A = yield strength
D = ultimate tensile strength
Strain = the quantification of the deformation resulting from stress on a material (dL/L = strain)
Stress = force per unit area. Can mentally just think of it as force
Elastic Region
- Once the force is remove, it will return to original length
- The amount of deformation by the force is the slope-> that is the material’s Young’s Modulus of Elasticity
- Hook’s law of proportionality followed
Yield Point
- Point A
- Has 3 phases in it separate by 2 pointts
- Proportional limit
- Before this it follows Hook’s law of poprotitonalty
- After that it is non linear so more force will cause more strain
- But it can still bounce back to normal
- Elastic Limit
- This is the yield point
Plastic Region
- Past this point, the deformation is permanent
- To see what exactly the deformity is, you draw a line down parallel to the young’s slope
Material will first elastically deform. In this phase, the relationship between strain and stress is linear.
Strain hardeniing
Ultimate Tensile Strength
After this there is “Necking”
Necking
- Decrease in cross sectional area until failure aka fracture
Toughness
- AUC
- Amount of energy a material can absorb before failing
Then you hit the Yield point. At the yield the material will now undergo permanent plastic deformation.
Ultimate Tensile strength when the material “breaks”. Fracture is actual gapping.
Toughness
-Area under curve is the toughness
Modulus of Elasticity
- Higher is
- More steep of a line
- More stiff
what is true about titanium plates
see less callous
they are stronger than stainless steel
cortical bone under the plate is less porous
they have greater tensile strength than stainless steel
WHEELESS:
Discussion:
– titanium is often selected as a material for metal plates or femoral stem implants due to its lower modulus of elasticity (as compared to other alloys);
- elastic modulus of stainless steel is 12 times EM of cortical whereas EM of titanium is 6 times of cortical bone;
– advantages:
– resistance to fatigue is excellent;
– it is easily worked, and 1/16 plates are radiolucent;
- metals ranked according to yield strength (highest to lowest);
- cast cobalt chrome > titanium > wrought cobalt chrome, stainless steel;
– resistance to corrosion:
- by itself titanium would have a high potential for oxidative corrosion;
- the titanium dioxide layer which coats the outer metal layer provide a major barrier to corrosion;
– disadvantages: this metal has an extremely low modulus of elasticity & low tensile strength;
– titanium plates and implants, therefore, have to be bulkier than stainless steel in order to provide same rigidity
The Spine Book 