10 августа, 2015 
Malyar The main durability aspects of bonded joints may now be summarised
as follows:
(1) water is a particularly aggressive environment for bonded joints, especially when the bonded assembly is also subjected to conditions of relatively high (normal) stress and temperature
(2) joints comprising adherends possessing high surface free energies, e. g. metals, are particularly susceptible to environmental attack. Failure usually occurs at the adhesive/substrate interface
(3) the principal mechanisms of environmental failure identified are:
(a) displacement of adhesive on the metal oxide by water, due
|
Epoxide |
Pretreatments |
||||||
|
Discipline/ |
Adher. |
(followed by |
Adhesion |
||||
|
Reference (No) |
application |
cold |
hot |
mat(s) |
degreasing) |
promoters |
|
|
Andrews & Stevenson (117) |
UK |
chem/academic |
/ |
ti |
polish |
||
|
Allen et at. (66) |
UK |
aerospace |
/ |
al |
various practical’ |
||
|
Althof (41, 95) |
Ger |
DFVLR |
/ |
al |
chem etch |
||
|
Bascom (108) |
USA |
admiralty |
/ |
al |
chem etch |
||
|
Bethune (118) |
USA |
aerospace |
/ |
al |
chem etch |
||
|
Bodnar (119) |
USA |
various |
/ |
al |
various |
||
|
Brewis et at. (94, 120) |
UK |
chem/academic |
/ |
al |
various |
||
|
Brockmann (121) |
Ger |
DFVLR |
/ |
al. st |
various |
||
|
Cherry & Thompson (109, 110) Aus |
chem/eng |
/ |
al |
chem etch |
|||
|
Comyn (90) |
UK |
chem/academic |
/ |
al |
various |
||
|
Cotter (93) |
UK |
aerospace |
/ |
al. ti |
chem etch |
||
|
Hockney (92) |
UK |
aerospace |
/ |
al. ti |
chem etch |
||
|
Wake (37) |
UK |
chem/academic |
/ |
a] |
chem etch |
||
|
Krieger (64) |
USA |
aerospace |
/ |
al |
chem etch |
||
|
Minford (122, 123) |
USA |
aerospace |
/ |
/ |
al |
various |
|
|
McMillan (59, 60) |
USA |
aerospace |
/ |
al |
various |
primers |
|
|
Venables (124) |
USA |
aerospace |
/ |
al |
various |
primers |
|
|
Albrecht (34) |
USA |
civ eng/bridges |
/ |
/ |
St |
||
|
Blight (125) |
SA |
civ eng |
/ |
st, cone |
? |
||
|
Bowditch & Stannard (113) |
UK |
admiralty |
/ |
st, cfrp |
grit blast |
SPT |
|
|
Brockmann (53) |
Ger |
DFVLR |
/ |
/ |
St |
grit blast |
|
|
Calder (126) |
UK |
civ eng/TRRL |
/ |
st, cone |
grit blast |
some primed |
|
|
Lloyd & Calder (127) |
UK |
civ eng/TRRL |
/ |
st, cone |
grit blast |
||
|
Mastronardi et at. (112) |
1 |
chem/academic |
/ |
st |
sandblast |
primers |
|
|
Garnish (128) |
UK |
adhesive manufr. |
/ |
st, s/st |
various |
||
|
Gledhill & Kinloch (106) |
UK |
MOD/weapons |
/ |
st |
grit blast |
||
|
Gledhill et at. (129) |
UK |
MOD/weapons |
/ |
st |
grit blast |
||
|
Gettings & Kinloch (114) |
UK |
MOD/weapons |
/ |
st |
grit blast |
silane |
|
|
Gettings & Kinloch (130) |
UK |
MOD/weapons |
/ |
s/st |
chem etch |
silane |
|
|
Hutchinson (115) |
UK |
civ eng |
/ |
st |
various |
silane |
|
|
Kinloch & Shaw (28) |
UK |
MOD/weapons |
/ |
st |
various |
silane |
|
|
Jones & Swamy (131) |
UK |
civ eng/repair |
/ |
st/conc |
|||
|
Ladner & Weder (132) |
Swi |
civ eng/repair |
/ |
st/conc |
grit blast |
primer |
|
|
Nara & Gasparini (133) |
USA |
civ eng/bridges |
/ |
st |
grit blast |
||
|
Stevenson (134) |
UK |
chem/offshore |
st |
grit blast |
primer |
||
|
Sykes (107) |
UK |
phys/academic |
/ |
st |
various |
||
|
Trawinski (135) |
USA |
aerospace |
/ |
st |
cold chem etch |
primers |
|
|
Walker (136) |
UK |
AW RE/we apons |
/ |
st |
grit blast |
silane |
|
|
References grouped more or |
less |
al |
aluminium & alloy |
||||
|
alphabetically in relation to adherend materials |
efrp |
carbon fibre reinf. plastic |
|||||
|
cone |
concrete |
||||||
|
st |
steel |
||||||
|
s/st |
stainless steel |
||||||
|
ti |
titanium |
|
Fracture |
|||||
|
Joint |
Const |
Exposure |
mechanics |
Interface |
|
|
type(s) |
stress |
environment |
approach |
problem |
Remarks |
|
‘blister’ |
water |
/ |
/ |
||
|
lap |
water |
/ |
evaluation of adhesives and pretreatments for aircraft repair |
||
|
‘thick’ lap |
water |
bondline shear stress-strain response |
|||
|
various |
/ |
water |
some |
/ |
REVIEW: stress corrosion |
|
cleavage |
/ |
water |
/ |
/ |
test techniques |
|
various |
some |
various |
some |
/ |
collection of papers |
|
lap |
water |
/ |
water diffusion through adhesive |
||
|
lap |
/ |
water, outdoor |
/ |
||
|
‘special’ |
water |
/ |
/ |
effect of shrinkage stress |
|
|
various |
water |
/ |
REVIEW: water diffusion |
||
|
lap |
some |
outdoor |
/ |
most extensive weathering trials |
|
|
various |
some |
outdoor |
ever reported and analysed for |
||
|
lap |
some |
outdoor |
/ |
temperate and tropical exposure |
|
|
various |
some |
water |
some |
/ |
design data |
|
lap |
some |
water, outdoor |
/ |
includes tropical exposure |
|
|
various |
some |
water, outdoor |
some |
/ |
REVIEWS: pretreatments and test methods |
|
various |
some |
water |
some |
/ |
REVIEW: bond durability |
|
various |
some outdoor |
work in progress |
|||
|
various |
some |
heat |
creep, thermal props only |
||
|
butt |
some |
water |
/ |
‘sacrificial’ pretreatment technology |
|
|
lap |
water, outdoor |
/ |
REVIEW: pretreatment |
||
|
plated beams |
some |
outdoor |
/ |
‘strength’ of ext. reinf. cone beams |
|
|
dye |
/ |
microstructural investigation |
|||
|
coatings |
water |
/ |
coatings & corrosion |
||
|
lap |
water |
/ |
test durations too short |
||
|
butt |
water |
/ |
thermodynamic approach |
||
|
butt |
water |
/ |
/ |
failure ‘model’ |
|
|
butt |
water |
/ |
surface analysis |
||
|
lap |
water |
/ |
/ |
surface analysis |
|
|
cleavage |
/ |
water |
/ |
/ |
evaluation of adhesives |
|
various |
some |
water |
/ |
/ |
REVIEW: fracture mechanics |
|
plated beams |
some |
water |
in progress: ‘strength’ only? |
||
|
plated beams |
some |
/ |
feasibility study |
||
|
lap & butt |
some |
water |
/ |
/ |
rubber/metal bond durability |
|
‘special’ |
water |
/ |
REVIEW: pretreatment |
||
|
lap |
water |
/ |
/ |
‘new’ pretreatment process |
|
|
wedge |
water |
/ |
coatings & corrosion |
||
|
‘pulloff & torque shear |
outdoor |
work in progress |
water = liquid or vapour
different liquid compositions constant or intermittent exposure different temperatures
|
to the rupture of secondary bonds. This may be predicted from thermodynamic considerations
(b) loss of strength and failure of the metal oxide itself due to subtle changes, e. g. hydration
(c) hydrolysis in the boundary layer of adhesive adjacent to the adherend surface, the properties of this layer being different from those of the bulk adhesive
(d) the formation of interfacial pressure pockets by osmosis, if soluble salts are present on the substrate surface
(e) interfacial corrosion, which may or may not be a postfailure phenomenon
(4) The kinetics of environmental failure are influenced by the diffusion of water through the adhesive. This may be altered by changing the adhesive’s composition
(5) • appropriate surface pretreatments must be employed to create
water-stable forces acting across the interface. The significance of this aspect is immense.
Information on the natural weathering behaviour of joints is very useful. By combining this information with data from ‘accelerated’ laboratory tests, some realistic predictions of service-lifetime may be made. Theoretical models of the pattern of bondline saturation of joints as a function of time of environmental exposure provide a useful appreciation of the possible extent of problems (e. g. Fig. 4.21). The process of joint failure, as observed in practice or in the laboratory, is frequently non-diagnostic; i. e. it rarely reveals the true cause, or the series of stages, leading to deterioration or failure.
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