GEEN1125: Finite Element Applications
Resit Coursework Questions
Start date: 11:59 pm on 6th July 2021 End Date: 11:59 pm on 17th July 2021
Course Tutor: Dr. Michael Okereke Email: m.i.okereke@gre.ac.uk
Phone: 01634 88 3580
Instructions
- Answer ALL questions in this Coursework booklet
- You have access to software at Nelson 128 laboratories where you can do this coursework. Alternatively, you can also remote log to virtual desktops which has all required software needed for this laboratory.
- All submissions will be via Turnitin on the Course Moodle Page in the section of the portal where 2021 Coursework Resit are specified.
- Do not email the course tutor your submissions as this will not be accepted.
- All your solutions will be in a Microsoft Word document which you should convert to a PDF file before uploading to the Course Moodle Page.
- Support resources are available on the Course Moodle page to help you with revising and answering these questions.
Q1.
A three-noded planar triangular truss, shown in Figure Q1, is subjected to a concentrated force, F = 10 kN at node, N2. The truss is made of a cylindrical bar of diameter, d = 3.0 mmand steel material of Young’s Modulus, E = 210 GPa. If the planar truss is fixed securely at node N1but has x- and y-axis roller supports at nodes N2and N3respectively.
Using the principles of Direct Stiffness Method, and from first principles, undertake the following calculations:
- Determine the three-member stiffness matrices, 𝑲𝑒, 𝑲𝑒 and 𝑲𝑒 for the bars.
1 2 3
[10 marks]
- Derive the structural stiffness matrix, KSfor this structure. [5 marks]
- Using the appropriate boundary condition, show all the steps and then determine the displacements at nodes N2and N3. [5 marks]
Note that you must show in detail all the steps required to determine all stiffness matrices.
Y
xX F =10kN
[0,0] [2,0]
FigureQ1
Q2.
A two-step cylindrical bar of total length 4m is subjected to a uniaxial force, F as shown in Figure Q2. To determine its nonlinear deformation whilst reducing computational cost, you decide to develop a new element formulation based on a three-noded 1D element whose isoparametric natural coordinates are given in Figure Q2.
- Derive the mapping function, ξ= f(x) needed to relate the xy-coordinate system to the isoparametric natural coordinates, ξ.
[2 mark]
- Derive the element’s three shape functions, namely N1,N2and N3.
[12 marks]
- Derive the strain-displacement matrix, Band evaluate its value when ξ=0.5.
[6 marks]
y
F
ξ
ξ=0 ξ=0.5 ξ=1.0
FigureQ2
Q3.
A 2D dogbone specimen, whose dimensions are given in Figure Q3, is made by extrude- cutting the gauge section of an initially rectangular specimen using the insert elliptical geometry. The specimen is made from aluminium of Young’s Modulus, E = 70GPa, Poisson ratio, v=0.33, and yield stress, σyield = 220 MPa. It has both gripped and loaded ends. The test specimen is imposed with a Dirichlet uniform displacement of ΔL = 4mm. You are to undertake the mesh density study to determine the appropriate mesh for subsequent investigation.
- Undertake tensile simulation of the specimen using seed sizes of 6,3, 0.5. Show the contour plots for plastic strain, PE for all simulations. Draw a convergence plot of Average PE versus number of elements. Comment on the implications of mesh density on simulation results. [10 marks]
ΔL = 4 mm
Gauge sect ion ext rude cut using
ellipse below
Loaded End, wit h prescribed
load, ΔL
Gripped End, f ixed securely
20 mm
40 mm
20 mm
40 mm
FigureQ3A
- In order to prescribe a kinematic constraint to a typical finite element model, Multi- Freedom Constraint (MFC) equations are required. Write the ABAQUS-style linear constraint equation for the following equations:
a. 0.5uN60 3.5uN78 2uN15 8.3uN15 3.2uN6 0.10uN54
3 2 1 3 1 2
b. uN4 3uN2 2uN5 3uN16 whereuN16 ce2uN3 buN4 ;
forc,bbeingconstants
2 1 1 2 2 3 1
[3 marks]
- An inverted T-section support structure, of dimensions given in FigureQ4, is designed to support a central column load on the load region zone. The two end faces of the horizontal bar are fixed securely in X, Y, and Z-axes. The bar is made of steel of Young’s Modulus, E=210GPa, Poisson ratio, v= 0.33and yield stress, σyield= 220MPa.
Run a simulation of the compressive behaviour of the structure by imposing concentrated load, U = 20 mm on the structure based on the following canonical equation:
𝑈𝐿𝑅𝑆𝑒𝑡 − 2.3log10 (20)𝑈𝑅𝑃𝑆𝑒𝑡 = 0
2 2
Where LRSet and RPSet are nodal sets for load region and reference point respectively. Show contour plots for von Mises stress, Misesand in-plane shear stress, S12. [7 marks]
Load Region
y z
x
125 mmFixed Face in XYZ
50 mm
200 mm
125 mmFixed Face in XYZ
50 mm
Ref erence Point
300 mm
50 mm
[- 500,- 500,- 500]
FigureQ3C,D
Q4.
The Rochester bridge consists of arched trusses with Figure Q4 showing a segment of the bridge. The total length of the bridge deck is 140 m with the span directly over the river measured at L =100m. Assume that the bridge is made of cylindrical
trusses of steel material with Young’s Modulus, E = 210 GPa and diameter, d = 40mm. The bridge is fixed securely at nodes N1, N2with roller supports at nodes N7 and N8.
The test load case under consideration represents a traffic pile-up of sedan cars of same sizes and weights which imposes a uniformly distributed load, ω = 3000 N/macting solely on the 100-m span of the bridge. The bridge deck has a rectangular cross-section of base, b=8mand thickness, h=5m.
The Rochester Bridge Trust has announced a competition for University of Greenwich MSc engineering students to undertake a detailed structural analysis of the current design with a view to identify probable improvements to extend the lifespan of the bride.
- Using MATFESETMsolver, undertake the FE simulation of the bridge and determine the absolute maximum displacement, 𝑣𝑛𝑢𝑚𝑒𝑟𝑖𝑐𝑎𝑙 of the bridge under the specified load case. Show contour plots of the deformed profile.
[8 marks]
- In order to understand the benefit of the arched truss design in limiting the deflection over the 100-mspan of the bridge, calculate the deflection of the
5𝜔𝐿4
bridge without the arched trusses using the equation: 𝑣𝑎𝑛𝑎𝑙𝑦𝑡𝑖𝑐𝑎𝑙 = 384𝐸𝐼
where L=bridge span, ω = distributed load, E=Young’s Modulus, and I=
𝑏ℎ3
area moment of inertia for rectangular section, i.e. 𝐼 =
.
12
[3 marks]
- Calculate the percentage improvement in limiting the deflection of the bridge by introducing the arched truss. Note that percentage improvement is calculated using the equation:
%𝐼𝑚𝑝𝑟𝑜𝑣𝑒𝑚𝑒𝑛𝑡 =
𝑣𝑎𝑛𝑎𝑙𝑦𝑡𝑖𝑐𝑎𝑙 − 𝑣𝑛𝑢𝑚𝑒𝑟𝑖𝑐𝑎𝑙
𝑣𝑎𝑛𝑎𝑙𝑦𝑡𝑖𝑐𝑎𝑙
× 100%
[3 marks]
- As part of a review of your analysis, you noticed that the actual Rochester Bridge truss is made from an I-section wide-flange beam of designation W150x18 and cross-sectional area, A = 1730 mm2. What is the percentage error introduced to your simulations by assuming a solid cylindrical truss configuration of diameter, d=20mm.
[2 marks]
- Suggest and use MATFESE to demonstrate the nature of one improvement of the bridge to ensure extended life span.
[4 marks]
N2
Figure Q4
Q5.
A unidirectional (UD) composite consists of circular E-glass fibre material embedded within a square-shaped polypropylene matrix. The UD composite has a 20% volumefraction of fibre with fibre diameters ranging from 1.5 um to 2.52 um. We want to use the principles of computational micromechanics to determine the effective properties of the test composite in a specific test direction.
For this study, three representative volume elements (RVEs) shown in Figure Q5Awere identified. The centre locations (in μm units) of the fibres within the matrix medium are given in Table Q5A. All three RVEs have a dimension of length, L = 10 μmand width, W=10μm. The fibre radius for each RVE type are given in TableQ5A. The properties of the fibre and polypropylene constituents are given in TableQ5B.
- Generate the virtual domains for all three RVE types ensuring that you trim off any boundary fibres to preserve the 20% volume fraction. [5 marks]
- Undertake an FEM simulation of tensile deformation along the X-axis for all three RVE types. Since this is a micromechanical study on a heterogeneous material, you MUSTusePeriodicBoundarycondition foryouranalysis.
Show contour plots of (a) Von-Mises Stress, Mises (b) displacement magnitude, UMagnitudeand (c) plastic strain, PEfor all three RVE types.
[8 marks]
- Determine the stress-strain (i.e. σ11vs ε11) graphs for the three RVEs showing the numerically determined Young’s Modulus, E11,numericaland Yield strength, σY,numericalof the test composite. [3 marks]
- Determine the analytically determined Young’s Modulus of the composite
based on the formula:
𝐸𝑚𝐸𝑓
𝐸11,𝑎𝑛𝑎𝑙𝑦𝑡𝑖𝑐𝑎𝑙 = 𝐸
𝑉 + 𝐸 𝑉
𝑚 𝑓 𝑓 𝑚
Where Emand Efare Young’s Moduli of the matrix and fibre respectively; Vf and Vm are volume fractions of the fibre and matrix constituents respectively.
Compare the analytical and numerical Young’s modulus values for the three RVE types. Comment on the effect of number of fibres within the RVE window on the effective properties of the test composite. [4 mark]
Figure Q5
TableQ5A:LocationsofFibresinthreeRVEs(inμmunits)
| Radius=1.26μm | Radius=1.00μm | Radius=0.75μm | ||||
| S/No | RVE 1 | RVE2 | RVE3 | |||
| X | Y | X | Y | X | Y | |
| 1 | 5 | 5 | 8.6 | 8.9 | 9.1 | 5.3 |
| 2 | 5.1 | 8.8 | 1.1 | 8.3 | ||
| 3 | 5.9 | 1.5 | 3.4 | 2.9 | ||
| 4 | 2.0 | 4.1 | 7.5 | 0.1 | ||
| 5 | 7.9 | 3.2 | 6.0 | 5.3 | ||
| 6 | 1.1 | 1.4 | 7.3 | 7.1 | ||
| 7 | 7.8 | 2.9 | ||||
| 8 | 4.0 | 0.6 | ||||
| 9 | 1.0 | 1.3 | ||||
| 10 | 7.5 | 10.1 | ||||
| 11 | 4.0 | 10.6 |
TableQ5B:Propertiesofinclusionsoftheunidirectionalcomposite
| Material | Young’sModulus, E [GPa] | Poissonratio, ν | Yieldstress, y [MPa] | Plasticstrain, p |
| Glass fibre particles | 73 | 0.20 | ||
| Polypropylene | 1.308 | 0.40 | 40 | 0.00 |
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