An Analysis of Dynamic Fracture in an Impact Test Specimen

1983 ◽  
Vol 105 (2) ◽  
pp. 124-131 ◽  
Author(s):  
T. Nishioka ◽  
M. Perl ◽  
S. N. Atluri
Keyword(s):  
Boundary Conditions ◽  
Crack Propagation ◽  
Dynamic Fracture ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Dynamic Fracture Toughness ◽  
Support Points ◽  
Singular Finite Element ◽  
Fast Fracture ◽  
Fracture Specimens

Numerical simulations of fast fracture in four cases of dynamic tear test experiments on 4340 steel are performed using a moving singular finite element method. The experimentally measured crack propagation histories are used as input data to the so-called generation phase simulations to determine the dynamic stress intensity factor histories. In most numerical analyses of dynamic fracture specimens, the load and support points have been treated as fixed boundary conditions. In the present paper, more realistic boundary conditions (contact/no-contact), in which the specimen can separate from the tup and the supports are introduced. The results are also discussed in the light of current controversies surrounding the dynamic fracture toughness properties governing crack propagation under impact loading.

Effect of the Stress Balance on Determination of Rock Dynamic Fracture Toughness Using Holed-Cracked Flattened Brazilian Disc

2011 ◽  
Vol 117-119 ◽  
pp. 71-76 ◽  
Author(s):  
Sheng Zhang ◽  
Xin Wen Li
Keyword(s):  
Fracture Toughness ◽  
Dynamic Fracture ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Fem Analysis ◽  
Dynamic Fracture Toughness ◽  
Necessary Condition ◽  
Brazilian Disc ◽  
Fracture Time ◽  
Early Loading

Based on the experimental and FEM analysis, it was discussed that the stress balance was not a necessary condition for determining rock dynamic fracture toughness accurately using holed-cracked flattened Brazilian disc. The dynamic stress distribution modes of disc sample with time change were analyzed from the early loading stage to continued loading process. It was proved that the fracture time may occur before the balance of stress was achieved. It was not necessary meet the condition of the stress balance using the experiment combined with numerical method. We could get dynamic fracture toughness, according to the dynamic stress intensity factor of the crack tip and fracture time.

Study of the Dynamic Crack Growth of a Planar Crack Front in Three-Dimensional Body Subjected to Mode I Loading

2008 ◽  
Author(s):  
Felicia Stan
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Dynamic Fracture ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Three Dimensional ◽  
Dynamic Fracture Toughness

In this paper, a methodology is presented for predicting crack growth rate along three-dimensional crack fronts under mode I dynamic loading conditions. Within the present methodology, for every point along the crack front the stress intensity factor matches the dynamic fracture toughness at the onset of propagation. In order to accurately evaluate the dynamic stress intensity factor the component separation method of the dynamic J integral is used. To overcome the difficulties in three-dimensional dynamic fracture simulations, the three-dimensional dynamic moving finite element method based on three-dimensional moving 20-noded isoparametric elements is used. In the absence of experimental measurements for dynamic fracture toughness, a new methodology to estimate the dynamic fracture toughness is proposed, i.e., a hybrid experimental-numerical approach, which makes use of numerically determined histories of the dynamic stress intensity factor. The values of the dynamic stress intensity factor are converted into dynamic fracture toughness based on the Weibull distribution. The predictive ability of the developed methodology is demonstrated through the prediction of the dynamic crack growth in Double Cantilever Beam (DCB) specimen of PMMA with different thickness.

X-Ray Fractography Evaluation of the Plastic Zones of Dynamic Fracture

1992 ◽  
Vol 36 ◽  
pp. 551-560
Author(s):  
Kazuyuki Matsui ◽  
Osamu Nakada ◽  
Yukio Hirose ◽  
Keisuke Tanaka
Keyword(s):  
Stress Intensity Factor ◽  
Plastic Zone ◽  
Dynamic Fracture ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Plastic Zone Size ◽  
Zone Size ◽  
X Ray Diffraction ◽  
X Ray ◽  
Plastic Zones

AbstractTo evaluate the plastic zones of dynamic fracture, instrumented Charpy impact tests of high carbon bearing steels are conducted. The amount of plastic zone size left on the fracture surface is evaluated from the X-ray diffraction profiles. An analysis is presented of the relationship between the X-ray diffraction profiles and fracture mechanics parameters. The results are discussed in correlations between dynamic stress intensity factor and absorbed energy values. A good correlation exists between the plastic zone size and the dynamic stress intensity factor.The fraction of retained austenite is determined from X-ray diffraction profiles at surfaces of fractures and also beneath the surfaces of fractures.It shows the work hardening is introduced by the strain energy in the plastic zones. The values of the proportionality constant, α, determined for various kinds of dynamic fracture are related to half-value breadth by the functionwhere B0 and BF are average of half-value breadth which are given by core of material and plastic zone of dynamic fracture.

scholarly journals Hole Defects Affect the Dynamic Fracture Behavior of Nearby Running Cracks

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
R. S. Yang ◽  
C. X. Ding ◽  
L. Y. Yang ◽  
P. Xu ◽  
C. Chen
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Dynamic Stress ◽  
Crack Path ◽  
Dynamic Stress Intensity Factor ◽  
Experimental System ◽  
Intersection Area

Effects of defects on the dynamic fracture behavior of engineering materials cannot be neglected. Using the experimental system of digital laser dynamic caustics, the effects of defects on the dynamic fracture behavior of nearby running cracks are studied. When running cracks propagate near to defects, the crack path deflects toward the defect; the degree of deflection is greater for larger defect diameters. When the running crack propagates away from the defect, the degree of deflection gradually reduces and the original crack path is restored. The intersection between the caustic spot and the defect is the direct cause of the running crack deflection; the intersection area determines the degree of deflection. In addition, the defect locally inhibits the dynamic stress intensity factor of running cracks when they propagate toward the defect and locally promotes the dynamic stress intensity factor of running cracks when they propagate away from the defect.

scholarly journals The dynamic asymmetric fracture test and determination of the dynamic fracture toughness of large-diameter cracked rock specimens

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 897-905
Author(s):  
Yiqiang Lu ◽  
Mingzhong Gao ◽  
Bin Yu ◽  
Cong Li
Keyword(s):  
Fracture Toughness ◽  
Dynamic Fracture ◽  
Split Hopkinson Pressure Bar ◽  
Impact Load ◽  
Failure Process ◽  
Large Diameter ◽  
Dynamic Stress Intensity Factor ◽  
Dynamic Fracture Toughness ◽  
Hopkinson Pressure Bar ◽  
Rock Specimens

We propose large-diameter (160 mm) pre-cracked chevron notched Brazilian disc (P-CCNBD) specimens were used to study the asymmetric fracture law and determine the dynamic fracture toughness of rock. Specimens were diametrically impacted by a split Hopkinson pressure bar. The dynamic fracture failure process of each specimen was monitored by crack propagation gauges and strain gauges. Each of the large-diameter P-CCNBD specimens was found to exhibit prominent asymmetric fracture under impact load. The stress equilibrium condition cannot be satisfied. The dynamic fracture toughness values of the rocks were measured using the experimental-numerical method rather than the quasi-static method. The calculation results showed that the dynamic fracture toughness of rocks increases with the dynamic loading rate. In addition, at the 3-D crack front, the dynamic stress intensity factor was found be substantially different at each point. These data suggest that the dynamic fracture toughness of P-CCNBD specimens should be calculated by removing the value affected by an edge arc crack and taking the average value of the remaining points.

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