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Research Papers: Materials and Fabrication

Evaluation of the Influence of Residual Stresses on Ductile Fracture

[+] Author and Article Information
Tobias Bolinder

Inspecta Technology AB,
Stockholm 112 18, Sweden
e-mail: tobias.bolinder@inspecta.com

Jonas Faleskog

Department of Solid Mechanics,
KTH Engineering Sciences,
Royal Institute of Technology,
Stockholm 100 44, Sweden
e-mail: faleskog@kth.se

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 21, 2011; final manuscript received May 8, 2015; published online August 6, 2015. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 137(6), 061408 (Aug 06, 2015) (9 pages) Paper No: PVT-11-1191; doi: 10.1115/1.4030655 History: Received October 21, 2011

In this work, the significance of residual stresses on ductile fracture is investigated by a set of experiments that are analyzed by finite element simulations. The treatment of residual stresses as expressed in fracture assessment procedures such as R6 is believed to be very conservative for ductile materials, when fracture occurs at high primary loads. Earlier numerical studies have reinforced this belief. This is supported in the current study. Tests on notched 3PB specimens with and without residual stresses were conducted on two ferritic steels. The residual stresses were introduced by applying a compressive preload on notched specimens. The tests were designed to achieve crack initiation at load levels around the plastic limit load. The crack growth in the tests was measured by a compliance method and by color marking of the crack surface. The crack tip driving force J was evaluated numerically for specimens with and without residual stresses. The experimental results show that the residual stresses clearly contribute to J at low primary loads. However, this contribution diminishes as the primary loads increase. The experimental results were also compared with results evaluated using the R6 procedure. These comparisons revealed overly high conservatism in R6 for cases with residual stresses compared to the ones for cases without residual stresses where less conservatism was evident.

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References

Figures

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Fig. 1

Base geometry of test specimen

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Fig. 2

Stresses normal to crack surface after preloading

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Fig. 3

Picture of middle section of the crack surface from a test specimen, showing the different crack fronts created by coloring and fatigue loading

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Fig. 4

Stress strain data from cyclic test compared with FEM predictions for Weldox 700

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Fig. 5

True stress–strain data from uni-axial tension test and data used in FE-models for A533B-1

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Fig. 6

Knife edge height e defined as the distance between specimen and points of measurement of CMOD

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Fig. 7

Experimental P-CMOD curves compared with FEM results for specimens with and without residual stresses, Material Weldox 700

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Fig. 8

Example of J-CMOD curves used in evaluating the J-integral from the experiments, specimen without residual stresses, material A533B-1

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Fig. 9

J-values calculated by abaqus and J-modified script for specimen from test program 3 with residual stresses at different primary load levels

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Fig. 10

The J-integral results versus crack growth for specimens with and without residual stresses

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Fig. 11

The J-integral results versus Lr for specimens with and without residual stresses

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Fig. 12

The J-integral results versus crack growth for specimens with and without residual stresses

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Fig. 13

The J-integral results versus Lr for specimens with and without residual stresses

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Fig. 14

The J-integral results versus crack growth for specimens with and without residual stresses

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Fig. 15

The J-integral results versus Lr for specimens with and without residual stresses

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Fig. 16

Different R6 curves used in the comparison with the experimental results

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Fig. 17

Estimated J results for test program 1 using the option 1 curve, normalized with experimentally evaluated J results, material Weldox 700

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Fig. 18

Estimated J results for test program 2 using the option 1 curve, normalized with experimentally evaluated J results, material Weldox 700

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Fig. 19

Estimated J results for test program 3 using the option 1 curve, normalized with experimentally evaluated J results, material A533B-1

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Fig. 20

Estimated J results for test program 1 using the option 2 curve, normalized with experimentally evaluated J results, material Weldox 700

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Fig. 21

Estimated J results for test program 2 using the option 2 curve, normalized with experimentally evaluated J results, material Weldox 700

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Fig. 22

Estimated J results for test program 3 using the option 2 curve, normalized with experimentally evaluated J results, material A533B-1

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