High strain rate mechanical behavior of polyurea

Materials & Design, 2013

Elastomeric polymers, like polyurea, are finding relevance in strengthening applications and as energy absorbing materials for structures and systems subjected to impulsive loadings. Understanding the dynamic behavior of these materials is essential for their application as an effective protective and retrofitting material. This paper presents the findings of a series of uniaxial tensile tests that were conducted on polyurea over the strain rate region from 0.006 to 388 s À1 . The stress-strain behavior of the polyurea sample was established at different strain rates, and key mechanical properties of the material were determined. The results indicate that the stress-strain behavior of the material at high strain rates were considerably non-linear and exhibited significant rate dependency. The characteristics of the stress-strain curves at quasi-static and at higher strain rates can be described as rate-dependent linear elastic/piecewise linear strain hardening. Based on the findings of the experiments, the influence of strain rate effects on the modulus and yield stress of the polymer were analyzed and empirical correlations to describe the dynamic increase factor (DIF) of the modulus of elasticity and the yield stress at high strain rates were proposed.

Polymer, 2007

The large deformation stressestrain behavior of thermoplasticeelastomeric polyurethanes and elastomeric-thermoset polyureas is strongly dependent on strain rate. Their mechanical behavior at very high strain rates is of particular interest due to their role as a protective coating on structures to enhance structural survivability during high rate loading events. Here we report on the uniaxial compression stressestrain behavior of a representative polyurea and a representative polyurethane over a wide range in strain rates, from 0.001 s À1 to 10,000 s À1 , successively marching through each order of magnitude in strain rate using equipment relevant for testing at each particular rate. These results are further analyzed in association with recently reported compressive data on the same materials by Yi et al. [Polymer 2006;47(1):319e29] and intermediate rate tensile data on the same polyurea by Roland et al. [Polymer 2007;48(2):574e8]. The polyurea tested is seen to undergo transition from a rubbery-regime behavior at low rates to a leathery-regime behavior at the highest rates, consistent with the earlier compression study as well as the recent tension study; the polyurethane tested is observed to undergo transition from a rubbery-regime behavior at the low rates to a glassy behavior at the highest rates. The uniaxial compression data for the polyurea are found to be fully consistent with the recently reported uniaxial tension data over the range of rates studied, demonstrating the consistency and complementary aspects of testing at high rates in both compression and tension.

Polymer, 2015

The dynamic tensile mechanical response of a soft polymer material (Clear Flex 75) is investigated using a split Hopkinson tension bar (SHTB). Stress-strain relations are derived to reveal the mechanical properties at moderate and high strain rates. These relations appear to be rate dependent. Under static loading, the polymer exhibits an elastomeric behaviour, while under dynamic loading, the response is elasto-plastic with a hardening branch. The critical strain rate for transition from a rubbery-like behaviour at low strain rates to a glassy-like behaviour at high strain rates at room temperature is determined. The axial and lateral deformation of the specimen in the SHTB test is recorded by a highspeed camera. The final fracture surface is examined by SEM to explore the physical origins of deformation and fracture behaviour: void formation, craze nucleation, craze extension, crack initiation and propagation. Meanwhile, a shielding mechanism is revealed by the observation of crazing and micro cracking in the crack tip zone, which contributes to the dynamic tensile toughness of CF 75 polymer material.

Philosophical Magazine, 2006

Presented here are the results of a systematic study of the viscoelastic properties of polyurea over broad ranges of strain rates and temperatures, including the high-pressure effects on the material response. Based on a set of experiments and a master curve developed by Knauss (W.G. Knauss, Viscoelastic Material Characterization relative to Constitutive and Failure Response of an Elastomer, Interim Report to the Office of Naval Research (GALCIT, Pasadena, CA, 2003.) for time-temperature equivalence, we have produced a model for the large deformation viscoelastic response of this elastomer. Higher strain-rate data are obtained using Hopkinson bar experiments. The data suggest that the response of this class of polymers is strongly pressure dependent. We show that the inclusion of linear pressure sensitivity successfully reproduces the results of the Hopkinson bar experiments. In addition, we also present an equivalent but approximate model that involves only a finite number of internal state variables and is specifically tailored for implementation into explicit finiteelement codes. The model incorporates the classical Williams-Landel-Ferry (WLF) time-temperature transformation and pressure sensitivity (M.L. Williams, R.F. Landel, and J.D. Ferry, J. Am. Chem. Soc., 77 3701 (1955)), in addition to a thermodynamically sound dissipation mechanism. Finally, we show that using this model for the shear behaviour of polyurea along with the elastic bulk response, one can successfully reproduce the very high strain rate pressure-shear experimental results recently reported by Jiao et al.

Materials & Design, 2014

A strain rate dependent constitutive material model to predict the high strain rate behaviour of polyurea has been proposed. The well-known nine parameter Mooney-Rivlin constitutive material model was considered as the base model in deriving the rate dependent material model. A rate dependent term was introduced into the original Mooney-Rivlin model and was validated using high strain material data for polyurea. Due to its simplified formation and extensive use in finite element codes such as LS-DYNA Ò and ANSYS Ò , improvement of the original model shows a higher significance in terms of constitutive model development for hyper-elastic materials. High strain rate tensile tests program has been conducted to obtained the material model parameters. Experimental and model prediction for both stress-strain and energy behaviour of the material indicates close agreement. Stress-strain non-linearity and high strain rate sensitivity of polyurea is also highlighted in this paper.

AIP Conference Proceedings, 2017

This paper reviews the literature on the response of polymers to high strain rate deformation. The main focus is on the experimental techniques used to characterize this response. The paper includes a small number of examples as well as references to experimental data over a wide range of rates, which illustrate the key features of rate dependence in these materials; however this is by no means an exhaustive list. The aim of the paper is to give the reader unfamiliar with the subject an overview of the techniques available with sufficient references from which further information can be obtained. In addition to the 'well established' techniques of the Hopkinson bar, Taylor Impact and Transverse impact, a discussion of the use of time-temperature superposition in interpreting and experimentally replicating high rate response is given, as is a description of new techniques in which mechanical parameters are derived by directly measuring wave propagation in specimens; these are particularly appropriate for polymers with low wave speeds. The vast topic of constitutive modelling is deliberately excluded from this review.

Construction and Building Materials, 2020

h i g h l i g h t s PU resins were prepared from the rapid reaction between PKO-p and MDI in the presence of PEG as the plasticizer. The uniaxial tensile characteristics under loading and unloading conditions and the cyclic softening behavior were examined. PUs are highly strain rate dependent and exhibits stress-strain non-linearity. The mechanical response of PUs can be described as hyper-viscoelastic.

AIP Advances

Polyurethane is a promising candidate for the potting of embedded electronics due to its shock absorbing properties. This paper discusses the less known strain hardening and shock mitigation properties of 4,4 ′-methylenediphenyl diisocyanate based polyurethane under dynamic loading. This study is reported in a strain rate range of 1600-2900 s −1 under compression using a split-Hopkinson pressure bar (SHPB). The experimental stress-strain behavior of polyurethane was modeled with Hollomon's equation to analyze its hardening behavior in dynamic environments. Jointly, the incident, reflected, and transmitted strain signals of the SHPB are analyzed in time and frequency domains to understand the shock absorbing properties of polyurethane. Polyurethane was found to absorb more shock for more intense loading. It was observed to mitigate 81% of shock energy with frequencies up to 10 kHz.

RSC Adv., 2015

The elastic properties of new polyurea elastomers have been studied by varying the segmental molecular weight and the chemical nature of the polymer end groups. Three different types of elastomers were synthesized leading to three different types of response. The elastomers with a high degree of polymerisation and primary amines as terminal groups show two plateaus: at high temperature, the common permanent plateau related to the rubber behaviour of elastomeric systems and, at low temperature, a transient plateau associated with the hydrogen bonding of the urea motives occurring in the interfacial zone between the soft polyetheramine and the hard crosslinker domains. The elastomers with a low degree of polymerization and primary amines as terminal groups show that the transient plateau is masked by the glassy plateau because the hydrogen bonds occur in the same temperature range as the glass transition effects, except for very slow heating rates for which the transient network can be resolved. Lastly, the elastomers with no hydrogen bonding just show the common step in the elastic behaviour from the rubbery to the glassy state.

Le Journal de Physique IV, 1991

-La réponse mécanique de plusieurs polymères ductiles d'utilisation courante a été étudiée en compression à des vitesses de déformation de 2,5 x 10 3 s-1 , à température ambiante et dans l'azote liquide (100 K). Une barre d'Hopkinson à impact direct (BHID) est utilisée pour déterminer les courbes contrainte-déformation dans ces conditions d'expérimentation. La cinématographie ultra-rapide (7 u.s entre images) est l'outil majeur pour déterminer la déformation à rupture, en particulier pour les polymères ayant une grande déformation à rupture, pour lesquels celles-ci n'apparaît pas dans la fenêtre de temps imposée par la BHID (285 us).