Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement

Matti Valo, Tapio Planman, Kim Wallin

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

In fracture toughness tests, the energy absorbed by the specimen is calculated from load versus load point displacement data. If tests are made with small CT-specimens, direct measurement of load point displacement is often not possible due to small specimen dimensions; subsequently, specimen displacement is measured on the front face of the specimen. The measured displacement is transferred into load point displacement with the help of a geometric rotation point concept. The measurements were performed with miniature CT-specimens of dimensions B = 4 mm, W = 8 mm having the integral clip seated on the specimen front face. The location of the rotation point was concluded from the measured initial compliance by applying the rotation point values of r = 0.5 and r = 0.13 and by comparing the calculated crack lengths with the measured crack lengths. The value of r = 0.5 was observed to be too high and the value r = 0.13 produced the measured crack lengths accurately. A linear combination of elastic and plastic deformations is proposed to be used for calculating the location of the rotation point outside the elastic loading range. The load line load–displacement curves were derived and the measured KJC-values were calculated with the assumptions r = 0.5 and with the linear combination described in the paper. The linear combination believed to be more relevant than the value r = 0.5 resulted in lower KJC-values than r = 0.5. However, the difference was only about 1.6 % in KJC-values, which changes the T0 values approximately by 1°C. Hence, the measured KJC-values are not sensitive to the exact location of the rotation point used in the analysis.
Original languageEnglish
Title of host publicationSmall Specimen Test Techniques
PublisherAmerican Society for Testing and Materials ASTM
Pages110-120
Volume6
ISBN (Print)978-0-8031-7597-6
DOIs
Publication statusPublished - 2015
MoE publication typeA4 Article in a conference publication
Event6th International Symposium on Small Specimen Test Techniques - Houston, United States
Duration: 29 Jan 201431 Jan 2014
Conference number: 6

Publication series

NameSelected Technical Papers
PublisherASTM
Volume1576
ISSN (Print)1949-4572

Conference

Conference6th International Symposium on Small Specimen Test Techniques
CountryUnited States
CityHouston
Period29/01/1431/01/14

Fingerprint

Cracks
Elastic deformation
Fracture toughness
Plastic deformation
Compliance

Keywords

  • fracture toughness test
  • miniature CT specimen
  • off-load line deflection
  • rotation point

Cite this

Valo, M., Planman, T., & Wallin, K. (2015). Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement. In Small Specimen Test Techniques (Vol. 6, pp. 110-120). American Society for Testing and Materials ASTM. ASTM Selected Technical Papers, Vol.. 1576 https://doi.org/10.1520/STP157620140010
Valo, Matti ; Planman, Tapio ; Wallin, Kim. / Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement. Small Specimen Test Techniques. Vol. 6 American Society for Testing and Materials ASTM, 2015. pp. 110-120 (ASTM Selected Technical Papers, Vol. 1576).
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abstract = "In fracture toughness tests, the energy absorbed by the specimen is calculated from load versus load point displacement data. If tests are made with small CT-specimens, direct measurement of load point displacement is often not possible due to small specimen dimensions; subsequently, specimen displacement is measured on the front face of the specimen. The measured displacement is transferred into load point displacement with the help of a geometric rotation point concept. The measurements were performed with miniature CT-specimens of dimensions B = 4 mm, W = 8 mm having the integral clip seated on the specimen front face. The location of the rotation point was concluded from the measured initial compliance by applying the rotation point values of r = 0.5 and r = 0.13 and by comparing the calculated crack lengths with the measured crack lengths. The value of r = 0.5 was observed to be too high and the value r = 0.13 produced the measured crack lengths accurately. A linear combination of elastic and plastic deformations is proposed to be used for calculating the location of the rotation point outside the elastic loading range. The load line load–displacement curves were derived and the measured KJC-values were calculated with the assumptions r = 0.5 and with the linear combination described in the paper. The linear combination believed to be more relevant than the value r = 0.5 resulted in lower KJC-values than r = 0.5. However, the difference was only about 1.6 {\%} in KJC-values, which changes the T0 values approximately by 1°C. Hence, the measured KJC-values are not sensitive to the exact location of the rotation point used in the analysis.",
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Valo, M, Planman, T & Wallin, K 2015, Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement. in Small Specimen Test Techniques. vol. 6, American Society for Testing and Materials ASTM, ASTM Selected Technical Papers, vol. 1576, pp. 110-120, 6th International Symposium on Small Specimen Test Techniques, Houston, United States, 29/01/14. https://doi.org/10.1520/STP157620140010

Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement. / Valo, Matti; Planman, Tapio; Wallin, Kim.

Small Specimen Test Techniques. Vol. 6 American Society for Testing and Materials ASTM, 2015. p. 110-120 (ASTM Selected Technical Papers, Vol. 1576).

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

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N2 - In fracture toughness tests, the energy absorbed by the specimen is calculated from load versus load point displacement data. If tests are made with small CT-specimens, direct measurement of load point displacement is often not possible due to small specimen dimensions; subsequently, specimen displacement is measured on the front face of the specimen. The measured displacement is transferred into load point displacement with the help of a geometric rotation point concept. The measurements were performed with miniature CT-specimens of dimensions B = 4 mm, W = 8 mm having the integral clip seated on the specimen front face. The location of the rotation point was concluded from the measured initial compliance by applying the rotation point values of r = 0.5 and r = 0.13 and by comparing the calculated crack lengths with the measured crack lengths. The value of r = 0.5 was observed to be too high and the value r = 0.13 produced the measured crack lengths accurately. A linear combination of elastic and plastic deformations is proposed to be used for calculating the location of the rotation point outside the elastic loading range. The load line load–displacement curves were derived and the measured KJC-values were calculated with the assumptions r = 0.5 and with the linear combination described in the paper. The linear combination believed to be more relevant than the value r = 0.5 resulted in lower KJC-values than r = 0.5. However, the difference was only about 1.6 % in KJC-values, which changes the T0 values approximately by 1°C. Hence, the measured KJC-values are not sensitive to the exact location of the rotation point used in the analysis.

AB - In fracture toughness tests, the energy absorbed by the specimen is calculated from load versus load point displacement data. If tests are made with small CT-specimens, direct measurement of load point displacement is often not possible due to small specimen dimensions; subsequently, specimen displacement is measured on the front face of the specimen. The measured displacement is transferred into load point displacement with the help of a geometric rotation point concept. The measurements were performed with miniature CT-specimens of dimensions B = 4 mm, W = 8 mm having the integral clip seated on the specimen front face. The location of the rotation point was concluded from the measured initial compliance by applying the rotation point values of r = 0.5 and r = 0.13 and by comparing the calculated crack lengths with the measured crack lengths. The value of r = 0.5 was observed to be too high and the value r = 0.13 produced the measured crack lengths accurately. A linear combination of elastic and plastic deformations is proposed to be used for calculating the location of the rotation point outside the elastic loading range. The load line load–displacement curves were derived and the measured KJC-values were calculated with the assumptions r = 0.5 and with the linear combination described in the paper. The linear combination believed to be more relevant than the value r = 0.5 resulted in lower KJC-values than r = 0.5. However, the difference was only about 1.6 % in KJC-values, which changes the T0 values approximately by 1°C. Hence, the measured KJC-values are not sensitive to the exact location of the rotation point used in the analysis.

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KW - off-load line deflection

KW - rotation point

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SN - 978-0-8031-7597-6

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BT - Small Specimen Test Techniques

PB - American Society for Testing and Materials ASTM

ER -

Valo M, Planman T, Wallin K. Rotation Point and KJC Estimations for Miniature CT-Specimens Based on Off-Load Line Displacement. In Small Specimen Test Techniques. Vol. 6. American Society for Testing and Materials ASTM. 2015. p. 110-120. (ASTM Selected Technical Papers, Vol. 1576). https://doi.org/10.1520/STP157620140010