Abrasion Resistance and High Speed Tensile Strength of Elastomers

1966 ◽  
Vol 39 (4) ◽  
pp. 823-840 ◽  
Author(s):  
Ruprecht Ecker

Abstract In earlier communications, we defined abrasion, especially of tires, as a thermal-oxidative process caused at high velocity of mechanical rupture. Other authors (e.g., Schallamach, Boggs, Zapp etc.), with theoretical and experimental tests, prove the importance of viscoelastic behavior as a characteristic property for abrasion. The results of experiments on six elastomers (NR, IR, BR, SBR, IIR, and EPT) compared in tire tread compounds are communicated and discussed in the present work. Tensile strength was determined over a temperature range of 20° to 140° C at deformation speeds of 10 to 20,000 % elongation per second. Forced, non-resonant vibrations were used to determine viscoelastic properties, e.g., resilience, storage modulus, and loss modulus. As abrasion is a consequence of frictional processes, coefficients of friction, dependent on temperature, were measured on dry, wet, and frosty asphalt/fine concrete track. The apparatus is briefly described. From these test results, an empirical relation established between abrasion, friction, viscoelastic properties, tensile strength at high speed and temperature allows one to predetermine the abrasion behavior of a vulcanizate in the laboratory.

Author(s):  
Kyuho Sim ◽  
Bonjin Koo ◽  
Jong Sung Lee ◽  
Tae Ho Kim

This paper presents the rotordynamic performance measurements and model predictions of a rotor supported on three-pad gas foil journal bearings (GFJBs) with various mechanical preloads. The rotor with its length of 240 mm, diameter of 40 mm, and weight of 19.6 N is supported on two GFJBs and one pair of gas foil thrust bearings (GFTBs), being a permanent magnet rotor of a high speed electric motor. Each bearing pad consisting of a top foil and a bump-strip layer is installed on a lobed bearing housing surface over the arc length of 120 deg along the circumference. Test three-pad GFJBs have four different mechanical preloads, i.e., 0 μm, 50 μm, 70 μm, 100 μm with a common radial nominal clearance of 150 μm. A series of speed-up tests are conducted up to 93 krpm to evaluate the effects of increasing mechanical preloads on the rotordynamic performance. Two sets of orthogonally positioned displacement sensors record the rotor horizontal and vertical motions at the thrust collar and the other end. Test results show that the filtered synchronous amplitudes change little, but the onset speed of subsynchronous motions (OSS) increases dramatically for the increasing mechanical preloads. In addition, test bearings with the 100 μm preload show a higher OSS in load-on-pad (LOP) condition than that in load-between-pads (LBP) condition. A comparison with test results for a one-pad GFJB with a single top foil and bump-strip layer reveals that three-pad GFJB has superior rotordynamic performance to the one-pad one. Finally, the test data benchmark against linear rotordynamic predictions to validate a rotor-GFJB model. In general, predicted natural frequencies of the rotor-bearing system and synchronous rotor motions agree well with test data. However, stability analyses underestimate OSSs recorded during the experimental tests.


Author(s):  
Weiqi Li ◽  
Duncan E. T. Shepherd ◽  
Daniel M. Espino

AbstractThe mechanical characterization of brain tissue has been generally analyzed in the frequency and time domain. It is crucial to understand the mechanics of the brain under realistic, dynamic conditions and convert it to enable mathematical modelling in a time domain. In this study, the compressive viscoelastic properties of brain tissue were investigated under time and frequency domains with the same physical conditions and the theory of viscoelasticity was applied to estimate the prediction of viscoelastic response in the time domain based on frequency-dependent mechanical moduli through Finite Element models. Storage and loss modulus were obtained from white and grey matter, of bovine brains, using dynamic mechanical analysis and time domain material functions were derived based on a Prony series representation. The material models were evaluated using brain testing data from stress relaxation and hysteresis in the time dependent analysis. The Finite Element models were able to represent the trend of viscoelastic characterization of brain tissue under both testing domains. The outcomes of this study contribute to a better understanding of brain tissue mechanical behaviour and demonstrate the feasibility of deriving time-domain viscoelastic parameters from frequency-dependent compressive data for biological tissue, as validated by comparing experimental tests with computational simulations.


2019 ◽  
Vol 285 ◽  
pp. 380-384
Author(s):  
Gerardo Sanjuan-Sanjuan ◽  
Ángel Enrique Chavez-Castellanos

The subject of this work is to investigate viscoelastic properties such as loss modulus (G ́ ́), storage modulus (G ́), complex shear modulus (G*), complex viscosity (η*) and loss angle () at different temperatures by means of a small-amplitude oscillatory test. These properties allow to provide information about materials structure. For this purpose, we employed a tin-lead alloy (Sn-15%Pb) which exhibits a similar microstructure to aluminum alloys and is the classic alloy for semisolid thixotropic studies. It is interesting to note that the Sn-15%Pb alloy exhibits a slightly decrease in storage modulus (G ́) over the entire frequency (0.01-10Hz) at high temperatures, showing its viscoelastic behavior. In addition, a detailed analysis of master curves (oscillatory tests) was made to relate the semisolid microstructure (solid fraction) with the plateau modulus (GN0) which is directly related with both molecular weight or percolation threshold in polymer and gels science respectively.


Holzforschung ◽  
2015 ◽  
Vol 69 (3) ◽  
pp. 265-271 ◽  
Author(s):  
Qianqian Tang ◽  
Mingsong Zhou ◽  
Dongjie Yang ◽  
Xueqing Qiu

Abstract Concentrated sodium lignosulfonate (NaLS) solutions have wide industrial applications. Therefore, the viscoelastic properties of NaLS in concentrations of 55%–63% have been investigated between 5°C and 55°C by means of a dynamic rheological technique, namely, the oscillatory rheological experiments were conducted in a rheometer in the small amplitude oscillatory mode. All solutions showed “shear-thinning” behavior over frequency. The complex viscosity (η*) increased and the loss tangent (tanδ) decreased with increasing concentrations. Both the storage modulus (G′) and the loss modulus (G″) increased with increasing frequencies and concentrations. The change in viscoelastic behavior was probably caused by stronger aggregation effects. However, the effects of temperature on the viscoelastic properties are more complex. For 60% NaLS, G′, G″, and η* decreased, but tanδ increased with increasing temperatures. When the temperature exceeded 20°C, G′, G″, and η* increased, but tanδ decreased, and the relaxation times were increased as a function of temperature. The change in viscoelasticity as a function of temperature may also be related to intermolecular aggregation and the swelling of aggregates. The conductivity experiments indicated that the formation of a greater strength of network structures at higher levels of concentrations between 55% and 63% and temperatures between 20°C and 55°C was probably responsible for elasticity enhancement.


2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hassan Ziari ◽  
Hassan Divandari ◽  
Seyed Mohammad Seyed Ali Akbar ◽  
Seyed Mohsen Hosseinian

Stone matrix asphalt (SMA) mixtures are one of the most resistant types of asphalt mixtures known to date that the bulk load is borne by the aggregate skeleton. In this research, the effect of crumb rubber powder (CRP), Vestenamer polymer, and warm additives, including Sasobit, ZycoTherm, and a porous and warm mix asphalt (PAWMA), was investigated on the moisture resistance of SMA mixtures. A segregation test was performed to determine the tendency of the polymer to separate from modified polymer bitumen under storage conditions. Also, a drain down sensitivity test was conducted to explore the bleeding phenomena and drain down of SMA mixtures. Finally, a boiling water test, as well as an indirect tensile strength (ITS) test, was applied to examine the sensitivity of mixtures to moisture. The segregation test results indicated that by the use of Vestenamer polymer, a conventional (low speed) mixer can be used instead of using a high-speed mixer, and this will be very important in the cost of rubber bitumen production. The drain down test results showed that cellulose fibers prevented the bitumen bleeding of SMA mixtures. Also, the results of the boiling water test indicated that CRP samples containing ZycoTherm had the highest moisture resistance compared to the other warm additives. Among various mixtures, 8% CRP-modified samples containing ZycoTherm resulted in the lowest amount of stripping in SMA mixtures, even more than the base sample. The ITS test results illustrated that the use of CRP, Vestenamer polymer, and warm additives had a significant effect on the ITS amounts of mixtures. Moreover, the samples containing ZycoTherm had the highest tensile strength ratio (TSR) compared to the other SMA samples.


Author(s):  
Kyuho Sim ◽  
Bonjin Koo ◽  
Jong Sung Lee ◽  
Tae Ho Kim

The paper presents the rotordynamic performance measurements and model predictions of a rotor supported on three-pad gas foil journal bearings (GFJBs) with various mechanical preloads. The rotor with its length of 240 mm, diameter of 40 mm, and weight of 19.6 N is supported on two GFJBs and one pair of gas foil thrust bearings (GFTBs), being a permanent magnet rotor of a high speed electric motor. Each bearing pad consisting of a top foil and a bump strip layer is installed on a lobed bearing housing surface over the arc length of 120 deg along the circumference. Test three-pad GFJBs have four different mechanical preloads, i.e., 0 μm, 50 μm, 70 μm, 100 μm with a common radial nominal clearance of 150 μm. A series of speed-up tests are conducted up to 93 krpm to evaluate the effects of increasing mechanical preloads on the rotordynamic performance. Two sets of orthogonally positioned displacement sensors record the rotor horizontal and vertical motions at the thrust collar and the other end. Test results show that the filtered synchronous amplitudes change little, but the onset speed of sub-synchronous motions (OSS) increases dramatically for the increasing mechanical preloads. In addition, test bearings with the 100 μm preload show a higher OSS in load-on-pad (LOP) condition than that in load-between-pads (LBP) condition. A comparison to test results for a one-pad GFJB with a single top foil and bump strip layer reveals that three-pad GFJB has superior rotordynamic performance to the one-pad one. Finally, the test data benchmark against linear rotordynamic predictions to validate a rotor-GFJB model. In general, predicted natural frequencies of the rotor-bearing system and synchronous rotor motions agree well with test data. However, stability analyses underestimate OSSs recorded during the experimental tests.


1974 ◽  
Vol 47 (4) ◽  
pp. 778-787 ◽  
Author(s):  
N. Nakajima ◽  
E. A. Collins ◽  
P. R. Kumler

Abstract The dynamic viscoelastic properties of four samples of butadiene—acrylonitrile raw elastomers, were obtained with a Rheovibron at 110 Hz and temperature range of −80 to 160°C. The complex properties were in agreement with the master curves obtained previously from stress-strain measurements. A master curve encompassing 13 decades of time was constructed using data from Mooney rheometer shear stress-strain, MTS high speed tensile stress-strain, and the Rheovibron. The master curve represents the rubbery region of viscoelastic behavior in terms of time, temperature, and the magnitude of deformation up to the breaking point. This study demonstrates that corresponding states can be found between small (ca. 1 per cent) and large deformation up to break (e.g., 1400 per cent).


1990 ◽  
Vol 18 (4) ◽  
pp. 262-281 ◽  
Author(s):  
J. T. Tielking ◽  
R. R. Hanson ◽  
A. J. Giacomin

Abstract Specimens cut from a 40 × 14 nylon cord aircraft tire were subjected to cyclic strain tests to measure the viscoelastic behavior. Spectral analysis was used to quantify nonlinearity in the stress response. Preliminary studies were made to ascertain the effects of specimen length and width on the test results. A bolted end constraint was developed to uniformly distribute the imposed strain through the thickness of the multiply carcass specimens. Test results show the effects of temperature, frequency, and strain level on the viscoelastic properties. Results are generally in agreement with earlier findings made using tubular test specimens.


2021 ◽  
Vol 71 (1) ◽  
pp. 77-83
Author(s):  
Zhu Li ◽  
Jiali Jiang ◽  
Jianxiong Lyu ◽  
Jinzhen Cao

Abstract In order to better understand the differences in orthotropic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) in frozen and non-frozen states, the storage modulus (E′) and loss modulus (E″) of the longitudinal, radial, and tangential specimens were investigated under water-saturated conditions with temperatures ranging from −120°C (or 30°C) to 280°C. Results revealed that the order of magnitude in E′ for each orientation was consistent for temperatures below 0°C, while the anisotropy in E′ was reduced due to the enhancement effect of ice. Frequency-dependent γ-relaxation was observed at approximately −96°C for all orthotropic directions. A sharp discontinuity in E′ occurred at approximately 0°C for each specimen, together with the corresponding sharp peak in the E″ spectrum. Furthermore, the frozen free water had an effect on the orthotropic viscoelastic behavior in the water-saturated specimens within the range of −120°C to 280°C. Specimens with a frozen history leveled off at the initial temperature ramping phase for each orientation, while a frozen history reduced the decline in stiffness of the wood specimens. Similar to the variations in E′, the dramatic loss of water increased the complexity of the E″ values. The loss of free water also had a pronounced effect on the viscoelastic properties during the temperature ramping process. Thus, in the wood industry, it necessary to consider the variations in the orthotropic viscoelastic performance of specimens under water-saturated conditions during the water loss process.


2016 ◽  
Vol 711 ◽  
pp. 103-110 ◽  
Author(s):  
José Luís Granja ◽  
Miguel Azenha

This paper aims to demonstrate the feasibility of a recently proposed approach (termed VisCoDyn) to assess the viscoelastic behaviour of concrete from the earliest ages, by introducing a known dynamic excitation to a simply supported specimen. The method involves the continuous monitoring of the response of the tested sample in terms of amplitude (force and displacement), as well as the evaluation of the phase lag between the applied force and the response. The acquired data is then used to calculate the storage and loss moduli, according to procedures that are normally used in the context of material testing in polymer science. Indeed, the loss modulus is known to be relatable to the viscoelastic properties of materials.The paper presents the current state of development of the VisCoDyn test methodology together with several test results obtain in specimens that were tested during the first 24 hours of curing. Parallel testing with other techniques is also presented for reference.


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