Crazing limit of polymers in creep and stress relaxation

The appearance of the first visible damage in polymers in the form of crazes or microcracks may be assumed to be a sign of failure. Experimental investigations have shown that in uniaxial creep and stress relaxation experiments, under isothermal conditions, a certain time between the quasi-spontaneous loading and visible crazing is needed. This ‘incubation time’ is very strongly dependent on the magnitude of the quasi-spontaneously applied stress or induced strain. Based on the Reiner-Weissenberg theory of strength, simple relations allowing the prediction of crazing are developed. The agreement between theoretical computation and experiment is very good.     

An environmental instrument for measuring creep and stress relaxation in polymers

The construction and operation of an instrument for measuring tensile stress relaxation and creep, particularly of polymers, is described. The instrument is comparatively inexpensive to build and enables measurements to be carried out in vacuo or in a controlled atmosphere of gas or vapor. The design is based on principles used for some earlier stress relaxometers modified to enable characterization of samples having a very wide range of moduli either as stress relaxation or, additionally, as creep measurements. The instrument can therefore be used to evaluate material properties of hard plastics or of soft rubbers when exposed to selected environments.     

Prediction of stress relaxation during high-speed stretching of synthetic thread

The viscoelastic characteristics obtained with a “family≓ of stress relaxation curves can be used to predict distortion of the stress-strain diagram in going to high deformation rates. Translated from Khimicheskie Volokna, No. 1, pp. 41–43, January–February, 1998.     

Mechanical spectroscopy connected to creep and stress relaxation in a high resistant silicon nitride

Silicon nitride processed by gas pressure sintering contains a very small amount of glassy phase and consequently exhibits a strong resistance to deformation until 1450 °C. Above this temperature, both relaxation kinetics and creep rate rapidly increase. To explain such a behaviour, the formation of a liquid phase by dissolution of YSiAlON phases was proposed. The present paper shows that mechanical spectroscopy argues for the existence of such a liquid phase at high temperature. The mechanical loss is very low in the as-sintered material. Nevertheless, the internal friction peak generally observed in silicon nitride, and attributed to the glass transition in the glassy pockets, is also observed in the gas pressure sintered silicon nitride. Moreover, the peak is much higher in annealed and “quenched” specimens and it increases with annealing time. These results show that the annealed and “quenched” material contains much more glassy phase and so argues for the dissolution of crystalline phases at high temperature.     

Tensile fatigue,stress relaxation,and creep behaviors of worsted core spun yarns

The objective of this research was to investigate the time‐dependent behaviors of yarns, which have significant bearings upon the properties of stretch fabrics made from them. In this study, 100% wool, wool–lycra (W‐L) (97 : 3), and polyester–wool–lycra (P‐W‐L) (52 : 45 : 3) blended yarns were considered. These yarns were subjected to the tensile fatigue failure, stress relaxation, and creep experiments. The findings showed that of these three yarns, P‐W‐L blend exhibited maximum fatigue lifetime, stress retention, and creep recovery, the pure wool yarn followed suit albeit to a lesser extent, whereas the W‐L blend made it least. The investigation suggests that wool alone with lycra as a core component is not sufficient to impart the expected properties upon stretch fabrics, rather a blend of polyester and wool with lycra as in the former would definitely make a worthwhile product. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Quantitative monitoring of polyethylene glycol in aqueous dimethyl acetamide mixtures in the manufacture of synthetic fibres

Conclusions -- A photometric procedure has been developed for the quantitative determination of the PEG (5000) content in precipitation bath solutions and technological solutions in the manufacture of synthetic fibres.-- Metrological characteristics of the procedure have been calculated.-- Equations have been given which describe the linear calibration curve for determining PEG (5000) in various aqueous dimethyl acetamide mixtures.Translated from Khimicheskie Volokna, No. 5, pp. 60–62, September–October, 1990.     

Thermal stress relaxation creep and microstructural evolutions of nanostructured SiC ceramics by liquid phase sintering

We explored the thermal relaxation creep characteristics of nanostructured SiC ceramics by bend stress relaxation (BSR) method. The effects of the differences in microstructure and secondary phases by liquid phase sintering at 1800 or 1900 °C were especially discussed, based on microstructural evolutions during the creep. The creep was characterized by the BSR ratio (m) of ～0.80 up to 1200 °C, and the proportion of amorphous phase as a secondary phase was related to the creep resistance at 1300 °C. The microstructural evolutions during the creep consisted firstly in the re-distribution of amorphous phase, probably as a consequence of its viscous flow, and secondly in an extensive nucleation and growth of cavities. Furthermore, the former enhanced inter-diffusion of Al–Y among intergranular areas above the ternary eutectic temperature, which caused the significantly reduced creep resistance, and the latter reflected the crystalline YAG decomposition as another secondary phase near 1500 °C.     

Prediction of creep of oriented polycaproamide fibres

A method of predicting permanent creep with dynamometric curves was proposed for oriented PA-6 monofilament. The curves of the changes in the modulus of elasticity in different stretching modes were used to estimate the effect of the change in the modulus of elasticity on the deformability of the monofilament in the creep mode.Blagoveshchensk Institute of Technology. Institute of Textile and Light Industry, St. Petersburg. Translated from Khimicheskie Volokna, No. 6, pp. 38–41, November–December, 1992.     

Study of creep,stress relaxation,and inverse relaxation in mulberry (Bombyx mori) and tasar (Antheraea mylitta) silk

The phenomena of creep, stress relaxation, and inverse relaxation/stress recovery were observed for mulberry and tasar silk. Instantaneous extension and secondary creep are both higher for tasar than for mulberry. The magnitude of inverse relaxation increases with the increase in peak tension and reduction in retraction for both varieties of silk. The extent of inverse relaxation was found to reduce because of cycling stressing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3077–3084, 2006