scholarly journals Dynamic Mechanical Properties and Visco-Elastic Damage Constitutive Model of Freeze–Thawed Concrete

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4056 ◽  
Author(s):  
Yan Li ◽  
Yue Zhai ◽  
Wenbiao Liang ◽  
Yubai Li ◽  
Qi Dong ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Damage Evolution ◽  
Dynamic Mechanical Properties ◽  
Freeze Thaw ◽  
Dynamic Mechanical ◽  
Damage Constitutive Model ◽  
Concrete Materials ◽  
The Difference ◽  
Stress Damage ◽  
Elastic Damage

To study the dynamic mechanical characteristics and constitutive relation of concrete materials under freeze–thaw (FT) cycle conditions, C35 concrete was taken as the research object in this paper, and FT tests were carried out with a freeze–thaw range of −20–20 °C and a freeze–thaw frequency up to 50 times. By using the separated Hopkinson pressure bar (SHPB) system, impact compression tests of concrete specimens under different FT cycle actions were developed, then the dynamic fracture morphology, fracture block distribution, stress–strain curve, peak stress and other dynamic mechanical properties of concrete were analyzed, and the influence law of FT action and strain rate was obtained. Through introducing the freeze–thaw deterioration damage factor and the stress damage variable, the dynamic visco-elastic damage constitutive equation of freeze–thawed concrete was constructed based on component combination theory. Furthermore, the damage evolution process and mechanism of freeze–thawed concrete materials were revealed. The research results show that the dynamic mechanical properties of concrete under a freeze–thaw environment are the combined results of the freeze–thaw deterioration effect and the strain rate strengthening effect. The dynamic visco-elastic damage constitutive model established in this paper can effectively describe the dynamic mechanical properties of freeze–thawed concrete, and has the characteristics of few parameters and good effect. The stress damage evolution path of concrete goes backward with the increase of FT cycles and the development speed gradually slows down. The greater the difference in FT cycles, the greater the difference in stress damage path.

Meso-Analysis of Dynamic Compressive Behavior of Recycled Aggregate Concrete Using BFEM

2019 ◽  
Vol 17 (06) ◽  
pp. 1950013 ◽  
Author(s):  
Liping Ying ◽  
Yijiang Peng ◽  
Hongming Yang
Keyword(s):  
Mechanical Properties ◽  
High Strain ◽  
Dynamic Mechanical Properties ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Aggregate Concrete ◽  
Dynamic Mechanical ◽  
Concrete Materials ◽  
Dynamic Damage

In this paper, the base force element method (BFEM) for dynamic damage problems is proposed. And the BFEM model was applied to investigate the dynamic mechanical behavior of recycled aggregate concrete (RAC). Any convex polygon recycled aggregate was simulated. A constitutive relationship of dynamic damage was given. The compression test under dynamic loadings on the recycled concrete specimen was simulated. The stress–strain softening curve, variation law of dynamic enhancement coefficient and the damage pattern were researched under different strain rates. The dynamic properties of recycled concrete materials at high strain rate are also studied. The effect of different aggregate distribution on the mechanical properties of concrete was studied. The results of dynamic calculation of recycled concrete materials by this method are compared with the experimental results. The numerical simulation results are in good agreement with the experimental results. The comparative analysis on the dynamic mechanical properties of RAC and natural aggregate concrete (NAC) was also studied. The results show that the BFEM can be used to analyze the dynamic mechanical properties of RAC and NAC under high strain rate, and can be used for large-scale engineering calculations.

scholarly journals Investigation of Dynamic Mechanical Properties of Coal after Freeze-Thaw Cyclic Conditions

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Shuang Gong ◽  
Wen Wang ◽  
Furui Xi ◽  
Wenlong Shen
Keyword(s):  
Mechanical Properties ◽  
Rock Slope ◽  
Dynamic Mechanical Properties ◽  
Rock Mechanic ◽  
Cycle Times ◽  
Freeze Thaw ◽  
Dynamic Mechanical ◽  
Experimental Apparatus ◽  
Coal Rock ◽  
Water Saturated

Due to the extensive excavation of the mine pit, a special frozen rock slope is formed, which transforms the permafrost (coal rock) of certain thickness in the frozen state to the melting state. To evaluate the dynamic mechanical properties and deformation characteristics of coal under cyclic freeze-thaw conditions, freeze-thaw experiments with different cycle times were conducted. And the mechanical properties of coal under quasistatic and dynamic conditions were investigated by using GCTS multifunctional rock mechanic experimental apparatus and SHPB dynamic loading apparatus, respectively. The results show that with the increase of freeze-thawing times, mass of both water-saturated and dried coal samples gradually decreased, the postpeak becomes gentler, and the specimens show ductile damage characteristics. The damage of the coal samples changed more after 30 freeze-thaw cycles, when deterioration of the coal samples was highest. The elastic modulus of the coal sample after freeze-thawing decreases continuously with the increase of the number of freeze-thaw cycles, and its trend decreases approximately linearly. Dynamic compressive strength of the coal samples decreases after freeze-thaw cycles, and this trend is consistent with the quasistatic loading conditions.

Dynamic Mechanical Properties of MWNTs/Phenolic Nanocomposites

2006 ◽  
Vol 306-308 ◽  
pp. 1073-1078 ◽  
Author(s):  
Meng Kao Yeh ◽  
Nyan Hwa Tai ◽  
Jia Hau Liu
Keyword(s):  
Mechanical Properties ◽  
Transition Temperature ◽  
Phenolic Resin ◽  
Loss Modulus ◽  
Impact Resistance ◽  
Dynamic Mechanical Properties ◽  
Tensile Failure ◽  
Dynamic Mechanical ◽  
Multi Walled Carbon Nanotube ◽  
The Difference

Two different types of multi-walled carbon nanotube (MWNT), the dispersed and the network MWNTs, were used to reinforce the phenolic resin. The MWNTs/phenolic nanocomposites were tested by a dynamic mechanical analyzer (DMA) to characterize their dynamic mechanical properties. The results showed that increasing the MWNT content can increase the storage modulus, the loss modulus and the glassy transition temperature of the MWNTs/phenolic nanocomposites. A subambient loss transition is seen in the nanocomposites with network MWNTs which results in a better impact resistance property in the nanocomposites. The glassy transition temperature of the nanocomposites with network MWNTs is higher than that of nanocomposites with dispersed MWNTs. The MWNT additive in phenolic resin can be used to improve the dynamic mechanical properties of the MWNTs/phenolic nanocomposites. The tensile failure morphologies of MWNTs/phenolic nanocomposites were also examined using field emission scanning electron microscope (FESEM) to explain the difference between the two types of nanocomposites.

Modeling of heterogeneous materials at high strain rates with machine learning algorithms trained by finite element simulations

2021 ◽  
pp. 2150001
Author(s):  
Xu Long ◽  
Minghui Mao ◽  
Changheng Lu ◽  
Ruiwen Li ◽  
Fengrui Jia
Keyword(s):  
Machine Learning ◽  
Mechanical Properties ◽  
High Strain ◽  
Dynamic Strength ◽  
Dynamic Mechanical Properties ◽  
Strain Rates ◽  
High Strain Rates ◽  
Dynamic Mechanical ◽  
Concrete Materials ◽  
Meso Scale

Great progress has been made in the dynamic mechanical properties of concrete which is usually assumed to be homogenous. In fact, concrete is a typical heterogeneous material, and the meso-scale structure with aggregates has a significant effect on its macroscopic mechanical properties of concrete. In this paper, concrete is regarded as a two-phase composite material, that is, a combination of aggregate inclusion and mortar matrix. To create the finite element (FE) models, the Monte Carlo method is used to place the aggregates as random inclusions into the mortar matrix of the cylindrical specimens. To validate the numerical simulations of such an inclusion-matrix model at high strain rates, the comparisons with experimental results using the split Hopkinson pressure bar are made and good agreement is achieved in terms of dynamic increasing factor. By performing more extensive FE predictions, the influences of aggregate size and content on the macroscopic dynamic properties (i.e., peak dynamic strength) of concrete materials subjected to high strain rates are further investigated based on the back-propagation (BP) artificial neural network method. It is found that the particle size of aggregate has little effect on the dynamic mechanical properties of concrete but the peak dynamic strength of concrete increases obviously with the content increase of aggregate. After detailed comparisons with FE simulations, machine learning predictions based on the BP algorithm show good applicability for predicting dynamic mechanical strength of concrete with different aggregate sizes and contents. Instead of FE analysis with complicated meso-scale aggregate pre-processing, time-consuming simulation and laborious post-processing, machine learning predictions reproduce the stress–strain curves of concrete materials under high strain rates and thus the constitutive behavior can be efficiently predicted.

scholarly journals Study on Dynamic Mechanical Properties and Damage Evolution Model of Siltstone

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Guoliang Zhang ◽  
Haipeng Jia ◽  
Shuaifeng Wu
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Stress Wave ◽  
Damage Evolution ◽  
Dynamic Mechanical Properties ◽  
Cumulative Damage ◽  
Peak Strain ◽  
Rapid Rise ◽  
Dynamic Mechanical ◽  
Stable Development

This paper is focused on exploring the dynamic mechanical properties and damage process of siltstone. For this purpose, different stress wave wavelengths (0.5 m∼2.0 m) and different strain rates (25 s−1∼120 s−1) were applied to siltstone specimens in the SHPB dynamic impact test. The experimental results show that the dynamic compressive strength of siltstone is linearly positively correlated with the strain rate, and the dynamic increase factor is linearly positively correlated with the natural logarithm of strain rate; the peak strain is linearly positively correlated with the strain rate, and the increase in wavelength causes the peak strain to increase. Through multiple impact tests, it is concluded that the cumulative damage to siltstone increases with the number of impacts. The cumulative damage curve exhibits an initial rapid rise, followed by a stable development, followed by another rapid rise. With increasing wavelength of the stress wave, the stable development of the curve gradually decreases, the cumulative damage to the siltstone is intensified, and the number of repeated impacts is reduced. Meanwhile, a model for damage evolution is established based on the inverse of the Gompertz function, and the physical meanings of the model parameters are determined. The model can reflect the influence of both stress wave parameters and impact times. Verification of the model demonstrates the rationality of the model and the correctness of the physical meaning of the parameters. The model could be applied in future studies of damage to sedimentary rocks.

scholarly journals Experimental investigation on the effect of platform heating on the dynamic mechanical properties of selective laser manufacturing of AlSi10Mg alloy

2021 ◽  
Vol 250 ◽  
pp. 05016
Author(s):  
Ben Amir ◽  
Eyal Grinberg ◽  
Yuval Gale ◽  
Oren Sadot ◽  
Shmuel Samuha
Keyword(s):  
Mechanical Properties ◽  
Three Dimensional ◽  
Stress Relief ◽  
Dynamic Mechanical Properties ◽  
Layer By Layer ◽  
Dynamic Mechanical ◽  
Machine Manufacturer ◽  
Laser Manufacturing ◽  
Lightweight Alloys ◽  
The Difference

Additive manufacturing (AM) is one of the emerging promising technology technologies of manufacturing prototypes. The process of AM is based on melting powder by an energetic beam layer by layer to create a three-dimensional body. One of the lightweight alloys that is being used for AM is AlSi10Mg. The process of manufacturing is controlled by several tens of parameters most of which are determined by the machine manufacturer. One of the important parameters is the building platform temperature. In the present study we took samples from different heights of the building platform and measured the dynamic mechanical properties of each sample. It was noted that after a stress relief treatment (SRT) the difference in the static and dynamic mechanical properties along the building direction changed differently. The dynamic mechanical properties of samples that were fabricated in proximity to the building platform did not change after the SRT, while the mechanical properties of the samples that were fabricated far from the platform changed dramatically and became like those that were fabricated near the building plate.

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