Term Creep Behavior Research Articles

Effect of Test Piece Size on Rheological Behavior of Wood Composites

The effect of size and the combined effect of the size and moisture sorption of test pieces on the long term creep behavior of wood composites were studied. Small-, wide-, and semisize test pieces from each of three commercial wood composites, particleboard (PB), oriented strand board (OSB), and medium density fiberboard (MDF) were tested. Three exposure regimes, constant 20°C/65%, a single change from 20°C/65% to 20°C/85%, and cyclic changes between 20°C/30% and 20°C/90% relative humidity (RH), were used. It was found that the width of test pieces had no effect while the length had a significant effect on long term behavior of wood composites, but the effect is in contrast to that of short term modulus of rupture (MOR) which ranged from 0.06 to 0.13 for the shape parameter and from 0.09 to 0.26 for the length parameter depending on the types of wood composites. The average ratio of the relative creep ( kc ) of small-:wide-:semisize was 1.14:1.13:1.00 for PB, 1.26:1.21:1.00 for MDF, and 1.24:1.24:1.00 for...

Creep resistant aluminium alloys and their applications

The CEC funded thematic network CREEPAL (BRRT -CT98 -5101) was established in 1998 to collect and disseminate information on the long term creep and thermal mechanical cycling behaviour of aluminium alloys. This paper presents some of the information gathered by consortium members and some additional industrial information related mainly to forging alloys. A short history of the use of aluminium alloys at elevated temperature is presented. The principal considerations required when evaluating aluminium alloys for use at temperatures in the 100-350°C range are detailed. The important microstructural mechanisms of creep in aluminium alloys are reviewed and the physical metallurgy of Hiduminium-RR.58 (2618A) is examined. The alloys that have found commercial application at elevated temperature are listed. Recent developments are described and opportunities for further development considered.

Creep behavior of bone cement: a method for time extrapolation using time-temperature equivalence.

The clinical lifetime of poly(methyl methacrylate) (PMMA) bone cement is considerably longer than the time over which it is convenient to perform creep testing. Consequently, it is desirable to be able to predict the long term creep behavior of bone cement from the results of short term testing. A simple method is described for prediction of long term creep using the principle of time-temperature equivalence in polymers. The use of the method is illustrated using a commercial acrylic bone cement. A creep strain of approximately 0.6% is predicted after 400 days under a constant flexural stress of 2 MPa. The temperature range and stress levels over which it is appropriate to perform testing are described. Finally, the effects of physical aging on the accuracy of the method are discussed and creep data from aged cement are reported.

Long Term Creep Behavior of Spent Fuel Cladding for Storage and Disposal

Long Term Creep Behavior of Spent Fuel Cladding for Storage and Disposal

Influence Of Local Damage On The CreepBehaviour Of High Speed Steels

High speed steels are investigated as to their short term creep behaviour. In uniaxial creep tests under constant stress a distinct influence of the distribution of primary and eutectic carbides on the creep curve was found. Micrographs show the developement of local damage due to carbide cleavage even in the early stage of the test. The creep deformation was numerically modelled by use of FEM on a microscopical scale. The role of particle arrangement and local damage was investigated by numerical studies.

エポキシ樹脂およびそれをマトリックスとするＣＦＲＰ繊維直角方向の曲げクリープ挙動

This paper is concerned with the prediction of flexural creep behavior of neat epoxy resin in CFRP and transversal direction of fibers in unidirectional CFRP. Short and medium term flexural creep tests for the epoxy resin were carried out at various temperatures. Long term creep behavior predicted by applying the reciprocation law between time and temperature to the short and medium term creep behavior measured at various temperatures is not well agreed with that measured by long term creep test at a constant temperature. Therefore, the modified reciprocation law between time and temperature was proposed. The long term creep behavior predicted by this modified law is fairly well agreed with that of measured directly. Furthermore, long term creep behavior in transversal direction of fibers in unidirectional CFRP predicted by applying the approximate average method to the long term creep behavior of matrix epoxy resin is fairly well agreed with that measured directly by the long term creep test of the CFRP.

エポキシ樹脂のクリープ挙動に及ぼすフィジカルエージングの影響

This paper is concerned with the effect of physical aging on flexural creep behavior of epoxy resin. Epoxy resins were subjected to various degrees of physical aging by different thermal history, i.e., rapidly cooled, slowly cooled and aged epoxy resin. Long term flexural creep tests on these resins were carried out at a constant temperature, and short term flexural creep tests were simultaneously carried out at various temperatures.The long term creep behavior of epoxy resin was obviously influenced by the degree of physical aging. The creep deformation decreased as the physical aging proceeded. Each long term creep behavior was estimated by applying the modified reciprocation law of time and temperature, which was proposed by a previous paper, to the short term creep behaviors. These estimated long term creep behaviors agree fairly well with the measured creep behaviors, in particular for physical aging proceeded epoxy resin. Furthermore, the time-temperature shift factor (horizontal shift factor) and temperature shift factor (vertical shift factor) of the modified reciprocation law of time and temperature decrease as the physical aging proceeds.

A technical assessment cement bonded wood particleboard

The paper summarises test work on cement bonded particleboards carried out at the Princes Risborough Laboratory over the last fifteen years. Evaluation of short term mechanical properties has been complemented by information on the long term creep behaviour of these boards. Assessment of short term performance has embraced both mechanical testwork and the reaction of the material to water; evaluation of long term performance, which is of more importance, involved quantifying the extent of creep under long term loading, the prediction of long term durability using various methods of accelerated ageing, the measurement of actual loss in performance under 10 years natural exposure, and the evaluation of the resistance of the product to biodeterioration. The paper ends with a general appraisal of these products and concludes that their outstanding merit lies in extending the application of wood based panels into areas where there is either a high risk of fire or moisture.

Manufacture of high stiffness solid rods by the hydrostatic extrusion of linear polyethylene. Part I: Influence of processing conditions

AbstractHigh stiffness solid rods, up to 25 mm diameter, have been produced by the solid phase hydrostatic extrusion of a single linear polyethylene grade. Factors affecting the processing behavior and the product properties, as characterized by the enhanced axial Young's modulus and long term creep behavior, have been examined and sources of product flaws have been identified. At high product diameters extrusion occurred in a predominantly adiabatic thermal régime, for which the magnitude of the temperature rise was estimated by measurement of the long periods of the products. This adiabatic regime allowed high production rates to be obtained at lower extrusion pressures, but caused a reduction in the Young's modulus of the products and limited the maximum degree of deformation which could be obtained in stable extrusions.

Manufacture of high stiffness solid rods by the hydrostatic extrusion of linear polyethylene. Part II: Effect of polymer grade

AbstractThe solid phase hydrostatic extrusion behavior of a range of linear polyethylenes, including methyl and butyl copolymer grades, has been compared in terms of processing behavior and product properties, for large diameter extrusions in the adiabatic thermal regime. The most useful improvements in both stiffness and long term creep behavior were obtained from medium melt flow index homopolymers, although such grades required higher forming pressures than the copolymers. This represents a reversal of the creep behavior trends observed for small diameter isothermal extrusions, where copolymer grades were superior. The engineering potential of hydrostatically extruded linear polyethylene is discussed.

Finite Element Modelling Of The CreepBehaviour Of A Small Glacier Under LowStresses

Knowledge of the creep properties of ice or ice-rich materials is important in a variety of geological features. Although the behaviour of large ice masses such as glaciers and ice sheets has been considered in great detail in the past decade or so and is thought to be reasonably well understood, the deformation (or rate of deformation) generated by low stresses are yet to be properly investigated. Such conditions may occur where snow patches are preserved under debris covers and may remain for many years, undergoing a slow deformation over that period of time. Similarly, the long term creep behaviour of ice-debris mixtures is little understood. This problem occurs especially where ice content of granular materials is well below saturation level, or when the debris is dispersed in thin ice masses. The paper presents a contribution to the on-going debate related to the nature of behaviour under the above stated conditions. It includes a geomorphological analysis of the problems and, more importantly, presents a finite element modelling of the creep behaviour of a small glacier underlying a thin layer of debris. The numerical analysis is based on a power law creep type equation for which parameters are adjusted to take into account the debris-ice interaction. The paper also presents a brief analysis of the specific case of the effect of size and position of an ice mass on the stability of a debris slope. GEOMORPHOLOGICAL ASPECTS OF ICE-DEBRIS CREEP Monitoring the long term behaviour of ice creep in the laboratory may be complemented by field observations which might be used to extend observations over many years. Extended creep tests are likely to be of use in certain engineering cases where ice or ice-rock mixtures are concerned. An example might be building piled structures in permafrost areas. Transactions on the Built Environment vol 5, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509

The influence of loading age and temperature on the long term creep behaviour of concrete in a sealed, moisture stable, state

Results of long term creep measurements on a number of concretes in a sealed state loaded at ages for 7 days to 400 days at temperatures ranging from 20° to 95° C, show that deformation increases directly with time when both deformation and time are plotted logarithmically. The change in creep rate from this deformation presentation was then related to temperature using a modified Arrhenius expression and indicated that a reasonable correlation existed for sealed, moisture stable, concrete for certain test conditions. Prediction of concrete deformation from multiphase composite material theory is shown to give erroneous long term creep predictions at this stage of its development.