41-60

Question 1

Sandwich and monolithic laminate:

Answer 1

● A sandwich can be considered analogous to the I-beam, where the caps (facings) carry in-plane
loads (and also bending loads) and the web (core) carries the shear loads.

● The goal of sandwich design is to space thin facings far enough apart to give a high bending stiffness to weight ratio without making core shear critical. It transmits loads between the facings,
provides sheer rigidity, and stabilizes the facings

Question 2

Matrix thermosets:

Answer 2

● Epoxy
● Toughened EP
● Bismaleimide
● Toughened BMI

Question 3

Name 3 types of reinforcing fibers:

Answer 3

● Graphite
● Aramid (Kevlar)
● Boron
● SiC
● Quartz
● Glass

Question 4

Describe the terms sizing and finish for carbon and glass fibers:

Answer 4

● Sizing - last step after etching - protective material (typically uncured epoxy) does not usually
promote adhesion, but is present to prevent fiber damage during fiber handling, pre-pregging and
weaving operations.

Question 5

What is valid for thermoplastic resins (without solvent):

Answer 5

● High viscosity 
● Post formable 
● Higher toughness than thermosets
● Required high processing temperature 
● Less solvent resistance than thermosets

Question 6

What type of thermoset resin would be used in an application where low outgassing and low moisture absorption is required (e.g. space application)

Answer 6

● Cyanate esters

Question 7

What is an A-basis value?

Answer 7

● A 95% lower confidence bound on the first percentile of a specified population - at least 99% of the population of values is expected to equal or exceed the “A” basis mechanical property allowable, with a confidence of 95%

Question 8

When can a low outlier be removed from the dataset?

Answer 8

● The cause must be identified to remove an outlier

Question 9

List 2 disadvantages of prepreg if compared to wet lamination:

Answer 9

● Expensive material
● Needs to be stored at temperatures of -18degs
● High investments in process (autoclave)

Question 10

What reinforcement (fibres) would be used if high toughness is required?

Answer 10

● Aramid fiber

Question 11

What material can be used as core in a sandwich material?

Answer 11

● Foam - PVC, PMI, PET

● Honeycomb - PP, PC, Aramid (NOMEX), AI

Question 12

What is a sandwich laminate and what are the advantages compared to a monolithic laminate?

Answer 12

● High bending stiffness to weight ratio

Question 13

What is a peel ply?

Answer 13

● PA or Polyester (<200deg), PTFE coated glass (>200deg) fabric which is removed after curing to
obtain an evenly roughened surface suitable for
○ Continued lamination on already cured laminate
○ Bonding
○ Removal of auxiliary material

Question 14

Describe shortly the building block approach in composite certification:

Answer 14

● Level 1: small specimen and element tests to characterize basic unnotched static material
properties, laminate fatigue response, material operational limit (MOL), etc.

● Level 2: Uses information from the first level to calculate internal loads, identify critical areas, predict critical failure modes

● Level 3: More complex static and fatigue testing

● Level 4: Full-scale static and fatigue testing to validate predicted internal loads, deflections and
failure modes

Question 15

For a given population, a high sample size is likely to increase the B-basis value compared to a low
sample size (True or False)

Answer 15

False

Question 16

Testing of bonded joints can be problematic because:

Answer 16

● Shear stress concentration at ends of joint due to elastic adherents
● Transverse peel stresses due to distortion (single lap joint)
● Transverse stresses at the ends of the joint due to induced bending moments (double lap joints)

Question 17

Describe the autoclave-prepreg process:

Answer 17

● Autoclave: closed vessel that allows application of pressure and heat
● Pressure: 50-100psi
● Perfectly definable fiber deposit
● Ideal fiber content
● Low porosity
● High surface quality
● High temperature resistance

Question 18

Design outlines for composite design:

Answer 18

● 45 or 135-degree plies on the surface

● Avoid grouping of 90-degree plies

Question 19

What are the basic requirements for electrochemical corrosion?

Answer 19

● Anode (ignoble)
● Cathode (noble)
● Electrolyte

Question 20

What is a local cell?
or microstructure (pitting corrosion):

Answer 20

● Concentration cell

● Formed due to:
○ heterogeneous surfaces
○ Local destruction of passive / surface layers
○ Concentration gradients in an electrolyte, phase boundaries
○ Inhomogeneity on surface