scholarly journals On the Fracture Evolution and Instability of Pyrite-Filled Marble Exposed to Freeze-Thaw-Compression Loads

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 4) ◽  
Author(s):  
Yu Wang ◽  
Haonan Yang ◽  
Chun Zhu ◽  
Shaohua Gao
Keyword(s):  
Progressive Failure ◽  
Failure Process ◽  
Peak Stress ◽  
Image Correlation ◽  
Natural Fracture ◽  
Open Pit ◽  
Full Field ◽  
Strain Concentration ◽  
Freeze Thaw ◽  
Stimulation Of

Abstract The preexistence of the geological discontinuities in cold regions is susceptible to freeze-thaw weathering and rock instability, and even the occurrence of geological hazards is strongly impacted by the discontinuities. Knowledge of how natural fracture affects the rock field deformation is crucial to rock stability prediction. This work is aimed at revealing the influences of freeze-thaw on failure process for pyrite-filled marble obtained from an open pit slope. All the tested marbles were selected to roughly have the same initial pyrite band; the full-field displacement and the progressive failure behaviors under uniaxial compression were qualitatively and quantitatively analyzed using 3D digital image correlation (3D DIC) technique. The testing results show that the previous freeze-thaw action weakens the cementation between the rock matrix and pyrite band; the peak stress and strain are obviously impacted by the freeze-thaw treatment. In addition, the stimulation of pyrite bands influences the displacement development and high strain concentration pattern. The stimulation of pyrite band results in the formation of strain concentration zone, and shear sliding occurs until rock failure. Moreover, it is found that the stimulation of pyrite band and its localized strain takes place progressively and develops fast for marble exposed to higher freeze-thaw treatment. It is suggested that the field deformation development depends on the stimulation of the pyrite bands.

Characterization of Mechanical Behavior of Polyurethane Foams Using Digital Image Correlation

2005 ◽  
Author(s):  
Helena (Huiqing) Jin ◽  
Wei-Yang Lu ◽  
Simon Scheffel ◽  
Michael K. Neilsen ◽  
Terry D. Hinnerichs
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Polyurethane Foams ◽  
Image Correlation ◽  
Compression Tests ◽  
Steel Cylinder ◽  
Full Field ◽  
Strain Concentration ◽  
The Impact ◽  
Dic Technique

Polyurethane foams have good energy absorption properties and are effective in protecting sensitive components from damages due to impact. The foam absorbs impact energy by crushing cells and undergoing large deformation. The complex deformation of the foam needs to be modeled accurately to simulate the impact events. In this paper, the Digital Image Correlation (DIC) technique was implemented to obtain the deformation field of foam specimens under compression tests. Images of foam specimen were continuously acquired using high-speed cameras. The full field displacement and strain at each incremental step of loading were calculated from these images. The closed-cell polyurethane foam used in this investigation was nominal 0.32 kg/m^3 (20 pcf). In the first experiment, cubic specimens were compressed uniaxially up to 60%. The full-field displacements and strains obtained using the DIC technique provide detailed information about the inhomogeneous deformation over the area of interest during loading. In the second experiment, compression tests were conducted for a simple foam structure - cubic foam specimens with a steel cylinder inclusion. The strain concentration at the interface between steel cylinder and foam was studied to simulate the deformation of foam in a typical application. In the third experiment, the foam was loaded from the steel cylinder during the compression. The strain concentration at the interface and the displacement distribution over the surface were compared for cases with and without a confinement fixture to study the effects of confinement. These experimental results demonstrate that the DIC technique can be applied to polyurethane foams to study the heterogeneous deformation. The experimental data is briefly compared with the results from modeling and simulation using a viscoplastic model for the foam.

scholarly journals Full-field deformation characteristics of anisotropic marble under compression revealed by 3D digital image correlation

2021 ◽  
Author(s):  
yu wang ◽  
zhengyang song ◽  
zhiqiang hou ◽  
chun zhu
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Progressive Failure ◽  
Three Dimensional ◽  
Image Correlation ◽  
Localized Deformation ◽  
Full Field ◽  
Strain Pattern ◽  
Field Displacement ◽  
3D Digital Image Correlation

This work aims to reveal the anisotropic full-field displacemnet and the progressive failure behaviors of interbedded marble under uniaxial compression using three dimensional digital image correlation (3D DIC) technique. The effects of the interbed orientation on the field displacement and strain pattern and the crack evolution were analyzed qualitatively and quantitatively. Testing results show that different stress strain responses can be generated depending on the interbed orientation, and the interbeds influence the localized deformation and high strain concentration pattern. The field displacement evolution curves present different pattern and are impacted by the localized deformation. In addition, the strain localization takes places progressively and develops at a lower rate for rock with 0° and 90° interbed than those of 30° and 60° interbed rock. The quick shear-sliding along the interbed leads to the minimum strength of rock having 30° interbed orientation. It is suggested that rock anisotropic field deformation is structure depended.

Effect of the meso-structure on the strain concentration of carbon-carbon composites with drilling hole

2018 ◽  
Vol 25 (4) ◽  
pp. 825-834
Author(s):  
Tiantian Yin ◽  
Xiaofeng Li ◽  
Yu Wang ◽  
Linghui He ◽  
Xinglong Gong
Keyword(s):  
Shear Bands ◽  
Three Dimensional ◽  
Damage Mechanism ◽  
Image Correlation ◽  
Homogeneous Material ◽  
Carbon Composites ◽  
Fem Model ◽  
Full Field ◽  
Strain Concentration ◽  
Drilling Hole

Abstract In this work, the influence of fiber/matrix meso-structure on the strain concentration of three-dimensional (3D) reinforced carbon-carbon composites with a drilling hole is discussed by experimental and numerical ways. The full-field digital image correlation (DIC) method is adopted to obtain the strain field of the experimental specimens, and the meso-FEM model with the consistent meso-structure of the experimental specimens is established to reveal the main deformation and damage mechanism. The results show that the strain concentration appeared off the location of ±90° hole tips, which is different with homogeneous material. Furthermore, the shear bands are observed and located on the region between the cut fiber yarn and the adjacent uncut one. The peculiarities are found connecting with the meso-structure. Moreover, the damage locations obtained from the meso-model show good agreements with the experimental fracture path, thereby, the analyses are verified.

Composite Material Failure Model Updating Approach Leveraging Nondestructive Evaluation Data

2021 ◽  
Vol 4 (3) ◽  
Author(s):  
Mohammadreza Bahadori ◽  
Emine Tekerek ◽  
Melvin Mathew ◽  
Mazur Krzysztof ◽  
Brian Wisner ◽  
...  
Keyword(s):  
Composite Material ◽  
Nondestructive Evaluation ◽  
Model Updating ◽  
Progressive Failure ◽  
Failure Process ◽  
Failure Model ◽  
Initiation Point ◽  
Evaluation Data ◽  
Full Field ◽  
Damage Initiation

Abstract A novel failure model updating methodology is presented in this paper for composite materials. The innovation in the approach presented is found in both the experimental and computational methods used. Specifically, a dominant bottleneck in data-driven failure model development relates to the types of data inputs that could be used for model calibration or updating. To address this issue, nondestructive evaluation data obtained while performing mechanical testing at the laboratory scale are used in this paper to form a damage metric based on a series of processing steps that leverage raw sensing inputs and provide progressive failure curves that are then used to calibrate the damage initiation point computed by full-field three-dimensional finite element simulations of fiber-reinforced composite material that take into account both intra- and interlayer damage. Such curves defined based on nondestructive evaluation data are found to effectively monitor the progressive failure process, and therefore, they could be used as a way to form modeling inputs at different length scales.

scholarly journals Investigation of the Effects of Freeze-Thaw Cycles on Geomechanical and Acoustic Characteristics of Tuff Specimens under Different Stress Paths

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Yong-gang Xiao ◽  
Chang-hong Li ◽  
Jie Cao ◽  
Yu Wang ◽  
Zhi-qiang Hou ◽  
...  
Keyword(s):  
Frequency Band ◽  
Physical And Mechanical Properties ◽  
Peak Stress ◽  
Open Pit ◽  
Natural State ◽  
Uniaxial Compression Test ◽  
Peak Strain ◽  
Loading Test ◽  
Freeze Thaw ◽  
Rock Samples

In the process of development and construction of open-pit mine slope in the high altitude and cold area, freeze-thaw (F-T) cycles have an important impact on rock engineering structure. F-T cycles lead to the decrease in physical and mechanical properties of rock, which is closely related to the stability of open-pit slope. In this paper, the influence of F-T cycles on geomechanical and acoustic emission (AE) characteristics of tuff specimens under different stress paths was studied by using F-T cycle treatment, in situ AE monitoring, and uniaxial loading test. The results indicated that under the same stress path, the cumulative AE count/energy of rock samples subjected to F-T cycles was less than that of rock samples not subjected to F-T cycles. The peak frequency distribution of AE signal during the loading process of rock specimen presented the phenomenon of frequency bands. The width of the low-frequency band of the rock samples subjected to F-T cycles was larger than that of the rock samples under the natural state. The frequency and width of the high-frequency band of the rock samples subjected to F-T cycles were larger than those of the rock samples under the natural state. The rock samples subjected to F-T cycles had higher plastic strain than those without F-T cycles. According to the uniaxial compression test results of F-T rock samples under different stress paths, the peak stress and peak strain have little change, but the AE characteristics were obviously different.

scholarly journals Study on the Progressive Failure Characteristics of Coal in Uniaxial and Triaxial Compression Conditions Using 3D-Digital Image Correlation

Energies ◽  
2018 ◽  
Vol 11 (5) ◽  
pp. 1215 ◽  
Author(s):  
Yang Tang ◽  
Seisuke Okubo ◽  
Jiang Xu ◽  
Shoujian Peng
Keyword(s):  
Digital Image Correlation ◽  
Uniaxial Compression ◽  
Digital Image ◽  
Progressive Failure ◽  
Triaxial Compression ◽  
Failure Process ◽  
Volumetric Strain ◽  
Image Correlation ◽  
Energy Evolution ◽  
3D Digital Image Correlation

To investigate the progressive failure process of coal, a series of uniaxial and triaxial compression tests were conducted and a novel 3D digital image correlation instrument with six cameras combined with a special transparent pressure cell was used for the strain measurement. The stress thresholds of coal were obtained in uniaxial and triaxial compression. The energy evolution during the compression was discussed, coupled with the crack volumetric strain. The field strain of the whole specimen surface and crack propagation at different stress levels were described to study the progressive failure mechanism of coal. The average stress level of crack initiation and crack damage of coal in uniaxial compression are 43.75% and 63.03%, while that in the triaxial compression are 74.53% and 89.84%, respectively. The dissipation energy evolution corresponds to the crack volumetric strain, while the elastic energy release leads to flake ejection and coal failure. The crack evolution and localization of coal indicated the progressive failure process that the coal sample undergoes in tension failure in uniaxial compression and in tension-shear failure in triaxial compression. The findings of this study can serve as a reference to understand the failure process of coal and improve the stability and safety of mining engineering.

Strain concentration during the compression of a carbon/epoxy composite after impact

2015 ◽  
Vol 6 (2) ◽  
pp. 279-289
Author(s):  
Martin Kadlec ◽  
Václav Kafka
Keyword(s):  
Composite Laminates ◽  
Numerical Models ◽  
Compressive Strain ◽  
Composite Plates ◽  
Image Correlation ◽  
Resin Matrix ◽  
Full Field ◽  
Content Type ◽  
Strain Concentration ◽  
The Impact

Purpose – Polymer composite panels are widely used in aeronautic and aerospace structures due to the high strength-to-weight ratios of these structures. The purpose of this paper is to determine the strain fields and failure mechanisms during the failure of the impacted composite laminates when subjected to compression. Design/methodology/approach – A series of compression-after-impact (CAI) tests was performed on composite plates 150×100×4 mm3 made of a carbon-fibre-reinforced epoxy resin matrix. A digital image correlation and fractographic analysis by means of optical and electron microscopy are used for this purpose. Findings – The full-field strain measurements indicate a concentrated band of compressive strain near the impact, where buckling occurs. The results indicate that the strain concentration factor can be considered to be a failure criterion. The shear strain visualisation around the impact reveals an area of heterogeneous deformation that is comparable to the detected delamination area acquired by an ultrasonic technique. Fibre and inter-fibre fractures are described for the particular impact site regions. Originality/value – These experiments could improve numerical models for the CAI analyses and help to build a new criterion for this severe failure mode.

scholarly journals Dynamic tensile properties, deformation, and failure testing of impact-loaded coal samples with various water content

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhen Wei ◽  
Ke Yang ◽  
Xiao-Lou Chi ◽  
Xiang He ◽  
Xin-Yuan Zhao ◽  
...  
Keyword(s):  
Water Content ◽  
Coal Sample ◽  
Failure Process ◽  
Strain Curve ◽  
Peak Stress ◽  
Test System ◽  
Image Correlation ◽  
Tensile Failure ◽  
Peak Strain ◽  
Rate Correlation

AbstractDisc coal samples with different water content were tested using the split Hopkinson press bar test system. Their dynamic tensile failure process was monitored via an ultra-high-speed digital image correlation system. The deformation trend and failure characteristics as a function of the water content were analyzed, and the water content effect on dynamic mechanical properties was investigated. The results demonstrated that the dynamic stress–strain curve of the coal samples consisted of four stages. As the water content increased, the coal sample brittleness degraded, while its ductility was enhanced. Quadratic polynomial functions can describe dynamic peak stress, peak strain, and loading pressure. Under different loading pressures, the dynamic peak stress exhibited a concave bending trend as the water content increased. The coal sample's dynamic tensile strength had a strong rate correlation, and the saturated coal sample exhibited the highest rate correlation. Under high-rate loading, the inertia effect and the Stefan effect of water in coal samples hinder the initiation and propagation of coal sample cracks, improving the coal sample's strength. The research results provide a basic theoretical basis for the prevention and control of rock burst in coal mines.

scholarly journals Stereo-DIC Measurements of a Vibrating Bladed Disk: In-Depth Analysis of Full-Field Deformed Shapes

2021 ◽  
Vol 11 (12) ◽  
pp. 5430
Author(s):  
Paolo Neri ◽  
Alessandro Paoli ◽  
Ciro Santus
Keyword(s):  
Single Point ◽  
Excitation Frequency ◽  
Phase Variation ◽  
Operating Conditions ◽  
Image Correlation ◽  
Response Analysis ◽  
Full Field ◽  
Low Speed ◽  
Bladed Disk ◽  
Depth Analysis

Vibration measurements of turbomachinery components are of utmost importance to characterize the dynamic behavior of rotating machines, thus preventing undesired operating conditions. Local techniques such as strain gauges or laser Doppler vibrometers are usually adopted to collect vibration data. However, these approaches provide single-point and generally 1D measurements. The present work proposes an optical technique, which uses two low-speed cameras, a multimedia projector, and three-dimensional digital image correlation (3D-DIC) to provide full-field measurements of a bladed disk undergoing harmonic response analysis (i.e., pure sinusoidal excitation) in the kHz range. The proposed approach exploits a downsampling strategy to overcome the limitations introduced by low-speed cameras. The developed experimental setup was used to measure the response of a bladed disk subjected to an excitation frequency above 6 kHz, providing a deep insight in the deformed shapes, in terms of amplitude and phase distributions, which could not be feasible with single-point sensors. Results demonstrated the system’s effectiveness in measuring amplitudes of few microns, also evidencing blade mistuning effects. A deeper insight into the deformed shape analysis was provided by considering the phase maps on the entire blisk geometry, and phase variation lines were observed on the blades for high excitation frequency.

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