Investigations on Cleavage Fracture Below and at General Yield

Dünnewald-Arfmann, H.; Twickler, M.; Twickler, R.; Dahl, Winfried

doi:10.1016/b978-0-08-034341-9.50034-6

Cited by 5 publications

(1 citation statement)

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“…The shown temperature dependence of the microscopic cleavage fracture stress may be caused not only by the lower yield stress directly but by the influence of ayS on the size of the process zone. By re-analyzing the datasets of [4] one could take the effect of the volume into consideration by regarding specimens with the same size of the plastic zone at different temperatures. This is possible by changing plastic zone radius, mm - Figure 11.…”

Section: Discussionmentioning

confidence: 99%

Temperature dependence of the microscopic cleavage fracture stress

Jüde-Esser¹,

Grimpe²,

Dahl³

1995

Steel Research

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The microscopic cleavage fracture stress aj which could be responsible for dramatic failure is commonly seen as a temperature independent material property. But a dependence on temperature was found in several former investigations. In this work new studies on cleavage fracture with low carbon steel C 10 were performed. The stress aj = a~r was determined with double-edge notched tensile (DENT) specimens at different temperatures and various crosshead speeds. In addition tests were made with four-point bend specimens (SENB4) according to Griffiths and Owen. A significant influence of temperature on the microscopic cleavage fracture stress was found.The explanation for this result is seen in terms of the thermal activation of dislocation movement, which is needed to produce the critical conditions for fracture. As temperature independence is proposed from the "Local Approach" a check up of this procedure is given and limitations of the "Weakest Link-model" are shown. Temperaturabhangigkeit der mikroskopischen Spaltbruchspannung. FOr das katastrophale Versagen eines Bauteils kann das Erreichen der mikroskopische Spaltbruchspannung aj verantwortlich sein. Aligemein wird diese kritische Spannung als unabhanqiq von Temperatur und Belastungsgeschwindigkeit angesehen. Eigene Untersuchungen hatten jedoch eine Abhanqigkeit von der Temperatur festgestellt. Daher wurden am Stahl C 10 Doppelkerbzugversuche (DENT) Ober einen weiten Temperatur-und Dehngeschwindigkeitsbereich und erqanzend Versuche an Vierpunktbiegeproben (SENB4) durchgefOhrt und mit Hilfe von FE-Rechnungen die mikroskopische Spaltbruchspannung aj = a~ax ermittelt. Die Untersuchungen ergaben eine deutliche Temperaturabhanqlqkelt von ot . Diese Temperaturabhangigkeit wird mit der thermisch aktivierten Versetzungsbewegung begrOndet, die notwendig ist, um die kritischen Bedingungen fOr Spaltbruch herzustellen. Da aus dem "Local Approach" eine Ternperaturunabhanqlqkelt gefolgert wird, wird dessen Aussaqefahlqkelt OberprOft. Die Grenzen des "Weakest Link-Modells" werden aufgezeigt.

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Section: Discussionmentioning

confidence: 99%

Temperature dependence of the microscopic cleavage fracture stress

Jüde-Esser¹,

Grimpe²,

Dahl³

1995

Steel Research

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Institute of Ferrous Metallurgy of the Technical University, RWTH, Aachen - IEHK - Part 4: Division of Materials Engineering

Dahl

1989

Steel Research

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Influence of quench ageing on the cleavage characteristic stress Sco of mild steel

et al. 1993

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The fracture behavior of mild steel A3 was investigated in uniaxial tension at different temperatures using specimens with conditions of annealing and quench ageing treatments respectively. It is indicated that cleavage characteristic stress Sco, is hardly affected by the precipitation of carbides during quench ageing.Catastrophic brittle fracture failure of ferritic steel structures at low temperatures is attributed to transgranular cleavage cracking along well-def'med, low-index crystallographic planes [1]. Consequently the microscopic resistance to cleavage fracture has always appealed to researchers in the field of brittle fracture. Now it is mostly accepted that cleavage cracks propagate to incur brittle fracture when the maximal principal local tensile stress o r j~ " exceeds the well-known microscopic cleavage fracture stress o'~ over some macrostructurally determined characteristic distance, i.e. the critical process zone at a sharp crack [2]. o'~ is considered a temperature-, loading rate-, and specimen geometry-independent material property [1]. However, it has been argued that the value of ~'f changes with temperature [3] and specimen geometry or loading condition [4]. Moreover, experimental data of o', were always larger than the cleavage stresses obtained in plain-tension tests, implying that an unique parameter relating to resistance of steels to cleavage for both plain-tension specimens and notched or cracked ones wouldn't exist. To resolve the dilemma, the prevailing endeavour towards a quantitative description of the cleavage stress has been made based on Weibull statistics [5][6][7]. In contrast with it, a new parameter, Sco, called "cleavage characteristic stress", has been recently proposed to characterize the microscopic resistance to cleavage fracture [4]. To give a definition, Sco is the fracture stress at the brittle-to-ductile transition temperature Tco of steels in plain-tension, below which the yield strength o approximately equals the true fracture stress S t and at • Y .• .which an abrupt curtailment of the ductlhty is observed (Fig. 1). The previous investigations [4,8,9] revealed that Sco by its nature is a critical stress for unblunted primary cracks to propagate across grain boundaries under advantageous conditions; combined with the yield strength, Sco controls the cleavage behavior in both plain-tension and notched or cracked specimens.

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Investigations on Cleavage Fracture Below and at General Yield

Cited by 5 publications

References 5 publications

Temperature dependence of the microscopic cleavage fracture stress

Temperature dependence of the microscopic cleavage fracture stress

Institute of Ferrous Metallurgy of the Technical University, RWTH, Aachen - IEHK - Part 4: Division of Materials Engineering

Influence of quench ageing on the cleavage characteristic stress Sco of mild steel

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