1) Adhesives applied to bolted connections can impact preload and friction forces, and proper surface preparation and gap size are important for curing. Lubricants should not be mixed with adhesives. 2) Design rules for bolted connections should prevent failure modes like loosening, corrosion, and fatigue. Calculations are needed to ensure reliability over the connection's lifetime including expected reuse. 3) Material properties, surface finishes, joint geometry, fastener type and quality all influence connection performance. Standardized components, proper installation procedures and testing can improve robustness.

1. 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 under
the head + adhesive in the thread is not
allowed
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.
Read the specific design rules, if not
applicable: use a gap between 0.07
and 0,15 mm
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 meant 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 meant for axial loads, see
previous remarks
( preventing galling) due to high
friction of 60°angle metric thread.
Galling Don’t use metric thread to transfer 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.
Fatigue Stripping of the female part, special design rules,
Guideline: use Rm<350: 2x deff , Rm>350 = 1xd
effective thread! Sufficient
Ductile materials are susceptible 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 of bolted connections
Lubrications @ bolts are meant 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
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,

2. Design rules Calculate if the design/ specification is
uncertain
Preventing diversity of failure modes 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 provides volume applying to the
design rule Lk/D
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
embrittlemeant
Be aware of the risks of ferritic grade bolts which
have tensile strength > 1000MPa, class ≥10,9
These grades are susceptible for hydrogen
embrittlemeant. (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 strength 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 circular)
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 aligning
purposes
( not described, however used 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 and
frequency of re-use
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
Electrical Conductivity Failure of software/ electrical components Materials do oxidize, these (artificial 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
Aware of the risk use a bolt clamping a spring.

3. 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 consequences
(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 secure 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, in stead of a line contact cause this a
pint contact.
use Wera bits
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 mythologies
possible: brazing/ integration/ gluing
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 more than 1 Countersunk in a connections,
connection is over constrained!
Countersunk Exceptions: in ductile materials, ( Al 5083/
polymers-wood) these materials "relaxate"
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 of the
supplier
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.
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 perpendicular 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 counder materials!)
Do not clamp plastics or take special precautions
Pretension loss: Over constrained joints
Galling, pretension loss, contamination

4. 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 Aluminum 5xxx/6xxx series and
similar, (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 mythologies, or use All Tight screws
Standardization,
preventing failure
modes
Describe a preferred bolt list: LEAN
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 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.
Fatigue Chamfers of the counderparts. 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
Tested and used @ NASA and
Aerospace industry
Electrical Conductivity Loss of grounding Earth rings, used for grounding of electrical
parts can ONLY be used ONCE, due to the
plastic deformation of these rings.
Galling Risk of press nuts. Misalignmeant during install base
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 environmeants
Electrical Conductivity Grounding Similar coatings like powder coating cause
electrical isolated parts, causing discharges
(software- Electrical Conductivity problems)
might lead to 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 be used, preventing 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.
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
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.

5. Standardization,
preventing failure
modes
Describe a preferred bolt list Think about the bolt interface, use ONE single
tool to disassembly the whole design.
LEAN
Design Choices Tuflock Tuflock screws can only be used ones, ( 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
( higher pretension force than
expected)
Adhesives Loctite 243 Use this adhesive from M4 and up Measured
Adhesives Loctite 222 Use this adhesive from ≤ M3 Measured
Adhesives Fatigue of glued items Prevent use of multiple types adhesives in one
assembly, preventing mistakes
Design rules Torque on drawings Specify torque, if necessary only at drawings:
assembly level.
Solution: for generic use, put bolt
torque scheme in a documeant
referred 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 environmeant Zn Hydrides
effects critical optical elemeants
Environmeant Vacuum/ N2/ hydrogen The environmeant has a large impact on the
friction coefficient of elements ( pretension
force)
Beibly layer will be affected, (
desintegration of layers)
Environmeant X-ray/ Gamma radiation. The environmeant has a large impact on the
friction coefficient of elements ( pretension
force)
Beibly layer will be affected, (
desintegration of layers)
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, ( created cavities
contain residue of grease/oil lead to undefined
friction coefficient: undefined pretension!
Therefore not allowed.
Emuge documeantation
Fatigue 3D printed bolts (e.g. titanium) Material is printed, not forged, therefor does
have an open micro crystalline structure
Fatigue Peek/ PA/Nylon fasteners Polymers expire stress relaxation when ever
tightened, so not be used for force- related
connections
could be used for sealing purposes, (
sealing a oilpump hole)
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
environmeant.
Design rules Back up slides