Creep Performance Prediction Method Through Short-term Stress Relaxation Tests
0
Citation
0
Reference
20
Related Paper
Abstract:
It was analyzed that the intrinsic limitation of present accelerated creep test methods,especially creep design method through stress relaxation tests with an exceeding pre-strain to elastic-strain.A set of short term stress relaxation tests of 1Cr10NiMoW2VNbN steel were carried out.Based on the relationship between stress relaxation and creep,the creep strain rate corresponding to the steady state creep stage were achieved through the stress relaxation test by using numerical analysis and a cross-plotting approach.And then,the second stage creep curves were constructed for high temperature strength design.An integrated accelerated creep test methodology through stress relaxation tests was therefore established.Results of creep tests indicate that the developed method can lead to a good agreement with the experimental data and thus is recommended in the creep performance prediction and strength design of high temperature components.Keywords:
Stress relaxation
Cite
A new prediction model of stress relaxation from creep data in terms of average creep rate was established. An incremental calculation procedure has been further established to obtain stress relaxation data from creep data. To validate the effectiveness of the proposed conversion models, the predicted results were compared with those obtained by the previous continuum damage mechanics model as well as the stress relaxation experimental data using 1Cr10NiMoW2VNbN steel. Results showed that the creep–stress relaxation conversion model based on the average creep rate is better than that based on the continuum damage mechanics model because the former avoids the dispersion effect of fracture strain data, although the predicted results from the two models are both well in agreement with the experiment data.
Stress relaxation
Experimental data
Cite
Citations (19)
Stress relaxation
Tension (geology)
Cite
Citations (11)
Stress relaxation
Work hardening
Austenitic stainless steel
Hardening (computing)
Cite
Citations (38)
Stress relaxation
Diffusion creep
Constant (computer programming)
Cite
Citations (34)
Cite
Citations (6)
In this paper a creep deformation model has been developed for Type 321 stainless steel which has been based on a modified version of the creep model that is used in the French fast reactor design code RCC-MR. The model has been evaluated using: 1) constant load creep data covering the temperature range from 550°C to 650°C and 2) constant displacement, stress relaxation data obtained from creep-fatigue tests at 650°C. Samples in the heat-treatment conditions of solution-treated, aged, and simulated ‘heat affected zone’ have been assessed. The standard RCC-MR model was fitted to the constant load data and provided good predictions of forward creep. However, when this model was used to predict stress relaxation it was observed that the model significantly over predicted creep strain rates and therefore the level of stress drop during each cycle. During constant load tests the stress remains relatively constant (noting that true stress does increase a small amount prior to rupture). However, in relaxation tests the stress varies significantly over the dwell. Due to the poor predictions of stress relaxation it was hypothesised that the fitted model did not capture the stress dependence of creep appropriately. The RCC-MR model was therefore modified to include a primary and secondary threshold stress term that is a function of the accumulated creep strain. This work indicates that the RCC-MR model, modified to include threshold stresses, can be used to provide good predictions of both forward creep and stress relaxation in Type 321 stainless steel. Further work is required to validate this model on stress relaxation data at additional temperatures and lower start of dwell stresses.
Stress relaxation
Constant (computer programming)
Diffusion creep
Cite
Citations (2)
Stress relaxation
Cite
Citations (2)
An analysis of test system misalignment is presented for the creep test. Sheet type rectangular 1100-0 aluminum specimens are used for discussion. It is found that the creep strain at the geometric centerline of the specimen is different than that at the neutral axis. However, this difference in the creep strain decreases with time. Generally, the effect of misalignment decreases with creep time. Creep tests conducted with long pullrods and large initial strain level (high creep stress) will tend to minimize the effect of misalignment.
Strain (injury)
Cite
Citations (1)
With the development of ultrasupercritical power generation technology, creep strength of high-temperature materials should be considered for safety evaluation and engineering design. However, long-time creep testing should be conducted by traditional creep assessment methods. This paper established a high-efficient prediction method for steady creep strain rate and creep strength based on short-term relaxation tests. Equivalent stress relaxation time and equivalent stress relaxation rate were defined according to stress relaxation characteristics and the Maxwell equation. An accelerated creep prediction approach from short-term stress relaxation tests was proposed by defining the equivalent relaxation rate as the creep rate during the steady stage. Stress relaxation and creep tests using high-temperature material 1Cr10NiMoW2VNbN steel were performed to validate the proposed model. Results showed that the experimental data are in good agreement with those predicted solutions. This indicates that short-term stress relaxation tests can be used to predict long-term creep behavior conveniently and reliably, and the proposed method is suitable for creep strength design and creep life prediction of 9–12%Cr steel used in ultrasupercritical unit at 600 °C.
Stress relaxation
Cite
Citations (23)
The θ projection concept was proposed to describe a wide range of creep curve shapes, and has been mainly studied for ferritic steels in which applied stresses were kept constant until rupture. In this paper, we examined whether it could also predict creep behavior when the applied stress was changed during creep deformation. Conventional creep tests of an austenitic stainless steel were conducted at 700°C. In a series of stress-change creep tests, the initial stress of 90 MPa was loaded for a given test duration, after which the stress was increased to 140 MPa. Creep strain produced by the initial stress was determined to range from the primary to the tertiary stage of creep. Employing the θ projection concept and the strain hardening law, creep behavior after the change of the applied stress was estimated. Estimated creep curves agreed well with experiments when the creep strain due to the initial stress was within the early part of the tertiary stage.
Stress relaxation
Austenitic stainless steel
Hardening (computing)
Cite
Citations (0)