Wednesday 24th September 2014
Student: Ivon Tshinkobo
Project supervisor: Dr Reza Oskouei
Project Result Seminar
:
Bachelor of Mechanical
Engineering
Project Title: Design of fretting corrosion testing
set-up for hip joint implants
Content












Introduction
Aim/Objective
Modular hip joint implant
Previous design
3D Model
Methodology
Force sensor
Piezo actuator
Displacement sensor
Slid unit
Design
Conclusion
Introduction
 Arthritis is the inflammation of the
joint.
 The main symptoms of arthritis are joint
pain and stiffness, which increases with
age.
 The most common type of arthritis is
osteoarthritis.
 Osteoarthritis causes cartilage which
hardens the tissue that covers the end
of the bones where they form a joint to
break down.
 Osteoarthritis of the hip presents pain,
stiffness, a reduced range of movement
and occasionally a feeling that the joint
will give way.
http://www.littleastonoasis.com/Pages/HipReplacement.aspx
Aims/Objective
 In this project, a testing set-up will be
designed in order to test fretting and
corrosion of hip joint implant materials
(Titanium alloy Co-Cr-Mo alloy). Head-neck
taper junction of hip implants suffers from
fretting and corrosion failure in total hip
replacement.
 The project thus aims to design a
laboratory based testing set-up for
investigating the metal failure at the
junction.
 Micro motion between component results
in fretting corrosion that can lead to
initiation of crevice corrosion.
 Repetitive motion lead to continuous
breakdown.
http://jbjs.org/content/95/10/865
Modular implants
 A modular-neck hip implant is a type of hip replacement that
has an interchangeable femoral neck. (The part between the
femoral stem and the head)
 This allows a surgeon to fit different-sized components to
custom device to match each patient’s unique anatomy.
 The problem with the metal-on-metal design is that metal
ball-and-socket can grind together and shed particles into the
body.
 Metal debris can irritate tissues and bone.
 Cause pain and other severe complications.
Modular implants
 Advantage: Restoring pain and giving
flexibility to the joint.
 Better designs have increased stability
and function so the implant feels more
natural to the patient.
 Disadvantage: metallic contact fretting
will occur.
 Result of metal debris from the modular
junction.
 Mechanical failure.
 Metal debris may cause local tissue to
react.
 Metal poisoning and corrosion.
 Tissue damage or causing death.
 Bone loss.
http://www.littleastonoasis.com/Pages/HipReplacement.aspx
Fretting: Small motions occur between tight
metal parts, a metal oxide in the form of a
powder is usually present.
Also fretting is the combination of
tribological and fracture behaviour of
materials, which are in contact together and
having small relative movement at the same
time.
Due to fretting, lifetime is significantly
reduced as compared to that when no
fretting takes place.
Corrosion: Material properties may degrade
with time due to various environmental
effects.
Previous Design




The normal load is applied by way of an
articulated arm on which calibrated weights are
hung.
Displacements and forces are recorded and
monitored during the experience.
The metal samples are connected to a
potentiostat and a saturated calomel reference
electrode was placed close to the contact in order
to measure electrochemical potential of the
fretting couple throughout the tests performed in
Ringer’s solution.
A system of data acquisition continuously records:
the friction coefficient, the tangential force–
displacement and the free corrosion potential.
Once placed in the solution and loaded, the
samples are left in contact during 30 min before
the beginning of the fretting test to allow the
stabilisation of the free corrosion potential
servo-hydraulic traction compression
machine.
3D Model
Load FN
50 Newton is applied to fretting pad
50 micrometre is applied to
specimen to generate relative
motion
Fretting pad
Corrosion surface
Specimen (Ti-6al-4v)
Measuring cell
Relative motion x
Piezo actuator applying relative
motion in continuous movement
Methodology








Design layout
Design components
- Force sensor
-Piezo actuator
-Displacement sensor
-Slid unit
-Design
-Final design
Force sensor
 With its paper-thin construction,
flexibility and force measurement
ability.
 The Thin Force sensor can measure
force between almost any two
surfaces, up to 2 kg.
 To ensure the most accuracy, a small
disc (included) can be placed directly
on the sensing pad before applying
force to the disc.
 This will ensure that all the force is
applied directly to the sensing pad
and not to the surrounding surface.
Piezo Actuator
 Pre-loaded Piezo Actuator
P-845.60
 Push Force 3000N
 Pull 700N +
 Maximum Travel range is
160 micrometre
Displacement measurement
OptoNCDT 1401-5













Laser nano sensor optoNCDT.
Measurement resolution of 0.6 micrometre.
Range of 5 mm.
Recording output such as displacements.
measurement system with an integrated digital signal
processor.
against almost any target without contacting the
object.
uses the triangulation principle to obtain.
an accurate non contact displacement measurement.
A laser diode projects a visible light spot onto the
surface of the target.
Part of the diffuse reflected light is then imaged
through an optical lens system on a sensing element.
The integrated signal processor evaluates the digital
image of the receiver and calculates the accurate
displacement reading.
The measured data are made available in analog or
digital format.
Connector
Displacement measurement
Technical data
Model
Measuring range
ILD 1401-5
5mm(.20")
Start of measuring range
20 mm (.79 ")
Mid of measuring range
22.5mm(.89“
End of measuring range
25 mm (.98 “
Linearity
10 μm
<±0.2%
Resolution
0,6 μm
dyn. at 1 kHz 0.05 % FSO
Measuring rate
Light source
Laser safety class
Vibration
Operating temperature
Storage temperature
analog
3 μm
1kH
semiconductor laser 1
mW, 670 nm (red)
class 2 IEC 60825-1 : 2001-11
15 g / 10 Hz ... 1 kHz
0 ... 55 °C (32 ... 130 °F
-20 ... 70 °C (-4 ... 158 °F)
4 ... 20 mA (1 ... 5 V with cable PC
1401-3/U)
Output
RS232
digital
Supply voltage
Electronics
11 ... 30 VDC, typ. 24 VDC / 50 mA
integral signal processor
Slider Unit
Parts of slid unit
CColour
olour
Numbers
Sizes
Pink
1
200x134
Gray
7
130x89
violet
6
134x100
Green
4
173x40
Blue
2
173x30
Gold
5
173x50
Red
3
175.5x70
Slider Unit
Measuring
cell
First design








Two metallic 40x40 Frames
Two piezo actuators
Metallic bed
Slid unit
Compression spring
Displacement sensor (141-5)
Force sensor
Load cell (500N)
How it is going to work
 In order to simulate the oscillatory tangential movement, a sinusoidal displacement is
generated by a linear preloaded piezo-actuator P-845.60 and a piezo-servo controller E-625.
 The maximum range of the piezo-actuator is 160 micrometer with a maximum push/pull
force of −3000 N and +700 N.
 The piezo-translator is equipped with an integrated strain gauge sensor with a high
measurement resolution of 1.8 nm in closed-loop operation.
 The displacements of the specimen are recorded by a laser nano sensor (optoNCDT 1401-5)
with a measurement resolution of 0.6micromete and range of 5mm .
 The measuring cell is mounted on a precision linear slide unit in a high rigid die set.
 The tangential force is measured by a piezoelectric or force sensor.
 The normal load is applied up to a maximum force of 500 N by a precompressed spring on the
fretting pad and monitored by a 500 N load cell.
 The contact stamp is pressed on the fretting sample which is fixed in the measuring cell.
 Potential measurements are carried out with a three-electrode arrangement with an
electrolyte bridge to analyze the corrosion behavior.
 Ringer’s solution is used at ambient conditions to simulate physiological fluids.
Displacement
measurement
Compression spring
Load cell
Measuring cell
Slider unit
Force sensor
Piezo actuator
Measuring cell
Displacement
sensor
Conclusion
 Previous design
-Mechanical/ Electronics system
-The normal load(Load cell) is applied by way of an articulated arm on which calibrated
weights are hung.
-Hydraulic actuator
The metal samples are connected to a potentiostat and a saturated calomel reference
electrode was placed close to the contact in order to measure electrochemical potential
of the fretting couple throughout the tests performed in Ringer’s solution.
 Current design
-Electronics System
-Metallic bass with two frames against each other
-The measuring cell is mounted on a precision linear slide unit in a high rigid die set
-Piezo actuator
-The normal load is applied up to a maximum force of 500 N by a precompressed
spring on the fretting pad and monitored by a 500 N load
Any Questions ?