Morphology and Mechanical Properties of Foamed Polyethylene Blends

Blends of polyethylene were foamed (593–782 kg/m3) by compression molding. Their morphology was investigated to understand the effect of polymer molecular structure. It was found that the cell diameter distribution can be approximated by a truncated normal distribution. Torsion, flexural and tensile properties were also measured at different strain rates. It was found that the shear, flexural and Young's moduli of blends and their foams increase with increasing strain rate, while their normalized moduli are almost unchanged. We also confirm that thin skins have a definite effect on shear and flexural moduli, but are negligible on tensile moduli. Finally, normalized yield strength and strain are almost independent on strain rate while break strain and toughness increase with increasing molecular weight and decreasing strain rate.

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Fully Atomistic Molecular Dynamics Computation of Physico-Mechanical Properties of PB, PS, and SBS

Nanomaterials ◽

10.3390/nano9081088 ◽

2019 ◽

Vol 9 (8) ◽

pp. 1088 ◽

Cited By ~ 1

Author(s):

Yang Kang ◽

Dunhong Zhou ◽

Qiang Wu ◽

Fuyan Duan ◽

Rufang Yao ◽

...

Keyword(s):

Molecular Dynamics ◽

Strain Rate ◽

Strain Hardening ◽

Md Simulation ◽

Md Simulations ◽

Strain Rates ◽

Young’S Moduli ◽

Plastic Modulus ◽

Styrene Butadiene ◽

Butadiene Styrene

The physical properties—including density, glass transition temperature (Tg), and tensile properties—of polybutadiene (PB), polystyrene (PS) and poly (styrene-butadiene-styrene: SBS) block copolymer were predicted by using atomistic molecular dynamics (MD) simulation. At 100 K, for PB and SBS under uniaxial tension with strain rate ε ˙ = 1010 s−1 and 109 s−1, their stress–strain curves had four features, i.e., elastic, yield, softening, and strain hardening. At 300 K, the tensile curves of the three polymers with strain rates between 108 s−1 and 1010 s−1 exhibited strain hardening following elastic regime. The values of Young’s moduli of the copolymers were independent of strain rate. The plastic modulus of PS was independent of strain rate, but the Young’s moduli of PB and SBS depended on strain rate under the same conditions. After extrapolating the Young’s moduli of PB and SBS at strain rates of 0.01–1 s−1 by the linearized Eyring-like model, the predicted results by MD simulations were in accordance well with experimental results, which demonstrate that MD results are feasible for design of new materials.

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Study on the Mechanical Properties of Soft Rock under Dynamic Uniaxial Compression

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.261-263.277 ◽

2004 ◽

Vol 261-263 ◽

pp. 277-282 ◽

Cited By ~ 2

Author(s):

Hai Bo Li ◽

Jun Ru Li ◽

Qing Chun Zhou ◽

Yong Qiang Liu ◽

X. Xia

Keyword(s):

Mechanical Properties ◽

Experimental Study ◽

Compressive Strength ◽

Strain Rate ◽

Uniaxial Compression ◽

Hard Rock ◽

Soft Rock ◽

Strain Rate Effect ◽

Strain Rates ◽

Young’S Moduli

The present paper introduces the experimental study on soft rock (analogized with mortar)under dynamic uniaxial compression at the strain rates from 10-5 to 101s-1. It is indicated that thecompressive strength of the soft rock increase with the increasing strain rate and the rising rates are higher than that of hard rock. The Young's moduli and Poisson's ratio of the soft rock increase with the increasing strain rate, but the rising rates are less than that of compressive strength. In addition, the mechanism of the strain rate effect of the soft rock is primarily analyzed based on the SEM results.

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Effect of Compressive Strain Rate on Auxetic Foam

Applied Sciences ◽

10.3390/app11031207 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1207

Author(s):

Olly Duncan ◽

Nicolas Bailly ◽

Tom Allen ◽

Yvan Petit ◽

Eric Wagnac ◽

...

Keyword(s):

Strain Rate ◽

Poisson’S Ratio ◽

Poisson's Ratio ◽

Strain Rates ◽

Open Cell ◽

Young’S Moduli ◽

Closed Cell ◽

Poisson's Ratios ◽

Poisson’S Ratios ◽

Cell Foam

Auxetic foams have previously been shown to have benefits including higher indentation resistance than their conventional counterparts, due to their negative Poisson’s ratio, making them better at resisting penetration by concentrated loads. The Poisson’s ratio and Young’s modulus of auxetic open cell foams have rarely been measured at the high compressive strain rates typical during impacts of energy absorbing material in sporting protective equipment. Auxetic closed cell foams are less common than their open cell counterparts, and only their quasi-static characteristics have been previously reported. It is, therefore, unclear how the Poisson’s ratio of auxetic foam, and associated benefits such as increased indentation resistance shown at low strain rates, would transfer to the high strain rates expected under impact. The aim of this study was to measure the effect of strain rate on the stiffness and Poisson’s ratio of auxetic and conventional foam. Auxetic open cell and closed cell polymer foams were fabricated, then compression tested to ~80% strain at applied rates up to 200 s−1, with Poisson’s ratios obtained from optical full-field strain mapping. Open cell foam quasi-static Poisson’s ratios ranged from −2.0 to 0.4, with a narrower range of −0.1 to 0.3 for closed cell foam. Poisson’s ratios of auxetic foams approximately halved in magnitude between the minimum and maximum strain rates. Open cell foam quasi-static Young’s moduli were between 0.02 and 0.09 MPa, whereas closed cell foams Young’s moduli were ~1 MPa, which is like foam in protective equipment. The Young’s moduli of the auxetic foams approximately doubled at the highest applied strain rate of 200 s−1.

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The effects of strain and strain rate on residual microstructures in copper

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143687 ◽

1986 ◽

Vol 44 ◽

pp. 420-421

Author(s):

M. F. Stevens ◽

P. S. Follansbee

Keyword(s):

Strain Rate ◽

Applied Stress ◽

Threshold Stress ◽

Rate Sensitivity ◽

Viscous Drag ◽

Strain Rates ◽

Strain And Strain Rate ◽

Threshold Strength ◽

Mechanism Transition ◽

Intrinsic Strength

The strain rate sensitivity of a variety of materials is known to increase rapidly at strain rates exceeding ∼103 sec-1. This transition has most often in the past been attributed to a transition from thermally activated guide to viscous drag control. An important condition for imposition of dislocation drag effects is that the applied stress, σ, must be on the order of or greater than the threshold stress, which is the flow stress at OK. From Fig. 1, it can be seen for OFE Cu that the ratio of the applied stress to threshold stress remains constant even at strain rates as high as 104 sec-1 suggesting that there is not a mechanism transition but that the intrinsic strength is increasing, since the threshold strength is a mechanical measure of intrinsic strength. These measurements were made at constant strain levels of 0.2, wnich is not a guarantee of constant microstructure. The increase in threshold stress at higher strain rates is a strong indication that the microstructural evolution is a function of strain rate and that the dependence becomes stronger at high strain rates.

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Features of accumulation of amounts of measurement error

Geodesy and Cartography ◽

10.22389/0016-7126-2017-928-10-58-63 ◽

2017 ◽

Vol 928 (10) ◽

pp. 58-63 ◽

Cited By ~ 1

Author(s):

V.I. Salnikov

Keyword(s):

Measurement Error ◽

Confidence Interval ◽

Normal Distribution ◽

Confidence Level ◽

Measurement Errors ◽

Truncated Normal Distribution ◽

Truncated Normal ◽

The Law ◽

Normal Law

The initial subject for study are consistent sums of the measurement errors. It is assumed that the latter are subject to the normal law, but with the limitation on the value of the marginal error Δpred = 2m. It is known that each amount ni corresponding to a confidence interval, which provides the value of the sum, is equal to zero. The paradox is that the probability of such an event is zero; therefore, it is impossible to determine the value ni of where the sum becomes zero. The article proposes to consider the event consisting in the fact that some amount of error will change value within 2m limits with a confidence level of 0,954. Within the group all the sums have a limit error. These tolerances are proposed to use for the discrepancies in geodesy instead of 2m*SQL(ni). The concept of “the law of the truncated normal distribution with Δpred = 2m” is suggested to be introduced.

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A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates

Journal of Composites Science ◽

10.3390/jcs5050130 ◽

2021 ◽

Vol 5 (5) ◽

pp. 130

Author(s):

Tan Ke Khieng ◽

Sujan Debnath ◽

Ernest Ting Chaw Liang ◽

Mahmood Anwar ◽

Alokesh Pramanik ◽

...

Keyword(s):

Mechanical Properties ◽

Strain Rate ◽

Polymer Composites ◽

Stress Transfer ◽

Natural Fibre ◽

Transfer Efficiency ◽

Strain Rates ◽

Reinforced Polymer ◽

Fibre Reinforced Polymer ◽

Fibre Matrix

With the lightning speed of technological evolution, the demand for high performance yet sustainable natural fibres reinforced polymer composites (NFPCs) are rising. Especially a mechanically competent NFPCs under various loading conditions are growing day by day. However, the polymers mechanical properties are strain-rate dependent due to their viscoelastic nature. Especially for natural fibre reinforced polymer composites (NFPCs) which the involvement of filler has caused rather complex failure mechanisms under different strain rates. Moreover, some uneven micro-sized natural fibres such as bagasse, coir and wood were found often resulting in micro-cracks and voids formation in composites. This paper provides an overview of recent research on the mechanical properties of NFPCs under various loading conditions-different form (tensile, compression, bending) and different strain rates. The literature on characterisation techniques toward different strain rates, composite failure behaviours and current challenges are summarised which have led to the notion of future study trend. The strength of NFPCs is generally found grow proportionally with the strain rate up to a certain degree depending on the fibre-matrix stress-transfer efficiency. The failure modes such as embrittlement and fibre-matrix debonding were often encountered at higher strain rates. The natural filler properties, amount, sizes and polymer matrix types are found to be few key factors affecting the performances of composites under various strain rates whereby optimally adjust these factors could maximise the fibre-matrix stress-transfer efficiency and led to performance increases under various loading strain rates.

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Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽

10.3390/ma14051257 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1257

Author(s):

Shuling Gao ◽

Guanhua Hu

Keyword(s):

Strain Rate ◽

Lateral Pressure ◽

Deformation Modulus ◽

Strain Curve ◽

Peak Stress ◽

Pressure Level ◽

Strain Rates ◽

Peak Strain ◽

Stress Strain Curve ◽

Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

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Using Artificial Neural Networks to Predict Influences of Heterogeneity on Rock Strength at Different Strain Rates

Materials ◽

10.3390/ma14113042 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3042

Author(s):

Sheng Jiang ◽

Mansour Sharafisafa ◽

Luming Shen

Keyword(s):

Neural Network ◽

Artificial Neural Network ◽

Strain Rate ◽

Network Model ◽

Neural Network Model ◽

Artificial Neural Network Model ◽

Rock Strength ◽

Strain Rates ◽

Filling Material ◽

Artificial Neural

Pre-existing cracks and associated filling materials cause the significant heterogeneity of natural rocks and rock masses. The induced heterogeneity changes the rock properties. This paper targets the gap in the existing literature regarding the adopting of artificial neural network approaches to efficiently and accurately predict the influences of heterogeneity on the strength of 3D-printed rocks at different strain rates. Herein, rock heterogeneity is reflected by different pre-existing crack and filling material configurations, quantitatively defined by the crack number, initial crack orientation with loading axis, crack tip distance, and crack offset distance. The artificial neural network model can be trained, validated, and tested by finite 42 quasi-static and 42 dynamic Brazilian disc experimental tests to establish the relationship between the rock strength and heterogeneous parameters at different strain rates. The artificial neural network architecture, including the hidden layer number and transfer functions, is optimized by the corresponding parametric study. Once trained, the proposed artificial neural network model generates an excellent prediction accuracy for influences of high dimensional heterogeneous parameters and strain rate on rock strength. The sensitivity analysis indicates that strain rate is the most important physical quantity affecting the strength of heterogeneous rock.

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Static Mechanical Properties of Expanded Polypropylene Crushable Foam

Materials ◽

10.3390/ma14020249 ◽

2021 ◽

Vol 14 (2) ◽

pp. 249

Author(s):

Przemysław Rumianek ◽

Tomasz Dobosz ◽

Radosław Nowak ◽

Piotr Dziewit ◽

Andrzej Aromiński

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Strain Rate ◽

Energy Absorption ◽

Experimental Tests ◽

Absorption Capacity ◽

Strain Rates ◽

Foam Density ◽

Energy Absorption Capacity ◽

Closed Cell

Closed-cell expanded polypropylene (EPP) foam is commonly used in car bumpers for the purpose of absorbing energy impacts. Characterization of the foam’s mechanical properties at varying strain rates is essential for selecting the proper material used as a protective structure in dynamic loading application. The aim of the study was to investigate the influence of loading strain rate, material density, and microstructure on compressive strength and energy absorption capacity for closed-cell polymeric foams. We performed quasi-static compressive strength tests with strain rates in the range of 0.2 to 25 mm/s, using a hydraulically controlled material testing system (MTS) for different foam densities in the range 20 g/dm3 to 220 g/dm3. The above tests were carried out as numerical simulation using ABAQUS software. The verification of the properties was carried out on the basis of experimental tests and simulations performed using the finite element method. The method of modelling the structure of the tested sample has an impact on the stress values. Experimental tests were performed for various loads and at various initial temperatures of the tested sample. We found that increasing both the strain rate of loading and foam density raised the compressive strength and energy absorption capacity. Increasing the ambient and tested sample temperature caused a decrease in compressive strength and energy absorption capacity. For the same foam density, differences in foam microstructures were causing differences in strength and energy absorption capacity when testing at the same loading strain rate. To sum up, tuning the microstructure of foams could be used to acquire desired global materials properties. Precise material description extends the possibility of using EPP foams in various applications.

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Comparison in Deformation Behavior, Microstructure, and Failure Mechanism of Nickel Base Alloy 625 under Two Strain Rates

Materials ◽

10.3390/ma14102652 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2652

Author(s):

Meng Liu ◽

Quanyi Wang ◽

Yifan Cai ◽

Dong Lu ◽

Tianjian Wang ◽

...

Keyword(s):

Strain Rate ◽

Deformation Behavior ◽

Tensile Deformation ◽

Base Alloy ◽

Inconel 625 ◽

Tensile Fracture ◽

Nickel Base Superalloy ◽

Strain Rates ◽

Tensile Fracture Surface ◽

Nickel Base

Tensile deformation behavior and microstructure of nickel-base superalloy Inconel 625 are investigated under different strain rates of 5 × 10−4 s−1 and 5 × 10−5 s−1. According to the experimental results, yield strength and ultimate tensile strength of the alloy increase with the increase in strain rate in room temperature. Microstructure results indicate that the size of dimples is smaller in the tensile fracture surface at low strain rate than the high strain rate, and the number of dimples is also related to the strain rates and twins appear earlier in the specimens with higher strain rates. Apart from Hollomon and Ludwik functions, a new formula considering the variation trend of strength in different deformation stages is deduced and introduced, which fit closer to the tensile curves of the 625 alloy used in the present work at both strain rates. Furthermore, the Schmid factors of tensile samples under two strain rates are calculated and discussed. In the end, typical work hardening behavior resulting from the dislocations slip behavior under different strain rates is observed, and a shearing phenomenon of slip lines cross through the δ precipitates due to the movement of dislocations is also be note.

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