Materials Exam 3

Stress vs strain

Stress: Force/Area measured in pascals

Strain: DL/L

Shear Stress and shear strain

Sheart stress = shear modulus * shear strain

Young’s Modulus

Slope of the linear portion of the stress strain curve.

If nonlinear curve, it can be tangent

Elastic Strain and Deformation

Elastic strain: When the strain is reversible (loading, unloading)

Elastic Deformation: Temporary deformation of materials shape that is reversing after removing the force or load

STRAIN IS REVERSIBLE AND INDEPENDENT OF TIME

Poisson’s ratio

• - Lateral strain / longitudinal strain

X or Y strain/ Z strain

Yield Strength

Max stress that can be applied before it starts to plastically deform (permanently deform)
Usually at end of linear region)

METALS HAVE A 0.2% offset

Ductility

Degree of plastic behavior before fraction

Resilience

Area under linear region until the yield strength

Elastic energy that can be stored in a unit volume → elastic response

Toughness

Energy required to deform a unit volume to failure

AREA UNDER ENTIRE STRESS STRAIN CURVE

Overview mechanical properties

True stress and strain

Hardness

materials resistance to localized plastic deformation

Elastic vs plastic behavior

Plastic is actual deformation slippage on a plane

Crystalline vs amorphous (elastic) polymer

Time-dependent strain

Creep Rate

Adsoprtion vs absorption

Adsorption: Molecules cling to surface

Absorption: Molecules penetrate into bulk material

Surface energy vs surface tension

High surface energy is hydrophilic

Charge charge interactions and hydrophobicity

Surface feature identification techniques

Scanning electron microscopy (SEM)

Atomic Force Microscopy (AFM)

Light microscopy

Composition Measuring techniques

X-ray photoelecton spectroscopy (XPS)

Attentuated total internal reflectance fourier transform infrared spectroscopy (ATR-FTIR)

Secondary ion mass spectrometry (SIMS)

TEM

Transmission electron microscopy

Beam passes through sample and can measure samples with thickness from 2-200 micrometers

Just looks at electron dense, not thickness

Scanning electron microscopy

Beam scans SURFACE

Gives an image of surface

AFM

Atomic Force Microscopy

Gains topographical info by small probe on surface.

Gives roughness info i think

XPS`

X-ray photoelectron spectroscopy

Gives info about superficial atomic layers composition

ATR-FTIR

Attenuated Total Internal Reflectance Fourier Transform Infrared spectroscopy

EM radiation pass through low density sample and analyze the surface characterization to monitor changes in surface composition

SIMS

Secondary Ion Mass Spectrometry

Characterize surface region of materials. Primary ions

Measures outer layer characterization

Protein interactions with biomaterials

What drives protein adsorption

Thermodynamics of protein adsorption

3 Steps of protein adsorption kinetics

10 fold concentration of lower and higher affinity proteins rule in vroman effectiveness

Easily denatured proteins adsorption

Because they denature, their conformation changes and allow more contacts. ADSORB MORE THAN STABLE PROEINS

Cadherins, selectins, and integrins

Cell adhesion: What is it

Link between cytoskeleton and ECM