Biomaterials Exam II: Mechanical Properties and Testing

Tension

"pulling" force or stress. Force is applied 'Normal" to the longitudinal surface. Positive Force on ad Positive Face.

Compression

A stress that pushes on or squeezes a material. Force is applied to "normal" to the longitudinal surface. Negative Force on a positive face.

shear stress

Tangential force per unit area acting on a surface

Torsion

act of twisting; stress due to twisting forces exerted on a body

Compression on top, tension on bottom, neutral in center

If you bend a beam like this where do you see tension and compression?

To make them intrinsic properties. That is to normalize the forces based on size. To make the resulting properties "material" properties not dependent on the size and shape of the part (that is make them intrinsic).

Why do we convert force and displacement into stress and stain?

Normal Stress

Force divided by cross sectional area

Strain

Change in length over original length

Pa (N/m)

What are the SI units of stress

Unitless but reported as %

What are the units of strain?

Young's Modulus of Elasticity

The ratio of normal stress to the longitudinal strain produced in a body...in the elastic region.

Plastic (or permanent), Elastic before

What kind of deformation do you have past the yield strength? Before?

yield strength

stress at which noticeable plastic deformation has occurred

Brittle

What kind of fracture is shown in the image (assuming a tension test was performed)?

Ductile

What kind of fracture is shown in the image (assuming a tension test was performed)?

Toughness

Mechanical property of a material that indicates the ability of the material to handle overloading before it fractures. Area under the stress-strain curve through failure. Units are in energy per volume (J/m^3)