scholarly journals Experimental and Theoretical Determination of the Frost-Heave Cracking Law and the Crack Propagation Criterion of Slab Track with Water in the Crack

2019 ◽  
Vol 9 (21) ◽  
pp. 4592 ◽  
Author(s):  
Fengzhuang Tong ◽  
Liang Gao ◽  
Xiaopei Cai ◽  
Yanglong Zhong ◽  
Wenqiang Zhao ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Opening ◽  
Evaluation Criteria ◽  
Image Correlation ◽  
Frost Heave ◽  
External Temperature ◽  
Slab Track ◽  
Initiation And Propagation ◽  
Evolution Laws

Crack propagation produced by frost heave affects the durability of slab-track structures in high-humidity and cold regions in China. This work is intended to reveal the evolution laws of frost-heave crack propagation, establish evaluation criteria for crack propagation, and investigate factors involved in frost-heave crack propagation. Firstly, by preparing slab-track specimens with initial cracks, an experiment of frost-heave crack propagation was designed. The process of frost-heave crack propagation was carried out by means of digital image correlation (DIC) technology and acoustic emission (AE) technology, respectively. These experiments revealed the evolution laws of generalized strain and AE events’ location during crack initiation and propagation, respectively, and the key parameters of micro-crack initiation strain and unstable propagation strain were obtained. By using theoretical and experimental analysis, a double-strain criterion for frost-heave crack propagation was proposed. Finally, factors involved in frost-heave crack propagation were investigated. The results show that crack initiation can be reflected by the crack-tip strain. The average micro-crack initiation strain and unstable propagation strain were found to be 224 με and 243 με, respectively. Moreover, it was found that the frost-heave crack propagation was caused by an ice plug which formed at the crack opening. When the crack width is larger than 2.7 mm and the external temperature is lower than −6.6 °C, cracks propagate easily under the frost-heave force.

Mixed Mode Effects on the Interfacial Crack Propagation

2004 ◽  
Vol 261-263 ◽  
pp. 357-362 ◽  
Author(s):  
B.S. Choi ◽  
Chia Yen Lee ◽  
Young Suck Chai
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Front ◽  
Mixed Mode ◽  
Crack Opening ◽  
Interfacial Crack ◽  
Bimaterial Interface ◽  
Negative Mode ◽  
Initiation And Propagation ◽  
Positive Mode

Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. Initial velocity of crack propagation is very dependent upon the mode-mixes. It increased with positive mode-mix due to the increase of stress singularities ahead of crack front and decreased with negative mode-mix resulting from the increase of the degree of compressive stress behind the crack front. Crack propagation was less accelerated with positive mode-mix than the negative mode-mix.

On the Topology Update of the Numerical Manifold Method for Multiple Crack Propagation

2021 ◽  
pp. 2150030
Author(s):  
Jun He ◽  
Shuling Huang ◽  
Xiuli Ding ◽  
Yuting Zhang ◽  
Dengxue Liu
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Numerical Method ◽  
Crack Tip ◽  
Search Method ◽  
Numerical Manifold Method ◽  
Crack Initiation And Propagation ◽  
Multiple Crack ◽  
Initiation And Propagation ◽  
Numerical Manifold

Crack initiation and propagation are the two key issues of concern in the geotechnical engineering. In this study, the numerical manifold method (NMM) is applied to simulate crack propagation and the topology update of the NMM for multiple crack propagation is studied. The crack-tip asymptotic interpolation function is incorporated into the NMM to increase the accuracy of the crack-tip stress field. In addition, the Mohr-Coulomb criterion with tensile cut off is adopted to be the crack propagation criterion to judge the direction of crack initiation and propagation. Then a crack tip searching method is developed to automatically update the position of the crack tips. The inapplicability of the original loop search method in the NMM is also illustrated and a novel loop search method based on manifold elements is developed for physical loop updating. Moreover, methods for the manifold element updating and physical cover updating are provided. Based on the above study, the developed numerical method is capable to simulate multiple crack propagation. At last, typical rock rupture problems are numerically simulated to manifest the effectiveness of the developed numerical method.

A Novel Fatigue Crack Monitoring Method Based on Nonlinear Dynamic Characteristics of Strain

2019 ◽  
Vol 20 (01) ◽  
pp. 2050016
Author(s):  
Dong Yang ◽  
Dan Li ◽  
K. S. C. Kuang
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Real Time ◽  
Nonlinear Dynamic ◽  
Crack Opening ◽  
Steel Structures ◽  
Monitoring Method ◽  
Strain Measurements ◽  
Crack Monitoring

This paper presents a novel fatigue crack monitoring method for steel specimens based on the smoothness priors method (SPM) and Tsallis entropy (TE) of strain measurements. The aim of the study is to detect initiation of a crack in steel specimens and subsequently to monitor its propagation under the fatigue load, based on real-time strain measurements. The nonlinear dynamic response of the structure was exploited since it degrades due to the initiation and subsequent propagation of the crack under the external dynamic excitation. The proposed method was experimentally validated. Here, the SPM is applied to decomposing the structural strain response into a nearly-stationary (NS) component and a low frequency aperiodic trend (LFAT) component. Features associated with crack initiation can be extracted from the NS component. The LFAT component, on the other hand, can be used to identify crack propagation. To tackle the singularity of the structural responses associated with a crack, the TE of the NS component was used in detection and monitoring of the crack in the steel specimen. Two other techniques, namely, acoustic emission (AE) sensor and crack opening displacement (COD) gauge were used for the purpose of calibration and comparison. The results show remarkable resemblance in terms of crack initiation and propagation identification exhibited by all three types of sensors, highlighting the potential of the proposed method for real-time detection and subsequent monitoring of crack propagation in steel structures.

Influence of Cooling Time t8/5 on Impact Toughness of P460NL1 Steel Welded Joints

2020 ◽  
Vol 1157 ◽  
pp. 154-160
Author(s):  
Simon A. Sedmak ◽  
Mihajlo Aranđelović ◽  
Radomir Jovicic ◽  
Dorin Radu ◽  
Ivica Čamagić
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Impact Energy ◽  
Welded Joint ◽  
Welding Process ◽  
Impact Testing ◽  
Cooling Time ◽  
Initiation And Propagation ◽  
Higher Temperature ◽  
Total Impact

The results of impact testing of welded joint specimens taken from a welded plate made of P460NL1 steel are presented in this paper, and analysed with regards to the cooling time t8/5, that was previously calculated. The aim was to determine how the cooling times that were measured, some of which were below the minimum required values, affected the toughness, in terms of total impact energy and its components, crack initiation and crack propagation energy. In addition, this analysis included the effects of temperatures measured at the opposite ends of the plate during the welding process, since this had also affected the cooling times for each welding pass. After observing the differences in total, crack initiation and propagation energy between the tested specimens taken from different parts of the welded plate, it was determined that the specimens from the part where the higher temperatures were measured had shown better, more uniform results, whereas the average total impact energy for specimens from both groups were very similar. It was also noticed that the ratio of crack propagation to crack initiation was more favourable (greater) in the case of specimens from the second group (with higher temperature), as the values of crack initiation energy decreased slightly and the crack propagation energy increased.

scholarly journals Fretting fatigue crack initiation and propagation in Ti6Al4V sheets under tribocorrosive conditions of artificial seawater and physiological solutions

2020 ◽  
Vol 234 (12) ◽  
pp. 1526-1534 ◽  
Author(s):  
Zeeshan Anjum ◽  
Masood Shah ◽  
Hassan Elahi ◽  
Mushtaq Khan ◽  
Mohammad Mujahid ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Testing Machine ◽  
Fatigue Crack Initiation ◽  
Physiological Solution ◽  
Fretting Corrosion ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Dry Conditions ◽  
Phosphate Buffered Saline

The interaction of mechanical components experiencing relative movements and cyclic loads in a corrosive environment is known as fretting corrosion or tribocorrosion. In the current work, the mechanism of crack initiation and propagation in dovetail slots of Ti6Al4V samples (in contact with carbide rods) under fretting corrosion conditions was investigated. A newly developed test rig installed on a universal testing machine was used to conduct tests at 20 Hz frequency under 5 and 7.5 kN fretting loads. Tests were conducted at room temperature in 3.5% NaCl and phosphate-buffered saline solutions. Crack propagation in all samples was examined by a metallurgical microscope, and the detailed analysis of fractured samples was carried out by a scanning electron microscope. In comparison to dry conditions, early crack initiation and faster crack propagation were observed in salt and physiological solution environments. Colored spots and large amounts of chlorine, sodium, and oxygen were found around cracks, and plastically deformed regions in the 3.5% NaCl environment provided the evidence of a corrosive attack. Large amounts of oxygen, phosphorous, chlorine, potassium, and sodium were detected in the phosphate-buffered saline environment.

scholarly journals Investigation of Low-Cycle Bending Fatigue of AISI 9310 Steel Spur Gears

2007 ◽  
Author(s):  
Robert F. Handschuh ◽  
Timothy L. Krantz ◽  
Bradley A. Lerch ◽  
Christopher S. Burke
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Test Machine ◽  
Spur Gears ◽  
Crack Initiation And Propagation ◽  
Bending Fatigue ◽  
Initiation And Propagation ◽  
Single Tooth ◽  
Relationship Of ◽  
The Relationship

An investigation of the low-cycle bending fatigue of spur gears made from AISI 9310 gear steel was completed. Tests were conducted using the single-tooth bending method to achieve crack initiation and propagation. Tests were conducted on spur gears in a fatigue test machine using a dedicated gear test fixture. Test loads were applied at the highest point of single tooth contact. Gear bending stresses for a given testing load were calculated using a linear-elastic finite element model. Test data were accumulated from 1/4 cycle to several thousand cycles depending on the test stress level. The relationship of stress and cycles for crack initiation was found to be semi-logarithmic. The relationship of stress and cycles for crack propagation was found to be linear. For the range of loads investigated, the crack propagation phase is related to the level of load being applied. Very high loads have comparable crack initiation and propagation times whereas lower loads can have a much smaller number of cycles for crack propagation cycles as compared to crack initiation.

Fatigue Crack Growth Behavior of Threaded Pipe Couplings

2011 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Patrick De Baets ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Crack Opening ◽  
Bending Test ◽  
Crack Initiation And Propagation ◽  
Accurate Knowledge ◽  
Initiation And Propagation

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.

Fatigue Crack Propagation in Haynes 230: A Comparison between Single and Polycrystal Crack Closure Levels

2016 ◽  
Vol 258 ◽  
pp. 243-248 ◽  
Author(s):  
Stefano Beretta ◽  
Stefano Foletti ◽  
Silvio Rabbolini ◽  
Huseyin Sehitoglu
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Closure ◽  
Driving Forces ◽  
Crack Opening ◽  
Image Correlation ◽  
Accurate Estimation ◽  
Haynes 230 ◽  
Local Measurements ◽  
Plasticity Induced Crack Closure

An experimental campaign was developed to evaluate fatigue crack growth in Haynes 230. The effects of plasticity induced crack closure were investigated with Digital Image Correlation. In particular, crack opening levels were measured with the digital extensometer technique, which allowed the evaluation of crack flanks relative displacements. Experimental results were compared with a reference da/dn – ΔKeff curve and with the data of a previous study, which analyzed single crystal propagation. It was found that the adoption of crack closure local measurements provided an accurate estimation of crack propagation driving forces, since all the experimental points from single crystals and polycrystals collapse onto the da/dn – ΔKeff curve.

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