Application of the linear matching method to creep-fatigue failure analysis of cruciform weldment manufactured of the austenitic steel AISI type 316N(L)

This paper demonstrates the recent extension of the Linear Matching Method (LMM) to include cyclic creep assessment [1] in application to a creep-fatigue analysis of a cruciform weldment made of the stainless steel AISI type 316N(L). The obtained results are compared with the results of experimental studies implemented by Bretherton et al. [2] with the overall objective to identify fatigue strength reduction factors (FSRF) of austenitic weldments for further design application. These studies included a series of strain-controlled tests at 550°C with different combinations of reversed bending moment and dwell time Δt. Five levels of reversed bending moment histories corresponding to defined values of total strain range Δεtot in remote parent material (1%, 0.6%, 0.4%, 0.3%, 0.25%) were used in combination with three variants of creep-fatigue conditions: pure fatigue, 1 hour and 5 hours of dwell period Δt of hold in tension. An overview of previous works devoted to analysis and simulation of these experiments [2] and highlight of the LMM development progress could be found in [3]

The implications of constitutive model selection in hyperelastic parameter identification

Hyperelastic constitutive models are investigated and compared on their ability to predict the elastic, isothermal and rate-independent response of rubber. Constitutive model parameters are identified in an optimization problem by minimizing the difference between homogeneous experimental data and their analytical solutions. The results are presented for ten hyperelastic constitutive models over four case studies where varying extents of experimental data are used. The choice of constitutive model is found to determine how accurately experimental data is fitted, though this has different implications depending on the extent of available experimental data. With a complete data set, an accurate fit generally indicates an overall accurate prediction of the material’s response. However, an accurate fit to a reduced set of experimental data may not indicate an accurate prediction of the overall response. With reduced data, accurate predictions are obtained only if the constitutive model is capable of predicting unfitted deformations and the appropriate experimental data is used

Improvement of leak tightness for swellable elastomeric seals through the shape optimization

Swellable packers have been widely employed in various oil & gas applications. Downhole conditions are difficult to reproduce using physical testing environments, but can be simulated in a virtual environment using CAE software. A better understanding of packers’ mechanical behaviour in downhole conditions would provide a higher confidence and improvement in existing engineering design practices for the manufacturing of packers. The numerical simulation can be incorporated into optimisation procedures searching for an optimal shape of packers aiming to minimise the time to seal the borehole and maximise the contact pressure between the seal and borehole. Such an optimisation would facilitate the development of a packer with various designs optimised for different downhole conditions. The objective of this work is to develop a design tool integrated into Abaqus/CAE to implement parametric numerical studies using implicit and explicit FE-simulations. However, development of such a CAE plugin is associated with a number of technical challenges specific to this class of multiphysics problems, which are addressed in this research and discussed in the paper

Literature research in relevant fields to understand pressure relief valve leak tightness in a static closed state

Currently, no review of literature exists which attempts to understand the leakage phenomenon of metal-to-metal seal contact Pressure Relief Valves (PRV) for static closed positions as they reach the set pressure point. This paper attempts to do just that by drawing on inspiration from other research areas such as: metal-to-metal contact and gasket seals. The key topics of interest surrounding the leakage of fluid through a gap are: fluid flow assumptions; surface characteristics and its deformation; and experimental techniques used to quantify leakage. The fluid flow assumptions relating to the gap height such as transmissivity and diffusivity are found to be directly linked to the surface roughness and the surfaces deformations. Traditionally the summing method has been used to represent two rough surfaces at a micro scale from which the Tsukizoe and Hisakado theory has been applied for deformation of the micro contact in a plastic manner. The path the fluid also takes through the gap is investigated with recent work using computational methods to determine that path. Current experimental leakage quantification techniques are also discussed. Finally, the future development of PRV static leakage is examined

Consideration of fluid-structure interaction with the CEL approach for the FE-prediction of a blow-off pressure for an elastomeric seal

Assessment of leakage performance is a fundamental aspect in the design of elastomeric fluid seals. The key characteristic of the leakage performance is the blow-off pressure - when it is reached a seal no longer adequately performs its function. Realistic simulation of these phenomena under different conditions (amount of preload, pressure build-up rate, etc.) would facilitate improvement in the seal design methodology and would allow efficient optimisation of a seal design. For an accurate prediction of the blow-off pressure, Fluid-Structure Interaction (FSI) needs to be considered, since the geometrical disposition of the seal, its deformation and its contact conditions with respect to the main structure are adversely affected by the fluid flow and fluid pressure. In this study, the most advanced FSI technique currently available is employed for the numerical simulation - the Coupled Eulerian-Lagrangian (CEL) approach in ABAQUS [1]. This project leads the way for future work, to validate these results and determine the accuracy of the technique and its applications for more complex analyses

Assessment of leak tightness for swellable elastomeric seals considering fluid-structure interaction with the CEL approach

Swellable elastomeric seal is a type of specifically engineered packer that swell upon contact with wellbore fluids. Assessment of leakage tightness is a fundamental aspect in the design of swellable packers, since they should guarantee a reliable sealing under extreme pressures of the downhole fluids. Numerical capability of the leakage pressure prediction would facilitate improvement in the packer design methodology. Previous work was focused on investigation of the non-parametric optimisation capability seeking for an optimal external shape with a goal to maximise the grip of a packer with a borehole. The verification of an optimised design was done with a dynamic FE-simulation of packer's failure by extrusion under an excessive pressure. The downside of that verification analysis was that Abaqus/Explicit solver couldn't implement a realistic adaptive pressure application due to changing packer disposition and contact conditions. This simulation challenge is addressed in this paper by application of the Coupled Eulerian-Lagrangian (CEL) approach in Abaqus/Explicit, which provides the ability to simulate a class of problems where the fluid-structure interaction (FSI) is important

High cycle fatigue analysis in the presence of autofrettage compressive residual stress

An experimental and numerical investigation of the effect of residual compressive stress on the high cycle fatigue life of notched low carbon steel test specimens is presented. Experimentally determined cyclic stress strain curves for S355 low carbon steel are utilized in a Finite Element Analysis plasticity modelling framework incorporating a new cyclic plasticity material model representative of cyclic hardening and softening, cyclic mean stress relaxation and ratcheting behaviors. Fatigue test results are presented for standard tensile fatigue test specimens and novel double notch specimens. Double notch specimens are tested with and without compressive residual stress prior-induced through tensile overload. It is shown that cyclic plasticity phenomena have a significant influence on the induced residual stress distribution and also on material behavior when fatigue tested in the high cycle regime. It is observed that higher initial compressive residual stresses magnitude does not necessarily lead to a longer fatigue life. Finite Element Analysis using the new cyclic plasticity material model shows this behavior is due to combined residual stress redistribution under fatigue test cyclic loading and cyclic hardening effects. A fatigue life methodology based on the stress-life approach augmented by a critical distance method is proposed and shown to give good agreement with experimental results for test specimens with no induced residual stress. The results obtained for specimens with induced residual stress are more conservative but the degree of conservatism is significantly lower than that in the conventional stress life approach. The proposed methodology is therefore suitable for analysis and design assessment of components with pre-service induced compressive residual stress, such as autofrettaged pressure components

Ultrasonic fatigue testing of structural steel welded joints

In order to evaluate fatigue properties within the very high cycle fatigue (>107 cycles) regime in a feasible timeframe, ultrasonic fatigue testing is necessary. This involves exciting specimens at their natural frequency of 20 kHz. As the fatigue performance of welds beyond the conventionally assumed fatigue limit has not been extensively studied, this research aims to investigate the fatigue behaviour of structural steel welds up to the gigacycle (109 cycles) regime. A welded specimen that features the toe and root features that fatigue cracks typically originate from was developed. The design process and fatigue results obtained will be discussed