scholarly journals Numerical modelling of dynamic spalling test on rock with an emphasis on the influence of pre-existing cracks

2017 ◽  
Vol 50 (2) ◽  
pp. 63-76
Author(s):  
Timo Saksala
Keyword(s):  
Static Loading ◽  
Good Accuracy ◽  
Rock Sample ◽  
Rock Fracture ◽  
Dynamic Tensile Strength ◽  
Nite Element ◽  
Strain Rate Hardening ◽  
Spalling Test ◽  
Explicit Dynamic ◽  
Structural Cracks

This article deals with numerical modeling of rock fracture under dynamic tensileloading and the related prediction of dynamic tensile strength. A special emphasis is laid on theinfluence of pre-existing natural microcrack populations as well as structural (articial) cracks.For this end, a previously developed 3D continuum viscodamage-embedded discontinuity modelis employed in the explicit dynamic nite element simulations of the spalling test. This modelis capable of modelling the eect of natural microcracks populations always present in rocks aswell as to capture the strain rate hardening eect of quasi-brittle materials. In the numericalsimulations of spalling test on Bohus granite, it is shown that the model can predict the pull-pack velocity of the free end of the intact rock sample and the eect of structural cracks witha good accuracy. According to the simulations, the effect of microcrack populations, modeledhere as pre-embedded discontinuity populations, is weaker than the corresponding eect underquasi-static loading

scholarly journals Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2108
Author(s):  
Guanlin Liu ◽  
Youliang Chen ◽  
Xi Du ◽  
Peng Xiao ◽  
Shaoming Liao ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Damage Evolution ◽  
Rock Sample ◽  
Rock Fracture ◽  
Damage Threshold ◽  
Crack Development ◽  
Energy Evolution ◽  
Shear Cracks ◽  
Compression Tests ◽  
Microcrack Propagation

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

scholarly journals Stress Evaluation for Segmental Concrete Box Girder Diaphragm

2018 ◽  
Vol 65 ◽  
pp. 08001
Author(s):  
Pei San Alice Lim ◽  
Wen Yi Choo ◽  
Chuan Fang Ong ◽  
See Hung Lau
Keyword(s):  
Static Loading ◽  
Transverse Direction ◽  
Torsional Rigidity ◽  
Three Dimensional ◽  
Element Model ◽  
Box Girder ◽  
Stress Evaluation ◽  
Analysis And Design ◽  
Stress Behavior ◽  
Structural Cracks

The box girder component is a major breakthrough in the construction field for its effective geometry behavior and high torsional rigidity. However, the analysis and design of the box girder are complex due to its three dimensional behavior i.e. torsion, distortion and bending in longitudinal and transverse direction. In this paper, the use of finite element model in evaluating the stresses behavior for segmental box girder diaphragm under static loading is demonstrated. The analysis is carried out for both permanent and variable actions based on Eurocode. Parametric study is carried out to evaluate the effects of different parameters on the stress behavior for box girder. This study contributes to a better insight of the stress behavior for box girder such that, under service, the stresses developed will not contribute to significance structural cracks that will affect the serviceability of the structure.

scholarly journals Influence of Rock Strength on the Propagation of Slotted Cartridge Blasting-Induced Directional Cracks

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Yun Shu ◽  
Peng Shao ◽  
Chao Dong ◽  
Zhen Cao ◽  
Xinwei Yi
Keyword(s):  
Rock Strength ◽  
Rock Fracture ◽  
Propagation Length ◽  
Primary Crack ◽  
Influence Mechanism ◽  
Rock Fracture Mechanics ◽  
Concentration Degree ◽  
Strength Rock ◽  
Explicit Dynamic ◽  
Radial Cracks

Based on theories of explosive mechanics and rock fracture mechanics, the influence mechanism of rock strength on the propagation length of the primary crack in the directional fracture blasting with slotted cartridge has been investigated deeply to propose the relation equation between the rock strength and the propagation length of the primary crack. Theoretically, the maximum length am of the primary crack increases with the enhancing rock strength parameters. The explicit dynamic analysis software LS-DYNA has been used to simulate the slotted cartridge blasting in the mudstone, sandstone, and granite with different strengths in order to reveal the effect of rock strength on the propagation length and velocity of the primary crack and the stress distribution characteristics in rock. The numerical results show the primary crack easily bifurcates and attain a much shorter propagation length in the mudstone with the minimum strength, and there are radial cracks appearing in the nonslotted direction. When rock strength rises, the propagation length, velocity, and duration of the primary crack and the concentration degree of effective stress in the slotted direction will all increase in the sandstone and granite, but there is an opposite influence trend of rock strength in the stage of the initial guide crack’s formation. The cracking velocity has an overall oscillation downtrend whose swing amplitude enhances clearly with the increasing rock strength, signifying the more unsteady propagation of the primary crack in the higher strength rock.

Microstructural and fractographic characterization of B4C-Al cermets tested under dynamic and static loading

1989 ◽  
Vol 47 ◽  
pp. 562-563
Author(s):  
Gyeung Ho Kim ◽  
Mehmet Sarikaya ◽  
D. L. Milius ◽  
I. A. Aksay
Keyword(s):  
Thin Film ◽  
Mechanical Properties ◽  
Fracture Toughness ◽  
Static Loading ◽  
Carbon Deposition ◽  
Full Density ◽  
Unique Combination ◽  
Strong Component ◽  
Reaction Products

Cermets are designed to optimize the mechanical properties of ceramics (hard and strong component) and metals (ductile and tough component) into one system. However, the processing of such systems is a problem in obtaining fully dense composite without deleterious reaction products. In the lightweight (2.65 g/cc) B4C-Al cermet, many of the processing problems have been circumvented. It is now possible to process fully dense B4C-Al cermet with tailored microstructures and achieve unique combination of mechanical properties (fracture strength of over 600 MPa and fracture toughness of 12 MPa-m1/2). In this paper, microstructure and fractography of B4C-Al cermets, tested under dynamic and static loading conditions, are described.The cermet is prepared by infiltration of Al at 1150°C into partially sintered B4C compact under vacuum to full density. Fracture surface replicas were prepared by using cellulose acetate and thin-film carbon deposition. Samples were observed with a Philips 3000 at 100 kV.

CREDO RADON UA – INFORMATION MODEL FOR CALCULATION OF ROAD CONSTRACTION

2019 ◽  
pp. 34-42
Author(s):  
Volodymyr Karedin ◽  
Nadiya Pavlenko
Keyword(s):  
Design Process ◽  
Static Loading ◽  
Computer Aided Design ◽  
Experimental Studies ◽  
Construction Materials ◽  
Residual Deformation ◽  
Road Construction ◽  
Information Support ◽  
Existing Structures ◽  
Road Pavement

CREDO RADON UA software provides an automated calculation of the strength of the pavement structures of non-rigid and rigid types, as well as the calculation of the strengthening of existing structures. In the article, one can see the main features and functionality of the CREDO RADON UA software, the main points in the calculations according to the new regulations. Information support of the design process includes necessary databases, informational and helping materials that make up the full support of the pavement design process. The concept of CREDO RADON UA 1.0 software is made on the use of elasticity theory methods in calculations of initial information models of pavements. Performing optimization calculations, the roadwear in CREDO RADON UA is designed in such a way that no unacceptable residual deformation occurs under the influence of short-term dynamic or static loading in the working layer of the earth bed and in the structural layers during the lifetime of the structure. The calculation algorithms were made in accordance with the current regulatory documents of Ukraine. CREDO RADON UA software allows user to create information bases on road construction materials and vehicles as part of the traffic flow for calculations. The presented system of automated modeling makes it easier for the customer to control the quality of design solutions, to reasonably assign designs to layers of reinforcement, to quickly make comparisons of calculations of different designs for the optimal use of allocated funds. Prospects for further improvement of the program should be the results of theoretical and experimental studies on filling the databases, which are used as information support for automated design of road structures. Keywords: CREDO RADON UA, road, computer-aided design, repair project, road pavement, strengthening, construction, rigid pavement, elasticity module, a transport stream, calculation method, information support, dynamic or static loading.

Enhanced Brady-Tachy Heart Automotive (BT-Heartomotive) Device for Heart Rate Monitoring during Driving

2020 ◽  
Vol 17 (1) ◽  
pp. 7599-7606
Author(s):  
M. A. H. Mohd Adib ◽  
N. H. M. Hasni
Keyword(s):  
Heart Rate ◽  
Mobile Applications ◽  
Good Accuracy ◽  
Rate Measurement ◽  
Road Accidents ◽  
Heart Rate Monitoring ◽  
Physical Conditions ◽  
Car Accidents ◽  
Heart Rate Level ◽  
Main Components

Driving with brady-tachy syndrome is one of the main causes of car accidents. In order to prevent drivers from brady-tachy driving, there is a strong demand for driver monitoring systems. Other than problems in driving attitudes and skills, road accidents are also caused by uncontrollable factors such as medical conditions and drowsiness. These factors can be avoided by having early detection. Therefore, the brady-tachy heart automotive so-called BT-Heartomotive device is developed. This BT-Heartomotive device can detect early signs of drowsiness and health problems by measuring the heart rate of the drivers during driving. The device also could use the data to send an alert to the passengers that they’re in precaution. The device shows a good accuracy in the detection of the heart rate level. The device comprised three main components; wristband, monitor and integrated mobile applications. Heart rate measurement can reveal a lot about the physical conditions of an individual. The BT-Heartomotive device is simple, easy to use and automated.

The Microwave Emission Aspects by Rock Fracture Experiment

2016 ◽  
Vol 136 (5) ◽  
pp. 227-234
Author(s):  
Rikuya Hanawa ◽  
Kuniaki Shibata ◽  
Kenji Saegusa ◽  
Tadashi Takano
Keyword(s):  
Rock Fracture ◽  
Microwave Emission ◽  
Rock Fracture Experiment

Techniques for assessing the performance of circuit materials at microwave and millimetre-wave frequencies

2003 ◽  
Vol 783 ◽  
Author(s):  
Charles E Free
Keyword(s):  
Loss Tangent ◽  
Good Accuracy ◽  
Low Cost ◽  
Resonant Cavity ◽  
New Technique ◽  
Millimetre Wave ◽  
A New Technique

This paper discusses the techniques that are available for characterising circuit materials at microwave and millimetre wave frequencies. In particular, the paper focuses on a new technique for measuring the loss tangent of substrates at mm-wave frequencies using a circular resonant cavity. The benefits of the new technique are that it is simple, low cost, capable of good accuracy and has the potential to work at high mm-wave frequencies.

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