Dynamic Effects in Hopkinson Bar Four-Point Bend Fracture

Jiang, Fengchun; Vecchio, Kenneth S.

doi:10.1007/s11661-007-9301-8

“…Clearly, the peak load varies as a function of wedge length, and it increases with increasing wedge length, the loading bar with wedge length of 40 mm has a maximum load compared to others. For the case of the loading bar without wedge, theoretically speaking, there should be no oscillations in load-time re- sponse curve created, while the oscillations with relatively large amplitude are still seen at the initial time of the load vs. time response, which are ProchhammerChree oscillations [8], the inherent nature of the stress wave propagation along the elastic bar even in pulseshaped Hopkinson bar test. The loading-point displacement can be experimentally measured using the incident and reflected pulses via Eq.…”

Section: Effect Of Wedge Length On Load and Displacement Responsementioning

confidence: 95%

“…However, the Hopkinson bar loading experimental technique that can be used to study various dynamic fracture properties of materials under a stress-intensity factor rate ∼ 10 6 MPa m 1/2 s −1 are still being developed [2][3][4][5][6][7][8]. The one-bar (one incident loading bar)/three-point bending (3PB) impact setup [9][10][11][12][13][14][15][16] is currently the most popular setup used to determine the dynamic fracture toughness of materials under stress wave loading, since this loading configuration has some advantages: (1) the loading rate acquired in such one-bar/3PB loaded fracture test is higher than that in Charpy impact test [17][18][19][20][21][22][23][24][25][26]; (2) the dynamic response of fracture specimen can be determined via *Corresponding author: tel.…”

Section: Introductionmentioning

confidence: 99%

“…Using these two stress pulses, the dynamic load and loadingpoint displacement of the fracture specimen are determined and employed for calculating the dynamic stress intensity factor [5]. Combined with the crack initiating time of fracture specimen detected using an adequate method, the dynamic fracture toughness is then measured using above-mentioned procedure [7][8]14]. It is clear that the accuracy of the measurement of dynamic fracture toughness is influenced by the dynamic stress intensity factor determined by two global mechanic parameters: dynamic load and displacement.…”

Section: Introductionmentioning

confidence: 99%

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Effect of loading wedge length on the propagation of stress pulse in Hopkinson bar apparatus

GUO¹,

WANG²,

SHEN³

et al. 2021

km

0

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In order to study the effect of the loading wedge length on the propagation behavior of stress pulse in a Hopkinson bar loaded fracture test, non-uniform loading bars with different wedge lengths of 0, 3, 15.5 and 40 mm have been machined from a certain rod. The Hopkinson bar loading experiment is performed on one-bar/three-point bend fracture loading system without the bending specimen to avoid the effect of specimen configuration on the reflected pulse. The results indicate that the high-frequency oscillations of the reflected pulse are enhanced and the rise time of the reflected pulse increased with increasing wedge length, i.e. the dispersion effect becomes seriously with increasing wedge length. As a consequence, the oscillations in the load-time curves determined using the incident and reflected pulses are more severe for the wedge with larger length. The loading-point displacements calculated are identical when the wedge lengths are 0 and 3 mm. Therefore, to decrease the effect of wedge length on stress pulse propagation and to make the loading interface linear contact with a specimen, the wedge length should be designed as small as possible.K e y w o r d s : Hopkinson pressure bar, wedge-shaped, non-uniform, stress pulse

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“…In a study of a C45 low carbon steel, Klepaczko [10] observes a minimum of the plane strain fracture toughness at 10 4 MPa √ ms −1 . Furthermore, Klepaczko [11] points out that low strain hardening favours the formation of a minimum fracture toughness at high loading rates.…”

Section: Introductionmentioning

confidence: 99%

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

Henschel

¹

,

Krüger

²

2015

EPJ Web of Conferences

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Abstract. Dynamic crack initiation with crack-tip loading rates ofK ≈ 2 · 10 6 MPa √ ms −1 in a high strength G42CrMoS4 steel was investigated. To this end, a previously developed split Hopkinson pressure bar with four-point bending was utilised. Vnotched and pre-cracked Charpy specimens were tested. The detection of dynamic crack initiation was performed by analysing the dynamic force equilibrium between the incident and the transmission bar. Additionally, the signal of a near-field strain gauge and high-speed photography were used to determine the instant of crack initiation. To account for vibrations of the sample, a dynamic analysis of the stress intensity factor was performed. The dynamic and static analyses of the tests produced nearly the same results when a force equilibrium was achieved. Fracture-surface analysis revealed that elongated MnS inclusions strongly affected both the dynamic crack initiation and growth. Blunting of the precrack did not take place when a group of MnS inclusions was located directly at the precrack tip. Due to the direction of the elongated MnS inclusions perpendicular to the direction of crack growth, the crack could be deflected. The comparison with a 42CrMo4 steel without elongated MnS inclusions revealed the detrimental effect in terms of resistance to crack initiation. Taking the loading-rate dependency into consideration, it was shown that there was no pronounced embrittlement due to the high loading rates.

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“…[1][2][3][4][5]. It enables the determination of forces and displacements on both the loading and support faces of the specimen [4,5].…”

Section: Introductionmentioning

confidence: 99%

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

Henschel

¹

,

Krüger

²

2016

View full text Add to dashboard Cite

Abstract. Dynamic crack initiation with crack-tip loading rates ofK ≈ 2 · 10 6 MPa √ ms −1 in a high strength G42CrMoS4 steel was investigated. To this end, a previously developed split Hopkinson pressure bar with four-point bending was utilised. Vnotched and pre-cracked Charpy specimens were tested. The detection of dynamic crack initiation was performed by analysing the dynamic force equilibrium between the incident and the transmission bar. Additionally, the signal of a near-field strain gauge and high-speed photography were used to determine the instant of crack initiation. To account for vibrations of the sample, a dynamic analysis of the stress intensity factor was performed. The dynamic and static analyses of the tests produced nearly the same results when a force equilibrium was achieved. Fracture-surface analysis revealed that elongated MnS inclusions strongly affected both the dynamic crack initiation and growth. Blunting of the precrack did not take place when a group of MnS inclusions was located directly at the precrack tip. Due to the direction of the elongated MnS inclusions perpendicular to the direction of crack growth, the crack could be deflected. The comparison with a 42CrMo4 steel without elongated MnS inclusions revealed the detrimental effect in terms of resistance to crack initiation. Taking the loading-rate dependency into consideration, it was shown that there was no pronounced embrittlement due to the high loading rates.

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Dynamic Effects in Hopkinson Bar Four-Point Bend Fracture

Cited by 20 publications

References 38 publications

Effect of loading wedge length on the propagation of stress pulse in Hopkinson bar apparatus

Effect of loading wedge length on the propagation of stress pulse in Hopkinson bar apparatus

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

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