scholarly journals MODELLING OF TIME-DEPENDENT BEHAVIOUR OF PARTICULATE THERMOSET POLYMERS

2021 ◽  
Vol 30 ◽  
pp. 131-134
Author(s):  
Jan Vozáb ◽  
Jan Vorel
Keyword(s):  
Numerical Model ◽  
Free Volume ◽  
Maxwell Model ◽  
Nonlinear Creep ◽  
Free Volume Model ◽  
Generalized Maxwell Model ◽  
Linear Creep ◽  
Preliminary Study ◽  
Deviatoric Part ◽  
Dependent Behaviour

A preliminary study of a numerical model describing the behaviour of polymer-based composites is presented. The numerical model consists of three main parts. The first is the microplane M4 model, which is the main part of the model and is used to simulate elastoplastic behaviour and damage. The second part consists of a generalized Maxwell model, which adds the effect of linear creep of the material to the calculation. The last part is a free volume model that extends the linear creep to the nonlinear creep. The creep is calculated on the deviatoric part of the normal stress of each microplane, which allows the model to capture the polymer behaviour adequately without adjusting the free volume of the model.

scholarly journals Effect of an Improved Yasutomi Pressure-Viscosity Relationship on the Elastohydrodynamic Line Contact Problem

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Vincenzo Petrone ◽  
Adolfo Senatore ◽  
Vincenzo D'Agostino
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Free Volume ◽  
Experimental Studies ◽  
Line Contact ◽  
Volume Model ◽  
Free Volume Model ◽  
Pressure Area ◽  
New Formulation ◽  
Lubricant Viscosity

This paper presents the application of an improved Yasutomi correlation for lubricant viscosity at high pressure in a Newtonian elastohydrodynamic line contact simulation. According to recent experimental studies using high pressure viscometers, the Yasutomi pressure-viscosity relationship derived from the free-volume model closely represents the real lubricant piezoviscous behavior for the high pressure typically encountered in elastohydrodynamic applications. However, the original Yasutomi correlation suffers from the appearance of a zero in the function describing the pressure dependence of the relative free volume thermal expansivity. In order to overcome this drawback, a new formulation of the Yasutomi relation was recently developed by Bair et al. This new function removes these concerns and provides improved precision without the need for an equation of state. Numerical simulations have been performed using the improved Yasutomi model to predict the lubricant pressure-viscosity, the pressure distribution, and the film thickness behavior in a Newtonian EHL simulation of a squalane-lubricated line contact. This work also shows that this model yields a higher viscosity at the low-pressure area, which results in a larger central film thickness compared with the previous piezoviscous relations.

Free volume model for positronium decay in molecular materials

1969 ◽  
Vol 28 (11) ◽  
pp. 760-761 ◽  
Author(s):  
B.V. Thosar ◽  
V.G. Kulkarni ◽  
R.G. Lagu ◽  
Girish Chandra
Keyword(s):  
Free Volume ◽  
Molecular Materials ◽  
Volume Model ◽  
Free Volume Model ◽  
Positronium Decay

EXPERIMENTAL RESEARCH ON VISCOELASTICITY PROPERTY OF DIFFERENT LAYERS PERIODONTAL LIGAMENT UNDER COMPRESSION

2021 ◽  
pp. 2150050
Author(s):  
JINLAI ZHOU ◽  
YANG SONG ◽  
CHENGUANG XU ◽  
CHUNQIU ZHANG ◽  
XUE SHI
Keyword(s):  
Elastic Modulus ◽  
Periodontal Ligament ◽  
Creep Compliance ◽  
Relaxation Modulus ◽  
Maxwell Model ◽  
Kelvin Model ◽  
Generalized Maxwell Model ◽  
Relaxation Stress ◽  
Generalized Kelvin Model ◽  
Fitting Accuracy

The periodontal ligament (PDL) exhibits different material mechanical properties along the long axis of the teeth. To explore the creep and the relaxation effects of dissimilar layers of PDL, this paper took the central incisors of porcine mandibular as experimental subjects and divided them perpendicular to the teeth axis into five layers. Creep experiments and relaxation experiments on five layers were conducted to obtain the creep compliance and relaxation modulus at different layers. Linear elastic model, generalized Kelvin model, and generalized Maxwell model were used to describe the major characteristics of the PDL: Instantaneous elasticity, creep and relaxation. Fitting accuracy of three-parameter, five-parameter, and seven-parameter of the model was compared, and the constitutive equations of different layers were established by the least square method. The results presented that the creep strain and the relaxation stress of PDL were exponentially correlated with time under different loading conditions. Different layers showed a significant effect on the creep strain and relaxation stress of PDL. Along the long axis of the teeth, the changing rule of the creep compliance and relaxation modulus of each layer showed quite the contrary, and the instantaneous elastic modulus first decreased to the minimum, then increased to the maximum. Higher instantaneous elastic modulus led to lower creep compliance and higher relaxation modulus. The generalized Kelvin model and the generalized Maxwell model well characterized the creep and relaxation properties of PDL. Fitting accuracy increased with the number of model parameters. The relaxation time of PDL was about one order of magnitude shorter than the creep retardation time, which indicated that the relaxation effect lasted shorter than the creep effect.

scholarly journals Nonlinear creep in a steel-reinforced concrete beam

2020 ◽  
Vol 17 (5) ◽  
pp. 108-116
Author(s):  
S. O. Chepilko ◽  
Keyword(s):  
Reinforced Concrete ◽  
Concrete Beam ◽  
Reinforced Concrete Beam ◽  
Reinforced Concrete Beams ◽  
Nonlinear Creep ◽  
Short Term ◽  
Nonlinear Integral Equations ◽  
Steel Reinforced Concrete ◽  
Linear Creep ◽  
Resolving System

Problems of taking into account nonlinear creep in steel- reinforced concrete beams are considered basing on the integral equation of viscous-elastic-plasticity of concrete. There has been obtained the resolving system of nonlinear integral equations, a linearization of this system has been carried out, its asymptotic solutions have been written out for the theory of elastic heredity case. The analysis of taking into account nonlinear creep has been performed compared with the linear creep equations and an instantaneous (short-term) loading allowing for concrete’s nonlinear diagram.

Identification of Viscoelastic Properties of Finite Element Structures With Joints

1997 ◽  
Author(s):  
Torsten Herrmann ◽  
Valdas Chaika
Keyword(s):  
Finite Element ◽  
Viscoelastic Properties ◽  
Sparse Matrix ◽  
Maxwell Model ◽  
Least Square ◽  
Identification Algorithm ◽  
Domain Identification ◽  
Generalized Maxwell Model ◽  
Maxwell Models ◽  
Complex Modal Analysis

Abstract Identification of the damping and stiffness parameters of the composite joints in finite element structures is analyzed. For the modeling of the viscoelastic properties of the joints the classical Voigt-Kelvin and generalized Maxwell model (three parameter solid) are used. A time domain identification algorithm for classically and non-classically damped dynamic systems is developed. It is based on the application of an extended Kalman filter and least square technique. The algorithm uses complex modal analysis and sparse matrix technology. Both force and base excited systems are considered. Experimental verification of the identification results is carried out on a test structure. The accuracy of the modeling of damping in the joint using the Voigt-Kelvin and generalized Maxwell models is investigated.

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