Effect of physical ageing on mechanical behaviour of an elastomeric glass under combined pressure and temperature

Vijayan, Kalyani; Tang, C.‐L.; Pae, K. D.

doi:10.1016/0032-3861(88)90355-2

Cited by 10 publications

(4 citation statements)

References 29 publications

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“…The ageing behaviour is very much similar to many amorphous polymers and elastomeric glasses [4]. It also reveals the memory effect when the samples …”

Section: Discussionmentioning

confidence: 88%

“…structure of a semicrystalline polymer like PP is very complex, It has been shown that the Young's modulus is proportional to 6 = (V(t)-V~)/V~ where Vo~ is the equilibrium volume, provided that the compressive material response is linear elastic [4], as 1/E = A(P, T) (1/6 -1/cS~), Many semicrystalline polymers can be expected to undergo physical ageing. In view of the evidence shown in this paper, one must reassess experimental data produced in the past at low temperatures (below Tg), such as dynamic mechanical studies or at high pressures (above Pg), such as stressstrain behaviour, without regard to physical ageing 2.2 ~ and memory effects.…”

Section: >-mentioning

confidence: 99%

“…Physical ageing of polymeric glasses with regard to high pressure has been studied by many investigators in recent years [1][2][3][4]. Memory effect of the glasses has also been revealed when they were given temperature and/or pressure perturbations [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

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Physical ageing of polypropylene in glassy state

Min

Pae

1989

J Mater Sci

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Physical ageing behaviour of a semicrystalline polymer, polypropylene, has been studied at a pressure-temperature state (P = 2.5 kbar, T = 15 ° C) for which the amorphous region is in the glassy state. Polypropylene contains 57% crystallinity and its glass transition temperature at atmospheric condition is -20 °C. The ageing behaviour was monitored by measuring the Young's modulus (E) from the stress-strain curves as a function of ageing time up to 200 h. The Young's modulus of the rapidly pressure quenched samples increased at 0.4% per ageing hour of the initial value for up to 30 h and tapered off thereafter. The glassy polypropylene also exhibited a memory behaviour ,when it was given a pressure perturbation.

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“…The ageing behaviour is very much similar to many amorphous polymers and elastomeric glasses [4]. It also reveals the memory effect when the samples …”

Section: Discussionmentioning

confidence: 88%

Section: >-mentioning

confidence: 99%

See 1 more Smart Citation

Physical ageing of polypropylene in glassy state

Min

Pae

1989

J Mater Sci

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“…The increased mobility for PDG has been demonstrated in various experimental studies, including but not limited to scattering characterization, ,− mechanical testing, ,,, dielectric spectroscopy, ,− thermal conductivity, , calorimetry, ,− ,, and dilatometry, ,,,,,,, of which the last one, the dilatometric method, allows one to perform in situ pressure jumps and thermal cycles and to measure the anomalous pressure–volume–temperature (PVT) behavior of the PDG in comparison to the corresponding CG. When heating a PDG from the glassy to the liquid state, dilatometric studies show devitrification prior to T g accompanied by little or no overshoot of the extrapolated liquid line, , whereas an aged (or densified) CG overshoots the extrapolated liquid line at T f and devitrifies at temperatures above the nominal T g .…”

Section: Introductionmentioning

confidence: 99%

Mobility of Pressure-Densified and Pressure-Expanded Polystyrene Glasses: Dilatometry and a Test of KAHR Model

2021

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The structural recovery of pressure-densified (PDG) and, for the first time, pressure-expanded (PEG) glasses are experimentally investigated using pressurizable dilatometry. Both glasses show early devitrification on heating, indicating that these glasses have more mobility, compared to the conventional isobarically formed glass. The Kovacs−Aklonis−Hutchinson−Ramos (KAHR) model of structural recovery is able to reasonably predict the behavior of the pressure-expanded glass, but the KAHR model fails with the pressure-densified glass. The results suggest two limitations of the model: (i) the structural recovery is assumed to depend on the instantaneous liquid state and (ii) the same relaxation kinetics are assumed for the temperature and pressure perturbations. Modification of the KAHR model, allowing the departure from equilibrium, δ, to initially depend on the liquid state that the glass came from and to evolve toward the state that the glass is going to, improves the ability of the model to predict the early devitrification for the pressure-densified glass. Another modification of the KAHR model, allowing the temperature and pressure perturbations to relax independently of one another, results in effectively capturing the increased thermal expansion coefficient of glass lines during heating, as well as a "memory"-like aging behavior, for the pressuredensified glass.

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An investigation of the yield and postyield behavior and corresponding structure of poly(methyl methacrylate)

Hasan

Boyce

et al. 1993

J Polym Sci B Polym Phys

244

142

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The mechanical behavior of glassy polymers is time and temperature dependent as evidenced by their viscoelastic and viscoplastic response to loading. The behavior is also known to depend strongly on the prior history of the material, changing with time and temperature without chemical intervention. In this investigation, we examine the effects of this process of physical aging on the yield and postyield behavior and corresponding evolution in the structural state of glassy polymers. This has been achieved through a systematic program of uniaxial, isothermal, constant strain–rate tests on poly(methyl methacrylate) (PMMA) specimens of different thermal histories and by performing positron annihilation lifetime spectroscopy (PALS) measurements prior to and after mechanical deformation. PALS is an indicator of the free volume content, probing size and density of free volume sites and can be considered to be a measurement of structural state. The results of the mechanical tests show that aging acts to increase both the initial yield stress and the amount of strain softening which occurs subsequent to yield. Moreover, the amount of strain softening was found to be independent of strain rate indicating that softening is related to an evolution in structure as opposed to deformation kinetics. Furthermore, after sufficient inelastic straining, the initial thermal history is completely erased as evidenced by identical values of flow stress following strain softening, for both annealed and quenched polymer. Strong confirmation of the structural state or free volume related nature of the strain softening process is obtained by our companion PALS measurements. PALS detects an increase in the size of free volume sites following inelastic deformation and finds the initially annealed and quenched specimens to posses the same post‐deformation distribution. The size of sites is found to evolve steadily with inelastic strain until it attains a steady‐state value. This evolution of free volume with strain follows the observed softening of the flow stress to a steady‐state value. These results provide experimental evidence that an increase in free volume with inelastic straining accompanies the strain softening phenomenon in glassy polymers and that strain softening is indeed a de‐aging process. Based on our experimental results a mechanistically based constitutive model has been formulated to describe the effects of thermal history on the yield and postyield deformation behavior of glassy polymers up to moderate strains. The model is found to successfully capture the effects of physical aging, strain softening, strain rate, and temperature on the inelastic behavior of glassy polymers when compared with experimental results. © 1993 John Wiley & Sons, Inc.

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Effect of physical ageing on mechanical behaviour of an elastomeric glass under combined pressure and temperature

Cited by 10 publications

References 29 publications

Physical ageing of polypropylene in glassy state

Physical ageing of polypropylene in glassy state

Mobility of Pressure-Densified and Pressure-Expanded Polystyrene Glasses: Dilatometry and a Test of KAHR Model

An investigation of the yield and postyield behavior and corresponding structure of poly(methyl methacrylate)

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