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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.

gradual accumulation


The development of additional local failures with increasing loads or time is termed as " _____ ______"

damage accumulation


The branch of mechanics which deals with the study of initiation and accumulation of damage until and including complete rupture is called, "____ _____"

damage mechanics


What are the types of defects that generally occur in a composite?

fibre-matrix debonding
fibre misalignment
cut or broken fibre
voids and blisters
matrix cracking and crazing
density variation
improper curing of resin
impact damage
abrasion and scratches
machining problems


What are the two main sources which can introduce defects and/or damage in a composite?

fabrication/process defects
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.

Fibre Fracture/Breaking


When does fibre kinking first start at?

site of fibre misalignment or local defects


What region is kinking of fibres taking place?

kink band


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.

fibre bending


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.

fibre splitting


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?

matrix cracking
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


The matrix cracks which are parallel to the fibre direction cause significant ____ _____, whereas the matrix cracks perpendicular (sometimes undetectable) to the fibre direction cause ____ degradation in modulus.

modulus degradation,