1. Numerical Study of the Impact
Response and Ballistic Limit of
AA2024 Friction Stir Welded
Aircraft Panels
Student: Adrian Azorin Albero
Supervisor: Dr Tom De Vuyst Introduction
Aims and Objectives
FEA Simulation of Base Material Behaviour
MSc Advanced Lightweight Structures and Impact 2013-2014
Friction Stir Welding is a novel environmentally
friendly welding technique able to produce higher
joint properties than conventional processes.
Methodology
FEA Simulation of the Weld Ballistic Performance
Contact: a.azorinalbero@cranfield.ac.uk
Crashworthiness, Impacts and Structural
Mechanics Group (CISM)
Conclusions Future Work
It has reached the potential of replacing existing joining processes used in
the aerospace industry, such as riveting, with a significant weight reduction.
However, if used to join exterior skin of aircraft components, welds represent weak regions
likely to experience impact of different projectiles, including bird-strike and engine debris.
Simulation and experimental tests to investigate the behaviour of friction stir welded aircraft panels when
subjected to this sort of impacts are essential to raise the level of confidence on this new welding technology.
 Implement aluminium anisotropy on base material and
study its influence on the impact behaviour with hard
and soft projectiles.
 Model the different level of material anisotropy present
at each weld region and implement residual stresses.
 Predict ballistic limit distributions across the weld region
for different projectile shapes.
Literature Review Anisotropic material
models in LS-DYNA
Technical work
Weld material
characterisation
Implementation of anisotropic behaviour on base
material and weld regions FE models
Hard projectiles models
Bird model validation
Final weld model for prediction of impact
behaviour and ballistic limit distribution
Impact tests
Impact tests with Cranfield Single Stage Gas Gun
Experimental setup:
 AA2024-T3 sheets
 120mm x 120mm x 3.175mm
 Projectiles:
o Steel sphere: 11.9mm diameter
o Steel cube: 9.5mm edge length
o Gelatine bird: 88.6mm length
25mm diameter
Sheet FE model:
120mm
 Two opposite edges fully restrained
 Barlat’s anisotropic material model
(*MAT_033)
 91126 solid elements
 Eroding single surface contact
Sphere
Ballistic limit study
(Simulation results)
Cube (Flat)
Cube (Corner)
Cube (Edge)
Residual velocity: Projectile velocity after
penetration of the
sheet
Weld region FE
modelling approach
Close-up of
the weld
region
Four different microstructures:
 Weld Nugget (WN)
 Thermo-Mechanically Affected Zone (TMZ)
 Heat Affected Zone (HAZ)
 Base Material (BM)
[1]
20mm
Different material
properties and level
of anisotropy for the
different weld regions
WN TMZTMZHAZ HAZ BMBM
3.175mm
SPH*
Bird
(*) SPH: Smooth Particle Hydrodynamics
[1] Lockwood W. et al. (2002), “Mechanical response of friction stir welded AA2024: experiment and modelling”, Materials Science and Engineering
 Predicted sheet ballistic limit is lower when material anisotropy is
implemented, independently from the projectile shape.
 Weld region provides a loss in ballistic limit for hard projectiles and higher
deflections for bird-strike, when compared to the base material behaviour.
 Implementation of different level of material anisotropy at each weld
region has a significant effect on the overall weld ballistic performance.
 Model the aluminium sheet using an SPH approach and compare ballistic
limit results predicted with the different hard projectile shapes.
 Perform impact experiments with homogeneous plates simulating each
weld region in order to validate Barlat’s anisotropic coefficients used for
modelling the weld area.
Sphere Cube (Flat)
Cube (Corner) Cube (Edge)