scholarly journals Effects of loading rate on strength and deformation characteristics of gypsum mixed sand

2019 ◽  
Vol 92 ◽  
pp. 05008
Author(s):  
Zain Maqsood ◽  
Junichi Koseki ◽  
Hiroyuki Kyokawa
Keyword(s):  
Strain Rate ◽  
Axial Strain ◽  
Constitutive Modelling ◽  
Strain Rates ◽  
Deformation Characteristics ◽  
Wide Range ◽  
Strength And Deformation ◽  
Loading Tests ◽  
Rational Evaluation ◽  
Strain Responses

It has been unanimously acknowledged that the strength and deformation characteristics of bounded geomaterials, viz. cemented soils and natural rocks, are predominantly governed by the rate of loading/deformation. Rational evaluation of these time-dependent characteristics due to viscosity and ageing are vital for the reliable constitutive modelling. In order to study the effects of ageing and loading/strain rate (viscosity) on the behaviour of bounded geomaterials, a number of unconfined monotonic loading tests were performed on Gypsum Mixed Sand (GMS) specimens at a wide range of axial strain rates; ranging from 1.9E-05 to 5.3E+00 %/min (27,000 folds), and at different curing periods. The results indicate shifts in the viscous behaviour of GMS at critical strain rates of 2.0E-03 and 5.0E-01 %/min. In the light of this finding, the results are categorized into three discrete zones of strain rates, and the behaviour of GMS in each of these zones is discussed. A significant dependency of peak strength and stress-strain responses on strain rate was witnessed for specimens subjected to strain rates lesser than 2.0E-03 %/min, and the effects of viscosity/strain rate was found to be insignificant at strain rate higher than 5.0E-01%/min.

scholarly journals Tensile Behavior of Polyetheretherketone over a Wide Range of Strain Rates

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Zakaria El-Qoubaa ◽  
Ramzi Othman
Keyword(s):  
Constitutive Equation ◽  
Strain Rate ◽  
Volume Change ◽  
Axial Strain ◽  
Rate Sensitivity ◽  
Tensile Behavior ◽  
Image Correlation ◽  
Strain Rates ◽  
Wide Range ◽  
The Impact

Polyetheretherketone (PEEK) is used in several engineering applications where it has to bear impact loads. Nevertheless, the tensile behavior has only been studied in the quasi-static range of loading rates. To address the lack of data in the impact strain rate range, the tensile mechanical behavior of PEEK is investigated at room temperature over a large range of strain rates (from 0.001 to 1000/s). The macroscopic volume change is studied under uniaxial tension using digital image correlation (DIC) method, showing a significant dilatation that reaches 16% at a logarithmic axial strain of 40%. The true stress-strain behavior is therefore established based on the measured volume change. Elsewhere, the yield stress shows a significant sensitivity to strain rate. Besides, a new constitutive equation is proposed to take into account the increase in strain rate sensitivity at high strain rates. It assumes an apparent activation volume which decreases as the strain rate increases. The new constitutive equation gives similar results when compared to the Ree-Eyring equation. However, only three material constants are to be identified and are physically interpreted.

scholarly journals Bounding Surface Elasto-Viscoplasticity: A General Constitutive Framework for Rate-Dependent Geomaterials

2018 ◽  
Author(s):  
Zhenhao Shi ◽  
James Hambleton ◽  
Giuseppe Buscarnera
Keyword(s):  
Strain Rate ◽  
Axial Strain ◽  
Constitutive Law ◽  
Strain Rates ◽  
Bounding Surface ◽  
Rate Dependent ◽  
Wide Range ◽  
Modified Cam Clay ◽  
Constitutive Parameters ◽  
New Framework

A general framework is proposed to incorporate rate and time effects into bounding surface (BS) plasticity models. For this purpose, the elasto-viscoplasticity (EVP) overstress theory is combined with bounding surface modeling techniques. The resulting constitutive framework simply requires the definition of an overstress function through which BS models can be augmented without additional constitutive hypotheses. The new formulation differs from existing rate-dependent bounding surface frameworks in that the strain rate is additively decomposed into elastic and viscoplastic parts, much like classical viscoplasticity. Accordingly, the proposed bounding surface elasto-viscoplasticity (BS-EVP) framework is characterized by two attractive features: (1) the rate-independent limit is naturally recovered at low strain rates; (2) the inelastic strain rate depends exclusively on the current state. To illustrate the advantages of the new framework, a particular BS-EVP constitutive law is formulated by enhancing the Modified Cam-clay model through the proposed theory. From a qualitative standpoint, this simple model shows that the new framework is able to replicate a wide range of time/rate effects occurring at stress levels located strictly inside the bounding surface. From a quantitative standpoint, the calibration of the model for over-consolidated Hong Kong marine clays shows that, despite the use of only six constitutive parameters, the resulting model is able to realistically replicate the undrained shear behavior of clay samples with OCR ranging from 1 to 8, and subjected to axial strain rates spanning from 0.15%/hr to 15%/hr. These promising features demonstrate that the proposed BS-EVP framework represents an ideal platform to model geomaterials characterized by complex past stress history and cyclic stress fluctuations applied at rapidly varying rates.

scholarly journals Experimental Investigation on Strength and Deformation Characteristics of Red Sandstone at Strain Rates of 10−2∼55 s−1

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Jie Shi ◽  
Zongmu Luo ◽  
Huachao Liu ◽  
Dan Wang ◽  
Haipeng Shen ◽  
...  
Keyword(s):  
Strain Rate ◽  
Elastic Strain ◽  
Strain Energy ◽  
Loading Condition ◽  
Elastic Strain Energy ◽  
Strain Rates ◽  
Deformation Characteristics ◽  
Intermediate Strain Rate ◽  
Blasting Excavation ◽  
Strength And Deformation

The mechanical properties of rocks under low to intermediate strain rate are of great importance for seismic engineering, rock impact, and blasting excavation. To study the strength and deformation characteristics of sandstone subjected to low-medium speed impact loading, the complete stress-strain relationships of uniaxial compression at strain rates of 10−2∼55 s−1 were obtained utilizing MTS and drop weight impact test devices. It is indicated that the dynamic compressive strength of sandstone in the range of intermediate strain rate increases approximately linearly with the strain rate under the quasi-static loading condition, while increasing nonlinearly under the dynamic loading condition. The deformation and fracture process of sandstone still consists of pore compaction stage, elastic deformation stage, instable microcrack propagation stage, and brittle fracture stage. The peak stress, critical strain, and residual strain increase with an increase in the strain rate, and the corresponding fracture mode changes from shear failure to split failure. The evolution law of total absorbed strain energy with deformation coincides with that of stored elastic strain energy for sandstone at the intermediate strain rate. The effect of the strain rate on elastic strain energy is more significant than that of dissipated strain energy. Furthermore, both the brittleness and fracture degree of sandstone become more remarkable with the strain rate increasing.

Strain-Rate Effect on the Tensile Behaviour of High Strength Alloys

2011 ◽  
Vol 82 ◽  
pp. 124-129 ◽  
Author(s):  
Ezio Cadoni ◽  
Matteo Dotta ◽  
Daniele Forni ◽  
Stefano Bianchi
Keyword(s):  
Strain Rate ◽  
Rate Sensitivity ◽  
High Strength ◽  
Constitutive Law ◽  
Tensile Behaviour ◽  
Strain Rates ◽  
Cross Sectional ◽  
Split Hopkinson Tensile Bar ◽  
Wide Range ◽  
First Results

In this paper the first results of the mechanical characterization in tension of two high strength alloys in a wide range of strain rates are presented. Different experimental techniques were used for different strain rates: a universal machine, a Hydro-Pneumatic Machine and a JRC-Split Hopkinson Tensile Bar. The experimental research was developed in the DynaMat laboratory of the University of Applied Sciences of Southern Switzerland. An increase of the stress at a given strain increasing the strain-rate from 10-3 to 103 s-1, a moderate strain-rate sensitivity of the uniform and fracture strain, a poor reduction of the cross-sectional area at fracture with increasing the strain-rate were shown. Based on these experimental results the parameters required by the Johnson-Cook constitutive law were determined.

Strength and deformation of frozen saturated sand at −30 °C

1982 ◽  
Vol 19 (1) ◽  
pp. 104-107 ◽  
Author(s):  
V. R. Parameswaran ◽  
M. Roy
Keyword(s):  
Strain Rate ◽  
Power Law ◽  
Quartz Sand ◽  
Peak Strength ◽  
Strain Rates ◽  
Saturated Sand ◽  
Ideal Plastic ◽  
Strength And Deformation ◽  
Power Law Equation

Frozen saturated quartz sand containing 20% moisture by weight, when deformed at −30 °C at various strain rates, showed various modes of behaviour such as visco-plastic, almost ideal plastic, and brittle with little plasticity with increasing order of strain rate. The values of peak strength observed for strain rates between 5 × 10−7 and 6 × 10−3 s−1 were in the range 15–42 MPa, stress being related to strain rate by a power-law equation.

Strain Rate Effect on Shear Behavior of Open-Graded Aggregates

2017 ◽  
Vol 2655 (1) ◽  
pp. 64-70 ◽  
Author(s):  
Thomas Gebrenegus ◽  
Jennifer E. Nicks ◽  
Michael T. Adams
Keyword(s):  
Strain Rate ◽  
Axial Strain ◽  
Shear Behavior ◽  
Strain Rate Effect ◽  
Rate Effect ◽  
Strength Parameter ◽  
Strain Rates ◽  
Rate Dependency ◽  
Confining Stress ◽  
Dilation Angle

Despite their wide application as construction materials in various earthworks built by state and local transportation agencies, the role of physical and mechanical factors in the strength and deformation behavior of crushed, manufactured open-graded aggregates (OGAs) is not well studied. In this investigation, the strain rate dependency of strength–deformation behaviors of two commonly employed crushed aggregates with small (12.7 mm) and large (38.1 mm) sizes is investigated. A 150-mm diameter triaxial testing device was used to conduct a drained compression test at five strain rates, ranging from 0.000083%/s to 0.0083%/s. To evaluate the significance of confining stress and density on the effect of strain rates, the shear tests were conducted at 34 kPa and 207 kPa effective confining stress levels, with the samples compacted at loose (30%) and dense (95%) relative densities. The peak friction angle, maximum dilation angle, secant modulus, and axial strain at which the aggregates started to dilate were determined to evaluate the strain rate effect on the shear behavior of OGAs. The results demonstrate that within the imposed quasistatic strain rate ranges, only the dilation angle showed an increasing trend with the increase in strain rate, whereas other extracted strength parameters were less sensitive to strain rate for both OGAs tested. Hence, the selection of strain rates according to ASTM specifications is appropriate for conducting strength parameter tests, used by practitioners for the design of geotechnical structures, on OGAs under quasistatic conditions.

scholarly journals Dynamic Mechanical Characteristics and Constitutive Modeling of Rail Steel over a Wide Range of Temperatures and Strain Rates

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Peijie Liu ◽  
Yanming Quan ◽  
Guo Ding
Keyword(s):  
Strain Rate ◽  
Mechanical Behavior ◽  
Split Hopkinson Pressure Bar ◽  
Rail Steel ◽  
Strain Rates ◽  
Dynamic Mechanical ◽  
Flow Response ◽  
Strain And Strain Rate ◽  
Average Absolute Relative Error ◽  
Wide Range

Rail steel plays an indispensable role in the safety and stability of the railway system. Therefore, a suitable constitutive model is quite significant to understand the mechanical behavior of this material. Here, the compressive mechanical behavior of heat-treated U71Mn rail steel over a wide range of strain rates (0.001 s−1–10000 s−1) and temperatures (20°C–800°C) was systematically investigated via uniaxial quasistatic and dynamic tests. The split Hopkinson pressure bar (SHPB) apparatus was utilized to perform dynamic mechanical tests. The effects of temperature, strain, and strain rate on the dynamic compressive characteristics of U71Mn were discussed, respectively. The results indicate that the flow response of U71Mn is both temperature-sensitive and strain rate-sensitive. However, the influence of temperature on the flow response is more remarkable than that of strain rate. On the basis of the experimental data, the original and modified Johnson-Cook (JC) models of the studied material were established, respectively. Using correlation coefficient and average absolute relative error parameters, it is revealed that better agreement between the experimental and predicted stress is reached by the modified JC model, which demonstrates that the modified one can characterize the mechanical behavior of the studied material preferably.

THERMOMECHANICAL RESPONSE OF THE ROTARY FORGED WHA OVER A WIDE RANGE OF STRAIN RATES AND TEMPERATURES

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5431-5437 ◽  
Author(s):  
W. G. GUO ◽  
C. QU ◽  
F. L. LIU
Keyword(s):  
Strain Rate ◽  
Dislocation Motion ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Thermomechanical Response ◽  
Tension Tests ◽  
Wide Range ◽  
Physically Based ◽  
Split Hopkinson ◽  
Modeling Prediction

This paper is to understand and model the thermomechanical response of the rotary forged WHA, uniaxial compression and tension tests are performed on cylindrical samples, using a material testing machines and the split Hopkinson bar technique. True strains exceeding 40% are achieved in these tests over the range of strain rates from 0.001/s to about 7,000/s, and at initial temperatures from 77K to 1,073K. The results show: 1) the WHA displays a pronounced changing orientation due to mechanical processing, that is, the material is inhomogeneous along the section; 2) the dynamic strain aging occurs at temperatures over 700K and in a strain rate of 10-3 1/s; 3) failure strains decrease with increasing strain rate under uniaxial tension, it is about 1.2% at a strain rate of 1,000 1/s; and 4) flow stress of WHA strongly depends on temperatures and strain rates. Finally, based on the mechanism of dislocation motion, the parameters of a physically-based model are estimated by the experimental results. A good agreement between the modeling prediction and experiments was obtained.

High Strain-Rate Compressive Behavior and Constitutive Modeling of Selected Polymers Using Modified Ramberg-Osgood Equation

2014 ◽  
Vol 566 ◽  
pp. 80-85
Author(s):  
Kenji Nakai ◽  
Takashi Yokoyama
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Compressive Stress ◽  
Constitutive Modeling ◽  
High Strain ◽  
Strain Rates ◽  
Stress Strain ◽  
Strain Behavior ◽  
Least Squares Fit ◽  
Wide Range

The present paper is concerned with constitutive modeling of the compressive stress-strain behavior of selected polymers at strain rates from 10-3 to 103/s using a modified Ramberg-Osgood equation. High strain-rate compressive stress-strain curves up to strains of nearly 0.08 for four different commercially available extruded polymers were determined on the standard split Hopkinson pressure bar (SHPB). The low and intermediate strain-rate compressive stress-strain relations were measured in an Instron testing machine. Six parameters in the modified Ramberg-Osgood equation were determined by fitting to the experimental stress-strain data using a least-squares fit. It was shown that the monotonic compressive stress-strain behavior over a wide range of strain rates can successfully be described by the modified Ramberg-Osgood constitutive model. The limitations of the model were discussed.

The Effects of Fines on Post Liquefaction Strength and Deformation Characteristics of Sand

2012 ◽  
Vol 594-597 ◽  
pp. 23-27 ◽  
Author(s):  
Yan Li Wang ◽  
Yong Wang
Keyword(s):  
Axial Strain ◽  
Strain Curve ◽  
Critical Value ◽  
Deformation Characteristics ◽  
Compression Tests ◽  
Recovery Stage ◽  
Fines Content ◽  
System A ◽  
Strength Recovery ◽  
Strength And Deformation

This study has been carried out to determine how the fines content affects the post liquefaction strength and deformation characteristics of sand. With the GDS dynamic triaxial system, a series of monotonic undrained compression tests of the sand after liquefaction with variation in fines content from 0 to 40% were conducted, and effects of fines content on the post liquefaction strength and deformation characteristics of sand were analyzed. Results show that with the addition of fines up to a fines content of 30%, the stress-strain curve moves downward and axial strain at low intensive stage is increased, beyond this critical value of fines content the trend is reversed. However, shear strength of post-liquefied sand first decreases with increasing fines content, and beyond the critical value of fines content it increases with increasing fines content at the strength recovery stage when are subjected to monotonic loading. At the same time, the strength recovery rate decreases firstly and then increases with the increasing fines content.

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