Chapter 4 Flashcards by Grace Williams

Q

What are the 5 types of stress?

Be STriCT

A

Tensile, compression, bending, shear, and torsion.

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Q

If a tension force is applied to a bar, what force is at the center of te bar on a cross sectional plane?

A

Compression is the counter force.

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Q

What is a material’s ability to accomodate stress called?

AKA, limiting stress that can be tolerated.

A

Strength

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Q

What happens to a material if any of its types of strength are exceeded?

A

It will permanently deform or break.

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Q

What are the units of strength? How is labelled with a material?

A

MPa; usually in a range like 51 MPa to 53 MPa.

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Q

Limiting strengths are determined by _ _ _ _ _ _?

A

Testing!

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Q

What 5 things can you gather from a tensile test (think of the tensile graph).

A

Yield strength, % reduction in an area, % elongation, tensile strength (ofc), and modulus of elasticity.

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Q

Within Mechanical properties, which group do these belong to?

Tensile, yield, compression, fleural, shear, creep, stress rupture.

A

Strength

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Q

Within Mechanical properties, which group do these belong to?

% elongation, % reduction on area, bend readius.

A

Formability

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Q

Within Mechanical properties, which group do these belong to?

Modulus of elasticity, flexural modulus, ad shear modulus.

A

Stiffness

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Q

Within Mechanical properties, which group do these belong to?

Impact strength, notch sensitivity, and critical stress intensity factor.

A

Toughness

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Q

Within Mechanical properties, which group do these belong to?

Hardness, wear resistance, and fatigue strength.

A

Durability

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Q

What is the official name of the tensile tester? Why is it called that but not referred to that typically?

A

The universal test machine is called that because it can be used to test compression, shear, and flexural strentgh as well as tensile, but it mostly used for tensile tesing.

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Q

What is a special device that clamps on the body of the test sample to convert length to an electrical measurement called?

A

An extensometer!

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Q

What are the pre-test marks made on a sample with known lengths?

What is the length btwn them called?

A

Gage marks!

Gage length!

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Q

What is the special device called that converts force into electrical movement for tensile testing?

A

A transducer

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Q

What is the term used for materials that exhibit a linear modulus in the elastic range?

After Robery Hooke!

A

Hookean materials

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Q

What is the transition point from linearity to nonlinearity on a tensile graph called?

Is it always the same as the yield point? AKA does it stop being elastic?

A

The proportional limit

No! Sometimes, even if not linear, the elasticity goes past the prop lim bc of the 0.2% offset.

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Q

At what point of the curve is the ultimate tensile strength?

A

The tippy top.

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Q

Define plastic deformation.

A

Permanment increase in length.

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Q

What are the 2 types of stress-strain curves?

A

1 ) Engineering curve (force / original area ; uses original length)
2) True curve (force / instantaneous area ; uses instantaneous length)

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Q

Why is 0.2% offset a thing?

A

Because the yield point can be hard to determine, so engineers offset strain by 0.2%.

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Q

What is the stress at the 0.2% offset?

A

Yield strength! (Psi or Pa)

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Q

Work hardening is _ _ _ _ than cross sectional area reduction BEFORE the ultimate tensile strength point and is _ _ _ _ than the cross sectional area reduction AFTER that point.

A

Greater; less

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The area around the ultimate tensile strength point represents _ _ _ _ _ that is happening to the actual specimen.

Necking!

Name tensile bar testing specimen.

“Round” testing bar

What 2 measurements are taken after a tensile test?

Final center specimen diameter and new gage length.

What is the property called that expresses a materials ability to be stretched or drawn?

Ductility

How ductility reported from a tensile test?

The % elongation or % reduction in area

When comparing the ductility of materials, always verify that the percent elongation data are based on the same _ _ _ _ _ _ _ .

Gage length!

What is work hardening (aka strain hardening)?

When a metal is plastically deformed, interactions with dislocations in the material's structure can cause the material to become stronger and harder.

How do you solve for strain hardening exponent **n**?

true stress = K (true strain) ^ n | K = strength coefficient

What process is used to form car fenders?

Deep drawing (metal sheet presses into molf by punch).

What part of the graph reveals a material's **resilience**?

The area under the elastic part of the curve. (up to yield point basically)

What part of the graph reveals a material's **toughness**?

The area under the plastic deformation part of the curve. (after the yield point basically)

What is the standard gage length for specimens?

2 inches ish

Based on the Huber von Mises-Henkey distortion energy theory, the following relationship is useful: | (Refers to shear)

shear yield strength = 57% of the tensile yield strength

What are the chemical fomulas?

1) C + O2 = CO2 2) CO2 + C = 2CO 3) 2FeO3 + 3C = 4Fe + 3CO2 4) Fe2O2 + 3CO = 2Fe + 3 CO2

Stiffness and rigidity are calculated from the what modulus?

Shear Modulus!

Wear resistance and durability are associated with what property?

Hardness

Explain Mohs Hardness tests.

Consists of scratching the material's surface with something.

Explain Brinell Hardness Test.

10 mm diameter ball is pushed into surface and diameter of effect is measured. That number is used to calculate a Brinell Hardness number (HB).

Exlplain Rockwell Hardness Tests.

What is the typical test method for polymers and elastomers?

Shore Durometer: hardness is measured by pushing a spring loaded needle intothe material.

Knoop/Vickers: indenter, load range, application.

diamond, 1-2000g, microhardness of all/any

Brinell: indenter, load range, application.

Ball, 500 & 3000 kg, soft steels

HRA: indenter, load range, application.

diamond, 50 kg, cemented carbides

HRB: indenter, load range, application.

ball, 100 kg, soft steels & nonferrous metals

HRC: indenter, load range, application.

diamond, 150 kg, hardened metals (thick)

HRN: indenter, load range, application.

diamond, 15 & 30 & 45 kg, hard thin sheet metals

HRR: indenter, load range, application.

ball, 10 kg, polymers

HRT: indenter, load range, application.

ball, 15 & 30 & 45 kg, thin soft metals

What is the only hardness test (s) that measure ceramic hardnesses?

Knoop or Vickers

How do you get absolute hardness? What are its units? | What's the other hardness unit?

A microhardness machine; measured in kg/mm^2 | GPa lol

Define toughness.

The energy required to fracture a given volume of material. Measured in units of energy (joules, foot-pounds, etc).

Decribe what a bloom, billet, slab, and plate look like.

Billet is small skinny cylindrical or rectangular, bloom is wider billet and rectangular, slab is thick wood 2x4 lookin shape, plate is like a flatened widened slab.

How to calculate pressure tensile strength (in ksi or psi) from carbon content.

Carbon pt x 120 + (.8 - carbon pt) x 40 In other words, .8 = 100%. The carbon content represent the pearlite content exactly and pearlite is 120 ksi. The ferrite content would be what's left so .8 minus the carbon content and multiplied by ferrite strength 40 ksi.

How do you get the **fracture touvhness parameter**?

Impact test taht propagates crack in material.

What 2 tests are typically used to get toughness?

Impact and fracture tests.

What is a material's ability to withstand *shock loading*?

Impact Strength | ft-lbs or J/cm^3

Impact strength can be affected by _ _ _ _ _ _.

Temperature

What is a **dynamic tear**?

Drop weight impact testing

What is the ship reference in the north atlantic waters with all the ship failures about?

They're about the discovery of how steel significantly decreases toughness at low temperatures.

What is the **nil ductility temperature**?

The temperature at which the toughness of the material drops below some predetermined value.

How many load cycles does a fatigue test need to consider a material to hve *infinite life*?

10 million cycles!

Endurance limit is the same as what?

Fatigue Strength

What strength is expressed as the stress necessary to produce 0.1% strain in 1000 h?

Creep Strength

Creep is not too important below what temperature?

800 F

How is **stress rupture strength** related to creep strength?

It is the stress at which a part will fail under sustainedload at *elevated temperature*.