Abstract:Numerical simulation is carried out to investigate the effect of loading rate on dynamic fracture initiation toughness including the crack-tip constraint. Finite element analyses are performed for a single edge cracked plate whose crack surface is subjected to uniform pressure with various loading rate. The first three terms in the Williams' asymptotic series solution is utilized to characterize the crack-tip stress field under dynamic loads. The coefficient of the third term in Williams' solution, A 3 , was u… Show more
“…Thus, the observed increase in crack initiation toughness is attributed to the time required to reach a critical stress state ahead of the crack tip over a critical distance. The similar investigations on the effect of loading rate were conducted by Kalthoff (1986) who predicted the existence of an incubation time for crack initiation and by Kim and Chao (2007) who proposed a crack-tip constraint model. Liu et al (1998) analytically modelled the experimental measurements of Ravi-Chandar and Knauss (1984a) for Homalite-100 material by estimating the critical SIF on the basis of different critical distance δ.…”
An experimental investigation is conducted to study the quasi-static and dynamic fracture behaviour of sedimentary, igneous and metamorphic rocks. The notched semi-circular bending method has been employed to determine fracture parameters over a wide range of loading rates using both a servo-hydraulic machine and a split Hopkinson pressure bar. The time to fracture, crack speed and velocity of the flying fragment are measured by strain gauges, crack propagation gauge and high-speed photography on the macroscopic level. Dynamic crack initiation toughness is determined from the dynamic stress intensity factor at the time to fracture, and dynamic crack growth toughness is derived by the dynamic fracture energy at a specific crack speed. Systematic fractographic studies on fracture surface are carried out to examine the micromechanisms of fracture. This study reveals clearly that: (1) the crack initiation and growth toughness increase with increasing loading rate and crack speed; (2) the kinetic energy of the flying fragments increases with increasing striking speed; (3) the dynamic fracture energy increases
“…Thus, the observed increase in crack initiation toughness is attributed to the time required to reach a critical stress state ahead of the crack tip over a critical distance. The similar investigations on the effect of loading rate were conducted by Kalthoff (1986) who predicted the existence of an incubation time for crack initiation and by Kim and Chao (2007) who proposed a crack-tip constraint model. Liu et al (1998) analytically modelled the experimental measurements of Ravi-Chandar and Knauss (1984a) for Homalite-100 material by estimating the critical SIF on the basis of different critical distance δ.…”
An experimental investigation is conducted to study the quasi-static and dynamic fracture behaviour of sedimentary, igneous and metamorphic rocks. The notched semi-circular bending method has been employed to determine fracture parameters over a wide range of loading rates using both a servo-hydraulic machine and a split Hopkinson pressure bar. The time to fracture, crack speed and velocity of the flying fragment are measured by strain gauges, crack propagation gauge and high-speed photography on the macroscopic level. Dynamic crack initiation toughness is determined from the dynamic stress intensity factor at the time to fracture, and dynamic crack growth toughness is derived by the dynamic fracture energy at a specific crack speed. Systematic fractographic studies on fracture surface are carried out to examine the micromechanisms of fracture. This study reveals clearly that: (1) the crack initiation and growth toughness increase with increasing loading rate and crack speed; (2) the kinetic energy of the flying fragments increases with increasing striking speed; (3) the dynamic fracture energy increases
“…Both Belenky et al [17] and Kim and Chao [19] reported significant increases in fracture toughness at increased loading rates for monolithic ceramics.…”
Numerical modelling of a series of experimental Single Edge V-Notched Beam tests was carried out for a number of grades of polycrystalline cubic boron nitride using the finite volume method (FV) and cohesive zone model approach.The effect of notch root radius observed experimentally was reproduced numerically via a unique CZM for each material examined. It was also found that the shape of the cohesive zone model can be significant, especially when the material has a relatively high fracture energy. It was also demonstrated that the experimentally observed drop in fracture toughness with increase in test rate was not explainable in terms of the system dynamics. It was found that in order to predict the experimental fracture loads for a range of loading rates, it was necessary to modify the CZM in such a way as to preserve the micro-structural length scale information of the material embedded within the CZM.
“…Fracture behavior of brittle material with innate flaws has attracted much attention recently. Extensive researches on crack initiation, propagation and coalescence have been conducted by using the specimens containing single flaw or multiple flaws in either artificial materials or real rocks under static loads, 1-6 impact loads [7][8][9][10][11][12][13][14][15][16] or blasting loads. 17 Classical fracture mechanics has gone so far as to answer a large number of questions about fracture behavior under various kinds of loads, but for the issue of a running crack approaching a pre-existing crack, there still remain a multitude of unanswered or partially unanswered aspects, such as how the pre-existing crack would affect the running crack?…”
Brittle material usually contains plenty of cracks or micro‐cracks, which raises a question that how a pre‐existing crack affects a running crack as they are approaching. In order to investigate such issue, impact experiments were conducted by using double crack semi‐circle (DCSC) specimens. Polymethyl methacrylate (PMMA) was selected to make the DCSC specimens, and a modified SHPB system was used to perform the impact tests. The finite difference code AUTODYN was employed to simulate the crack propagation behavior and propagation path, and the simulated crack paths agree well with the impact test results. Meanwhile the stresses around the crack tips were analyzed and the crack propagation direction was investigated. To calculate the crack dynamic stress intensity factors (DSIFs), finite element code ABAQUS was employed. The results show that the spacing D between the vertical crack tip and the inclined crack center affects the stress distribution and fracture behavior of the vertical crack largely. As the vertical crack approaches the inclined crack, the crack speed is slow down, and tensile stress appears at the inclined crack tip. As the spacing D is small than 50 mm, the vertical crack connects with the middle area of the inclined crack. As the spacing D is 50 mm, the vertical crack connects with either the middle area or the upper tip of the inclined crack. As the spacing D is larger than 50 mm, the vertical crack coalesces with the upper crack tip.
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