Study on dynamic fracture behavior of mode I crack under blasting loads

Crack dynamic propagation properties and arrest mechanism under impact loading

Dynamic crack propagation in elastic-perfectly plastic solids under plane stress conditions

Study on the arresting mechanism of two arrest-holes on moving crack in brittle material under impacts

1. The mechanism of the effect of the frequency and form of trajectory of cyclic loading upon the speed of crack propagation was examined from the fracture mechanics viewpoint. 2. In steel 00Kh12N3D a reduction in sinusoidal loading frequency of 20 times (from 2000 to 100 cycles/min) leads to an increase of 1.6 times in the speed of crack development. 3. The speed of fatigue crack propagation in steel 00Kh12N3D is expressed by the following experimentally obtained relationship:C=1.61.10−10‡K3.07n−0.22 4. In steel 15Kh2NMFA the speed of crack growth does not depend upon the frequency of sinusoidal loading and is expressed by the relationshipC=3.86.10−11‡K3.16. 5. A reduction in the frequency of loading with a rectangular form of trajectory leads to a reduction in the speed of crack development in steels 00Kh12N3D and 15Kh2NMFA. 6. The speed of the fatigue crack is less with impact loading than with a sinusoidal form of load trajectory.

Dynamic behavior of a running crack crossing mortar-granite interface with different interface inclinations

This article presents the results of acoustic emission (AE) monitoring of crack propagation in 2024-T3 clad aluminum panels repaired with adhesively bonded octagonal and elliptical boron/epoxy composite patches using FM-73 adhesive under tension–tension fatigue loading. Two crack propagation gages and four broadband AE sensors were used to monitor crack initiation and propagation, respectively. The acquired AE signals were processed in time and frequency domain to identify sensor features correlated with fatigue cycle and crack propagation, which were used to train neural networks for predicting crack length. The results show that AE events are correlated with crack propagation, and crack propagation signals can be differentiated from signals due to matrix cracking, fiber breakage, and shear of the composite patch. Three back-propagation cascade feed-forward networks were trained to predict crack length using number of fatigue cycles, number of AE events, and number of fatigue cycles and number of AE events together as inputs, respectively. It was found that network with fatigue cycles as input gave good results, while the network with just AE events as input gave greater error. However, the network using both fatigue cycles and number of AE events as inputs to predict crack length gave much better results.

U-Net learning for the automatic identification of the sandstone crack tip position to determine mixed-mode stress intensity factors utilizing digital image correlation method

Initiation and propagation of a penny-shaped crack in a finitely deformed incompressible elastic medium

Dynamic caustics and its applications

The article investigates the different types of cracks and kinetics of propagation of cracks in main structural components and welds of the support blocks of fixed offshore platforms. Describes the process of metal fatigue for offshore installations. The article provides methods for calculating of the stress intensity factor and describes the methods of calculation for some cases. Based on the analysis of scientific studies, the author provides methods allowing to calculate two parameters describing the kinetics of crack propagation in relation to the elements and welded joints of offshore fixed platforms, namely the methods of calculation of threshold and critical stress intensity factor. On the basis of the conducted research the author constructed the kinetic chart of the development of fatigue cracks in relation to the elements and welded joints of the supporting blocks of fixed offshore platforms. In addition, the author gives the equation in which it is possible to determine the growth rate of fatigue cracks in various areas of the kinetic diagram.

In this paper, the problem of crack initiation and propagation under compression shear load is investigated experimentally. The influence of far-field compression stress perpendicular to the crack surface on the initiation and propagation of the crack in brittle material is emphasizeded. With the help of the two-axis loading test machine, the two shaft displacements and forces can be adjusted freely during loading. Thus a kind of single-edge symmetric double-crack compression-shear specimen is designed. During the loading, the compression stress stoped as it reaches a series of preset values, while the shear stress increases monotonically till to the crack initiation and propagation. Then the crack initiation and propagation law of compression shear crack under different preset compression stresses can be obtained. It can be find from the test that as the compression stresses relatively smaller, along with the preset compression stress increases, the crack initiation angle increases and the deviation of crack propagation path from the initial crack direction changes severely. As the compression stress reached a definated value, the initiation angle is not changed. It can be find from the test sample that the two crack surfaces are contacted after this definated value of compression stress. The results show that the effect of compression stress on the crack propagation can be divided into two stages according to whether the crack surface contacted or not. Before the crack closed, the influence of compression stress on crack initiation load, crack initiation angle and propagation path increases,when the preset compression stress increases the crack initiation load and the crack initiation angle increase, and the propagation path deviates from the initial crack direction severely. After the crack closed, although the compression stress increases, the crack initiation angle and the critical compression shear stress ratio are keep unchanged. In addition, there existes a certain correspondence between the crack initiation angle and the compression-shear stress ratio at the time of crack initiation. When the ratio of compression-shear stress at the crack initiation increases, the crack initiation angle increases, and vice versa.

This paper deals with a non-destructive detection method of the generation time, the crack length and the propagation speed of fatigue crack in spot-welded joints under tensile-shear load.In case of spot-welded joints, fatigue cracks generate usually at the neighborhood of nugget tips of the weld interface, and propagate toward outer surfaces of the sheets. Accordingly, it is very difficult to observe and measure the crack length, consequently the generation time and the propagation speed of crack by using conventional measuring devices.Authors developed a non-destructive method of fatigue crack, which the generation time, the crack length and the propagation speed of fatigue crack can be quantitatively estimated by utilizing infomation obtained from the strain gages bonded on the electrode indentations of spot welds. Specimens used in this experiment are made of various kinds of thin steel sheets.Main conclusions obtained in this study are as follows:(1) The propagation length of fatigue crack is related with both mean strain and strain range of out-put of the strain gage, and the changing rate of strain range is specially useful for fatigue crack detection.(2) The generation time and the propagation speed of fatigue crack can be estimated easily from relationship between the number of cycles and the crack length, which is established in advance for an individual test piece.

Nowadays, in various industries, in particular in nuclear energy, to determine the fracture toughness, along with standard tests of compact specimens, which are quite expensive and complex, methods are developed to determine these characteristics by impact tests of Charpy specimens using different correlations between Charpy impact fracture energy (CVN) and critical stress intensity factor (J-integral). The paper analyzes correlation and analytical methods, the authors of which consider them universal for a certain class of steels. Correlation methods are divided into one-stage and two-stage. One-stage methods allow to obtain the value of the critical stress intensity factor by the known fracture energy. Two-stage methods in the first stage offer the calculation of the dynamic critical stress intensity factor, in the second the temperature shift and obtaining a static critical stress intensity factor. Analytical methods according to the іmpact fracture diagram of the specimen allow to construct a J-R curve and calculate the value of the J-integral. A series of fracture tests of CT specimens made of heat-resistant steel 22K was carried out, the reference temperature T0 was determined according to the single-temperature method of the ASTM-1921 standard and the Master curve was constructed. A series of standard Charpy specimens impact tests in the temperature range -50…+100°С was performed using an instrumented drop-weight impact testing machine equipped with a high-speed registration system. According to the results of Charpy specimens impact tests, the fracture toughness were determined using different methods. It is established that both analytical and correlation methods cannot be universal and can be used to determine the fracture toughness of 22K steel. Therefore, a new exponential correlation was proposed between the fracture energy of the Charpy specimens and the critical stress intensity factor for heat-resistant steel 22K.

Experimental observations on the effect of thermal treatment on the crack speed and mode I and II fracture toughness in brittle and ductile rocks

Under long-term dynamic water pressure, weld zones in vertical shaft pressure-bearing steel pipes are prone to cracking induced by welding residual stresses (WRSs), which may further propagate and threaten structural safety. This study investigates the effects of initial crack angle and position on crack tip stress and propagation path under the influence of WRSs. Using the XFEM combined with a DFLUX-based thermomechanical simulation, a numerical model of crack growth in vertical shaft steel pipes is developed. Results indicate that increasing the initial crack angle raises the stress intensity factor, while crack-tip residual stress initially increases and then decreases, reaching a maximum value of 457.9 MPa when the initial crack angle is 30°. When WRSs are considered, localized stress concentration at the crack tip intensifies, leading to higher stress, stress amplitude, and stress intensity factor, with the amplitude peaking at 365.49 MPa. Moreover, cracks located outside the weld exhibit higher stress intensity factors than those inside. Overall, WRS, crack angle, and crack location all contribute to crack propagation, with crack angle being the dominant factor. Cracks within welds and oriented between 15° and 45° exhibit a significantly higher likelihood of propagation. These findings aid in identifying hazardous crack scenarios and provide guidance for the operation and monitoring of pressure pipelines.