Effect What Root cause/ Solution References/ books

Adhesives Adhesives @ bolts, Double/ triple more pretension force. Due to a

decrease of friction, decrease the amount of

torque, an adhesive behaves in first instance

(before curing) as a lubrication: can lead to

fatigue of the joint. The red area is thread

friction, green: head friction, yellow: left over

pretension force

Adhesives Inserting the applied adhesive at the fastener

into the potted hole: =>mounted surface and -

clamped surface contaminated due it’s

capillarity of the adhesive, " =>hydrostatic

bearing" Apply the adhesive in the female

threaded hole

Adhesives Some adhesives are anaerobic, causing not

curing of the adhesive! Residue of the

adhesive is present between the clamped

surfaces, unintentionally, causing " hydrostatic

behavior"

Lubrications

Lubrications Never apply a combination of a lubrication AND

an adhesive.

Don't mix the adhesive and lubrication,the risk

is not curing of the adhesive. Lubrication unter

the head + adhesive in the thread is NOT

DONE

Lubrications Re-use of the lubricated bolted connection The friction, (head or thread) will decrease

drastically, after multiple re-use the lub will

degrade=> increase of the friction. [uncertain

connection]

Adhesives Read the design rules of adhesives Every type of adhesive reacts/ cured in

different manner

Due to curing of the application

Adhesives Do not strain the glued connection during

curing

Adhesives does not cure properly, on macro

scale the polymer chain will break.

Adhesives Expiry date ( lifetime) After the expiry date time the adhesive does

not cure properly, check or use new tube

Adhesives Store the adhesive according specification Temperature and humidity effects the quality

of the adhesive, close the tube after use.

Adhesives Gap width To large or to small gap cause improper curing,

read the use-instructions of the adhesive.

Adhesives Gap width, Fatigue To large gap cause a large shear modus

Adhesives Machining roughness finish and the -

direction influence the robustness of the

joint

< 0.8 finish is not suitable for a robust design, (

the adhesive has no "anchors in the surface")

apply Ra>0.8, surface tension is to low

Surface Texture Correlations with

Tensile Adhesive Strength, by

Stephan Siegmann, EMPA Thun,

Switzerland

Re-use Don't re-use a glued connection before

tapping and cleaning the joint

Residue of broken glued particles cause no

curing/ effect of galling

Safety Calculate the Bolted connections in hoisting/

lifting tools, acc the legislation ( machine

guidelines)

Use a safety factor of 3 for the bolted

connection preventing human injury, use the

SF in the whole chain from threaded female

hole to eg. Bracket.

According SEMI S2, safety issue.

Galling Metric fasteners are not mend for translations,

use power or leadscrews,

Lubrication is preliminary solution, after re-use

the lub is "scrapped" off

( preventing galling) due to high

friction of 60°angle metric thread.

Galling Metric bolts are not mending for axial loads,

see previous remarks

( preventing galling) due to high

friction of 60°angle metric thread.

Galling Don’t use metric thread to bring 2 parts together

(damaging of the nut!)

Due to high friction between the interfaces the

lubricated parts damage will occur: pretension

force will be uncertain.

Design rules of bolted connections

Lubrications @ bolts are mend for higher pretension force or preventing galling

What is critical connection? Answer: a critical connection is a connection which has effect on the joint it self ( failure modes) loss of function or it effects the

surrounding area, the loss bolt/nut cause eg. Electrical contact or cause a collision in a transfer modes.

What is not critical connection? Is than a bolted connection necessary? What will occur when the bolt is not present?

Attach the adhesive always in the female part,

not at the male part,

Fatigue Stripping of the female part, special design rules,

Guideline: use Rm<350: 2x deff , Rm>350 = 1xd

effective thread! Sufficient

Ductile materials are suspectible for stress

relaxation+> preload loss of the connection=>

shear of the connection, effective thread:

depth thread (-) run in (-) run out (-)the first

lead

Design rules Calculate if the design/ specification is

uncertain

Preventing diversity of failure modes http://www.roymech.co.uk/Useful_T

ables/Screws/Thread_Calcs.html

Design rules Calculate if the design/ specification is

uncertain

Calculate the torque of the combined

materials and put it in a scheme, (re-use)

Design rules Do use Lk/D comparison >3 better is to use 5. Preventing autonomous loosening, calculate

the torque

Use the rule of Roloff Matek/ VDI

2230-1

Design rules Calculate the critical bolted connection Preventing autonomous loosening Use the rule of Roloff Matek/ VDI

2230-1

Design rules If the design don't have the volume use All-

tight screws

Preventing autonomous loosening Solid connection, use All Tight screws

®Design rules Potted holes gives you space to apply to the

design rule Lk/D comparison

Standardization,

preventing failure

modes

Don’t develop your own bolt, use always a

standardized one, otherwise use derived from.

Fatigue strength differs from standardized

ones! (-20%)

Hydrogen

embrittlement

Be aware of the risks of ferritic grade bolts which

have tensile strength > 1000MPa, class ≥10,9

These grades are suspectible for hydrogen

embrittlement. (during manufacturing phase,

especially the Zn/ passivated), the fasteners

have to be annealed within 2 hours @ 450C,

(prevent this)

Acc ISO 9857

Temperature Decrease of fatigue strenght at elevated

temperatures

the Rm/Rp factor decrease @ elevated

temperatures ( eg. @300C, decrease of 40%)

Material properties Don’t use for the bolted connection the same

hardness, (HRc) for the mating parts

(without lubrication) risk of galling, eg. AISI

316 vs. A4 bolt

Design rules The spring cause additional axial load, this

effects the pretension force drastically, due to

stress relaxation of the spring ( material

properties) the connection will be uncertain

Design rules Calculate this connection Use the rule of Roloff Matek/ VDI

2230-1

Design rules Check the thread friction between the mating

parts, (ask supplier) if not measure

Measuring with torsion test rig

Design rules Sequence of tightening at an array of bolts

(rectangle or circulair)

Preventing loss of function, neighbors or

opposite fasteners can get loose, if not

applied.

Design rules Tightening method, applicable for high

pretensioned transferred positions

Eliminating relaxation and/or tolerance bow a

sequence of tightening method can be applied:

rule 75% 1st , 90%-2nd and 3th time tightening

100%. Can also be applied for alligning

purposes

( not described, however used for

decades in the automotive industry)

Corrosion Corrosion of the bolted joint Be aware of galvanic corrosion by using

multiple alloys of the bolted connection,

caused by the humidity or the environment

(eg. Demi- water)

Re-use Undefined pretension: How often will the

connection be dis-assembled during lifetime

Re-use of the bolted connection change the

friction, this can be positive as negative,

depending of the used materials

Re-use Undefined pretension: How often will the

connection be dis-assembled during lifetime

Re-use of the bolted connection more than 5

times! an increase of friction will occur. Result:

undefined pretension force: solution, apply

lubrication or new usage fasteners

Aware of the risk use a bolt clamping a spring.

Electrical Conductivity Failure of software/ electrical components Materials do oxidate, these (artifical eg.

Anodizing) layers cause electrical discharges or

floating electrical contacts, use electrical

conductive surfaces ( eg NiP)

Friction Preventing slip/ failure of the connection (Macro/

micro)

The surface topology (roughness and

machining condition) has an impact on the

clamped situation, calculate the risk of slip

Guide to Design Criteria for Bolted

and Riveted Joints: Second Edition

Material properties Be aware of the elastic and plastic deformation of

the whole connection.

Cause pretension loss of the connection Roark’s Formulas: for Stress and

Strain

Magnetic field Magnetic fields/ EMC? Ferritic and A2 grades cause changes in the

magnetic field. Use class A4

Surface deposition Large film thickness cause peeling, shear

forces, threaded holes which are "filled" with

the coating, cause the female thread is not acc

specification

How larger the film thickness of the

coating how sevire the

consequencies (depending of type

coating) ISO 4042

Surface deposition Dedicated coatings “whiskers”, especially at

fasteners: don't develop your own fastener!

(don't apply artificial deposition

technologies, which are not proven)

Design rules Don’t use a metric bolt to tighten an another

bolt

Design rules Don’t use a metric bolt to tighten under an

angle?

Slotted hole Slotted hole pretension loss Fasteners in Slotted holes cause pretension

loss of +70%, caused by relaxation of the base

material, solution: use hardened washers

1/3dk of screw head, min 58 HRC.

Fasteners and Welds for Structural

Connections

Tooling Failure of screwhead Never use the ball end of allen keys to tighten

screws, point contact is worse in stead of a line

contact.

Shear Prevent shear force at the bolted connection. Pretension loss and shear forces cause cutting

behavior of the joint

Material properties Loss of pretension force, to attention of transport CTE of materials is not linear

Design rules Loss of pretension force GD&T has a large impact of the reliability of

the joint, use a tolerance bow for a solid

connection

Design rules Bolts needed? Check: are there other bonding methologies

possible: brazing/ intergration/ glueing

Design rules FMEA Root cause analysis prevent 95% design

mistakes

Design rules DFA Design for Assembly, can the joint be torqued?

And how?

Design rules DFM Design for Manufacturing, check how it's been

made

Countersunk > 1 Countersunk, connection is over

constrained!

Countersunk Exceptions: in ductile materials, ( Al 5083/

polymers) these materials "settle" however

think about pretension loss in the female

threaded feature

Inserts Plastics/ polymers (incl High end (PEEK))

experience stress relaxation, use inserts

(ACME- inserts)

Inserts Use suitable drilling size before applying

inserts. ( every material alloy reacts different

on inserts) read mounting instructions

White zone

Inserts Reliable 100% not all inserts are reliable, ACME inserts are

the most reliable, read mounting instructions

Alternative: ENSAT 337/338

Inserts Use a small potted hole whenever the ACME

inserts are used, preventing the locking pins

are above the surfce after assembly.

ACME inserts are more expensive,

however 100% reliable, (other inserts

are unreliable due to geometric and

metallurgical parameters which

influence the joint.

Do not clamp plastics or take special precautions

Pretension loss: Over constrained joints

Galling, pretension loss, contamination

Inserts Anodized surfaces. In general: the hardness of inserts is less than

the hardness of the materials which have been

used. Especially with anodized surfaces, apply

first the insert, than anodized the surface.

Close the hole before applying the surface

technology

Inserts Failure Never mount an insert manually, preventing

non perpendicluar fit

Geometric Pretension loss or galling Clamped surface has to be parallel to each

other, plates/ modules which are not parallel

are risk, the bolt is the weakest part.

Geometric Pretension loss or galling The bolted combination must be

perpendicular. ( inserts in counter materials!)

Weldnuts Take precautions of weld nuts. Due to thermal

expanding effects (welding process)

Weldnuts Female thread contamination by welding

spatter, if used: re tap. No fastener inside

during welding, spatter cause galling.

Design rules failure modes, without indication Be aware of notches and other stress

concentration factors

Inserts Pretension loss or galling Use inserts in Aluminium 5xxx/6xxx series and

similair, (Rm<350)

Safety Test the bolted connection on a shaker if you are

not sure about the connection.

Preventing loss of function, critical modules ACC IEC norm:? Depending of the

design: Investigate the transport

spec! during engineering phase

(especially flight cargo!)

Standardization,

preventing failure

modes

Prevent use bolts < M3, Uncertain coefficient of friction, due to

tolerance bow, ( this differ from larger sizes)

use other methologies, or use All Tight screws

Standardization,

preventing failure

modes

Describe a preferred bolt list

Fatigue Take precautions about cavities in a bolted

connection

Failure modes, without indication Specified acc. ISO

Fatigue Thread quality, shank radius bolt, Depending how the bolt is made, does have

effect on the mechanical properties ( Rm/RP)

Specified acc. ISO

Fatigue Torsion in the bolt. L/D>8 bolts expire torsion, especially in high

torqued systems, causing the bolt acts like a

spring, uncertain pretension. Prevent these

long fasteners

Material properties Annealing of the bolt/ cold/ hot forged/

machined

Depending how the bolt is made, effects the

mechanical properties ( Rm/RP) must be rolled

Galling Burrs which are created in the manufacturing

process

Galling Burrs which are created in the Logistic/

transport process ( especially larger size (

>M10)

Tooling Use proper tooling. Deviation pro brand can be huge. ( tolerance

bow) With Wera + have the best results been

achieved. (reported by ASML)

Fatigue Chamfers of the counterparts. Burrs/ flakes/

cavities.

Failure modes, without indication Acc ISO 14715

Fatigue

Design Choices “nord lock” rings don’t prevent autonomous

loosening,

when the bolted connection is calculated, a

nordlock ring is not a solution, use All-Tight

screws when no other solution is applicable

Tested and used @ NASA and

Aerospace industry

Electrical Conductivity Loss of grounding Earth rings, used for grounding of electrical

parts, or preventing static electricity can ONLY

be used ONCE, due to the plastic deformation

of these rings, these loose their functionality.

Galling Risk of press nuts. Misallignment during install base

Galling

Manufacturing problems ( producing bolts)

Establish enough pictures from the fatigue mode, good analysis gives insights what can be better! Learned lessons, don’t give the bolt

always the blame. Look at the counterparts.

Describe a preferred bolt list, which the team uses eliminating the differentiation of

screws/ bolts, preventing bolts are been used in the short threaded holes and

v.v.,also: eliminating spare parts. ( cheaper), allow exceptions.

Magnetic field Class A4 Class A4 ( stainless steel AISI 316) are

expensive, use these only whenever necessary

Corrosion Stainless steel bolts Class A2 ( AISI 304) are suitable for "most"

applicable environments

Electrical Conductivity Grounding Similair coatings like powder coating cause

electrical isolated parts, causing discharges

and (software- Electrical Conductivity

problems) can also lead human safety issues

Fatigue Prevent use of low round head screws These screws can not fully torqued (eg. ISO 7380)

Fatigue Slotted cheese head and cross-recessed-pozidrive

Philips screws

Don't use these, prevening wear-out effects

and accidently slide out towards other parts.

Fatigue Slotted head and cross-recess- Philips screws To use these fasteners: you have to push and

turn, otherwise the screwdriver won't stick in

the screw head. Causing failure modes of the

head. Preventing wear out effects.

Standardization,

preventing failure

modes

Describe a preferred bolt list Think about the bolt interface, use ONE single

tool to disassembly the whole design.

Design Choices Tuflock Use Tuflock screws only ones, use their

functionallity after one time use, ( also particle

contamination)

Design Choices Nylock nuts Nylock nuts are an alternative having a robust

connection

Design Choices Spring washer Prevent use of washer, no added value,

generate particle generation

Design Choices Washers Prevent use of washer, no added value, with

exception of slotted holes.

Design Choices Blind holes Prevent use of blind holes, machining residue

is hardly to clean, also preventing of chips/

burrs

( higher pretension force than

expected)

Adhesives Loctite 243 Use this adhesive from M4 and up ( not recommendend)

Adhesives Loctite 222 Use this adhesive from ≤ M3 ( not recommendend)

Adhesives Fatigue of glued items Prevent use of multiple types adhesives in one

assembly, preventing mistakes

Design rules Torque on drawings Specify torque, if neceassary only at drawings:

assembly level.

Solution: for generic use, put bolt

torque scheme in an OTB document

refered to:

Contamination Zn plated screws Zn Plated fasteners ( eg. 10,9/ 8,8) cause Zn

contamination during use/ re-use, Zn particles

go airborne, this influence Optical elements

and vacuum parts

Contamination Zn plated screws Zn cause in vacuum environment Zn Hydrides

effects critical optical elements

Environment Vacuum/ N2/ hydrogen The environment has a large impact on the

friction coefficient of elements ( pretension

force)

Beibly layer

Standardization,

preventing failure

modes

Colors Don't use Stainless steel and blanc passivated

in one design, preventing mixing them up.

stainless steel fasteners have in

general lower tensile strength

(exceptions- bumax 109/120)

Design rules Rolled female threaded parts Cold forming of female threaded parts cause

undefined pretension, ( in created cavities

residue of grease/oil lead to undefined friction

coefficient: undefined pretension! Therefore

not allowed.

Emuge documentation

COG Zn plated and stainless steel screws Are stainless steel screws really needed, if so

apply class A2 (AISI 304) good chemical

resistant, Use class A4 only for magnetic

environment.

Design rules Back up slides