Materials Study Guide

carbon fibers are not necessarily stronger than glass fibers, but exhibit much higher modulus (stiffness)

True

Which form of reinforcement is the most difficult to conform to a shape, such as a transtibial socket, without wrinking?

woven fabric

what is special about loctite

anaerobic reaction

name 3 forms of fibrous reinforcement materials used in O&P laminations

-Braid

-Unidirectional

-Woven

-Mat

-Knit

-Filament

-Strand

-Tow

-Yarn

-Tape

-Fabric

-Cloth

what type of foam lining would be best used for a pt wearing a KAFO who has neuropathy and is incontinent?

closed cell foam

Which of the following statements comparing thermoset composites to thermoplastics is false?

-Thermosets exhibit less creep

-Thermosets exhibit improved machinability

-Thermosets exhibit greater impact resistance

-Thermosets exhibit improved machinability

-Thermosets exhibit greater impact resistance

aramid fibers (kevlar) properties include high strength, lightweight, high modulus and toughness (good impact resistance) True/False

true

the only way to inc. the strength in a lamination is to inc. the number of layer reinforcement used

False

-can use fillers and additives

important mechanical characteristics to consider when choosing a foam for a prosthesis/orthosis are

-durometer

-stiffness

-compressibility

Composites can provide a specific strength 4-6 times greater than steel or aluminum. What formula defines specific strength?

strength/density

What is this piece of equipment

Router/Trautman

the purpose of a promotor is to enable the catalyst (initiator) to cure the polyester resin at room temperature at a reasonable rate of cure

true

density and durometer are two terms that describe the same material property (True/False)

False

-Density refers to the mass per unit volume of a substance

-Durometer (Shore hardness) measures a material's resistance to indentation or localized deformation, essentially its hardness

Rubber cement would be a good adhesive to use when gluing a sole onto a CROW boot

False

-rubber cement is for temporary adhesion

-try barge

when creating a 3D test socket, which process comes first?

CAD

advantages of epoxy over polyester

-inc. adhesion

-inc. strength

-inc. corrosion protection

the file like tool used to remove plaster from positive molds is called a:

rasp/surform

carbon fibers exhibit these properties

-high modulus

-high strength

-elasticity to failure

-good creep resistance

-good fatigue resistance

this tool would be ideal to remove a large amount of plaster from a mold, such as for a TF or KAFO job

draw knife

the material used for detailed impressions that loses volume as it dries is called:

alginate

when applying barge to adhere a pad to a SAFO, what are two things you must do in order for the pad to adhere properly?

put barge on both the pad and the AFO then let it dry

rigid thermosets have _______ chains and ________ crosslinks

short, many

what is the name of this tool?

yates clamps

the side bender tool is used to remove unintended bends in which plane?

sagittal

material selection and knowledge of materials can affect ______

-component selection

-structural integrity

-function of the device

-fabrication techniques utilized

what are the 3 types of space lattices

-cubic

-hexagonal

-tetragonal

what does SDS stand for

safety data sheet

the equation for calculating deflection is:

Ymax = (-FL^3)/(48El.)

How is the deflection related to the length of the beam?

exponentially

what property does impact testing test for?

notch sensitivity

when it comes to metal work, _____ are the tools used to contour uprights/bands and a _______ can be used to give a finished look to metal components after bending.

-bending irons

-flap wheel

4 types of mechanical stress

-tensile

-compressive

-flexural

-shear

explain why it is critical in this project (metal) to ensure both the calf and thigh bands do not have contours or bends in the no-bend zone?

The ends of the calf bands and thigh bands will be bent to a 90 degree angle. This plus not contouring in the no bend zones ensures that the calf band and the uprights can sit flushed together.

This is optimum for stability, cosmesis and allows for easier rivitting.

an object with a higher moment of inertia about a certain axis than that of another shape of the same material will deflect _____ when the same load is applied to both objects.

Less

what are normal flaws that cause the actual strength of a metal to be much less than its theoretical strength

-notches

-rough surface

-nonmetallic impurities

-flaws in crystal lattice

-micro cracks in grains

which of the following describes the test behavior of a specimen that returns to its original shape after being deformed?

elastic deformation

what is the recommended minimum and maximum spacing between rivets?

Min = 3x rivet diameter

Max = 2-4x thickest material

the diameter of a rivet must be at least the size of the thickest piece of material being fastened

true

2 heat treating techniques to inc. the ductility of a particular steel are:

tempering and annealing

What does each point represent on the stress-strain curve?

A: proportional strength

B: yield point

C: ultimate strength

what is the best example of a cast you'd want to fill with vermiculite added into the plaster?

knee disarticulation (large casts)

the applied stress in a structure is calculated by which two methods

-applied load/cross-sectional area

-Strain x Modulus

toughness refers to a materials ability to absorb mechanical energy without fracturing

true

match the curves with the term that best describes their mechanical behavior

A: brittle

B: high strength

C: tough

in their solid state, all metals are crystalline

true

Name this tool

AK length gauge

for identical x-sections and loading conditions (stress), steel will strain (deflect) 1/3 as much as aluminum

true

the pair of tools used to contour metal uprights (and other metal work) are called:

bending irons

what is the appropriate order of operations when tapping metal to fasten 2 pieces together?

-center punch material

-drill small diameter hole in both materials

-drill large (through) hole in 1 material

-tap 1 piece of metal being fastened

the change in the length, divided by the original length of a test specimen, is the calculation for deforming what?

strain

benefits of using the CAD/CAM process of impression taking and fabrication

-reduced physical space needed for mold storage

-precise locations for modifications

-measurements can be repeated and are accurate

-justification for insurance coverage

-ease of global modifications

-time from casting to delivery is reduced

a material must be crystalline to be transparent

false

when making a positive plaster mold, what can quicken the activation process

-warm/hot water

-table salt

ductility refers to a materials ability to be mechanically formed into shape without destroying the integrity of the material

true

an appropriate tool for cutting a small piece of plastic (ex: gillette post for UCBL) in preparation for thermoforming would be a ___________.

band saw

elastomers can be thermoplastic or thermoset

true

clear check socket materials

-surlyn

-durrplex

-vivak

-PETG

crystalline polymers tend to have _________ shrinkage as compared to amorphous polymers

increased

what type of oven is best for heating thicker plastics (> 3/16 inches thick)

convection

2 different vacuum thermoforming methods used in orthotics and prosthetics for forming thermoplastics

drape and bubble

rigid plaster bandage has a _______ reaction.

exothermic

flaws that can be produced in the plastic part by overheating the sheet materials prior to drape forming

-burn

-yellow

-thin pull

-brittle

thermoplastics commonly used in O&P

-HDPE

-LDPE

-LLDPE

-PP

-Copoly

-surlyn

-PETG

-durplex

-vivak

-kydex

-PE

major property differences between polypropylene homopolymer and polypropylene copolymer

-copolymer is less rigid

-copolymer has inc. impact strength in low temps

-copolymer is opaque

the following variables should be monitored when applying plaster bandage: water temp, air temp, room temp, cast thickness, to avoid a _____ reaction which could ______ the pt

-exothermic

-burn/injure/hurt

What is this and what is it used for?

-Cut tube (aka cut-off, strip, surgical)

-remove a cast

why would you use copolymer over regular polypropylene

-improved impact strength

-improved performance at low temps

guidelines for dec. internal stress when drapeforming

-hot mold

-hot sheet

-rapid vacuum

where would you find emergency medical treatment information if someone accidentally ingested a toxic chemical?

-MSDS (material safety data sheet)

-MDS

-label

-SDS

______ repeatedly soften when heated and harden when cooled. ________ undergo a chemical change during processing.

-thermoplastics

-thermoset

density of a material can be expressed as lbs/in^2 (True/False)

False

-lbs/in^3

what effect do 90 degree elbows between the vacuum surge tank and mold have

inc. time to achieve max vacuum

because plastic molecules are subject to degradation by ______, and the degradation will rapidly accelerate, you should use _______ to confine and control the breakdown

-heat & light

-stabilizers

when a plastic material is subject to a constant load for an extended period of time, and deformation or strain continues to inc. without an inc. in load or stress, the material is said to be experiencing _________.

creep

high density polyethylene (HDPE) is made in 2 variants trade named ortholen and subortholen. How do these differ in mechanical property from regular HDPE?

-harder to melt

-better fatigue resistance

-tougher

-more strength

what material is more likely to experience creep

thermoplastics

thermoplastics, such as polypropylene, provide little energy return and are subject to fatigue

true

when is alginate or two part silicone most commonly used

upper extremity prosthetics

plastics are built upon _____ chemistry in combination with some other element or elements

carbon

what happens when molecular imbalance increases?

the inter-molecular attraction increases

a linear polymer can be compared to a strand of _______. In effect it is ___ units wide but ___ of units long

-spaghetti

- 1

- 1,000's

Identify the forces or bonds which hold polymer chains together

A: Secondary bonds

B: Primary bonds

attraction forces within and between the chains determine polymer characteristics

Elastomer: when stretched will return to its original shape

Plastic: when made to flow or stretch will not return to its original shape

Fiber: usually pre-stressed or pre-stretched and similar to jute or raw silk

molecular weight will tell you how long the chain is

false

the degree of polymerization identifies the number of repeat units in a chain

true

should an active foreign molecule enter the system, it may break the long chains

true

most polymers resist the flow of electrical current

true

as MW is inc. the polymer becomes softer and more waxy

false

as the symmetry of a chain inc. so does the melting point

true

because plastic molecules are subject to degradation by _____ or _____ and the degradation will rapidly accelerate, you should use _____ to confine and control the breakdown

-heat

-UV light

-stabilizer

to create a limpness effect, suppleness, or softening ________ are added to the plastic compounds

plasticizers

when different monomers are polymerized together as a composite molecule, you have a _____

copolymer

when molecular chains are packed close together and are made parallel to each other at a number of points they form ______

crystallites

3 types of chains and their level of symmetry

Isotactic: high symmetry

Syndiotactic: moderate symmetry

Atactic: random symmetry

What type of polymers are shown?

A: Branch

B: network

A polymer which is formed by inc. the heat applied and cannot be made to flow or melt is called a _______

Polymers which can be made to soften and take on a new shape as heated and pressure are applied and then subsequently cooled are called _______

-Thermosets

-Thermoplastics

Styrene

-used in packaging

-typically a clear sheet but can be puffed with gases to create a foam

-low cost

-brittle, attacked by solvents with poor weathering qualities

Vinyls

-either rigid and tough or plasticized for limpness

-used in such articles as raincoats or upholstery

acrylic

-good outdoor weathering and relatively high softening point

-normally used in outdoor signs

olefin polymers

-engineering plastic

-may use Ziegler catalysts to create molecular structure distinguished by inc. stiffness, tensile strength, etc.

flurocarbon polymers

-thin film such as teflon

-has outstanding weathering characteristics, resists heat and is tough and flexible

-uses fluorine rather than other halogens