Three Dimensional Effects Near a Crack Tip in a Ductile Three Point Bend Specimen. Part 2. An Experimental Investigation Using Interferometry and Caustics

1988 ◽  
Author(s):  
Alan T. Zehnder ◽  
Ares J. Rosakis
Keyword(s):  
Experimental Investigation ◽  
Three Dimensional ◽  
Crack Tip ◽  
Bend Specimen ◽  
Dimensional Effects ◽  
Point Bend

Three-Dimensional Effects Near a Crack Tip in a Ductile Three-Point Bend Specimen: Part II—An Experimental Investigation Using Interferometry and Caustics

1990 ◽  
Vol 57 (3) ◽  
pp. 618-626 ◽  
Author(s):  
Alan T. Zehnder ◽  
Ares J. Rosakis
Keyword(s):  
Experimental Investigation ◽  
Large Scale ◽  
Three Dimensional ◽  
Time History ◽  
Fracture Initiation ◽  
Optical Methods ◽  
J Integral ◽  
Bend Specimen ◽  
Dimensional Effects ◽  
Point Bend

An experimental investigation is undertaken to assess three-dimensional effects near a crack front in a ductile three-point bend specimen. The possibility of using the optical method of caustics for the measurement of the J-integral in the presence of large-scale yielding and three-dimensional fields is also investigated. Experiments using the optical methods of caustics by reflection and Twyman-Green interferometry are performed simultaneously on either side of the test specimen. The load and load-point displacement are also measured. The experimental results are compared with very good agreement to the results of a finite element simulation of the experiment. The caustics experiments are used to obtain a calibration relation between the value of the J-integral and the caustic diameter for load levels up to fracture initiation. It is proposed that such a calibration be used in dynamic fracture initiation experiments for the measurement of the time history of the dynamic J-integral.

Three-Dimensional Effects Near a Crack Tip in a Ductile Three-Point Bend Specimen: Part I—A Numerical Investigation

1990 ◽  
Vol 57 (3) ◽  
pp. 607-617 ◽  
Author(s):  
R. Narasimhan ◽  
A. J. Rosakis
Keyword(s):  
Plane Strain ◽  
Plane Stress ◽  
Crack Front ◽  
Three Dimensional ◽  
Crack Tip ◽  
Upper And Lower Bounds ◽  
Thickness Variation ◽  
Bend Specimen ◽  
Dimensional Effects ◽  
Point Bend

A simultaneous numerical and experimental investigation is undertaken to assess three-dimensional effects and HRR dominance near a crack front in a ductile 3-point bend specimen. In parallel to the three-dimensional calculations, a plane-strain and a plane-stress analysis of the same in-plane specimen geometry is performed to obtain upper and lower bounds for the three-dimensional calculation. The radial, angular, and thickness variation of the stresses and displacements are studied in great detail from contained yielding to fully plastic conditions. The results indicate that the plane-strain HRR field prevails in the interior of the specimen very near the crack front even for moderate extents of yielding. On the other hand, for distances from the crack tip exceeding about half a specimen thickness, plane-stress conditions are approached. The calculations presented here model a series of laboratory experiments involving three independent experimental techniques. Details regarding the experiments and comparisons of the experimental measurements with numerical calculations and theory are emphasized in Part II of this work.

Analyzing Stress Wave Propagation in a Hollow Bar Loaded Three-Point Bend Fracture Test Using Numerical Methods

2015 ◽  
Vol 782 ◽  
pp. 252-260 ◽  
Author(s):  
Raja Ahsan Javed ◽  
Shi Fan Zhu ◽  
Chun Huan Guo ◽  
Feng Chun Jiang
Keyword(s):  
Wave Propagation ◽  
Stress Wave ◽  
Crack Tip ◽  
Small Sample ◽  
Stress Wave Propagation ◽  
Stress And Strain ◽  
Bend Specimen ◽  
Transient Time ◽  
Propagation Behavior ◽  
Point Bend

Modified Hopkinson pressure bar apparatus is widely used to investigate the dynamic fracture behavior of materials at higher rate loading. While using a small sample for fracture toughness testing, plane strain conditions are compromised. In the current work, a large diameter two-bar/ three-point bend fracture setup is used to analyze stress wave propagation behavior within a larger cracked specimen. The experimental setup model consists of striker, incident bar, loading pin, cracked three-point specimen, span and transmission bar. The model is prepared using ANSYS software and the transient dynamic analysis technique is used to simulate the dynamic load. The effects of increased transient time on the stress wave propagation behavior within the cracked sample and the stress and strain values at the crack tip of the three-point bend specimen are analyzed. In addition, the effects of the hollow striker, the hollow incident bar and the specimen span are studied. It is found that during large specimen testing, an increase in the transient time results in the lower stress and strain values in the specimen crack-tip. The relationship of the specimen span, the striker and the incident bars with the strain values in the specimen is analyzed and a method for the three-point bend specimen testing at the higher strain rates is also proposed.

Statistical and Constraint Loss Size Effects on Cleavage Fracture–Implications to Measuring Toughness in the Transition

2005 ◽  
Vol 128 (3) ◽  
pp. 305-313 ◽  
Author(s):  
H. J. Rathbun ◽  
G. R. Odette ◽  
T. Yamamoto ◽  
M. Y. He ◽  
G. E. Lucas
Keyword(s):  
Cleavage Fracture ◽  
Pressure Vessel ◽  
Size Effects ◽  
Three Dimensional ◽  
Crack Tip ◽  
Systematic Investigation ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Point Bend ◽  
The Individual

A systematic investigation of the effects of specimen size on the cleavage fracture toughness of a typical pressure vessel steel is reported. Size dependence arises both from: (i) statistical effects, related to the volume of highly stressed material near the crack tip, that scales with the crack front length (B) and (ii) constraint loss, primarily associated with the scale of plastic deformation compared to the un-cracked ligament dimension (b). Previously, it has been difficult to quantify the individual contributions of statistical versus constraint loss size effects. Thus, we developed a single variable database for a plate section from the Shoreham pressure vessel using a full matrix of three point bend specimens, with B from 8 to 254 mm and b from 3.2 to 25.4 mm, that were tested at a common set of conditions. The University of California Santa Barbara (UCSB) b-B database was analyzed using three-dimensional finite element calculation of the crack tip fields combined with a cleavage model calibrated to the local fracture properties of the Shoreham steel. This paper focuses on the possible significance of these results to the Master Curve standard as formulated in ASTM E 1921. The statistical scaling procedure to treat variations in B used in E 1921 was found to be reasonably consistent with the UCSB b-B database. However, constraint loss for three point bend specimens begins at a deformation level that is much lower than the censoring limit specified in E 1921. Unrecognized constraint loss leads to a nonconservative, negative bias in the evaluation of To, estimated to be typically on the order of −10°C for pre-cracked Charpy specimens.

On the Extent of Dominance of Asymptotic Elastodynamic Crack-Tip Fields: Part I—An Experimental Study Using Bifocal Caustics

1991 ◽  
Vol 58 (1) ◽  
pp. 87-94 ◽  
Author(s):  
Sridhar Krishnaswamy ◽  
Ares J. Rosakis
Keyword(s):  
High Speed ◽  
Dynamic Stress ◽  
Dynamic Stress Intensity Factor ◽  
Three Dimensional ◽  
Crack Tip ◽  
Mode I ◽  
Transient Effects ◽  
Crack Tip Fields ◽  
Optical Configuration ◽  
Point Bend

The question of the domain of dominance of mode I asymptotic elastodynamic crack-tip fields is investigated experimentally for the cases of dynamically loaded stationary cracks as well as dynamically propagating cracks. The experiments reported are on three-point bend specimens loaded dynamically using a drop-weight tower. An optical configuration leading to a bifocal high-speed camera is proposed. This is used in conjunction with the method of caustics to obtain apparent dynamic stress intensity factor measurements simultaneously from two different regions around the crack tip. The results of this study indicate that three-dimensional and transient effects necessarily have to be taken into account in the interpretation of dynamic fracture experiments.

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