Dynamic J-Integral Evaluation of Three-Point-Bend Beams with Various Geometrical Dimensions

2011 ◽  
Vol 488-489 ◽  
pp. 630-633
Author(s):  
Marius Gintalas ◽  
Antanas Žiliukas ◽  
Kaspars Kalniņš
Keyword(s):  
Fracture Toughness ◽  
Plastic Material ◽  
Rectangular Cross Section ◽  
Estimation Method ◽  
Displacement Curve ◽  
Elastic Plastic ◽  
Load Line ◽  
Load Line Displacement ◽  
Specimen Test

J-Integral is the main effective and commonly used tool for cracked elastic-plastic material resistance assessment. Determination of fracture toughness under impact loading conditions is related with problems of crack length measurement. Nevertheless, current experimental techniques restrict the specimen’s geometry taking into account span and height ratio, which is equal to four. Evaluation of fracture toughness estimation method which requires only experimental load-line displacement curve of single specimen is research object of dynamic fracture mechanics. This article proposes an approach of impact fracture toughness determination of elastic-plastic steel from single any size specimen test. Load-line displacement data obtained from three-point-bending tests of rectangular cross section specimens with V form single edge notch was used for J-integral calculation. Five series of specimens with different geometry were manufactured from ductile steel and tested.

Determination of J-Integral Using the Load-COD Record for Circumferential Through-Wall Cracked Pipes

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Nam-Su Huh ◽  
Yun-Jae Kim
Keyword(s):  
Crack Opening ◽  
Estimation Method ◽  
J Integral ◽  
Opening Displacement ◽  
Element Analysis ◽  
Load Line ◽  
Load Line Displacement ◽  
Η Factor ◽  
J Estimation

The present paper provides experimental J estimation equation based on the load-crack opening displacement (COD) record for testing the circumferential through-wall cracked pipe under combined tension and bending. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic η-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks (small crack angle), whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

Scaling of Pop-Ins During Brittle Fracture Testing

2019 ◽  
Author(s):  
O. J. Coppejans ◽  
C. L. Walters
Keyword(s):  
Fracture Toughness ◽  
Analytical Method ◽  
Offshore Structures ◽  
Specimen Size ◽  
Small Scale ◽  
Unstable Fracture ◽  
Displacement Curve ◽  
Fracture Toughness Test ◽  
Key Factor

Abstract Measurement of the fracture toughness of steel is important for the assurance of the safety of ships and offshore structures, especially when these structures are made of thick sections and/or applied in cold environments. One key factor that will affect the determination of the fracture toughness is a pop-in, which is a short event in which unstable fracture is initiated and then self-arrests. If the pop-in is large enough, it will be used to calculate the fracture toughness. Pop-ins are believed to be the products of local brittle zones, which occur randomly at crack tips and have finite sizes. Fracture toughness testing codes have ways of determining whether a pop-in is critical (thus, identifying the maximum force and displacement to be used in the determination of the toughness of the material) or not important (thus, allowing for the test to proceed). In an ongoing project on the use of small-scale fracture specimens to predict standard fracture toughness test results, we would like to know how pop-in acceptance criteria should be scaled for specimen size. It is expected that the physical size of the brittle zones that cause pop-ins is invariant of specimen size, meaning that the contribution of the pop-in will be proportionally more important for smaller specimens. An analytical method for relating the pop-ins on one specimen size to another specimen size is developed. This method is partially verified by observations on the size of a local brittle zone observed on a fracture surface and the effect of that pop-in on the force-displacement curve during a CTOD test. The analytical method showed that an equivalent pop-in for a small-scale specimen is indeed larger, but that the effect was subtle.

A Study on the Estimation of Fracture Behaviour for a Circumferentially Through-Wall Cracked Pipe

2007 ◽  
Vol 120 ◽  
pp. 15-20
Author(s):  
Weon Keun Song ◽  
Jae Sil Park
Keyword(s):  
Fracture Behavior ◽  
Standard Specimen ◽  
Separation Method ◽  
Experimental Results ◽  
Displacement Curve ◽  
Fracture Test ◽  
Load Line ◽  
Load Line Displacement ◽  
Load Separation ◽  
Geometry Function

It is known that fracture characteristics are changed due to the geometric configuration. Also, it is known that toughness data obtained from the standard specimen test are conservative to predict fracture behavior of the real piping. Thus fracture behavior by tests of pipes would to be applied to the integrity evaluation for the piping system. However, fracture test with real pipe is not only difficult to perform but also very expensive, and requires lots of experience. So an estimation method of pipe’s fracture behavior is necessary to solve this problem. The objective of this thesis is to propose a method to estimate the fracture behavior of a pipe from the result of the standard specimen fracture test. For this, fracture tests for standard specimens and pipes are conducted. The resultant load - load-line displacement record of the standard specimen was transformed to that of a pipe by load separation method. To begin with, the load versus load-line displacement curve of a standard specimen extracted from a pipe is normalized by a geometry function of the CT specimen. Then this normalized curve was converted to pipe’s load versus displacement curve by a geometry function of pipe. To verify the constraint factor and the geometric function of pipe, finite element analyses were performed. To demonstrate the proposed method, experimental results of pipes are compared with predicted results. Calculated results from CT specimens are similar to experimental results of pipes. Therefore the transformability from a CT specimen to a pipe by load separation method is proved. Consequently the applicability of the proposed method was proved.

Experimental Determination of Elastic and Plastic LLD Rates During Creep Crack Growth Testing

2017 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
K. M. Nikbin ◽  
D. W. Dean
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Current Method ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement ◽  
Final Failure ◽  
Complex Crack

Elastic and plastic load line displacement (LLD) rates are often ignored when analyzing Creep Crack Growth (CCG) tests due to difficulties in accurately determining their value for complex crack morphologies typical of creep. Instead, the total LLD rate is assumed to be entirely due to creep. This simplistic approach overestimates the crack tip characterizing parameter C* which is non-conservative. This paper presents a review of the current method of interpreting CCG test data in ASTM E1457 and proposes an improved approach which accounts for the elastic and plastic LLD rates. Estimations of the elastic and plastic LLD rate are obtained from a partial unload immediately after load-up and a full unload, at the end of the test, prior to final failure. Some finite element validation of this method is presented. Implementing this approach will facilitate more realistic CCG laws.

Relation Between Front-Face and Load-Line Displacements on a C(T) Specimen by Elastic-Plastic Analysis

2015 ◽  
Author(s):  
Naoki Miura ◽  
Yasunori Momoi ◽  
Masato Yamamoto
Keyword(s):  
Conversion Factor ◽  
Direct Determination ◽  
Front Face ◽  
Surveillance Program ◽  
Irradiation Embrittlement ◽  
Element Analysis ◽  
Razor Blade ◽  
Elastic Plastic ◽  
Load Line ◽  
Load Line Displacement

The use of miniature C(T) specimens makes it possible for the direct determination of the reference temperature of reactor pressure vessel steels, because they can be taken from the broken halves of the Charpy specimens used for surveillance program to monitor neutron irradiation embrittlement. Fracture toughness tests using C(T) specimens usually need the measurement of load-line displacement, however, it is difficult to mount a clip gauge inside the miniature specimen due to the limitation of the specimen size. A pair of knife edges is machined at the front face of the miniature C(T) specimen to mount a clip gauge with razor blade tips, and the front-face displacement is translated to the load-line displacement. When front-face displacement measurements are made, the load-line displacement can be inferred by multiplying the measured values by the constant 0.73. This conversion factor has been simply derived from the assumption of the linear deformation around a supposed point of rotation. In this study, the conversion factor was directly evaluated by using a three-dimensional elastic-plastic finite element analysis for the miniature C(T) specimens, and the adequacy of the conversion factor was investigated.

The determination of fracture toughness for a porous elastic-plastic solid

1987 ◽  
Vol 33 (2) ◽  
pp. 111-124
Author(s):  
A. Jagota ◽  
C. Y. Hui ◽  
P. R. Dawson
Keyword(s):  
Fracture Toughness ◽  
Elastic Plastic

An X-Specimen Test for Determination of Thin-Walled Tube Fracture Toughness

2009 ◽  
pp. 214-214-13 ◽  
Author(s):  
HH Hsu ◽  
KF Chien ◽  
HC Chu ◽  
RC Kuo ◽  
PK Liaw
Keyword(s):  
Fracture Toughness ◽  
Thin Walled Tube ◽  
Specimen Test ◽  
Thin Walled
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