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Fiber Reinforced Composites > Remainder > Flashcards

Remainder Flashcards

1
Q

Special aspect of tensile testing for composites

A

Use of end tabs

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2
Q

Materials used for end tabs in tensile testing of composites

A

E-glass-epoxy

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3
Q

Purpose of end tabs for tensile testing of composites

A

To reduce stress concentration in gripped area and promote tensile failure mode

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4
Q

Tensile testing off-axis means

A

Fibers not aligned with pull direction

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5
Q

Tensile-testing extensional stiffness matrix complication

A

A16, A26 != 0

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6
Q

Shape of deformation expected in off-axis tensile testing

A

S-shaped deformation

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7
Q

Comparison of stress-strain curves for CF vs. GF

A

CF has higher modulus, higher strength, lower elongation

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8
Q

Stress-strain curve for tensile-cross-ply laminate

A

Contains a knee, representing failure of 90 ply

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9
Q

Significance of first knee in multi-directional laminate stress-strain curve

A

Failure of first ply

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10
Q

FPF acronym

A

First ply failure

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11
Q

Failure prediction acronym: SLT

A

Longitudinal tensile strength

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12
Q

Failure prediction acronym: SLTS

A

In-plane shear strength

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13
Q

Destructive inspection techniques

A

Microscopy

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14
Q

Microscopy D/ND?

A

Destructive

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15
Q

Non-destructive inspection techniques

A

Coordinate measurement, ultrasound, thermography

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16
Q

Coordinate measurement D/ND?

A

ND

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17
Q

Ultrasound D/ND?

A

ND

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18
Q

Thermography D/ND?

A

ND

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19
Q

Defects examined in manufacturing inspection

A

Porosity, delamination, poor cure, resin-rich/resin-poor areas

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20
Q

Defects examined in in-service inspection

A

Cracks, delamination, trapped water, hole damage, burns

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21
Q

Thermal profile of thermoplastic manufacturing

A

Highest temp after heating; convection losses in transport; conduction losses in forming and consolidation

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22
Q

Manufacturing of thermoplastic composites

A

Heating, transport, forming, consolidation, demolding

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23
Q

Thermoplastic vs. thermoset viscosity

A

Lower viscosity needed for thermoplastics

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24
Q

Important difference of thermoplastics vs. thermosets

A

Thermoplastics can be softened and remolded.

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25
Q

Thermoplastic advantages vs. thermosets

A

No refrigeration needed, long shelf life, short processing, high toughness, remeltable, recyclable, fusion bonding

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26
Q

Thermoplastic disadvantages vs. thermosets

A

High melting viscosity results in voids; residual stress from thermal expansion; crystallinity from slow cooling rates

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27
Q

Three types of welding

A

Resistance welding, induction welding, ultrasonic welding

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28
Q

Welding can only be used with what type of composite

A

Thermoplastic composites

29
Q

Ultrasonic welding description

A

Parts are held together under pressure with an energy director between them; a sonotrode is used to apply ultrasonic (20-50 kHz) vibrations creating heat for welding

30
Q

Induction welding description

A

Parts are held together with a susceptor between them; an alternating magnetic field generates heat used to weld them together.

31
Q

Speed ranking of joining methods:

A

Ultrasonic > induction > resistance > adhesive

32
Q

Resistance welding description

A

Parts are held together via insulating blocks with a heating element between them. Electric current is passed through heating element, forming a weld

33
Q

Machining is not preferred compared to

A

Manufacturing and curing to net shape

34
Q

Traditional machining methods include

A

Turning, drilling, milling, sawing

35
Q

Non-traditional machining methods include

A

Water jet cutting, laser machining, electric discharge machining

36
Q

Drilling vs. milling

A

Drilling motion is along axis of rotation; milling is perpendicular to axis of rotation

37
Q

Special drill bit needed for composites

A

Polycrystalline diamond drill bits or submicron diamond particle coated drill bits

38
Q

Why special drill bit needed for drilling composites

A

Carbon fiber composites are very abrasive

39
Q

Why sawing composites is difficult compared to other materials

A

CF is abrasive and does not transfer heat very well; saws can result in delamination

40
Q

Special saws needed for composites

A

Diamond tip/WC grit saw blade with special tooth design (non-tooth-style)

41
Q

Waterjet machining composites

A

High pressure (90k psi) water with abrasive material to cut CFRP

42
Q

Waterjet advantages

A

Fast, low heat, no cutting blade, dust prevented

43
Q

Waterjet disadvantages

A

Edge finish, tapered edge, high capital investment, high operating cost

44
Q

Waterjet tapered edge caused by

A

Bend from fixturing

45
Q

Lasercutting advantages

A

High accuracy, no cutting force

46
Q

Lasercutting disadvantages

A

HAZ, low cutting speeds for thick parts, high capital investment, hazardous volatiles

47
Q

Two types of joining methods

A

Mechanical fastening & adhesive bonding

48
Q

Steps of mechanical fastening

A

Machine structure, select appropriate fastener, assemble & inspect

49
Q

Primary advantage of mechanical fastening

A

Disassembly

50
Q

Primary disadvantage of mechanical fastening

A

Stress concentration

51
Q

Geometric parameters of concern in mechanical fastening

A

e/d, w/d, h/d, spacing

52
Q

e/d mechanical fastening

A

edge distance to bolt hole diameter

53
Q

w/d mechanical fastening

A

width to bolt hole diameter

54
Q

h/d mechanical fastening

A

laminate thickness to bolt hole diameter

55
Q

Failure modes in bolted laminates

A

shear-out, net tension failure, cleavage, bearing failure

56
Q

Preferred failure mode in bolted laminates

A

bearing failure

57
Q

How to generally optimize mechanical fastening parameters

A

Increase ratios and spacing

58
Q

Steps of adhesive bonding

A

Prepare surface, apply adhesive, co-cure

59
Q

Surface prep for composite laminates

A

Use abrasive/nylon cloth in vacuum bag and remove prior to bonding; dry prior to bond

60
Q

Bond joints in order of strength increasing

A

Single lap, double lap, single/double strap, stepped lap, scarf joint

61
Q

Advantage of adhesive bonding

A

Load distributed across large area, better for large integrated structures

62
Q

Disadvantage of adhesive bonding

A

Permanent, sensitive to surface prep, limits service conditions

63
Q

Surface preparation of metal ranked by bond strength

A

Anodize > grit blast > degrease

64
Q

Epoxy adhesive important points

A

High moisture and temperature are bad for adhesion strength

65
Q

Fiber orientation distribution (SFC) is affected by

A

Original distribution, fiber concentration, matrix properties, mold design, process temp. and pressure.

66
Q

How flow affects fiber orientation distribution

A

Shear flow aligns in flow direction; extensional flow aligns perpendicular to flow.

67
Q

Common fiber orientation direction

A

Skin in longitudinal, core in transverse

68
Q

Sandwich components

A

Facesheet, core, adhesive

69
Q

Sandwich manufacturing methods

A

Bonding (pre-cured) vs. co-cure (uncured adhesive + prepreg)

Fiber Reinforced Composites (2 decks)

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