scholarly journals Prediction Models of Shear Parameters and Dynamic Creep Instability for Asphalt Mixture under Different High Temperatures

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2542
Author(s):  
Junxiu Lv ◽  
Xiaoyuan Zhang
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Stress Level ◽  
Prediction Models ◽  
Asphalt Mixture ◽  
Confining Pressure ◽  
Shear Strength Parameters ◽  
Dynamic Creep ◽  
Shear Stress Level ◽  
Creep Instability

This study mainly investigates the prediction models of shear parameters and dynamic creep instability for asphalt mixture under different high temperatures to reveal the instability mechanism of the rutting for asphalt pavement. Cohesive force c and internal friction angle φ in the shear strength parameters for asphalt mixture were obtained by the triaxial compressive strength test. Then, through analyzing the influence of different temperatures on parameters c and φ, the prediction models of shear strength parameters related to temperature were developed. Meanwhile, the corresponding forecast model related to confining pressure and shear strength parameters was obtained by simplifying the calculation method of shear stress level on the failure surface under cyclic loading. Thus, the relationship of shear stress level with temperature was established. Furthermore, the cyclic time FN of dynamic creep instability at 60 °C was obtained by the triaxial dynamic creep test, and the effects of confining pressure and shear stress level were considered. Results showed that FN decreases exponentially with the increase in stress levels under the same confining pressure and increases with the increase in confining pressure. The ratio between shear stress level and corresponding shear strength under the same confining pressure was introduced; thus, the relationship curve of FN with shear stress level can eliminate the effect of different confining pressures. The instability prediction model of FN for asphalt mixture was established using exponential model fitting analysis, and the rationality of the model was verified. Finally, the change rule of the parameters in the instability prediction model was investigated by further changing the temperature, and the instability forecast model in the range of high temperature for the same gradation mixture was established by the interpolation calculation.

scholarly journals Determination of Reynolds Shear Stress Level for Hemolysis

ASAIO Journal ◽  
2018 ◽  
Vol 64 (1) ◽  
pp. 63-69 ◽  
Author(s):  
Choon-Sik Jhun ◽  
Megan A. Stauffer ◽  
John D. Reibson ◽  
Eric E. Yeager ◽  
Raymond K. Newswanger ◽  
...  
Keyword(s):  
Shear Stress ◽  
Stress Level ◽  
Reynolds Shear Stress ◽  
Shear Stress Level

scholarly journals A Stochastic Model Based on Fiber Breakage and Matrix Creep for the Stress-Rupture Failure of Unidirectional Continuous Fiber Composites 2. Non-linear Matrix Creep Effects

2021 ◽  
Vol 9 ◽  
Author(s):  
Amy Engelbrecht-Wiggans ◽  
Stuart Leigh Phoenix
Keyword(s):  
Shear Stress ◽  
Stress Level ◽  
Load Transfer ◽  
Stress Rupture ◽  
Fiber Composites ◽  
Linear Matrix ◽  
Non Linear ◽  
The Matrix ◽  
Shear Stress Level ◽  
Fiber Breaks

Stress rupture (sometimes called creep-rupture) is a time-dependent failure mode occurring in unidirectional fiber composites under high tensile loads sustained over long times (e. g., many years), resulting in highly variable lifetimes and where failure has catastrophic consequences. Stress-rupture is of particular concern in such structures as composite overwrapped pressure vessels (COPVs), tension members in infrastructure applications (suspended roofs, post-tensioned bridge cables) and high angular velocity rotors (e.g., flywheels, centrifuges, and propellers). At the micromechanical level, stress rupture begins with the failure of some individual fibers at random flaws, followed by local load-transfer to neighboring intact fibers through shear stresses in the matrix. Over time, the matrix between the fibers creeps in shear, which causes lengthening of local fiber overload zones around previous fiber breaks, resulting in even more fiber breaks, and eventually, formation clusters of fiber breaks of various sizes, one of which eventually grows to a catastrophically unstable size. Most previous models are direct extension of classic stochastic breakdown models for a single fiber, and do not reflect the micromechanical detail, particularly in terms of the creep behavior of the matrix. These models may be adequate for interpreting experimental, composite stress rupture data under a constant load in service; however, they are of highly questionable accuracy under more complex loading profiles, especially ones that initially include a brief “proof test” at a “proof load” of up to 1.5 times the chosen service load. Such models typically predict an improved reliability for proof-test survivors that is higher than the reliability without such a proof test. In our previous work relevant to carbon fiber/epoxy composite structures we showed that damage occurs in the form of a large number of fiber breaks that would not otherwise occur, and in many important circumstances the net effect is reduced reliability over time, if the proof stress is too high. The current paper continues our previous work by revising the model for matrix creep to include non-linear creep whereby power-law creep behavior occurs not only in time but also in shear stress level and with differing exponents. This model, thus, admits two additional parameters, one determining the sensitivity of shear creep rate to shear stress level, and another that acts as a threshold shear stress level reminiscent of a yield stress in the plastic limit, which the model also admits. The new model predicts very similar behavior to that seen in the previous model under linear viscoelastic behavior of the matrix, except that it allows for a threshold shear stress. This threshold allows consideration of behavior under near plastic matrix yielding or even matrix shear failure, the consequence of which is a large increase in the length-scale of load transfer around fiber breaks, and thus, a significant reduction in composite strength and increase in variability. Derivations of length-scales resulting from non-linear matrix creep are provided as Appendices in the Supplementary Material.

scholarly journals Application of the ANFIS to analysis of results from soil testings

2014 ◽  
Vol 13 (2) ◽  
pp. 007-015
Author(s):  
Ewa Daniszewska
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Fuzzy Model ◽  
Experimental Tests ◽  
Triaxial Tests ◽  
Physical Parameters ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Ground Sample ◽  
Neuro Fuzzy

The article was analyzed in order to test applicability and capability of the ANFIS tool used for interpretation of results of triaxial shear tests on loamy soils sampled near Olsztyn. The ANFIS system in the Matlab software programme was used to model and determine relationships between the shear stress and soil resistance parameters in a triaxial shear test apparatus. It has been demonstrated that the achieved shear strength parameters are significantly affected by the variables tested during the triaxial experiments and physical parameters of a given soil sample, but also by the loading increment rate during the tests. It is extremely important to adjust the rate of loading during a test according to the preliminary characterization of a tested ground sample so as to have some control over the obtained ground strength parameters. The neuro-fuzzy model has been constructed based on a set of values obtained after a series of experimental tests, including values of ground shear strength parameters. The database used for the neuro-fuzzy modelling consisted of 6 different ground parameters for each of the 12 shear stress rates applied during the triaxial tests. The learnability was verified on a database composed of the test results – a neuro-fuzzy model was built from learning sets and its accuracy was verified by sets of tests to which the model was applied for the first time. The results obtained from the ANFIS model did not diverge substantially from the ones obtained directly by performing the physical tests. The ANFIS proved to be highly universal and easy to operate. It accounted for the multi-faceted nature of interrelationships between ground parameters.

Temporary stability of steep, noncemented and lightly cemented soil slopes

2015 ◽  
Vol 52 (9) ◽  
pp. 1374-1384
Author(s):  
Poul V. Lade ◽  
Jerry A. Yamamuro
Keyword(s):  
Shear Strength ◽  
Slope Stability ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Compression Tests ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Dense Sand ◽  
Soil Slopes ◽  
Access To Water

Many steep soil slopes are apparently stable beyond what is indicated by slope stability analysis. The mechanism of slope stability in dilating soils is explained in detail, and the development of shear strength in such soils is demonstrated by drained and undrained tests on dense sand. It is argued that appropriate shear strength parameters for analysis of slope stability in dilating materials describe the residual strength. It is explained how reliance on peak shear strength parameters is unsafe, because the component of shear strength created by the additional effective confining pressure caused by development of suction due to inhibited dilation can be exhausted by either access to water or by drying the soil. The fleeting phenomenon of apparent additional shear strength causes super-stability of the slope. Exhaustion of the soil’s capacity to dilate results in reduction of shear strength and instability of the steep slope. It is difficult to predict the time when the soil’s capacity to dilate is exhausted and when the consequent decline in shear strength occurs. This is because this decline occurs with access to water. This is demonstrated by triaxial compression tests on saturated and partly saturated, dilating specimens.

Shear modulus of cohesionless soil: variation with stress and strain level

1992 ◽  
Vol 29 (1) ◽  
pp. 157-161 ◽  
Author(s):  
Martin Fahey
Keyword(s):  
Shear Stress ◽  
Shear Modulus ◽  
Shear Strain ◽  
Stress Level ◽  
Strain Curve ◽  
Strain Level ◽  
Cohesionless Soil ◽  
Backbone Curve ◽  
Stress Strain ◽  
Shear Stress Level

The value of the secant shear modulus (G) of sand measured in cyclic tests reduces as the amplitude of cycling increases. As a first approximation, it is assumed that the curve joining the extreme points of stress–strain (τ–γ) loops of different amplitudes (a so-called "backbone curve") is hyperbolic. The shear strength (τmax) of sand is directly proportional to the mean effective confining pressure (p′), whereas the maximum shear modulus (G0) is proportional to (p′)n, with n being between 0.4 and 0.5. Based on these assumptions, it is shown that at the same shear strain level, different G/G0 values should be expected at different p′ values. One of the features of a hyperbolic τ–γ curve is that there is a unique linear relationship between G/G0 and normalized shear stress level (defined as τ/τmax), independent of p′. Therefore, considering the normalized shear stress level rather than the shear strain level may be a more logical and unifying way of examining the variation in G/G0. Key words : shear modulus, hyperbolic stress–strain curve, pressuremeter test.

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