Flashcards in Quiz 3 Deck (22):
What is failure?
Complete de-functioning of the structure.
The local level failure is called, "____"
In case of fibrous composites the term "local" refers to the individual constituent phases ---- _____ and ______
fibre and matrix
It is important to note that the ultimate failure of a laminate takes place by ___ _____ of damage.
The development of additional local failures with increasing loads or time is termed as " _____ ______"
The branch of mechanics which deals with the study of initiation and accumulation of damage until and including complete rupture is called, "____ _____"
What are the types of defects that generally occur in a composite?
cut or broken fibre
voids and blisters
matrix cracking and crazing
improper curing of resin
abrasion and scratches
What are the two main sources which can introduce defects and/or damage in a composite?
in-field or service defects
The damage mechanism in a fibrous composite are broadly categorized as ....
Micro-level damage mechanism
Macro-level damage mechanism
coupled micro-macro-level damage mechanism
Local level mechanism are further sub categorized based on constituent level as ...
fibre level damage mechanism
matrix level damage mechanism
coupled fibre-matrix level damage mechanism
What is considered to be the most catastrophic mode of failure in laminates? and why?
fibre failure mode
fibre is a load carrying consituent
The fibre breaks into two or more pieces along its length when the axial tensile stress (or strain) in the fibre exceeds the axial strength (or maximum allowable strain) of the fibre. This kind of fracture
occurs in brittle fibres. Such fractures are more catastrophic in nature than other modes of fibre
The fibre fracture may also take place in shearing when the shear stress or strain exceeds the maximum allowable stress or strain.
When does fibre kinking first start at?
site of fibre misalignment or local defects
What region is kinking of fibres taking place?
Kink band is oriented at an _____ with respect to fire direction.
This type of failure occurs when the axial load on the fibre is compressive in nature. The axial
compressive stress causes the fibre to buckle.
fibre buckling or kinking
The bending of fibre can take place under flexural load. The bending of fibres also depends upon the
properties of fibre and matrix along with the fibre arrangement.
The fibre fails in this mode when the transverse or hoop stresses in the fibre exceeds the maximum
allowable value. Further, this can also happen when these stresses in the interface/interphase region
(region in matrix very close to the fibre) exceed the maximum allowable stress.
The hoop stresses can also cause the radial cracking of the fibre. This type of cracking is seen in
some of the fibres
fibre radial cracking
What are the two main damage mechanisms in matrix?
fibre interfacial debonding
What are the two types of matrix cracks that are developed in a unidirectional lamina? Either perpendicular or parallel to the fibre direction.
1, crack developed when axial stress in lamina is tensile in nature.
2, cracks are developed when the inplane transverse stress in the lamina is tensile in nature