Crack closure

About: Crack closure is a research topic. Over the lifetime, 28157 publications have been published within this topic receiving 588158 citations.

Crack propagation in an elastic solid subjected to general loading—I. Constant rate of extension

Abstract: A particular motion of a half-plane crack in an elastic solid subjected to general loading is considered. The loading is prescribed so that the mode of deformation of the crack is the plane-strain opening mode. The crack is initially at rest and then, at a certain instant, begins to move with a constant velocity which is less than the Rayleigh wave speed. A fundamental solution is derived for particular loading on the body which makes it possible to obtain the solution for the complete dynamic stress field due to crack extension by linear superposition. The details of the solution are worked out for the dynamic stress intensity factor for the moving crack. It is found that the stress intensity factor varies almost linearly with the crack speed, from the static value at zero speed to zero at the Rayleigh wave speed. Some numerical results are also presented for the shape of the crack tip as a function of crack speed. Finally, the energy-release rate of the moving crack tip is plotted as a function of crack-tip speed.

Crack point stress singularities at a bi-material interface

Abstract: A continuing study of plane stress singularities at corners and cracks has been extended to the case of a crack in. a hard (soft) material ending normal to a continuous interface with a soft (hard) material. The increase (decrease) in stress singularity over the homogeneous material case. which is of the characteristic inverse square root of distance from the crack point, is given for all relative rigidities between zero and infinity. Associated changes in the principal stress and distortion strain energy density distribution are also discussed, along with indications of application to such situations as microcrack growth near grain boundaries and earth faults in layered strata.

A Comparison of the J -lntegral and CTOD Parameters for Short Crack Specimen Testing

Abstract: This study investigates the applicability of the J-integral test procedure to test short crack specimens in the temperature region below the initiation of ductile tearing where J 1 c cannot be measured. The current J-integral test procedure is restricted to determining the initiation of ductile tearing and requires that no specimen demonstrates brittle cleavage fracture. The J 1 c test specimen is also limited to crack-depth to specimen-width ratios (a/W) between 0.50 and 0.75. In contrast, the crack tip opening displacement (CTOD) test procedure can be used for testing throughout the entire temperature-toughness transition region from brittle to fully ductile behavior. Also, extensive research is being conducted to extend the CTOD test procedure to the testing of short crack specimens (alW ratios of approximately 0.15). The CTOD and J-integral fracture parameters are compared both analytically and experimentally using square (cross-section) three-point bend specimens of A36 steel with a/W ratios of 0.50 (deep crack) and 0.15 (short crack). Three-dimensional elastic-plastic finite element analyses are conducted on both the deep crack and the short crack specimens. The measured J-integral and CTOD results are compared at various levels of linear-elastic and elastic-plastic behavior. Experimental testing is conducted throughout the lower shelf and lower transition regions where stable crack growth does not occur. Very good agreement exists between the analytical and experimental results for both the short crack and deep crack specimens. Results of this study show that both the J-integral and the CTOD fracture parameters work well for testing in the lower shelf and lower transition regions where stable crack growth does not occur. A linear relationship is shown to exist between J-integral and CTOD throughout these regions for both the short and the deep crack specimens. These observations support the consideration to extend the J-integral test procedure into the temperature region of brittle fracture rather than limiting it to J 1 c at the initiation of ductile tearing. Also, analyzing short crack three-point bend specimen (a/W < 0.15) records using the load versus load-line displacement (LLD) record has great potential as an experimental technique. The problems of accurately measuring the CMOD of short crack specimens in the laboratory without affecting the crack tip behavior may be eliminated using the J-integral test procedure.

An experimental investigation into dynamic fracture: I. Crack initiation and arrest

Abstract: Problems of dynamic crack propagation are examined experimentally in a series of four papers. In this paper, the first of this series, crack initiation and arrest are investigated in thin sheets of Homalite-100. It is found that as the rate of loading increases to as high as 105 MPa/sec, the stress intensity factor required to initiate crack growth increases markedly. Crack arrest resulting from a simulated pressurized semi-infinite crack in an unbounded medium was found to occur abruptly. There was no continuous deceleration and the crack always stopped at a constant value of the stress intensity factor, which value was lower than the stress intensity factor required for quasi-static crack growth initiation. The second paper in this series deals with the occurrence of micro cracks at the front of the running main crack which control the rate of crack growth. The micro cracks are recorded by real time photography. By the same means it is shown that these micro cracks grow and turn away smoothly from the direction of the main crack in the process of branching. The third contribution establishes the hitherto unreported occurrence that cracks can propagate rapidly with constant velocity even though the stress intensity factor varies considerably during this propagation. This velocity is determined by the initial stress wave loading on the crack tip, and is changed, within limits, only by stress pulses of sufficient magnitude and brevity of rise time. The final paper in the series deals with the effect of stress waves on the behavior of running cracks, in particular with the influence of stress waves on the branching phenomenon. Also, crack curving under transient stress waves is examined. These results are believed to apply to materials other than Homalite 100 and the reasons for this belief are discussed in this first contribution.

Fracture under complex stress — The angled crack problem

Abstract: Experiments are described in which thin plates of polymethylmethacrylate were fractured with cracks set at various angles to an applied uniaxial stress. While there is substantial agreement with previous analytical predictions, it is shown that inclusion of the stress component parallel to the crack can improve the correlation between linear theory and experiment, using a critical stress at a critical distance interpretation of the stress intensity factor criterion.