1. Analysis of
and strain in
human bone
1
By
Nabapallab Deka
Structural Engineering
Civil Engineering Department
NIT Silchar

2. Organic Components
(e.g. collagen)
Inorganic Components
(e.g., calcium and phosphate)
65-70%
(dry wt)
H2O
(25-30%)
one of the body’s
hardest
structures
viscoelastic
ductile
brittle
Biomechanical Characteristics of Bone
25-30%
(dry wt)

3. Strength and Stiffness of Bone Tissue
It is evaluated using relationship between applied load and amount
of deformation which is represented by LOAD -
DEFORMATION CURVE
Bone Tissue Characteristics
Anisotropic Viscoelastic Elastic Plastic

4. Properties of Bone
 An organic material, bone can often be considered in the same way
as man-made engineering materials.
 Factors affecting properties include:
Age
Gender
Location in the body
Temperature
Mineral content
Amount of water present
Disease, e.g. osteoporosis.

5. Stress = Force/Area Strain = Change in Length or Angle/original dimension
Note: Stress-Strain curve is a normalized Load-Deformation Curve

6. elastic
region
plastic region
fracture/failure
Stress(Load)
Strain (Deformation)
stress
strain
Elastic & Plastic responses

7. Elastic Biomaterials (Bone)
•Elastic/Plastic characteristics
Brittle material fails before
permanent deformation
Ductile material deforms
greatly before failure
Bone exhibits both properties
Load/deformation curves
deformation (length)
ductile material
elastic
limit
bone
brittle material

8. Anisotropic response
behavior of bone is dependent
on direction of applied load
Bone is strongest along
long axis - Why?

9. fracture
fracture
Load
deformation
Visco-elastic Response
Behavior of bone is dependent on rate at which load is
applied.
Bone will fracture sooner
when load applied slowly

10. Compression Tension Shear Torsion Bending
Mechanical Loading of Bone

11. •Vertebral fractures
1. cervical fractures
spine loaded through head
e.g., football, diving, gymnastics once
“spearing” was outlawed in football the
number of cervical injuries declined
dramatically.
2. lumbar fractures
weight lifters, linemen, or gymnasts
spine is loaded in hyperlordotic (aka swayback)
position.
Compressive Loading

12. Tensile Loading
Main source of tensile load is muscle.
Tension can stimulate tissue growth
Fracture due to tensile loading is usually an avulsion,
other injuries include sprains, strains, inflammation, bony deposits.
When the tibial tuberosity experiences excessive loads from quadriceps
muscle group develop ,the condition is known as Osgood-Schlatter’s
disease

13. Shear Forces
It is created by the application of
compressive, tensile or a combination of
these loads.

14. Usually a 3- or 4-point
force application
Bending Forces

15. Torsional Forces
Caused by a twisting force
produces shear, tensile, and
compressive loads
tensile and compressive loads are
at an angle
spiral fracture can develop
from this load

16. Modulus
Bone can be considered to consist primarily of collagen fibres and an inorganic
matrix, and so on a simple level it can be analysed as a fibre composite.
 The Young’s Modulus of aligned fibre composites can be calculated using the Rule
of Mixtures and the Inverse Rule of Mixtures for loading parallel and perpendicular to
the fibres respectively.


17. Young’s Modulus measurement

18. Observations
 For the transverse direction, the composite model closely agrees with
experimental values. However, in the longitudinal direction the difference is
large.
 A better approximation would be to model it as a two level composite.
 Actual values of Young’s Modulus are given below

19. Tensile and Compressive Strength
 There is a large variation in measured values of both the tensile and
compressive strength of bone. Different bones in the body need to support
different forces, so there is a large variation in strength between them.
 Additionally, age is an important factor, with strength often decreasing
as a person gets older.

20. Elasticity
 Bone mineral is a ceramic material and exhibits normal Hook’s
elastic behaviour, i.e. a linear stress-strain relationship.
 In contrast, collagen is a polymer that exhibits a J-shaped stress-
strain curve.
Typical stress-strain curves for compact bone, tested in tension or
compression in the wet condition, are approximately a straight line.
Bone generally has a maximum total elongation of only 0.5 - 3%, and
therefore is classified as a brittle rather than a ductile solid.

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