Why Test Materials???

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Why Test Materials???

Very early material test. Archimedes in Greece ~ 250 BC used grappling hooks for the defense of Syracuse.


Course OutlineMechanical Properties of MaterialsViscoelasticity

CreepRelaxationHyperelasticity

ElectroForce TechnologyDynamic Mechanical Analysis (DMA/DMTA)

FatigueFracture Mechanics

Crack Growth & Fracture Toughness


Course OutlineBiomaterial Stimulation and TestingBone TissueSpinal DevicesDental Wear SystemStent – Graft Testing

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Mechanical Properties of Materials

One of the earliest material testing systems from Leonardo da Vinci.


Linear response of force and displacement in spring element.


Consider a rod with initial length L which is stretched to a length L'.

The strain measure e, a dimensionless ratio, is defined as the ratio of elongation with respect to the original length.

3


Consider a rod with cross-sectional area A with a force applied to the end, F.

The stress in the rod σ, is equal to the force divided by the cross-sectional area, A.

FA

σ =

F

A


σεE=

Response for a perfectly elastic material

FdK=


If you reorganize the variables you get another useful equation.

The deflection of the rod is equal to the product of the force times the length, divided by the product of the area times the modulus.

F LAE

d=

F

A

d

L

4


d

LOriginalRadius εtransverseεaxial

= -

FinalRadius

Poisson’s ratio is also a material property often measured during tensile testing and is equal to:

Typical values of Poisson’s ratio for elastic behavior is 0.25 to 0.33. A value of 0.5 means there is no change in volume for a given loading condition.

Equations have been formulated that relate applied force and displacement to stress and strain for bending and other geometries. They typically are more complicated than for simple tension or compression.


Typical test specimen geometries.


For Elastic deformation, energy supplied to deform the body (strain energy) is stored in the body as potential energy and is available to return the body to its original (unstressed) size and shape once the applied loading is removed.

There is no loss of energy during loading and unloading

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Most materials display some nonlinear behavior.

It is called plastic behavior if there is permanent strain (strain does not return to zero after unloading).


The total strain is equal to the sum of the elastic strain and the plastic strain.


For metals, energy is dissipated as heat when the plastic region is reached.

For elastic-plastic materials, energy is dissipated only in the plastic region, i.e. relatively large strains (or stresses).

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Tensile/compressive loading and unloading results in this figure

• The loop OABCO is the hysteresis loop• area enclosed by this loop=total

strain energy dissipated• how does energy dissipate?

heat -- friction, viscous dissipation

Sometimes the transition between elastic and plastic deformation is very sharp.



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Typical material properties measured and reported:


ModulusYield Stress (tangent, secant, offset, upper and lower)Ultimate stress/strainStrain to failureEnergy to failurePoisson’s ratio (if transverse strain is available)Etc.

Typical graphical data with markings


8


Shear versus Axial

For small deformations, shear strain is defined by=d/l

Shear strains cause a change in shape but not in volume.

Shear stress is equal to the shear force divided by the shear area.

Shear stress is proportional to shearstrain by the shear modulus, G in the elastic region. G~E/3


γ

• Torsional shear strain (γ)

θa

h

No volume change …

γ = θ a / h

Questions about the introduction to Mechanical Properties of

Materials??


9

What is Viscoelasticity?

If you apply a force to a solid, it deforms to some extent.

If you apply a force to a liquid it deforms continuously. It flows.

A viscoelastic material is part solid, part liquid.

Introduction to Viscoelasticity


ViscoelasticityDefinition: time-dependent material behavior where the

stress response of that material depends on both the strain applied and the strain rate at which it was applied!

�Examples:

biological materialspolymersmetals at high temperatures


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Elastic versus viscoelastic behaviorsFor a constant applied strain

An elastic material has a unique material responseA viscoelastic material has infinite material responses depending on the strain-rate



Elastic SolidStress is only a function of strain σ=σ(ε)For linearly elastic, we have a single modulus, E or G

Viscous FluidStress is only a function of strain rate σ=σ(dε/dt)Proportionality constant is the viscosity, η


Maxwell ModelStress is a function of strain and strain-rate σ=σ(ε, dε/dt)2 Constants -- k,c

Kelvin-Voigt ModelStress is a function of strain and strain-rate σ=σ(ε, dε/dt)2 Constants -- k,c

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• Under repetitive loading, a viscoelastic material will heat up. Energy is dissipated regardless of whether strains (or stresses) are small or large;– some energy is dissipated

with dashpots (as heat)– some energy is stored in

springs– area in the hysteresis loop is

a function of loading rate


Viscoelastic behavior -- MemoryBecause of the time dependent material behavior of viscoelastic materials, their behavior is dependent on the history of loading and are said to have a ‘memory.’That is, viscoelastic materials remember the history of deformations they undergo and then react accordingly.

This means that you must know the sequence of applied loading to create tests that predict real life performance or match data from other test protocols.



Because the mechanical response of a viscoelastic material is a function of load magnitude and rate, we must specify both during a theoretical analysis or experimental study.

Ramp rate and levelFrequency and end levels

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Questions about the introduction to Viscoelasticity??


Definition of Creep test: Apply force (stress) and measure the displacement(strain) response.

Think of putting a weight on a sponge and having water slowly leak out and the sponge slowly compress.

Introduction to Creep


Creep test

Elastic material strain remains constant

A viscoelastic solid will eventually recover completely to zero strain after stress is removed

A viscoelastic fluid will never completely recover after stress is removed

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Introduction to Creep1. Instantaneous deformationmainly elastic

2. Primary/transientSlope of strain vs. time decreases with time: work-hardening

3. Secondary/steady-state Rate of straining is constant: balance of work-hardening and recovery

4. Tertiary Rapidly accelerating strain rate up to failure: formation of internal cracks, voids, grain boundary separation, necking, etc.

Stages of Creep


Parameters of creep behaviorThe stage secondary/steady-state creep is of longest duration and the steady-state creep rate is the most important parameter of the creep behavior in long-life applications.

Another parameter, especially important in short-life creepsituations, is time to rupture, or the rupture lifetime tr

Questions about the introduction to

Creep??


14

Introduction to Stress Relaxation

Definition of Stress-relaxation test:Apply displacement (strain) and measure the force (stress) response.

Think of a long walk on the beach . . .


Stress-relaxation test

Elastic material stress remains constant

A viscoelastic solid will never completely relx unless the strain is removed

A viscoelastic fluid will eventually completely relax to zero


15


Relaxation data

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10 12 14 16 18 20

Time (sec)

Forc

e (N

)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Dis

plac

emen

t (m

m)

Force Displacement



The conversion of Stress-relaxation test data to viscoelastic properties assumes that the displacement happens instantaneously. In reality, there is a finite ramp period and a settling time at the requested displacement.

To minimize error, the ramp to level should be as quick as possible and there should be minimal overshoot or settling after the displacement has been achieved.

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Questions about the introduction to Creep/Relaxation??


Cyclic data on rubber

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Displacement (mm)

Load

(N)

Introduction to Hyperelasticity

Hyperelasticity determines properties of elastomers at high strain levels (> 50% strain) typically for use in FEA material models.

Cycle 20

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Displacement (mm)

Forc

e (N

)

Cycle 20

Loading for 20th cycle

-5

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Displacement (mm)

Forc

e (N

)

Initial data

Requires Engineering Judgement

•Use Stable(?) 20th Cycle•Use Upload of 20th Cycle


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Loading for 20th cycle

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Displacement (mm)

Forc

e (N

)

Initial data Corrected data

•Correct for offset


Bi-axial material characterization


Planar shear (Pure shear)


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Hyperelasticity??


ElectroForce®

Linear Motor

Moving magnet -stationary coil design

Rare earth magnets

Advanced flexure design

No friction & no stiction = frictionless operation

No hydraulic oil or air required

Bose ElectroForce® Technology

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ElectroForce® Advantages

High performance: Static/One cycle a day to 200 Hz

High-resolution control and measurability: millinewton & nanometers

No hoses, no oil - just plug it in and start testing

Some motors can be place in an incubator and run at 100% humidity

Billions of cycles with minimum maintenance

Quiet operation

Reduces your operating costs

10 year warranty on ElectroForce Linear Motor

ElectroForce® Advantages

Closed-loop Testing System

Actuator/mover in crosshead:Linear Motor

Load Reaction frame assembly

Load cell:Usually on non-moving side of load train

Displacement transducer

Controller with: • Control Software• Data Acquisition• Data Analysis

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WinTest® Control System

4 kHz update rate

Up to 8 channels control

Up to 32 channels signal

conditioning

Real-time scope and meters

Drop down menu test set up

Table-top system

Dynamic Force range: ±225 N (High Force option ±450 N)

Performance: Static to 200 Hz

Dynamic stroke: 13.0 mm (± 6.5 mm)

ElectroForce® Series 32003200

Table-top or free standing

Dynamic Force range: ±3 kN

Performance: Static to 100 Hz

Dynamic stroke: 25 mm (± 12.5 mm)

ElectroForce® Series 3300The Versatile Choice for Dynamic Testing

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• Force capacities up to 15 kN

• Dynamic stroke 50 mm

• Static up to 100 Hz performance

ElectroForce® 3500

Dynamic Mechanical Analysis

In the Dynamic Mechanical Analysis (DMA) test:• a sinusoidal signal is input

into the specimen • load and deflection timed

data is collected• amplitude and the phase

angle (δ) between the signals is determine, typically using the values of the fundamental frequency of a Fourier Transform

Introduction to DMA

22

DMA properties are used to predict the behavior of materials or components as a function of

• temperature, • frequency, • dynamic vibration • mean condition

Introduction to DMA

DMA properties can be used to: • Monitor the state of cure of an elastomer• Determine the glass transition of a polymer• Predict vibration isolation performance• Predict traction and rolling resistance of tires• Predict seal performance• Monitor changes as a function of fatigue

The DMA software has even been used to measure the coefficient of thermal expansion!

Introduction to DMA

Polypropylene and Clay Composite as a function of compound

Composite versus pure pp

0

500

1000

1500

2000

2500

3000

3500

-40 -30 -20 -10 0 10 20 30 40

Temperature (C)

Mod

ulus

(N/m

m^2

)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

E* composite E* pure pp tan delta composite tan delta pure pp

Introduction to DMA

Glass transition test on polypropolene and polypropolene-based-nanocomposite

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DMA Analysis CalculationsESG has relied on two industry testing standards to develop the analysis included in the DMA application software.

• American Society for Testing and Materials (ASTM) D 5992-96 Standard Guide for Dynamic Testing of Vulcanized Rubber and Rubber-Like Materials Using Vibratory Methods.

• Society of Automotive Engineers J1085 NOV95 Testing Dynamic Properties of Elastomeric Isolators.

Introduction to DMA

Introduction to DMA

Fourier Analysis Data Requirements

We use MATLAB to calculate the Fourier series parameters and display data. MATLAB requires a minimum of 2 complete cycles of data.

The Fourier analysis requires that the total number of data points equal 2n. ESG DMA uses 1024 points.

The Fourier analysis works best if complete cycles of data are used (data starts and stops at the same place in a sine wave).

ESG DMA software manages all of these requirements automatically.

Introduction to DMA

This is an example of data with evenly spaced timed data.

-1.5

-1

-0.5

0

0.5

1

1.5

0 2 4 6 8 10 12

Time (sec)

Forc

e

-1.5

-1

-0.5

0

0.5

1

1.5

Dis

plac

emen

t

ForceDisplacement

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Typical ESG DMA test

• timed data on top

• Fourier analysis on the bottom (frequency and amplitude for force and displacement)

Introduction to DMA

Introduction to DMA

The three measurements (amplitude of force and displacement and phase(δ)) are then used to determine the

• Dynamic Stiffness (K*)• K’ = Storage stiffness = K* (cos δ)• K” = Loss stiffness = K* (sin δ)

These can be converted to material Dynamic Modulus measurements using standard shape factors for rectangular, cylindrical, three point bend, and shear.

Introduction to DMA

25

Other calculated properties are;

•Tan delta (tangent of the phase angle)

•Damping (C) •Transmissibility (Tr)•Compliance (J*)•Hysteresis

Equations for these calculations can be found in the DMA section of the WinTest manual.

Introduction to DMA

DMA data plotted as a function of temperature with shape factor included.

Introduction to DMA

The DMA software allows the user to define• Frequency• Temperature• Dynamic amplitude• Mean level• Hold at Mean level• Hold at temperature• Cycles before Data

Acquisition

for eachtest condition

Introduction to DMA

26

In addition to timed data or spectral analysis, the DMA software allows the display of

X vs. Y (Hysteresis loops)

Amplitude results

Calculated DMA results

Introduction to DMA

X vs. Y (Hysteresis loops) Amplitude results

Introduction to DMA

Example of Stiffness or Modulus as a function of a changing control parameter.

Example of Tg determination

Introduction to DMA

27

Exported to an ASCII file with all the test information.

Introduction to DMA


Dynamic Mechanical Analysis??

Introduction to DMA

What is Fatigue???

Fatigue is failure of a component or structure from cyclic loading at stresses below the materials ultimate strength, and in some cases, below the materials yield strength.

Introduction to Fatigue

28



Fatigue failures


Historical DevelopmentThe term “Fatigue” was first used in England to describe failure of iron girders subjected to repeated deflection.

Fatigue failures became very troublesome with the advent of the steam engine and the railroads.

The most famous of the early fatigue researchers was August Wohler (~1850-1875). He was interested in explaining why railroad axles were failing.

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30




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Most testing is single axis. The real world is multi-axial. No standard currently exists for this testing. WinTest provides good tools to conduct both single and multi-axial testing.

Thermal effects are also important. TMF (Thermal Mechanical Fatigue) combines the effects of both and is often used for predicting fatigue life of components such as turbine blades. Specialized application software is required to manage the function generation and data acquisition requirements of TMF.


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Questions about the introduction to Fatigue??


Introduction to Fracture Mechanics

Examples of failures


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Who uses Fracture Mechanics?Pressure vessels (leak before fail)

Power generationOil-Gas industry

Material producersNaval industryCivil Engineering (bridges, buildings, etc.)AerospaceAutomotiveBiomedicalOthers?



(tensile) (shear) (tearing)


35


Typical types of tensile fracture specimens


Compact Tension

Edge Crack

Center Crack


Most often used specimen geometries

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There are two related fields of study in Fracture Mechanics;

Crack growthFracture toughness

Crack growth studies help predict how quickly a crack will grow when a structure is subjected to typical loading.

Fracture toughness studies help predict the conditions where an existing crack will grow in an unstable manner.

The combination of the two help determine inspection requirements to detect critical cracks prior to catastrophic failures like those shown in the introduction to this section.

Questions about the introduction to Fracture Mechanics??


37

Introduction to Crack Growth

Typical Crack growth data.

Crack length as a function of cycles and applied force


Typical Crack growth data.

Crack growth rate as a function of Stress Intensity

F = geometry effect∆S = Stress Amplitudeaavg = average crack length


Crack growth curve including initiation, stable growth, and unstable growth to failure.

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Comparison of crack growth behaviors of different materials.


Crack growth in 4 pt bend bone specimen (UC Berkeley)


Bovine Dentin Compact Tension (CT) crack growth data. (UMBC)

39


Crack growth tests can include the influence of environment (hydrogen embrittlement, corrosion, temperature, etc.). It can also include strain rate or viscoelastic dependencies (vary frequency, vary hold times, vary ramp rates, etc.)

Crack growth tests are typically K controlled (constant K, K shed, K increasing) so some real-time measure or estimate of the crack length is required.

Questions about the introduction to Crack Growth??


Biomaterial Stimulation and Growth

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BioDynamic™ Test Instrument for Tissue Engineering and Biomaterials Research

BioDynamic™ Test Instrument Applications

Characterization of biomaterials, scaffolds, tissues, and tissue-engineered constructs in a biological environmentBeyond bioreactors

Simulate in vivo conditionsPerform long term tests in a sterile environmentPrecise control of test parametersCharacterize properties

BioDynamic™ Test Instrument

Characterization of biomaterials, scaffolds, tissues, and tissue-engineered constructs in a biological environment

Beyond bioreactorsSimulate in vivo conditionsPerform long term tests in a sterile environmentPrecise control of test parametersCharacterize properties

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Compact Vertical Frames

20 N and 5 mm displacement 200 N and 12.7 mm displacement

BioDynamic™ Test Instrument Components

Frame with motorsChamber with manifoldsSensors• Load cells of different capacities and resolutions with axial motors• Displacement transducers in each motor• Two catheter-type pressure transducers with each vascular

systemFlow perfusion loopEnvironment (cell culture incubator)WinTest software

Transparent Full-View sides for observation or strain measurements

Multiple chamber ports for filling/draining chamber, flow inlets/outlets, fluid sampling, sensors

BioDynamic™ Chamber

Locks on the push rods hold specimen in stable position

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Vascular chamber with axial and pulsatile manifolds

Modular Design

BioDynamic™ Chamber

Orthopaedic chamber with porous platens (left) and BioDynamic grips (right)

BioDynamic Tensile Grips

Tensile Grips BioDynamic Grips

Clamp Design Self-tightening Mechanism

BioDynamic Compression Platens

Standard porous and non-porous platens (indented; require 2.2 mm minimum sample thickness)

Optional porous platens can be used with (left) or without (right) membrane around the sample (flat faces suitable for very thin samples)

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Porous Porous PlatensPlatens

Ported Ported ExtensionsExtensions

Low Friction Low Friction Dynamic SealsDynamic Seals

Modular DesignModular Design

Instrumentation Instrumentation PortsPorts

Simple Simple Position Position LocksLocks

Axial Manifold

Chamber StandChamber Stand

Stand for support of chamber during assembly inside of sterile hood

Vertical for Disk Specimen Mounting

Horizontal and Partially Filled with Media

Additional Chamber Incubation with or without Perfusion Flow

Chamber Ports and Sensors

Flow inlets/outletsChamber filling/drainingFluid sampling for off-line measurementsSensors

Load cells of different capacities and resolutions with axial motors

Displacement transducers in each motor

Catheter-type pressure transducers with vascular systems

Optical micrometer for vascular distension

Digital video extensometer for strain measurements

pH, dissolved oxygen, lactate/glucose, temperature

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Soft Tissue Characterization and Stimulation

Axial tension & compression Axial tension & compression ––linear motorslinear motorsDynamic pressure Dynamic pressure –– linear motorslinear motorsMean flow Mean flow –– peristaltic and gear peristaltic and gear pumpspumps

ForceForceDisplacementDisplacementStressStressStrain Strain Radial distensionRadial distensionDynamic pressureDynamic pressureDynamic Mechanical Dynamic Mechanical Analysis Analysis –– viscoelastic viscoelastic propertiesproperties

Nutrient Flow Loop

Peristaltic pump (shown) for orthopaedic applications

0.1-280 ml/minup to 4 pump heads per drive

BioDynamic™ Testing PlatformNutrient Flow for Vascular Applications

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Incubator Setup

ElectroForce®

Applications

Hydrogel Characterization

Research Need: Characterize a very soft hydrogel sample in compression to determine its dynamic mechanical properties

ElectroForce Application: Evaluate the sample stiffness and viscoelastic properties using an ElectroForce 3100, compression platens, and a gram-force load cell

Specimen: Polyvinyl alcohol hydrogel cylinder (3 x 3 mm)

Sample stiffness tests were conducted with:• forces in the mN range• very slow displacement rate (0.02 mm/s)

Dynamic Mechanical Analysis (DMA)

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Hydrogel Testing ResultsHydrogel Testing Results

Orthopaedic ApplicationsBone/Cartilage

2-80 mm platen spacingNonporous platens for compressionPorous platens for compression tests and direct perfusion through the specimensAxial loading and dynamic flow

Sheffield University

Mechanical force plays an important role in bone growth and repair

47

Bone Tissue EngineeringDr Gwendolen Reilly, Anuphan Sittichokechaiwut, and Anthony J. Ryan, University of Sheffield

Day5 Day7 Day90

1

2

3

4

5

6

Youn

g's

mod

ulus

of e

last

icity

(KPa

)

Unloaded Loaded

00.020.040.060.08

25 35 45 55 65time (s)

stra

in

E22E11E12

0.50.60.70.80.9

1

0.5 1 1.5displacement (mm)

load

(N)

Strain Measurements

Gel-Del Technologies Inc. Small Diameter Vascular Graft

TestBench BioDynamicPulsatile stimulationPressure controlMikro-tip catheter pressure transducer (Millar)Laser micrometer with 0.05 µm resolution (Keyence) 50 lb load cell

Composite material3 mm ID30 mm long

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0

20

40

60

80

100

7.34

7.36

7.38

7.4

7.42

0 50 100 150 200 250 300 350 400

pressure (mmHg)

diameter (mm)

pres

sure

(mm

Hg) diam

eter (mm

)

time (s)

0

40

80

120

160

200

240

280

320

7.9

8

8.1

8.2

8.3

8.4

8.5

0 200 400 600 800

pressure (mmHg)

diameter (mm)

pres

sure

(mm

Hg) diam

eter (mm

)

time (sec)7.9

8

8.1

8.2

8.3

8.4

8.5

0 40 80 120 160 200 240 280 320

diam

eter

(mm

)

pressure (mmHg)

7.34

7.36

7.38

7.4

7.42

7.44

0 20 40 60 80 100

diam

eter

(mm

)

pressure (mmHg)

Gel-Del Technologies Inc. (St. Paul, MN)

Vascular Graft Tissue Engineering Professor Robert Tranquillo and Katie Ahmann University of Minnesota

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5

puls

atile

com

man

d (m

l)

time (s)

26

27

28

29

30

31

32

3.3

3.31

3.32

3.33

3.34

3.35

3.36

3.37

0 5 10 15

lumen pressure (mmHg) diameter (mm)

lum

en p

ress

ure

(mm

Hg)

diameter (m

m)

time (s)

Simultaneous characterization and stimulationNo need to remove specimen to characterizeCharacterize specimen as it is being stimulated

Material characterizationViscoelastic properties (modulus, stiffness, tan delta, etc)Strength, creep and stress relaxation

StimulationTension, compression, dynamic pressure

Physiological environmentNutrient flow loop Temperature, humidity and gas exchange

BioDynamic™ Testing PlatformFeatures

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Biocompatible and autoclavable materials

Push rod seal design minimizes friction and yet maintains sterile environment – very important in applying small forces and displacements to weak specimens

Flow loop is designed to minimize any “dead zones” to better ensure nothing collects in the system & complete sterilization is achieved

Chambers are designed for easy transfer in and out of any of our systems

BioDynamic™ Testing PlatformFeatures

Summary

Complete system to provide simultaneous & continuous characterization & stimulation

Chambers for cardiovascular & orthopaedic tissues and biomaterials

Comprehensive characterization capabilities: force, displacement, stress, strain, radial distension, dynamic pressure, dynamic mechanical analysis

Comprehensive stimulation capabilities: tension, compression, pulsatile

Axial and Pulsatile Frames

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Multi-frame Configurations

Torsion Loading

Axial-torsion, pulsatile-torsion, axial-pulsatile-torsion

Torsional specs2.8 Nm (ortho)1.0 Nm (vascular)8 Hz±25 degrees

Off-axis pulsatile

BioDynamic 5900 Test Instrument

4-specimen chamberCompression⎯ 0.3 MPa (5 mm specimens)⎯ ±3 mm⎯ 0.01-1 Hz

Pulsatile flow⎯ 0.3 MPa (2250 mmHg)⎯ 0.3 mL/pulse⎯ 0.01-1 Hz⎯ Mean flow (1-10 mL/min)

Cyclic hydrostatic pressure⎯ 1-10 mL/min⎯ 0.3 MPa

450 N (100 lb) load cell per sampleTransparent, flexible membrane around each sample

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BD-5900

Bone Research

Bone Tissue ResearchMicrotesting

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1 mm

Testing Solution:

ElectroForce 3200 system used to characterize specimens in tests with these parameters:

Displacement loading rate of 10 µm/secDisplacement range of 0.5 mm (0.1 µm resolution) Load range of 10 N (1 µN resolution)Specimens were kept moist with water spray

Load Vs Displacement

0

1

2

3

4

5

6

7

0 20 40 60 80

Displacement (Microns)

Load

(N)


Research Need:Micromechanical Testing of small bone specimens to determine the mechanical properties

ELectroForce application:A 3200 was used with a standard system load cell [225 N (50 lbf)] and LVDT [±6.5 mm (±0.25”)] to apply specific load levels to the specimen and measure the corresponding displacement changes.

Specimens:Micro-machined human cortical bone


Cyclic Creep of Cortical Bone

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

0 100 200 300 400 500 600 700Time (seconds)

Load

(N)

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Dis

plac

emen

t (m

m)

Load (N) Disp (mm)

Testing Solution: ELectroForce 3200 system used to perform multicycliccreep tests to characterize the bone specimens:

parallelpiped specimens 0.8mm~1.2mm x 0.8mm~1.2mm x 0.6mmloads corresponding to stress

values of 35, 65, 70, 75, 80, and 85 MPaassociated displacement changes

on the micron level

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Research Need: Improved knowledge of bone growth/healing

ELectroForce application: 3- or 4- point bend test to determine differences in healing efficacy from genomic phenotyping and drug therapies.

Specimens: Mouse, rat, and rabbit bones

Bone Research

Rotary Actuator Torsion Axis

Bone Research

Linear ActuatorVertical Axis

Testing Solution: ElectroForce 3200 Axial/Torsion system used to conduct bend tests on specimen

TestBench Axial-Torsion test system

• ASTM testing of metallic medical bone screws (F543-02)

• fracture fixation or maxillofacial applications

• 3 Tests to determine:Torsion propertiesDriving torqueAxial pullout strength

Bone Screw Implant Testing

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Spinal Devices

The SpineThe Spinal Column is compose of 5 segments:

- Cervical- Thoracic- Lumbar- Sacral- Coccyx (Tailbone)

Each segment has the following number of vertebrae:

Cervical – 7Thoracic – 12Lumbar – 5Sacral – 5Coccygeal – 4

Motions of the Spine

In addition to the compressive loading and moments that are applied to the spine, the following are the descriptions of the motions:

• Flexion – forward bending

• Extension – backward bending

• Lateral bending – side-to-side bending

• Rotation – rotation of the torso longitudinally

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Spine

Standard and Customized equipment for standardized tests

Customer supplied gripping/fixtures/bathsAxial, bi-axial (axial-torsion), multi-axial system configurationsStatic and dynamic testing protocol

The purpose of many of these devices is to alleviate or manage pain and preserve motion.

Spinal Devices

ASTM F1717 - Standard Test Methods for Spinal Implant Constructs in a Vetebrectomy Model

ASTM F2077 – Intervertebral Body Fusion Devices

BAK Vista Interbody Fusion Device - Zimmer

RAY Threaded Fusion Cage -Stryker

ROI Spine Fusion – LDR Spine

InterfixThreadedFusion Device -Medtronic

This standard describes methods for statically and dynamically testing intervertebral body fusion device assemblies that have been designed to promote arthrodesis (bone or joint fusion) at a given spinal segment.

Testing consists of:

1) Axial compression test

2) Compression-Shear test

3) Torsion Testing

All tests may be run in ambient conditions or in a physiologic solution

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ElectroForce Solutions:

ElectroForce 3330

ElectroForce 3520

ASTM F2077 – Intervertebral Body Fusion Devices

Background Information

• spinal therapy and implant industry continues to grow

• kinematic analysis of the spine remains the topic of discussion due to complex biomechanics

• need to better understand spinal motions and loading characteristics

• in response to this need Bose has developed a kinematic spine simulator

Spine Simulation Applications

Spine Biomechanics – general research into spine biomechanics – loading and kinematics, the completion of three-dimensional spine stiffness matrices

Spine Fixation Methods – research to understand the impact of various fixation methods on spine performance from a motion preservation standpoint

Interbody Fusion – evaluation of fusion techniques and determination of how this affects other motions of the spine segmentally

Disc Replacement Efficacy – range of motion studies for intervertebral disc replacement devices

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Spine Simulator Description

Base platform for the spine simulator is a servopneumatic axial-torsion materials test system

Combination of additional electric motors provide overturning moments and translations

Total of up to nine actuators provide axial compression and rotation, flexion-extension, lateral bending, and anterior-posterior and left-right translations

Each axis is independently controlled in either displacement/rotation or force/torque control

Spine Simulator Specifications

Table 1. 9-Axes Kinematic Spine Simulator Forces and Motions

±50 mm±1000 NLeft/Right

±50 mm±1000 NAnt./Post.

±60o± 15 NmLat. Bend

+120o/-60o±15 NmFlex./Ext.

±50o±74 NmRotation

±50 mm±5.6 kNAxial

MotionLoad

intent is to be able to apply a compressive load that follows the natural curvature of the spine

loading is applied via cables that are run through eyelets which are fixed on vertebral bodies

design consists of a torsion motor, a tension balancing mechanism, and two load cells

applies 1200 N of compressive load and allows for 40 mm of translation

Load Follower Capability

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ASTM F2346 - Spinal Disc Static and Dynamic Characterization

The methods in this standard describe tests for characterizing the static and dynamic properties of intervertebral disc replacement devices.

Testing consists of:

1) Axial compression test

2) Compression-Shear test

3) Torsion Testing

Testing fixtures are similar to those used in ASTM F2077.

Charite - DePuy Flexicore - Spinecore

ProDisc – Spine SolutionsMaverick - Medtronic

Kineflex – Spinal Motion

Theken – eDisc

ElectroForce Solutions:

ElectroForce 3330

ElectroForce 3520

ASTM F2346 - Spinal Disc Static and Dynamic Characterization

HIGHHIGH--SPEED FATIGUE TESTING OF A METALSPEED FATIGUE TESTING OF A METAL--ONON--METAL INTERVERTEBRAL DISC PROSTHESISMETAL INTERVERTEBRAL DISC PROSTHESIS

LL--5252--0160.10160.1--AA

Cyclic loading was conducted at 60Hz and 40Hz for the axial and shear tests, respectively, using the “Null” or voltage control to maintain maximum and minimum load levels of –3,250 and –300N during testing. Cyclic data was acquired after 15,000 cycles and at subsequent intervals of 250,000 cycles. At these acquisition intervals, data was sampled at 2500Hz for 0.2 seconds. Testing was terminated at 10 million cycles or at device failure.

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Spine BiomechanicsSingle Spinal Disc Wear Simulator for functional &

kinematic wear assessment

The IVD replacements from the previous tests also need to undergo fatigue and wear assessment tests

Both ASTM and ISO have drafts of standards/test methods in the process of being approved

Developed a single-station prototype spinal disc fatigue and wear simulator

Designed to meet ASTM and ISO test requirements

Single-Station Prototype

Spine BiomechanicsSpinal Disc Wear Simulator for functional & kinematic

wear assessment

Axial Loading2000 N compressive force

Axial Rotation±6° and ±10 Nm

Lateral Bend±6° and ±12 Nm

Extension Flexion±7.5° (15° included angle) and ±10 Nm

Configurations include Cervical, Lumbar, and Cervical/Lumbar

Designed to meet ASTM and ISO test requirements

Spine Biomechanics

ASTM Test Parameters for Lumbar and Cervical IVD Replacements

± 6o± 7.5o± 6o100 N StaticCervical

± 6o± 7.5o± 3o1200 N StaticLumbar

Lateral BendingFlex. / Exten.Axial RotationAxial LoadingDisc Type

It should be noted that while it is not the “recommended” loading condition in the ASTM standard, they do allow for dynamic loading at 50% to 150% of the static loads. Phasing of the motions is described in the standard.

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Dental Devices

Dental Wear System

3330 based system, includes:

• 3330 Axial only system

• Additional horizontal linear motor

• Breadboard base extension

• Multi-axis load cell (3 axes)

• Dental software package (DTL)

• Specimen chamber optional

Dental Wear Simulator Vertical Actuator Profile

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Dental Wear Simulator Actuator Waveform Profiles

Overshoot on retract

Loading profile

Disp1 = Vertical Actuator

Disp2 = Horizontal Actuator

Fz = Vertical Load

Dental Implant Tests Endosseous Implants

Dental Wear Simulator -Peak Valley Data

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Dental Biomaterials TestsFatigue Crack Growth and Bending (Dentin, Composite, and the interface) –using the ElectroForce 3200. Both quasi-static and fatigue testing.

Stent – Graft Testing

What is a Stent ?

Stents are used in many other parts of the vascular system to hold veins

and arteries open.

A Stent is a scaffold. Often laser cut from a metal tube, it is used to open up partially blocked blood vessels such as the coronary arteries.

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Why Test?

1954 De Havilland Comets

2004 In Vivo Stent Fractures

To understand unexpected failures! To compare product!

Pulsatile Fatigue Testing

• Since 1994 Radial distention has been the benchmark test.

• 10 year life test (more than 380 million cycles)

Recent StandardsISO (International) Standards:• ISO-25339-1 * (2003) for Vascular Grafts

• ISO-25339-2 * (Pending approval) for Vascular Stents

ASTM International Standards:• ASTM F1828-97 Standard Specification for Ureteral Stents

• ASTM F2079-02 Elastic Recoil of Balloon-Expandable Stents

• ASTM F2081-01 Dimensional Attributes of Vascular Stents

• ASTM F2394-04 Securement of Balloon Expandable Stent

• ASTM F2477-06 * Pulsatile Fatigue Durability

US FDA Guidance *:• http://www.fda.gov/cdrh/ode/guidance/1545.pdf

(*) Written with technical input from Bose-ESG

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Testing Standards

Pulsatile FatigueASTM F 2477-0710 year fatigue life . . .

At least 380 million cyclesStraight tubesTest each size of same design37 C +/- 2CSaline (PBS) or justify alternative

How to Test a Stent ?

“Pressure Control Method”• Uses a thin walled “mock artery” of

known ‘compliance’.

• Cycle pressure between 80 - 160mm Hg

Advantages:• Simple analog to physiology

Disadvantages:• Need to have ‘physiological’ tubes of

known compliance. Compliance must be constant through-out the test.

• Tests must be run at slower frequencies due to tube dynamics.

There are two methods to duplicate the distention caused by the heart beat.

Pulsatile Distension Fatigue“Distention Control Method”• Uses a thick walled “mock artery”. Compliance

is not as important.

• The outer diameter of the tube is measured and used for control.

Advantages:• Accurate change in diameter is used.

• Tests are faster since the thick walled tube reacts better at higher test frequencies.

• Changes in tube compliance due to ageing do not affect the test.

There are two methods to duplicate the distention caused by the heart beat. Distension Control & Pressure Control.

This is the principle behind the patented Bose 9100 Series SGT’s.

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ElectroForce® 9110 SGTPulsatile Durability Test Instrument

Basic Configuration

BOSE Linear Motor

BOSE Linear Motor

Distribution Manifolds

Mock Arteries

Bellows Assy Bellows Assy

Stents may be deployed into the Mock Arteries through the fittings

In this case as many as (2) coronary stents may be placed in each of the 12 Mock Arteries for a total of 24 samples per test.


Laser Micrometer to measure Stent Distension

Radial Distention Measurement System


Stent Distension may be measured at any point along the length of the stent

Test Protocol may

require daily

measurements at

the proximal,

medical, and distal

positions of each

device.

Regular measurements of the position of the device in the mock artery ensure that

migration is noticed immediately

Distal

Proximal

Medial

Mock Artery

Stent # 1

Stent # 2

Radial Distention Measurement System

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(2 mm to 10 mm diameter ID/lumen Mock Arteries)

Pulsatile Fatigue for small vesselsElectroForce® 9110-12 Stent/Graft Test Instrument

Configuration ExamplesStented Grafts for the Abdominal Aorta

The 9120-4B AAA Stent/Graft Test

Instrument(10mm to 32mm dia)

Stented Grafts for the Larger Thoracic Aorta

The largest SGT on the Market Today!

The 9150-6 Thoracic Stent/Graft Test

Instrument (22 mm to 50 mm)

Multi-mode CoronaryStent Testing

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Coronary Stents:BreakAre seldom straightAre subjected to large deflectionsAre often ‘overlapped’ w/other stents

Vascular Simulation:Pulsatile DurabilityBending DurabilityExtension DurabilityRotation Durability

Design Considerations:Easy device accessMultiple samplesVisibilityProgrammabilityFlexibilityCombined Loading

Coronary Stent Durability/FatigueMulti-Axis Coronary Stent Test Instrument

Passive Multi-ModeFatigue Durability

ElectroForce® 9510-12 Multi-Axis Coronary Stent Test Instrument

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ElectroForce® 9210-12Test SystemDES Coated Stent Testing

New Capabilities!New Capabilities!

DES Stent Coating Durability Next Gen Requirements

10 year Simulated pulsatile fatigue test (400,000,000 cycles)

Pulse on a bend (Static Bend)

Overlapped stents(Static Bend)

Large sampleNeed to quantify particulate

(microscopic & chemical analysis)

Bioabsorbable coatings/stents(strength & endurance characteristics)

DES Stent Coating Durability

Accelerated Fatigue with Particle Capture

• Individual Capture for each stent

• Ability to capture deployment particles when installed in straight tubes (acute durability).

• Ability to continue a full term fatigue test on same stents (chronic durability).

• Ability to capture timed samples on all (12) stents automatically. (Programmable)

• May be triggered by cycle count

• May be triggered by time

• May be triggered by filter condition

• Fatigue run to target duration

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ElectroForce® 9210-12 SGT

ElectroForce 9210-12 DES SGT

Particle Characterization Module

Optional Water Purity Modules

Features:• Multiple samples

12 Tube Base system• Programmable Pulsatile

DistentionMean Flow with programmablecyclic pulse flow

• Isolated Flow:• Particle Counting

Simple Sampling (off-lineanalysis)In-line, real-time sampling

• Particle Capture:Automated filter change

Testing DES & BD Stents in a Bench top Biological Environment

Viable porcine artery perfused in nutrient solution (reduced volume)

In-Vitro Biological DES TestsReal-Time & Accelerated Pulsatile & Flow testing

DES deployed in viable artery via pushrods

DES may be deployed in viable arteries and studied under physiological orsemi-accelerated pulsatile distension and flow conditions.

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DES Delivery

Drug penetration affected by tissue strain and loading frequency

Cell delivery and retention dependent on tissue loading

Ability to mimic loading and perfusion conditions

Drug screening, dosage and delivery rate

Bioabsorbable Stent StudiesDegradation under dynamic conditions

Effect of flow/pressure and extension/compression

Hydrolytic or enzymatic degradation

Degradation products

Media sampling

Real-time monitoring

Effect on mechanical properties

BioDynamic™ Testing PlatformPerfusion Flow Loop

ElectroForce® 5270 BioDynamic Multi-chamber Configuration for DES Stent Development

Individual or common perfusion possible

Axial frame Pulsatile frame

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Multi-ModePeripheral Stent Testing

Define the Loading Environment

The Femoral & Popliteal arteries (SFA) (Large bend, compression, rotation & pulsatile loading)

The Tibial Arteries (Similar loading to the SFA)

The Renal Arteries (Small rotation, bend, tension & pulsatile loading)

The Carotid Arteries (Small rotation, bend, tension & pulsatile loading)

Fatigue profile:Pulsatile Distention component

Bending component

Extension/Compression component

Rotation component

Peripheral Stent Durability/FatigueMulti-Axis Peripheral Stent Test Instrument

CompressionCompressionCompressionImage courtesy of Image courtesy of ““Endovascular TodayEndovascular Today””

Extension / ContractionExtension / ContractionExtension / Contraction

Torsion Torsion Torsion

FlexionFlexionFlexion

+ Pulsatile + Pulsatile DistentionDistention

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Physiological LoadingCoronary

Short Straight

Non-CoronaryLong stentsAccount for multi-mode

Regulatory Requirements

Test Complex Loading

Simplified Loading is a great start for verification of FEA models and material properties.

Unfortunately stents in the body are subject to loading from several motions at any one time.

To simulate the in-vivo conditions we must combine loading in a bench test and choose the appropriate amplitudes and frequency of each motion.

Vascular Simulation:• Pulsatile Durability

• Bending Durability

• Extension Durability

• Rotation Durability

Peripheral Stent Durability/FatigueMulti-Axis Peripheral Stent Test Instrument

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ElectroForce® 9410-8 Multi-Axis Peripheral Stent Test Instrument

Programmable loading for:• SFA/Popliteal Artery Stents

• Tibial Artery Stents

• Carotid Artery Stents

• Renal Artery Stents

Applications for testing non-radialfatigue of:• Peripheral Stents

• Overlapped Stents

• Coated Stents

• 10 year Life or ‘Fatigue to Fracture’

ElectroForce® 9410-8 Multi-Axis Peripheral Stent Test Instrument

Power & Control

Electronics

Distention, Rotation & Flow

Systems

Tension & Bend

Systems

Laser Micrometer

System

Saline Mean Pressure Source

Operator’s PC Monitor & Keyboard

Laser Micrometer

Straight Tube

Fatigue & FractureTesting of Cardiovascular

Materials & Structures

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Stented Endovascular Graft Hook Fatigue

Every AAA graft is held in place at the proximal (upstream) end by a set of nitinol ‘barbs’ that hook into the healthy aorta to keep the AAA device from migrating ‘south’. The hooks are subject to fracture and failure.

Hooks to be tested

Cyclic Tensile Loading

Fatigue & FractureExamples of Test Specimens


Testing for Fatigue LifeThere are several makes of Vena Cava Filters based on the tee-pee design with radiating struts.

To successfully test the structure for fatigue durability (or determine the fatigue limit) the device needs to be cycled from its full extension to fully compressed. This would require nearly 30 to 50 mm travel.

A common method to test would be to test individual legs (or struts).

Septal Occluder


Testing for Fatigue LifeThere are several makes of Septal Occluders based on a NiTi structure.

As this is a device that is placed in the heart it must show durability of a minimum of 15 years of equivalent loading or 600,000,000 cycles of loading in a fatigue test.

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Testing for Fatigue LifeRather than performing tension-tension fatigue on straight wire samples, material properties may be obtained from tension-tension fatigue of a bend geometry that represents the material that has been cut, formed, processed, and prepared similar to the finished product.

The ‘diamond’ specimen shown above is one example of such a material test specimen.

Proceedings SMST-2003


ElectroForce® 3200 MSF-12Multiple Sample Fatigue System

12 Sample 12 Sample loading sites loading sites w/ load cellsw/ load cells

Low mass Low mass ‘‘spiderspider’’

(The only moving object.)(The only moving object.)

Load cells are Load cells are above the bath.above the bath.

37C Saline Bath37C Saline Bath• Temperature Controlled &

covered

• Flat Transparent sides for videographic validation.

• Front & Rear open to provide access to samples.

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Load cells are Load cells are above the bathabove the bath..

100 mm100 mm(between mounting surfaces)(between mounting surfaces) Removable Removable

‘‘DoorsDoors’’






Load cells are Load cells are above the bath.above the bath.

37C Saline Bath37C Saline Bath• Temperature Controlled &

covered

• Flat Transparent sides for videographic validation.

• Front & Rear open to provide access to samples.

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WinTest Control SoftwareFor (12) Sample Fatigue Testing

Individual Meters Individual Meters to monitor load to monitor load for each station!for each station!

Upper & Lower Limits Upper & Lower Limits for Displacement or for Displacement or

LoadLoad

Easy to Read on Easy to Read on ONE ScreenONE Screen

Thank you for your attention

www.bose-electroforce.com

Why Test Materials???

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