Mech Properties + Mat Experience

Material property

A materials trait based off of the kind and magnitude of its response to a specific stimulus.

Types of properties

Mechanical, Electrical, Magnetic, Thermal, Optical, Deteriorative

Ashby Chart/Plot

A plot that allows for the analysis of multiple material properties for a range of different materials in one plot - commonly used in material selection.

Common metal properties

Dense, stiff, strong, ductile, opaque, thermal conductivity, electrical conductivity

Common Ceramic Properties

Stiff, strong, brittle, hard, opaque, non magnetic. BAD UNDER TENSION - CRACKS WHICH ARE COMMON ACT AS STRESS CONCENTRATORS. GOOD UNDER COMPRESSION - CRACKS ARE SELF FIXED

Common Polymer Properties

Low density, ductile, chemically inert, electrical and thermal insulators, LOW MPS, non magnetic

Common Composite Properties

Hard to recycle, expesnive, depends on application (best of both worlds)

All types of load application

Tension, torsional, compression, shear

ENGINEERING Stress equation

Sigma = F/original A vs current A for true. — can calculate true/engineering via experimental data or through the eqs inking the two!!!!!!!

True Strain vs ENGINEERING strain and why + DO NOT FORGET

Epsilon = deltal/instantaneous l vs epsilon = deltal/ original length. - use engineering as its hard to measure true strain - DONT FORGET SIGNS FOR COMPRESSION OR TENSION VERY IMPORTANT!!!

Young’s modulus + what kind of property?

E =sigma/epsilon - material but can vary depending on external factors such as temperature

Strain Offsetting goal and how its done

Used to approximated the yield strength of materials where its unclear.

Calculate gradient of elastic region - offset it by 0.2% strain (up to x = 0.002) then draw up to reach graph = answer.

Poissons ratio (EQ NOT GIVEN) + key requirements of sample + what kind of property?

V = NEGATIVE transverse epsilon/axial epsilon. + usually for isotopic only to remain a material prop. + usually only considered for within the elastic region. + both material or structural

Range of possible poissons ratios and what they mean

-1 to 0.5.

<0 to -1 = the material expands when pulled on (usually synthetic material structures only)

0 = no perpendicular deformation when a force is applied.

0.5. = incompressible, i.e. rubber - volume is constant.

Types of attitudes/biases

Explicit. = conscious + self-reportable

Implicit. = unconscious + 2nd party report

Explicit (conscious) data collection methods + examples of bias

SDS - semantic differential scales - a plot of consciously provided data about where a material lies between two bipolar adjectives according to that group of individuals. E.g Jade = more popular in Asia + Ppl may be more accustomed to steel wool rather than steel bars so rough to smooth varies.

Implicit (unconscious) data collection methods + example of bias

Takes into account reaction speed, eye tracking and other subconscious choices by asking more OPEN ENDED QS. Altered objects more likely to be perceived as waste - i.e. scrunched up bottle.

Types of material senses

Gustatory - taste

Olfactory - smell

Haptic - touch

Auditory - sound

Visual - sight

ISO/ANISOTROPIC + example

Uniform properties in all directions around the material. I.e. graphite with laminar structure is weak via shear but strong with compression (depending on orientation) - hence used in pencils.

Stress strain graph pts

Plastic Deformation definition and explanation

The point at which the material test piece is no longer able to return to its original shape once the load has been removed. (Permanent)

Bonds are broken under load between atoms and new bonds are formed - the piece may still retract once load is removed but not to its original shape.

When does hookes law no longer apply

Beyond limit of proportionality

If forces are applied to the object in multiple dimensions (as we saw w poissons - they affect eachother)

Ductility definition(s) - material property that once again varies due to external conditions like temp - can go from glassy (brittle when cold) to rubbery (ductile when warm) ** BECAUSE BONDS STRENGTHEN WHEN TEMP DROPS.:. Layers can’t slide over eachother as well.

A measure of the plastic deformation sustained as fracture. - How well a material is able to undergo tensile and compressive forces without fracturing - i.e turned into a wire.

Calculated either through:

%elongation or %reduction in area (eqs not given but self explanatory)

Hardness test

Brunel (sphere)

Vickers (v therefore diamond shape)