rf9 physics of failure sliding contact phenomena material related failure

RF9

Physics of Failure

Sliding contact phenomenaMaterial related failure

RF9 Program Day 2

slide 2RF9 - Physics of Failure2013

9:00-9:15 Introduction

9:15-9:30 Friction related failures

9:30-10:00 Demo load capacity of sliding contacts

10:00-10:15 Break

10:30-11:30 PoF Friction

11:30-11:45 Application of gained results

11:45-12:30 PoF Wear

12:30-13:30 Lunch

13:30-14:00 Demo Dry Sliding and EP additives

14:00-15:00 PoF Material selection

15:00-15:15 Break

15:15-16:15 PoF Lubrication


16:45-17:00 Summary of the day

Adv Eng Design Page 222

Material & Coating Selection

RF9 - Physics of Failure – Material Selection


Case study Storm surge Barrier


A movable storm surge barrier is constructed making dikes along the river unnecessary.




F=35.000 Metric Tonnes Loadm=15.000 Metric Tonnes Load

p<150 MPaµ<0.1

Material selection ?


Material & Coating Selection


7.1 Materials in relative slidingMetals, polymers, technical ceramics

7.2 Coatings and surface treatmentsSurface treatments and classification

7.3 Material selectionCase study: storm surge barrier


Material Selection: Metals

PF9 - Physics of Failure – Material Selection

steel, bronze, cast iron…




Why metal-metal combinations are always lubricated. Without lubrication:

Metals of relative high hardness:

+ Relative good wear resistance(class 4)

- High friction, scatter(µ=0.3...0.6)

Metals of relative low hardness:+ Relative low friction

(µ=0.08...0.14)- High wear rate

(class 6)

Without lubricationSevere adhesive friction / adhesive wear

Seminar - Physics of Failure2013

Case 1




How to reduce friction and wear due to adhesion Combinations of a non-metal against a metal Carburizing or nitriding High hardness of both surfaces Difference in hardness of a factor between 3 to 5 High roughness Strong oxide film Lubricant, liquid or solid Thin layer with low shear strength.

0

c.max 0

/ ,

f

c

q F v Fv

q A pv A Ld

T T qR

T Tpv

RA

slide 122013


Material Selection: Polymers


Dependent on heat conduction

µ(p,v)




Polymers• Thermoplastics

two types of thermoplastics- crystalline- amorphous

• Thermosetscannot be reshaped by heatingare stiff and strong in relation to thermoplasticsare often reinforced with glass or carbon fibers

• Elastomersrubbery polymers, can stretch easily and

instantly return to its original shape when released.




Thermoplastics

+ Do not need to be lubricated+ Low weight+ Injection molding

- Low stiffness and strength - Mechanical properties strongly depend on temp - Poor heat conduction, large thermal expansion - Large machining tolerances




Amorphous plastics+ Less mold shrinkage - Susceptible to chemical attack - Lower wear resistance

Crystalline plastics+ Higher strength and rigidity+ Higher wear resistance+ Good chemical resistance to oils and grease

(silicone based oils, water, soap…)




price




Self lubricating plastics are compounded with- PTFE, MoS2, Graphite, Silicone oil, Aramid fibres

Fiber reinforced plastics are reinforced with

- Glass fibers, Carbon fibers Steel counter surface

- HRc>50, Ra=0.3-0.4 μm Aramid fibers

- Improves resistance to abrasion especially against counter surfaces of lower hardness such as aluminum and plastics.

The low friction is a result of a strongly

adhering transfer film on the counter surface

Water lubrication precludes the formation of a

dry lubricant film, resulting in high wear rate

Adv Eng Design Page 258, 261




Case 2


Bronze St.50 (1.0050)

Pmax=10…20 MPa

Pmax=5…10 MPa

Failure mode:




How to reduce friction and wear due to adhesion Combinations of non-metals or a non-metal against a metal Carburizing or nitriding High hardness of both surfaces Difference in hardness of a factor between 3 to 5 High roughness Strong oxide film Lubricant, liquid or solid Thin layer with low shear strength.




Difference in hardness of a factor between 3 to 5 Less tendency to adhesion (Pb, Sn) Good embed ability for abrasive particles Leveling out of stress concentrations




Main bearing

Marine bearing




Elastic supportPorous bearing

Oil circulation within the pores




Porous iron

Hardened shaft




Porous bronze (PbSn) bearings

μ=0.06-0.10, k=0.3-0.9 10-15 m2/N, PV=1.75 106 Pa·m/s

Adv Eng Design Page 306, 35, 221

Case 3


Layered molecular structure of graphite

slide 312013




How to reduce friction and wear due to adhesion1) : Combinations of a non-metal against a metal Carburizing or nitriding High hardness of both surfaces Difference in hardness of a factor between 3 to 5 High roughness Strong oxide film Lubricant, liquid or solid Thin layer with low shear strength

Stainless steel

Thin oxide layer

Stainless steel bolts require special purpose lubricants

Adv Eng Design Page 306, 35, 221

Case 3


Successful application in clearance fits to prevent fretting corrosion (left) or galling (right)


AF-Coating(MoS2, graphite)




Successful application in screw joints

Particle orientation after initial sliding

AF-Coating, P>100MPa, µ<0.1






How to reduce friction and wear due to adhesion1) : Combinations of non-metals or a non-metal against a metal Carburizing or nitriding High hardness of both surfaces Difference in hardness of a factor between 3 to 5 High roughness Strong oxide film Lubricant, liquid or solid Thin layer with low shear strength

Galvanized

High corrosion resistance




How to reduce friction and wear due to adhesion Combinations of a non-metal against a metal Carburizing or nitriding High hardness of both surfaces Difference in hardness of a factor between 3 to 5 High roughness Strong oxide film Lubricant, liquid or solid Thin layer with low shear strength.

Case 4


Material Selection: Tech. Ceramics


Al2O3 = AluminaSiC = Silicon CarbideSi3N4 = Silicon NitrideZrO2 = ZirconiaZTA = Zirconia Toughened Alumina

+ High hardness and wear resistance+ Low specific weight+ Excellent high temperature properties+ Resistance to corrosive environment - Low toughness (brittle)




+ High resistance to abrasive wear (elastic deformation)+ High resistance to adhesive wear (small γ/H ratio)

1/3~HHigh surface energy but small ratio of surface energy and hardness




Hydrodynamic bearing operatingin abrasive environment (Pavg= 6 MPa)




Jewel bearings

Industrial jewels

Diamond pivots


Case 5



Material Selection: Coatings & surface treatments


Bonding strength




Advantage of dissimilar materials(Metallurgical incompatible materials).


Material Selection


Introducing residual compressive stressesup to half the yield strength in order to improve the fatigue strength.

Laser peening imparts a layer of compressive stress that is four times deeper than that attainable from conventional shot peening




Nickel and chromium plating




Laser cladding

Laser cladding is an effective way to refurbish and improve worn or damaged industrial components




Substrate low alloyedC-steel, Clad materialStellite 21

Pre-machining: removal of worn and with lubricant diffused material

Post-machining to required dimensions




Al2O3 TiO2

WC

HVOF Spraying




CVD -TiN




Adhesive wear(Galling)

DLC coatings in sheet metal forming, µ<0.1




Summary• The wear resistance of a machine part

is determined by the wear resistance of it’s surface.

• This means that for the surface other demands can be made than for the bulk material

• There are plenty of options to improve the surface quality• Treatments in the surface / on the surface

+ hard surface + tough core


Case study Storm surge BarrierHalf of the Netherlands is below sea level. To prevent flooding dikes along the coast line are raised to delta level.

Raising the dikes along the river are unwanted and would be very expensive. A dam isn’t possible while the seaport of Rotterdam must remain accessible.


F=35.000 tonnesm=15.000 tonnes

p<150 MPaµ<0.1

Material selection ?




The allowable pressure in sliding contacts between metals is limited by seizure

Steel – cast iron 5…10 MPa, μ=0.12…0.18 Steel - CuSn or CuAl alloys 10…20 MPa, μ=0.12…0.18

In screw joints contact pressures up to 100 MPa are common, but the sliding motion is limited to one single move and μ=0.12…0.18 Zinc plated to prevent

corrosion and seizure.


Solid lubricants


Successful application in screw joints

Particle orientation after initial sliding

AF-Coating, P>100MPa, µ<0.1






Solid lubricants are used for conditions where conventional lubricants are inadequate

Reciprocating motion, fretting Improvement of running in conditions Extreme contact pressures Shock loading High temperatures Ceramics




P<150MPa, µ<0.1



Adhesive wear between casting steel parts

High maintenance costs

What to do?

How to prevent failure µ>0.1?



The problem:High maintenance costs (wear by seizure)

The challenge: Find a tribo system (material combination)that sustains high contact pressures in sliding motion andshow minimal friction and minimal wear.

The solution: ?



The solution: ?Only limited possibilities to modify the realized construction.

Alternative lubricant or coating system? Boundary Lubricated metal - metal contacts p<20MPa, µ>0.1 Thermoset – metal contacts p<150 MPa, µ>0.1 Polymer – metal contacts p<10 MPa, µ<0.1



Polymer – metal contacts only for limited contact pressure?

Coulombs law: If the load is doubled the friction is doubled.Not for polymers!



PE against epoxy resin, p>150 MPa, µ=0.02…0.06F > 7000 kN (700 tonnes).

Cast steel

UHMWPE

Carbon fiber

Cast steel with epoxy coating



Testing of a special engineered turning cutter


500 holes in each ball joint


SummaryThe problem:

High maintenance costs (wear by seizure)The solution: Polymer discs, expansion blocked by

carbon fiber rings, sliding against epoxy coated steel surface.Performance: Contact pressures up to 150 MPa,

coefficient of friction μ < 0.05, lifetime > 5 km sliding distance, maintenance limited to overhauling of the epoxy coatingafter a large number of moves.



Material Selection

Summary• Several different material combinations have been

discussed with respect to their applications.• Metals, metal alloys, thermoplastics, thermosets,

ceramics and many coatings or surface treatments.• There is not an ideal material combination for

sliding contacts in general.• In machine design metal-metal combinations are

common and it is demonstrated that these combinationsneed to be lubricated.

RF9 Program Day 2

slide 84RF9 - Physics of Failure2013

9:00-9:15 Introduction

9:15-9:30 Friction related failures

9:30-10:00 Demo load capacity of sliding contacts

10:00-10:15 Break

10:30-11:30 PoF Friction


11:45-12:30 PoF Wear

12:30-13:30 Lunch

13:30-14:00 Demo Dry Sliding and EP additives

14:00-15:00 PoF Material selection

15:00-15:15 Break

15:15-16:15 PoF Lubrication


16:45-17:00 Summary of the day

rf9 physics of failure sliding contact phenomena material related failure

Documents

pof material selection

day slide

failure material selection

slide 2rf9 physics

adv eng design page

metals rf9 physics

high wear rate slide

polymers rf9 physics