Localized stress relaxation by impression testing

Chu, S. N. G.; Li, J.C.M.

doi:10.1016/0025-5416(80)90222-0

Cited by 36 publications

(4 citation statements)

References 9 publications

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“…Inspired by the uniaxial relationship above, when a flat punch (cylindrical) indenter is employed in the indentation stress relaxation test, we define an effective indentation strain rate as the ratio between the indentation plastic displacement rate and the characteristic depth of the plastic zone (which is comparable to the punch diameter, D [19,20]), that is, εind = ẋind p /D = −ẋ ind e /D, where the indentation elastic displacement rate ẋind e can be calculated as ẋind e = Ḟ ind /S ind with F ind the applied indentation force and S ind the contact stiffness. Similarly, we define an effective applied indentation stress as σ ind = F ind /A, where A is the cross-section area of the flat punch indenter.…”

Section: Resultsmentioning

confidence: 99%

Characterization of strain rate sensitivity and activation volume using the indentation relaxation test

Yue

Chen

2010

J. Phys. D: Appl. Phys.

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We present the possibility of extracting the strain rate sensitivity, activation volume and Helmholtz free energy (for dislocation activation) using just one indentation stress relaxation test, and the approach is demonstrated with polycrystalline copper. The Helmholtz free energy measured from indentation relaxation agrees well with that from the conventional compression relaxation test, which validates the proposed approach. From the indentation relaxation test, the measured indentation strain rate sensitivity exponent is found to be slightly larger, and the indentation activation volume much smaller, than their counterparts from the compression test. The results indicate the involvement of multiple dislocation mechanisms in the indentation test.

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Section: Resultsmentioning

confidence: 99%

Characterization of strain rate sensitivity and activation volume using the indentation relaxation test

Yue

Chen

2010

J. Phys. D: Appl. Phys.

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“…The time dependent penetration depth is recorded, from which the impression velocity is calculated. Previous studies [2][3][4][5][6][7][8][9] have demonstrated that the impression creep test gives similar stress and temperature dependences of the creep behaviour to the conventional creep tests. The advantage of using the impression creep is that multiple impression tests can be made on one sample of small size, which reduces the microstructural variation and offers a simple and inexpensive way for the preparation of samples.…”

Section: Introductionmentioning

confidence: 92%

Impression creep of a Sn60Pb40 alloy: the effect of electric current

Chen¹,

Yang²

2008

J. Phys. D: Appl. Phys.

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Solder joints provide electrical and mechanical interconnections in microelectronic circuits and devices. The mechanical behaviour of the solder joints plays an important role in determining the reliability and lifetime of microelectronic devices. Using the impression technique, the effect of electric current on the creep deformation of a Sn60Pb40 alloy was studied in the temperature range of 323–383 K and under the punching stress of 9.7–110 MPa. During the test, a constant dc electric current was passed through the sample, which introduced electromechanical interaction. A steady state creep was observed under the action of the dc electric current and punching stress. The steady state impression velocity increased with the increase in the electric current for the same punching stress, and the stress dependence of the impression velocity followed Eyring's relation. The apparent activation energy decreased linearly with the square of the electric current due to the increase in atomic mobility driven by the electric current.

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“…The stress relaxation behavior of materials leading to a steady state condition has been observed in other materials. [19][20][21] Thus, in composites with 4 % of volume fractions SiC (nano) produced by mechanical alloying, compacting with a compression force of 620 MPa, and sintering at 873 K, the primary stress relaxation rate decreases due to the creation of immobilized dislocations (pinning at the nano-reinforcement). Correspondingly, the existence of voids (depending on the indenter size) in the form of drops, or more relaxation, are observable in graphs.…”

Section: Methodsmentioning

confidence: 99%

Impression relaxation and creep behavior of Al/SiC nanocomposite

Kakhki

Nategh²,

Mirdamadi³

2016

Mater. Tehnol.

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In the present study, Al-4 % of volume fractions of SiC composites were produced by mechanical alloying and the powders were gradually compacted at a pressure of 620 MPa. The post-compaction samples were sintered under an argon atmosphere at 873 K and the corresponding creep results were obtained from impression-relaxation. Additionally, compression techniques were investigated at high temperature (723 K). Enforcement rates of 8.3 × 10 -3 and 0.83 × 10 -3 mm s -1 and indenter depths of 0.5 mm and 0.8 mm were selected. Results showed a constant relation between stress relaxation and compression creep rate. Under different conditions of impression-relaxation this constant was 1000 for compression stress of 30 MPa and 32.5 MPa, and 400 for compression stress of 35 MPa, subsequently. This coefficient was affected by the porosity and was stable for different indenter depths and enforcement rates. The variations in the steady state relaxation rate were reasonable because of different nano-SiC distributions and porosities in the form of drops. Moreover, in spite of the enforcement rate decrease, the nanosized reinforcing particles caused a decrease of the relaxation rate. It should be mentioned that the constant coefficient calculated will be useful to estimate the fracture time which uses the strain rate calculated from impression-relaxation in industrial applications. Keywords: Al-SiC, creep, impression relaxation, nanocomposite, powder processing V {tudiji so bili izdelani kompoziti Al-4 % volumenskega dele`a SiC z mehanskim legiranjem, prahovi pa so bili postopoma stisnjeni do tlaka 620 MPa. Stisnjeni vzorci so bili nato sintrani v atmosferi argona na 873 K. Iz sprostitve pri vtiskovanju je bila dobljena povezava z rezultati lezenja. Dodatno so bile preiskovane tehnike stiskanja pri visoki temperaturi (723 K). Izbrani sta bili hitrosti vtiskovanja 8,3 × 10 -3 mm s -1 kot tudi 0,83 × 10 -3 mm s -1 pri globini vtiska 0,5 mm in 0,8 mm. Rezultati so pokazali konstanten koeficient med sprostitvijo napetosti in hitrostjo lezenja pri tla~enju. Vrednost konstante je bila pri razli~nih pogojih sprostitve vtiska 1000 pri napetostih stiskanja 30 MPa, 32,5 MPa in 400 pri napetosti stiskanja 35 MPa. Na koeficient vpliva tudi poroznost, stabilen pa je pri razli~nih globinah vtisa in hitrostih vtiskovanja. Tudi rezultati sprostitve so bili ob~utljivi zaradi razli~ne razporeditve SiC nanodelcev in poroznosti v obliki kapljic. Poleg tega, kljub zmanj{evanju hitrosti vtiskovanja, nanoutrjevalci zmanj{ajo hitrost sprostitve. Pomembno je omeniti, da bo iz hitrosti obremenjevanja in spro{~anja pri vtiskovanju izra~unani konstantni koeficient uporaben za napovedovanje~asa poru{itve pri industrijski uporabi. Klju~ne besede: Al-SiC, lezenje, sprostitev pri vtiskovanju, nanokompozit, obdelava prahu

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Localized stress relaxation by impression testing

Cited by 36 publications

References 9 publications

Characterization of strain rate sensitivity and activation volume using the indentation relaxation test

Characterization of strain rate sensitivity and activation volume using the indentation relaxation test

Impression creep of a Sn60Pb40 alloy: the effect of electric current

Impression relaxation and creep behavior of Al/SiC nanocomposite

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