Biomedical Engineering Reference
In-Depth Information
8.9.1 Objectives
• To illustrate the relation between the stress,
σ
, applied to a material and the
,
observed in it
• To illustrate the tensile strength of material
strain,
ε
8.9.2 Activity 9: Strength of a Spring
8.9.2.1 Necessary Materials
- Rubber strip spring scale
- Ruler
- Pet bottle with 2 l volume
- Water
8.9.2.2 Procedure
1. The cross-sectional area of the rubber that constitutes the spring scale decreases
as the rubber is submitted to increasing force. However, we will consider it
constant. Measure the cross-sectional area in m
2
, before the application of any
force.
2. Make a small hole near the mouth of the pet bottle in order to hook the clip of the
rubber strip spring scale, as shown in Fig.
8.4
of Activity 1.
3. Submit the rubber strip spring scale to increasing weight by adding water to the
bottle until the rubber breaks. Write the values of the weights and the respective
increase in the rubber length, until its rupture. For this, you should control the
volume of added water. Plot the graph of stress,
σ
,
as a function of strain,
ε
, and
compare it with the graph of Fig.
7.5
. Remember that stress
σ ¼
T
applied
/
A
¼
x
/
x
o
.
4. Determine the tensile strength at the point of rupture of the rubber strip.
weight/area and the strain
ε ¼
Δ
