Articles de revues : « Elastic lifetime »

1

Parker, A. P., S. N. Endersby, T. J. Bond, J. H. Underwood, S. L. Lee et J. Higgins. « Stress Concentration, Stress Intensity, and Fatigue Lifetime Calculations in Autofrettaged Tubes Containing Axial Perforations Within the Wall ». Journal of Pressure Vessel Technology 119, n^o 4 (1 novembre 1997) : 488–93. http://dx.doi.org/10.1115/1.2842334.

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Elastic, elastic-plastic and experimental stress analyses, and fatigue lifetime predictions are presented for thick cylinders containing multiple, axial holes within the wall. The holes are generally semi-elliptical (including semi-circular), and the cylinders are autofrettaged after introduction of the holes and are subsequently subjected to cyclic pressurization of the bore. Two potentially critical failure locations are identified; a fracture-mechanics based design methodology is proposed; elastic and elastic-plastic finite element (FE) analyses are undertaken. The elastic FE analysis predicts hoop stresses at the bore resulting from internal pressurization which are some 7 percent higher than those for the equivalent plain tube. For a given hole size and location and for nominal overstrains of 40 percent or greater, the residual compressive stress at the bore is reduced by approximately 15 percent below the value for a plain tube of the same radius ratio. Two experimental investigations are reported, one based upon X-ray diffraction, to measure residual stresses and stress gradients, and the other based upon radial tube slitting, to measure opening angle. They confirm most features of the residual stress profiles predicted from FE analysis with the exception of high compressive residual stresses and stress gradients immediately adjacent to the hole boundaries. Appropriate use of the residual stress information permits prediction of tube lifetimes for cracks emanating from the bore and from the hole. For the geometry and loading under consideration, the more critical location is predicted to be the hole boundary, the lifetime for failures originating from this point being some 60 percent of the lifetime for cracks originating at the bore.

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Pazdera, Lubos, Libor Topolar, Jaroslav Smutny et Kristyna Timcakova. « Nondestructive Testing of Advanced Concrete Structure during Lifetime ». Advances in Materials Science and Engineering 2015 (2015) : 1–5. http://dx.doi.org/10.1155/2015/286469.

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The paper reports on measurements and analysis of the measurements during hardening and drying of specimens using selected acoustic nondestructive testing techniques. An integrated approach was created for better understanding of the relations between the lifetime cycle and the development of the mechanical properties of concrete. Acoustic emission, impact echo, and ultrasonic techniques were applied simultaneously to the same mixtures. These techniques and results are presented on alkali-activated slag mortars. The acoustic emission method detects transient elastic waves within the material, caused by the release of cumulated stress energy, which can be mechanical, thermal, or chemical. Hence, the cause is a phenomenon which releases elastic energy into the material, which then spreads in the form of an elastic wave. The impact echo method is based on physical laws of elastic stress wave propagation in solids generated by mechanical impulse. Ultrasonic testing is commonly used to find flaws in materials or to assess wave velocity spreading.

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Kansy, J., T. Suzuki, T. Ogawa et M. Murakami. « Study of poly(methylphenylsilylenemethylene) by elastic thermalization lifetime analysis ». Radiation Physics and Chemistry 58, n^o 5-6 (juin 2000) : 545–50. http://dx.doi.org/10.1016/s0969-806x(00)00215-2.

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Kondrashov, Oleg V., Timur R. Galimzyanov, Rodion J. Molotkovsky, Oleg V. Batishchev et Sergey A. Akimov. « Membrane-Mediated Lateral Interactions Regulate the Lifetime of Gramicidin Channels ». Membranes 10, n^o 12 (25 novembre 2020) : 368. http://dx.doi.org/10.3390/membranes10120368.

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The lipid matrix of cellular membranes is an elastic liquid crystalline medium. Its deformations regulate the functionality and interactions of membrane proteins,f membrane-bound peptides, lipid and protein-lipid domains. Gramicidin A (gA) is a peptide, which incorporates into membrane leaflets as a monomer and may form a transmembrane dimer. In both configurations, gA deforms the membrane. The transmembrane dimer of gA is a cation-selective ion channel. Its electrical response strongly depends on the elastic properties of the membrane. The gA monomer and dimer deform the membrane differently; therefore, the elastic energy contributes to the activation barriers of the dimerization and dissociation of the conducting state. It is shown experimentally that channel characteristics alter if gA molecules have been located in the vicinity of the conducting dimer. Here, based on the theory of elasticity of lipid membranes, we developed a quantitative theoretical model which allows explaining experimentally observed phenomena under conditions of high surface density of gA or its analogues, i.e., in the regime of strong lateral interactions of gA molecules, mediated by elastic deformations of the membrane. The model would be useful for the analysis and prediction of the gA electrical response in various experimental conditions. This potentially widens the possible applications of gA as a convenient molecular sensor of membrane elasticity.

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5

P, Contreras. « A Tale of the Scattering Lifetime and the Mean Free Path ». Physical Science & ; Biophysics Journal 6, n^o 2 (12 octobre 2022) : 1–12. http://dx.doi.org/10.23880/psbj-16000225.

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The idea of applying the scattering lifetime calculated from the imaginary part of the zero temperature elastic scattering cross-section to study a hidden self-consistent damping in two spaces of importance for non-equilibrium statistical mechanics is proposed. It is discussed its relation with the classical phase space from statistical mechanics and the configuration space from nonrelativistic quantum mechanics. This idea is contrasted with the mean free path values in three elastic collision regimes. The main exercise is to study the behavior of a self-consistent probabilistic distribution function in a space we have called the reduced phase space since it is related to the scattering lifetime. This exercise has been solved in two unconventional superconductors for which several calculations are discussed. One of them is to obtain the scattering phase shift from the inverse strength of an atomic potential and the other is to build several phases with different nodal configuration of the superconducting order parameter and show that the imaginary self-consistent part of the scattering cross-section is always positive for two compounds: the triplet strontium ruthenate and the singlet doped with strontium lanthanum cuprate when three models of superconducting order parameters are used: the quasi-point, the point and the line nodal cases. We finally compare the frequency dispersion in the anomalous skin effect with singular shapes of the Fermi surface with the frequency dispersion in the scattering lifetime and their respective mean free paths. This idea is useful because it intuitively explores the nonlocality of this type of hidden self-consistent damping for those incoherent fermionic quasiparticles.

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Guo, Shiwen, et Jie Yan. « Structural-Elastic Determination of the Lifetime of Biomolecules Under Force ». Biophysical Journal 114, n^o 3 (février 2018) : 577a. http://dx.doi.org/10.1016/j.bpj.2017.11.3155.

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Song, Ming Xin, Rui Wu, Qian Liu, Hong Wang, Zuo Bao Cao, Ming Hua Chen et Jing Hua Yin. « Reliability Research of Capacitive RF-MEMS Switch ». Advanced Materials Research 753-755 (août 2013) : 2507–10. http://dx.doi.org/10.4028/www.scientific.net/amr.753-755.2507.

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This paper presents the model of capacitive RF-MEMS switch for the lifetime prediction. The model is based on dielectric charging failure mechanism. The simulation results show that lifetime can reach 1000 hours when elastic coefficient (K) adopts 4-16N/m, Si3N4 as dielectric material, 0.4-1μm of dielectric thickness, 2-5μm of plate distance, less than 20V of driven voltage.

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Qian, Jin, Jizeng Wang et Huajian Gao. « Lifetime and Strength of Adhesive Molecular Bond Clusters between Elastic Media† ». Langmuir 24, n^o 4 (février 2008) : 1262–70. http://dx.doi.org/10.1021/la702401b.

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Parker, A. P., J. H. Underwood et D. P. Kendall. « Bauschinger Effect Design Procedures for Autofrettaged Tubes Including Material Removal and Sachs’ Method ». Journal of Pressure Vessel Technology 121, n^o 4 (1 novembre 1999) : 430–37. http://dx.doi.org/10.1115/1.2883726.

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Autofrettage is used to introduce advantageous residual stresses into pressure vessels and to enhance their fatigue lifetimes. The Bauschinger effect serves to reduce the yield strength in compression as a result of prior tensile plastic overload and can produce lower compressive residual hoop stresses near the bore than are predicted by “ideal” autofrettage solutions (elastic/perfectly plastic without Bauschinger effect). A complete analysis procedure is presented which encompasses representation of elastic-plastic uniaxial loading material behavior and of reverse-loading material behavior as a function of plastic strain during loading. Such data are then combined with some yield criterion to accurately predict elastic-plastic residual stress fields within an autofrettaged thick cylinder. Pressure for subsequent reyielding of the tube is calculated. The numerical procedure is further used to determine residual stress fields after removal of material from inside diameter (i.d.) and/or outside diameter (o.d.), including the effects of any further plasticity. A specific material removal sequence is recommended. It is shown that Sachs’ experimental method, which involves removing material from the i.d., may very significantly overestimate autofrettage residual stresses near the bore. Stress ranges and stress intensity factors for cracks within such stress fields are calculated together with the associated fatigue lifetimes as such cracks propagate under cyclic pressurization. The loss of fatigue lifetime resulting from the Bauschinger effect is shown to be extremely significant.

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Shlyannikov, Valery, Ivan Ishtyryakov et Rustam Yarullin. « Life-time prediction for aviation GTE compressor disk based on mixed-mode and multi-axial fracture resistance parameters ». MATEC Web of Conferences 300 (2019) : 11001. http://dx.doi.org/10.1051/matecconf/201930011001.

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This study is concerned with analysis of fatigue crack growth and life-time prediction for aviation GTE compressor disk under operation conditions. For consideration were different combinations of rotational speed, temperature, surface flaw form and sizes as well as elastic-plastic titanium alloy BT3-1 properties are employed. A crack growth rate equation is derived involving the fracture process zone size and nonlinear stress intensity factor. The assessments of the structural integrity of the rotating disk are compared for elastic and elastic-plastic solutions. It is stated that the traditional elastic crack growth models overestimate the residual fatigue lifetime with respect to the nonlinear fracture mechanics approach.

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11

Brown, M. W. « Aspects of Fatigue Crack Growth ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 202, n^o 1 (janvier 1988) : 19–29. http://dx.doi.org/10.1243/pime_proc_1988_202_082_02.

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The propagation of fatigue cracks under low levels of cyclic stress can be modelled by linear elastic fracture mechanics. Elastic-plastic parameters must be used for the higher stress amplitudes of conventional S–N curves in both the low and the high cycle fatigue regimes. The occurrence of different modes of crack growth is discussed and the use of a propagation law to predict component lifetime is demonstrated.

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Xing, Zhong Wen, Jun Bao, Xue Chun Li et Yu Ying Yang. « Micromechanism of Plastic Deformation on Elastic Modulus ». Materials Science Forum 546-549 (mai 2007) : 713–18. http://dx.doi.org/10.4028/www.scientific.net/msf.546-549.713.

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The key to enhance the precision of sheet metal stamping parts is accurate prediction and control of the springback. And one of the dominant factors of springback is the elastic modulus. The change of elastic modulus with plastic deformation was experimentally studied for the annealed LY12 and the annealed LF21 aluminum alloy respectively, and the changing role of elastic modulus with plastic deformation was obtained. By inverse pole figure from the X-ray diffraction analysis, the effects of the material original textures and their changing with plastic deformation on the elastic modulus were studied. And by positron annihilation lifetime spectrum , the influence of lattice distortion caused by crystal defect during plastic deformation on the elastic modulus was investigated. The micromechanism of the elastic modulus changing with plastic deformation for aluminum alloy is revealed, which lays a foundation for improving the stamping parts’ precision.

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Poduška, Jan, Pavel Hutař, Andreas Frank, Gerald Pinter et Luboš Náhlík. « Lifetime Calculation of Soil-Loaded Non-Pressure Polymer Pipes ». Key Engineering Materials 827 (décembre 2019) : 141–46. http://dx.doi.org/10.4028/www.scientific.net/kem.827.141.

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Outstanding durability of plastic pressure and non-pressure pipes can cause difficulties, when a reasonable lifetime estimation is needed. It is impossible to prove the lifetime by testing, but there is a method of calculation that can provide a certain idea about the expected lifetime. The lifetime estimation is based on the assumption that the failure occurs as a result of the slow crack growth mechanism and it is calculated using the linear elastic fracture mechanics approach. Numerical simulations of crack growth in the pipe are necessary for this calculation. These simulations must consider various effects that can play a role in the lifetime. This paper deals with the lifetime calculations of a pressure and a non-pressure corrugated pipe considering the soil loads acting on pipes when they are buried. In the simulation of the pressure pipe, a combination of loads is applied that consists of internal pressure, residual stress and the soil loads. The influence of the loads is discussed. The non-pressure corrugated pipe is loaded by the soil loads only.

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14

Chen, Liu Caroline, Zonghe Lai, Zhaonian Cheng et Johan Liu. « Reliability Investigation for Encapsulated Isotropic Conductive Adhesives Flip Chip Interconnection ». Journal of Electronic Packaging 128, n^o 3 (7 août 2005) : 177–83. http://dx.doi.org/10.1115/1.2227057.

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Isotropic conductive adhesives (ICA) are gaining more and more application interests in electronic manufacturing, however, their failure mechanism is not been fully understood. In this paper we present reliability investigations on an encapsulated ICA flip chip interconnection. Experimental work included product lifetime measurement, cross section observation, and whole module warpage scanning. Results revealed that the chip-size effect on the ICA lifetime was obvious. A theoretical analysis was conducted with Finite Element Method (FEM) simulation. Viscoelastic models for adhesives and underfill materials were employed, and the comparison with an elastic model was made. Calculated equivalent stresses Seqv and shear stress σxy fitted well with the experimental lifetime measurement, thus a lifetime relationship similar to the Coffin-Manson formula was established to predict the thermal fatigue life of an encapsulated ICA flip chip. Furthermore, the influences of underfill properties on the ICA reliability were discussed.

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Contreras, P., Dianela Osorio et E. Yu Beliayev. « Dressed behavior of the quasiparticles lifetime in the unitary limit of two unconventional superconductors ». Low Temperature Physics 48, n^o 3 (mars 2022) : 187–92. http://dx.doi.org/10.1063/10.0009535.

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We compare the quasiparticle lifetime behavior in the unitary limit of two unconventional superconductors dressed by nonmagnetic impurity scattering to differentiate an anomalous functional behavior in its shape when the disorder concentration is changed in a triplet paired model with respect to the well behave singlet model. For singlet paired superconductors, the functional shape of the lifetime due to elastic scattering around the nodal regions in the reduced elastic scattering space, does not change with the disorder concentration, but for a triplet model with a tiny gap, an anomalous drop in shape is observed only when small values of disordering are added. We use a 2D tight-binding parametrization to study the reduced phase space of the first Brillouin zone, where the low-energy scattering is restricted to the nodal/quasinodal regions for two irreducible representations of the crystal lattice. A new class of Wigner probabilistic distribution functions is discussed for triplet superconductors.

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Bouaziz, Rami, Laurianne Truffault, Rouslan Borisov, Cristian Ovalle, Lucien Laiarinandrasana, Guillaume Miquelard-Garnier et Bruno Fayolle. « Elastic Properties of Polychloroprene Rubbers in Tension and Compression during Ageing ». Polymers 12, n^o 10 (14 octobre 2020) : 2354. http://dx.doi.org/10.3390/polym12102354.

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Being able to predict the lifetime of elastomers is fundamental for many industrial applications. The evolution of both tensile and compression behavior of unfilled and filled neoprene rubbers was studied over time for different ageing conditions (70 °C, 80 °C and 90 °C). While Young’s modulus increased with ageing, the bulk modulus remained almost constant, leading to a slight decrease in the Poisson’s ratio with ageing, especially for the filled rubbers. This evolution of Poisson’s ratio with ageing is often neglected in the literature where a constant value of 0.5 is almost always assumed. Moreover, the elongation at break decreased, all these phenomena having a similar activation energy (~80 kJ/mol) assuming an Arrhenius or pseudo-Arrhenius behavior. Using simple scaling arguments from rubber elasticity theory, it is possible to relate quantitatively Young’s modulus and elongation at break for all ageing conditions, while an empirical relation can correlate Young’s modulus and hardness shore A. This suggests the crosslink density evolution during ageing is the main factor that drives the mechanical properties. It is then possible to predict the lifetime of elastomers usually based on an elongation at break criterion with a simple hardness shore measurement.

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Ghodrati Amiri, Gholamreza, Gholamreza Abdollahzadeh Darzi et Javad Vaseghi Amiri. « Design elastic input energy spectra based on Iranian earthquakes ». Canadian Journal of Civil Engineering 35, n^o 6 (juin 2008) : 635–46. http://dx.doi.org/10.1139/l08-013.

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The goal of this paper is to propose input energy spectra applicable to seismic design of structures based on Iranian earthquakes. In terms of input energy, these spectra represent the load effects of a strong earthquake that a structure may encounter during its lifetime. For this purpose, from among 1800 existing earthquake records in Iran, 110 records were selected. By using these records and through dynamic response analyses, the design input energy spectra for four ground types, defined by the Iranian earthquake code of practice, have been derived.

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Song, Ming Xin, Guo Xu Zheng et Rui Wu. « Dielectric Charging Failure Analysis of RF-MEMS Switch ». Applied Mechanics and Materials 274 (janvier 2013) : 170–73. http://dx.doi.org/10.4028/www.scientific.net/amm.274.170.

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MEMS devices commercialization is hindered by reality problems. Among them main problem is caused by dielectric charging. This paper studies charging model and charges distribution which are constructed on adhesion failure. Lifetime prediction formula is given. Simulation results show that under the condition of low driven voltage requirement, lifetime is bigger than 1000 hours when elastic coefficient (K) adopts 4-16N/m, 0.4-1μm for dielectric thickness, 2-5μm for plate distance and S3iN4 as dielectric material. At last, C-V performances inflected by dielectric charging is studied by theoretical calculations and analyzing positive or negative charging respectively.

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Wang, Binjie, Shouguang Sun, Shuang Ma et Xi Wang. « Fatigue damage and reliability assessment of subway train bogie frames under operating conditions ». Advances in Mechanical Engineering 12, n^o 1 (janvier 2020) : 168781402090359. http://dx.doi.org/10.1177/1687814020903590.

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Fatigue cracks developed on subway train bogie frames before reaching the designed lifetime, which poses great challenges to operational safety. This article presents a structural fatigue reliability assessment method combining both the in-service measurement of dynamic stress and probabilistic approach for lifetime prediction. It was found that curved interval with rail corrugation can induce the elastic vibration and the modal stress on the frame, which caused the accelerated accumulation of the fatigue damage. The predicted failure mileage for the welding joint with 99% reliability was only 340,000 km, which agreed well with the real operation situation.

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Zhang, Jian-Zhi, David H. Leach et Richard K. Chang. « Photon lifetime within a droplet : temporal determination of elastic and stimulated Raman scattering ». Optics Letters 13, n^o 4 (1 avril 1988) : 270. http://dx.doi.org/10.1364/ol.13.000270.

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Qian, Jin, Jizeng Wang, Yuan Lin et Huajian Gao. « Lifetime and Strength of Periodic Bond Clusters between Elastic Media under Inclined Loading ». Biophysical Journal 97, n^o 9 (novembre 2009) : 2438–45. http://dx.doi.org/10.1016/j.bpj.2009.08.027.

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Parker, Anthony P. « A Critical Examination of Sachs’ Material-Removal Method for Determination of Residual Stress ». Journal of Pressure Vessel Technology 126, n^o 2 (1 mai 2004) : 234–36. http://dx.doi.org/10.1115/1.1689357.

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Sachs’ method is an experimental procedure used primarily in the determination of residual stresses in autofrettaged thick cylinders. In its usual form it involves fixing axial and hoop direction strain gauges to the OD of a tube; strain readings are then obtained after each incremental removal of material from the bore. Sachs’ analysis assumes that the remaining tube unloads in linear-elastic fashion throughout the process and that superposition may therefore be employed to quantify the residual stresses within the original tube. By numerical simulation of two complete Sachs’ experimental sequences with “open end” conditions it is demonstrated that the assumption of elastic unloading is invalidated by the Bauschinger effect. Sachs’ method thereby overestimates compressive residual bore hoop stresses in a typical tube by between 24% and 43%. If used as the basis for cyclic pressurization fatigue lifetime predictions with pre-existing cracks, such discrepancies will cause overestimates in fatigue lifetime of an order of magnitude. Sachs’ experimental procedure is therefore not recommended as a reliable or conservative method for determination of residual stress.

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Rjelka, Marek, Martin Barth, Sven Reinert, Bernd Koehler, Joachim Bamberg, Hans Uwe Baron et Roland Hessert. « Third Order Elastic Constants and Rayleigh Wave Dispersion of Shot Peened Aero-Engine Materials ». Materials Science Forum 768-769 (septembre 2013) : 201–8. http://dx.doi.org/10.4028/www.scientific.net/msf.768-769.201.

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Aero-engine components exposed to high mechanical stresses are made of high-strength alloys and additionally, they are surface treated by shot peening. This process introduces compressive residual stress into the material making it less sensitive to stress corrosion cracking and fatigue and therefore benefits the components performance and lifetime. Moreover cold work is induced in an amount depending on the peening parameters. To approximate the remaining lifetime, a quantitative, non-destructive method for stress assessment is required. It was shown that surface treatment of such alloys can be characterized by broadband Rayleigh wave dispersion measurements. However, the relative contributions of residual stress and cold work, respectively, remained an open point. This paper presents the determination of third order elastic constants (TOEC) for IN718 and Ti6246, providing, together with a model for the inversion of dispersion data, a quantitative access to the acoustoelastic effect. Finally, some measurements of differently treated samples are given.

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Hutař, Pavel, Martin Ševčík, Luboš Náhlík, Adreas Frank, Jaroslav Kučera et Gerald Pinter. « Numerical Lifetime Prediction of Polymer Pipes Taking into Account Residual Stress ». Key Engineering Materials 577-578 (septembre 2013) : 169–72. http://dx.doi.org/10.4028/www.scientific.net/kem.577-578.169.

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In this paper a methodology for assessment of residual stress effects on crack behaviour in the polymer pipe is developed. For simplicitys sake, a linear distribution of residual stresses across the pipe wall is assumed. Linear elastic fracture mechanics is used for the fracture mechanics analysis of the cracked pipe. An approximate relation for the stress intensity factor estimation for a crack in a polymer pipe, with residual stress taken into account is suggested and discussed. The methodology presented can be helpful for a rapid lifetime estimation of polyolefin pipelines.

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Bryaskova, R., R. Mateva, N. Djourelov et M. Krasteva. « Study of multiblock polyamide-6/Poly-(isoprene) copolymers by positron annihilation spectroscopy ». Open Chemistry 6, n^o 4 (1 décembre 2008) : 575–80. http://dx.doi.org/10.2478/s11532-008-0073-9.

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AbstractPositron annihilation lifetime spectroscopy (PALS) has been used to determine the free volume in multiblock polyamide-6/poly-(isoprene) copolymers (PA-6/PI), synthesized via activated anionic bulk copolymerization. The diisocyanate functionalized telechelic PI, blocked with caprolactam (CL) has been used as a commoner and an activator at the same time. The elastic PI block incorporated into the main chain of PA-6 affects the amorphous and crystal phase of the copolymer leading to changing in degree of crystallinity. The positron annihilation lifetime spectroscopy (PAL) and Doppler broadening of annihilation line (DBAL) technique in a set of pure PA-6 and PA-6/PI copolymers with two different compositions have been applied and evaluation of the size of free-volume holes (pores), localized mainly in the disordered regions of the PA-6/PI copolymer by measuring the o-Ps lifetime (τ3) and o-Ps intensity (I3) has been performed.

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Pietrzak, Ryszard, et Roman Szatanik. « The Effect of Impact Pressure on Positron Lifetime in Ultra High Molecular Weight Polyethylene (PE-UHMW)Chirulen®1120 ». Materials Science Forum 666 (décembre 2010) : 85–88. http://dx.doi.org/10.4028/www.scientific.net/msf.666.85.

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The paper presents the results of investigations of the effect of impact pressure (in the range of both elastic and plastic deformations) on the parameters of the positron lifetime spectra in PE-UMHW polymer known under the trade mark Chirulen1120. The changes in the long-living component of the positron lifetime spectrum, connected with the annihilation of o-Ps in the pick-off process, are analyzed in dependence on the impact energy. The impact duration in the Charpy’s tests depending on the impact energy was measured, too. The dependencies of the radius of the volume of empty spaces in which the positronium annihilates, on the impact pressure were determined applying the Eldrup-Tao model.

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Zivkovic, Miroslav, Snezana Vulovic et Rodoljub Vujanac. « Assessment of the drum remaining lifetime in thermal power plant ». Thermal Science 14, suppl. (2010) : 313–21. http://dx.doi.org/10.2298/tsci100507030z.

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In this paper analysis of stress and thermal-elastic-plastic strain of the drum is performed. Influence of modified thickness, yield stress and finite element model of welded joint between pipe and drum on assessment of the remaining lifetime of the drum in the thermal power plant is analyzed. Two analyses are compared. In the first, drum is modeled by shell and by 3D finite elements with projected geometrical and material data of drum. Then, the drum is modeled by shell and by 3D finite elements with modified thickness and yield stress. The analysis show that detailed modeling of stress concentration zones is necessary. Adequate modeling gives lower maximal effective plastic strain and increased number of cycles and, in that case, 3D finite elements are better comparing to shell finite elements.

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Szabó, Dániel. « Linear elastic finite element investigation of titanium specimen produced by Additive Manufacturing ». International Journal of Engineering and Management Sciences 4, n^o 4 (9 septembre 2019) : 85–91. http://dx.doi.org/10.21791/ijems.2019.4.9.

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Nowadays orthopaedic implants are mainly fabricated from solid material (titanium alloy). The mechanical properties of these implants are much stronger than human bone tissue’s properties, and this leads to fixation problems and a short lifetime, but today these problems can be eliminated with the usage of metal additive manufacturing. The mechanical properties of the implants can be influenced on demand with the variation of the material structure using different sizes and types of unit cells for building up its structure.

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Funabashi, Masahiro, Fumi Ninomiya, Akihiro Oishi, Akihiko Ouchi, Hideaki Hagihara, Hiroyuki Suda et Masao Kunioka. « Highly Accelerated Aging Method for Poly(ethylene terephthalate) Film Using Xenon Lamp with Heating System ». Journal of Polymers 2016 (21 avril 2016) : 1–9. http://dx.doi.org/10.1155/2016/8547524.

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PET films were degraded at temperature higher than 100°C with steam and xenon light by using the newly developed system. Degradation products obtained using the proposed and conventional systems were essentially the same, as indicated by the similar increase in the intensity of the carbonyl peak near 1685 cm−1 in the FT-IR spectra of irradiated specimens and spectrum of original PET film. Elastic moduli derived from the stress-strain (SS) curves obtained in tensile tests were almost the same in the case of the proposed and conventional systems and were independent of the heating temperature, light intensity, and irradiation time. Tensile strength of degraded PET films decreases with increasing heating temperature. Tensile strengths of PET films degraded at same temperature decrease linearly with increasing intensity of xenon light. The lifetime at 90% strength of PET films was calculated. Attempts were made to express this lifetime as functions of the light intensity and the reciprocal of the absolute temperature by using the Eyring model. Estimated lifetime 15.9 h of tensile test using Eyring model for PET film agreed with the lifetime 22.7 h derived from data measured using the xenon weather meter.

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Pautrel, Xavier. « ENVIRONMENTAL POLICY, EDUCATION AND GROWTH : A REAPPRAISAL WHEN LIFETIME IS FINITE ». Macroeconomic Dynamics 16, n^o 5 (5 décembre 2011) : 661–85. http://dx.doi.org/10.1017/s1365100510000830.

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When finite lifetime is introduced in a Lucas [Journal of Monetary Economics 22 (1988), 3–42] growth model where the source of pollution is physical capital, the environmental policy may enhance the growth rate of a market economy, whereas pollution does not influence educational activities, labor supply is not elastic, and human capital does not enter the utility function. The result arises from the generational turnover effect due to finite lifetime and it remains valid under conditions when the education sector uses final output as well as time to accumulate human capital. This article also demonstrates that ageing reduces the positive influence of environmental policy when growth is driven by human capital accumulation à la Lucas in the overlapping-generations model of Yaari [Review of Economic Studies 32 (1965), 137–150] and Blanchard [Journal of Political Economy 93 (1985), 223–247].

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WILKOWSKI, JACEK, MAREK BARLAK, JOANNA WACHOWICZ, ROMAN BOTTGER et ZBIGNIEW WERNER. « Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tools life during particleboard milling ». Annals of WULS, Forestry and Wood Technology 106 (15 janvier 2019) : 62–66. http://dx.doi.org/10.5604/01.3001.0013.7738.

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Nano-scale hardness and elastic modulus of WC-Co composites and their relationship to the tool life during particleboards milling. The paper summarizes the results of the technique of hardness and elastic modulus determination using a load and displacement sensing indentation experiments. During the tests these properties were measured in nano-scale for different types of WC-Co composites using the Anton Paar TriTec Ultra Nano Hardness Tester (UNHT). In addition, durability examination of WC-Co tools during milling of particleboard was carried out. In the final stage, the correlation of the studied properties with the lifetime of tools was analyzed. The studies have revealed a relationship between micro-hardness and the total cutting length of the WC-Co tools.

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Khurgin, Jacob B., Sanyam Bajaj et Siddharth Rajan. « Elastic scattering by hot electrons and apparent lifetime of longitudinal optical phonons in gallium nitride ». Applied Physics Letters 107, n^o 26 (28 décembre 2015) : 262101. http://dx.doi.org/10.1063/1.4938745.

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Someya, Satoshi, Keiko Ishii, Tetsuo Munakata et Masayuki Saeki. « Lifetime-based measurement of stress during cyclic elastic deformation using mechanoluminescence of SrAl_2O_4:Eu^2+ ». Optics Express 22, n^o 18 (3 septembre 2014) : 21991. http://dx.doi.org/10.1364/oe.22.021991.

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Druyanov, B., et I. Roman. « Lower bound for LCF lifetime and its application to safe design of elastic viscoplastic structures ». International Journal of Solids and Structures 43, n^o 16 (août 2006) : 4673–86. http://dx.doi.org/10.1016/j.ijsolstr.2005.06.013.

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Koh, Seung-Kee. « Elastic-plastic stress analysis and fatigue lifetime prediction of cross-bores in autofrettaged pressure vessels ». KSME International Journal 14, n^o 9 (septembre 2000) : 935–46. http://dx.doi.org/10.1007/bf03185796.

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Nguyen-Tri, Phuong, Ennouri Triki et Tuan Anh Nguyen. « Butyl Rubber-Based Composite : Thermal Degradation and Prediction of Service Lifetime ». Journal of Composites Science 3, n^o 2 (5 mai 2019) : 48. http://dx.doi.org/10.3390/jcs3020048.

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Butyl rubber-based composite (BRC) is one of the most popular materials for the fabrication of protective gloves against chemical and mechanical risks. However, in many workplaces, such as metal manufacturing or automotive mechanical services, its mechanical hazards usually appear together with metalworking fluids (MWFs). The presence of these contaminants, particularly at high temperatures, could modify its properties due to the scission, the plasticization and the crosslinking of the polymer network and thus lead to severe modification of the mechanical and physicochemical properties of material. This work aims to determine the effect of temperature and a metalworking fluid on the mechanical behavior of butyl rubber composite, dealing with crosslinking density, cohesion forces and the elastic constant of BRC, based on Mooney–Rivlin’s theory. The effect of temperature with and without MWFs on the thermo-dynamical properties and morphology of butyl membranes was also investigated. The prediction of service lifetime was then evaluated from the extrapolation of the Arrhenius plot at different temperatures.

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Linins, Oskars, Juris Krizbergs et Irina Boiko. « Wear Estimation Using 3D Surface Roughness Parameters ». Key Engineering Materials 527 (novembre 2012) : 167–72. http://dx.doi.org/10.4028/www.scientific.net/kem.527.167.

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The aim of this work is to propose a methodology of lifetime prediction of details by new approach for linear wear intensity determination using 3D surface roughness parameters. For qualitative evaluation of the wear process the linear wear intensity (Ih), which may be determined separately for the plastic and elastic contact, is commonly used. Since the elastic contact is mainly required in pairs of details in mechanical engineering in these paper this kind of contact was examined. In our research, the random surface model was used. The surface machined with abrasive instruments (grinding, polishing, honing, etc) has the irregular shape of surface roughness, which can be described with random function. Irregular surface is expressed by a random field h(x, y) of two variables x and y which are Cartesian coordinates of a surfaces point, where the height of roughness asperity h(x, y) has a normal probability distribution. In wear research the probability theory was used. Further in deformed volume calculation, as well as in determination of the length of the surface’s contact the 3D surface roughness parameters were used. The strong correlation between 3D roughness parameters Sa (arithmetic mean height) and Str=Rsm1/Rsm2 (texture aspect ratio of the surface) was revealed. As a result of research, the methodology of lifetime prediction of details by new approach for linear wear intensity determination using 3D surface roughness parameters was elaborated and proposed. After calculation of linear wear intensity Ih, it is possible to estimate lifetime of wearing details. So, at a first time in wear estimation the 3D surface roughness parameters were used. The results of this work have wide practical application, for example in design, texture specification on drawings etc.

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Gope, Jhuma, Sushil Kumar, A. Parashar, S. Dayal, C. M. S. Rauthan et P. C. Srivastava. « Effect of Hydrogen Content and Bonding Environment on Mechanical Properties of Hydrogenated Silicon Films Deposited by High-Frequency PECVD Process ». ISRN Nanomaterials 2012 (17 juillet 2012) : 1–9. http://dx.doi.org/10.5402/2012/429348.

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The mechanical properties of hydrogenated silicon thin films deposited using high-frequency PECVD process were studied, which certainly have importance for optoelectronic devices particularly for getting stability and long operating lifetime in harsh conditions. Nanoindentation technique was used to measure the load versus displacement curves, hardness (H), elastic modulus (E), plastic resistance parameter (H/E), elastic recovery (ER), and plastic deformation energy (Ur), while laser scanning stress measurement setup was used to measure the intrinsic stress of these films. The concentration of bonded hydrogen in these films was found in the range of 3.6 to 6.5 at. % which was estimated using integrated intensity of IR absorption peak near 640 cm−1. Dependence of mechanical properties of these films on hydrogen content and bonding environment has been investigated. The film containing minimum hydrogen content (3.6%) shows the maximum elastic recovery (52.76%) and minimum plastic deformation energy (3.95×10−10 J). Surface roughness measured by AFM was found to decrease with the increase in hydrogen content in the film. The dependency of stress on the plasma frequency and applied power has also been discussed.

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Tandon, R., T. E. Buchheit et D. M. Berry. « Elastic property differences in a multi-mode optical fiber and the effect on predicted mechanical lifetime ». Journal of Non-Crystalline Solids 358, n^o 6-7 (avril 2012) : 1009–13. http://dx.doi.org/10.1016/j.jnoncrysol.2012.01.032.

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Liu, Chun, Jean-Lou Lebrun et François Sibieude. « An Advanced Technique for High Temperature X-Ray Elastic Constant and Stress Investigations ». Advances in X-ray Analysis 36 (1992) : 411–22. http://dx.doi.org/10.1154/s0376030800019030.

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AbstractA high temperature in situ X-Tay diffraction (HTXRD) instrument was devised for residual stress (RS) and X-ray elastic constant (XECs) investigations. The aim was to gain a better understanding of the stresses developed during high temperature oxidation, which is essential for the lifetime improvement of refractory alloys. The investigators use sin2ψ method to survey the stress evolution during oxidation in both the scale and the substrate, and differential method to determine the XECs that relate the measured/measurable deformation to the stress state of the materials studied. The stresses on the Ni/NiO system are measured in situ. The XECs are determined on XC75 steel samples. This paper presents the theories of stresses and XECs determined by HTXRD and briefly discusses the experimental results.

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Ziegler, Lisa, Ursula Smolka, Nicolai Cosack et Michael Muskulus. « Brief communication : Structural monitoring for lifetime extension of offshore wind monopiles : can strain measurements at one level tell us everything ? » Wind Energy Science 2, n^o 2 (12 septembre 2017) : 469–76. http://dx.doi.org/10.5194/wes-2-469-2017.

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Abstract. Operators need accurate knowledge on structural reserves to decide about lifetime extension of offshore wind turbines. Load monitoring enables us to directly compare design loads with real loading histories of the support structure in order to calculate its remaining useful lifetime. Monitoring of every hot spot is technically and financially not feasible. This paper presents a novel idea for load monitoring of monopiles. It requires strain measurements at only one level convenient for sensor installation, such as tower bottom. Measurements are converted into damage equivalent loads for 10 min time intervals. Damage equivalent loads are extrapolated to other locations of the structure with a simulation model and statistical algorithm. For this, structural loads at all locations of the monopile are calculated with aero-hydro-elastic software and updated finite element models. Damage equivalent loads at unmeasured locations are predicted from the simulation results with a k-nearest neighbor regression algorithm. The extrapolation was tested with numerical simulations of an 8 MW offshore wind turbine. Results show that damage can be predicted with an error of 1–3 % if this is done conditional on mean wind speed, which is very promising. The load monitoring concept is simple, cheap and easy to implement. This makes it ideal for making decisions on lifetime extension of monopiles.

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Cseh, Dávid, et Valéria Mertinger. « X-Ray Diffraction Measurements of Residual Stress Induced by Surface Compressing Methods ». Materials Science Forum 729 (novembre 2012) : 199–204. http://dx.doi.org/10.4028/www.scientific.net/msf.729.199.

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Residual stresses have a fundamental effect on the operational behaviour and lifetime of industrial products. The fatigue resistance of machine parts can be increased by introducing residual compressive stresses into the surface region. For certain machine parts especially in the vehicle industry the residual stress is strongly demanded by the quality control. For this reason, measuring the stress accurately is becoming increasingly important. The Almen test, which only gives a qualitative result, is widely used in the industry. Shot peening and rolling are methods which are suitable for creating elastic residual stresses. This paper examines the technologies used by Rába Futómű Nyrt. to increase the lifetime by means of residual stress. We performed analysis of the residual stress of samples shot peened the same way but under different heat treatment states. We compared the residual stress values of burnished and hardened shaft joints, and the residual stress states of gear made of hardened alloy, comparing the carbonized ones to ones which were shot peened under small intensity.

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Siles, S., Gérard Moya, A. Si Ahmed et Jerzy Kansy. « Positron Annihilation Study of Collagen Biopolymer : Comparison between the Three-Component and the Elastic Thermalization Lifetime Analyses ». Materials Science Forum 363-365 (avril 2001) : 331–33. http://dx.doi.org/10.4028/www.scientific.net/msf.363-365.331.

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Kansy, J., T. Suzuki, T. Ogawa et M. Murakamic. « “Study of poly(methylphenylsilylenemethylene) by elastic thermalization lifetime analysis” [Radiation Physics and Chemistry 58 (2000) 545-550 ». Radiation Physics and Chemistry 60, n^o 6 (mars 2001) : 651. http://dx.doi.org/10.1016/s0969-806x(01)00211-0.

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Vrbka, J., Z. Knésl et L. Holuŝa. « Finite element modelling of the elastic-plastic stress and strain state and lifetime of the belt chamber ». High Pressure Research 8, n^o 1-3 (février 1992) : 522–24. http://dx.doi.org/10.1080/08957959108260722.

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Andrievskiy, Anatoliy, Elena Chaban et Vladimir Moskvichev. « Durability assessment and rational fastening to Traction Engine of gear housing of an electric locomotive ». Proceedings of Petersburg Transport University 19, n^o 2 (22 juin 2022) : 182–92. http://dx.doi.org/10.20295/1815-588x-2022-19-2-182-192.

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Purpose: To investigate the dependence of workload of an electric locomotive gear housing on the parameters of its attachment to a traction motor. To determine own oscillation frequencies under various conditions of its attachment to a traction motor. To propose technical solution allowing to reduce the workload of gear housing in the case of abnormal operation of its attachment to a traction motor. To propose an algorithm for housing lifetime calculation taking into account its fastening parameters. Methods: The values of gear housing own frequencies are obtained by solving the system of Lagrange differential equations of the second kind. Created with this purpose mathematical model of mechanical system under consideration takes into account an elastic nature of housing attachment to a traction motor. Results: The influence of conditions and parameters of gear housing attachment to a traction motor on its workload and, correspondingly, its lifetime is shown. The algorithm for gear housing lifetime calculation is proposed, taking into account its fastening conditions and parameters. The significant influence of workload abnormal modes on housing durability is shown. Practical importance: Constructive solution is proposed that reduces gear housing workload in the case of abnormal conditions of attachment to a traction motor. The algorithm for estimating gear housing durability in the case of redistribution of workloads between its reference points has been developed.

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Zouhar, Michal, Laura Vallet, Pavel Hutař et Luboš Náhlík. « Life Time Estimation of the Multilayer Plastic Pipes ». Key Engineering Materials 452-453 (novembre 2010) : 33–36. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.33.

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In the contribution solution of special fracture mechanics problems connected with multi-layer plastic pipes was investigated. The assumptions of linear elastic fracture mechanics were accepted. A complex three-dimensional numerical model of multi-layer pipe system consisting of main (functional) pipe and protective layers has been suggested and numerically solved by finite element method. Two basic problems connected with lifetime expectation of multilayer pipe system have been considered and discussed, namely: question of fracture mechanics description of multilayered pipe system and corresponding measurements of the material properties. The suggested approach can help for more accurate estimation of the multilayer pipe damage.

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Liptáková, Tatiana, Lenka Markovičová, Viera Zatkalíková et Dušan Gaňa. « The Visco-Elastic Behavior of PA+PAI Composites with Fiber Glass after UV Degradation ». Periodica Polytechnica Transportation Engineering 47, n^o 4 (15 mai 2018) : 329–34. http://dx.doi.org/10.3311/pptr.12108.

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The polymeric composites on the base of the PA+PAI filled by glass fibres are usually used in automotive industry and also exposed to natural atmosphere. The research is focused on resistance study of the mentioned composites in simulated atmospheric conditions. The tested specimens contented 10, 20 and 30 % of the glass fibres and they were exposed in UV box with defined time and intensity of UV radiation and temperature. The mentioned factors have a considerable influence on utility and lifetime of product made of the polymeric composite. The effect of the exposition on the composites behaviour was evaluated microscopically, by rheological measurements and impact tests. By the rheological measurements the changes of visco-elastic parameters (complex viscosity, moduli of elasticity and plasticity) were studied after different times of exposition in the UV box as well as chosen mechanical properties.

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Colin, Xavier, Mouna Ben Hassine et Moussa Nait-Abelaziz. « CHEMO-MECHANICAL MODEL FOR PREDICTING THE LIFETIME OF EPDM RUBBERS ». Rubber Chemistry and Technology 92, n^o 4 (1 octobre 2019) : 722–48. http://dx.doi.org/10.5254/rct.19.81469.

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ABSTRACT A chemo-mechanical model has been developed for predicting the long-term mechanical behavior of EPDM rubbers in a harsh thermal oxidative environment. Schematically, this model is composed of two complementary levels: The “chemical level” calculates the degradation kinetics of the macromolecular network that is introduced into the “mechanical level” to deduce the corresponding mechanical behavior in tension. The “chemical level” is derived from a realistic mechanistic scheme composed of 19 elementary reactions describing the thermal oxidation of EPDM chains, their stabilization against oxidation by commercial antioxidants but also by sulfide bridges, and the maturation and reversion of the macromolecular network. The different rate constants and chemical yields have been determined from a heavy thermal aging campaign in air between 70 and 170 °C on four distinct EPDM formulations: additive free gum, unstabilized and stabilized sulfur vulcanized gum, and industrial material. This “chemical level” has been used as an inverse resolution method for simulating accurately the consequences of thermal aging at the molecular (concentration changes in antioxidants, carbonyl products, double bonds, and sulfide bridges), macromolecular (concentration changes in chain scissions and cross-link nodes), and macroscopic scales (weight changes). Finally, it gives access to the concentration changes in elastically active chains from which are deduced the corresponding changes in average molar mass MC between two consecutive cross-link nodes. The “mechanical level” is derived from a modified version of the statistical theory of rubber elasticity, called the phantom network theory. It relates the elastic and fracture properties to MC if considering the macromolecular network perfect, and gives access to the lifetime of the EPDM rubber based on a relevant structural or mechanical end-of-life criterion. A few examples of simulations are given to demonstrate the reliability of the chemo-mechanical model.

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Chandra, B. P., V. K. Chandra et Piyush Jha. « Elastico-Mechanoluminescence of Thermoluminescent Crystals ». Defect and Diffusion Forum 347 (décembre 2013) : 139–77. http://dx.doi.org/10.4028/www.scientific.net/ddf.347.139.

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Elastico-mechanoluminescence (EML) is a type of luminescence induced by elastic deformation of solids. The present paper reports the elastic-ML of thermoluminescent crystals such as X-or γ-irradiated alkali halide crystals, ZnS:Mn, and ultraviolet irradiated persistent luminescent crystals. Generally, all the elastico-mechanoluminescent crystals are thermoluminescent, but all the thermoluminescent crystals are not the mechanoluminescent. The elastico-mechanoluminescence spectra of crystals are similar to their thermoluminescence spectra. Both the elastico-mechanoluminescence and thermoluminescence arise due to the de-trapping of charge carriers. As elastico-ML of persistent luminescent crystals depends on both the density of filled traps and piezoelectric field, the intense thermoluminescent crystals may not be the intense mechanoluminescent crystals. When a sample of X-or γ-irradiated alkali halide crystal, UV-irradiated persistent luminescent microcrystals mixed in epoxy resin, or a film of ZnS:Mn nanoparticles is deformed in the elastic region by the pressure rising at fixed pressing rate for a particular time, or by a pressure of triangular form, or by a pressure pulse, then after a threshold pressure, initially the EML intensity increases with time, attains a maximum value and later on it decreases with time. In the first case, the fast decay time of EML is related to the time-constant for stopping the moving crosshead of the testing machine; in the second case, generally the fast decay does not appear; and in the third case, the fast decay time is equal to the rise time of the pressure pulse. However, in all the cases, the slow decay time is related to the lifetime of re-trapped charge carriers in the shallow traps lying in the region where the piezoelectric field is negligible. When the sample is deformed by the pressure rising at fixed pressing rate for a particular time, or pressure of triangular form, then the ML appears after a threshold pressure and the transient EML intensity increases linearly with the applied pressure; however, the total EML intensity increases quadratically with the applied pressure. The EML intensity of persistent luminescent crystals decreases with increasing number of pressings. However, when these crystals are exposed to UV light, then the recovery of EML intensity takes place. The mechanical interaction between the bending segment of dislocations and filled electron traps is able to explain the elastico-ML of X-or γ-irradiated alkali halide crystals. However, the piezoelectrically-induced de-trapping model is suitable for explaining the ML of persistent luminescent crystals and ZnS:Mn. The investigation of elastico-ML may be helpful in understanding the thermoluminescence and the investigation of thermoluminescence may be helpful in understanding elastico-ML. Furthermore, similar to the thermoluminescence, the mechanoluminescence may also find application in radiation dosimetry. Expressions are derived for the elastico-ML of thermoluminescent crystals, in which a good agreement is found between the experimental and theoretical results. Finally, the application of the elasticoML of thermoluminescent crystals in light sources, displays, imaging devices, sensing devices, radiation dosimetry and in non-destructive testing of materials are discussed.Contents of Paper

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