Experimental and Numerical Analysis of Initial Plasticity in P91 Steel Small Punch Creep Samples

Abstract

To date, the complex behaviour of small punch creep test (SPCT) specimens has not been completely understood, making the test hard to numerically model and the data difficult to interpret. This paper presents a novel numerical model able to generate results that match the experimental findings. For the first time, pre-strained uniaxial creep test data of a P91 steel at 600 • C have been implemented in a conveniently modified Liu and Murakami creep damage model in order to simulate the effects of the initial localised plasticity on the subsequent creep response of a small punch creep test specimen. Finite element (FE) results, in terms of creep displacement rate and time to failure, obtained by the modified Liu and Murakami model are in good agreement with experimental small punch creep test data. The rupture times obtained by the FE calculations which make use of the non-modified creep damage model are one order of magnitude shorter than those obtained by using the modified constitutive model. Although further investigation is needed, this novel approach has confirmed that the effects of initial localised plasticity, taking place in the early stages of small punch creep test, cannot be neglected. The new results, obtained by using the modified constitutive model, show a significant improvement with respect to those obtained by a 'state of the art' creep damage constitutive model (the Liu and Murakami constitutive model) both in terms of minimum load-line displacement rate and time to rupture. The new modelling method will

Characterization of cyclic behavior, deformation mechanisms, and microstructural evolution of MarBN steels under high temperature conditions

“…Anhysteretic tests with path symmetry during the unloading have been conducted to investigate the long-term viscous effects (below and above the yield) and also to reach and reveal the equilibrium stress response of the material at different strain levels. The reason of conducting such experimental investigation is motivated by the fact that some conventional power plant components are exposed to elevated temperature conditions that activate significant amounts of creep (long term viscous effects) for stress much lower than any reasonable interpretation of yield (Cortellino et al, 2017). So, it is of great interest to characterize the material behaviour below the yield and see if it remains elastic.…”

Investigation on the deformation and microstructure evolution of P91 steel in short-term small punch creep test

“…As pointed out by the researchers like Hyde et al, [13][14][15] the strain state and large deformation that takes place before the first stage. The initial bending deformation mechanism plays an important role in the first stage 14 and quantitatively explains the effect of initial plasticity on creep rate and creep mechanism.…”

“…The initial bending deformation mechanism plays an important role in the first stage 14 and quantitatively explains the effect of initial plasticity on creep rate and creep mechanism. 15 The strengthening strain level during the plastic deformation could also affect the structure of the dislocation network. 16 Although many researchers demonstrated that higher level of deformation during SPCT could cause the difference between the results obtained by the two methods, the understanding of a relationship between large deformation in uniaxial creep test and the creep patterns of SPCT is still limited.…”

Determination of creep properties from small punch test using experimental correlation

“…The ratio can be used for planning test load but it is not suitable for creep property assessment. If Chakrabarty model is used to predict the creep properties, the difference between the prediction and the uniaxial tests are commonly reported [23][24][25][26][27][28]. It has been shown that the Ψ ratio is not a constant but depends on both stress and temperature.…”