Application of a modified strain transient dip test in the determination of the internal stresses of PVC under tension

A modified strain transient dip test which involves the design of a load reduction apparatus to perform rapid step unloading and extrapolating to zero extension rate has been developed to measure the internal stresses (recovery and effective stress) of PVC under uniaxial tension. This simple technique appears to be consistent with other internal stress measurement techniques. It was found that the effective stress approaches a limiting value with applied strain and an extrapolated yield point could be defined. The limiting value is a function of the strain rate during the initial load application. The general increase in applied stress (at fixed applied strain) with crosshead speed was attributed to the increase in magnitude of the effective stress. The maximum peak ratio of effective over recovery stress, at each crosshead speed, could indicate that it was the energy-dissipating part of the material that played a dominant role in the early stages of the deformation while the energy-storage part dominated the latter stages.     

Structural-mechanical and thermophysical properties of modified polyvinyl chloride

On the basis of a systematic investigation of the viscoelastic properties of polyvinyl chloride filled with waste from mineral fertilizer and phosphoric acid production in the form of highly dispersed phospho-gypsum, the specific heat is calculated and the energy of interaction of the structural elements of the system matrix is determined, together with the effective thermal conductivity coefficient, with allowance for energy dissipation by the elements of the structure.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 6, pp. 987–994, June, 1991.     

改性石墨烯/聚氯乙烯复合材料的制备及性能

采用不同含量的硅烷偶联剂γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）对石墨烯（GE）进行改性,将改性GE（KH-GE）与聚氯乙烯（PVC）进行熔融混炼制备KH-GE/PVC复合材料。通过FTIR、Raman、XRD、TEM和SEM表征改性前后GE结构变化,并考察了KH-GE/PVC复合材料的力学性能、导电性能及稳定性能。结果表明,GE∶KH570质量比为1∶2时,KH-GE的层间距较大,改善了GE的团聚,使GE在PVC基体中的分散得到了改善。随着KH-GE含量的增加,KH-GE/PVC复合材料的力学性能显著提高,当KH-GE质量分数为1.5wt%时,KH-GE/PVC复合材料的拉伸强度和断裂伸长率分别为23.98 MPa和226.78%,比未添加KH-GE的PVC复合材料分别提高了51.1%和65.73%;相对于纯PVC,当KH-GE质量分数为1.5wt%时,对应的50%热失重（T_50%）及90%热失重（T_90%）分别从289.81℃和486.01℃提高到298.51℃和596.53℃,提高了KH-GE/PVC复合材料的热稳定性,导电性也显著提高。     

Internal and effective stresses in high-temperature creep evaluated from transient dip tests and dislocation bowing

Because creep of metals and alloys is modelled on the basis of microstructural observations, it has been shown that there is a difference between the mathematical treatment of high-temperature deformation and the real material behaviour. One idea to consider is to split the applied stress into a part depending on the substructure (the internal stress which has to be reached to start dislocation motion) and a part describing the resistance to the glide motion of dislocations (the effective stress). For ferritic chromium steel these quantities have been measured by means of the stress transient dip test technique. This leads to mean values of internal and effective stresses for the whole specimen. Additionally, local stresses acting on individual dislocations are evaluated from dislocation bowing for a wide range of applied stresses. The results show that the ratio of internal to applied stress decreases with increasing applied stresses, which, on the other hand, causes a large increase of effective stresses. Dislocation bowing stresses show a similar dependence. Compared to the results of dip tests, the determination of local stresses leads to less accurate results and to a large deviation of results within small regions of one specimen. Therefore, it is only valuable for comparison purposes.     

Some studies of deformation processes in fully-spherulitic polypropylene

The deformation of isotactic polypropylene has been studied by optical microscopy of thin sections cut from bulk tensile specimens. An attempt has been made to relate the three different deformation zones within a spherulite to the cross-hatched structure peculiar to polypropylene.     

Finite element analysis of time-dependent inelastic deformation in the presence of transient thermal stresses

A finite element formulation for the solution of time-dependent inelastic deformation problems for metallic structures, in the presence of transient thermal stresses, is presented in this paper. A rate formulation of the equations is used and any of a number of recently proposed combined creep-plasticity constitutive models with state variables can be adopted to describe material behaviour. The computer program developed can solve planar (plane strain and stress) and axisymmetric problems. Using one of the above-mentioned constitutive models, numerical results are presented for several illustrative problems, and comparisons of results, using either the quasi-steady or the unsteady diffusion equation for the determination of the temperature field, are carried out.     

Role of recovery in high temperature constant strain rate deformation

A model based on the three-dimensional distribution of dislocations is used to delineate the role of recovery during high temperature constant strain rate deformation. The model provides a good semi-quantitative explanation for classical work-hardening as well as for high temperature work-softening resulting from rapid recovery. It predicts linear work-hardening, whereby the ratio of the work-hardening rate,H, to the shear modulus,G, is constant when a crystal is tested in the absence of recovery. The slope of the stress-strain curve, θ, for high temperature deformation is related to the low temperature work-hardening rateH; the dislocation annihilation rate , the flow stress a, the free dislocation density ρ, the strain rate , and a parameter which is sensitive to the dislocation distribution. A modified version of the Bailey-Orowan equation for simultaneous work-hardening and recovery during constant strain rate deformation which is derived from the model takes the form

Evaluation of permanent deformation characteristics of unmodified and Polyethylene Terephthalate modified asphalt mixtures using dynamic creep test

One of the major types of plastics that can be found in Municipal Solid Waste (MSW) is Polyethylene Terephthalate (PET) which is a non-biodegradable semi-crystalline thermoplastic polymer, and is considered as polyester material. Generating large amount of waste PET, mainly as bottles, would cause environmental hazards by disposing in landfills. This paper aims to evaluate effects of utilizing waste PET flakes as modifier in asphalt mixture as an alternative solution to overcome the potential risks arise from producing large amount of waste PET as well as evaluating the deformation characteristics of unmodified and PET modified asphalt mixtures. To achieve this aim, different percentages of PET were designated for this investigation, namely: 0%, 0.2%, 0.4%, 0.6%, 0.8% and 1% by weight of aggregate particles, and dynamic creep test was performed at different stress levels (300 kPa and 400 kPa) and temperatures (10 °C, 25 °C and 40 °C). Consequently, Zhou three-stage model was developed. The results showed that permanent deformation characteristics of asphalt mixture were considerably improved by utilization of PET modification, when the permanent strain was remarkably decreased in PET modified mixture compared to the conventional mixture at all stress levels and temperatures. Besides, based on Zhou model, it was concluded that elastic and visco-elastic properties of asphalt mixture were improved by application of PET modification.     

On the quantification of quenching transient thermal stresses in brittle solids using Vickers indentations

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of additives on the global mechanical behavior and the microscopic strain localization in wood reinforced polypropylene composites during tensile deformation investigated using digital image correlation

The structural integrity of polypropylene (PP) matrix composites reinforced by natural wood fibers is investigated by digital image correlation (DIC) coupled with tensile tests. The use of the material as an alternative construction material requires extensive understanding of its micromechanical properties, which primarily define its performance. Addition of several additives such as coupling agents is common practice for such materials. These ingredients improve the performance of these materials mainly by improvement of the chemical and physical interactions between the nonpolar matrix and the polar wood fibers. These interactions facilitate the transfer of the applied deformation particularly in the interphase region between the polymer matrix and the reinforcing fibers. Such localized changes can influence the performance of the material specially its micromechanical behavior. The DIC via photogrammetry was used to study the spatial distribution of the accumulated plastic surface strain, which is based on pattern recognition of the surface before and after straining. The heterogeneous strain distribution reveals a structural inhomogeneity of the material. The magnitude of local strain was much higher than the global strain, suggesting preferred regions for plastic deformation formed by the microstructure.     

Ductile tearing simulation of Battelle pipe test using simplified stress‐modified fracture strain concept

In this paper, numerical ductile tearing simulation results are compared with six circumferential through‐wall and surface cracked pipes made of two materials (SA‐333 Gr. 6 and A106 Gr. B carbon steels), performed at Battelle. For simulation, a model using a simplified fracture strain model is employed, by analysing tensile data of the material. By comparing experimental J‐R data with FE simulation results, the damage model dependent on the element size is determined based on the ductility exhaustion concept. The model is used to simulate ductile tearing behaviour of six circumferential through‐wall and surface cracked pipes. In all cases, simulated results agree well with experimental load, crack length and crack mouth opening displacement versus load line displacement data.     

Mechanical behavior and deformation micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate

The mechanical behavior and the deformation and failure micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10⁻³ s⁻¹ to 10⁻¹ s⁻¹. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.     

A comparison of transport properties for concrete using the ponding test and the accelerated chloride migration test

In order to develop a better understanding of the relationship between 90-day salt ponding test and accelerated chloride migration test (ACMT; the electrochemical technique is applied to accelerate chloride ion migration), the transport properties for concrete obtained from ACMT are compared to the diffusion coefficient from ponding test. The plain cement concrete, fly ash concrete, and slag concrete with different w/b ratios (0.35, 0.45, 0.55, and 0.65) were used. In this study, the total chloride content and penetration depth of concretes were measured after the ponding test, and the Fick's second law of diffusion was fitted to the data from experiment to determine the diffusion coefficient. The non-steady-state diffusion coefficient, the migration coefficient, and the current corresponding to the 30000 coulomb, charge passed obtained from ACMT in the previous works were compared with the diffusion coefficients obtained from ponding test. Parallel tests show that the diffusion coefficients obtained from ponding test correspond well with the non-steady-state diffusion coefficient, the migration coefficient, and the current corresponding to the 30000 coulomb charge passed obtained from ACMT, although the diffusion coefficient measured by ponding test is different from that measured by the ACMT in non-steady state and steady state.

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Résumé Pour mieux comprendre la relation entre l'essai de trempage dans l'eau salée pendant 90 jours et l'essai accéléré de migration de chlorure (ACMT; la technique électro-chimique est employée pour accélérer lamigration des ions chlorure), les propriétés de transport du béton obtenues par l'ACMT sont comparées au coefficient de diffusion de l'essai de trempage. Du ciment simple, des cendres volantes ainsi que des scories avec des rapports eau/liant différents (0.35, 0.45, 0.55 et 0.65) ont été utilisés. Dans cette étude, la teneur totale en chlorure et la profondeur de pénétration des ciments ont été mesurées après l'essai de trempage, et la seconde loi de diffusion de Fick correspond aux données tirées, d'expériences visant à déterminer le coefficient de diffusion. Le coefficient de diffusion de l'état non stationnaire, le coefficient de migration, et le courant de charge passé correspondant à 30000 coulombs obtenu à partir de l'ACMT d'expériences précédentes ont l'eté comparés aves les coefficients obtenus à partir de l'essai de trempage. Des essais parallèles montrent que les coefficients obtenus à partir de l'essai de trempage correspondent bien au coefficient de diffusion de l'état non stationnaire, le coefficient de migration, et le courant de charge passé correspondant à 30000 coulombs après l'ACMT, bien que le coefficient de diffusion mesuré par l'essai de trempage soit différent, dans les états non stationnaire et stationnaire de celui mesuré par l'ACMT.

     

Antiplasticization of polyvinyl chloride in relation to crazing and fracture behaviour

Experiments were carried out to study the effects of small amounts (10 p.h.r.) of tricresylphosphate in polyvinylchloride on the crazing behaviour and fracture toughness over a wide range of temperatures. Crazing was induced by water/methanol mixtures and the critical crazing strain was measured as a function of immersion time and methanol concentration. Fracture toughness was measured on single-edge notched specimens in tension over three decades of strain rate in the temperature range −80 to 60°C. The 60 sec isochronous critical crazing strain displayed a minimum at around room temperature in an approximately parabolic fashion; the plasticized polymer exhibiting lower trough values, while the two curves intersected at both low and high temperatures. The fracture toughness curves, on the other hand, exhibited intermediate peaks, associated with β relaxations. The addition of plasticizers to the polymer reduced considerably the heights of the peaks and, once more, the two curves intersected at high temperature and merged at low temperature. From a comparison of the two sets of data, it is suggested that embrittlement due to antiplasticization is associated with a reduction in stability of the crazes as a result of the depression of β relaxations.     

The relationship between charge passed and the chloride concentrations in anode and cathode cells using the accelerated chloride migration test

In this study the electrochemical technique is applied to accelerate chloride ion migration in cement-based material to estimate its permeability. Specimens with six fine aggregate volume fractions were cast and tested. For all test series, the chloride concentrations both in anode and cathode cells as well as the electrical current were simultaneously monitored in the accelerated chloride migration test. The chloride migration rates of anode and chloride cells were used to assess the permeability of cement-based materials. A good correlation was observed between the chloride migration rate of anode cell and cathode cell. And, a good correlation was also observed between the chloride concentration in anode cell, the chloride concentration in cathode cell and charge passed obtained from the accelerated chloride migration test.

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Résumé La technique electrochimique est appliquée pour accélérer la migration des ions chlorure dans des matériaux à base de ciment pour estimer leur perméabilité. Des échantillons avec six granulats fins ont été préparés et testés. Dans tous ces tests, les concentrations dans les cellules anode et cathode ainsi que les courants, électriques ont été simultanément suivis. Le taux de migration dans les cellules anode et cathode a été utilisé pour évaleur la perméabilité des matériaux testés. Une bonne corrélation a été observée entre le taux de migration de chlorure dans la cellule anode et dans la cellule cathode. Une bonne corrélation a aussi été observée entre ces concentrations et la charge passée obtenue de ces tests de migration de chlorure accélérés.