Magnitude Of Creep Strain Research Articles

Effect of pre-strain on creep aging behavior of 2524 aluminum alloy

As an advanced manufacturing technology, creep age forming (CAF) has been developed to form large aluminum panels. However, industrial processes often involve complex thermo-mechanical treatments. For instance, it is necessary to impose a plastic strain after solution heat treatment to relieve quench stresses. In this work, the effect of tensile pre-strain before CAF on creep aging behavior of 2524 aluminum alloy is investigated by constant-stress creep aging test, Transmission Electron Microscope (TEM) and mechanical properties test. It is found that the magnitude of creep strain is greatly increased with the increase of pre-strain. Moreover, the peak strength of the creep aged AA2524 is enhanced and the time to reach the peak strength is decreased with the increases of pre-strain. TEM observations revealed that the precipitation process of AA2524 is accelerated due to pre-strain treatment. With the increase of pre-strain, the average size of S (Al2CuMg) phases is reduced. Meanwhile, the density and homogeneity of S phases are improved. Thus, it can be concluded that the pre-strain can evidently improve the formability, mechanical properties and microstructures of AA2524 in creep age forming process.

Investigating the Unrecovered Displacement of Glass Fibre Reinforced Polymers Due to Manufacturing Conditions

In this industrial case study, the effect of processing conditions on the cure progression as well as the magnitude of creep strain due to storage/post-operations after de-moulding was investigated via a wet lay-up manufacturing of a glass fibre reinforced polymer (GFRP), commonly used in boat building. In addition, how the creep and the related permanent deformation in its recovery stage can be prevented or controlled was a focus of the study. Dynamic Mechanical Analysis (DMA) was used to monitor the creep rate of test samples while a constant stress was applied to mimic the sagging condition of GFRP parts during assembly stages. Differential Scanning Calorimetry (DSC) was used to determine the degree of cure as well as the glass transition temperature (Tg) at different curing temperatures. A direct relationship was found between the curing and the operating temperatures, and the unrecovered displacement seen in the final GFRP part. The unrecovered displacement was hypothesized to occur mainly due to a combination of cure progression and creep during the manufacturing process. Namely, cure progression results in the development of stiffness retaining the elastic deformation, while creep can create irreversible viscous flow. The results obtained may be particularly helpful to manufacturers of open moulded parts to prevent the costly consequence from excessive recurring of parts after de-moulding. doi:10.12783/issn. 2168-4286/2.2/Milani

Creep deformation properties of creep strength enhanced ferritic steels

Creep deformation properties of creep strength enhanced ferritic steels were investigated. Good linear relationships between creep strain vs. time and creep rate vs. time were observed within a transient stage in a double logarithmic plot. It was appropriately expressed by a power law rather than exponential law, logarithmic law and Blackburn’s equation. With decrease in stress, a magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term. Life fraction of the time to specific strain of 1% creep strain and 1% total strain, to time to rupture tended to increase with decrease in stress. A time to 1% total strain, that is a parameter for design of high temperature components, was observed in the transient creep stage in the short-term regime, however, it shifted to the accelerating creep stage in the long-term regime. Difference in stress dependence of the minimum creep rate was observed in the high- and low-stress regimes with a boundary condition of 50% of 0.2% offset yield stress. Stress dependence of the minimum creep rate in the high stress regime was equivalent to a strain rate dependence of flow stress observed in tensile test, and a magnitude of stress exponent, n, in the high stress regime decreased with increase in temperature from 20 at 550°C to 10 at 700°C. On the other hand, n value in the low stress regime was about 5, and creep deformation in the low stress regime was considered to be controlled by dislocation climb.

Long-term creep deformation property of modified 9Cr–1Mo steel

The first volume of “Atlas of Creep Deformation Properties” was published on modified 9Cr–1Mo steels in March 2007, as a part of the NIMS (National Institute for Materials Science) Creep Data Sheet series. Creep deformation properties up to about 70,000 h have been investigated. No clear steady-state creep stage has been observed, and creep deformation of the steel consists of transient and accelerating creep stages. Good linear relationships between creep strain vs. time and creep rate vs. time were observed within a transient stage in a log–log plot. It was appropriately expressed by a power law rather than an exponential law, logarithmic law and Blackburn's equation. With decrease in stress, the magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term region. Life fraction of the time to specific strain of 1% creep strain and 1% total strain, to time to rupture tended to increase with decrease in stress. The time to 1% total strain, that is an important parameter for design of high temperature components, was observed to lie in the transient creep stage in the short-term regime, however, it shifted to the accelerating creep stage in the long-term regime. For evaluation of long-term creep strength properties, an experimental creep test data should be extrapolated in consideration of the stress dependence of creep deformation properties.

Varying temperature and creep of silicate grouted sand

This paper illustrates the impact of temperature variation on the creep behaviour of sodium silicate–600B ester permeated Leighton Buzzard sand, where the temperature of triaxial cell water in which the grouted sand samples is installed is raised and lowered between 20·C and 30·C at different time intervals during the constant loading tests. It has been found that creep strain is temperature sensitive at nominal silicate concentrations of 40% to 60% by volume and both the magnitude of creep strain and its rate increase with increase in temperature and vice versa. Also described is the temperature controlled apparatus developed for creep testing of grouted soils, where the temperature can be maintained at the specified temperature within ±1·C.