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Research Papers: Design and Analysis

Assessment of Fracture Toughness Using Small Punch Tests of Prenotched Specimens

[+] Author and Article Information
Yangyan Zheng

School of Mechanical and Power Engineering,
Nanjing Tech University,
Nanjing 210028, China;
Special Equipment Safety Supervision
Inspection Institute,
Jiangsu 210036, China
e-mail: yangyanz@hotmail.com

Xiao Chen

School of Mechanical and Power Engineering,
Nanjing Tech University,
Nanjing 210028, China;
Special Equipment Safety Supervision
Inspection Institute,
Jiangsu 210036, China

Zheng Yang

School of Mechanical and Power Engineering,
Nanjing Tech University,
Nanjing 210028, China

Xiang Ling

School of Mechanical and Power Engineering,
Nanjing Tech University,
Nanjing 210028, China
e-mail: xling@njtech.edu.cn

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 12, 2017; final manuscript received June 2, 2017; published online August 2, 2017. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 139(5), 051205 (Aug 02, 2017) (7 pages) Paper No: PVT-17-1012; doi: 10.1115/1.4037046 History: Received January 12, 2017; Revised June 02, 2017

In this paper, line- and ring-notched small punch test (SPT) specimens were studied; a three-dimensional (3D) model of a ring-notched SPT specimen was established using the contour integral method, and the validity of the model was verified using ring-notched specimens. The stress and strain fields were analyzed using numerical simulations of a ring-notched SPT specimen, and the change in the stress gradient during deformation was considered. To verify the finite element model, the results of the numerical simulations were compared with those of three-point bending tests and a Gurson–Tvergaard–Needleman (GTN) model. Compared with the line-notched specimen, the ring-notched specimen was more suitable for notch propagation analysis and fracture toughness evaluation. The results of the numerical simulations were in good agreement with those of the experiments, which showed that the numerical model used in this study was correct. For a notch that initiated when the load reached its maximum value, the value of the J integral was 335 × 10−6 kJ/mm2, and at time 0.85Pmax, the value of the J integral was 201 × 10−6 kJ/mm2, and the difference from the result of the three-point bending test was 14.4%. For a notch that initiated during the stretching deformation stage, the relevant fracture toughness was 225 × 10−6 kJ/mm2, and the difference from the result of the three-point bending test was 3%.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

The specimen of SPT

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Fig. 2

Schematic diagram of SPT device

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Fig. 3

True stress and strain curve of Q345R

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Fig. 4

Two differently notched SPT specimens

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Fig. 5

The morphology of the normal SPT specimen after fracture (see color figure online)

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Fig. 6

The morphology of the ring-notched SPT specimen after fracture (see color figure online)

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Fig. 7

The morphology of the line-notched SPT specimen after fracture

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Fig. 8

Comparison of load–deformation curves for three types of sample

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Fig. 9

3D model of a notched SPT specimen

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Fig. 10

Hexahedron of 20 nodes collapsed to a surface

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Fig. 11

Hexahedron of 27 nodes collapsed to a surface

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Fig. 12

Comparison of the experimental and numerical load–displacement curves

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Fig. 13

Distribution of the stress field of a ring-notched SPT specimen

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Fig. 14

Distribution of the strain field of a notched SPT specimen

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Fig. 16

The value of void volume fraction compared to the load–displacement curve

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