scholarly journals NMR Pore Structure and Dynamic Characteristics of Sandstone Caused by Ambient Freeze-Thaw Action

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Bo Ke ◽  
Keping Zhou ◽  
Hongwei Deng ◽  
Feng Bin
Keyword(s):  
Energy Absorption ◽  
Dynamic Characteristics ◽  
Peak Stress ◽  
Dynamic Mechanical Properties ◽  
Freeze Thaw ◽  
Densification Curve ◽  
Splitting Failure ◽  
Increasing Trend ◽  
Axial Splitting ◽  
Weathering Effects

For a deeper understanding of the freeze-thaw weathering effects on the microstructure evolution and deterioration of dynamic mechanical properties of rock, the present paper conducted the nuclear magnetic resonance (NMR) tests and impact loading experiments on sandstone under different freeze-thaw cycles. The results of NMR test show that, with the increase of freeze-thaw cycles, the pores expand and pores size tends to be uniform. The experimental results show that the stress-strain curves all go through four stages, namely, densification, elasticity, yielding, and failure. The densification curve is shorter, and the slope of elasticity curve decreases as the freeze-thaw cycles increase. With increasing freeze-thaw cycles, the dynamic peak stress decreases and energy absorption of sandstone increases. The dynamic failure form is an axial splitting failure, and the fragments increase and the size diminishes with increasing freeze-thaw cycles. The higher the porosity is, the more severe the degradation of dynamic characteristics is. An increase model for the relationships between the porosity or energy absorption and freeze-thaw cycles number was built to reveal the increasing trend with the freeze-thaw cycles increase; meanwhile, a decay model was built to predict the dynamic compressive strength degradation of rock after repeated freeze-thaw cycles.

scholarly journals Dynamic Characteristics of Sandstone under Coupled Static-Dynamic Loads after Freeze-Thaw Cycles

2020 ◽  
Vol 10 (10) ◽  
pp. 3351
Author(s):  
Bo Ke ◽  
Jian Zhang ◽  
Hongwei Deng ◽  
Xiangru Yang
Keyword(s):  
Energy Absorption ◽  
Dynamic Characteristics ◽  
Shear Failure ◽  
Strain Curve ◽  
Peak Stress ◽  
Peak Strain ◽  
Compression Stress ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Freeze Thaw

The effect of temperature fluctuation on rocks needs to be considered in many civil engineering applications. Up to date the dynamic characteristics of rock under freeze-thaw cycles are still not quite clearly understood. In this study, the dynamic mechanical properties of sandstone under pre-compression stress and freeze-thaw cycles were investigated. At the same number of freeze-thaw cycles, with increasing axial pre-compression stress, the dynamic Young’s modulus and peak stress first increase and then decrease, whereas the dynamic peak strain first decreases and then increases. At the same pre-compression stress, with increasing number of freeze-thaw cycles, the peak stress decreases while the peak strain increases, and the peak strain and peak stress show an inverse correlation before or after the pre-compression stress reaches the densification load of the static stress–strain curve. The peak stress and strain both increase under the static load near the yielding stage threshold of the static stress–strain curve. The failure mode is mainly shear failure, and with increasing axial pre-compression stress, the degree of shear failure increases, the energy absorption rate of the specimen increases first and then decreases. With increasing number of freeze-thaw cycles, the number of fragments increases and the size diminishes, and the energy absorption rates of the sandstone increase.

scholarly journals Dynamic characteristics and fractal representations of crack propagation of rock with different fissures under multiple impact loadings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bing Sun ◽  
Shun Liu ◽  
Sheng Zeng ◽  
Shanyong Wang ◽  
Shaoping Wang
Keyword(s):  
Fractal Dimension ◽  
Crack Propagation ◽  
Crack Growth ◽  
Impact Test ◽  
Fractal Theory ◽  
Dynamic Change ◽  
Fractal Dimensions ◽  
Peak Stress ◽  
Dynamic Mechanical Properties ◽  
Gravitational Potential Energy

AbstractTo investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. The box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks and a fractal model of crack growth over time is established based on fractal theory. The results demonstrate that under impact test conditions of the same mass and different heights, the energy absorbed by sandstone accounts for about 26.7% of the gravitational potential energy. But at the same height and different mass, the energy absorbed by the sandstone accounts for about 68.6% of the total energy. As the fissure dip increases and the number of fissures increases, the dynamic peak stress and dynamic elastic modulus of the fractured sandstone gradually decrease. The fractal dimensions of crack evolution tend to increase with time as a whole and assume as a parabolic. Except for one fissure, 60° and 90° specimens, with the extension of time, the increase rate of fractal dimension is decreasing correspondingly.

scholarly journals Dynamic crushing behavior of closed-cell aluminum foams based on different space-filling unit cells

2021 ◽  
Vol 21 (3) ◽  
Author(s):  
S. Talebi ◽  
R. Hedayati ◽  
M. Sadighi
Keyword(s):  
Surface Area ◽  
Dynamic Behavior ◽  
Energy Absorption ◽  
Peak Stress ◽  
Absorption Capacity ◽  
Unit Cell ◽  
Lattice Structures ◽  
Energy Absorption Capacity ◽  
Closed Cell ◽  
Unit Cells

AbstractClosed-cell metal foams are cellular solids that show unique properties such as high strength to weight ratio, high energy absorption capacity, and low thermal conductivity. Due to being computation and cost effective, modeling the behavior of closed-cell foams using regular unit cells has attracted a lot of attention in this regard. Recent developments in additive manufacturing techniques which have made the production of rationally designed porous structures feasible has also contributed to recent increasing interest in studying the mechanical behavior of regular lattice structures. In this study, five different topologies namely Kelvin, Weaire–Phelan, rhombicuboctahedron, octahedral, and truncated cube are considered for constructing lattice structures. The effects of foam density and impact velocity on the stress–strain curves, first peak stress, and energy absorption capacity are investigated. The results showed that unit cell topology has a very significant effect on the stiffness, first peak stress, failure mode, and energy absorption capacity. Among all the unit cell types, the Kelvin unit cell demonstrated the most similar behavior to experimental test results. The Weaire–Phelan unit cell, while showing promising results in low and medium densities, demonstrated unstable behavior at high impact velocity. The lattice structures with high fractions of vertical walls (truncated cube and rhombicuboctahedron) showed higher stiffness and first peak stress values as compared to lattice structures with high ratio of oblique walls (Weaire–Phelan and Kelvin). However, as for the energy absorption capacity, other factors were important. The lattice structures with high cell wall surface area had higher energy absorption capacities as compared to lattice structures with low surface area. The results of this study are not only beneficial in determining the proper unit cell type in numerical modeling of dynamic behavior of closed-cell foams, but they are also advantageous in studying the dynamic behavior of additively manufactured lattice structures with different topologies.

Assessment of Weathering Effects on Rock Mass Structure

2014 ◽  
Vol 72 (1) ◽  
Author(s):  
Seyed Vahid Alavi Nezhad Khalil Abad ◽  
Edy Tonnizam Mohamad ◽  
Ibrahim Komoo ◽  
Roohollah Kalatehjari
Keyword(s):  
Rock Mass ◽  
Stereographic Projection ◽  
Granitic Rock ◽  
Rock Mass Structure ◽  
Joint Spacing ◽  
Specific Relation ◽  
Joint Characteristics ◽  
Increasing Trend ◽  
Weathering Effects

This paper presents an assessment of weathering effect to the rock mass structure by studying the joint characteristics of tropically weathered granite. Joint survey was performed by scanline method and the results were analyzed statistically by stereographic projection plots. The overall trend of mean joint spacing followed a sharp decrement from fresh to moderately weathered zone and then a slight increment to highly and completely weathered zones, whereas the overall trend of mean joint trace length showed a gradual decrement over progress of weathering. In addition, the degree of joints inclination and weathering zones revealed an increasing trend in the percentage of horizontal joints from fresh to completely weathered rocks, while no specific relation was found between the numbers of major joint set and different weathering zones. The results of this study may contribute to understanding the behavior and better classification of weathered granitic rock mass as a heterogeneous mass in engineering works.

scholarly journals Degradation of Mechanical Behavior of Sandstone under Freeze-Thaw Conditions with Different Low Temperatures

2021 ◽  
Vol 11 (22) ◽  
pp. 10653
Author(s):  
Jingwei Gao ◽  
Chao Xu ◽  
Yan Xi ◽  
Lifeng Fan
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Mechanical Behavior ◽  
Energy Absorption ◽  
Uniaxial Compressive Strength ◽  
Dynamic Strength ◽  
Freezing Temperature ◽  
P Wave ◽  
Freeze Thaw ◽  
P Wave Velocity

This study investigated the effects of freezing temperature under freeze-thaw cycling conditions on the mechanical behavior of sandstone. First, the sandstone specimens were subjected to 10-time freeze-thaw cycling treatments at different freezing temperatures (−20, −40, −50, and −60 °C). Subsequently, a series of density, ultrasonic wave, and static and dynamic mechanical behavior tests were carried out. Finally, the effects of freezing temperature on the density, P-wave velocity, stress–strain curves, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption of sandstone were discussed. The results show that the density slightly decreases as temperature decreases, approximately by 1.0% at −60 °C compared with that at 20 °C. The P-wave velocity, static and dynamic uniaxial compressive strength, static elastic modulus, and dynamic energy absorption obviously decrease. As freezing temperature decreases from 20 to −60 °C, the static uniaxial compressive strength, static elastic modulus, dynamic strength, and dynamic energy absorption of sandstone decrease by 16.8%, 21.2%, 30.8%, and 30.7%, respectively. The dynamic mechanical behavior is more sensitive to the freezing temperature during freeze-thawing cycling compared with the static mechanical behavior. In addition, a higher strain rate can induce a higher dynamic strength and energy absorption.

Influence of Fibre Treatment and Matrix Modification on Mechanical Properties of Flax Fibre Reinforced Mortars after Freeze/Thaw Cycles

2022 ◽  
Author(s):  
Bojan Poletanovic ◽  
Katalin Kopecsko ◽  
Ildikó Merta
Keyword(s):  
Mechanical Properties ◽  
Energy Absorption ◽  
Linseed Oil ◽  
Absorption Capacity ◽  
Flax Fibre ◽  
Energy Absorption Capacity ◽  
Freeze Thaw ◽  
Flax Fibres ◽  
Matrix Modification ◽  
Compressive And Flexural Strengths

The aim of this study was to examine the influence of flax fibre protection with the linseed oil and a matrix modification with cement substitution with metakaolin (in 10wt% and 15wt%) on the mechanical properties of cement-based mortars under severe environmental conditions of freeze/thaw cycles. Cement-based mortars (with the dimension of 40x40x160 mm3) were reinforced by 10mm long discrete flax fibres (Linumusitatissimum) and exposed to 51 freeze/thaw cycles under laboratory condition. Their compressive and flexural strengths, as well as specific energy absorption capacity were measured after freeze/thaw cycles and compared to the results of mortars cured for same time in water. Under freeze/thaw cycles mortars reinforced with linseed oil-treated fibres showed the same range of degradation of the compressive and flexural strengths, however, a more pronounced degradation of energy absorption capacity compared to non-treated fibre reinforced mortars was observed. The matrix modification, by partial cement substitution with metakaolin showed optimistic results under freeze/thaw cycles. The compressive strength when cement was partially substituted with metakaolin (in both dosages) increased whereas the flexural strength was slightly lower in case of 10wt% substitution and markedly lower under higher (15wt%) cement substitution. The most relevant is that the decrease of the energy absorption capacity of the fibre reinforced mortar was completely prevented when cement was substituted with metakaolin. It is shown that the energy absorption of the non-treated fibre reinforced mortars increases by 27% when cement was substituted with metakaolin (both 10wt% and 15wt%).

Cushioning energy absorption of composite layered structures including paper corrugation, paper honeycomb and expandable polyethylene

2019 ◽  
Vol 54 (3) ◽  
pp. 176-191 ◽  
Author(s):  
Yanfeng Guo ◽  
Meijuan Ji ◽  
Yungang Fu ◽  
Dan Pan ◽  
Xingning Wang ◽  
...  
Keyword(s):  
Energy Absorption ◽  
Specific Energy ◽  
Peak Stress ◽  
Layered Structures ◽  
Absorption Efficiency ◽  
Compression Stress ◽  
Static Compression ◽  
Specific Energy Absorption ◽  
Energy Absorption Efficiency ◽  
Paper Honeycomb

The composite layered structures including paper corrugation, paper honeycomb and expandable polyethylene are innovative structures of cushioning energy absorption, and the compression and impact resistances of the expandable polyethylene can be enhanced by laminating the corrugated paperboard or honeycomb paperboard. This article evaluated the compression performance and cushioning energy absorption of the composite layered structures by the static compression and drop impact compression tests. On one hand, the static compression properties showed that the total energy absorption, energy absorption per unit volume and stroke efficiency of the composite layered structures were all higher than those of expandable polyethylene. The specific energy absorption was enhanced with the increase in compression strain but almost not affected by the compression rate. The specific energy absorption of the composite layered structures including the expandable polyethylene and honeycomb paperboard was greater than those of the expandable polyethylene and corrugated paperboard. The energy absorption efficiency of the composite layered structures including the expandable polyethylene and corrugated paperboard was large for the low compression stress level, yet that of the composite layered structures including the expandable polyethylene and honeycomb paperboard was large for the high compression stress level. On the other hand, the dynamic compression characteristics showed that the peak stress, energy absorption per unit area, energy absorption per unit volume and specific energy absorption of the composite layered structures embodying paper sandwich cores and expandable polyethylene had linear increasing trends with the increase of drop shock energy. At the same drop impact condition, the composite layered structures including the honeycomb paperboard and expandable polyethylene had better cushioning energy absorption, the peak stress decreased by 23.6% on average, the energy absorption efficiency raised by 8.85% on average and the specific energy absorption increased by 18.1% on average than those including the corrugated paperboard and expandable polyethylene. Therefore, the corrugated paperboard and honeycomb paperboard can helpfully improve the cushioning energy absorption of the expandable polyethylene, and the composite layered structures embodying the expandable polyethylene, corrugated paperboard and honeycomb paperboard may hold excellent packaging protection.

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