Viscoelastic and Damage Model of Polyethylene Pipe Material for Slow Crack Growth Analysis

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Yue Zhang ◽  
Xiangpeng Luo ◽  
Jianfeng Shi
Keyword(s):  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Failure Process ◽  
Damage Model ◽  
Material Behavior ◽  
Damage Effect ◽  
Resistance Testing ◽  
Testing Time ◽  
Pipe Material

Polyethylene (PE) pipe is widely used for oil and gas transportation. Slow crack growth (SCG) is the main failure mechanism of PE pipes. Current SCG resistance testing methods for PE pipes have significant drawbacks, including high cost, time-consuming, and uncertain reliability. Alternative method is in need to reduce the testing time and cost. In this paper, a numerical model is proposed by taking the viscoelastic and damage effect of PE material into account. The material behavior is described on the basis of linear viscoelastic integral constitutive model, along with the damage effect in effective configuration concept. A three-dimensional (3D) incremental form of a viscoelastic and damage model is derived and implemented by abaqus UMAT. It is found that the curve of tensile displacement versus time, as well as the curve of crack opening displacement (COD) versus time from numerical results fit well with those from the standard Pennsylvania Notch Test (PENT; ASTM 1473). Based on the proposed model, SCG failure process is analyzed, and the effects of damage parameters on SCG process are furtherly studied and discussed.

Viscoelastic and Damage Model of Polyethylene Pipe Material for Slow Crack Growth Analysis

2017 ◽  
Author(s):  
Yue Zhang ◽  
Xiangpeng Luo ◽  
Jianfeng Shi
Keyword(s):  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Failure Process ◽  
Viscoelastic Model ◽  
Material Behavior ◽  
Damage Effect ◽  
Resistance Testing ◽  
Testing Time ◽  
Pipe Material

Polyethylene (PE) pipe is widely used for oil and gas transportation. Slow crack growth (SCG) is the main failure mechanism of PE pipes. Current SCG resistance testing methods for PE pipes have significant drawbacks, including high cost, time-comsuming and uncertain reliability. Alternative method is in need to reduce the testing time and/or cost. In this paper, a numerical model is proposed by taking the viscoelastic and damage effect of PE material into account. The material behavior is described on the basis of linear viscoelastic integral constitutive model, along with damage effect in effective configuraion concept. Three dimensional incremental form of damage viscoelastic model is derived and implemented by ABAQUS UMAT. It is found that the curve of tensile displacement via time, as well as the curve of crack opening displacement via time from numerical results fit well with those from the standard PENT test (ASTM 1473). Based on the proposed model, SCG failure process is analyzed, and the effects of damage parameters on SCG process are furtherly studied and discussed.

The Fracture Toughness of Hardened Tool Steels

1987 ◽  
Vol 109 (4) ◽  
pp. 314-318 ◽  
Author(s):  
D. F. Watt ◽  
Pamela Nadin ◽  
S. B. Biner
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Compact Tension ◽  
Testing Procedure ◽  
Tool Steels ◽  
Opening Displacement ◽  
Tempering Temperature ◽  
Toughness Testing

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

Slow Crack Growth Resistance of Parent and Joint Materials From PE4710 Piping for Safety-Related Nuclear Power Plant Piping

2011 ◽  
Author(s):  
S. Kalyanam ◽  
D.-J. Shim ◽  
P. Krishnaswamy ◽  
Y. Hioe
Keyword(s):  
Crack Growth ◽  
Nuclear Power ◽  
Power Plants ◽  
Slow Crack Growth ◽  
Nuclear Industry ◽  
Pipe Material ◽  
Service Water ◽  
Hdpe Pipe ◽  
Pipe Materials ◽  
Hdpe Pipes

HDPE pipes are considered by the nuclear industry as a potential replacement option to currently employed metallic piping for service-water applications. The pipes operate under high temperatures and pressures. Hence HDPE pipes are being evaluated from perspective of design, operation, and service life requirements before routine installation in nuclear power plants. Various articles of the ASME Code Case N-755 consider the different aspects related to material performance, design, fabrication, and examination of HDPE materials. Amongst them, the material resistance (part of Article 2000) to the slow crack growth (SCG) from flaws/cracks present in HDPE pipe materials is an important concern. Experimental investigations have revealed that there is a marked difference (almost three orders less) in the time to failure when the notch/flaw is in the butt-fusion joint, as opposed to when the notch/flaw is located in the parent HDPE material. As part of ongoing studies, the material resistance to SCG was investigated earlier for unimodal materials. The current study investigated the SCG in parent and butt-fusion joint materials of bimodal HDPE (PE4710) pipe materials acquired from two different manufacturers. The various stages of the specimen deformation and failure during the creep test are characterized. Detailed photographs of the specimen side-surface were used to monitor the specimen damage accumulation and SCG. The SCG was tested using a large specimen (large creep frame) as well as using a smaller size specimen (PENT frame) and the results were compared. Further, the effect of polymer orientation or microstructure in the bimodal HDPE pipe on the SCG was studied using specimens with axial and circumferential notch orientations in the parent pipe material.

Mechanism of Slow Crack Growth in Polyethylene: A Finite Element Approach

2015 ◽  
Author(s):  
Xiangpeng Luo ◽  
Jianfeng Shi ◽  
Jinyang Zheng
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Failure Time ◽  
Bulk Material ◽  
Slow Crack Growth ◽  
Damage Model ◽  
Constitutive Models ◽  
Fe Model ◽  
Notch Angle ◽  
Craze Zone

Slow crack growth (SCG) is a common failure mode in underground polyethylene (PE) piping which was designed for 50-year services. It had been revealed by experiments that the SCG process is caused by continuous propagation of the craze zone at the crack tip through the bulk material. However, the mechanism of SCG failure has not been understood clearly. The eXtended Finite Element Method (XFEM) is found to be an effective tool for locally non-smooth features (voids, cracks, etc.) in solid or fluid mechanics solutions. In this paper the time-dependent property of PE was considered, a viscoelastic constitutive model was used for the bulk material. To represent the material deterioration during SCG, a damage model was developed for the craze zone. Combined with the XFEM, the process of the Pennsylvania Notched Test (PENT), which had been widely applied for characterizing resistance of SCG for PE pipes or resins, was analyzed based on the proposed finite element (FE) model containing the two constitutive models. The numerical results were then compared with the experimental data in literatures. It showed that the failure time and final notch angle were in agreement with the experimental observations. Based on the verified FE model, strain distributions along the boundary of the crack were studied and the shortcomings of this model were discussed.

Development of Crack Growth Curves and Correlation to Sustained Pressure Test Results for Cell Classification 445574C High Density Polyethylene Pipe Material

2013 ◽  
Author(s):  
Timothy M. Adams ◽  
Jason Hebeisen ◽  
Jie Wen ◽  
Douglas Munson
Keyword(s):  
Crack Growth ◽  
High Density Polyethylene ◽  
Failure Time ◽  
Slow Crack Growth ◽  
Growth Curves ◽  
High Density ◽  
Pipe Material ◽  
Test Results ◽  
Cell Classification ◽  
Failure Times

Code Case N755-1 of the ASME Boiler and Pressure Vessel Code, Section III, Division 1 Code currently permits the use of high density polyethylene (HDPE) in buried Safety Class 3 piping systems. There have been concerns with the Slow Crack Growth (SCG) of HDPE emanating from scratches that may occur during fabrication or installation. The possible use of tensile coupon tests for determining the life span of the pipe with surface scratches could provide a more cost effective testing method than does the use of sustained pressurized crack pipe tests. This paper presents the results of further investigation into the SCG rates of notched PE 4710 HDPE pipe made from a cell classification 445574C bimodal resin. The da/dt versus KI curves were developed from notched coupon testing. Standard fracture methods were then used to predict the failure time of the notched pressurized pipe specimens subjected to long-term hydraulic stress. The results for the SCG depth of the externally notched sustained pressurized pipe tests are provided along with the notched coupon test results. The actual failure times of the notched pressurized pipe tests are compared to the predicted failure times for the same specimens.

Scratch Tip Radius Effects on K-Controlled Slow Crack Growth in PE Pipe

2008 ◽  
Author(s):  
Carlos R. Corleto ◽  
Brian B. Cole
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Large Diameter ◽  
Material Behavior ◽  
Element Analysis ◽  
Pipe Model ◽  
Industry Practice ◽  
Notch Tip ◽  
Tip Radius

A study to evaluate the effect of scratch tip radius on stress intensity factor (K) controlled slow crack growth (SCG) was performed to establish whether a plastics pipe industry practice to allow scratches 10% the thickness of the pipe, could still be allowed on large diameter pipes with blunt scratches. A series of finite element analyses were done using a 1/4 two-dimensional (2-D) notched pipe model assuming a 12-in diameter pipe with a standard dimentional ratio (SDR) of 11, a notch ten times smaller than its thickness, notch tip ratios ranging from 16 to 0.0459, and linear elastic material behavior. Results indicate K-controlled SCG would occur if the ratio of notch tip radius to notch depth is less than 0.1667, although this ratio is probably very conservative due to scratch tip blunting from the formation of a craze zone ahead of crack tips in polyethylene (PE) pipes. However, for ratios greater than 0.5, ductile failures could be induced for internal pressures yielding high hoop stresses and at high temperatures. This is due to the fact that stress concentration factors for relatively blunt notches can still induce maximum scratch tip stresses several times higher than the hoop stress of an unscratched pipe. The results of this finite element analysis could be validated experimentally using ASTM D2837-01 following notching procedures given in ISO 13479 with modified cutters to obtain several notch tip radii.

Assessment of Geometry Independent Fracture Resistance Characteristics Based on Local Approach

2005 ◽  
Vol 297-300 ◽  
pp. 2403-2409 ◽  
Author(s):  
Yoon Suk Chang ◽  
T.R. Lee ◽  
Jae Boong Choi ◽  
Young Jin Kim
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Mechanical Damage ◽  
Material Behavior ◽  
Ductile Crack ◽  
Local Approach ◽  
Ductile Crack Growth ◽  
Comparison Results

The influences of stress triaxiality on ductile fracture have been emphasized to explain the geometry independent fracture resistance characteristics of specimens and structures during past two decades. For the estimation of this material behavior, two-parameter global approach and local approach can be used as case by case manner. Recently, the interests for the local approach and micro-mechanical damage model are increased again due to progress of computational environments. In this paper, the applicability of the local approach has been assessed through a series of finite element analyses incorporating both modified GTN model and Rousselier model. The ductile crack growth behaviors are examined to guarantee the transferability on different sizes and geometries of C(T) specimens and SE(T) specimens. The material fitting constants are determined from calibration of tensile tests and numerical analyses results, and used to simulate the fracture behaviors of typical specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. The comparison results show a good agreement and the two damage models are regarded as promising solutions for ductile crack growth simulation.

Sign in / Sign up

Export Citation Format

Share Document