ENG4094/ENG5053

Sep 2024

Graded Assignment (2)

Due 12:00 29th November 2024

This report is worth 60% of your total grade for the Computational Stress Analysis half of the course.

Overview

After over a decade in use, the operators of an offshore drilling rig found a failure in a safety critical bracket. Subsequent investigation and analysis showed that, due to hydrogen uptake over several years, the strength of the titanium alloy the bracket was made from had increased but that the ductility had significantly decreased.

Lab tests were conducted to simulate the environment that the titanium alloy had been subjected to and mechanical tests were carried out to determine the degraded material properties of the alloy.

You have been contracted as a finite element analysis expert to develop a simulation to determine what applied load the bracket will fail at, given the degraded material properties.

Problem description

Develop a finite element simulation in Abaqus to determine the applied load at which the bracket will fail.

Geometry: You will need to appropriately defeature the geometry and import the bracket  geometry into Abaqus.  The bracket geometry is shown in Figure  1.  The geometry of the bracket is provided in the form. of a SolidWorks part file (Bracket_SolidWorks.SLDPRT). You will also need to simplify the geometry using the skills you have learned in this course.

Constitutive Material Model: You will need to develop a constitutive material model for the degraded titanium alloy. The material model should be capable of capturing the following features of the stress-strain response:

•   Elasticity

•   Onset of plasticity i.e. yield behaviour

•   Strain hardening to ultimate tensile strength (UTS)

To simplify the model, you can make the following assumptions:

•   Isotropic linear elasticity

•   Poisson’sratio, ν = 0.31

•   Density, ρ = 4420 kg m–3

•   Isotropic plasticity (strain rate and temperature independent)

•   Failure occurs when the material reaches its UTS

The  mechanical  behaviour  of the  degraded  titanium  alloy  has  been  characterised through a series of tensile tests, with representative engineering stress versus strain data given in Tensile_test_data_titanium_degraded.xlsx.

Boundary and Loading Conditions: The bracket is held in place by bolts at five points and sits flat against a rigid surface, as shown in Figure 1. You can assume that the surfaces marked in red do not move. The load is statically applied to the top surface of the cylinder, which is marked in green with green arrows highlighting the direction of the load.

Figure 1: Offshore bracket design with boundary and loading conditions

Report

Submission due 12:00 29th November 2024:

•   Type - Engineering report

•   Length - 10 pages

•   Font - 11pt Arial (or 12pt Times New Roman)

•   Figures/Plots - Maximum of 8

•   Online submission to Moodle

The report should include, at least:

•   Description and justification of how you defeatured and simplified the bracket geometry.

•   Description of you how meshed the geometry and justification for the type of elements you chose to mesh the part with.

•   Description of the constitutive material model you chose and how you determined the parameters used in the model.

•   Description of how you applied the boundary conditions.

•   Recommendations to the offshore  drilling rig operators  i.e.  what is  the maximum load that can be applied to the bracket (remember to include an appropriate factor of safety!).

•   Recommendations for further experiments and simulations to better predict the mechanical behaviour of the bracket.