midterm

Interlaminar Shear

Refers to the shear stress that occurs between the layers of a composite material, typically in structures experiencing bending loads.

ammonia with one
or more hydrogen atoms
replaced by organic groups

Matrix Dominated Properties

Properties related to the matrix in composite materials, including compressive strength, off-axis bending stiffness, interlaminar shear strength, and service temperature.

Flexural Modulus

A measure of a material's stiffness or resistance to bending.

Glass Transition Temperature (Tg)

The temperature at which a matrix transitions from a rigid to a rubbery state, affecting its performance.

Wet Tg

The glass transition temperature of the matrix resin in a wet state, which dictates the maximum service temperature without degradation.

Unidirectional Material

A composite where fibers run in one direction, providing the highest strength-to-weight ratio.

Quasi-isotropic Composite

A composite designed to have equal strength in multiple directions, typically using an equal number of plies at 0°, 90°, +45°, and -45° angles.

Sandwich Core Structure

A composite structure consisting of thin outer skins bonded to a lightweight core material, resulting in higher bending stiffness-to-weight ratio compared to solid laminates.

Warp Clock System

An internationally recognized system for controlling fiber orientation in composite manufacturing.

Nesting

The placement of woven cloth plies so that dominant fiber directions align, enhancing performance.

Stacking

The arrangement of plies in a layup without regard to fiber orientation.

Three Risks to Service Life

Fuels and oils, ultraviolet light, acids/alkalies that can degrade composite materials.

Lightening Strike Protection (LSP)

Methods to provide a conductive path for lightning protection, such as bonding aluminum foil or mesh to the composite structure.

Absorption

Exposure route where chemicals enter through the eyes, hands, and skin.

Inhalation

Exposure route involving breathing substances into the lungs.

Injection

Exposure route where foreign material is introduced into the bloodstream or tissue.

Ingestion

Exposure route involving swallowing harmful chemicals.

Adhesive Bonding

A process that transfers loads between substrates by creating a bond.

Co-curing

The process of curing laminate while bonding it to another uncured structure.

Co-bonding

Curing of two or more elements where at least one has already been fully cured.

Secondary Bonding

Joining pre-cured composite parts with adhesive bonding.

Surface Preparation

The process of treating surfaces to ensure strong chemical attachment and effective bonding.

Thermoset Resins

Resins used for high strength structures that bond through cross-linking.

Thermoplastic Resins

Resins that offer toughness and allow for fast processing.

A-Stage of Cure Cycle

low viscosity that can be diluted.

B-Stage of Cure Cycle

Viscous and tacky stage of resin allowing for storage and handling.

C-Stage of Cure Cycle

where the resin is cross-linked and insoluble.

Moisture Contamination

Occurs when prepreg is exposed to air, allowing condensation to form on the material.

Flow

The phase when resin is at its lowest viscosity and maintains this for a period.

Vitrification

When resin transitions to a glassy solid at a given temperature.

Cure

The process by which a resin achieves its full intended properties.

Solid Laminate Panels

Woven cloth, Unidirectional tape, Highest strength:weight

Quasi-isotropic

Discontinuous fibers in
random orientation or
continuous oriented to
provide equal strength in
edgewise tension or compressive loads

Ply layup Table

Table is used on composite panel drawing to define the ply layup
sequence, ply numbers and/or part numbers, orientation requirements,
splice control and other pertinent information

Effects service life

 Fuels and Oils
 Hydraulic fluids
 Deicing/Anti-Icing Fluids
 Acids/Alkalis
 Solvents
 Paint Strippers
 Ultraviolet light
 Infrared

Galvanic Corrosion

 Isolate carbon fiber from
metal with dielectric.
 Mechanical fasteners
should be selected with
separation.

Conductive paths can be established

Bonding aluminum foil to the structure as the outermost ply

 Bonding aluminum or copper mesh to the structure either as the
outermost ply or embedded within a syntactic surfacing film
 Incorporating strands of conductive material into the laminate

LSP Materials

Metal Mesh or Foil
 Thin metal alloys and metallized fibers

LSP Prepregs
 Pre-embedded woven or non-woven metal meshe

purpose of the matrix

bond and/or encapsulate
the fibers allowing the loads to be able to transfer from
each fiber to others

In-plane shear

Important for structures
which experience torsional
loading

Tg concerns

Getting to specific temp dosent mean it is fully cured exam its recent strength

Polyester

Inexpensive with good environmental resistance but lower strength and higher shrinkage than epoxies.

Vinyl Ester

Better environmental resistance and strength than polyester, with less shrinkage than polyester but more than epoxy; higher cost than polyester.

Epoxy

Superior adhesion, high elongation factors, and good environmental resistance; more expensive than polyester and vinyl ester

Phenolic

Brittle with poor adhesive characteristics but excellent static dissipation and good chemical/flame resistance.

Polyurethane:

High toughness, fracture resistance, higher elongation properties, and good adhesive properties; lower cost compared to most epoxies.

Benzoxazine

Similar flame resistance and low smoke toxicity to phenolic; long-term room temperature storage and adaptable to closed molding processes

Cyanate Ester

Excellent balance of mechanical performance and toughness; sensitive to moisture uptake prior to processing.

Bismaleimide (BMi

Can be thermoset or thermoplastic, requires high-temperature cure, difficult to process, but good flame resistance and low smoke toxicity.

Fastening

Loads transferred at
fastened joint
 Build up of thickness to
accommodate fastener grip
length, countersink, and
bearing and shear strength of
joint
 Fastener spacing and edge
distance critical
 Best for very thick laminate
joints

supported film

requires a carrier

unsupported film

no control bond line thickens

Reticulated film adhesives

Designed to be heated with a hot
airgun so the adhesive runs to edges
and down into the cell walls of a
honeycomb core

micro ballons, mircobeads

control bond line thickness

surface free enegry value

sfev

higher

SFEV of the surface must be raised
to an equal or ______ value than
the surface tension value (STV) of
the adhesive

water break testing

The process of pouring water onto
a surface and observing the
results in order to determine that a
bonded surface has sufficient
surface energy to achieve proper
adhesion

Liquid, paste, and film

What are three forms that adhesives can take?

Lower viscosity

What is a key characteristic of liquid adhesives?

Thinner bondlines

What kind of bond lines do liquid adhesives create?

they may not wet out well

What is a disadvantage of using paste adhesives?

To keep the surface clean and provide enhanced surface energy

What is peel ply used for in surface preparation?

To achieve a suitable Surface Free Energy Value (SFEV

What is the goal of mechanical abrasion in surface preparation?

Moisture ingress

: What can deep mechanical scratches on a surface lead to?

lint free cloth

preferred wipes

commerical grade

inexpensive undocumented contaminant level solvent

reagent grade

solvent, expensive, certified clean, pre bond cleaning

honey comb

bonding to core materials, i Film adhesive specifically designed to provide fillet in core Large bond surface loaded in shear

bonding to core materials, Must have sufficient adhesive to
wet porous foam surface and
actively attach to material
Adhesive bond to foam core is
much stronger than core material
itself.
Failures – along depth of surface
pores “Zip-line” failure

crystalline

what type has issues with thermoplastic hot/wet perfromace bonding

fusion bonding

Involves heating and
melting the thermosplastic
polymer on the bond
surface of components and
they pressing the surfaces
together for consolidation
and solidification

Thermabond Process or
Dual Resin Bonding

Laminate surfaces are
layered with additional
layer of lower melting
point PEI film on surface
Surfaces joined by
placing one more ply of
the PEI film or prepreg
between and applying
local heating to melt
the fil but not the
substrate

bonding

what is prefered of joint designs

use large diameter fasteners with high bearing strength and an interference fit

For mechanical fastening of thick composites

titanium and stainless steel

what types of fasteners

carbide diamond coated

drilling carbon and glass firber

brad point

drilling aramid fiber and reinforced composites