Accuracy Of Constitutive Model Research Articles

An investigation on the cyclic deformation and service life of a reusable liquid rocket engine thrust chamber wall

PurposeRegeneratively cooled thrust chamber is a key component of reusable liquid rocket engines. Subjected to cyclic thermal-mechanical loadings, its failure can seriously affect the service life of engines. QCr0.8 copper alloy is widely used in thrust chamber walls due to its excellent thermal conductivity, and its mechanical and fatigue properties are essential for the evaluation of thrust chamber life. This paper contributes to the understanding of the damage mechanism and material selection of regeneratively cooled thrust chambers for reusable liquid rocket engines.Design/methodology/approachIn this paper, tensile and low-cycle fatigue (LCF) tests were conducted for QCr0.8 alloy, and a Chaboche combined hardening model was established to describe the elastic-plastic behavior of QCr0.8 at different temperatures and strain levels. In addition, an LCF life prediction model was established based on the Manson–Coffin formula. The reliability and accuracy of models were then verified by simulations in ABAQUS. Finally, the service life was evaluated for a regenerative cooling thrust chamber, under the condition of cyclic startup and shutdown.FindingsIn this paper, a Chaboche combined hardening model was established to describe the elastoplastic behavior of QCr0.8 alloy at different temperatures and strain levels through LCF experiments. The parameters of the fitted Chaboche model were simulated in ABAQUS, and the simulation results were compared with the experimental results. The results show that the model has high reliability and accuracy in characterizing the viscoplastic behavior of QCr0.8 alloy.Originality/value(1)The parameters of a Chaboche combined hardening constitutive model and LCF life equation were optimized by tensile and strain-controlled fatigue tests of QCr0.8 copper alloy. (2) Based on the Manson–Coffin formula, the reliability and accuracy of constitutive model were then verified by simulations in ABAQUS. (3)Thermal-mechanical analysis was carried out for regeneratively cooled thrust chamber wall of a reusable liquid rocket engine, and the service life considering LCF, creep and ratcheting damage was analyzed.

Constitutive model and forming limit prediction of AA5182-O aluminium alloy sheet in electromagnetic forming

Based on the electromagnetic hole-flanging (EMHF) experiment and numerical simulation, the inverse identifications of Johnson-Cook (J-C), Huh-Kang (H-K), Allen-Rule-Jones (A-R-J) and Cowper-Symonds (C-S) constitutive models were performed for AA5182-O aluminium alloy sheet at high strain rates. The accuracy of constitutive models was inspected by comparing the simulated height and thickness with experimental ones. The flow stress curves of AA5182-O aluminium alloy sheet at high strain rates were investigated. Based on the Marciniak-Kuczynski (M-K) model and constitutive models, the electromagnetic forming limit curves (EMFLC) of AA5182-O aluminium alloy sheet were predicted. The results show that the constitutive models at high strain rates can be determined by inverse identification on basis of EMHF. The flow stress curves at high strain rates predicted by different constitutive models are significantly distinguished. The constitutive model directly affects the numerical prediction of EMFLC. The EMFLC with J-C and A-R-J models shows little strain rate sensitivity, the EMFLC with H-K model shows positive strain rate sensitivity at a certain range of strain rate, and the EMFLC with C-S model shows significantly positive strain rate sensitivity.

Shape controlling and property optimization of TA32 titanium alloy thin-walled part prepared by hot forming

The hot flow behaviors, microstructure evolution and fractographs were studied to optimize the hot forming process of the TA32 titanium alloy thin-walled part. A set of microstructure-based constitutive equations were developed based on the experimental data, which described the relationships among the hot flow stresses and the evolution of phase volume fraction, dislocation density, grain size and damage. The constitutive model was imported into ABAQUS 6.14 to simulate the hot forming process for a typical thin-walled part. The effective strain, dislocation density and damage distribution as well as forming defects of formed parts under different process parameters were predicted. A qualified part without wrinkling and fracture defects was produced at a loading speed of 5 mm/s at 800 °C by the modified blank shape, where the maximum damage value was only 18.3%. The accuracy of constitutive model and finite element (FE) simulation was verified by the microhardness tests, which indicates that the FE model based on physical internal-state variables can well optimize the hot forming process of TA32 titanium alloy complex parts.

Data-Driven Constitutive Model for the Inelastic Response of Metals: Application to 316H Steel

Predictions of the mechanical response of structural elements are conditioned by the accuracy of constitutive models used at the engineering length-scale. In this regard, a prospect of mechanistic crystal-plasticity-based constitutive models is that they could be used for extrapolation beyond regimes in which they are calibrated. However, their use for assessing the performance of a component is computationally onerous. To address this limitation, a new approach is proposed whereby a surrogate constitutive model (SM) of the inelastic response of 316H steel is derived from a mechanistic crystal plasticity-based polycrystal model tracking the evolution of dislocation densities on all slip systems. The latter is used to generate a database of the expected plastic response and dislocation content evolution associated with several instances of creep loading. From the database, a SM is developed. It relies on the use of orthogonal polynomial regression to describe the evolution of the dislocation content. The SM is then validated against predictions of the dead load creep response given by the polycrystal model across a range of temperatures and stresses. When the SM is used to predict the response of 316H during complex non monotonic loading, extrapolating to new loading conditions, it is found that predictions compare particularly well against those from the physics-based polycrystal model.

An Efficient Generalized Plasticity Constitutive Model with Minimal Complexity and Required Parameters

Numerical analyses precision performed by software, depends mostly on the accuracy of constitutive model. Therefore, the issue of accuracy has led to significant achievements in the development of constitutive models simulating the mechanical behavior of soils. However, these constitutive models often needs to a lot of parameters to be calibrated for each type of soil, and it’s considered as a disadvantage. especially, when the model parameters should be obtained through trial and error, the number of the parameters becomes a considerable issue. This paper presents an advanced constitutive model. Despite requiring much lower number of model parameters, it provides the same level of accuracy in compression of other advanced constitutive models for sand in literature. To show that the presented model achieved to this purpose, it is evaluated by various experimental data and some predictions made by two successful advanced models in literature. Consequently, it shows the presented model can accurately predict the sand behavior under different conditions despite using smaller number of parameters. Also, the accuracy of the presented model is on a par with advanced constitutive models available in the geotechnical engineering literature.

Rheology of an LDPE melt in reversing multi-step shear and elongational flows

The hypotheses of separability and irreversibility, which have greatly improved the accuracy of constitutive models of the KBKZ type are tested in reversing step shear and elongational deformations. A reversing double-step deformation is a severe test for constitutive models and a new rheometer has been developed to perform this type of deformation, both in shear and elongation, in a single machine.