ME Failures Quiz 3

What are some typical characteristics of

ceramics?

Hard, brittle, high compressive strength compared to tensile strength

Composed of two elements- metal & nonmetal

How do ceramics fracture?

Brittle fracture, typically transgranular along cleavage planes; can be

intergranular

What parameters influence fracture

patterns in brittle materials?

Stress state, driving force (hi or low stress), strength of material

What is crazing?

The formation of small interconnected microvoids by fibrils which form due to localized yielding in polymer fractures

What is cavitation?

Void nucleation & growth in polymers during failure; enhances shear yielding

What is shear yielding?

Banding along max shear directions that form during alignment of polymer chains

during deformation.

What is the key difference between thermoplastic and thermosetting

plastics and why?

Thermoplastics melt and can be reformed while thermosets degrade at high temps

What is the typical type of bonding in thermosets?

Thermoset molecules within a chain are bonded by primary chemical bonds & the

chains are held together by strong covalent bonds.

What is the typical type of bonding in thermoplastics?

Thermoplastic molecules are held together by covalent bonds and the chains are held

together by intermolecular forces

What does amorphous and crystalline mean in reference to

polymers?

Amorphous means the chains are randomly intertwined with no organization.

Crystallization of polymers refers to an alignment of their molecular chains.

What give polymers their light weight?

They mostly contain C and H molecules

What is vulcanizing

An irreversible chemical reaction usually at high temperatures, and usually involving

the addition of sulphur compounds to strengthen polymers

What is a copolymer?

A polymer made by reaction of two different monomers

What is polymerization?

Process of reacting monomer molecules together in a chemical reaction to form

polymer chains

What are the effects of strain rate and temperature on polymers?

As temperature increases, the strength decreases, but the elongation to failure

increases. Increased strain rate, results in increased yield stress.

Sketch the copolymer configurations for alternating, block, random,

and graft

For two monomers A & B:

• Alternating, an alternating pattern: A-B-A-B-A-B-A-B-A-B-A-B-A

• Random, in no particular order: A-A-B-A-B-B-A-A-A-B-A

• Block, all of one type of monomer are grouped together and joined by a covalent bond:

A-A-A-A-B-B-B-B

• Graft, main chain of one monomer with branches of the other monomer coming off of it: