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Drozdov A.D.,Danish Technological Institute DTI
International Journal of Solids and Structures | Year: 2010

Observations are reported in uniaxial cyclic tensile tests (loading-unloading with various maximum strains) on high density polyethylene at temperatures ranging from room temperature up to 90 °C. It is demonstrated that the maximum stress per cycle and an apparent residual strain (measured at the instant when the tensile force vanishes under retraction) strongly decrease with temperature. The latter seems unexpected as the interval of temperatures covers the α-relaxation temperature, which is conventionally associated with activation of additional mechanisms for inelastic flow. A model is developed that captures the decrease in residual strain with temperature. Adjustable parameters in the stress-strain relations are found by fitting the experimental data. The effects of temperature and maximum strain per cycle on residual strains are studied numerically. © 2010 Elsevier Ltd. All rights reserved. Source


Drozdov A.D.,Danish Technological Institute DTI
Computational Materials Science | Year: 2011

Experimental data are reported on isotactic polypropylene in tensile cyclic tests with a strain-controlled program (150 cycles) and various maximum strains. A model is developed in cyclic viscoplasticity of semicrystalline polymers. The constitutive equations describe the mechanical response along each individual cycle of loadingunloading. Material constants in the stressstrain relations are found by fitting observations during several first cycles. For cyclic deformation with a large number of cycles, phenomenological equations are introduced to account for the effect of plastic flow and damage accumulation on adjustable parameters. It is demonstrated that the model qualitatively predicts changes in maximum stress and minimum strain per cycle with number of cycles. The stressstrain relations are applied to assess growth of residual strain under cyclic loading with large (tens of thousand) number of cycles. © 2011 Elsevier B.V. All rights reserved. Source


Drozdov A.D.,Danish Technological Institute DTI
International Journal of Solids and Structures | Year: 2011

Observations are reported on a polymer composite (polyamide-6 reinforced with short glass fibers) in tensile relaxation tests with various strains, tensile creep tests with various stresses, and cyclic tests with a stress-controlled program (ratcheting with a fixed maximum stress and various minimum stresses). Constitutive equations are developed in cyclic viscoelastoplasticity of polymer composites. Adjustable parameters in the stress-strain relations are found by fitting observations in relaxation tests and cyclic tests (16 cycles of loading-unloading). It is demonstrated that the model correctly predicts experimental data in creep tests and dependencies of maximum and minimum strains per cycle on number of cycles up to fatigue fracture of specimens. The influence of strain rate and minimum stress on number of cycles to failure is studied numerically. © 2011 Elsevier Ltd. All rights reserved. Source


Thybring E.E.,Danish Technological Institute DTI
International Biodeterioration and Biodegradation | Year: 2013

The relation between modification intensity and decay resistance of modified wood is investigated based on a compilation of experimental data from literature for six different modification techniques. The purpose is to expand our knowledge on the mechanism of wood modification, in particular how decay resistance is achieved. Decay resistance of modified wood appears to be related to reduction in maximum moisture capacity of the cell wall. The analysis indicates that decay cannot progress below 25% moisture content. The moisture exclusion efficiency (MEE) and anti-swelling efficiency (ASE) are both discussed as means of quantifying modification efficacy. Both MEE and ASE have advantages and disadvantages, but MEE seems to provide a threshold for decay resistance unaffected by type of modification. However, MEE cannot be determined at water saturation and the use of it as a measure for modification efficacy therefore relies on the assumption that MEE is more or less similar at saturation and below. © 2013 Elsevier Ltd. Source


Drozdov A.D.,Danish Technological Institute DTI
International Journal of Solids and Structures | Year: 2014

Constitutive equations are derived for the viscoplastic behavior of a host medium driven by diffusion of guest atoms. With reference to the trapping concept, two states of a guest atom are distinguished: mobile and immobilized (due to alloying with the host matrix). This allows propagation of a sharp interphase to be described between regions rich and poor in guest atoms. The model is applied to study the mechanical response of a spherical electrode particle in a Li-ion battery. Ability of the constitutive equations to capture basic phenomena observed in anode particles under lithiation is demonstrated by numerical simulation. © 2013 Elsevier Ltd. All rights reserved. Source

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