer was added.
Statistical analysis of hdpe fatigue lifetime springerlink. The reason for this accelerated yielding under fatigue is not quite so apparent. Below a critical pressure the crack arrests but above the whole pipeline may be fractured. The need for reliable corrosion, resistant pipe to rehabilitate existing pipelines and for new pipeline installation by horizontal directional drilling methodology led to the emergence of polyethylene pe.
Engineering and manufacturing science and technology, general building materials evaluation service life building materials durability cracking materials observations fatigue materials fatigue testing. The type of irradiation gamma or electron beam or manufacturing method extrusion or molding did not affect fatigue crack propagation resistance. The geometries of fatigue cracks are described for each case. Fatigue crack propagation fcp of injectionmoulded polystyrene ps and 955, 8515 and 7030 pshighdensity polyethylene hdpe blends at loading frequencies of 2 and 20 hz was studied. In the fcp response, a fatigue crack deceleration stage range i and an acceleration stage range ii could be distinguished. Fatigue is one of the primary reasons for the failure of structural components. Kasakevich ml, moet a 1990 comparative crack layer analysis of fatigue and creep crack propagation in high density polyethylene. Mechanisms of fatiguecrack propagation in ductile and.
To this end, a new astm test method for fatigue crack propagation fcp specific to uhmwpe is being developed. Fatigue crack propagation resistance was reduced in proportion to the irradiation dose. Pdf highdensity polyethylene hdpe pipes are being extensively used for gas, water, sewage, and waste water distribution systems. Tail phenomenon and fatigue crack propagation of pcabs. Pdf fatigue crack propagation from notched specimens of. The fcp results showed that increasing the hdpe content caused a progressive reduction of the fatigue crack growth rates, especially when a styreneethylene butylenestyrene sebs terpolymer was added as a. Pdf fatigue tests were performed on circumferentially notched bars cnb of high density polyethylene in order to analyse the kinetics and. Fatigue crack propagation rate logarithm crack growth rate versus logarithm stress intensity factor range for a nimov steel.
It can be noted the presence of the tunneling effect because of a large difference in stress states along the notch crack. However, in most of pipeline parts, fatigue may occur without any previously formed crack. In hdpe, mica reduces fcp rates resulting in a higher resistance to fatigue crack propagation. The use of crack layer theory to predict the lifetime of the. For fatigue, fatiguecrack propagation, and fracture data, however, design allowable values are usually not available and the data are presented in terms of typical or average values. Temperature and loading frequency effects on fatigue crack growth. Introduction fracture mechanics fatigue crack propagation. Pdf slow crack propagation in polyethylene under fatigue at. Filler material particles contained in the hdpe pipe material play an important role of stress concentrators and help in microvoid nucleation, which promotes crack growth via crazing. Figure 5a and 5b exhibits the characteristics fractured surfaces. Once a crack has initiated, each loading cycle will grow the crack a small amount, typically producing striations on some parts of the fracture surface. This study aims to compare different statistical methods and distributions, in order to give convenient modeling of tensile and fatigue test results of commercially available polyethylene compression molded sheets. Solid mechanics fatigue crack propagation anders ekberg 7 20 pariso law paris law can be written as d d a n. An investigation of the influence of crystalline microstructure on fatigue crack propagation fcp in high.
Find stress intensity factor for the current geometry 2. The slope and intercept correspond to the values of m and log a, respectively. Materials and methods discussion given the commonality of the test specimen and crack analysis system, the only potential differences were due to the sample. Fatigue crack growth testing 101 20140604 quality magazine.