scholarly journals Study on Multi-Step Creep Aging Behavior of Al-Li-S4 Alloy

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 807
Author(s):  
Yunlong Ma ◽  
Feng Xia ◽  
Lihua Zhan ◽  
Yongqian Xu
Keyword(s):  
Mechanical Properties ◽  
Steady State ◽  
Creep Rate ◽  
Yield Strength ◽  
Stress Level ◽  
New Technology ◽  
Steady State Creep ◽  
Steady Creep ◽  
Slow Increase ◽  
Creep Stage

Creep age forming (CAF) is a new technology developed for manufacturing large aluminum components in the aerospace industry. Aluminum–lithium alloys may be used in aerospace components because of their high modulus, specific strength and specific stiffness. Therefore, the creep deformation, mechanical properties and aging precipitation of Al-Li-S4 alloy under CAF conditions were studied. It was found that the creep behavior presents double steady state creep stages during the creep aging process. With the increase of stress level, the first steady creep rate increased, but the second steady creep rate was slightly reduced. Coincidentally, in the first steady state creep stage, the yield strength of the studied alloy also showed a slow increase stage. TEM observation showed that Al-Li-S4 alloy mainly contains two precipitation phases, T1 phase and θ’ phase. A few precipitates form during the first steady creep stage. Then, a lot of nucleation and growth of T1 phase resulted in rapid increase of yield strength. At the same time, the increase of stress level effectively inhibited the growth of T1 phase, which resulted in these strengthening phases being more uniform, and thus improved the mechanical properties of materials. On this basis, the relationship between the multi-step behaviors of creep, mechanical properties and aging precipitates are discussed. It is considered that the main reasons for the multi-step phenomenon of creep and mechanical properties are strongly related to the nucleation, growth and distribution of T1 phase.

scholarly journals A Creep Model of Asphalt Mixture Based on Variable Order Fractional Derivative

2020 ◽  
Vol 10 (11) ◽  
pp. 3862
Author(s):  
Wenbo Luo ◽  
Bo Li ◽  
Yongjun Zhang ◽  
Boyuan Yin ◽  
Jingling Dai
Keyword(s):  
Mechanical Properties ◽  
Stress Level ◽  
Asphalt Mixture ◽  
Primary Creep ◽  
Creep Model ◽  
Creep Process ◽  
Variable Order ◽  
Time Varying ◽  
Steady Creep ◽  
Creep Stage

In order to quantitatively describe the time-varying mechanical properties of asphalt mixture during creep process, a nonlinear viscoelastoplastic creep model was proposed, by using variable-order fractional calculus. The differential order of the variable-order fractional element of the model is no longer constant, but a variable that changes with time, which reflects the changes of the mechanical properties of the material during the creep process. Whereas the tertiary creep phase is modeled by the viscoplastic element with time-varying viscosity, which is attributed to damage evolution. The uniaxial creep compression tests of AC-13C asphalt mixture under different stress levels (0.7 MPa, 0.9 MPa, 1.1 MPa, 1.3 MPa, 1.5 MPa, 1.7 MPa) were carried out with MTS-809 testing machine at 25 °C, and the test results were analyzed by the model using Levenberg–Marquardt optimization algorithm. It is shown that creep damage occurs when the applied stress exceeds a certain critical value, and the damage incubation time depends on the applied stress level. The higher stress decreases the damage incubation time. The model is in good agreement with the experimental results, and is applicable to describe the entire creep process, which consists of primary, steady and tertiary stages. Moreover, the variation of the model parameter can describe the change of viscoelastic properties of the material during the creep process. The differential order of the variable-order fractional element is constant during the primary creep stage, indicating that the creep behavior of the asphalt mixture is linear viscoelastic in small strain range. For the same stress level, the fractional order of the steady creep stage is greater than that of the primary creep stage, and it increases with the increasing stress level, which shows that the viscous behavior in the steady creep is more remarkable than that in the primary creep, and the higher the stress level, the more prominent the viscous performance exhibits.

On Statistical Properties of High Temperature Creep Rupture Data in STS304 Stainless Steels

2006 ◽  
Vol 326-328 ◽  
pp. 553-556
Author(s):  
Seon Jin Kim ◽  
Yu Sik Kong ◽  
Young Jin Roh ◽  
Won Taek Jung
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Stainless Steels ◽  
Probability Distributions ◽  
Creep Rupture ◽  
Steady State Creep ◽  
Rupture Time ◽  
Steady State Creep Rate ◽  
Rupture Data ◽  
Short Time

This paper deals with the statistical properties of short time creep rupture characteristic values (for example, creep rupture time, steady state creep rate, total creep rate, initial strain, etc.) in STS304 stainless steels. From short time creep rupture tests performed by constant stresses at three different elevated temperatures 600, 650 and 700, the scatter and probability distributions were investigated for rupture time, total creep rate, steady state creep rate, initial strain, and others. The effect of temperature on the statistical scatter of rupture time was the smallest at 700. The effect of stress on the statistical scatter of rupture time was smaller with increasing stresses. The probability distributions of short time creep rupture data were well followed 2-parameter Weibull.

On Creep Rupture Characteristics in STS304 Stainless Steels

2006 ◽  
Vol 326-328 ◽  
pp. 1309-1312
Author(s):  
Seon Jin Kim ◽  
Yu Sik Kong ◽  
Young Join Noh ◽  
Won Taek Jung ◽  
Sang Woo Kwon
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Stress Exponent ◽  
Stainless Steels ◽  
Elevated Temperatures ◽  
Creep Rupture ◽  
Steady State Creep ◽  
Rupture Time ◽  
Steady State Creep Rate ◽  
Creep Stress

In this study, the creep rupture tests of STS304 stainless steels were investigated at three different elevated temperatures of 600, 650 and 700 under the constant creep stresses. Creep rupture characteristics such as creep stress, creep rupture time, steady state creep rate and so on were evaluated. The behaviors of creep rate curve and initial strain are compared at three different elevated temperatures. The stress exponent (n) at 600, 650 and 700 based on steady state creep rate showed 22.5, 20.6 and 11.4 respectively. By increasing the temperature, the stress exponent is decreased. At the temperature of 700, the lowest stress exponents are shown and this behavior is also observed in the case of stress exponent based on rupture time. The creep life prediction by LMP method is presented and the equation of this result is as follows: T(logtr+20)=-0.005152-14.56+24126.

A Parametric Approach to Cyclic Creep

1976 ◽  
Vol 43 (1) ◽  
pp. 28-32
Author(s):  
V. M. Radhakrishnan
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Maximum Stress ◽  
Pure Aluminum ◽  
Cyclic Creep ◽  
Steady State Creep ◽  
Strain Accumulation ◽  
Parametric Approach ◽  
Steady State Creep Rate ◽  
Reference Stress

Investigations have been carried out to study the effect of oscillating stress on the strain accumulation in pure aluminum at elevated temperature. The creep rate under the oscillating stress has been found to increase with increasing value of the alternating component of the stress and is somewhat higher than the steady-state creep rate corresponding to the maximum stress, in the range of temperature used. The rupture time is inversely proportional to the cyclic creep rate. A model for obtaining the reference stress has been proposed and based on the data obtained, a parametric approach is presented.

scholarly journals A statistical model to predict the steady-state creep rate

2014 ◽  
Vol 63 (2) ◽  
pp. 028101
Author(s):  
Li Jing-Tian ◽  
Wang Jian-Lu ◽  
Zhang Bang-Qiang ◽  
Rong Xi-Ming ◽  
Ning Xi-Jing
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Statistical Model ◽  
Steady State Creep ◽  
Steady State Creep Rate
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