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.

Study on Dimensional Tolerances Required for Miniature C(T) Specimens

2015 ◽  
Author(s):  
Naoki Miura ◽  
Yasunori Momoi ◽  
Masato Yamamoto
Keyword(s):  
Equivalent Stress ◽  
Three Dimensional ◽  
Direct Determination ◽  
Reference Temperature ◽  
Surveillance Program ◽  
Specimen Thickness ◽  
Irradiation Embrittlement ◽  
Element Analysis ◽  
Three Dimensional Finite Element ◽  
Present Standard

The Master Curve approach using the miniature C(T) specimens with 4 mm-thickness is a promising method 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. The dimensional tolerances of standard C(T) specimens are relatively provided in the present standard, ASTM E1921, consequently, absolute dimensional tolerances are severer for smaller specimens. In this paper, the effect of the tolerances of key dimensions on the elastic-plastic equivalent stress intensity factor derived from the J-integral, KJ, was calculated using three-dimensional finite element analysis. Even if the dimensional tolerances for the miniature C(T) specimens based on the present standard were mitigated in some degree (as examples, the tolerance of specimen thickness of ±0.08 mm was mitigated to ±0.1 mm, the tolerance of specimen width of ±0.04 mm was mitigated to ±0.1 mm), the variations of KJ and reference temperature were negligibly small. The use of the mitigated dimensional tolerances with adequate accuracy of fracture toughness evaluation was ascertained.

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.

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.

Experimental Observation of Front-Face-Displacement and Load-Line-Displacement in CT and Bend Specimens During Fracture Toughness Tests

2009 ◽  
Author(s):  
Bong-Sang Lee ◽  
Sang-Yoon Park ◽  
Min-Chul Kim
Keyword(s):  
Fracture Toughness ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Front Face ◽  
Analytical Relationship ◽  
Conservative Estimate ◽  
Crack Mouth ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement

The master curve method described in ASTM E1921 provides a tool for using small specimens such as sub-sized CT and PCVN specimens for standard fracture toughness testing. However, a direct measurement of the load-line displacement of small specimens is not practical for standard fracture toughness tests. Mostly, the front-face displacement or the crack mouth opening displacement can be measured and converted into the load-line displacement by using an analytical relationship proposed by several investigators. Since those relationships were deduced from numerical calculations of the loaded specimens, experimental deviations may occur because of specimen indentation, rotation and arm bending during an actual testing. It is clear that the determination of fracture toughness is influenced by the accuracy of the estimation of load-line displacement as well as the load measurement. In this study, the relationship between the load-line displacement and the front-face displacement or the crack mouth displacement was investigated experimentally by using a series of CT and Bend specimens modified to measure the two displacements simultaneously during a single test. The results showed that the front-face measurement of CT specimens may result in about 3% more conservative estimate of fracture toughness. In the case of bend specimens, the crack mouth opening displacement measurement may result in about 7% non-conservative estimate of fracture toughness than the load-line measurement.

Study on Dimensional Tolerances Required for Miniature C(T) Specimens

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Naoki Miura ◽  
Yasunori Momoi ◽  
Masato Yamamoto
Keyword(s):  
Equivalent Stress ◽  
Three Dimensional ◽  
Reference Temperature ◽  
Surveillance Program ◽  
Specimen Thickness ◽  
Irradiation Embrittlement ◽  
Element Analysis ◽  
Dimensional Finite Element ◽  
Key Dimensions ◽  
Three Dimensional Finite Element

The Master Curve approach using miniature C(T) specimens with 4 mm thickness is promising for directly determining the reference temperature of reactor pressure vessel (RPV) steels because they can be taken from the broken halves of the Charpy specimens used in the surveillance program to monitor neutron irradiation embrittlement. The relative dimensional tolerances of standard C(T) specimens are provided in the present ASTM E1921 standard; consequently, the absolute dimensional tolerances are stricter for smaller specimens. In this study, the effect of the tolerances of key dimensions on the elastic–plastic equivalent stress intensity factor derived from the J-integral, KJ, was calculated using three-dimensional finite-element analysis. Even if the dimensional tolerances for the miniature C(T) specimens based on the present standard were mitigated in some degree (as examples, the tolerance of specimen thickness of ±0.08 mm was mitigated to ±0.1 mm; and the tolerance of specimen width of ±0.04 mm was mitigated to ±0.1 mm), the variations of KJ and the reference temperature were negligibly small. Furthermore, the use of the mitigated dimensional tolerances with adequate accuracy for evaluating the fracture toughness was ascertained.

Effect of Defect on Elastic/Plastic and Creep Behavior of Bone: A Finite Element Study

2007 ◽  
Author(s):  
A. Ajdari ◽  
P. K. Canavan ◽  
H. Nayeb-Hashemi ◽  
G. Warner
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Trabecular Bone ◽  
Fatigue Loading ◽  
Dimensional Structure ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Local Bone ◽  
Osteoporotic Vertebral Fractures

Three-dimensional structure of trabecular bone can be modeled by 2D or 3D Voronoi structure. The effect of missing cell walls on the mechanical properties of 2D honeycombs is a first step towards understanding the effect of local bone resorption due to osteoporosis. In patients with osteoporosis, bone mass is lost first by thinning and then by resorption of the trabeculae [1]. Furthermore, creep response is important to analyze in cellular solids when the temperature is high relative to the melting temperature. For trabecular bone, as body temperature (38 °C) is close to the denaturation temperature of collagen (52 °C), trabecular bone creeps [1]. Over the half of the osteoporotic vertebral fractures that occur in the elderly, are the result of the creep and fatigue loading associated with the activities of daily living [2]. The objective of this work is to understand the effect of missing walls and filled cells on elastic-plastic behavior of both regular hexagonal and non-periodic Voronoi structures using finite element analysis. The results show that the missing walls have a significant effect on overall elastic properties of the cellular structure. For both regular hexagonal and Voronoi materials, the yield strength of the structure decreased by more than 60% by introducing 10% missing walls. In contrast, the results indicate that filled cells have much less effect on the mechanical properties of both regular hexagonal and Voronoi materials.

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